Publications

Hydrogen fuel cell systems are a viable option for electrified aero engines due to their efficiency and environmental benefits. However integrating these systems presents challenges notably in terms of overall system weight and thermal management. Heat exchangers are crucial for the effective thermal management system of electric propulsion systems in commercial electrified aviation. This paper provides a comprehensive review of various heat exchanger types and evaluates their potential applications within these systems. Selection criteria are established based on the specific requirements for air and hydrogen heat exchangers in electrified aircraft. The study highlights the differences in weighting criteria for these two types of heat exchangers and applies a weighted point rating system to assess their performance. Results indicate that extended surface microchannel and printed circuit heat exchangers exhibit significant promise for aviation applications. The paper also identifies key design challenges and research needs particularly in enhancing net heat dissipation increasing compactness improving reliability and ensuring effective integration with aircraft systems.

The LCOH calculator manual explains the methodology behind the calculator in detail and demonstrates how the calculator can be used.<br/>In this second version the default prices are updated based on the latest data available in the calculator and a new use case is introduced on changing the economic lifetime and cost of capital of an electrolysis installation.

Sorption-enhanced steam reforming (SorESR) is an advanced thermochemical process integrating in-situ CO2 capture via solid sorbents to significantly enhance hydrogen production and purity. By coupling CO2 adsorption with steam reforming SorESR shifts the reaction equilibrium toward increased H₂ yield surpassing the limitations of conventional steam reforming (SR). The efficacy of SorESR critically depends on the physicochemical properties of the solid CO2 sorbents employed. This review critically evaluates widely studied sorbents including Ca-based Mg-based hydrotalcite-like and alkali ceramic sorbents focusing on their CO2 capture capacity reaction kinetics thermal stability and cyclic durability under SR conditions. Furthermore recent progress in multifunctional sorbent-catalysts that synergistically facilitate catalytic steam reforming alongside CO2 sorption is critically discussed. Moreover the review summarises recent performance achievements and proposes strategies to improve sorbent capacity and reaction kinetics thereby making the SorESR process more appealing for commercial applications. Large-scale SorESR implementation is expected to substantially increase hydrogen production efficiency while concurrently reducing CO2 emissions and advancing sustainable energy technologies. This review offers novel insights into the development of advanced sorbent-catalyst systems and provides new strategies for enhancing SorESR efficiency and scalability for commercial H2 Production.

The passive combination of fuel cells and supercapacitors possesses promising applications in the automotive industry due to its ability to decrease stack size maintain peak power capacity improve system productivity and go away with the need for additional control all without Direct current to Direct Current (DC/DC) converters. This research describes the steps to create and evaluate a fuel cell (FC) and supercapacitor (SC) passive hybrid electrical system for a 60-V lightweight vehicle. Also study offers a thorough design approach and model and experimentally to validate every passive hybrid testing station component. When both concepts are stable the voltage errors are about 2 % and 3 % respectively for fuel cells and supercapacitors. The results of the experiments provide more evidence that the passive design is effective under step loads and driving cycles. The results of the measurements match the models used to simulate the passive hybrid system if a step load voltage is used. A smaller FC stack is possible since the fuel cell controls the steady-state current. Alternatively the supercapacitors provide varying currents because of their reduced resistance. This study use a driving cycle to show that the FC stack can lower its output to 25 % of the peak power required by the load.

Hydrogen blending offers significant potential for decarbonizing natural gas-based thermal processes particularly in the steel and cement sectors. Due to its distinct combustion properties compared to natural gas – such as lower minimum air requirements and altered flame speeds – the hydrogen fraction of the fuel must be monitored for combustion control. In this study we present an ultrasonic time-of-flight measurement system for hydrogen concentrations of 0–40% in natural gas. The system is verified with test gas mixtures at laboratory scale and validated in a technical-scale setup using a real blower burner (< 60 kW). We evaluate uncertainty of the hydrogen fraction measurement and analyze the influence of varying natural gas compositions. We show that standard uncertainties below 4% can be achieved without knowledge of the specific natural gas composition. Our results provide insights for measurement system design and support the safe application of hydrogen in thermal systems for industrial processes.

