France

Hydrogen is a key energy carrier that could play a crucial role in the transition to a low-carbon economy. Hydrogen-related technologies are considered flexible solutions to support the large-scale implementation of intermittent energy supply from renewable sources by using renewable energy to generate green hydrogen during periods of low demand. Therefore a short-term increase in demand for hydrogen as an energy carrier and an increase in hydrogen production are expected to drive demand for large-scale storage facilities to ensure continuous availability. Owing to the large potential available storage space underground hydrogen storage offers a viable solution for the long-term storage of large amounts of energy. This study presents the results of a survey of potential underground hydrogen storage sites in Italy carried out within the H2020 EU Hystories “Hydrogen Storage In European Subsurface” project. The objective of this work was to clarify the feasibility of the implementation of large-scale storage of green hydrogen in depleted hydrocarbon fields and saline aquifers. By analysing publicly available data mainly well stratigraphy and logs we were able to identify onshore and offshore storage sites in Italy. The hydrogen storage capacity in depleted gas fields currently used for natural gas storage was estimated to be around 69.2 TWh.

Urban air mobility (UAM) defined as safe and efficient air traffic operations in a metropolitan area for manned aircraft and unmanned aircraft systems is being researched and developed by industry academia and government. This kind of mobility offers an opportunity to construct a green and sustainable sub-sector building upon the lessons learned over decades by aviation. Thanks to their non-polluting operation and simple air traffic management electric vertical take-off and landing (eVTOL) aircraft technologies are currently being developed and experimented with for this purpose. However to successfully complete the certification and commercialization stage several challenges need to be overcome particularly in terms of performance such as flight time and endurance and reliability. In this paper a fast methodology for sizing and selecting the propulsion chain components of an eVTOL multirotor aerial vehicle was developed and validated on a reduced-scale prototype of an electric multirotor vehicle with a GTOW of 15 kg. This methodology is associated with a comparative study of energy storage system configurations in order to assess their effect on the flight time of the aerial vehicle. First the optimal pair motor/propeller was selected using a global nonlinear optimization in order to maximize the specific efficiency of these components. Second five energy storage technologies were sized in order to evaluate their influence on the aerial vehicle flight time. Finally based on this sizing process the optimized propulsion chain gross take-off weight (GTOW) was evaluated for each energy storage configuration using regression-based methods based on propulsion chain supplier data.

The main purpose of this article is to provide a short review of proton exchange membrane electrolyzer (PEMEL) modeling used for power electronics control. So far three types of PEMEL modeling have been adopted in the literature: resistive load static load (including an equivalent resistance series-connected with a DC voltage generator representing the reversible voltage) and dynamic load (taking into consideration the dynamics both at the anode and the cathode). The modeling of the load is crucial for control purposes since it may have an impact on the performance of the system. This article aims at providing essential information and comparing the different load modeling.

The Global Hydrogen Review is an annual publication by the International Energy Agency that tracks hydrogen production and demand worldwide as well as progress in critical areas such as infrastructure development trade policy regulation investments and innovation. The report is an output of the Clean Energy Ministerial Hydrogen Initiative and is intended to inform energy sector stakeholders on the status and future prospects of hydrogen while also informing discussions at the Hydrogen Energy Ministerial Meeting organised by Japan. Focusing on hydrogen’s potentially major role in meeting international energy and climate goals the Review aims to help decision makers fine-tune strategies to attract investment and facilitate deployment of hydrogen technologies at the same time as creating demand for hydrogen and hydrogen-based fuels. It compares real-world developments with the stated ambitions of government and industry. This year’s report includes a focus on demand creation for low-emission hydrogen. Global hydrogen use is increasing but demand remains so far concentrated in traditional uses in refining and the chemical industry and mostly met by hydrogen produced from unabated fossil fuels. To meet climate ambitions there is an urgent need to switch hydrogen use in existing applications to low-emission hydrogen and to expand use to new applications in heavy industry or long-distance transport.

To contribute to a more diverse and efficient energy infrastructure large quantities of hydrogen are requested for industries (e.g. mining refining fertilizers…). These applications need large scale facilities such as dozens of electrolyzer stacks from atmospheric pressure to 30 bar with a total capacity ranging from 100 up to 400 MW and associated hydrogen storage from a few to 50 tons.

Local use can be fed by electrolyzer in 20 feet container and stored in bundles with small volumes. Nevertheless industrial applications can request much bigger capacity of production which are generally located in buildings. The different technologies available for the production of hydrogen at large scale are alkaline or PEM electrolyzer with for example 100 MW capacity in a building of 20000 m3 and hydrogen stored in tube trailers or other fixed hydrogen storage solution with large volumes.

These applications led to the use of hydrogen inside large but confined spaces with the risk of fire and explosion in case of loss of containment followed by ignition. This can lead to severe consequences on asset workers and public due to the large inventories of hydrogen handled.

This article aims to provide an overview of the strategy to safely design large scale hydrogen production facilities in buildings through benchmarks based on projects and literature reviews best practices & standards regulations. It is completed by a risk assessment taking into consideration hydrogen behavior and influence of different parameters in dispersion and explosion in large buildings.

This article provides recommendations for hydrogen project stakeholders to perform informed-based decisions for designing large scale production buildings. It includes safety measures as reducing hydrogen inventories inside building allocating clearance around electrolyzer stacks implementing early detection and isolation devices and building geometry to avoid hydrogen accumulation.

This study explores the integration and optimization of a hydrogen-based energy system emphasizing the use of metal hydride (MH) storage coupled with Proton Exchange Membrane Fuel Cell Micro Combined Heat and Power (PEMFC MCHP) system for residential applications. MH storage coupled to a heat pump operates at charging and discharging pressures of 10 bar. COMSOL model in 6.1 version using heat transfer in solids and fluids in brinkman equations modules is validated by experimental data and uses machine learning (Feedforward Neural Networks) for predictive modeling of MH dynamics. Smaller 500 NL tanks were found to have high mass-specific heat demand but faster hydrogen gas kinetics reaching (~77 % capacity in one hour) whereas larger 6500 NL (~57 %/hour) absorb hydrogen gas more gradually but reduce thermal management intensities. Using 13 × 500 NL tanks reach ~25 % discharge in 1 h but require ~2170 Wh heating whereas one 6500 NL tank only attains ~48.5 % discharge yet uses ~1750 Wh illustrating a trade-off between faster kinetics and lower thermal load. A genetic algorithm identified an optimal configuration of two 6500 NL tanks that covered ~68 % of total hydrogen gas consumption and 65 % of production at a maximum of 2.4 kW heating and 2.45 kW cooling. Additional comparisons with 170 bar compressed storage revealed lower instantaneous thermal requirements for high-pressure gas tanks. Adding a 170 bar compressed H2 alongside the 10 bar MH system hydrogen gas coverage rose from ~70 % to ~97 % when storage expanded to 200 Nm3 but at the cost of higher compression energy. The proposed MH-based approach especially at moderate pressures with carefully planned tank geometries achieves enhanced operational flexibility for a residential 120 m2 building’s space heating and hot water while machine learning optimizations further refine charge–discharge performance.

