Transmission, Distribution & Storage

As Europe transitions away from natural gas dependency and accelerates its adoption of renewable energy 12 green hydrogen has emerged as a key energy carrier for industrial and automotive applications. Similarly plans 13 to export hydrogen and ammonia from resource-rich regions like Australia and the Middle East to major importers 14 such as Japan and South Korea underline the global commitment to decarbonization. Central to these efforts is 15 the advancement of efficient hydrogen compression technologies which are essential for establishing a 16 sustainable hydrogen supply chain. This study provides a comparative analysis of two key hydrogen compression 17 technologies categorized under positive displacement and non-mechanical systems. The evaluation emphasizes 18 the technical characteristics energy efficiency and potential applications of these systems in the emerging 19 hydrogen economy. Special focus is placed on electric motor-driven compressors which integrate advanced 20 materials and optimized designs to enhance efficiency and minimize energy consumption. By addressing the gap 21 in comparative evaluations this paper offers insights into the performance and sustainability of these technologies 22 contributing to the development of cost-effective and reliable hydrogen supply systems.

Hydrogen as a clean energy source has gradually become an important choice for the energy transformation in the world. Utilizing existing natural gas pipelines for hydrogen-blended transportation is one of the most economical and effective ways to achieve large-scale hydrogen transportation. However hydrogen can easily penetrate into the pipe material during the hydrogen-blended transportation process causing damage to the properties of the pipe. The heat-affected zone (HAZ) of the weld being the weakest part of the pipeline is highly sensitive to hydrogen embrittlement. The microstructure and properties of the grains in the heat-affected zone undergoes changes during the welding process. Therefore this paper divides the HAZ of X80 welded pipes into three sub-HAZ namely the coarse-grained HAZ fine-grained HAZ and intercritical HAZ to study the hydrogen behavior. The results show that the degree of hydrogen damage in each sub-HAZ varies significantly at different strain rates. The coarse-grained HAZ has the highest hydrogen embrittlement sensitivity at low strain rates while the intercritical HAZ experiences the greatest hydrogen damage at high strain rates. By combining the microstructural differences within each sub-HAZ the plastic damage mechanism of hydrogen in each sub-HAZ is analyzed with the aim of providing a scientific basis for the feasibility of using X80 welded pipes in hydrogen-blended transportation.

Hydrogen serves as a key clean-energy carrier with the main hurdles lying in safe efficient transport and storage (gas or liquid) and in end-use energy conversion. Liquid hydrogen (LH) as a high-density method of storage and transportation presents cryogenic insulation as its key technical issues. In LH storage tanks the performance of high vacuum multilayer insulation (HVMLI) will decline due to hydrogen release and leakage from the microscopic pores of steel which significantly destroy the vacuum layer. The accumulation of residual gases will accelerate thermal failure shorten the service life of storage tanks and increase safety risks. Adsorption is the most effective strategy for removing residual gases. This review aims to elucidate materials methods and design approaches related to hydrogen storage. First it summarizes adsorbents used in liquid hydrogen storage tanks including cryogenic adsorbents metal oxides zeolite molecular sieves and non-volatile compounds. Second it explores experimental testing methods and applications of hydrogen adsorbents in storage tanks analyzing key challenges faced in practical applications and corresponding countermeasures. Finally it proposes research prospects for exploring novel adsorbents and developing integrated systems.

Pressure collapse in sloshing cryogenic liquid hydrogen tanks is a challenge for existing models which often diverge from experimental data. This paper presents a novel lumped-parameter model that overcomes these limitations. Based on a control volume analysis our approach simplifies the complex non-equilibrium physics into a single dimensionless ordinary differential equation governing the liquid’s temperature. We demonstrate this evolution is controlled by one key parameter: the interfacial Nusselt number (). A method for estimating directly from pressure data is also provided. Validated against literature data the model predicts final tank temperatures with deviation of 0.88K (<5% relative error) from measurements thereby explaining the associated pressure collapse. Furthermore our analysis reveals that the Nusselt number varies significantly during a single sloshing event—with calculated values ranging from a peak of 5.81 × 105 down to 7.58 × 103—reflecting the transient nature of the phenomenon.

This article presents the findings of a bibliometric analysis of scientific publications in journals and materials indexed in the SCOPUS and Web of Science databases covering the broad topic of underground hydrogen storage (UHS). The use of VOSviewer software for keyword analysis enabled the identification of four key research areas related to UHS. These areas include hydrogen and hydrocarbon reservoir engineering; hydrogen economy and energy transformation; processes in hydrogen storage sites including lessons from CO2 sequestration; and the geology engineering and geomechanics of underground gas storage. The interdisciplinary nature of UHS research emphasises the synergy of research across diverse fields. A bibliographic analysis allowed for the identification of areas of intensive research and new directions of work related to UHS key research centres and the dynamics of the development of research topics related to UHS. This study revealed the chronological dispersion of the research results their geographical and institutional variability and the varying contributions of major publishing journals. The research methodology used can serve as an inspiration for the work of other researchers.

Geological storage is an integral element of the green energy transition. Geological formations such as aquifers depleted reservoirs and hard rock caverns are used mainly for the storage of hydrocarbons carbon dioxide and increasingly hydrogen. However potential adverse effects such as ground movements leakage seismic activity and environmental pollution are observed. Existing research focuses on monitoring subsurface elements of the storage while on the surface it is limited to ground movement observations. The review was carried out based on 191 research contributions related to geological storage. It emphasizes the importance of monitoring underground gas storage (UGS) sites and their surroundings to ensure sustainable and safe operation. It details surface monitoring methods distinguishing geodetic surveys and remote sensing techniques. Remote sensing including active methods such as InSAR and LiDAR and passive methods of multispectral and hyperspectral imaging provide valuable spatiotemporal information on UGS sites on a large scale. The review covers modelling and prediction methods used to analyze the environmental impacts of UGS with data-driven models employing geostatistical tools and machine learning algorithms. The limited number of contributions treating geological storage sites holistically opens perspectives for the development of complex approaches capable of monitoring and modelling its environmental impacts.