In the context of mounting concerns over carbon emissions and the need to accelerate the energy transition green hydrogen has emerged as a strategic solution for decarbonizing hard-to-abate sectors. This paper introduces a methodological innovation by proposing the Green Hydrogen Efficiency Index (GHEI) a unified and quantitative framework that integrates multiple stages of the hydrogen value chain into a single comparative metric. The index encompasses six core criteria: electricity source water treatment electrolysis efficiency compression end-use conversion and associated greenhouse gas emissions. Each are normalized and weighted to reflect different performance priorities. Two weighting profiles are adopted: a first profile which assigns equal importance to all criteria referred to as the balanced profile and a second profile derived using the analytic hierarchy process (AHP) based on structured expert judgment named the AHP profile. The methodology was developed through a systematic literature review and was applied to four representative case studies sourced from the academic literature covering diverse configurations and geographies. The results demonstrate the GHEI’s capacity to distinguish the energy performance of different green hydrogen routes and support strategic decisions related to technology selection site planning and logistics optimization. The results highlight the potential of the index to contribute to more sustainable hydrogen value chains and advance decarbonization goals by identifying pathways that minimize energy losses and maximize system efficiency

As the global transition to carbon neutrality accelerates hydrogen energy has emerged as a key alternative to fossil fuels due to its potential to reduce carbon emissions. Many countries including Korea are constructing hydrogen refueling stations; however safety concerns persist due to accidents caused by equipment failures and human errors. While various accident analysis models exist the application of the root cause analysis (RCA) technique to hydrogen refueling station accidents remains largely unexplored. This study develops an RCA modeling map specifically for hydrogen refueling stations to identify not only direct and indirect causes of accidents but also root causes and applies it to actual accident cases to provide basic data for identifying the root causes of future hydrogen refueling station accidents. The RCA modeling map developed in this study uses accident cause investigation data from accident investigation reports over the past five years which include information on the organizational structure and operational status of hydrogen refueling stations as well as the RCA handbook. The primary defect sources identified were equipment defect personal defect and other defects. The problem categories which were the substructures of the primary defect source “equipment defect” consisted of four categories: the equipment design problem the equipment installation/fabrication problem the equipment reliability program problem and the equipment misuse problem. Additionally the problem categories which were the substructures of the primary defect source “personal defect” consisted of two categories: the company employee problem and the contract employee problem. The problem categories which were the substructures of the primary defect source “other defects” consisted of three categories: sabotage/horseplay natural phenomena and other. Compared to existing accident investigation reports which identified only three primary causes the RCA modeling map revealed nine distinct causes demonstrating its superior analytical capability. In conclusion the proposed RCA modeling map provides a more systematic and comprehensive approach for investigating accident causes at hydrogen refueling stations which could significantly improve safety practices and assist in quickly identifying root causes more efficiently in future incidents.

The integration of Variable Renewable Energy (VRE) sources in power systems is increased for a sustainable environment. However due to the intermittent nature of VRE sources formulating efficient economic dispatching strategies becomes challenging. This systematic review aims to elucidate the economic value creation of Artificial Intelligence (AI) in supporting the integration of VRE sources into power systems by reviewing the role of AI in mitigating costs related to balancing profile and grid with a focus on its applications for generation and demand forecasting market design demand response storage solutions power quality enhancement and predictive maintenance. The proposed study evaluates the AI potential in economic efficiency and operational reliability improvement by analyzing the use cases with various Renewable Energy Resources (RERs) including wind solar geothermal hydro ocean bioenergy hydrogen and hybrid systems. Furthermore the study also highlights the development and limitations of AI-driven approaches in renewable energy sector. The findings of this review aim to highlight AI’s critical role in optimizing VRE integration ultimately informing policymakers researchers and industry stakeholders about the potential of AI for an economically sustainable and resilient energy infrastructure.