In the pursuit of establishing a sustainable fuel cell (FC) energy system this review highlights the necessity of examining the operational principles technical details environmental consequences and economic concerns collectively. By adopting an integrated approach the review research into various fuel cells types extending their applications beyond transportation and evaluating their potential for seamless integration into sustainable practices. A detailed analysis of the technical aspects including FC membranes performance and applications is presented. The environmental impact of hydrogen generation through fuel cell/electrolyzer is quantitatively assessed emphasizing a comparative emission footprint against traditional hydrogen generation methods. Economic considerations of fuel cell technology adoption are explored through an extensive examination of market growth and forecasts and investments into the FC systems. Some flagship commercial projects of FC technology are also discussed along with their future prospective. The article concludes with a thorough analysis of challenges associated with FC adoption encompassing membrane research performance hurdles infrastructure development and application-specific challenges. This all-round review serves as an indispensable tool for academicians and policymakers providing a directed and comprehensive FC perspective.

Natural hydrogen (H2) holds promising potential as a clean energy source but its exploration remains challenging due to limited knowledge and a lack of quantitative tools. In this context identifying active H2 seepage areas is crucial for advancing exploration efforts. Here we focus on sub-circular depressions (SCDs) that often mark high H2 concentration in soils thought to correspond to deeper fluxes seeping at the surface making them promising targets for exploration. Coupling open-access Google Earth© images and in-field H2 measurement data an artificial intelligence model was trained to detect seepage zones. The model achieves an average precision of 95 % detects and maps seepage zones in new regions like Kazakhstan and South Africa highlighting its potential for global application. Moreover preliminary spatial analyses show that geological features control the distribution of H2-SCDs that can emit billions of tons of H2 at the scale of a sedimentary basin. This study paves the way for a faster and more efficient methodology for selecting H2 exploration targets. Plain Language Summary. Natural hydrogen is a promising clean energy source but it remains difficult to explore due to a lack of accessible tools. In this study we used free satellite images (Google Earth©) and in-field hydrogen measurements to identify specific surface features - small sub-circular depressions (SCDs) - that often mark areas where hydrogen is seeping from underground. We trained an artificial intelligence model to detect these depressions using a dataset of confirmed hydrogen-emitting SCDs collected across five countries. Thanks to this diversity in the training data the model can be applied at a global scale having learned to recognize a wide variety of structures associated with hydrogen seepage. To validate its effectiveness the model was tested on two random regions - in Kazakhstan and South Africa - and successfully identified over a thousand new potential hydrogen-emitting depressions. With an average precision of 95 % this tool offers a fast and reliable way to map natural hydrogen seepage zones helping guide future exploration efforts worldwide.

Greenhouse gas anthropogenic emissions have triggered global warming with increasingly alarming consequences motivating the development of carbon-free energy systems. Hydrogen is proposed as an environmentally benign energy vector to implement this strategy but safe and efficient large-scale hydrogen storage technologies are still lacking to develop a competitive Hydrogen economy. LOHC (Liquid Organic Hydrogen Carrier) improves the storage and handling of hydrogen by covalently binding it to a liquid organic framework through catalytic exothermic hydrogenation and endothermic dehydrogenation reactions. LOHCs are oil-like materials that are compatible with the current oil and gas infrastructures. Nevertheless their high dehydrogenation enthalpy platinoid-based catalysts and thermal stability are bottlenecks to the emergence of this technology. In this review hydrogen storage technologies and in particular LOHC are presented. Moreover potential reactivities to design innovative LOHC are discussed.

This article proposes a novel open-circuit switch fault diagnosis method (FDM) for a three-level interleaved buck converter (TLIBC) in a hydrogen production system based on the water electrolysis process. The control algorithm is suitably modified to ensure the same hydrogen production despite the fault. The TLIBC enables the interfacing of the power source (i.e. low-carbon energy sources) and electrolyzer while driving the hydrogen production of the system in terms of current or voltage. On one hand the TLIBC can guarantee a continuity of operation in case of power switch failures because of its interleaved architecture. On the other hand the appearance of a power switch failure may lead to a loss of performance. Therefore it is crucial to accurately locate the failure in the TLIBC and implement a fault-tolerant control strategy for performance purposes. The proposed FDM relies on the comparison of the shape of the input current and the pulse width modulation (PWM) gate signal of each power switch. Finally an experimental test bench of the hydrogen production system is designed and realized to evaluate the performance of the developed FDM and fault-tolerant control strategy for TLIBC during post-fault operation. It is implemented with a real-time control based on a MicroLabBox dSPACE (dSPACE Paderborn Germany) platform combined with a TI C2000 microcontroller. The obtained simulation and experimental results demonstrate that the proposed FDM can detect open-circuit switch failures in one switching period and reconfigure the control law accordingly to ensure the same current is delivered before the failure.

As highlighted by the recent roadmaps from the European Union and the United States water electrolysis is the most valuable high-intensity technology for producing green hydrogen. Currently two commercial low-temperature water electrolyzer technologies exist: alkaline water electrolyzer (A-WE) and proton-exchange membrane water electrolyzer (PEM-WE). However both have major drawbacks. A-WE shows low productivity and efficiency while PEM-WE uses a significant amount of critical raw materials. Lately the use of anion-exchange membrane water electrolyzers (AEM-WE) has been proposed to overcome the limitations of the current commercial systems. AEM-WE could become the cornerstone to achieve an intense safe and resilient green hydrogen production to fulfill the hydrogen targets to achieve the 2050 decarbonization goals. Here the status of AEM-WE development is discussed with a focus on the most critical aspects for research and highlighting the potential routes for overcoming the remaining issues. The Review closes with the future perspective on the AEM-WE research indicating the targets to be achieved.

