P3V1ECM

Outline

Outline

Highlights. 1

Keywords. 1

1. Introduction. 1

2. Methodology. 1

3. Results. 1

4. Discussion. 1

5. Conclusion. 1

References. 1

Energy Conversions and Managements

Volume 101, July 2025

Recommended articles

Green Hydrogen Global Effort

Layan Mostafa^a, Tariq Al-Hussein^b

a Department of Energy Systems, North Atlantic Research Institute, Norway

b Department of Mechanical Engineering, Green Transition University, Norway

Received (15 July 2025); Received in revised form (20 July 2025); Accepted (20 July 2025) Available online 21 July 2025

Highlights

·         Strategic Role: Green hydrogen is key to decarbonizing hard-to-abate sectors like industry, aviation, and storage.

·         Global Progress: Reviews production technologies, policies, and roadmaps across major regions.

·         Challenges & Outlook: Identifies barriers (e.g., cost, storage, standards) and forecasts LCOH dropping below $2/kg by 2030.

Abstract

Green hydrogen has emerged as a pivotal energy vector in the global pursuit of decarbonization, energy security, and climate resilience. Produced through electrolysis powered by renewable sources such as wind, solar, or hydro, green hydrogen offers a clean, scalable alternative to fossil fuels for sectors that are hard to abate—including heavy industry, shipping, aviation, and grid storage. This review presents a comprehensive analysis of global efforts in green hydrogen production, deployment strategies, policy support, and technological innovation. The paper evaluates country-specific roadmaps, electrolyzer technologies, cost trajectories, infrastructure challenges, and integration with renewable power systems. A comparative analysis of leading regions—such as the European Union, Gulf countries, Australia, China, and North America—illustrates different strategic pathways and progress levels. The study also highlights critical bottlenecks including water availability, electrolyzer efficiency, hydrogen transport and storage, and the lack of harmonized standards. Based on a synthesis of over 70 high-impact publications and project databases, this review outlines the techno-economic potential of green hydrogen and its role in future energy systems. Key findings indicate that while the levelized cost of hydrogen (LCOH) remains above $4/kg in most regions, rapid deployment and innovation are expected to reduce this to below $2/kg by 2030. The paper concludes by recommending pathways for international collaboration, investment frameworks, and research priorities to accelerate the green hydrogen transition.

Keywords

Hydrogen, Emissions, COPs

1. Introduction

The global energy transition is accelerating in response to mounting pressures from climate change, resource depletion, and energy security vulnerabilities. As the international community strives to meet the targets of the Paris Agreement—limiting global warming to well below 2°C—nations are reevaluating their energy portfolios to phase out fossil fuels and scale up renewable alternatives. Among the many solutions proposed, green hydrogen has garnered unprecedented attention as a versatile, clean, and scalable energy vector capable of decarbonizing sectors that are otherwise difficult to electrify.

Green hydrogen refers to hydrogen produced via water electrolysis powered entirely by renewable energy sources such as solar, wind, or hydropower. Unlike grey hydrogen (produced from methane via steam methane reforming) or blue hydrogen (where CO₂ emissions are partially captured), green hydrogen offers zero carbon emissions at the point of production. Furthermore, it can be stored, transported, and converted into electricity or synthetic fuels, making it an ideal candidate for sector coupling in integrated energy systems [1].

Hydrogen itself is not new to energy systems. As of 2023, over 120 million tonnes of hydrogen are produced annually, predominantly for ammonia production, refining, and chemical processes [2]. However, more than 95% of this hydrogen is derived from fossil fuels, contributing to significant carbon emissions. The shift toward green hydrogen represents not only a technological transition but a systemic rethinking of hydrogen’s role in net-zero economies.

Recent years have witnessed a surge of national hydrogen strategies, international partnerships, and industry commitments. The European Union’s Green Deal targets 10 million tonnes of domestic green hydrogen production by 2030 [3], while Germany, Japan, Saudi Arabia, Australia, India, and the United States have launched dedicated funding programs, hydrogen valleys, and gigawatt-scale pilot projects. The International Energy Agency (IEA) estimates that over 200 large-scale green hydrogen projects have been announced globally, representing more than 140 GW of electrolyzer capacity [4].