Hydrogen spark-ignition direct-injection engines result in no carbon emissions at use but NOX remains a challenge. This study demonstrates that with lean combustion (ϕ < 0.38) in-cylinder NOX can be reduced to a quarter of the current maritime regulatory limit. An original contribution of this work is the use of speciesresolved emissions formation across multiple engine load conditions. A novel chemically detailed combustion modelling framework was developed in CHEMKIN-Pro incorporating the evolution of the CRECK C1–C3 NOX mechanism for improved high-pressure accuracy. The framework was extensively validated using crank-angleresolved data across 9–18 bar loads. The model accurately reproduced pressure traces heat release angles and NOX. Mechanistic analysis revealed a shift from thermal Zeldovich NOX to intermediate-species (notably N2Odriven) as equivalence ratio and pressure varied. The findings highlighted the use of a high-fidelity chemical kinetic modelling framework not only to match experimental results but to gain physically grounded insight into actionable near-zero emission strategies.

Thermo-catalytic decomposition (TCD) presents a promising pathway for producing hydrogen from natural gas without emitting CO2. This process represents a form of fossil fuel decarbonization where the byproduct rather than being a greenhouse gas is a solid carbon material with potential for commercial value. This study examines the dynamic behavior of TCD showing that carbon formed during the reaction first enhances and later dominates methane decomposition. Three types of carbon materials were employed as starting catalysts. Methane decomposition was continuously monitored using on-line Fourier transform infrared (FT-IR) spectroscopy. The concentration and nature of surface-active sites were determined using a two-step approach: oxygen chemisorption followed by elemental analysis through X-ray photoelectron spectroscopy (XPS). Changes in the morphology and nanostructure of the carbon catalysts both before and after TCD were examined using high-resolution transmission electron microscopy (HRTEM). Thermogravimetric analysis (TGA) was used to study the reactivity of the TCD deposits in relation to the initial catalysts. Partial oxidation altered the structural and surface chemistry of the initial carbon catalysts resulting in activation energies of 69.7–136.7 kJ/mol for methane. The presence of C2 and C3 species doubled methane decomposition (12% → 24%). TCD carbon displayed higher reactivity than the nascent catalysts and sustained long-term activity.

The resilience and sustainable development of modern power distribution systems faces escalating challenges due to increasing renewable integration and extreme events. Traditional single-system approaches often overlook the spatiotemporal coordination of cross-domain restoration resources. In this paper we propose a multi-stage resilience enhancement method that employs transportation and hydrogen energy systems. This approach coordinates the pre-event preventive allocation and multi-stage collaborative scheduling of diverse restoration resources including remote-controlled switches (RCSs) mobile hydrogen emergency resources (MHERs) and hydrogen production and refueling stations (HPRSs). The proposed framework supports cross-stage dynamic optimization scheduling enabling the development of adaptive resource dispatch strategies tailored to the characteristics of different stages including prevention fault isolation and service restoration. The model is applicable to complex scenarios involving dynamically changing network topologies and is formulated as a mixed-integer linear programming (MILP) problem. Case studies based on the IEEE 33-bus system show that the proposed method can restore a distribution system’s resilience to approximately 87% of its normal level following extreme events.

This report aims to summarise the status of the European hydrogen policy landscape. It is based on the information available at the European Hydrogen Observatory (EHO) website the leading source of data on hydrogen in Europe. The data presented in this report is based on research conducted by Hydrogen Europe until the end of July 2024 but also goes beyond this timeline for major policies legislations or standards implemented recently. This report builds upon the previous version published in April 2024 which reflected data as of August 2023 providing updated insights on European policies and legislation national strategies national policies and legislation and codes and standards. Interactive data dashboards can be accessed on the website: https://observatory.cleanhydrogen.europa.eu/ The EU policies and legislation section provides insights into the main European policies and legislation relevant to the hydrogen sector which are briefly summarized on content and their potential impact to the sector. The national hydrogen strategies chapter offers a comprehensive examination of the hydrogen strategies adopted in Europe. It summarizes the quantitative indicators that have been published (targets and estimates) and provides brief summaries of the different national strategies that have been adopted. The section referring to national policies and legislation focuses on the policy framework measures incentives and targets in place that have an impact on the development of the respective national hydrogen markets within Europe. The codes and standards section provides information on current European standards and initiatives developed by the standardisation bodies including CEN CENELEC ISO IEC OIML The standards are categorised according to the different stages of the hydrogen value chain: production distribution and storage and end-use applications.

