international journal of hydrogen energy 50 (2024) 310e333 1

Available online at www.sciencedirect.co m

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journal homepage: www.elsevier.com/locate/he

Green hydrogen: A pathway to a sustainable

energy future
Qusay Hassan a,*, Sameer Algburi b, Aws Zuhair Sameen c, Hayder M.
Salman d, Marek Jaszczur e
a Department of Mechanical Engineering, University
of Diyala, Diyala, Iraq b College of Engineering, Al-
Kitab University, Kirkuk, Iraq
c College of Medical Techniques, Al-Farahidi University,

Baghdad, Iraq d Department of Computer Science, Al-

Turath University College, Baghdad, Iraq
e
Faculty of Energy and Fuels, AGH University of Science and Technology, Krakow, Poland

highlights

Green hydrogen offers a sustainable solution to reduce fossil fuel dependency, decarbonizing key sectors.
Analyzed policies from the EU, Australia, Japan, the US, and Canada to foster green hydrogen technologies.
Discussing challenges: green hydrogen potential, tech limits, infrastructure, costs, regs, and public views.
Emphasized the importance of R&D and offers accelerating the adoption of green hydrogen technologies.

a r t ic l e in f o a bs t r a c t

Article history: The development of sustainable energy sources has become a major challenge for society. Green hydrogen,
Received 8 June 2023 produced through the electrolysis of water using renewable energy sources, offers a potential solution to
Received in revised form reducing our dependence on fossil fuels. The paper examines the integration of green hydrogen into various
sectors, such as transportation, industry, power generation, and heating, highlighting its potential to
10 August 2023
decarbonize traditionally carbon-intensive areas. Furthermore, it analyses the strategies and policies
Accepted 27 August 2023 employed by the European Union, Australia, Japan, the United States, and Canada to drive
Available online 06 October 2023

Keywords: the development and adoption of green hydrogen technologies. The challenges and barriers that need to be
Green hydrogen addressed to fully realize the potential of green hydrogen, such as technological limitations, infrastructure
Renewable energy development, costs and economic feasibility, regulatory and policy frameworks, and public perception and
acceptance, have been investigated. Recommendations for overcoming these challenges and accelerating
Electrolysis
the adoption of green hydrogen technologies are provided, and the importance of research and
 international journal of hydrogen energy 50 (2024) 310e333 2

Energy security
Policy
development in this sector is emphasized.
© 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

* Corresponding author.
E-mail address: qusayhassan_eng@uodiyala.edu.iq (Q. Hassan).
https://doi.org/10.1016/j.ijhydene.2023.08.321
0360-3199/© 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

potential to become a key component in the

1. Introduction transition to a more sustainable future.

The increasing concerns over climate change and Green hydrogen is a promising technology
the impact of human activity on the that has been gaining momentum in recent years
environment have led to a growing demand for as a potential solution to the challenges of
sustainable energy sources. The world has transitioning to a sustainable energy future [4,5].
witnessed a steady rise in global energy The concept of green hydrogen refers to the
consumption and electrical energy consumption process of producing hydrogen gas through
in recent years, driven by population growth, electrolysis, using renewable energy sources
economic development, and technological such as solar, wind, or hydroelectric power.
advancements. In recent years the upward trend Unlike the conventional method of producing
has been shaped by a complex interplay of hydrogen from natural gas, green hydrogen is
factors, including industrial expansion, considered an environmentally friendly and
urbanization, and increased access to electricity sustainable option as it emits no greenhouse
in developing regions. According to the gases during its production and use [6,7].
International Energy Agency (IEA) or the World The transition to renewable energy sources
Bank, the global energy consumption raised and sustainable practices has been an ongoing
form 13,647 Mtoe on 2015 to 14,477 Mtoe on discussion for decades, with the primary
2021, and theglobalenergy consumption motivation being the urgent need to reduce
raisedform 23,127kWh on 2015 to 26,841 kWh greenhouse gas emissions and mitigate the
on 2021 Mtoe as presented in Fig. 1 [1,2]. effects of climate change. Hydrogen has long
The traditional reliance on fossil fuels has been identified as a potential alternative to
become untenable in the face of these traditional fossil fuels due to its high energy
challenges, and there is a need to explore density, versatility, and low environmental
alternative energy sources that are both impact [8]. However, until recently, the
sustainable and cost-effective [3]. One such production of hydrogen was mainly derived from
alternative is green hydrogen, which has the non-renewable sources such as natural gas, coal,
and oil, which not only have a significant
 international journal of hydrogen energy 50 (2024) 310e333 3

environmental impact but also contribute to the which have the potential to offer a zeroemissions
depletion of finite resources [9]. The emergence alternative to traditional fossil fuel vehicles. In the
of green hydrogen as a viable alternative to power generation sector, green hydrogen can be
conventional hydrogen production methods has used to generate electricity through fuel cells,
created new opportunities for the integration of which convert hydrogen into electricity without
renewable energy sources into the energy mix. producing any harmful emissions [12]. This has
The green hydrogen pathway offers a significant the potential to revolutionize the power industry,
potential to decarbonize various sectors, which is currently heavily reliant on fossil fuels.
including transportation, industry, and power One of the key benefits of green hydrogen is its
generation, and thereby contribute to the global ability to reduce greenhouse gas emissions [13].
efforts to reduce greenhouse gas emissions and When hydrogen is produced using renewable
mitigate the effects of climate change. energy sources, it is a zeroemissions fuel,
meaning that it does not produce any harmful
Green hydrogen is produced through the
pollutants when burned. This makes it an ideal
process of electrolysis, which involves the
alternative to traditional fossil fuels, which are a
separation of water molecules into their
major contributor to greenhouse gas emissions
constituent hydrogen and oxygen atoms using
and the resulting climate change. The use of
electricity [10]. When the electricity used in the
green hydrogen in transportation, power
process is generated from renewable sources,
generation, and industrial processes could
such as wind or solar power, the resulting
therefore significantly reduce the carbon
hydrogen is known as green hydrogen. Unlike
footprint of these sectors and help to mitigate the
traditional hydrogen production, which is often
effects of climate change. Another benefit of
derived from fossil fuels such as natural gas,
green hydrogen is its ability to enhance energy
green hydrogen offers a much cleaner and more
security [14]. As a clean and renewable fuel,
sustainable alternative [11]. Green hydrogen has
green hydrogen offers a more secure energy
a wide range of potential applications, ranging
supply than traditional fossil fuels, which are
from transportation and power generation to
subject to fluctuations in price and supply. The
industrial processes such as steel and cement
use of green hydrogen could therefore reduce our
production. In the transportation sector, green
dependence on imported fossil fuels, enhance
hydrogen can be used to power fuel cell vehicles,

14600
Global Electrical Energy Consumption (TWh)

27000

14400 26500
Global Energy Consumption (Mtoe)

26000

14200 COVID-19
(2020) 25500

25000
14000
24500

13800 24000

23500
13600
23000

2015 2016 2017 2018 2019 2020 2021

Fig. 1 e Global energy and electricity consumption for the period (2015e2021) [1,2].
 international journal of hydrogen energy 50 (2024) 310e333 4

energy independence, and promote greater Yu et al. [19] provides insights into low-carbon
energy security [15]. hydrogen production methods, focusing on green,
blue, and aqua hydrogen. It examines the
Several articles reported used a green
differences and benefits of each method,
hydrogen for sustainable future. Falcone et al.
emphasizing their contributions to reducing
[16] reviews the concept of a hydrogen economy
carbon emissions. The study discusses the green
in the context of sustainable development goals.
hydrogen production from renewable sources,
It examines the potential of hydrogen as a clean
blue hydrogen with carbon capture and storage,
energy source and its contributions to achieving
and aqua hydrogen utilizing electrolysis with
environmental and social objectives. The study
nuclear power. The results presented a potential
offers policy insights and recommendations to
of these methods in advancing a low-carbon
promote the integration of hydrogen technologies
hydrogen economy and fostering sustainable
into sustainable development strategies. Its
energy transitions. In addition, offers valuable
outcomes emphasize the importance of aligning
information on the various low-carbon hydrogen
hydrogen policies with broader sustainability
production pathways and their significance in
goals and explores the role of publicprivate
addressing climate change and achieving
partnerships in driving innovation and investment.
environmental goals.
Oliveira et al. [17] explored the concept of a green
hydrogen economy as a pathway to achieving a While green hydrogen presents a sustainable
renewable energy society. It discusses the alternative to traditional fossil fuels with its
potential of green hydrogen as an alternative potential to cut greenhouse gas emissions,
energy source across various sectors and bolster energy security, and enable long-distance
compares its benefits to traditional energy energy storage and transport, its widespread
sources. The study emphasizes the importance of adoption faces hurdles. Primary among these is
collaborations between public and private sectors its high production cost, attributed to the
to accelerate innovation and investment in green expenses tied to renewable energy and
hydrogen technologies. Additionally, it addresses electrolysis equipment. However, as renewable
the environmental benefits of green hydrogen energy becomes more affordable and
and its role in reducing greenhouse gas emissions. investments in green hydrogen surge, these costs
The results examine the scalability and potential are expected to decline. Moreover, the current
limitations of green hydrogen production for lack of a comprehensive infrastructure for
large-scale adoption. Abadand [18] discussed production, storage, and transportation requires
green hydrogen characterisation initiatives, substantial investment, encompassing the
focusing on definitions, standards, guarantees of creation of extensive electrolysis facilities,
origin, and challenges. It examines the efforts to transportation pipelines, and hydrogen fueling
establish clear definitions and criteria for green stations. To fully harness its revolutionary
hydrogen production and certification. The study potential acrosstransportation, power, and
explores the importance of guarantees of origin to industry sectors, policymakers, investors, and
ensure transparency and credibility in the green society must prioritize green hydrogen,
hydrogen market. The outcomes highlighted the channeling significant resources and research
challenges associated with standardization and into overcoming these challenges for a
the need for harmonized approaches in sustainable future.
characterizing green hydrogen.
1.1. Importance of green hydrogen in the global energy mix
 international journal of hydrogen energy 50 (2024) 310e333 5