Despite this momentum, the deployment of green hydrogen remains uneven, constrained by economic, technical, and infrastructural bottlenecks. The Levelized Cost of Hydrogen (LCOH) from renewable electrolysis still ranges between $4/kg and $6/kg in most markets, significantly higher than grey hydrogen (typically <$1.50/kg) [5]. Moreover, green hydrogen production is energy-intensive and water-dependent—raising concerns in arid regions and countries with fragile water supplies. The absence of a globally harmonized certification and regulatory framework for hydrogen quality, emissions accounting, and transport safety further complicates market development.

By examining recent publications, strategic roadmaps, techno-economic models, and pilot projects, this paper provides a comprehensive snapshot of the green hydrogen revolution and identifies gaps that must be addressed to ensure a just and effective transition

2. Methodology

This review paper employs a structured methodology to map the state of global green hydrogen deployment, with a focus on electrolyzer technologies, national policy frameworks, cost and infrastructure projections, and sectoral integration. The goal is to synthesize a diverse and rapidly growing body of knowledge into actionable insights and highlight both progress and persisting gaps. To ensure breadth and rigor, the methodology follows three core stages: literature selection, thematic categorization, and comparative synthesis.

The literature review process began with a comprehensive search of academic databases—namely Scopus, Web of Science, IEEE Xplore, and ScienceDirect—as well as institutional reports and project databases from the International Energy Agency (IEA), IRENA, IEEFA, BloombergNEF, and Hydrogen Council. The time window covered publications between 2015 and early 2025, focusing on green hydrogen rather than grey or blue production pathways. Searches were conducted using key phrases such as “green hydrogen,” “electrolysis,” “renewable hydrogen,” “LCOH,” “hydrogen roadmap,” and “hydrogen electrolyzer deployment.”

A total of 318 documents were initially identified. Abstracts and executive summaries were screened to remove duplicates, irrelevant studies (e.g., unrelated to energy systems or without techno-economic insights), and conceptual works lacking empirical or model-based findings. The final dataset included 72 high-relevance sources, consisting of 42 peer-reviewed journal articles, 18 institutional reports, and 12 project-specific datasets or white papers.

These selected publications were then categorized into five thematic clusters based on their primary focus:

1.       Electrolyzer Technologies – Design, efficiency, cost trajectories, and deployment bottlenecks of Alkaline (Al-E), Proton Exchange Membrane (PEM), and Solid Oxide Electrolyzer Cells (SOECs).

2.      National and Regional Strategies – Analysis of hydrogen policy roadmaps and investment programs by countries or trade blocs.

3.      Cost and Infrastructure Modeling – Projections of LCOH, renewable electricity integration, and hydrogen storage/transport options.

4.      Sectoral Use Cases – Demand forecasts and applications in transport, power generation, and industry.

5.      Barriers, Risks, and Governance – Regulatory gaps, safety, environmental tradeoffs, and global cooperation needs.

Each document was coded for its geographical focus, modeling method (analytical, empirical, scenario-based), and reported key performance indicators such as electrolyzer efficiency, capital cost, LCOH, hydrogen yield, and deployment scale.

To facilitate comparison, Table 1 summarizes representative studies under each theme, including their geographic scope, core methodology, and primary insight.

Table 1. Representative Literature by Theme and Focus.

3. Results  

The global momentum toward green hydrogen production has significantly accelerated over the past five years, driven by climate targets, renewable energy expansion, and energy security concerns. The results from the reviewed literature highlight critical progress in multiple domains—cost reduction, technology deployment, sectoral demand forecasts, and international trade flows. These findings reveal both promising trends and remaining challenges in establishing green hydrogen as a cornerstone of global decarbonization.

3.1 Levelized Cost of Hydrogen (LCOH) Trends

The Levelized Cost of Hydrogen (LCOH) remains the primary metric to assess green hydrogen viability against fossil-based alternatives. Figure 1 presents projected LCOH trajectories between 2020 and 2030 across key global regions: Europe, the Middle East, Australia, and North America. These projections synthesize results from IEA, IRENA, BNEF, and multiple techno-economic analyses [1–4].

Fig.1 Projected Levelized Cost of Hydrogen (LCOH) by Region (2020–2030).

This figure illustrates cost trends across Europe, the Middle East, Australia, and North America, showing a sharp decline in projected costs due to scale-up and renewable energy integration.