Hydrogen (H2) fuel is one of eco-friendly resources for delivering de-carbonized and sustainable electricity supply in line with the UN’s Sustainable Development Goals 7 and 13 for affordable and clean energy and climate change action respectively. This paper presents a state-of-the art review of the H2 energy resource in terms of its history and evolution production techniques global economy market perspective and application to microgrid systems. It also introduces a systematic classification of the fuel. The production techniques examined include: the thermal approach such as the reforming gasification and thermochemical processes; the photocatalytic approach otherwise called artificial photosynthesis; the biological and photonic approach that involves the photolysis photo-fermentation dark fermentation CO gas fermentation and biomass valorization processes to produce H2 while the electrical approach is based on the chemical dissociation of electrolytes into their constituent ions by the passage of electric current. A particular attention is paid to the potential of the H2 resource in running some energy generators in microgrid systems such as the internal combustion engines microturbines and the fuel cells that are useful for combined heat and power application. The paper introduces different technical configurations topologies and processes that involve the use of green H2 fuel in generating systems and the connection of bus bars power converters battery bank and the electrical and thermal loads. The paper also presents hybrid fuel cell (FC) and PV system simulation using System Advisor Model (SAM) to showcase the use of H2 fuel in a micogrid. The paper provides insightful directions into the H2 economy smart electrical grid and the future prospects.

The increasing interest in off-grid green hydrogen production has elevated the importance of reliable techno-economic assessment (TEA) tools to support investment and planning decisions. However limited operational data and inconsistent modeling approaches across existing tools introduce significant uncertainty in cost estimations. This study presents a comprehensive review and comparative analysis of seven TEA tools—ranging from simplified calculators to advanced hourly based simulation platforms—used to estimate the Levelized Cost of Hydrogen (LCOH) in off-grid Hydrogen Production Plants (HPPs). A standardized simulation framework was developed to input consistent technical economic and financial parameters across all tools allowing for a horizontal comparison. Results revealed a substantial spread in LCOH values from EUR 5.86/kg to EUR 8.71/kg representing a 49% variation. This discrepancy is attributed to differences in modeling depth treatment of critical parameters (e.g. electrolyzer efficiency capacity factor storage and inflation) and the tools’ temporal resolution. Tools that included higher input granularity hourly data and broader system components tended to produce more conservative (higher) LCOH values highlighting the cost impact of increased modeling realism. Additionally the total project cost—more than hydrogen output—was identified as the key driver of LCOH variability across tools. This study provides the first multi-tool horizontal testing protocol a methodological benchmark for evaluating TEA tools and underscores the need for harmonized input structures and transparent modeling assumptions. These findings support the development of more consistent and reliable economic evaluations for off-grid green hydrogen projects especially as the sector moves toward commercial scale-up and policy integration.

Electrolysis of abundant seawater resources is a promising approach for hydrogen production. However the high-concentration chloride ion in seawater readily induces the chlorine evolution reaction (CER) resulting in catalyst degradation and decreased electrolysis efficiency. In recent years the electrooxidation of small organic molecules (e.g. methanol) biomass-derived compounds (e.g. 5-hydroxymethylfurfural) and plastic monomers (e.g. ethylene glycol) has been seen to occur at lower potentials to substitute for the traditional oxygen evolution reaction (OER) and CER. This alternative approach not only significantly reduces energy consumption for hydrogen production but also generates value-added products at the anode. This review provides a comprehensive summary of research advancements in value-added electrooxidation reaction-assisted seawater hydrogen production technologies and emphasizes the underlying principles of various reactions and catalyst design methodologies. Finally the current challenges in this field and potential future research directions are systematically discussed.