The importance of green hydrogen in the global Enhancing energy security: by producing green
energy mix can be attributed to its potential to hydrogen from local renewable energy sources,
address some of the most pressing challenges countries can decrease their reliance on
faced by the world today, including climate imported fossil fuels, improving energy security
change, energy security, and sustainable and reducing geopolitical risks [24]. This
development. As a clean and versatile energy diversification of energy sources also
carrier, green hydrogen offers a range of benefits contributes to a more resilient and robust
that make it a vital component in our quest to energy infrastructure.
decarbonize the global economy.
Economic growth and job creation: The
development and deployment of green
Tackling climate change: green hydrogen is
hydrogen technologies can spur innovation,
produced through the electrolysis of water
economic growth, and job creation. As
using renewable energy sources, such as solar,
countries invest in the infrastructure needed
wind, or hydropower. This process results in
to produce, store, and transport green
zero greenhouse gas emissions, making green
hydrogen, new industries and employment
hydrogen a clean and sustainable alternative
opportunities will emerge, supporting a more
to fossil fuels [20,21]. By incorporating green
sustainable and inclusive global economy
hydrogen into the global energy mix, it can
[25,26].
reduce our dependence on carbonintensive
energy sources and significantly decrease the
The importance of green hydrogen in the
emissions responsible for climate change.
global energy mix lies in its potential to address
Energy storage and flexibility: green hydrogen climate change, enhance energy security, and
can be stored and transported easily, making support sustainable development. By tapping
it an ideal solution for energy storage and grid into this clean and versatile energy source, it can
balancing. This is particularly important as the drive the global transition towards a low-carbon
world increasingly relies on intermittent future and build a more resilient, prosperous,
renewable energy sources, which require and eco-friendly world.
effective storage solutions to maintain grid
stability [22]. Green hydrogen can be 1.2. Objectives of the study

converted back into electricity using fuel cells

or combusted to generate heat, providing a The primary objective of this research paper is to
flexible and reliable source of energy for provide a comprehensive analysis of green
various applications. hydrogen and its potential for fostering a
sustainable energy future. To achieve this, the
Decarbonizing hard-to-abate sectors: some paper explored various aspects of green
industries, such as heavy transport, aviation, hydrogen, including its production technologies,
and steel manufacturing, are difficult to applications in different sectors, environmental
electrify or decarbonize using conventional and socio-economic benefits, and the challenges
renewable energy sources. Green hydrogen and barriers that need to be addressed for its
can serve as a low-carbon fuel or feedstock in widespread adoption. Furthermore, the paper
these sectors, providing a pathway to reduce examined strategies and policies for promoting
emissions in areas where other solutions may green hydrogen deployment, drawing on case
be less feasible [23]. studies from around the world to illustrate best
practices and lessons learned.
 international journal of hydrogen energy 50 (2024) 310e333 6

The novelties and new insights in this text can 5. Emphasizing R&D: emphasizes the importance
be highlighted as follows: of research and development in the sector,
suggesting that continuous innovation and
1. Comprehensive sectoral integration: the paper
improvement are crucial for making green
does not just consider green hydrogen as an
hydrogen a viable alternative to traditional
alternative energy source in a narrow context.
energy sources.
It goes beyond traditional boundaries and
investigates the application of green hydrogen By providing a holistic understanding of green
across various sectors such as transportation, hydrogen potential as a key component in the
industry, power generation, and heating. This global energy transition, where the research
wideranging approach underlines the paper contributed the growing body of knowledge
extensive utility of green hydrogen. on sustainable energy solutions and inspire
further research, development, and innovation in
2. International approach: looks at the strategies the field of green hydrogen technologies.
and policies employed by the European Union,
Australia, Japan, the United States, and
Canada. This international perspective allows 2. Green hydrogen production technologies
for a comparative analysis of different policy
Green hydrogen is produced through the process
approaches and could provide important
of water electrolysis using renewable energy
lessons for other nations in their efforts to
sources such as solar and wind power. This
adopt green hydrogen technologies. technology has the potential to provide a clean,
3. Addressing a broad spectrum of challenges: reliable, and cost-effective source of energy, with
the paper acknowledges and analyses a wide a wide range of applications in the transportation,
industrial, and residential sectors. In recent years,
variety of barriers to the adoption of green
there has been significant research and
hydrogen - technological limitations,
development in green hydrogen production
infrastructure development, cost and technologies, with various methods and
economic feasibility, regulatory and policy technologies being developed to increase
frameworks, and public perception and efficiency and reduce costs. In this context, this
acceptance. This all-encompassing review section aims to provide an overview of the
different green hydrogen production
allows for a more comprehensive
technologies, their advantages, and challenges,
understanding of the challenges faced in the
and their potential applications in the energy
adoption of green hydrogen technologies. sector.
4. Providing concrete recommendations: the
2.1. Overview of electrolysis processes
study not only identifies the challenges but
also provides recommendations for Electrolysis is a process in which an electric
overcoming these barriers. This practical current is passed through an electrolyte to cause
approach is vital for converting theoretical a non-spontaneous chemical reaction. In the
knowledge into actionable policies. context of green hydrogen production,
electrolysis is used to split water molecules into
 international journal of hydrogen energy 50 (2024) 310e333 7

hydrogen and oxygen gases using an electric Overall reaction: 2H2O(l) -> 2H2(g) þ O2(g).
current. Hydrogen production from water is a The produced hydrogen gas can then be
process involves splitting water (H2O) into captured and utilized for various applications,
hydrogen (H2) and oxygen (O2) using an electrical including fuel cell vehicles, energy storage, and
current as presented in schematical of Fig. 2. This industrial processes.
process is considered a clean and sustainable

Fig. 2 e Schematic of water electrolysis process.

method for generating hydrogen gas, which can

be used as a versatile energy carrier [27]. It is important to note that water electrolysis
requires a source of electricity to drive the
Water electrolysis typically requires an reaction. The electricity can come from renewable
electrolyzer, which consists of two electrodesdan sources like solar or wind power, making
anode and a cathodedsubmerged in water [28]. hydrogen production through water electrolysis a
The electrodes are made of conductive materials, sustainable and carbon-free process.
such as metals or metal oxides. When an electric
current is passed through the water, several 2.1.1. Alkaline electrolysis (AE)
reactions occur: Alkaline electrolysis is a process used to produce
hydrogen gas (H2) from water (H2O) using an
At the anode: Oxidation reaction takes place,
electrolyte solution containing hydroxide ions
generating oxygen gas and releasing electrons.
(OH-). This process takes place in an electrolytic
cell, which consists of two electrodes (anode and
2H2O(l) -> O2(g) þ 4Hþ(aq) þ 4e- cathode) submerged in an alkaline electrolyte
solution, usually a mixture of potassium
At the cathode: Reduction reaction occurs,
hydroxide (KOH) or sodium hydroxide (NaOH)
producing hydrogen gas.
dissolved in water [29,30]. Fig. 3 show the
schematic diagram of alkaline eater electrolysis.
4H2O(l) þ 4e- -> 2H2(g) þ 4 OH-(aq )
 international journal of hydrogen energy 50 (2024) 310e333 8

The overall reaction for alkaline electrolysis is as Electric current: The applied current drives the
follows: electrolysis reaction by providing the
2H2O(l) / 2H2(g) þ O2( g ) necessary energy to break the chemical bonds
in water molecules. The amount of hydrogen
Thisreaction occursin twohalf-reactions,one at and oxygen produced is proportional to the
theanode and one at the cathode. electric charge passed through the cell. This
relationship can be described by Faraday laws
At the anode of electrolysis [33]:

( oxidation ): 4OH-(aq) / Q¼n*F

2H2O(l) þ O2(g) þ 4eAt the where Q is the electric charge(in coulombs), n

is the number of moles of the substance
produced or consumed, and F is Faraday
cathode (reduction):
constant (approximately 96,485 C/mol). In the
case of hydrogen production from water
electrolysis [34]:
4H2O(l) þ 4e- / 2H2(g) þ 4 OH-(aq )

The key components and variables of alkaline Q ¼ 2 * n(H2) *F

electrolysis.
The current density (A/m2) and cell voltage are
Electrolyte: The electrolyte in alkaline important parameters that affect the efficiency
electrolysis is a solution of potassium and cost of the electrolysis process.
hydroxide (KOH) or sodium hydroxide (NaOH)
in water, typically at a concentration of
20e40% by weight [31]. The role of the
electrolyte is to increase the conductivity of the
solution and provide a medium for the
transport of ions between the electrodes.