The power-to-methanol (PtMeOH) will play a crucial role as a form of renewable chemical energy storage. In this paper PtMeOH techno-economics are assessed using the promising configuration from the previous work (Mbatha et al. [1]). This study evaluated the effect of parameters such as the CO2 emission tax electricity price and CAPEX reduction on the product methanol economic parity with respect to a reference case. Superior to previous economic studies a scenario where an existing methanol synthesis infrastructure is 100 % retrofitted with the promising electrolyser is assessed in terms of its economics and the associated economic parity. The volatile South African electricity market is considered as a case study. The sensitivity of the PtMeOH and green H2 profitability are checked. Grid-connected and standalone renewable energy PtMeOH scenarios are assessed. Foremost generalisable effect trends of these parameters on the net present value (NPV) and the levelized cost of methanol(LCOMeOH) and H2 (LCOH2) are discussed. The results show that economic parity of H2 (LCOH2 = current selling price = 4.06 €/kg) can be reached with an electricity price of 30 €/MWh and 70 % of the CAPEX. While the LCOMeOH will still be above 2 €/kg at 80 % of the CAPEX and electricity price of 20 €/MWh. This indicates that even if the CAPEX reduces to 20 % of its original in this study and the electricity price reduces to about 20 €/MWh the LCOMEOH will still not reach economic parity (LCOMeOH > current selling price = 0.44 €/kg). The results show that to make the retrofitted plant with a minimum of 20 years of life span profitable a feasible reduction in the electricity price to below 10 €/MWh along with favourable incentives such as CO2 credit and reduction in CAPEX particularly that of the electrolyser and treatment of the PtMeOH as a multiproduct plant will be required.

The MultHyFuel project aims to develop evidence-based guidelines for the safe implementation of Hydrogen Refueling Stations (HRS) in a multi-fuel context. As a part of the generation of good practice guidelines for HRS Hazardous Area Classification (HAC) methodologies were analyzed and applied to case studies representing example configurations of HRS. It has been anticipated that Negligible Extent (NE) classifications might be applicable for sections of the HRS for instance a hydrogen generator. A NE zone requires that an ignition of a flammable cloud would result in negligible consequences. In addition depending on the pressure of the system IEC 60079-10-1:2020 establishes specific requirements in order to classify the hazardous area as being of NE. One such requirement is that a zone of NE shall not be applied for releases from flammable gas systems at pressures above 2000 kPag (20 barg) unless a specific detailed risk assessment is documented. However there is no definition within the standard as to the requirements of the specific detailed risk assessment. In this work an example for a specific detailed risk assessment for the NE classification is presented:<br/>• Firstly the requirements of cloud volume dilution and background concentration for a zone of NE classification from IEC 60079-10-1:2020 are analyzed for hydrogen releases from equipment placed in a mechanically ventilated enclosure.<br/>• Secondly the consequences arising from the ignition of the localized cloud are estimated and compared to acceptable harm criteria in order to assess if negligible consequences are obtained from the scenario.<br/>• In addition a specific qualitative risk assessment for the ignition of the cloud in the enclosure was considered incorporating the estimated consequences and analyzing the available safeguards in the example system.<br/>Recommendations for the specific detailed risk assessment are proposed for this scenario with the intention to support improved definition of the requirement in future revisions of IEC 60079-10-1.

This study develops a framework for designing hydrogen supply chains (HSC) in island territories using Mixed Integer Linear Programming (MILP) with a multi-period approach. The framework minimizes system costs greenhouse gas emissions and a risk-based index. Corsica is used as a case study with a Geographic Information System (GIS) identifying hydrogen demand regions and potential sites for production storage and distribution. The results provide an optimal HSC configuration for 2050 specifying the size location and technology while accounting for techno-economic factors. This work integrates the unique geographical characteristics of islands using a GIS-based approach incorporates technology readiness levels and utilizes renewable electricity from neighboring regions. The model proposes decentralized configurations that avoid hydrogen transport between grids achieving a levelized cost of hydrogen (LCOH) of €8.54/kg. This approach offers insight into future options and incentive mechanisms to support the development of hydrogen economies in isolated territories.

The development of hydrogen production technologies as well as new uses represents an opportunity both to accelerate the ecological transition and to create an industrial sector. However the risks associated with the use of hydrogen must not be overlooked. The mitigation of a hydrogen explosion in an enclosure is partly based on prevention strategies such as detection and ventilation but also on protection strategies such as explosion venting. However in several situations such as in highly constrained urban environments the discharge of the explosion through blast walls could generate significant overpressure effects outside the containment which are unacceptable. Thus having alternative mitigation solutions can make the effects of the explosion acceptable by reducing the flame speed and the overpressure loading or suppressing the secondary explosion. The objective of this paper is to present the experimental study of the mitigation of hydrogen-air deflagration in a 4 m3 vented enclosure by injection of aqueous foam. After a description of the experimental set-up the main experimental results are presented showing the influence of aqueous foam on flame propagation (Fig. 1). Different foam expansion ratios were investigated. An interpretation of the mitigating effect of foam on the explosion effects is proposed based on the work of Kichatov [5] and Zamashchikov [2].

Fuel cell electric vehicles are getting deployed exponentially in Europe. Hydrogen fuel quality regulations are getting into place in order to protect customers and ensure end-users satisfactory experiences. It became critical to have the capability to sample and analyse accurately hydrogen fuel delivered by hydrogen refuelling stations in Europe. This study presents two separate comparisons: the first bilateral comparison between two sampling systems (H2 Qualitizer) and (“H2 Sampling System” of Air Liquide) and the interlaboratory comparison between NPL and Air Liquide on hydrogen fuel quality testing according to EN 17124. The two sampling systems showed equivalent results for all contaminants for sampling at 70 MPa hydrogen refuelling stations. The two laboratories showed good agreement at 95% confidence level. Even if the study is limited due to the low number of samples it demonstrates the equivalence of two sampling strategies and the ability of two laboratories to perform accurate measurement of hydrogen fuel quality.

With increasing global interest in molecular hydrogen to replace fossil fuels more attention is being paid to potential leakages of hydrogen into the atmosphere and its environmental consequences. Hydrogen is not directly a greenhouse gas but its chemical reactions change the abundances of the greenhouse gases methane ozone and stratospheric water vapor as well as aerosols. Here we use a model ensemble of five global atmospheric chemistry models to estimate the 100-year time-horizon Global Warming Potential (GWP100) of hydrogen. We estimate a hydrogen GWP100 of 11.6 ± 2.8 (one standard deviation). The uncertainty range covers soil uptake photochemical production of hydrogen the lifetimes of hydrogen and methane and the hydroxyl radical feedback on methane and hydrogen. The hydrogeninduced changes are robust across the different models. It will be important to keep hydrogen leakages at a minimum to accomplish the benefits of switching to a hydrogen economy.