Underground hydrogen storage (UHS) in basaltic rocks offers a scalable solution for large-scale sustainable energy needs yet its efficiency is limited by poorly constrained pore-scale hysteresis during cyclic hydrogenbrine flow. While basaltic rocks have been extensively studied for carbon sequestration and critical mineral extraction the pore-scale physics governing cyclic hydrogen-brine interactions particularly the roles of snap-off wettability and hysteresis remain inadequately understood. This knowledge gap hinders the development of predictive models and optimization strategies for UHS performance. This study presents a pore-scale investigations of cyclic hydrogen-brine flow in basaltic formations combining micro-computed tomography imaging with pore network modelling. A systematic workflow is employed to evaluate the effects of repeated drainage-imbibition cycles on multiphase flow properties under varying wetting regimes with emphasis on hysteresis evolution and its influence on recoverable hydrogen. Model validation is achieved through a novel benchmarking approach that incorporates synthetic fractures and morphological scaling enabling calibration against experimental capillary pressure and relative permeability. Results show that hydrogen trapping is primarily governed by snap-off and pore-body isolation particularly within large angular pores exhibiting high aspect ratios and limited connectivity. Strong hysteresis is observed between drainage and imbibition with hydrogen saturations averaging 85% predominantly in larger pore spaces compared to a residual saturation of 61% following imbibition. Repeated cycling leads to a gradual increase in residual saturation which eventually stabilizes indicating the onset of a hysteresis equilibrium state. Wettability emerges as a critical second-order control on displacement dynamics. Shifting from strongly to weakly water-wet conditions reduces capillary entry pressures enhances brine re-invasion and increases hydrogen recovery efficiency by ∼6%. These findings offer mechanistic insights into capillary trapping and wettability effects providing a framework for optimizing UHS reactive and abundant yet underutilized basalt formations and supporting ongoing global decarbonization efforts through reliable subsurface hydrogen storage.

As environmental pollution has become a global concern regulations on carbon emissions from maritime activities are being implemented and interest in using renewable energy as fuel for ships is growing. Hydrogen which does not release carbon dioxide and has a high energy density can potentially replace fossil fuels as a renewable energy source. Notably storage of hydrogen in a liquid state is considered the most efficient. In this study a 0.7 m3 liquid hydrogen fuel tank suitable for small vessels was designed and a structural analysis was conducted to assess its structural integrity. The extremely low liquefaction temperature of hydrogen at −253 ◦C and the need for spatial efficiency in liquid hydrogen fuel tanks make vacuum insulation essential to minimize the heat transfer due to convection. A composite insulation system of sprayed-on foam insulation (SOFI) and multilayer insulation (MLI) was applied in the vacuum annular space between the inner and outer shells and a tube-shaped supporter made of a G-11 cryogenic (CR) material with low thermal conductivity and high strength was employed. The material selected for the inner and outer layers of the tank was STS 316L which exhibits sufficient ductility and strength at cryogenic temperatures and has low sensitivity to hydrogen embrittlement. The insulation performance was quantitatively assessed by calculating the boil-off rate (BOR) of the designed fuel tank. Structural integrity evaluations were conducted for nine load cases using heat transfer and structural analyses in accordance with the IGF code.

As the global economy moves toward net-zero carbon emissions large-scale energy storage becomes essential to tackle the seasonal nature of renewable sources. Underground hydrogen storage (UHS) offers a feasible solution by allowing surplus renewable energy to be transformed into hydrogen and stored in deep geological formations such as aquifers salt caverns or depleted reservoirs making it available for use on demand. This study thoroughly evaluates UHS concepts procedures and challenges. This paper analyzes the most recent breakthroughs in UHS technology and identifies special conditions needed for its successful application including site selection guidelines technical and geological factors and the significance of storage characteristics. The integrity of wells and caprock which is important for safe and efficient storage can be affected by the operating dynamics of the hydrogen cycle notably the fluctuations in pressure and stress within storage formations. To evaluate its potential for broader adoption we also examined economic elements such as cost-effectiveness and the technical practicality of large-scale storage. We also reviewed current UHS efforts and identified key knowledge gaps primarily in the areas of hydrogen–rock interactions geochemistry gas migration control microbial activities and geomechanical stability. Resolving these technological challenges regulatory frameworks and environmental sustainability are essential to UHS’s long-term and extensive integration into the energy industry. This article provides a roadmap for UHS research and development emphasizing the need for further research to fully realize the technology’s promise as a pillar of the hydrogen economy

The transition to a renewable energy system based mainly on an electricity and hydrogen infrastructure places new requirements and constraints on the infrastructure systems involved. This study investigates the impact of future hydrogen storage demands on a representative salt cavern considering two cases: a regional focus on Lower Saxony with high wind energy penetration and a national perspective on Germany with a PV-dominated mix of installed capacities. A numerical model is developed for in-depth assessment of the thermodynamics inside the cavern. Hydrogen storage profiles generated from 2045 renewable electricity projections for Germany reveal substantial storage demands. Key parameters such as hydrogen production and storage share turnover rate and storage interval length vary significantly between the two cases. In the Lower Saxony case high wind shares lead to increased turnover rates and reduced required working gas volumes but also result in steeper pressure and temperature gradients inside the cavern and necessitate larger compressor systems. In contrast the PV-dominated Germany case experiences lower internal cavern stresses but requires more flexible surface components to manage frequent fluctuations in hydrogen flow. These findings underscore the complex interplay between regional power mixes storage facility design and operational requirements.

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.

Hydrogen energy is valued for its diverse sources and clean low-carbon nature and is a promising secondary energy source with wide-ranging applications and a significant role in the global energy transition. Nonetheless hydrogen’s low energy density makes its largescale storage and transport challenging. Liquid hydrogen with its high energy density and easier transport offers a practical solution. This study examines the global hydrogen liquefaction methods with a particular emphasis on the liquid nitrogen pre-cooling Claude cycle process. It also examines the factors in the helium refrigeration cycle—such as the helium compressor inlet temperature outlet pressure and mass—that affect energy consumption in this process. Using HYSYS software the hydrogen liquefaction process is simulated and a complete process system is developed. Based on theoretical principles this study explores the pre-cooling refrigeration and normal-to-secondary hydrogen conversion processes. By calculating and analyzing the process’s energy consumption an optimized flow scheme for hydrogen liquefaction is proposed to reduce the total power used by energy equipment. The study shows that the hydrogen mass flow rate and key helium cycle parameters—like the compressor inlet temperature outlet pressure and flow rate—mainly affect energy consumption. By optimizing these parameters notable decreases in both the total and specific energy consumption were attained. The total energy consumption dropped by 7.266% from the initial 714.3 kW and the specific energy consumption was reduced by 11.94% from 11.338 kWh/kg.

Green ammonia is a promising hydrogen derivative which enables intercontinental transport of dispatchable renewable energy. This research describes the development of a model which optimizes a global green ammonia network considering the costs of production storage and transport. In generating the model we show economies of scale for green ammonia production are small beyond 1 million tonnes per annum (MMTPA) although benefits accrue up to a production rate of 10 MMTPA if a production facility is serviced by a new port or requires a long pipeline. The model demonstrates that optimal sites for ammonia production require not only an excellent renewable resource but also ample land from which energy can be harvested. Land limitations constrain project size in otherwise optimal locations and force production to more expensive sites. Comparison of current crude oil markets to future ammonia markets reveals a trend away from global supply hubs and toward demand centers serviced by regional production.