Zero-emission fuels are expected to drive the maritime sector decarbonisation with hydrogen emerging as a long-term solution. This study aims to investigate by using CFD modelling a hydrogen fuelled marine dual-fuel engine to identify operating settings ranges for different hydrogen energy fractions (HEF) as well as parametrically optimise the diesel fuel injection timing and temperature at inlet valve closing (IVC). A large marine four-stroke engine with nominal power of 10.5 MW at 500 rev/m is considered assuming operation at 90 % load and hydrogen injection in the cylinders intake ports. CFD models are developed for several operating scenarios in both diesel and dual-fuel modes. The models are validated against measured data for the engine diesel mode and literature data for a hydrogen-fuelled light-duty engine. A convergence study is conducted to select the grid compromising between computational effort and accuracy. Parametric runs for 20 % 40 % and 60 % HEF with different IVC temperature and diesel start of injection are modelled to quantify the engine performance emissions and combustion characteristics. A single parameter optimisation is conducted to determine the most effective pilot diesel injection timings. The results reveal the IVC temperature range for stable hydrogen combustion to avoid incomplete combustion at low IVC temperature and knocking above 360 K. The proposed settings lead to higher peak heat release rate and in-cylinder pressure compared to the diesel mode without exceeding the permissible in-cylinder pressure rise limits for 60 % HEF. However NOx emissions increase to 12.9 g/kWh in the dual-fuel mode. The optimal start of injection (SOI) for the diesel fuel in the case of 60 % HEF is found 8 ◦CA BTDC resulting in an indicated thermal efficiency of 43.2 % and stable combustion. Advancing SOI beyond the optimal value results in incomplete combustion. This is the first study on hydrogen use in large marine four-stroke engines providing insights for the engine design and operation and as such it contributes to the maritime industry decarbonisation efforts.

In this paper developed in the context of the Clean Sky 2 project SIENA (Scalability Investigation of hybrid-Electric concepts for Next-generation Aircraft) an extensive analysis is carried out to identify and accelerate the development of innovative propulsion technologies and architectures that can be scaled across five aircraft categories from small General Aviation airplanes to long-range airliners. The assessed propulsive architectures consider various components such as batteries and fuel cells to provide electricity as well as electric motors and jet engines to provide thrust combined to find feasible aircraft architectures that satisfy certification constraints and deliver the required performance. The results provide a comprehensive analysis of the impact of key technology performance indicators on aircraft performance. They also highlight technology switching points as well as the potential for scaling up technologies from smaller to larger aircraft based on different hypotheses and assumptions concerning the upcoming technological advancements of components crucial for the decarbonization of aviation. Given the considered scenarios the common denominator of the obtained results is hydrogen as the main energy source. The presented work shows that for the underlying models and technology assumptions hydrogen can be efficiently used by fuel cells for propulsive and system power for smaller aircraft (General Aviation commuter and regional) typically driven by propellers. For short- to long-range jet aircraft direct combustion of hydrogen combined with a fuel cell to power the on-board subsystems appears favorable. The results are obtained for two different temporal scenarios 2030 and 2050 and are assessed using Payload-Range Energy Efficiency as the key performance indicator. Naturally introducing such innovative architectures will face a lack of applicable regulation which could hamper a smooth entry into service. These regulatory gaps are assessed detailing the level of maturity in current regulations for the different technologies and aircraft categories.

The year 2024 saw a year of important developments for the Clean Hydrogen JU continuing built on the achievements of previous years and intensifying the efforts on hydrogen valleys. With a total operational commitment of EUR 203 million and the launch of 22 new projects the overall portfolio reached a total number of 147 projects under active management towards the end of the year. The budget execution reached the outstanding level of 98% in for commitments and 84% in payments in line with previous year showing the JU’s continued effort to use the available credits. In 2024 the JU launched a call for proposals with a budget of EUR 113.5 million covering R&I activities across the whole hydrogen value chain to which was added an amount of EUR 60 million from the RePowerEU plan focusing on hydrogen valleys. That amount served for valleys-related grants and the “Hydrogen Valleys Facility” tender designed for project development assistance that will support Hydrogen Valleys at different levels of maturity. The Hydrogen Valleys concept has become a key instrument for the European Commission to scale up hydrogen technology deployment and establish interconnections between hydrogen ecosystems. At the end of 2024 the Clean Hydrogen JU has already funded 20 hydrogen valleys. This support was complemented by additional credits from third countries and the optimal use- of leftover credits from previous years allowing the award of 29 new grants from the call for 2024.