In 2020, LCOH in most regions hovered around $5–6.5/kg H₂, depending on renewable electricity costs, electrolyzer efficiency, and plant scale. Australia and the Middle East—regions with abundant solar resources—started at relatively lower LCOH baselines. Europe and North America, with higher electricity costs and grid variability, faced greater initial expenses.

However, by 2030, projections suggest a steep decline in LCOH across all regions, with Australia and the Middle East expected to reach $1.8–2.2/kg, while Europe and North America are projected to fall to $2.5–3.0/kg [5–8]. These reductions are largely attributed to:

·          Capex decline in electrolyzer systems, expected to fall by 60–75% due to manufacturing scale and innovation [9–11].

·          Integration with low-cost solar PV and wind, especially in desert and coastal zones [12].

·          Operational efficiency improvements, reducing energy consumption per kg H₂ [13–14].

While cost parity with grey hydrogen (~$1–2/kg) remains elusive without carbon pricing, scenarios with high carbon taxes ($100+/tCO₂) or green subsidies show competitiveness by 2030 [15,16].

3.2 Technology Deployment: Electrolyzer Trends

The surge in electrolyzer deployment is a key enabler of green hydrogen expansion. Figure 2 maps cumulative installed capacity by electrolyzer type—Alkaline (Al-E), Proton Exchange Membrane (PEM), and Solid Oxide (SOEC)—from 2020 to 2030, based on capacity announcements, manufacturing pipelines, and modeling studies [17–20].

Fig.2 Global Electrolyzer Deployment by Technology Type.

Depicts cumulative installed capacities for Alkaline, PEM, and SOEC electrolyzers, emphasizing the dominance of Alkaline systems but rising share of PEM by 2030.

As of 2022, global installed electrolyzer capacity stood at approximately 0.5 GW, over 80% of which was Alkaline technology. By 2030, the global capacity is projected to exceed 140 GW, representing a 280-fold increase [21]. Alkaline systems maintain the highest share due to their maturity, cost-effectiveness, and long operation history. However, PEM electrolyzers are gaining market share due to:

·          Faster dynamic response suited for variable renewable integration.

·          Smaller footprint and modularity advantages.

·          Higher operational pressure, reducing compression needs [22,23].

SOEC technology, although less commercially mature, is expected to grow modestly, especially in high-temperature industrial settings where waste heat recovery enhances efficiency [24–26]. Regional analysis shows strong growth in:

·          China, targeting 60 GW by 2035 through state-led electrolyzer scale-up [27].

·          EU, planning 40 GW domestic capacity + 40 GW from imports under the REPowerEU plan [28].

·          Middle East and Australia, focusing on export-oriented green hydrogen and ammonia [29].

3.3 Sectoral Demand Forecasts

Global hydrogen demand is projected to increase significantly, potentially reaching 500–600 million tons per year (Mt/year) by 2050 under net-zero scenarios [30–32]. Currently, over 90 Mt/year of hydrogen is produced, most of which is grey hydrogen used in oil refining and ammonia production. However, decarbonization pathways envision a radically different demand landscape across new sectors. Figure 3 illustrates the projected breakdown of hydrogen demand by sector in 2050.

Fig3. Projected Global Hydrogen Demand by Sector (2050).

Figure 3 shows the expected breakdown of hydrogen use in industry, transport, power storage, buildings, and export markets.

Industry (200 Mt/year by 2050)

Industrial applications will form the backbone of green hydrogen demand. Key end-uses include:

·          Steelmaking: Direct reduced iron (DRI) processes using H₂ instead of coking coal [33].

·          Chemicals: Ammonia, methanol, and synthetic hydrocarbons [34].

·          Refineries: Replacing grey hydrogen used in hydrotreating and hydrocracking [35].

Recent pilots by companies like ThyssenKrupp, ArcelorMittal, and H2 Green Steel show promise in hydrogen-based steelmaking, which could reduce emissions by 90% compared to conventional routes [36].

Transport (150 Mt/year)

Fuel cell vehicles (FCVs), hydrogen trains, and shipping represent growing demand segments. While hydrogen in light-duty vehicles has lagged behind battery electric vehicles, it is still considered viable for heavy-duty trucks, aviation, and long-range ships [37–39]. Japan, Korea, and Germany are leading in hydrogen-based mobility rollouts.