Following the growing use of hydrogen in the industry gas explosions have become a critical safety issue. Computational Fluid Dynamic (CFD) and in particular the Large Eddy Simulation (LES) approach have already shown their great potential to reproduce such scenarios with high fidelity. However the computational cost of this approach is an obvious limiting factor since fine grid resolutions are often required in the whole computational domain to ensure a correct numerical resolution of the deflagration front all along its propagation. In this context Adaptive Mesh Refinement (AMR) is of great interest to reduce the computational cost as it allows to dynamically refine the mesh throughout the explosion scenario only in regions where Quantities of Interest (QoI) are detected. This study aims to demonstrate the strong potential of AMR for the LES of explosions. The target scenario is a hydrogen-air explosion in the GraVent explosion channel [1]. Using the massively parallel Navier- Stokes compressible solver AVBP a reference simulation is first obtained on a uniform and static unstructured mesh. The comparison with the experiments shows a good agreement in terms of absolute flame front speed overpressure and flow visualisation. Then an AMR simulation is performed targeting the same resolution as the reference simulation only in regions where QoI are detected i.e. inside the reaction zones and vortical structures. Results show that the accuracy of the reference simulation is recovered with AMR for only 12% of its computational cost.

The aim of this paper is the design and implementation of an advanced model predictive control (MPC) strategy for the management of a wind–solar microgrid (MG) both in the islanded and grid-connected modes. The MG includes energy storage systems (ESSs) and interacts with external hydrogen and electricity consumers as an extra feature. The system participates in two different electricity markets i.e. the daily and real-time markets characterized by different time-scales. Thus a high-layer control (HLC) and a low-layer control (LLC) are developed for the daily market and the real-time market respectively. The sporadic characteristics of renewable energy sources and the variations in load demand are also briefly discussed by proposing a controller based on the stochastic MPC approach. Numerical simulations with real wind and solar generation profiles and spot prices show that the proposed controller optimally manages the ESSs even when there is a deviation between the predicted scenario determined at the HLC and the real-time one managed by the LLC. Finally the strategy is tested on a lab-scale MG set up at Khalifa University Abu Dhabi UAE.

Green hydrogen is becoming increasingly popular with academics institutions and governments concentrating on its development efficiency improvement and cost reduction. The objective of the Ministry of Petroleum Mines and Energy is to achieve a 35% proportion of renewable energy in the overall energy composition by the year 2030 followed by a 50% commitment by 2050. This goal will be achieved through the implementation of feed-in tariffs and the integration of independent power generators. The present study focused on the economic feasibility of green hydrogen and its production process utilizing renewable energy resources on the northern coast of Mauritania. The current investigation also explored the wind potential along the northern coast of Mauritania spanning over 600 km between Nouakchott and Nouadhibou. Wind data from masts Lidar stations and satellites at 10 and 80 m heights from 2022 to 2023 were used to assess wind characteristics and evaluate five turbine types for local conditions. A comprehensive techno-economic analysis was carried out at five specific sites encompassing the measures of levelized cost of electricity (LCOE) and levelized cost of green hydrogen (LCOGH) as well as sensitivity analysis and economic performance indicators. The results showed an annual average wind speed of 7.6 m/s in Nouakchott to 9.8 m/s in Nouadhibou at 80 m. The GOLDWIND 3.0 MW model showed the highest capacity factor of 50.81% due to its low cut-in speed of 2.5 m/s and its rated wind speed of 10.5 to 11 m/s. The NORDEX 4 MW model forecasted an annual production of 21.97 GWh in Nouadhibou and 19.23 GWh in Boulanoir with the LCOE ranging from USD 5.69 to 6.51 cents/kWh below the local electricity tariff and an LCOGH of USD 1.85 to 2.11 US/kg H2 . Multiple economic indicators confirmed the feasibility of wind energy and green hydrogen projects in assessed sites. These results boosted the confidence of the techno-economic model highlighting the resilience of future investments in these sustainable energy infrastructures. Mauritania’s north coast has potential for wind energy aiding green hydrogen production for energy goals.

One of the significant safety concerns in large-scale storage and transportation of liquefied (cryogenic) hydrogen (LH2) is the formation of flammable hydrogen/air mixtures after leakages during storage or transportation. Especially in maritime transportation hydrogen accumulations could occur within large and congested geometries. The installation of passive auto-catalytic recombiners (PARs) is a suitable mitigation measure for local areas where venting is insufficient or even impossible. Numerical models describing the operational behavior of PARs are required to allow for optimizing the location and assessing the efficiency of the mitigation measure. In the present study the operational behavior of a PAR with a compact design has been experimentally investigated. In order to obtain data for model validation an experimental program has been performed in the REKO-4 facility a 5.5 m³ vessel. The test procedure includes two phases steady-state and dynamic. The results provide insights into the hydrogen recombination rates and catalyst temperatures under different boundary conditions.

As part of the ongoing transition from fossil fuels to renewable energies advances are particularly expected in terms of safe and cost-effective solutions. Publicising instances of such advances and emphasising global safety considerations constitute the rationale for this communication. Knowing that high-strength steels can prove economically relevant in the foreseeable future for transporting hydrogen in pipelines by limiting the pipe wall thickness required to withstand high pressure one advance relates to a bench designed to assess the safe transport or renewableenergy-related buffer storage of hydrogen gas. That bench has been implemented at the technology readiness level TRL 6 to test initially intact damaged or pre-notched 500 mm-long pipe sections with nominal diameters ranging from 300 to 900 mm in order to appropriately validate or question the use of reputedly satisfactory predictive models in terms of hydrogen embrittlement and potential corollary failure. The other advance discussed herein relates to the reactivation of a previously fruitful applied research into safe mass solid-state hydrogen storage by magnesium hydride through a new public–private partnership. This latest development comes at a time when markets have started driving the hydrogen economy bearing in mind that phase-change materials make it possible to level out heat transfers during the absorption/melting and solidification/desorption cycles and to attain an overall energy efficiency of up to 80% for MgH2 -based compacts doped with expanded natural graphite.

Fuel cells and electric batteries are competing technologies for the energy transition in heavy transportation. We explore the conditions for the survival of a unique technology in the long term. Learning by doing suggests focusing on a single technology while differentiation and decreasing return to scale (cost convexity) favor diversification. Exogenous technical change also plays a role. The interaction between these factors is analyzed in a general model. It is proved that in absence of convexity and exogenous technical change only one technology is used for the whole transition. We then apply this framework to analyze the competition between fuel-cell electric buses (FCEBs) and battery electric buses (BEB) in the European bus sector. There are both learning by doing and exogenous technical change. The model is calibrated and solved. It is shown that the existence of a niche for FCEBs critically depends on the speed at which cost reductions are achieved. The speed depends both on the size of the niche and the rate of learning by doing for FCEBs. Public policies to decentralize the socially optimal trajectory in terms of taxes (carbon) and subsidies (learning by doing) are derived.