This article explores how the implementation of solar PV and transportation infrastructure – grid or hydrogen pipeline – has implications for various aspects of security cooperation and geopolitical powershifts. Highlighting the emerging intra-European green hydrogen pipeline project H2Med we examine the Portuguese geopolitical ambitions related to their geographical advantage for solar PV energy production. Using media and document analysis we identified two main axes of solar PV implementation in Portugal – one centered on resilience and one on exports – and further explored underlying and resulting tensions in neighboring countries’ energy strategies and cleantech innovation policies. Our analysis revealed that policy prioritizations in solar PV diffusion result in unequal effects on resilience energy security and power shifts. In particular solar PV implementations such as individual to local or regional grid-based ‘prosumption’ setups result in notably different geopolitical effects compared to large-scale solar PV to green hydrogen-production for storage and export. Thereby emerging possibilities of storage and long-distance trade of renewable energies have more significant implications on geopolitics and energy security than what is typically recognized.

The growing demand for sustainable solutions in the transportation sector and global decarbonization goals have fueled debate on using hydrogen as an energy source. Although hydrogen’s potential is recognized in Brazil its application in heavy-duty vehicles still faces structural and technological barriers. This study aimed to analyze the viability of hydrogen as an energy alternative for trucks in Brazil. The research adopted an exploratory qualitative approach based on the expert analysis method through semi-structured interviews with development engineers representatives of heavy-duty vehicle manufacturers and researchers specializing in hydrogen technologies. The data were organized into a thematic framework and interpreted using content analysis. The results show that although there is growing interest and ongoing initiatives challenges such as the cost of fuel cells the lack of refueling infrastructure and low technological maturity hinder large-scale adoption. From a theoretical perspective the study contributes by integrating specialized literature with practical insights from key industry players broadening the understanding of the energy transition. In practical terms it outlines some strategic paths such as expanding technological development and forming partnerships. From a social perspective it emphasizes the importance of hydrogen as a pillar for sustainable low-carbon mobility capable of positively impacting public health and mitigating climate change.

This report includes information on European training programmes educational materials and the trends and patterns of research and innovation activity in the hydrogen sector with data of patent registrations and publications. It is based on the information available at the European Hydrogen Observatory (EHO) website (https://observatory.cleanhydrogen.europa.eu/) the leading source of hydrogen data in Europe. The data presented in this report is based on research conducted until the end of August 2024. The training programmes section provides insights into major European training initiatives categorized by location. It allows filtering by type of training focus area and language. It covers a wide range of opportunities such as vocational and professional trainings summer schools and Bachelor's or Master's programmes. The education materials chapter summarizes the publicly accessible educational materials available online. Documents can be searched by educational level by course subject by language or by the year of release. The section referring to research and innovation activity analyses trends and patterns in the hydrogen sector using aggregated datasets of patent registrations and publications by country.