Underground hydrogen storage has gained interest in recent years due to the enormous demand for clean energy. Hydrogen is more diffusive than air with a smaller density and lower viscosity. These unique properties introduce distinctive hydrodynamic phenomena in hydrogen storage one of which is fingering. Fingering could induce the fluid trapped in small clusters of pores leading to a dramatic decrease in hydrogen saturation and a lower recovery rate. In this study numerical simulations are performed at the microscopic scale to understand the evolution of hydrogen saturation and the impacts of injection and withdrawal cycles. Two sets of micromodels with different porosity (0.362 and 0.426) and minimum sizes of pore throats (0.362 mm and 0.181 mm) are developed in the numerical model. A parameter analysis is then conducted to understand the influence of injection velocity (in the range of 10-2 m/s to 10-5 m/s) and porous structure on the fingering pattern followed by an image analysis to capture the evolution of the fingering pattern. Viscous fingering capillary fingering and crossover fingering are observed and identified under different boundary conditions. The fractal dimension specific area mean angle and entropy of fingers are proposed as geometric descriptors to characterize the shape of the fingering pattern. When porosity increases from 0.362 to 0.426 the saturation of hydrogen increases by 26.2%. Narrower pore throats elevate capillary resistance which hinders fluid invasion. These results underscore the importance of pore structures and the interaction between viscous and capillary forces for hydrogen recovery efficiency. This work illuminates the influence of the pore structures and the fluid properties on the immiscible displacement of hydrogen and can be further extended to optimize the injection strategy of hydrogen in underground hydrogen storage.

Electrochemical energy conversion systems are recognized as sustainable options for clean power generation. In conjunction with this the current hydrogen storage methods often suffer from limited storage density stability or high cost which motivate the search for alternative fuels with improved performance. This study is designed to investigate ammonium formate as an effective hydrogen storage medium and an efficient electrochemical fuel in electrochemical energy conversion systems. In order to perform the experimental tests stainless steel-stainless steel and aluminum-stainless steel electrode pairs are selected and examined under varying concentrations of potassium hydroxide sodium chloride and hydrogen peroxide at 80 ◦C and the system responses are then evaluated through voltage–time monitoring and polarization curve analysis. The aluminum-stainless steel configuration achieves the highest performance under 0.1 M potassium hydroxide and 10 % hydrogen peroxide reaching the voltages near ~ 900 mV and current densities of ~ 340 mA cm− 2 ; and the sodium chloride systems produce up to ~ 820 mV and ~ 310 mA cm− 2 while higher additive levels result in decreasing the voltages below 500 mV due to losses and side reactions. These findings confirm that moderate additive concentrations and optimized electrode pairing significantly enhance efficiency positioning ammonium formate as a low-cost energy-dense fuel suitable for decentralized and portable applications.

Wind power-to-gas concepts have a high potential to sustainably cover the increasing demand for hydrogen as an energy carrier and raw material as it has been shown in the past that there is an enormous potential in energy overproduction which currently remains unused due to the shutdown of wind turbines. Thus there is barely experience in maritime production offshore storage and transport of large quantities of liquid hydrogen (LH2) due to the developing market. Instead tank designs refer to heavy standard onshore storage and transport applications with vacuum insulated double wall hulls made from austenitic stainless steel and comparatively high thermal diffusivity and conductivity. This reduces cost effectiveness due to inevitable boil-off and disregards some other requirements such as mechanical and cyclic strength and high corrosion resistance. Hence new concepts for LH2 tanks are required for addressing these issues. Two innovative technical concepts from space travel and high-temperature applications were adopted combined and qualified for use in the wind-power-to-gas scenario. The focus was particularly on the high requirements for transport weight insulation and cryogenic durability. The first concept part consisted of the implementation of FRP (fiber-reinforced plastics)–steel hybrid tanks which have a high potential as a hull for LH2 tanks. However these hybrid tanks are currently only used in the space sector. Questions still arise regarding interactions with coatings production material temperature resilience and design for commercial use. Thermally sprayed thermal barrier coatings (TBC) in turn show promising potential for surfaces subject to high thermal and mechanical stress. However the application is currently limited to use at high temperatures and needed to be extended to the cryogenic temperature range. The research on this second part of the concept thus focused on the validation of standard MCrAlY alloys and innovative (partially) amorphous metal coatings with regard to mechanical-technological and insulating properties in the low temperature range. This article gives an overview regarding the achieved results including manufacturing and measurements on a small tank demonstrator.

Accurately predicting hydrogen adsorption behavior is essential to developing efficient materials with storage capacities approaching those of liquid hydrogen and surpassing the performance of conventional compressed gas storage systems. Grand canonical Monte Carlo (GCMC) simulations accurately predict adsorption isotherms but are computationally expensive limiting large-scale material screening. We employ GPU-accelerated threedimensional classical density functional theory (DFT) based on the SAFT-VRQ Mie equation of state with a first-order Feynman–Hibbs correction to model hydrogen adsorption in [Zn(bdc)(ted)0.5] MOF-5 CuBTC and ZIF-8 at 30 K 50 K 77 K and 298 K. Our approach generates adsorption isotherms in seconds compared to hours for GCMC simulations with quantum corrections proving crucial for accurate low-temperature predictions. The results show good agreement with GCMC simulations and available experiments demonstrating classical DFT as a powerful tool for high-throughput material screening and optimizing hydrogen storage applications.

The green hydrogen economy is evolving rapidly accompanied by the need to establish trading routes on a global scale. Currently several technologies arecompeting for a leadership role in future hydrogen value chains. Within thiscontext liquid organic hydrogen carrier (LOHC) technology represents an excellent solution for large-scale storage and safe transportation of hydrogen.This article presents LOHC technology recent progress as well as further potential of this technology with focus on benzyltoluene as the carrier material.Furthermore this contribution offers an insight into previous and ongoingproject development activities led by Hydrogenious LOHC Technologies togetherwith an evaluation of the economic viability and an overview of the regulatory aspects of LOHC technology.

This paper provides a comprehensive review of Type IV hydrogen tanks with a focus on materials manufacturing technologies and structural issues related to high-pressure hydrogen storage. Recent advances in the use of advanced composite materials such as carbon fibers and polyamide liners useful for improving mechanical strength and permeability have been reviewed. The present review also discusses solutions to reduce hydrogen blistering and embrittlement as well as exploring geometric optimization methodologies and manufacturing techniques such as helical winding. Additionally emerging technologies such as integrated smart sensors for real-time monitoring of tank performance are explored. The review concludes with an assessment of future trends and potential solutions to overcome current technical limitations with the aim of fostering a wider adoption of Type IV tanks in mobility and stationary applications.