Electrodes: The anode and cathode are

typically made from a material that is resistant
to corrosion and has good catalytic activity,
such as nickel, stainless steel, or a noble metal
like platinum. The electrodes are submerged
in the electrolyte solution, and an electric
current is applied between them [32].
 international journal of hydrogen energy 50 (2024) 310e333 9

Efficiency: The efficiency of alkaline electrolysis (PEM) sandwiched between them. The cell is
is influenced by several factors, including the filled with an electrolyte, typically water or an
electrode material, electrolyte concentration, acidic solution[37,38]. Fig.4 show theschematic

Fig. 3 e The schematic diagram of alkaline water electrolysis.

temperature, and pressure. The theoretical cell diagramof PEM electrolysis.

voltage for water electrolysis at standard
Anode reaction (Oxidation): At the anode,
conditions (25 C and 1 atm) is 1.23 V, but in
water molecules are oxidized, resulting in the
practice, it is usually higher (1.8e2.2 V) due to
release of oxygen gas, protons, and electrons:
overpotentials caused by various energy losses
[35].
2H2O(l) -> O2(g) þ 4Hþ(aq) þ 4e-
The energy efficiency of the process can be
Proton transport through the membrane: The
calculated using the following equation:
PEM selectively allows the passage of protons
Energy efficiency (%) ¼ (Theoretical cell (Hþ) but blocks the flow of electrons (e). Thus,
voltage/Actual cell voltage) * 100. only protons can move through the membrane
from the anode to the cathode compartment [39].
Alkaline electrolysis typically has an energy
efficiency of 60e80% [36].

By optimizing the process parameters and

using advanced materials, alkaline electrolysis
can be an effective and sustainable method for
hydrogen production from water.

2.1.2. Proton exchange membrane (PEM) electrolysis

The PEM electrolysis cell consists of an anode, a
cathode, and a proton exchange membrane
 international journal of hydrogen energy 50 (2024) 310e333 10

Cathode reaction (reduction): At the cathode,

the protons received from the anode combine
with electrons supplied from an external circuit to

Fig. 4 e The schematic diagram of PEM electrolysis.

form hydrogen gas:

4Hþ(aq) þ 4e- -> 2H2(g)

The overall reaction represents the

combination of the anode and cathode reactions,
demonstrating the conversion of water into
hydrogen and oxygen gases [40]:

2H2O(l) -> 2H2(g) þ O2(g)

The hydrogen gas produced at the cathode and

the oxygen gas generated at the anode can be
collected separately for further use.

The PEM electrolysis process requires an

external power source, usually electricity, to drive
the electrolysis reaction. The power source
supplies the necessary energy to split water
molecules into hydrogen and oxygen gases [41]. It
is important to note that PEM electrolysis is an
efficient and clean method for hydrogen
production, especially when powered by
renewable energy sources. The proton exchange
membrane enables the selective transport of
protons, facilitating the separation of hydrogen
and oxygen gases. This makes PEM electrolysis a
 international journal of hydrogen energy 50 (2024) 310e333 11

promising technology for generating hydrogen as 2O2-(aq) þ 4e- -> O2( g )

a sustainable energy carrier.
Overall reaction: The overall reaction
2.1.3. Solid oxide electrolysis represents the combination of the anode and
The Solid Oxide Electrolysis (SOE) process, also cathode reactions, illustrating the production of
known as high-temperature electrolysis, is a hydrogen gas and oxygen gas from the
method for producing hydrogen gas (H2) from electrolysis of water:
water (H2O) using a solid oxide electrolysis cell.
Fig. 5 show the schematic diagram of PEM H2O(g) -> H2(g) þ O2( g )
electrolysis.
The hydrogen gas produced at the anode and
The detailed explanation of the SOE process, the oxygen gas generated at the cathode can be
along with the relevant equations: collected separately for further use or storage.
The SOE cell consists of a solid oxide The SOE operates at high temperatures,
electrolyte, typically a ceramic material such as typically between 700 and 1000 Celsius, to
yttria-stabilized zirconia (YSZ). The cell has an facilitate the movement of oxygen ions through
anode and a cathode, which are typically made of the solid oxide electrolyte [43,44]. The SOE
a porous nickel-YSZ composite [42]. process requires a source of heat or electrical
Anodereaction(Oxidation): energy to sustain the high-temperature
attheanode,steam(H2O)is fed into the cell, and it operation. The high-temperature environment
reacts with the anode material, typically nickel, to enables efficient electrolysis of water and the
produce hydrogen gas (H2) and oxygen ions (O2-): production of hydrogen gas. The SOE offers the
advantage of utilizing excess renewable energy
H2O(g) þ 2e- -> H2(g) þ 2O2-(aq) or waste heat from industrial processes for
hydrogenproduction, makingit a promising
The oxygen ions produced at the anode can technology for sustainable hydrogen generation.
migrate throughthe solid oxideelectrolytedue to
its high-temperature operation. 2.2. Comparison of production technologies

This section summaries a compression of green

hydrogen production technologies available,
including AE, PEM Electrolysis, and SOE based on
several aspects, which showed in Table 1.

Each technology has its own set of advantages

and considerations. Alkaline electrolysis is a
mature technology with lower capital costs, PEM
electrolysis offers higher efficiency and
versatility, while SOE provides high
thermodynamic efficiency but requires higher
temperatures and specialized applications. The
Cathode reaction (Reduction): At the cathode,
choice of technology depends on factors such as
oxygen ions (O2-) combine with electrons (e)
scale, energy source availability, desiredpurity,
supplied from an external circuit to form oxygen
and specific application requirements.
gas (O2):
 international journal of hydrogen energy 50 (2024) 310e333 12

2.3. Current state of green hydrogen production

 international journal of hydrogen energy 50 (2024) 310e333 13

Fig. 5 e The schematic diagram of SOE electrolysis.

Green hydrogen, produced through the electrolysis of water using renewable energy sources, is gaining
momentum as a viable solution for decarbonizing various sectors and achieving carbon neutrality. The
current state of green hydrogen production is witnessing significant progress in terms of production
capacity and cost, driving the global transition towards a sustainable and low-carbon future.

2.3.1. Production capacity

The production capacity of green hydrogen has been steadily increasing in recent years. Pilot projects
and demonstration facilities are also playing a crucial role in expanding production capacity. These
initiatives provide valuable insights into the scalability and feasibility of green hydrogen technologies.
Where the global percentage of green hydrogen form the total hydrogen production not increase to
17% as presented in Fig. 6.

Table 1 e A comparison of production technologies of AE, PEM, and SOE [45,46].

Aspect Alkaline Electrolysis PEM Electrolysis Solid Oxide
Electrolysis
Operating temperature <100 C <100 C 700e1000 C
Efficiency Moderate (60e70%) High (70e80%) High (>80 % )
Capital costs Moderate Higher Higher
Durability Relatively shorter lifespan Relatively longer lifespan Longer lifespan
Electrolyte Alkaline (KOH or NaOH) Proton exchange membrane Solid oxide ( ceramic material)
(solid polymer)
Electrolyte conductivity Moderate High High
Response time Slow Fast Fast
Scale Industrial-scale Small-scale Industrial-scale
Compatibility with renewable energy Less compatible Compatible Less compatible
Integration with other technologies Less flexible Flexible Less flexible
Heat requirements Low Low High
Catalysts Potassium hydroxide (KOH) Platinum or other precious metals None or mixed oxide materials

System complexity Low Moderate High

Fuel purity High High High
Heat management Simple Moderate Complex

The greenhydrogenmarket has hugest green hydrogen production for the period
 international journal of hydrogen energy 50 (2024) 310e333 14

Fig. 8 show the green hydrogen production cost

for Germany, United States, China, Japan, and
Australia for period 2015e2021, which is ranged
between $1.5/kg - $2.2/kg [49,50].