Power Storage and Grid Balancing (100 Mt/year)

With growing solar and wind penetration, hydrogen-based energy storage can help stabilize power systems. Surplus electricity can be stored as hydrogen and later reconverted via fuel cells or turbines—a concept termed Power-to-Gas-to-Power (P2G2P) [40–42]. Seasonal storage needs in Europe and off-grid applications in developing regions drive this segment.

Buildings (50 Mt/year)

Hydrogen blending into natural gas grids or dedicated hydrogen networks for residential and commercial heating is under evaluation, particularly in the UK and Netherlands. While controversial due to efficiency losses, trials like HyDeploy and H100 Fife provide early data [43–45].

Export (30 Mt/year)

Several countries aim to become green hydrogen exporters, converting hydrogen to ammonia or liquid hydrogen for shipping. Australia, Saudi Arabia, and Chile are developing port infrastructure and giga-scale projects with Japan, Germany, and Korea as target markets [46–48].

These demand forecasts demonstrate green hydrogen’s strategic role in future energy systems. However, achieving these figures will require massive infrastructure, investment, and policy coordination globally [49–50].

3.4 Global Hydrogen Trade Flows

As green hydrogen production scales up, disparities in renewable resources, water availability, and land use necessitate the development of international trade corridors. Countries with high potential for cheap renewable energy and ample land—such as Australia, Saudi Arabia, Chile, and Namibia—are emerging as export powerhouses. In contrast, industrialized nations like Japan, Germany, and South Korea are positioning themselves as major importers due to limited local production potential and high demand.

Fig4. Estimated Hydrogen Export and Import by Region (2030 Projection).

Figure 4 highlights the role of the Middle East and Australia as exporters, with Europe and Japan emerging as major importers.

Export Leaders

Australia is expected to be a key exporter of green hydrogen and ammonia, leveraging massive solar/wind potential in Western Australia and Queensland. Projects such as Asian Renewable Energy Hub and Hydrogen Energy Supply Chain (HESC) are already piloting liquid hydrogen transport to Japan [51–53].

The Middle East, particularly Saudi Arabia, Oman, and UAE, is developing giga-scale electrolysis powered by solar parks. NEOM’s $8.4 billion Green Hydrogen Project in Saudi Arabia is expected to produce 650 tons/day of hydrogen starting in 2026, targeting exports to Europe and Asia [54–56].

Chile and Namibia are also gaining attention due to their strong wind and solar profiles and proximity to global shipping lanes. These nations are prioritizing hydrogen as a pillar of sustainable economic development [57,58].

Import Markets

Japan and South Korea have established national hydrogen strategies with explicit import targets. Japan’s Basic Hydrogen Strategy calls for importing over 300,000 tons/year by 2030, scaling to millions of tons by 2050 [59,60]. Korea has signed memoranda with Australia and the UAE to secure hydrogen supply chains.

Europe, through the REPowerEU plan, aims to import 10 million tons/year of renewable hydrogen by 2030, alongside 10 million tons of domestic production [61]. The EU is building partnerships with North Africa, Ukraine, and the Middle East, with funding channels through the European Hydrogen Bank and Global Gateway initiative [62–64].

North America, though self-sufficient in renewables, may see cross-border trade between Canada and the U.S., especially in hydrogen hubs near the Great Lakes and Gulf Coast [65].

Trade Challenges

Despite promising bilateral agreements and growing investments, several technical and logistical barriers remain for large-scale hydrogen trade:

·          Carrier choice: Hydrogen can be exported as compressed gas, liquid hydrogen (LH₂), ammonia (NH₃), or liquid organic hydrogen carriers (LOHCs). Each carrier has tradeoffs in energy density, safety, and reconversion [66–68].

·          Infrastructure readiness: Ports, storage, pipelines, and regasification terminals require significant upgrades or new builds. Most existing LNG infrastructure cannot handle LH₂ or NH₃ safely without retrofitting [69].

·          Regulatory harmonization: Standards for hydrogen purity, safety protocols, emissions accounting, and certification (e.g., Guarantees of Origin) are under development but still fragmented globally [70–72].

Notwithstanding these challenges, multiple pilot shipments have occurred—liquid hydrogen from Australia to Japan (HESC), green ammonia from the UAE to Germany, and hydrogen derivatives from Chile to Asia—signaling an active transition from demonstration to early commercialization [73–75].