Underground hydrogen storage is critical for supporting the transition to renewable energy systems addressing the intermittent nature of solar and wind power. Despite its promise as a carbon-neutral energy carrier there remains limited understanding of the geomechanical behavior of subsurface reservoirs under hydrogen storage conditions. This knowledge gap is particularly significant for fast-cycling operations which have yet to be implemented on a large scale. This review evaluates current knowledge on the geomechanics of underground hydrogen storage focusing on risks and challenges in geological formations such as salt caverns depleted hydrocarbon reservoirs saline aquifers and lined rock caverns. Laboratory experiments field studies and numerical simulations are synthesized to examine cyclic pressurization induced seismicity thermal stresses and hydrogen-rock interactions. Notable challenges include degradation of rock properties fault reactivation micro-seismic activity in porous reservoirs and mineral dissolution/precipitation caused by hydrogen exposure. While salt caverns are effective for low-frequency hydrogen storage their behavior under fast-cyclic loading requires further investigation. Similarly the mechanical evolution of porous and fractured reservoirs remains poorly understood. Key findings highlight the need for comprehensive geomechanical studies to mitigate risks and enhance hydrogen storage feasibility. Research priorities include quantifying cyclic loading effects on rock integrity understanding hydrogen-rock chemical interactions and refining operational strategies. Addressing these uncertainties is essential for enabling large-scale hydrogen integration into global energy systems and advancing sustainable energy solutions. This work systematically focuses on the geomechanical implications of hydrogen injection into subsurface formations offering a critical evaluation of current studies and proposing a unified research agenda.

The H2STORE collaborative project investigates potential geohydraulic petrophysical mineralogical microbiological and geochemical interactions induced by the injection of hydrogen into depleted gas reservoirs and CO2- and town gas storage sites. In this context the University of Jena performs mineralogical and geochemical investigations on reservoir and cap rocks to evaluate the relevance of preferential sedimentological features which will control fluid (hydrogen) pathways thus provoking fluid-rock interactions and related variations in porosity and permeability. Thereby reservoir sand- and sealing mudstones of different composition sampled from distinct depths (different: pressure/temperature conditions) of five German locations are analysed. In combination with laboratory experiments the results will enable the characterization of specific mineral reactions at different physico-chemical conditions and geological settings.

The high potential of hydrogen as a key factor on the pathway towards a climate neutral economy leads to rising demand in technical applications where gaseous hydrogen is used. For several metals hydrogen-metal interactions could cause a degradation of the material properties. This is especially valid for low carbon and highstrength structural steels as they are commonly used in natural gas pipelines and analyzed in this work. This work provides an insight to the impact of hydrogen on the mechanical properties of an API 5L X65 pipeline steel tested in 60 bar gaseous hydrogen atmosphere. The analyses were performed using the hollow specimen technique with slow strain rate testing (SSRT). The nature of the crack was visualized thereafter utilizing μCT imaging of the sample pressurized with gaseous hydrogen in comparison to one tested in an inert atmosphere. The combination of the results from non-conventional mechanical testing procedures and nondestructive imaging techniques has shown unambiguously how the exposure to hydrogen under realistic service pressure influences the mechanical properties of the material and the appearance of failure.

The large-scale integration of renewable energy sources leads to daily and seasonal mismatches between supply and demand and the curtailment of wind power. Hydrogen produced from surplus wind power offers an attractive solution to these challenges. In this paper we consider a large offshore wind park and analyze the need for hydrogen storage at the onshore and offshore sides of a large transportation pipeline that connects the wind park to the mainland. The results show that the pipeline with line pack storage though important for day-to-day fluctuations will not offer sufficient storage capacity to bridge seasonal differences. Furthermore the results show that if the pipeline is sufficiently sized additional storage is only needed on one side of the pipeline which would limit the needed investments. Results show that the policy which determines what part of the wind power is fed into the electricity grid and what part is converted into hydrogen has a significant influence on these seasonal storage needs. Therefore investment decisions for hydrogen systems should be made by considering both the onshore and offshore storage requirements in combination with electricity transport to the mainland.

Nanomaterials have attracted great interest in recent years because of the unusual mechanical electrical electronic opticalmagnetic and surface properties. The high surface/volume ratio of these materials has significant implications with respectto energy storage. Both the high surface area and the opportunity for nanomaterial consolidation are key attributes of thisnew class of materials for hydrogen storage devices. Nanostructured systems including carbon nanotubes nano-magnesiumbased hydrides complex hydride/carbon nanocomposites boron nitride nanotubes TiS2/MoS2 nanotubes alanates polymernanocomposites and metal organic frameworks are considered to be potential candidates for storing large quantities of hydrogen.Recent investigations have shown that nanoscale materials may offer advantages if certain physical and chemical effects related tothe nanoscale can be used efficiently. The present review focuses the application of nanostructured materials for storing atomicor molecular hydrogen. The synergistic effects of nanocrystalinity and nanocatalyst doping on the metal or complex hydrides forimproving the thermodynamics and hydrogen reaction kinetics are discussed. In addition various carbonaceous nanomaterialsand novel sorbent systems (e.g. carbon nanotubes fullerenes nanofibers polyaniline nanospheres and metal organic frameworksetc.) and their hydrogen storage characteristics are outlined.

According to the European Hydrogen Strategy hydrogen will solve many of the problems with energy storage for balancing variable renewable energy sources (RES) supply and demand. At the same time we can see increasing popularity of the so-called energy communities (e.g. cooperatives) which (i) enable groups of entities to invest in manage and benefit from shared RES energy infrastructure; (ii) are expected to increase the energy independence of local communities from large energy corporations and increase the share of RES. Analyses were conducted on 2000 randomly selected energy cooperatives and four energy cooperatives formed on the basis of actual data. The hypotheses assumed in the research and positively verified in this paper are as follows: (i) there is a relationship between hydrogen storage capacity and the power of RES which allows an energy community to build energy independence; (ii) the type of RES generating source is meaningful when optimizing hydrogen storage capacity. The paper proves it is possible to build “island energy independence” at the local level using hydrogen storage and the efficiency of the power-to-power chain. The results presented are based on simulations carried out using a dedicated optimization model implemented by mixed integer programming. The authors’ next research projects will focus on optimizing capital expenditures and operating costs using the Levelized Cost of Electricity and Levelized Cost of Hydrogen methodologies.