The cost competitiveness of green hydrogen is

expected to improve further as the industry
matures and benefits from technological
advancements and increased production volumes,
which is required several years to drop to the
conventional hydrogen cost. Fig. 9 show the
conventional hydrogen production cost for
Germany, United States, China, Japan, and
Australia for period 2015e2021, which is ranged
between $4.5/ kg - $9.2/kg [49]. Government
support and policy incentives, such as carbon
pricing mechanisms and investment subsidies, are
also instrumental in driving down costs and
making green hydrogen more economically viable.

The current state of green hydrogen production

showcases significant advancements in
production capacity and cost dynamics. Countries
such as Germany, United States, China,
 n 3
e 4
e 2
r
G 1
2

0
international journal of hydrogen energy 50 (2024) 310e333 15
2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021

Fig. 6 e Global green hydrogen production percentage from total production for period 2010e2021
[47,48]. (For interpretation of the references to color in this figure legend, the reader is referred to the
Web version of this article.)
Fig. 7 e Green hydrogen production for Germany, United States, China, Japan, and Australia for period
2010e2021 [47,48]. (For interpretation of the references to color in this figure legend, the reader is
referred to the Web version of this article.)

Fig. 8 e Green hydrogen production cost for Germany, United States, China, Japan, and Australia for
period 2015e2021 [47,49]. (For interpretation of the references to color in this figure legend, the reader is
referred to the Web version of this article.)
 international journal of hydrogen energy 50 (2024) 310e333 16

Fig. 9 e Conventional hydrogen production cost for Germany, United States, China, Japan, and Australia
for period 2015e2021 [47,49].

Table 2 e Comparative of a green hydrogen and existing energy sources.

Energy Source Production Infrastructure Market & Policy Environmental Future Cost
Cost & Storage Factors Impact Trends
Cost
Green Hydrogen Currently high due to the Significant costs due to Dependent on subsidies, Very low environmental Expected to decrease
cost of electricity for challenges in storage and carbon pricing, and other impact, offers significant with technology
electrolysis and cost of transportation policy measures, varies by carbon reduction improvements and
electrolyzers region cheaper renewable
electricity
Fossil Fuels (Coal, Oil, Low, due to established Existing, mature Market mature, but future High environmental Stable or increasing due
Natural Gas) technologies and infrastructure keeps costs costs may increase with impact, major source of to regulatory pressures
extraction methods low carbon pricing and regulatory greenhouse gas and finite resources
constraints emissions

Nuclear Energy High initial investment, High due to safety Market mature, public Low carbon emissions, Stable or decreasing
but stable operating measures and waste acceptance varies significantly but issues with waste with advancements in
costs disposal requirements by region disposal and potential technology
for accidents

Renewables (Wind, Decreasing due to Varies, storage solutions Dependent on subsidies and Very low environmental Expected to continue
Solar, Hydro) improvements in such as batteries can add policy measures, varies by impact decreasing
technology and significant costs region
economies of scale
Biofuels Varies, often higher than Similar to fossil fuels, but Dependent on subsidies and Lower carbon emissions Varies, potential to
fossil fuels due to some differences based policy measures, varies by than fossil fuels, but decrease with
production process on type of biofuel region potential negative technology
impacts on biodiversity improvements
 international journal of hydrogen energy 50 (2024) 310e333 17

drive green hydrogen production towards cost unit costs might drop due to economies of scale,
parity with conventional hydrogen production the initial capital requirement can be daunting.
methods. The current momentum in production The technological intricacies of managing such
expansive setups introduce new challenges,
capacity expansion and cost reduction highlights
especially around systems integration and
the promising future of green hydrogen as a key
optimization. Additionally, the demands on
player in achieving global decarbonization goals. resources, particularly water and renewable
Table 2 show more understanding the energy, spike, potentially
economic feasibility and cost comparisons of leadingtocompetitionwithotheressentialuses.Thiss
green hydrogen against existing energy sources calealso amplifies environmental considerations,
involves examining several components. not just from a production perspective but also
due to the infrastructure's footprint. Safety
2.4. Large-scale green hydrogen production projects
concerns escalate with the sheer volume of
hydrogen in play, necessitating enhanced
There are several large-scale green hydrogen
measures and protocols. The public's perception
production projects were planned or under
of green hydrogen can also shift, from viewing
development in several countries which
pilot projects as innovative endeavors to
summarized some of them in Table 1.
expressing concerns over large-scale operations,
Green hydrogen production, when evaluated especially if they are in or near populated areas.
at the scale of pilot projects, offers a glimpse into Navigating the regulatory landscape becomes
its potential as a sustainable energy source. more intricate, given the need for comprehensive
These smaller initiatives often serve specific frameworks that might even need to address
communities or applications and can international standards, especially if the hydrogen
comfortably leverage existing infrastructure with is to be transported across borders. Lastly, the
minor tweaks. Economically, they might not simplicity of a localized supply chain transforms
always stand on their own feet and could be into a potentially global network with its inherent
bolstered by grants or subsidies. Their modest logistics challenges.
scale makes technological glitches easier to
In essence, while the promise of green
troubleshoot and manage, while the
hydrogen shines bright, the journey from pilot
environmental and safety concerns remain
projects to large-scale production is laden with
localized and relatively easy to address.
challenges, demanding a holistic, informed, and
However, transitioning from these pilot projects
strategic approach.
to large-scale production is no simple feat.
Table 3 e The large-scale green hydrogen production projects
When considering the larger canvas of
[51,52].
widespread green hydrogen production, the
Project name Capacity Country
dynamics shift significantly. Asian Renewable Energy 26 GW Australia
Hub (AREH)
Infrastructure needs become monumental,
spanning massive facilities for production, Western Green Energy Hub 50 GW Australia
storage, and transportation. Economically, while (WGEH)

1. Applications of green hydrogen

NortH2 10 GW Netherlands

Green hydrogen, produced using renewable energy sources has a

wide range of applications across various sectors, including energy,
transportation, industry, and more. Fig. 10
 international journal of hydrogen energy 50 (2024) 310e333 18

HyDeal Ambition 95 GW solar power, aiming for Spain, France, and

blue hydrogen, thereby reducing greenhouse
3.6 million tonnes Germany
gas emissions in these industries.
NEOM - Green Hydrogen 4 GW Saudi Synthetic
Arabia fuels: green hydrogen can be
Plant
combined with captured carbon dioxide to
Green Hydrogen for Multiple green hydrogen create synthetic fuels such as methane,
United Kingdom
Scotland production sites, focused on
transport applications
methanol, ammonia, and other hydrocarbons
Heide Refinery 700 MW Germany[59]. These fuels can be used for
transportation, power generation, or as a
GigaFactory - HydrogenPro 1 GW Norwayfeedstock for various industries.

Heat and heating systems: green hydrogen can

Hyport Duqm - Green 1.8 GW solar and wind power, Oman
targeting 1 million tonnes
be used for space heating and water heating in
Hydrogen and Ammonia
Plant residential, commercial, and industrial
demonstrated the green hydrogen application, in buildings. Hydrogen can be combusted in
addition description and key applications of green boilers or used in fuel cells to produce heat and
electricity simultaneously, providing clean and
hydrogen presented in this section as:
efficient heating solutions [60,61]. Green
hydrogen-based heating systems can help
Power generation: green hydrogen can be used
reduce the carbon footprint of buildings and
to generate electricity through fuel cells or by
contribute tothedecarbonization of theheating
burning it in combustion turbines [53]. This
sector. Aviation: research is being conducted
provides a clean and efficient way to produce
on using green hydrogen as a fuel for aviation.
power for residential, commercial, and
While this application is still in the early stages
industrial purposes.
of development, it has the potential to
Transportation: green hydrogen is a promising significantly reduce the carbon footprint of the
fuel for various transportation modes, aviation sector.
including cars, buses, trucks, trains, and even
Agriculture: green hydrogen can be used to
ships [54,55]. Using hydrogen fuel cells in
produce ammonia, which is a key component
vehicles provides a zero-emission alternative to
in fertilizers. Using green hydrogen for
fossil fuels, with water as the only by-product.
ammonia production can help reduce the
Energy storage: green hydrogen can be used to environmental impact of the agricultural
store excess renewable energy, such as solar or sector [62].
wind power. When renewable energy
Hydrogengrids: similarto natural gas grids,
generation exceeds demand, green
hydrogengrids can distribute green hydrogen
hydrogencan be producedthroughelectrolysis,
to various end-users. Hydrogen pipelines can
stored,and then used later to generate
transport hydrogen over long distances,
electricity through fuel cells or combustion
enabling the establishment of regional or
turbines [56,57].
national hydrogen networks. Hydrogen grids
Industrial processes: many industries, such as can facilitate the integration of renewable
steel, chemicals, and refining, rely heavily on energy sources, optimize resource allocation,
hydrogen as a feedstock [58]. Green hydrogen and support the scalability and widespread
can replace the traditionally produced grey or adoption of green hydrogen across multiple
applications [63,64].
 international journal of hydrogen energy 50 (2024) 310e333 19