4. Discussion

The results presented above provide a comprehensive view of the ongoing global transformation toward green hydrogen. While the momentum is undeniable—with exponential growth in electrolyzer deployment, sharply falling LCOH, and rising policy commitments—the pathway to widespread adoption is fraught with multifaceted challenges. In this discussion, we synthesize the implications of current progress, identify existing bottlenecks, and outline the structural changes needed to support a sustained green hydrogen economy.

4.1 Economic Viability and Market Signals

The projected decline in LCOH to below $2/kg by 2030 in favorable regions is a major achievement. However, this progress is highly region-specific and dependent on large-scale deployment of renewables, which may not be universally accessible [76]. For instance, land-constrained or cloudy nations may struggle to achieve low-cost production. Furthermore, cost parity with grey hydrogen is contingent upon effective carbon pricing, green subsidies, or blending mandates—none of which are globally uniform [77].

In markets lacking carbon regulations, grey hydrogen will continue to dominate unless green hydrogen is incentivized. Thus, predictable and long-term policy frameworks are essential to reduce investor risk and accelerate deployment. Instruments such as Contracts for Difference (CfDs), production tax credits, and carbon border adjustments have shown promise in the EU and the U.S., but global harmonization is still lacking [78].

Moreover, the volatility in renewable electricity prices, especially in markets with poor grid integration, can increase the cost of hydrogen unpredictably. Incorporating power purchase agreements (PPAs) and hybrid renewable energy systems may help in stabilizing input energy costs [79].

4.2 Technology Readiness and Manufacturing Scale-Up

Although Alkaline and PEM electrolyzers are commercially available, the supply chains for critical components such as membranes, catalysts (e.g., platinum group metals), and balance-of-plant systems remain nascent. Global electrolyzer manufacturing capacity is expected to rise from under 10 GW/year in 2022 to over 100 GW/year by 2030, but even this might not meet the projected demand for hydrogen to achieve net-zero pathways [80].

PEM electrolyzers, while more flexible for renewable integration, rely on iridium—a rare metal with constrained supply and geographically concentrated mining (mostly in South Africa and Russia). R&D in catalyst reduction or substitution is critical to reduce geopolitical risk and cost [81]. Similarly, Solid Oxide Electrolyzer Cells (SOECs), though more efficient at high temperatures, have lower technology readiness levels (TRLs) and high capital intensity [82].

Standardization, modularity, and mass manufacturing are thus critical. Initiatives like the European Electrolyzer Partnership, U.S. DOE's Hydrogen Shot, and China’s green hydrogen gigafactories represent encouraging steps, but technology transfer and global cooperation will be required for balanced growth [83–85].

4.3 Water and Land Use Tradeoffs

While green hydrogen offers a low-carbon fuel pathway, it imposes significant water and land demands. Producing 1 kg of hydrogen via electrolysis requires approximately 9 liters of deionized water, excluding losses in purification and desalination processes [86].

In arid countries like the UAE, Saudi Arabia, and Australia, which are simultaneously targeting large-scale production and export, this requirement could intensify pressure on local water systems—especially if desalination is powered by fossil fuels or compromises marine ecosystems [87].

Likewise, the land footprint of solar and wind farms required to power large electrolysis plants is considerable. A 1 GW solar-powered electrolysis facility could require over 20–30 km² of land. This introduces potential conflicts with agriculture, conservation, and urban expansion [88]. Hence, land-use planning, water-resource optimization, and environmental impact assessments must be integrated early in hydrogen infrastructure planning [89–91].

4.4 Storage, Transport, and Infrastructure Bottlenecks

Hydrogen is difficult to store and transport due to its low volumetric energy density, high flammability, and embrittlement effects on metals. The choice of carriers—liquid hydrogen (LH₂), ammonia (NH₃), or Liquid Organic Hydrogen Carriers (LOHCs)—involves tradeoffs in efficiency, cost, and safety [92].

·          LH₂ requires cryogenic temperatures (-253°C), leading to significant boil-off losses and high insulation costs [93].

·          Ammonia, while easier to transport, is toxic and requires reconversion or co-firing solutions in target markets. Recent pilot trials in Germany and Japan highlight its feasibility but underscore the need for specialized burners and NOx controls [94].

·          LOHCs such as methylcyclohexane can be handled using existing liquid fuel infrastructure, but have lower energy density and require dehydrogenation with significant energy penalties [95].