Hydrogen storage technologies are key enablers for the development of low-emission sustainable energy supply chains primarily due to the versatility of hydrogen as a clean energy carrier. Hydrogen can be utilized in both stationary and mobile power applications and as a lowenvironmental-impact energy source for various industrial sectors provided it is produced from renewable resources. However efficient hydrogen storage remains a significant technical challenge. Conventional storage methods such as compressed and liquefied hydrogen suffer from energy losses and limited gravimetric and volumetric energy densities highlighting the need for innovative storage solutions. One promising approach is hydrogen storage in metal hydrides which offers advantages such as high storage capacities and flexibility in the temperature and pressure conditions required for hydrogen uptake and release depending on the chosen material. However these systems necessitate the careful management of the heat generated and absorbed during hydrogen absorption and desorption processes. Thermal energy storage (TES) systems provide a means to enhance the energy efficiency and cost-effectiveness of metal hydride-based storage by effectively coupling thermal management with hydrogen storage processes. This review introduces metal hydride materials for hydrogen storage focusing on their thermophysical thermodynamic and kinetic properties. Additionally it explores TES materials including sensible latent and thermochemical energy storage options with emphasis on those that operate at temperatures compatible with widely studied hydride systems. A detailed analysis of notable metal hydride–TES coupled systems from the literature is provided. Finally the review assesses potential future developments in the field offering guidance for researchers and engineers in advancing innovative and efficient hydrogen energy systems.

To consider an appropriate evaluation method for hydrogen compatibility slow strain rate tensile (SSRT) tests were conducted on high strength piping materials cold-worked type 316 austenitic stainless steel (SUS316CW) and iron-based superalloy A286 used in hydrogen stations for two years.<br/>SUS316CW used at room temperature in 82 MPa gaseous hydrogen contained 7.8 mass ppm hydrogen. The SSRT test of SUS316CW was conducted in nitrogen at -40 °C. The fracture surface showed dimples and no hydrogen embrittlement behavior was observed. While the SSRT test of SUS316CW in 70 MPa gaseous hydrogen at -40 °C showed a slight decrease in reduction area and a brittle fracture morphology in the outer layer. This was considered to be the effect of high-pressure gaseous hydrogen during the SSRT test in addition to the pre-contained hydrogen.<br/>A286 used at -40 °C in 82 MPa gaseous hydrogen contained negligible hydrogen (0.14 mass ppm). SSRT tests were conducted at 150 °C in 70 MPa gaseous hydrogen and in air and showed a low relative reduction in area (RRA) value. To investigate the decrease in the RRA we switched the gas from hydrogen to air in the middle of the SSRT test and closely examined the RRA values and fracture morphology including side cracks. The hydrogen embrittlement was found to originate from the elastic deformation region. Stress cycling in the elastic deformation region also accelerated the effect of hydrogen. These were attributed to an increase in the lattice hydrogen content. While in the plastic deformation region hydrogen trapped in the defects and hydrogen through the generated surface cracks increased the hydrogen content at the crack tips reducing the RRA value. And there was a good correlation between the crack lengths and RRA values.<br/>Then hydrogen embrittlement mechanism depends on the operating conditions (stress and temperature) of the material and evaluating the hydrogen compatibility of materials by controlling their hydrogen content and strain according to the service environment is desirable.

The hydrogen storage cylinder lining was taken as the research object. The injection model of the cylinder liner was developed employing 3D software a two-cavity injection molding system was built and Moldfow was utilized for analysis to determine the best combination of injection molding process parameters. The efects of injection process parameters (melt temperature mold temperature holding pressure holding time and cooling time) on the evaluation index were analyzed by orthogonal experiment L16(45 ). The prediction data of IV hydrogen storage cylinder lining under diferent parameters were obtained by the range analysis method. The multi-objective optimization problem of injection molding process was transformed into a single-objective optimization problem by using the grey correlation analysis method. The optimal parameters such as melt temperature 270 °C mold temperature 80 °C packing pressure 55 MPa packing time 20 s and cooling time 13 s were obtained. Taguchi method was adopted to obtain SNR (signal-to-noise ratio) while range and variance methods were used for analysis. The results showed that warpage was 0.4892 mm the volume shrinkage was 12.31% the residual stress in the frst direction was 98.13 MPa and the residual stress in the second direction was 108.1 MPa. The comprehensive index was simultaneously most impacted by the melt temperature.

The chances of a global hydrogen economy becoming a reality have increased significantly since the COVID pandemic and the war in Ukraine and for net zero carbon emissions. However intercontinental hydrogen transport is still a major issue. This study suggests transporting hydrogen as a gas at atmospheric pressure in balloons using the natural flow of wind to carry the balloon to its destination. We investigate the average wind speeds atmospheric pressure and temperature at different altitudes for this purpose. The ideal altitudes to transport hydrogen with balloons are 10 km or lower and hydrogen pressures in the balloon vary from 0.25 to 1 bar. Transporting hydrogen from North America to Europe at a maximum 4 km altitude would take around 4.8 days on average. Hydrogen balloon transportation cost is estimated at 0.08 USD/kg of hydrogen which is around 12 times smaller than the cost of transporting liquified hydrogen from the USA to Europe. Due to its reduced energy consumption and capital cost in some locations hydrogen balloon transportation might be a viable option for shipping hydrogen compared to liquefied hydrogen and other transport technologies.

Hydrogen energy has been proposed as a reliable and sustainable source of energy which could play an integral part in demand for foreseeable environmentally friendly energy. Biomass fossil fuels waste products and clean energy sources like solar and wind power can all be employed for producing hydrogen. This comprehensive review paper provides a thorough overview of various hydrogen storage technologies available today along with the benefits and drawbacks of each technology in context with storage capacity efficiency safety and cost. Since safety concerns are among the major barriers to the broad application of H2 as a fuel source special attention has been paid to the safety implications of various H2 storage techniques. In addition this paper highlights the key challenges and opportunities facing the development and commercialization of hydrogen storage technologies including the need for improved materials enhanced system integration increased awareness and acceptance. Finally recommendations for future research and development with a particular focus on advancing these technologies towards commercial viability.