These applications demonstrate the versatility 4. Environmental and socio-economic

of green hydrogen and its potential to play a benefits

Fig. 10 e Green hydrogen applications. (For interpretation of the references to color in this figure legend, the
reader is referred to the Web version of this article.)

significant role in the global transition to cleaner

and more sustainable energy sources. The Green hydrogen, produced using renewable
progress of green hydrogen utilization over the energy sources offers various environmental and
years can be summarized in Table 4. socio-economic benefits. These benefits
contribute to the global transition towards a
As green hydrogen production costs continue
more sustainable and low-carbon future:
to decrease and more large-scale projects are
developed, its applications will likely expand even 4.1. Environmental benefits
further.
Carbon emissions reduction: green hydrogen is
produced through electrolysis, which utilizes
renewable energy sources such as wind, solar,
or hydroelectric power. The process emits no
greenhouse gases during hydrogen
 Table 4 e History of green hydrogen utilization progress [65].
Year Progress of green hydrogen utilization
international journal of hydrogen energy 50 (2024) 310e333 20
2015 Initial research and development efforts focused on green hydrogen production technologies,
primarily electrolysis. Limited pilot projects and feasibility studies conducted to assess the viability of green hydrogen
applications.
2016 Growing interest in green hydrogen as a clean energy solution. Advancements in electrolyze technology
to improve efficiency and reduce costs. Small-scale green hydrogen projects initiated in various sectors, including energy
storage and transportation.
2017 Increased investments and collaborations to advance green hydrogen technologies. Demonstration
projects launched to showcase the feasibility and potential of green hydrogen in different applications, such as power
generation and industrial processes.
2018 Scaling up of green hydrogen projects, supported by favorable policies and incentives. Expansion of electrolyze
manufacturing capacities to meet growing demand. Recognition of green hydrogen role in decarbonization strategies and
efforts to integrate it into national energy plans.
2019 Rapid growth of green hydrogen projects worldwide, driven by increasing awareness of climate change and the need for
clean energy solutions. Large-scale deployments in power generation, transportation, and industrial sectors. Expansion of
hydrogen infrastructure, including refueling stations and pipelines.
2020 Acceleration of green hydrogen adoption as governments and industries prioritize clean energy
transitions. Investments in large-scale green hydrogen production facilities and partnerships between public and private
sectors. Advancements in hydrogen storage and transportation technologies.
2021 Continued momentum in the development and deployment of green hydrogen projects globally.
Integration of green hydrogen into national energy strategies of multiple countries. Technological advancements to
enhance the efficiency and cost-effectiveness of electrolyzes. Growing recognition of green hydrogen potential in
decarbonizing hard-to-abate sectors.

production. When used as a fuel, green Job creation and economic growth: the
hydrogen combustion or utilization in fuel development and deployment of green
cells produces only water vapor as a by- hydrogen technologies create new
product, significantly reducing carbon employment opportunities across the value
emissions compared to fossil fuel-based chain,
alternatives [66,67]. This helps mitigate
including manufacturing, construction, operation,
climate change and reduce air pollution.
and maintenance of hydrogen production
Air quality improvement: by replacing fossil fuel facilities, infrastructure development, and
combustion with green hydrogen, harmful air
research and development activities [69]. The
pollutants such as particulate matter, nitrogen
transition to a hydrogen-based economy can
oxides (NOx), sulfur oxides (SOx), and volatile
organic compounds (VOCs) are eliminated [68]. stimulate economic growth, attract investments,
This leads to improved air quality, reducing the and contribute to sustainable development.
negative health impacts associated with Energy independence and security: green
pollution and enhancing the overall well-being hydrogen can be produced locally, reducing
of communities. reliance on imported fossil fuels. This enhances
energy independence and strengthens energy
Water conservation: green hydrogen production
security by diversifying energy sources and
consumes water during the electrolysis
reducing vulnerability to supply disruptions [70].
process. However, the overall water
Countries with abundant renewable resources
consumption can be minimized by using
can leverage green hydrogen to achieve energy
advanced water recycling and purification
self-sufficiency and reduce geopolitical risks
techniques. Additionally, green hydrogen
associated with fossil fuel dependencies.
production can potentially utilize wastewater
or desalinated water, minimizing freshwater Regional development and community
consumption and promoting sustainable water resilience: the establishment of green hydrogen
management. projects in rural or underdeveloped areas can
foster regional development and bring economic
opportunities to communities. This includes the
4.2. Socio-economic benefits
 international journal of hydrogen energy 50 (2024) 310e333 21

deployment of renewable energy infrastructure, 5. Challenges and barriers to green hydrogen

adoption
the creation of local jobs, and the development
of local supply chains [71]. Green hydrogen can
Green hydrogen is widely considered a promising
also contribute to the resilience of communities
solution for decarbonizing various sectors, such
by providing decentralized power generation,
as transportation and industrial processes.
improving energy access, and supporting disaster
However, its adoption faces several challenges
resilience through energy storage capabilities.
and barriers. Here are some key ones:
Technological innovation and knowledge
transfer: the transition to a hydrogen-based 5.1. Technological limitations and scalability
economy stimulates research, development, and
innovation in various sectors, including Green hydrogen is produced primarily through
renewable energy, electrolysis technologies, fuel electrolysis, which involves splitting water into
cells, and hydrogen storage [72,73]. This fosters hydrogen and oxygen using electricity from
technological advancements and knowledge renewable sources. Although this technology is
transfer, driving progress in clean energy proven and mature, there are still some
solutions and supporting the growth of related limitations to overcome. For instance, improving
industries. It also enables the export of expertise the efficiency of the electrolysis process,
and technologies, fostering international developing more robust and durable electrolysis,
collaboration and trade opportunities. and increasing the energy density of hydrogen
storage systems are ongoing challenges.
Table 5 show the environmental benefits of
Scalability is another concern, as large-scale
green hydrogen compared to other clean energy
deployment of green hydrogen would require
options and its potential in reducing greenhouse
massive investments in renewable energy
gas emissions.
infrastructure, which may not be feasible in the
short term. 5.2. Infrastructure development

Green hydrogen requires a dedicated

infrastructure for production, storage, transport,
and distribution. Developing this infrastructure
can be challenging due to the high investment
required, and the lack of existing hydrogen-
specific networks. Transportation of hydrogen is
also more complicated than other fuels, as
hydrogen has a low energy density, making it
 Table 5 e The comparison, emphasizing the environmental benefits and potential of green hydrogen against
other clean energy options.
international journal of hydrogen energy 50 (2024) 310e333 22
Aspect Green Hydrogen Solar & Wind Nuclear energy BiofuelsHydropower
GHG Emissions Zero emissions at Zero emissions Low-carbon source, Reduced emissions Low emissions, but
point of use. during operation. but some emissions compared to fossil methane can be
during fuel cycle. fuels, but still emits produced in
CO2. reservoirs.
Other Pollutants Produces only water None. Concerns about Potential pollutants Potential impact on vapor when used.radioactive waste.
during production water quality.
and combustion.
Intermittency & Acts as energy Intermittent; needs Steady power Can be stored and Acts as both energy Storage
storage, bridging storage solutions like generation but has used as needed, generation and gaps of renewable batteries.
refueling periods. similar to fossil storage. energy production. fuels.
Environmental Minimal if produced Land use for solar Radioactive waste, Land use changes, Disruption to aquatic
Impact sustainably. panels and wind land use, and water deforestation, ecosystems,
changes turbines. use concerns. competition with in water courses.
food crops.
Decarbonization Can decarbonize Primarily for Mainly for electricity Alternative to Primarily for
Potential hard-to-abate electricity generation. gasoline and diesel electricity
sectors. generation. in transportation. generation.
Contribution to GHG Can store renewable Clean energy Clean energy Can replace fossil Clean energy
Reductionenergy, replace generation without generation with fuels in transport, generation with
carbon-intensive GHG emissions. minimal GHG reducing GHG potential for storage. industry sources,
emissions. emissions. decarbonize transport, replace natural gas in heating, and blend into gas grids.