A growing share of renewable energy production in the energy supply systems is key to reaching the European political goal of zero CO2 emission in 2050 highlighted in the green deal. Linked to the irregular production of solar and wind energies which have the highest potential for development in Europe massive energy storage solutions are needed as energy buffers. The European project HyPSTER [1] (Hydrogen Pilot STorage for large Ecosystem Replication) granted by the Clean Hydrogen Partnership addresses this topic by demonstrating a cyclic test in an experimental salt cavern filled with hydrogen up to 3 tons using hydrogen that is produced onsite by a 1 MW electrolyser. One specific objective of the project is the assessment of the risks and environmental impacts of cyclic hydrogen storage in salt caverns and providing guidelines for safety regulations and standards. This paper highlights the first outcome of the task WP5.5 of the HyPSTER project addressing the regulatory and normative frameworks for the safety of hydrogen storage in salt caverns from some selected European Countries which is dedicated to defining recommendations for promoting the safe development of this industry within Europe.

This paper proposes a numerical setup for 3D-CFD in-cylinder simulations of H2-fuelled internal combustion engines. The flamelet G-equation model based on Verhelst and Damkohler-like ¨ correlations for laminar and turbulent flame speeds respectively is used to reproduce the flame propagation. The validation against experimental data from a homogeneous-mixture port-injection engine enables a focus on combustion simulation by minimising stratification uncertainties. Accurate flame propagation modelling is identified as the main challenge. The results on different operating conditions confirm the predictive capabilities of the framework thanks to the agreement with the experimental pressure traces combustion indicators and flame imaging. Notably combustion rate predictions remain accurate even without considering the flame thermo-diffusive instability as the turbulence effect dominates at the investigated conditions. The combustion regime is analysed by a modified Borghi-Peters diagram and it ranges from flamelet to thin reaction zones. This highlights the numerical setup flexibility which accurately simulates combustion across different regimes.

Ammonia a molecule that is gaining more interest as a fueling vector has been considered as a candidate to power transport produce energy and support heating applications for decades. However the particular characteristics of the molecule always made it a chemical with low if any benefit once compared to conventional fossil fuels. Still the current need to decarbonize our economy makes the search of new methods crucial to use chemicals such as ammonia that can be produced and employed without incurring in the emission of carbon oxides. Therefore current efforts in this field are leading scientists industries and governments to seriously invest efforts in the development of holistic solutions capable of making ammonia a viable fuel for the transition toward a clean future. On that basis this review has approached the subject gathering inputs from scientists actively working on the topic. The review starts from the importance of ammonia as an energy vector moving through all of the steps in the production distribution utilization safety legal considerations and economic aspects of the use of such a molecule to support the future energy mix. Fundamentals of combustion and practical cases for the recovery of energy of ammonia are also addressed thus providing a complete view of what potentially could become a vector of crucial importance to the mitigation of carbon emissions. Different from other works this review seeks to provide a holistic perspective of ammonia as a chemical that presents benefits and constraints for storing energy from sustainable sources. State-of-the-art knowledge provided by academics actively engaged with the topic at various fronts also enables a clear vision of the progress in each of the branches of ammonia as an energy carrier. Further the fundamental boundaries of the use of the molecule are expanded to real technical issues for all potential technologies capable of using it for energy purposes legal barriers that will be faced to achieve its deployment safety and environmental considerations that impose a critical aspect for acceptance and wellbeing and economic implications for the use of ammonia across all aspects approached for the production and implementation of this chemical as a fueling source. Herein this work sets the principles research practicalities and future views of a transition toward a future where ammonia will be a major energy player.

Of all the alternatives to hydrocarbon fuels hydrogen offers the greatest long-term potential to radically reduce the many problems inherent in fuel used for transportation. Hydrogen vehicles have zero tailpipe emissions and are very efficient. If the hydrogen is made from renewable sources such as nuclear power or fossil sources with carbon emissions captured and sequestered hydrogen use on a global scale would produce almost zero greenhouse gas emissions and greatly reduce air pollutant emissions. The aim of this work is to realise a traceability chain for hydrogen flow metering in the range typical for fuelling applications in a wide pressure range with pressures up to 875 bar (for Hydrogen Refuelling Station - HRS with Nominal Working Pressure of 700 bar) and temperature changes from −40 °C (pre-cooling) to 85 °C (maximum allowed vehicle tank temperature) in accordance with the worldwide accepted standard SAE J2601. Several HRS have been tested in Europe (France Netherlands and Germany) and the results show a good repeatability for all tests. This demonstrates that the testing equipment works well in real conditions. Depending on the installation configuration some systematic errors have been detected and explained. Errors observed for Configuration 1 stations can be explained by pressure differences at the beginning and end of fueling in the piping between the Coriolis Flow Meter (CFM) and the dispenser: the longer the distance the bigger the errors. For Configuration 2 where this distance is very short the error is negligible.

The MultHyFuel Project funded by the Clean Hydrogen Partnership aims to achieve the effective and safe deployment of hydrogen as a carbon-neutral fuel by developing a common strategy for implementing Hydrogen Refueling Stations (HRS) in a multifuel context. The project hopes to contribute to the harmonisation of existing regulations codes and standards (RCS) by generating practical theoretical and experimental data related to HRS.<br/>This paper presents how a set of safety critical scenarios have been identified from the initial preliminary as well as detailed risk analysis of three different hydrogen refueling station configurations. To achieve this a detailed examination of each potential hazardous phenomenon (DPh) or major accident event at or near the hydrogen dispenser was carried out. Particular attention is paid to the scenarios which could affect third parties external to the refueling station.<br/>The paper presents a methodology subdivided into the following steps:<br/>♦ determination of the consequence level and likelihood of each hazardous phenomenon<br/>♦ the classification of major hazard scenarios for the 3 HRS configurations specifically those arising on the dispensing forecourt;<br/>♦ proposal of example preventative control and/or mitigation barriers that could potentially reduce the probability of occurrence and/ or consequences of safety critical scenarios and hence reducing risks to a tolerable level or to as low as reasonably practicable.

Green hydrogen generated from water through renewable energies like solar and wind is a key player in sus tainable energy. It only produces water when used making it a clean energy source. However the inconsistent nature of solar and wind energy highlights the need for storage solutions where green hydrogen is promising. This study uniquely combines green hydrogen (GH) and renewable energy (RE) domains using a comprehensive bibliometric approach covering 2018–2022. It identifies emerging trends collaboration networks and key contributors that shape the global landscape of GH research. Our findings show a significant yearly growth in this research field averaging 93.56 %. The study also identifies China Germany India and Italy as leaders among 76 countries involved in this area. Research trends have shifted from technical details to social and economic factors. Given the increasing global commitment to achieving carbon neutrality understanding the evolution and integration of GH within RE systems is essential for guiding future research policy-making and technology development. The analysis categorizes the research into seven main themes focusing on green hydrogen’s role in energy transition and storage. Other vital topics include improving hydrogen production methods assessing its climate impact examining its environmental benefits and exploring various production techniques like water electrolysis and photocatalysis. Our analysis reveals a 93.56 % annual growth rate in GH research highlighting key challenges in storage integration and policy development and offering a roadmap for future studies. The study highlights areas needing more exploration such as better storage methods integration with existing energy infrastructures risk management and policy development. The advancement of green hydrogen as a sustainable energy solution depends on innovative research international collaboration and supportive policy frameworks.