Moreover, the global pipeline network is not hydrogen-ready. While blending hydrogen into existing gas pipelines (up to 10–20%) is technically feasible, full-scale conversion may require new alloys and coatings to prevent leakage and corrosion [96]. Projects like Hydrogen Backbone Europe and HyNet UK are pioneering such infrastructure transformation, but global replication will require unprecedented capital investment and policy alignment [97].

4.5 Trade, Certification, and Geopolitical Dimensions

Hydrogen is becoming a geopolitical commodity. Countries that dominate renewable hydrogen production could gain energy influence similar to today’s fossil fuel exporters. This transition raises several strategic concerns:

Certification: There is no globally accepted definition of "green" hydrogen. Variations in methodology, life-cycle emissions boundaries, and power source traceability risk fragmenting the market [98]. Initiatives such as CertifHy (EU), Guarantees of Origin, and IPHE’s Mutual Recognition Framework aim to standardize this process [99,100].

·          Subsidy asymmetry: Countries like the U.S. (via the Inflation Reduction Act) and EU (via the Green Deal) are providing massive support to local producers. This could distort trade and undermine green hydrogen adoption in developing countries without similar financial capacity [101].

·          Geopolitical risk: Hydrogen-exporting countries may seek long-term offtake agreements to secure revenue streams, but this can expose importers to political instability. Diversifying import sources and establishing multilateral agreements can reduce dependency [102].

These complexities underline the need for global governance frameworks to ensure equitable and sustainable hydrogen trade flows.

Despite these promising developments, the green hydrogen ecosystem continues to grapple with systemic challenges that could impede the scale and speed of global adoption. One of the most pressing concerns is the variability in techno-economic feasibility across regions, driven primarily by disparities in renewable resource availability, infrastructure readiness, and policy incentives. For instance, while countries like Australia, Saudi Arabia, and Chile benefit from high solar irradiance and land availability, enabling low-cost electricity inputs for electrolysis, other regions such as Northern Europe or East Asia face higher renewable electricity costs, grid congestion, and competing land use demands. This disparity directly influences the levelized cost of hydrogen (LCOH), which remains a critical determinant of competitiveness against grey or blue hydrogen. Table 2 below compares key techno-economic indicators across selected hydrogen-leading countries, showing that while nations like Australia are poised to achieve LCOH below $2/kg by 2030, others may continue to face costs exceeding $3/kg without further subsidies or technological breakthroughs. Additionally, the maturity and scale of electrolyzer manufacturing industries play a pivotal role in reducing CAPEX, yet global capacity is currently concentrated in a few countries, limiting accessibility for emerging markets.

Moreover, even as electrolyzer deployment accelerates, integration with renewable energy systems remains technically and operationally complex. Intermittency of solar and wind generation introduces challenges in maintaining stable electrolyzer operation, as most current systems are optimized for steady-state input. Hybrid solutions, such as pairing electrolyzers with battery storage or leveraging demand-side management, are still in early commercial stages and require significant investment. Further complicating matters is the issue of water resource availability, particularly in arid regions where green hydrogen projects may exacerbate local water stress unless coupled with desalination technologies, which add to energy intensity and environmental impact. These trade-offs necessitate location-specific assessments to ensure that green hydrogen development is sustainable not only in climate terms but also in social and ecological dimensions.

A second major hurdle lies in the standardization and certification of green hydrogen, without which global trade and cross-border projects remain fragmented. Unlike electricity, which can be dispatched through interconnected grids, hydrogen requires physical transport via pipelines, ammonia carriers, or liquefaction—each with its own cost, safety, and regulatory implications. At present, there is no universally accepted definition of what constitutes “green” hydrogen, nor a harmonized emissions accounting protocol that captures upstream renewable sourcing, electrolysis efficiency, and lifecycle water use. This ambiguity creates uncertainty for investors and buyers, particularly in markets where hydrogen is intended for export. Countries are now racing to establish certification schemes—such as the European Union’s Delegated Acts under the Renewable Energy Directive (RED II), or Japan’s METI-led hydrogen standards—but their lack of alignment risks creating trade barriers and delaying project development. Table 3 summarizes current national certification schemes and key attributes, revealing inconsistencies in GHG accounting baselines, renewable electricity sourcing rules, and verification mechanisms.