With the issue of energy shortages becoming increasingly serious the need to shift to sustainable and clean energy sources has become urgent. However due to the intermittent nature of most renewable energy sources developing underground hydrogen storage (UHS) systems as backup energy solutions offers a promising solution. The thick and regionally extensive salt deposits in Unit B of Southern Ontario Canada have demonstrated significant potential for supporting such storage systems. Based on the stratigraphy statistics of unit B this study investigates the feasibility and stability of underground hydrogen storage (UHS) in salt caverns focusing on the effects of cavern shape geometric parameters and operating pressures. Three cavern shapes—cylindrical cone-shaped and ellipsoid-shaped—were analyzed using numerical simulations. Results indicate that cylindrical caverns with a diameter-to-height ratio of 1.5 provide the best balance between storage capacity and structural stability while ellipsoid-shaped caverns offer reduced stress concentration but have less storage space posing practical challenges during leaching. The results also indicate that the optimal pressure range for maintaining stability and minimizing leakage lies between 0.4 and 0.7 times the vertical in situ stress. Higher pressures increase storage capacity but lead to greater stress displacements and potential leakage risks while lower pressure leads to internal extrusion tendency for cavern walls. Additionally hydrogen leakage rate drops with the maximum working pressure yet total leakage mass keeps a growing trend.

The subject of this study is the analysis of influence of capillary threshold pressure and injection well location on the dynamic CO2 and H2 storage capacity for the Lower Jurassic reservoir of the Sierpc structure from central Poland. The results of injection modeling allowed us to compare the amount of CO2 and H2 that the considered structure can store safely over a given time interval. The modeling was performed using a single well for 30 different locations considering that the minimum capillary pressure of the cap rock and the fracturing pressure should not be exceeded for each gas separately. Other values of capillary threshold pressure for CO2 and H2 significantly affect the amount of a given gas that can be injected into the reservoir. The structure under consideration can store approximately 1 Mt CO2 in 31 years while in the case of H2 it is slightly above 4000 tons. The determined CO2 storage capacity is limited; the structure seems to be more prospective for underground H2 storage. The CO2 and H2 dynamic storage capacity maps are an important element of the analysis of the use of gas storage structures. A much higher fingering effect was observed for H2 than for CO2 which may affect the withdrawal of hydrogen. It is recommended to determine the optimum storage depth particularly for hydrogen. The presented results important for the assessment of the capacity of geological structures also relate to the safety of use of CO2 and H2 underground storage space.

The transport of hydrogen in used natural gas pipelines is a strategic key element of a pan-European hydrogen infrastructure. At the same time accurate knowledge of the hydrogen quality is essential in order to be able to address a wide application range. Therefore an experimental investigation was carried out to find out which contaminants enter into the hydrogen from the used natural gas pipelines. Pipeline elements from the high pressure gas grid of Austria were exposed to hydrogen. Steel pipelines built between 1960 and 2018 which were operated with odorised and pure natural gas were examined. The hydrogen was analysed according to requirements of ISO14687: 2019 Grade D measurement standard. The results show that based on age odorization and sediments different contimenants are introduced. Odorants hydrocarbons but also sulphur compounds ammonia and halogenated hydrogen compounds were identified. Sediments are identified as the main source of impurities. However the concentrations of the introduced contaminants were low (6 nmol/mol to 10 μmol/mol). Quality monitoring with a wide range of detection options for different components (sulphur halogenated compounds hydrocarbons ammonia and atmospheric components) is crucial for real operation. The authors deduce that a Grade A hydrogen quality can be safely achieved in real operation.

Thanks to the advantages of cleanliness high efficiency extensive sources and renewable energy hydrogen energy has gradually become the focus of energy development in the world’s major economies. At present the natural gas transportation pipeline network is relatively complete while hydrogen transportation technology faces many challenges such as the lack of technical specifications high safety risks and high investment costs which are the key factors that hinder the development of hydrogen pipeline transportation. This paper provides a comprehensive overview and summary of the current status and development prospects of pure hydrogen and hydrogen-mixed natural gas pipeline transportation. Analysts believe that basic studies and case studies for hydrogen infrastructure transformation and system optimization have received extensive attention and related technical studies are mainly focused on pipeline transportation processes pipe evaluation and safe operation guarantees. There are still technical challenges in hydrogen-mixed natural gas pipelines in terms of the doping ratio and hydrogen separation and purification. To promote the industrial application of hydrogen energy it is necessary to develop more efficient low-cost and low-energy-consumption hydrogen storage materials.

Hydrogen threatens the structural integrity of metals and thus predicting hydrogen-material interactions is key to unlocking the role of hydrogen in the energy transition. Quantifying the interplay between material deformation and hydrogen diffusion ahead of cracks and other stress concentrators is key to the prediction and prevention of hydrogen-assisted failures. In this work a generalised theoretical and computational framework is presented that for the first time encompasses: (i) stress-assisted diffusion (ii) hydrogen trapping due to multiple trap types rigorously accounting for the rate of creation of dislocation trap sites (iii) hydrogen transport through dislocations (iv) equilibrium (Oriani) and non-equilibrium (McNabb-Foster) trapping kinetics (v) hydrogen-induced softening and (vi) hydrogen uptake considering the role of hydrostatic stresses and local electrochemistry. Particular emphasis is placed on the numerical implementation in COMSOL Multiphysics releasing the relevant models and discussing stability discretisation and solver details. Each of the elements of the framework is independently benchmarked against results from the literature and implications for the prediction of hydrogen-assisted fractures are discussed. The second part of this work (Part II) shows how these crack tip predictions can be combined with crack growth simulations.

This study investigated the impact of cushion gas type and presence on the performance of underground hydrogen storage (UHS) in an offshore North Sea aquifer. Using numerical simulation the relationship between cushion gas type and UHS performance was comprehensively evaluated providing valuable insights for designing an efficient UHS project delivery. Results indicated that cushion gas type can significantly impact the process's recovery efficiency and hydrogen purity. CO2 was found to have the highest storage capacity while lighter gases like N2 and CH4 exhibited better recovery efficiency. Utilising CH4 as a cushion gas can lead to a higher recovery efficiency of 80%. It was also determined that utilising either of these cushion gases was always more beneficial than hydrogen storage alone leading to an incremental hydrogen recovery up to 7%. Additionally hydrogen purity degraded as each cycle progressed but improved over time. This study contributes to a better understanding of factors affecting UHS performance and can inform the selection of cushion gas type and optimal operational strategies.

In this study we evaluate the technical viability of storing hydrogen in a deep UKCS aquifer formation through a series of numerical simulations utilising the compositional simulator CMG-GEM. Effects of various operational parameters such as injection and production rates number and length of storage cycles and shut-in periods on the performance of the underground hydrogen storage (UHS) process are investigated in this study. Results indicate that higher H2 operational rates degrade both the aquifer's working capacity and H2 recovery during the withdrawal phase. This can be attributed to the dominant viscous forces at higher rates which lead to H2 viscous fingering and gas gravity override of the native aquifer water resulting in an unstable displacement of water by the H2 gas. Furthermore analysis of simulation results shows that longer and less frequent storage cycles lead to higher storage capacity and decreased H2 retrieval. We conclude that UHS in the studied aquifer is technically feasible however a thorough evaluation of the operational parameters is necessary to optimise both storage capacity and H2 recovery efficiency.