In the frame of hydrogen-powered aircraft Airbus wants to understand all the H2 physics and explore every scenario in order to develop and manufacture safe products operated in a safe environment. Within the framework of a Large Eddy Simulation (LES) methodology for modeling turbulence a comparative numerical study of free under-expanded jet H2/AIR flame is conducted. The investigated geometry consists of straight nozzles with a millimetric diameter fed with pure H2 at upstream pressures ranging from 2 to 10 bar. Numerical results are compared with available experimental measurements such as; temperature signals using thermocouples. LES confirms its prediction capability in terms of shock jet structure and flame length. A particular attention is paid for capturing experimental unstable flame when upstream pressure decreases. Furthermore flame stabilization and flame anchoring are analyzed. Mechanisms of flame stabilization are highlighted for case 1 and stabilization criteria are tested. Finally an ignition map to reach flame stabilization is proposed for each case regarding the literature.

A new dimensionless number (DN) is proposed in order to evaluate the performance of a high-pressure vessel composite structure. It shows that very few composite part is used at its maximum loading potential during bursting. Today for 70 MPa on-board type IV composite tanks DN values close to 20%. The suggested DN will be a useful indicator for an industrial application. By maximizing the DN at the design phase it is possible to minimize the mass of the composite structure of a CPV to reduce the manufacturing time and cost. To increase the DN as close as possible to 100% it is necessary to succeed in increasing the overall loading of the composite structure to have better oriented fibre. For this it seems necessary to find new processes which make it possible to better orient the fibre.

Natural ventilation is a well-known passive mitigation method to limit hydrogen build-up in confined spaces in case of accidental release [1-3]. In most cases a basic design of H2 infrastructure is adopted and vents installed for natural ventilation are adjusted according to safety targets and constraints of the considered structure. With the growing H2 mobility market the demand for H2 refueling infrastructure in our urban environment is on the rise. In order to meet both safety requirements and societal acceptance the design of such infrastructure is becoming more important. In this study a novel design concept is proposed for the hydrogen refueling station (HRS) by modifying physical structure while keeping safety consideration as the top priority of the concept. In this collaborative project between Air Liquide and the University of Delaware an extensive evaluation was performed on new structures of the processing container and dispenser of HRS by integrating safety protocols via passive means. Through a SWOT analysis combined with the most relevant approaches including analytical engineering models numerical simulations [4] and dedicated experimental trials an optimized design was obtained and its safety enhancement was fully evaluated. A small-scale processing container and an almost full-scale dispenser were built and tested to validate the design concepts by simulating accidental H2 release scenarios and assessing the associated consequences in terms of accumulation and potential flammable volumes formation. A conical dispenser and a V-shaped roof-top processing container which were easy to build and implement were designed and tested for this proof-of-concept study. This unique methodology from conception fundamental analysis investigation and validation through experimental design execution and evaluation is fully described in this study.

The Federal Institute of Metrology METAS developed a Hydrogen Field Test Standard (HFTS) that can be used for field verification and calibration of hydrogen refuelling stations. The testing method is based on the gravimetric principle. The experimental design of the HFTS as well as the description of the method are presented here.

Hydrogen safety is a general concern because of the high reactivity compared to hydrocarbon-based fuels. The strength of knowledge in risk assessments related to the physical phenomena and the ability of models to predict the consequence of accidental releases is a key aspect for the safe implementation of new technologies. Nuclear safety considers the possibility of accidental leakages of hydrogen gas and subsequent explosion events in risk analysis. In many configurations the considered gaseous streams involve a large fraction of nitrogen gas mixed with hydrogen. This work presents the results of a large scale explosion experimental campaign for hydrogen-nitrogen-air mixtures. The experiments were performed in a 50 m3 vessel at Gexcon’s test site in Bergen Norway. The nitrogen fraction the equivalence ratio and the congestion level were investigated. The experiments are simulated in the FLACS-CFD software to inform about the current level of conservatism of the predictions for engineering application purposes. The study shows the reduced overpressure with nitrogen added to hydrogen mixtures and supports the use of FLACS-CFD-based risk analysis for hydrogen-nitrogen scenarios.

Decarbonising energy systems is a prevalent topic in the current literature on climate change mitigation but the additional climate burden caused by methane emissions along the natural gas value chain is rarely discussed at the system level. Considering a two-basket greenhouse gas neutrality objective (both CO2 and methane) we model cost-optimal European energy transition pathways towards 2050. Our analysis shows that adoption of best available methane abatement technologies can entail an 80% reduction in methane leakage limiting the additional environmental burden to 8% of direct CO2 emissions (vs. 35% today). We show that while renewable energy sources are key drivers of climate neutrality the role of natural gas strongly depends on actions to abate both associated CO2 and methane emissions. Moreover clean hydrogen (produced mainly from renewables) can replace natural gas in a substantial proportion of its end-uses satisfying nearly a quarter of final energy demand in a climate-neutral Europe.

The MultHyFuel project notably aims to produce the data missing for usable risk analysis and mitigation activity for Hydrogen Refuelling Stations (HRS) in a multi-fuel context. In this framework realistic releases of hydrogen that could occur in representative multi-fuel forecourts were studied. These releases can occur inside or outside fuel dispensers and they can interact with a complex environment notably made of parked cars and trucks. This paper is focused on the most critical scenarios that were addressed by a sub-group through the use of Computational Fluid Dynamics (CFD) modelling. Once the corresponding source terms for hydrogen releases were known two stages are followed:<br/>♦ Model Validation – to evaluate the CFD models selected by the task partners and to evaluate their performance through comparison to experimental data.<br/>♦ Realistic Release Modelling – to perform demonstration simulations of a range of critical scenarios.<br/>The CFD models selected for the Model Validation have been tested against measured data for a set of experiments involving hydrogen releases. Each experiment accounts for physical features that are encountered in the realistic cases. The selected experiments include an under-expanded hydrogen jet discharging into the open atmosphere with no obstacles or through an array of obstacles. Additionally a very different set-up was studied with buoyancy-driven releases inside a naturally ventilated enclosure. The results of the Model Validation exercise show that the models produce acceptable solutions when compared to measured data and give confidence in the ability of the models and the modellers to capture the behaviour of the realistic releases adequately. The Realistic Release Modelling phase will provide estimation of the flammable gas cloud volume for a set of critical scenarios and will be described at the second stage.