researchers, which can be a lengthy and complex

less economical to transport over long distances.
process. 5.5. Public perception and acceptance
Additionally, retrofitting existing natural gas
Public perception of hydrogen as a safe and
pipelines to accommodate hydrogen may present
sustainable energy source is essential for its
technical and safety challenges. 5.3. Costs and widespread adoption. However, there may be
economic feasibility concerns around the safety of hydrogen, given
its flammability and potential for explosion.
Green hydrogen is currently more expensive to Additionally, people may be resistant to change,
produce than hydrogen derived from fossil fuels preferring to stick with familiar energy sources
or natural gas reforming. This is primarily due to like gasoline or natural gas. Educating the public
the higher costs of renewable energy, electrolysis about the benefits and safety aspects of green
technology, and storage and transportation hydrogen will be critical in overcoming these
infrastructure. As a result, green hydrogen may barriers.
struggle to compete with other energy sources
Potential collaborations or partnerships
and hydrogen production methods, unless there
between the public and private sectors can be
is significant cost reduction or supportive policy
powerful catalysts for accelerating innovation and
frameworks in place.
investment across various industries. Both sectors
5.4. Regulatory and policy frameworks bring unique strengths to the table, and by
combining their resources, expertise, and
For green hydrogen to become a significant part networks, they can collectively tackle complex
of the global energy mix, it needs supportive challenges and drive transformative change. One
regulations and policy frameworks. Incentives area where such collaborations hold significant
such as carbon pricing, subsidies, and renewable potential is in advancing sustainable energy
energy targets can help drive the adoption of technologies, particularly in the case of green
green hydrogen. However, creating these hydrogen. In the realm of green hydrogen, the
policies requires collaboration between public sector, represented by governments and
governments, industry stakeholders, and research institutions, plays a critical role in
providing policy support and regulatory
 international journal of hydrogen energy 50 (2024) 310e333 23

frameworks. Public entities can allocate funding towards common goals, enabling faster progress
for research and development initiatives, in the adoption of green hydrogen. Governments
incentivize investments, and set ambitious may offer financial incentives, grants, or tax
sustainability goals to encourage the adoption of benefits to attract private investments, while
green hydrogen. Additionally, governments can private enterprises can provide real-world data
facilitate the establishment of pilot projects and and feedback on the practicality and viability of
demonstration plants, allowing for realworld green hydrogen technologies.
testing and validation of green hydrogen
technologies. These efforts create an enabling
environment for private enterprises to invest in 6. Strategies and policies for green hydrogen
the sector with more confidence, knowing that deployment
there is governmental commitment and support.
On the other hand, the private sector, comprising Strategies and policies for green hydrogen
businesses and industries, brings vital market- deployment aim to facilitate the development
driven solutions and capital investment and adoption of green hydrogen as a sustainable
capabilities. Companies involved in energy, and clean energy carrier. These strategies and
engineering, and related sectors possess the policies encompass a wide range of measures,
technical expertise required to develop, deploy, including setting ambitious targets, providing
and scale green hydrogen technologies. Their financial incentives, investing in research and
experience in commercializing innovations can development, and promoting infrastructure
help bridge the gap between research and development. The key elements of strategies
practical applications, facilitating the integration and policies for green hydrogen deployment
of green hydrogen into existing energy systems. which described detailly in this section as
Moreover, private entities have access to capital presented in Fig. 11.
markets, making it possible to mobilize substantial
6.1. Renewable energy expansion
financial investments to fund large-scale projects
and infrastructure development.

Through collaborations and partnerships, the

public and private sectors can leverage their
complementary strengths to accelerate
innovation in green hydrogen technology. Joint
research and development efforts can lead to
breakthroughs in cost-effective hydrogen
production methods, efficient storage
technologies, and advanced applications in
various industries, such as transportation,
industry, and power generation. These
collaborations can foster knowledge-sharing and
skill transfer between researchers and businesses,
nurturing a skilled workforce to drive the sector's
growth. Furthermore, public-private partnerships
can help mitigate the risks associated with new
technologies and market uncertainties. By sharing
the risks and rewards, the two sectors can work
 international journal of hydrogen energy 50 (2024) 310e333 24

Increasing the deployment of renewable energy

sources, such as solar and wind power, is a
fundamental strategy for green hydrogen
production. Governments can establish
ambitious renewable energy targets and
incentivize investment in renewable energy

Fig. 11 e Policies toward green hydrogen deployment. (For interpretation of the references to color in this figure
legend, the reader is referred to the Web version of this article.)
projects through subsidies, tax credits, and feed-
in tariffs. This expansion of renewable energy
capacity
 international journal of hydrogen energy 50 (2024) 310e333 25

ensures a sustainable and carbon-free electricity Governments should allocate substantial funding
supply for green hydrogen production. for research and development activities focused
on green hydrogen technologies, including
6.2. Electrolyser deployment and support
electrolysis, storage, and transportation. By
supporting R&D, governments can accelerate
Governments can provide financial incentives,
technological advancements, improve efficiency,
grants, and loans to promote the deployment of
and drive down the costs
electrolyser projects. This can help overcome the
high capital costs associated with electrolysers associated with green hydrogen production.
and encourage the establishment of large-scale Collaboration between industry, academia, and
green hydrogen production facilities. research institutions can foster innovation and
Additionally, funding research and development expedite the commercialization of new
initiatives focused on improving the efficiency technologies.
and cost-effectiveness of electrolysis
6.6. International cooperation and standards
technologies is essential to accelerate their
commercialization.
Encouraging international cooperation and
6.3. Infrastructure development harmonizing standards is crucial for the
development of a global green hydrogen market.
Developing a robust hydrogen infrastructure is Governments can facilitate collaboration among
critical for the widespread adoption of green countries to share best practices, research
hydrogen. Governments can support the findings, and expertise. Establishing common
construction of hydrogen refueling stations, standards for green hydrogen production,
hydrogen pipelines, and storage facilities storage, transportation, and usage ensures
through publicprivate partnerships or direct interoperability and facilitates trade, promoting
investments. Establishing a comprehensive economies of scale and cost reductions.
hydrogen distribution network enhances the 6.7. Sector integration and demonstration projects
accessibility and availability of green hydrogen,
thereby stimulating demand and market growth. Governments can promote sector integration by
6.4. Carbon pricing and market mechanisms
supporting demonstration projects that showcase
the use of green hydrogen across various sectors.
Implementing carbon pricing mechanisms, such For example, incentivizing the adoption of
as carbon taxes or cap-and-trade systems, can hydrogen fuel cell vehicles in transportation,
create a level playing field for green hydrogen by integrating greenhydrogen in industrial processes,
internalizing the cost of carbon emissions. This or utilizing it for grid balancing and energy storage
incentivizes the shift from carbon-intensive fuels purposes. These projects help build confidence,
to green hydrogen. Moreover, the creation of drive innovation, and provide valuable insights
hydrogen markets and the establishment of into the technical and economic viability of green
tradable hydrogen certificates can facilitate the hydrogen applications.
trading and transparent tracking of green
6.8. Education and workforce development
hydrogen, promoting its deployment across
regions and sectors. Investing in education and workforce
6.5. Research and development funding
development is essential for building a skilled
workforce to support the growth of the green
 international journal of hydrogen energy 50 (2024) 310e333 26

hydrogen industry. Governments can establish its potential to decarbonize various sectors, such
training programs, educational initiatives, and as industry, transport, power generation, and
partnerships with academic institutions to foster buildings. The strategy sets clear targets and
the development of a knowledgeable workforce outlines a range of measures to support the
specialized in green hydrogen technologies, development and deployment of green hydrogen
operations, and maintenance. technologies [74].

6.9. Long-term policy stability and support Targets: The EU aims to install 6 GW of green
hydrogen electrolysers by 2024 and at least 40
Providing long-term policy stability and regulatory GW by 2030. The strategyalso sets a targetto
certainty is crucial for attracting private produceup to 10 million metric tons of
investments in green hydrogen projects. renewable hydrogen by 2030. These targets
Governments can implement supportive policies, are designed to help the EU meet its climate
such as long-term off-take agreements, feed-in and energy goals, including the European
tariffs, and guaranteed purchase prices, to Green Deal, which aims to achieve climate
mitigate investment risks and ensure a stable neutrality by 2050.
market for green hydrogen. Policy frameworks
Investments: The European Commission
should prioritize sustainability, environmental
estimates that investments in green hydrogen
protection, and carbon reduction targets to
will range between V180e470 billion by 2050.
provide a clear and consistent direction for the
The EU will provide financial support through
green hydrogen industry.
various instruments, including the EU budget,
Overcoming the technological limitations and the European Investment Bank (EIB), and the
scalability challenges of green hydrogen adoption Innovation Fund. The strategy also encourages
requires a multifaceted approach, including the mobilization of private investments to
enhancing electrolysis efficiency, developing support green hydrogen projects.
durable and cost-effective electrolysis, advancing
Infrastructure: The strategy emphasizes the
hydrogen storage technologies, integrating
importance of developing a European
renewable energy sources, encouraging large-
hydrogen infrastructure, including the
scale deployment, and fostering collaboration and
repurposing and retrofitting of existing natural
innovation. By addressing these challenges, green
gas pipelines, as well as the construction of
hydrogen can become a viable and sustainable
new hydrogen pipelines and storage facilities.
energy carrier for the future.
The EU plans to create a European Hydrogen
Backbone, which will connect production sites
and demand centers across the continent.
7. Case studies: green hydrogen initiatives around
the world Research and innovation: The EU will invest in
research and innovation to develop new green
7.1. European Union hydrogen strategy
hydrogen technologies, reduce costs, and
improve the efficiency of the hydrogen value
The European Union (EU) has developed an
chain. The strategy highlights the role of the
ambitious Hydrogen Strategy to facilitate the
Clean Hydrogen Partnership, a public-private
transition to a climateneutral economy by 2050.
partnership that supports collaborative
The strategy aims to scale up the production and
research and innovation projects in the
use of green hydrogen across the EU, focusing on
hydrogen sector.
 international journal of hydrogen energy 50 (2024) 310e333 27