Green hydrogen produced from renewable energy sources such as wind and solar is increasingly recognized as a critical enabler of the global energy transition and the decarbonization of industrial and transport sectors. The successful adoption of green hydrogen and its derivatives is closely linked to production costs which can vary substantially between countries depending not only on resource potential but also on country-specific financing conditions. These differences arise from country-specific risk factors that affect the costs of capital ultimately influencing investment decisions. However comprehensive assessments that integrate these risks with future cost projections for renewable energy green hydrogen and its synthetic downstream products are lacking. Using the Middle East and North Africa (MENA) as an example this study introduces a novel approach that allows to incorporate mainly qualitative country-specific investment risks into quantitative analyses such as costpotential and energy modelling. Our methodology calculates weighted average costs of capital (WACC) for 17 MENA countries under different risk scenarios providing a more nuanced assessment compared to traditional models that use uniform cost of capital assumptions. The results indicate significant variations in WACC such as between 4.67% in the United Arab Emirates and 24.84% in Yemen or Syria in the business-as-usual scenario. The incorporation of country-specific capital cost scenarios in quantitative analysis is demonstrated by modelling the cost-potential of Fischer-Tropsch (FT) fuels. The results show that countryspecific investment risks significantly impact costs. For instance by 2050 the starting LCOFs in high-risk scenarios can be up to 180% higher than in lowerrisk contexts. This underlines that while renewable energy potential and its cost are important it are the country-specific risk factors—captured through WACC—that have a greater influence in determining the competitiveness of exports and consequently the overall development of the renewable energy green hydrogen and synthetic fuel sectors.

Green hydrogen is increasingly recognized as a pivotal energy carrier in the global transition toward low-carbon energy systems. Beyond its established applications in industry and transportation the development of green hydrogen could accelerate its integration into the power generation sector thus enabling a more sustainable deployment of renewable energy sources. Vietnam endowed with abundant renewable energy potential—particularly solar and wind—has a strong foundation for green hydrogen. This emerging energy source holds significant potential to support the strategic objectives in recent national energy policies aligning with the country’s socio-economic development. However despite this promise the integration of green hydrogen into Vietnam’s energy system remains limited. This paper provides a critical review of the current landscape of green hydrogen in Vietnam examining both the opportunities and challenges associated with its production and deployment. Special attention is given to regulatory frameworks infrastructure readiness and economic viability. Additionally the study also explores the potential of green hydrogen in enhancing energy security within the context of the national energy transition.

Photocatalytic hydrogen (H2) production offers a promising solution to energy shortages and environmental challenges by converting solar energy into chemical energy. Hydrogen as a versatile energy carrier can be generated through photocatalysis under sunlight or via electrolysis powered by solar or wind energy. However the advancement of photocatalysis is hindered by the limited availability of effective visible light-responsive semiconductors and the challenges of charge separation and transport. To address these issues researchers are focusing on the development of novel nanostructured semiconductors and composite materials that can enhance photocatalytic performance. In this paper we provide an overview of the advanced photocatalytic materials prepared so far that can be activated by sunlight and their efficiency in H2 production. One of the key strategies in this research area concerns improving the separation and transfer of electron–hole pairs generated by light which can significantly boost H2 production. Advanced hybrid materials such as organic–inorganic hybrid composites consisting of a combination of polymers with metal oxide photocatalysts and the creation of heterojunctions are seen as effective methods to improve charge separation and interfacial interactions. The development of Schottky heterojunctions Z-type heterojunctions p–n heterojunctions from nanostructures and the incorporation of nonmetallic atoms have proven to reduce photocorrosion and enhance photocatalytic efficiency. Despite these advancements designing efficient semiconductor-based heterojunctions at the atomic scale remains a significant challenge for the realization of large-scale photocatalytic H2 production. In this review state-of-the-art advancements in photocatalytic hydrogen production are presented and discussed in detail with a focus on photocatalytic nanostructures heterojunctions and hybrid composites.

The potential for hydrogen to reshape energy systems has been recognized for over a century. Yet as decarbonization priorities have sharpened in many regions three distinct frontier areas are critical to consider: hydrogen produced from wind; hydrogen produced from nuclear power; and the development of natural hydrogen. These pathways reflect technology and policy changes including a 54% increase in the globally installed wind capacity since 2020 plus new signs of potential emerging in nuclear energy and natural hydrogen. Broadly speaking there are a considerable number of studies covering hydrogen production from electrolysis yet none systematically examine wind- and nuclear-derived hydrogen natural hydrogen or the policies that enable their adoption in key countries. This article highlights international policy and technology developments with a focus on prime movers: Germany China the US and Russia.