This work is part of the MULTHYFUEL E.U. research program [1] aiming at enabling the implementation of hydrogen dispersers in refuelling stations. One important challenge is the severity of accidents due to a leakage of hydrogen from a dispenser in the forecourt. The work presented in this paper deals with the quantification of the leakage scenarios in terms of frequencies and severities. The risk analysis exercise although performed by experts showed very large discrepancies between the frequencies of leakages of the same categories and even between the consequences. A large part of the disagreement comes from the failure databases chosen as shown in the paper. The mismatch between the components on which the databases have been settled and the actual hydrogen components may be responsible for this situation. However as it stands limited confidence can be laid on the outcome of the risk analysis.<br/>A new method is being developed to calculate the frequencies of the leakage and the flowrate based on an accurate description of each component and of each hazardous situation. For instance the possibility for a fitting to become untight due to pressure cycling is modelled based on the contact mechanics. Human errors can also be introduced by describing the tasks. In addition of the description of the method the application to a disperser is proposed with some comparison to experiments. One of the outcomes is that leakage cross sections can be much larger than expected.

The number of species and elementary reactions needed for describing the oxidation of fuels increases with the size of the molecule and in turn the complexity of detailed mechanisms. Although the kinetics for conventional fuels (H2 CH4 C3H8...) are somewhat well-established chemical integration in detonation applications remains a major challenge. Significant efforts have been made to develop reduction techniques that aim to keep the predictive capabilities of detailed mechanisms intact while minimizing the number of species and reactions required. However as their starting point of development is based on homogeneous reactors or ZND profiles reduced mechanisms comprising a few species and reactions are not predictive. The methodology presented here relies on defining virtual chemical species such that the thermodynamic equilibrium of the ZND structure is properly recovered thereby circumventing the need to account for minor intermediate species. A classical asymptotic expression relating the ignition delay time with the reaction rate constant is then used to fit the Arrhenius coefficients targeting computations carried out with detailed kinetics. The methodology was extended to develop a three-step mechanism in which the Arrhenius coefficients were optimized to accurately reproduce the one-dimensional laminar ZND structure and the D−κ curves for slightly-curved quasi-steady detonation waves. Two-dimensional simulations performed with the three-step mechanism successfully reproduce the spectrum of length scales present in soot foils computed with detailed kinetics (i.e. cell regularity and size). Results attest for the robustness of the proposed methodology/approximation and its flexibility to be adapted to different configurations.

In confined spaces hydrogen released with low momentum tends to accumulate in a layer below the ceiling; the concentration in this layer rises and can rapidly enter the flammability range. In this context ventilation is a key safety equipment to prevent the formation of such flammable volumes. To ensure its well-sizing to each specific industrial context it is necessary to dispose of reliable engineering models. Currently the existing engineering models dealing with the buoyancy-driven H2 dispersion in a ventilated enclosure mainly focus on the natural-ventilation phenomenon. However forced ventilation is in some situations more adapted to the industrial context as the wind direction and intensity remains constant and under control. Therefore two existing wind-assisted ventilation models elaborated by Hunt and Linden [1] and Lowesmith et al. [2] were tested on forced ventilation applications. The main assumption consists in assuming a blowing ventilation system rather than a suction system as the composition and velocity of the entering air are known. The fresh air enters the down opening and airhydrogen mixture escapes through the upper one. The adapted models are then validated with experimental data releasing helium rather than hydrogen. Experiments are conducted on a 1-m3 ventilated box controlling the release and ventilation rates. The agreement between both analytical and experimental results is discussed from the different comparisons performed.

In this work the wastewater obtained from the hydrothermal liquefaction of black liquor was treated and valorized for hydrogen production by supercritical water gasification (SCWG). The influence of the main process parameters on the conversion yield was studied. The experiments were conducted at three different temperatures (below and above the critical point of water): 350 ◦C 450 ◦C and 600 ◦C. The results showed that by increasing the temperature from 350 ◦C to 600 ◦C the total gas yield was highly improved (from 1.9 mol gas/kg of dried feedstock to 13.1 mol gas/kg of dried feedstock). The H2 composition was higher than that of CH4 and CO2 at 600 ◦C and the HHV of the obtained gas was 61.2 MJ/kg. The total organic carbon (TOC) removal efficiency was also improved by increasing the temperature indicating that the SCWG process could be used for both applications: (i) for wastewater treatment; (ii) for producing a high calorific gas. The experiments with the Raney-nickel catalyst were performed in order to study the catalyst’s influence on the conversion yield. The results indicated that the catalyst enhances carbon conversion and gas production from mild to higher temperatures. The maximum total gas yield obtained with this catalyst was 32.4 mol gas/kg of dried feedstock at 600 ◦C which is 2.5 times higher than that obtained at the same operating conditions without a catalyst. The H2 yield and the HHV of the obtained gas with the catalyst were 20.98 mol gas/kg dried feedstock and 80.2 MJ/kg respectively. However the major contribution of the catalytic SCWG process was the improvement of the total gas yield at mild operating temperatures (450 ◦C) and the obtained performance was even higher than that obtained at 600 ◦C without catalyst (17.81 mol gas/kg dried feedstock and 13.1 mol gas/kg dried feedstock respectively). This is a sustainable approach for treating wastewater at mild temperatures by catalytic SCWG.

The industry is advancing decarbonization in hydrogen production through water splitting technologies like water electrolysis which involves the hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode. Alkaline water electrolyser (AWE) is particularly suited for industrial applications due to its use of cost-effective and abundant nickel-based electrodes. However AWE faces significant challenges including energy losses from gas bubble coverage and poor detachment known as “bubble resistance”. Recent research highlights the role of power ultrasound in mitigating these issues by leveraging Bjerknes forces. These forces facilitate the ejection of larger bubbles and the coalescence of smaller ones enhancing gas removal. Additionally ultrasound improves mass transfer from the electrolyte to electrodes and boosts heat transfer via acoustic streaming and acoustic cavitation which the latter also enhances electrocatalytic properties for both HER and OER. However employing ultrasonic fields presents both benefits and challenges for scaling the system.

Green hydrogen a zero-carbon emission fuel has become a real competitor to transform the energy market thanks to improvements in the electrolysis process decreased costs and the presence of renewable energy resources. Energy industries have shown considerable progress in hydrogen production due to the incorporation of artificial intelligence (AI) knowledge through algorithms AI-based models and data programs. These techniques can greatly enhance the production storage and transportation of hydrogen fuel. The main goal of this article is to demonstrate the recent technological advancements and the influence of various AI techniques algorithms and models on the hydrogen energy sector along with this further examination of the energy policies of countries like China Japan India and South Korea. The key challenges related to these energy policies are addressed through standardized datasets AI models and optimized environmental conditions. This paper serves as a valuable resource for researchers engineers and practitioners interested in applying cutting-edge technologies to enhance hydrogen safety systems. AI-based models contribute to the overall shift towards a sustainable energy future by enhancing efficiency reducing costs and facilitating hydrogen energy commerce for Asian countries. This study accelerates the global investigation and tremendous applications of sophisticated machine-learning methodologies for producing renewable green hydrogen.