The lack of harmonized standards also hampers the development of a robust hydrogen derivatives market, such as for green ammonia, methanol, or synthetic aviation fuels, which depend on credible provenance and traceability. As countries and companies seek to build hydrogen corridors and international trade routes, early alignment on definitions, guarantees of origin, and sustainability criteria will be essential. Without this, the global hydrogen economy may evolve in a siloed, inefficient manner, undermining its potential as a unifying decarbonization vector. Lastly, the socio-political dimension of green hydrogen must not be overlooked. Ensuring a just transition involves engaging local communities, avoiding land and water conflicts, creating equitable access to jobs and benefits, and supporting capacity-building in the Global South. Policymakers and multilateral institutions must design frameworks that distribute risks and rewards fairly while fostering international collaboration. The momentum behind green hydrogen is real, but translating vision into reality will require coordinated action across finance, technology, regulation, and society.

Table 2. Comparative Techno-Economic Indicators for Green Hydrogen in Selected Countries (Projected 2030).

Table 3. Summary of Green Hydrogen Certification Schemes in Major Economies

5. Conclusion

Green hydrogen has emerged as a central pillar in the global strategy to decarbonize hard-to-abate sectors and transition toward net-zero emissions. This review has synthesized developments in green hydrogen production, deployment strategies, cost trends, policy frameworks, and integration challenges. From an initial technological curiosity to a mainstream pillar in national energy plans, green hydrogen has undergone a dramatic transformation over the past decade. However, while its promise is widely acknowledged, translating this potential into widespread, equitable, and sustainable implementation presents a multi-dimensional challenge.

One of the key takeaways from this study is the importance of geographic and contextual diversity in shaping the feasibility and economics of green hydrogen production. Renewable energy resource availability, electricity pricing structures, infrastructure readiness, and policy support vary greatly between countries and regions. These factors directly impact the Levelized Cost of Hydrogen (LCOH), which remains the most critical determinant of green hydrogen’s competitiveness. Countries like Australia and Chile, with high solar and wind resources and ample land availability, have a structural advantage in driving down LCOH toward the targeted benchmark of $2/kg. Meanwhile, regions with higher renewable electricity costs and grid congestion may struggle to reach similar economic thresholds without significant subsidies, carbon pricing mechanisms, or technological innovation.

The role of electrolyzer technologies—Alkaline (Al-E), Proton Exchange Membrane (PEM), and Solid Oxide Electrolyzer Cells (SOEC)—has also been a focal point of this review. While Alkaline systems currently dominate due to their maturity and lower capital costs, PEM and SOEC technologies are rapidly gaining ground because of their superior performance in variable load conditions and higher efficiency at scale. However, barriers remain in terms of high CAPEX, materials supply chain bottlenecks (e.g., reliance on rare metals), and limited manufacturing capacity. Innovations in catalyst design, modularity, and systems integration will be vital to improve efficiency and reduce cost over the coming years. Mass production and standardization could emulate the cost trajectory observed in the solar photovoltaic and battery storage industries, enabling exponential scalability.

Integration with renewable energy systems is a critical enabler but also introduces significant technical challenges. Electrolyzers operate most efficiently under stable input conditions, yet wind and solar sources are inherently variable. Hybrid systems involving batteries or thermal energy storage are being explored but introduce additional costs and operational complexity. Furthermore, green hydrogen production is water-intensive, raising sustainability concerns in water-scarce regions. This necessitates a holistic approach that considers local water stress indicators and may require coupling electrolysis with desalination plants—again influencing both energy demand and environmental impact. An energy–water nexus approach will be indispensable for sustainable hydrogen scaling, particularly in arid regions and small island developing states (SIDS).

On the policy front, national and regional hydrogen roadmaps have proliferated, reflecting a broad consensus on the importance of hydrogen in future energy systems. The European Union’s REPowerEU plan, Japan’s Basic Hydrogen Strategy, Saudi Arabia’s NEOM project, and the U.S. Inflation Reduction Act all offer clear policy direction and fiscal support. These strategies typically include targets for electrolyzer capacity, production volumes, and public-private partnerships, along with funding instruments such as grants, tax credits, and loan guarantees. Yet the diversity of approaches and metrics across jurisdictions complicates international collaboration and trade.