This research investigates the potential of using bedded salt formations for underground hydrogen storage. We present a novel artificial intelligence framework that employs spatial data analysis and multi-criteria decision-making to pinpoint the most appropriate sites for hydrogen storage in salt caverns. This methodology incorporates a comprehensive platform enhanced by a deep learning algorithm specifically a convolutional neural network (CNN) to generate suitability maps for rock salt deposits for hydrogen storage. The efficacy of the CNN algorithm was assessed using metrics such as Mean Absolute Error (MAE) Mean Squared Error (MSE) Root Mean Square Error (RMSE) and the Correlation Coefficient (R2 ) with comparisons made to a real-world dataset. The CNN model showed outstanding performance with an R2 of 0.96 MSE of 1.97 MAE of 1.003 and RMSE of 1.4. This novel approach leverages advanced deep learning techniques to offer a unique framework for assessing the viability of underground hydrogen storage. It presents a significant advancement in the field offering valuable insights for a wide range of stakeholders and facilitating the identification of ideal sites for hydrogen storage facilities thereby supporting informed decisionmaking and sustainable energy infrastructure development.

The addition of small amounts of certain gases such as O2 CO and SO2 may mitigate hydrogen embrittlement in high-pressure gas transmission pipelines that transport hydrogen. To practically implement such inhibition in gas transmission pipelines a comprehensive understanding and quantification of this effect are essential. This review examines the impact of various added gases to hydrogen including typical odorants on gaseous hydrogen embrittlement of steels and evaluates their inhibition effectiveness. O2 CO and SO2 were found to be effective inhibitors of hydrogen embrittlement. Yet the results in the literature have not always been consistent partly because of the diverse range of mechanical tests and their parameters. The absence of systematic studies hinders the evaluation of the feasibility of using gas phase inhibitors for controlling gaseous hydrogen embrittlement. A method to quantify the effectiveness of gas phase inhibition is proposed using gas phase permeation studies.

Hydrogen is deemed as a crucial component in the transition to a carbon-free energy system and researchers are actively working to realize the hydrogen economy. While hydrogen derived from renewable energy sources is a promising means of providing clean energy to households and industries its practical usage is currently hindered by difficulties in transportation and storage. Due to the extreme operating conditions required for liquefying hydrogen various hydrogen carriers are being considered which can be transported and stored at mild operating conditions and provide hydrogen at the site of usage. Among various candidates green hydrogen carriers obtained via carbon dioxide utilization have been proposed as an economically and environmentally feasible option. Herein the potential of using methanol and formic acid as green hydrogen carriers are evaluated regarding various production and dehydrogenation pathways within a hydrogen distribution system including the recycle of carbon dioxide. Recent progress in carbon dioxide utilization processes especially conversion of carbon dioxide captured in amine solutions have demonstrated promising results for methanol and formic acid production. This study analyzes seven scenarios that consider carbon dioxide utilization-based thermocatalytic and electrochemical methanol and formic acid production as well as different dehydrogenation pathways and compares them to the scenario of delivering liquefied hydrogen. The scenarios are thoroughly analyzed via techno-economic analysis and life cycle assessment methods. The results of the study indicate that methanol-based options are economically viable reducing the cost up to 43% compared to liquefied hydrogen delivery. As for formic acid only the electrochemical production method is profitable retaining 10% less cost compared to liquefied hydrogen delivery. In terms of environmental impact all of the scenarios show higher global warming impact values than liquefied hydrogen distribution. However results show that in an optimistic case where wind electricity is widely used electrochemical formic acid production is competitive with liquefied hydrogen distribution retaining 39% less global warming impact values. This is because high conversion can be achieved at mild operating conditions for the production and dehydrogenation reactions of formic acid reducing the input of utilities other than electricity. This study suggests that while methanol can be a shortterm solution for hydrogen distribution electrochemical formic acid production may be a viable long-term option.

The study presents a thermodynamic and economic assessment of different hydrogen storage solutions for heating purposes powered by PV panels of a 10-apartment residential building in Milan and it focuses on compressed hydrogen liquid hydrogen and metal hydride. The technical assessment involves using Python to code thermodynamic models to address technical and thermodynamic performances. The economic analysis evaluates the CAPEX the ROI and the cost per unit of stored hydrogen and energy. The study aims to provide an accurate assessment of the thermodynamic and economic indicators of three of the storage methods introduced in the literature review pointing out the one with the best techno-economic performance for further development and research. The performed analysis shows that compressed hydrogen represents the best alternative but its cost is still too high for small residential applications. Applying the technology to a big system case would enable the solution making it economically feasible.

The storage and transfer of energy require a safe technology to mitigate the global environmental issues resulting from the massive application of fossil fuels. Fuel cells have used hydrogen as a clean and efficient energy source. Nevertheless the storage and transport of hydrogen have presented longstanding problems. Recently liquid organic hydrogen carriers (LOHCs) have emerged as a solution to these issues. The hydrogen storage technique in LOHCs is more attractive than those of conventional energy storage systems like liquefaction compression at high pressure and methods of adsorption and absorption. The release and acceptance of hydrogen should be reversible by LOHC molecules following favourable reaction kinetics. LOHCs comprise liquid and semi-liquid organic compounds that are hydrogenated to store hydrogen. These hydrogenated molecules are stored and transported and finally dehydrogenated to release the required hydrogen for supplying energy. Hydrogenation and dehydrogenation are conducted catalytically for multiple cycles. This review elaborates on the characteristics of different LOHC molecules based on their efficacy as energy generators. Additionally different catalysts used for both hydrogenation and dehydrogenation are discussed.

The rapidly increasing production volume of clean hydrogen creates challenges for transport infrastructure. This study improves understanding of hydrogen transport options in Europe and provides more detailed analysis on the prospects for hydrogen transport in Finland. Previous studies and ongoing pipeline projects were reviewed to identify potential and barriers to hydrogen transport. A fatigue life assessment tool was built because material challenges have been one of the main concerns of hydrogen transportation. Many European countries aim at utilizing existing gas infrastructure for hydrogen. Conducted studies and pilot facilities have provided promising results. Hydrogen reduces the fatigue life of the pipeline but existing pipelines can be used for hydrogen if pressure variation is maintained at a reasonable level and the maximum operation pressure is limited. Moreover the use of existing pipelines can reduce hydrogen transport costs but the suitability of every pipeline for hydrogen must be analyzed and several issues such as leakage leakage detection effects of hydrogen on pipeline assets and end users corrosion maintenance and metering of gas flow must be considered. The development of hydrogen transport will vary within countries depending on the structure of the existing gas infrastructure and on the future hydrogen use profile.