Market development: The strategy outlines with both government and private sector
measures to create a market for green involvement. Some of these projects include:
hydrogen, including setting standards for
- Asian Renewable Energy Hub (AREH): A
renewable and low-carbon hydrogen,
establishing guarantees of origin, and large-scale renewable energy project aiming
incorporating green hydrogen into the EU to produce green hydrogen using wind and
Emissions Trading System (ETS). The EU will solar energy. The project plans to have a
also promote the use of green hydrogen in capacity of up to 26 GW and is expected to
sectors that are hard to decarbonize, such as export hydrogen to international markets,
steel production, heavy-duty transport, and the
particularly in Asia [77].
chemical industry.
- Woodside Energy H2TAS Renewable
International cooperation: The EU plans to
Hydrogen Project: This project in Tasmania
engage in international cooperation to
promote the global development and adoption aims to become a global producer of green
of green hydrogen. The strategy emphasizes hydrogen by 2030, leveraging the island
partnerships with neighbouring countries, such abundant hydropower and wind resources.
as those in North Africa, to harness their The government has developed the
renewable energy potential for green hydrogen Tasmanian Renewable
production. The EU also aims to develop a
global regulatory framework and standards for Hydrogen Action Plan to support the project
[78].
green hydrogen.
Research and development: The Australian
Renewable Energy Agency (ARENA) has been
7.2. Green hydrogen projects in Australia
actively supporting the research,
Green hydrogen has gained significant development, and deployment of
momentum in Australia, with the country aiming greenhydrogen technologies in Australia. In
to become a major global player in the hydrogen addition to providing funding for various
market. The Australian government has laid out a green hydrogen projects, ARENA has
roadmap for green hydrogen production and published a report on “Opportunities for
export,taking advantage of thecountryvast Australia from Hydrogen Exports” to assess the
renewableenergy resources, particularly solar and potential for hydrogen export markets and
wind [75]. identify priority areas for investment [79].

Infrastructure development: To support the

National hydrogen strategy: The National
growth of the green hydrogen industry,
Hydrogen Strategy, launched in November
Australia is working on developing the
2019, outlines the vision and priorities for the
necessary infrastructure, such as hydrogen
development of a clean, innovative,
production facilities, transportation and
competitive, and safe hydrogen industry in
distribution networks, and storage facilities.
Australia. The strategy focuses on producing
The government is also exploring potential
clean hydrogen for domestic use and export,
export markets and partnerships to ensure a
creating jobs, and reducing emissions [76].
stable demand for Australian green hydrogen.
Key projects and initiatives: Australia is home
to several ambitious green hydrogen projects,
 international journal of hydrogen energy 50 (2024) 310e333 28

Australian roadmap for green hydrogen Infrastructure development: The development

production focuses on leveraging the country of hydrogen infrastructure is a key component
abundant renewable energy resources, investing of Japan roadmap. This includes the
in research and development, supporting large- construction of hydrogen refueling stations
scale projects and initiatives, and developing the for FCEVs, the development of hydrogen
necessary infrastructure to support the growth pipelines, and the establishment of hydrogen
of the green hydrogen industry. import facilities. Japan is also exploring
international partnerships to secure a stable
7.3. Japan hydrogen society roadmap supply of hydrogen from overseas sources.

Japan vision for a hydrogen-based society is Regulatory and policy frameworks: Japan has
outlined in its Basic Hydrogen Strategy, which implemented various regulatory and policy
was released in December 2017. The strategy measures to support the hydrogen industry.
provides a comprehensive roadmap for the This includes subsidies for FCEVs and
development, adoption, and integration of hydrogen refueling stations, tax incentives for
hydrogen technologies to create a sustainable hydrogen-related investments, and the
and low-carbon energy system. Japan strategic inclusion of hydrogen in the country energy
approach is driven by its commitment to address mix. Japan also aims to develop international
climate change, reduce energy imports, and standards for hydrogen technologies, which
foster economic growth through the hydrogen will facilitate global collaboration and market
industry [80]. growth.

International cooperation: Japan strategy

Targets: The Basic Hydrogen Strategy sets
emphasizes the importance of international
targets for the expansion of hydrogenuse
cooperation in the development and
acrossdifferentsectors, such as power
deployment of hydrogen technologies. The
generation, transportation, and residential
country has engaged in several collaborative
applications. For instance, Japan aims to have
initiatives, such as the Hydrogen Energy
200,000 fuel cell electric vehicles (FCEVs) on
Ministerial Meeting (HEM), the International
the road and 320 hydrogen refueling stations
Partnership for Hydrogen and Fuel Cells in the
operational by 2025. By 2030, the country
Economy (IPHE), and bilateral partnerships
aims to achieve a cost reduction of green
with countries like Australia and Norway.
hydrogen to ¥30 per normal cubic meter
(approximately $0.27).
7.4. Green hydrogen in the United States and Canada
Research and development: Japan strategy strategy
highlights the importance of research and
development (R&D) in advancing hydrogen While the United States and Canada have not yet
technologies and reducing costs. The country developed a comprehensive joint roadmap for
supports R&D in various areas, including green hydrogen, both countries have individually
electrolysis, hydrogen storage, and taken steps to promote green hydrogen
transportation. The strategy also encourages production and utilization as part of their
collaboration between industry stakeholders, broader clean energyand climatechange
research institutions, and the government to strategies. Here are some key aspects of green
accelerate technological innovation. hydrogen initiatives in the United States and
Canada [81,82].
 international journal of hydrogen energy 50 (2024) 310e333 29

7.4.1. United States Investments: The Canadian government has

The U.S. Department of Energy (DOE) has committed to investing in hydrogen projects
launched the Hydrogen Program, which focuses through various funding programs, such as the
on research, development, and deployment of Strategic Innovation Fund, the Clean Fuel Fund,
hydrogen technologies, including green and the Low Carbon Economy Fund.
hydrogen production through water electrolysis.
The program aims to reduce the cost of Infrastructure development: Canada strategy
hydrogen production, increase efficiency, and emphasizes the need for infrastructure
improve the performance of hydrogen systems development to support the growth of the
[83]. hydrogen sector, including hydrogen
production facilities, distribution networks, and
H2@Scale: This initiative explores the potential refueling stations.
for widescale hydrogen production and International cooperation: The strategy
utilization in the United States. H2@Scale underscores the importance of international
supports research and development in collaboration in advancing hydrogen
hydrogen production, storage, and end-use technologies, promoting global market growth,
applications, including green hydrogen and developing a robust hydrogen export
production from renewable energy sources. market.
Hydrogen Energy Earthshot: Launched in June
2021, the Hydrogen Energy Earthshot is part of Table 6 summaries the European union,
the DOE broader Energy Earthshots Initiative. Australia, Japan, United States and Canada
The Hydrogen Energy Earthshot aims to reduce strategies toward green hydrogen production.
the cost of clean hydrogen production to $1 While the United States and Canada have not
per kilogram within a decade, making it a more developed a joint roadmap for green hydrogen,
economically viable and competitive energy both countries are independently pursuing
carrier. strategies and initiatives to promote green
hydrogen production and use as part of their
clean energy transitions. These efforts include
7.4.2. Canada setting targets, investing in research and
Canada Hydrogen Strategy, released in December development, supporting infrastructure
2020, outlines a comprehensive vision for development, and engaging in international
leveraging hydrogen as a key component of its cooperation.
clean energy transition. The strategy highlights
the potential of green hydrogen production using The optimum strategy for green hydrogen
the country abundant renewable energy production can vary depending on the specific
resources, such as hydropower, wind, and solar context and regional characteristics. However,
energy [83e85]. based on the initiatives and commitments of
different regions, it can provide a hypothetical
Targets: The strategy aims to make Canada a assessment of the strategies mentioned. Fig. 12
top-three global hydrogen producer, increase show the approximate optimum strategy for
hydrogen use across various sectors, and green hydrogen production.
generate over 350,000 jobs in the hydrogen Explanation:
sector by 2050.
 international journal of hydrogen energy 50 (2024) 310e333 30

European Union hydrogen strategy: the

European Union has shown strong commitment
to green hydrogen and has set ambitious targets
and allocated substantial funding. The EU strategy
encompasses a comprehensive approach and
benefits from access to diverse renewable energy
sources, making it the highest allocated
percentage.