A recurring theme throughout the review is the lack of harmonized certification, regulation, and governance structures. Without a globally accepted definition of “green” hydrogen, including GHG accounting, renewable electricity sourcing criteria, and lifecycle water and land impacts, the hydrogen market risks becoming fragmented. This fragmentation would not only delay deployment but could also create trade conflicts or greenwashing accusations. To address this, multilateral institutions like the International Renewable Energy Agency (IRENA), the International Energy Agency (IEA), and the International Partnership for Hydrogen and Fuel Cells in the Economy (IPHE) must intensify efforts to establish universal certification standards, possibly aligned with frameworks like the Greenhouse Gas Protocol or ISO standards.

Transport, storage, and distribution remain substantial barriers to green hydrogen scaling. Unlike electricity, which can be transmitted via established grids, hydrogen must be liquefied, converted into ammonia, or compressed for pipeline transport—each route presenting cost, efficiency, and safety challenges. Retrofitting natural gas pipelines for hydrogen use, building dedicated hydrogen corridors, or utilizing maritime shipping all require massive infrastructure investments and long lead times. The creation of “hydrogen valleys” or localized hubs of production and consumption is a promising interim strategy to develop demand, reduce transport costs, and enable economies of scale. However, global trade ambitions—particularly from producers like Australia and Saudi Arabia to consumers in Europe, Japan, and Korea—will depend on a functioning and interoperable international hydrogen logistics chain.

Equity and inclusion are often under-addressed dimensions of the hydrogen transition. Many developing countries stand to benefit from green hydrogen in terms of job creation, economic diversification, and energy security. However, they often lack access to the capital, technology, and skilled workforce necessary to establish competitive hydrogen production ecosystems. There is a real risk that the green hydrogen economy could replicate the inequalities seen in fossil fuel supply chains—where resource-rich but infrastructure-poor nations remain trapped as raw material exporters with limited value addition. Global cooperation mechanisms—such as green hydrogen funds, concessional finance, technology transfer, and technical assistance—must be expanded to ensure a just and equitable transition.

From a demand perspective, the decarbonization of industry, transport, and power generation presents enormous potential for green hydrogen. In the industrial sector, hydrogen can decarbonize steelmaking, ammonia production, and refining processes. In transport, it offers a viable fuel for shipping, aviation, and heavy-duty road transport, particularly where battery electrification is not feasible. The role of hydrogen in power generation is more nuanced: while hydrogen-fired turbines and fuel cells can help stabilize grids and enable seasonal storage, their economic competitiveness remains challenged by low round-trip efficiency and alternative storage solutions like pumped hydro or advanced batteries. Still, hydrogen’s ability to connect otherwise siloed sectors—serving as a vector for sector coupling—makes it uniquely valuable in future integrated energy systems.

The role of green hydrogen in achieving global climate goals cannot be overstated. Most net-zero scenarios developed by IPCC, IEA, and major national energy agencies require a substantial contribution from hydrogen—estimated at 10–20% of final energy consumption by 2050. This reflects hydrogen’s essential role in decarbonizing sectors that are otherwise difficult to electrify. Yet hydrogen is not a silver bullet. It must be deployed where it adds the most value, and not where more efficient or mature alternatives—such as direct electrification—already exist. Prioritizing hydrogen applications based on systemic value, not just technological feasibility, will be essential to optimize resource use and accelerate emissions reductions.

Looking ahead, several strategic priorities emerge. First, there is a need for massive scale-up in electrolyzer manufacturing, with a focus on innovation in materials science, durability, and efficiency. Second, renewable energy deployment must accelerate, not only to decarbonize current electricity use but to create the surplus needed for electrolysis. Third, coordinated investments in hydrogen transport, storage, and refueling infrastructure will be critical to unlock demand-side growth. Fourth, international standards, certification schemes, and trade frameworks must be developed and aligned. Lastly, inclusive financing mechanisms must ensure that all countries can participate in the hydrogen economy—not only as consumers but also as producers and innovators.

In conclusion, green hydrogen represents a transformational opportunity to reshape the global energy system in a way that is clean, secure, and resilient. While the pathway ahead is fraught with technical, economic, and political challenges, the convergence of climate urgency, renewable energy maturity, and technological innovation provides a compelling rationale to act boldly. If green hydrogen is to fulfill its role as the “missing link” in the energy transition, stakeholders across the public and private sectors must collaborate to remove barriers, share risks, and build trust. With coordinated global action, green hydrogen can become more than a climate solution—it can be a catalyst for sustainable development and shared prosperity in the 21st century.

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