Developing new injection systems and combustion chambers for hydrogen is a central topic for the new generation of engines. In this effort simulations take a central role but methods developed for conventional hydrocarbons (methane kerosene) must be revisited for hydrogen. Validation then becomes an essential part and clean well documented experiments are needed to guaranty that computational fluid dynamics solvers are as predictive and accurate as expected. In this framework the HYLON case is a swirled hydrogen/air burner used by multiple groups worldwide to validate simulation methods for hydrogen combustion in configurations close to gas turbine burners with experimental data available through the TNF web site. The present study compares recent Raman spectroscopy and Particle Image Velocimetry measurements and Large Eddy Simulations (LES). The LES results are evaluated against a dataset comprising mean and RMS measurements of H2 N2 O2 H2O molar fractions temperature and velocity fields offering new insights into flame stabilization mechanisms. The simulations incorporate conjugate heat transfer to predict the combustor wall temperatures and are conducted for two atmospheric-pressure operating conditions each representing distinct combustion regimes diffusion and partially premixed. Novelty and significance statement Data on confined hydrogen flames in burner similar as industrial ones are limited. This work aims to fill this gap by performing multiple and simultaneous diagnostics on the swirled hydrogen-air flame called HYLON. For the first time in such a swirled configuration mean and RMS fields of temperature main species and velocities are compared to LES allowing new insight into the potential and limits of the models as well as the physics of these flames. These experimental results will be made available on TNF as over 30 research groups worldwide have expressed interest in using them.

Integrating microbial activity into underground hydrogen storage models is crucial for simulating longterm reservoir behavior. In this work we present a coupled framework that incorporates bio-geochemical reactions and compositional flow models within the Matlab Reservoir Simulation Toolbox (MRST). Microbial growth and decay are modeled using a double Monod formulation with populations influenced by hydrogen and carbon dioxide availability. First a refined Equation of State (EoS) is employed to accurately capture hydrogen dissolution thereby improving phase behavior and modeling of microbial activity. The model is then discretized using a cell-centered finite-volume method with implicit Euler time discretization. A fully coupled fully implicit strategy is considered. Our implementation builds upon MRST’s compositional module by incorporating the Søreide–Whitson EoS microbial reaction kinetics and specific effects such as bio-clogging and molecular diffusion. Through a series of 1D 2D and 3D simulations we analyze the effects of microbialinduced bio-geochemical transformations on underground hydrogen storage in porous media.These results highlight that accounting for bio-geochemical effects can substantially impact hydrogen loss purity and overall storage performance.

With the transition to a fully renewable energy grid arises the need for a green source of stability and baseload support which classical renewable generation such as wind and solar cannot offer due to their uncertain and highly-variable generation. In this paper we study whether green hydrogen can close this gap as a source of supplemental generation and storage. We design a two-stage mixed-integer stochastic optimization model that accounts for uncertainties in renewable generation. Our model considers the investment in renewable plants and hydrogen storage as well as the operational decisions for running the hydrogen storage systems. For the data considered we observe that a fully renewable network driven by green hydrogen has a greater potential to succeed when wind generation is high. In fact the main investment priorities revealed by the model are in wind generation and in liquid hydrogen storage. This long-term storage is more valuable for taking full advantage of hydrogen than shorter-term intraday hydrogen gas storage. In addition we note that the main driver for the potential and profitability of green hydrogen lies in the electricity demand and prices as opposed to those for gas. Our model and the investment solutions proposed are robust with respect to changes in the investment costs. All in all our results show that there is potential for green hydrogen as a source of baseload support in the transition to a fully renewable-powered energy grid.

Hydrogen is increasingly recognized as a key energy vector for achieving deep decarbonization across urban and industrial sectors. Supporting global efforts to reduce greenhouse gas (GHG) emissions and achieve the Sustainable Development Goals (SDGs) it is essential to understand the multi-sectoral role of the hydrogen value chain spanning production storage and end-use applications with particular emphasis on smart city systems and industrial processes. Green hydrogen production technologies including alkaline water electrolysis (AWE) proton exchange membrane (PEM) electrolysis anion exchange membrane (AEM) electrolysis and solid oxide electrolysis cells (SOECs) are evaluated in terms of efficiency scalability and integration potential. Storage pathways are examined across physical storage (compressed gas cryo-compressed and liquid hydrogen) material-based storage (solid-state absorption in metal hydrides and chemical carriers such as LOHCs and ammonia) and geological storage (salt caverns depleted gas reservoirs and deep saline aquifers) highlighting their suitability for urban and industrial contexts. In the smart city domain hydrogen is analyzed as an enabler of zero-emission transportation low-carbon residential and commercial heating and renewable-integrated smart grids with long-duration storage capabilities. System-level studies demonstrate that coordinated integration of these applications can deliver higher overall energy efficiency deeper reductions in life-cycle GHG emissions and improved resilience of urban energy systems compared with sector-specific approaches. Policy frameworks safety standards and digitalization strategies are reviewed to illustrate how hydrogen infrastructure can be embedded into interconnected urban energy systems. Furthermore industrial applications focus on hydrogen’s potential to decarbonize energy-intensive processes and enable sector coupling between electricity heat and manufacturing. The environmental implications of hydrogen deployment are also considered including resource efficiency life-cycle emissions and ecosystem impacts. In contrast to reviews addressing isolated aspects of hydrogen technologies this study synthesizes technological infrastructural and policy dimensions integrating insights from over 400 studies to highlight the multifaceted role of hydrogen in sustainable urban development and industrial decarbonization and the added benefits achievable through coordinated cross-sector deployment strategies.

Previous studies have demonstrated the potential benefit of a future hydrogen economy in terms of reducing CO2 emissions. The hydrogen leakage rate and the green hydrogen fraction in the mix were identified as key factors in maximising the climate benefit of this energy transition. This study highlights the importance of blue hydrogen production hypotheses for a climate-beneficial transition to a hydrogen economy. The benefits are substantial when blue hydrogen is produced properly using an efficient CO₂ sequestration hydrogen production plant and minimizing the rate of upstream CH₄ leakage. The rate of hydrogen leakage remains an important parameter to consider throughout the entire value chain. Based on various scenarios of the development of a 21st century hydrogen economy we estimate significant CO₂ emission reductions of 266–418 GtCO₂eq (up to 395–675 GtCO2eq in the case of a “high hydrogen demand” scenario) between 2030 and 2100. This cumulative reduction in CO₂ emissions translates into a reduction in global warming of 0.12–0.19 °C (0.18–0.30 °C for a “high hydrogen demand”) by the end of the century.