Green hydrogen strategy in Australia: Australia

possesses abundant renewable energy resources
and has demonstrated significant commitment to
green hydrogen. The country
 328

Table 6 e Compression of European union, Australia, Japan, United States and Canada strategies toward green hydrogen production [86e96].
internationaljournalofhydrogenenergy50(2024)31
Criteria European union hydrogen Green hydrogen projects Japan hydrogen society Green hydrogen in
the United strategy strategy in Australia roadmap States and Canada strategy
Targets - 6 GW of electrolyzers by 2024, - Asian Renewable Energy Hub: - 200,000 FCEVs and 320 hydrogen - U.S.: $1 per kg clean hydrogen
40 GW by 2030 26 GW capacity refueling stations by 2025 within a decade (Hydrogen En-
- 10 million metric tons of renew- - Tasmania: Global producer of - Green hydrogen cost reduction to ergy Earthshot)
able hydrogen by 2030 green hydrogen by 2030 ¥30 per Nm3 by 2030 - Canada: Top-three global
0
hydrogen producer by 2050
Research and Development - Clean Hydrogen Partnership - Supported by Australian Renew- - Collaboration between industry, - U.S. Hydrogen Program - Focus on cost reduction and effi- able Energy
Agency (ARENA) research institutions, and H2@Scale initiative ciency improvements - Woodside Energy HyNet Project government - Canada: Investment through
- R&D in electrolysis, hydrogen various funding programs storage, and transportation
Infrastructure Development - European Hydrogen Backbone - AREH: Export to domestic and - Construction of hydrogen refuel- - U.S.: H2@Scale initiative - Can-
- Retrofit existing natural gas international markets ing stations ada: Hydrogen production facilpipelines and construct new - HyP SA: Distribution to local -
Development of hydrogen pipe- ities, distribution networks, and pipelines and storage facilities homes and businesses lines and import facilities refueling stations
e33
Regulatory and Policy Frameworks - Standards for renewable and - Tasmania Renewable Hydrogen - Subsidies for FCEVs and - U.S.: DOE Hydrogen Program and low-carbon hydrogen3 Action Plan
hydrogen refueling stations Hydrogen Energy Earthshot
- Guarantees of origin - Incorpo- - Renewable Hydrogen Fund - Tax incentives for hydrogen- - Canada: Strategic Innovation
rating green hydrogen into the related investments Fund, Clean Fuel Fund, and Low
EU ETS - Inclusion of hydrogen in Japan Carbon Economy Fund
energy mix
International Cooperation - Partnerships with North Africa - Asian Renewable Energy Hub: - Hydrogen Energy Ministerial - U.S.: International cooperation for green hydrogen production
Export-oriented project Meeting (HEM) through DOE initiatives
- Development of global regulatory - International Partnership for - Canada: Emphasis on internaframework and standards Hydrogen and Fuel Cells in the tional
collaboration and export Economy (IPHE) market development
- Bilateral partnerships with countries like Australia and
Norway
 European Union
0 Australia Japan

international journal of hydrogen energy 50 (2024) 310e333 32

Unit

Fig. 12 e Optimum strategy for green hydrogen production. (For interpretation of the references to color in this

figure legend, the reader is referred to the Web version of this article.)
strategy leverages its natural advantage in enhancing energy security, fostering economic
renewables, including solar and wind power, growth, and decarbonizing various sectors.
warranting a substantial allocation.
Through the examination of various strategies
Japan hydrogen society strategy: Japan has been and policies employed by the European Union,
at the forefrontof hydrogen adoption and aimsto Australia, Japan, and the United States and Canada,
createa hydrogenbased society. While it faces it is evident that comprehensive planning,
challenges due to limited domestic renewable collaboration, and commitment are crucial to
energy resources, Japan strategy, research efforts, driving the development and adoption of green
and commitment warrant a notable percentage hydrogen technologies. While challenges and
allocation. barriers still exist, the recommendations presented
in this paper provide a roadmap for overcoming
Green hydrogen strategy in the United States and
these obstacles and accelerating the deployment of
Canada: both the United States and Canada have
green hydrogen technologies on a global scale.
recognized the potential of green hydrogen and are
making efforts to develop their strategies. While 8.1. Summary of the potential of green hydrogen as a key for
they possess significant renewable energy sustainable energy future
potential, their strategies are relatively nascent
compared to the European Union and Australia, As demonstrated throughout this paper, the green
resulting in a lower percentage allocation. hydrogen production and utilization can significantly
contribute to reducing greenhouse gas emissions,
It is important tonote that these percentages are enhancing energy security, and fostering economic
subjective and based on the current information growth. The integration of green hydrogen into
available. The optimal strategy for green hydrogen various sectors, such as transportation, industry,
production can vary depending on factors such as power generation, and heating, can help
policy implementation, market dynamics, decarbonize these traditionally carbon-intensive
technological advancements, and regional areas and pave the way for a more sustainable
characteristics. Continuous collaboration, energy future. Moreover, the geographical and
knowledge sharing, and policy advancements sectoral versatility of green hydrogen allows it to
among these regions can further optimize the complement other renewable energy sources and
strategies and facilitate the growth of the green energy storage solutions, increasing the overall
hydrogen industry. resilience and flexibility of energy systems.

The case studies of the European Union, Australia,

8. Conclusion
Japan, and the United States and Canada have
shown that strategic planning and collaboration
The green hydrogen holds immense potential as a among governments, private sector, and research
key component of a sustainable energy future. As institutions are crucial to the successful
outlined in this paper. The production and development and deployment of green hydrogen
utilization of green hydrogen can significantly technologies. By setting ambitious targets, investing
contribute to reducing greenhouse gas emissions, in research and development, developing supportive
330 international journal of hydrogen energy 50 (2024) 310e333

regulatory and policy frameworks, and fostering

 international journal of hydrogen energy 50 (2024) 310e333 33

international cooperation, these regions are taking Strengthen regulatory and policy frameworks:
significant strides towards realizing the potential of Implementing supportive regulatory and policy
green hydrogen as a key component of a sustainable frameworks, including subsidies, tax incentives,
energy future. However, challenges and barriers, and the inclusion of green hydrogen in energy and
such as technological limitations, infrastructure climate policies, will create a favorable
development, costs and economic feasibility, environment for green hydrogen production and
regulatory and policy frameworks, and public use.
perception and acceptance, must be overcome to
Foster public-private partnerships: Encouraging
fully realize the potential of green hydrogen.
collaboration between public and private sectors
Addressing these challenges through continued
can help share risks, pool resources, and drive the
research, innovation, collaboration, and policy
large-scale deployment of green hydrogen
support will be crucial in the years to come. As the
production technologies.
global community strives to achieve the goals set
forth in the Paris Agreement and transition to a low- Enhance international cooperation: Engaging in
carbon, sustainable energy system, green hydrogen international collaboration and knowledge-
has the potential to play a significant role. By sharing can accelerate the development and
harnessing the power of green hydrogen and deployment of green hydrogen technologies,
leveraging its unique properties, we can pave the facilitate technology transfer, and establish global
way for a more sustainable and decarbonized energy regulatory frameworks and standards.
future, ultimately benefiting the planet and future
Invest in education and workforce development:
generations.
Developing a skilled workforce capable of
8.2. Recommendations for overcoming challenges and supporting the growth of the green hydrogen
accelerating the adoption of green hydrogen technologies industry will be essential to meeting the demand
for specialized labour as the sector expands.
Overcoming the challenges and accelerating the
adoption of green hydrogen technologies is essential Promote public awareness and acceptance:
to harness the full potential of green hydrogen as a Addressing misconceptions and increasing public
key component of a sustainable energy future. As awareness of the benefits of green hydrogen as a
detailed in the paper several recommendations can clean and sustainable energy source can help
be implemented to address these challenges and overcome potential resistance to the deployment
foster the widespread adoption of green hydrogen of hydrogen technologies.
technologies:
By implementing these recommendations,
Enhance research and development: Continued stakeholders can work together to overcome the
investment in research and development is crucial challenges associated with green hydrogen and
for advancing green hydrogen production accelerate its adoption, ultimately contributing to
technologies, improving efficiency, reducing costs, the global transition towards a low-carbon,
and developing innovative applications across sustainable energy system. The success of green
various sectors. hydrogen technologies will depend on the combined
efforts of governments, industry, researchers, and
Develop and improve infrastructure: The expansion society at large. Through collaboration, innovation,
of green hydrogen production, storage, and commitment, we can unlock the potential of
distribution, and utilization infrastructure is vital green hydrogen and pave the way for a more
to support the growth of the green hydrogen sustainable and decarbonized energy future.
industry and ensure its seamless integration into
existing energy systems.
 international journal of hydrogen energy 50 (2024) 310e333 34

Declaration of competing interest [16] Falcone PM, Hiete M, Sapio A. Hydrogen economy and sustainable
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Curr Opin Green Sustainable Chem 2021;31:100506.
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competing financial interests or personal renewable energy society. Curr Opin Chem Eng
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