A new technical route to incorporate excess electricity (via green hydrogen generation by electrolysis) into a biorefinery to produce modern bioenergy (advanced biofuels) is proposed as a promising alternative. This new route involves storing hydrogen for mobile and stationary applications and can be a three-bird-one-stone solution for the storage of excess electrical energy storage of green hydrogen and high-value utilization of biomass.

Transitioning to a sustainable energy future necessitates innovative storage solutions for renewable energies where hydrogen (H₂) emerges as a pivotal energy carrier for its low emission potential. This paper explores unlined rock caverns (URCs) as a promising alternative for underground hydrogen storage (UHS) overcoming the geographical and technical limitations of UHS methods like salt rock caverns and porous media. Drawing from the experiences of natural gas (NG) and compressed air energy storage (CAES) in URCs we explore the viability of URCs for storing hydrogen at gigawatt-hour scales (>100 GWh). Despite challenges such as potential uplift failures (at a depth of approximately less than 1000 m) and hydrogen reactivity with storage materials at typical conditions (below temperatures of 100◦C and pressures of 15 MPa) URCs present a flexible scalable option closely allied with green hydrogen production from renewable sources. Our comprehensive review identifies critical design considerations including hydraulic containment and the integrity of fracture sealing materials under UHS conditions. Addressing identified knowledge gaps particularly around the design of hydraulic containment systems and the interaction of hydrogen with cavern materials will be crucial for advancing URC technology. The paper underscores the need for further experimental and numerical studies to refine URC suitability for hydrogen storage highlighting the role of URCs in enhancing the compatibility of renewable energy sources with the grid.

Hydrogen embrittlement (HE) of steels is extremely interesting topic in many industrial applications while a predictive physical model still does not exist. A number of studies carried out in the world are unambiguous confirmation of that statement. Bearing in mind multiple effects of hydrogen in certain metals the specific mechanism of hydrogen embrittlement is manifested depending on the experimental conditions. In this paper structural low carbon steel for pressure purposes grade 20 - St.20 (GOST 1050-88) was investigated. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant damaged due to high temperature hydrogen attack and HE during service as a result of the development of hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis hardness measurement impact strength testing (on instrumented Charpy machine) and microstructural characterization by optical and scanning electron microscopy - SEM/EDX. Based on multi-scale special approach applied in experimental investigations the results presented in this paper indicate the simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) mechanisms of HE depending on the local concentration of hydrogen in investigated steel. These results are consistent with some models proposed in literature about a possible simultaneous action of the HELP and HEDE mechanisms in metallic materials.

Typically polymeric materials experience material degradation anddamage over time in harsh environments. Improved understandingof the physical and chemical processes associated with possibledamage modes intended in high-pressure hydrogen gas exposedatmospheres will help to select and develop materials well suited forapplications fulfilling future energy demands in hydrogen as anenergy carrier. In high-pressure hydrogen gas exposure conditionsdamage from rapid gas decompression (RGD) and from aging inelastomeric as well as thermoplastic material components is unavoid-able. This review discusses the applications of polymeric materials ina multi-material approach in the realization of the “Hydrogen econo-my”. It covers the limitations of existing polymeric components thecurrent knowledge on polymeric material testing and characteriza-tion and the latest developments. Some improvements are sug-gested in terms of material development and testing procedures tofill in the gaps in existing knowledge in the literature.

Solar photovoltaic (PV)-based electricity production has gained significant attention for residential applications in recent years. However the sustainability and economic feasibility of PV systems are highly dependent on their grid-connected opportunities which may diminish with the increasing penetration of renewable energy sources into the grid. Therefore securing reliable energy storage is crucial for both grid-connected and off-grid PV-based residential facilities. Given the high capital costs and environmental issues associated with batteries hydrogen energy emerges as a superior option for medium to large residential applications. This paper proposes an innovative concept for PV-based green hydrogen production storage and utilization using solid oxide cells within residential micro-grids. It includes comprehensive techno-economic and environmental analyses of the proposed system utilizing dynamic solar data with a case study focusing on Calgary. The results indicate that seasonal hydrogen storage significantly enhances the feasibility of meeting the electricity demand of an off-grid residential community consisting of 525 households connected to a 4.6 MW solar farm. With the inclusion of Canadian clean hydrogen tax incentives the monthly cost per household is approximately $319 potentially decreasing to $239 with advancements in solid oxide cell technology and extended lifetimes of up to 80000 h. Furthermore implementing this system in Calgary could result in a monthly reduction of at least 250 kg of CO2 emissions per household.

Metal-organic frameworks (MOFs) have emerged as promising candidates for solid-state hydrogen storage owing to their exceptional specific surface area high pore volume and chemically tunable structural properties. In this work a diverse set of experimentally synthesized MOFs were evaluated to model and predict hydrogen storage capacity (wt%) using 4 key descriptors which are Brunauer–Emmett–Teller (BET) surface area pore volume operating pressure and temperature. Correlation analysis revealed positive associations between BET surface area pressure and pore volume with storage capacity and a negative association with temperature consistent with physisorption mechanism. Six machine learning models were developed: support vector regression (SVR) artificial neural networks (ANN) random forest (RF) Gaussian process regression (GPR) gradient boosting (GB) and a Committee of Expert Systems (CES) integrating all base learners. While GB was the top-performing standalone model the CES delivered the highest predictive fidelity (R2 = 0.9958 MSE = 0.0094) as confirmed by parity plots and residual analysis. SHapley Additive exPlanations (SHAP) corroborated the statistical feature rankings consistently identifying BET surface area and pressure as the most influential positive contributors in alignment with adsorption thermodynamics. Paired t-tests on root-mean-square error (RMSE) values confirmed statistically significant CES improvements over all individual models. The CES framework thus offers a dataefficient accurate and interpretable approach for rapid MOF screening with straightforward adaptability to other porous materials and adsorption-based energy storage systems.

The existing gas transmission pipeline network can be a convenient and cost-effective way to transport hydrogen. However hydrogen can cause hydrogen embrittlement (HE) of the steels used in pipeline construction. HE is typically manifested as a reduction in fracture toughness and ductility. To ensure structural integrity it is thus important to understand the fracture toughness of pipeline steels in hydrogen gas at pipeline pressures. This paper reviews (i) the influence of hydrogen on the fracture toughness of pipeline steels and (ii) the phenomena that occurs during fracture toughness tests of pipeline steel in air and hydrogen. Also reviewed are (i) the in fluence of hydrogen on tensile properties and (ii) the diffusion and solubility of hydrogen in pipeline steels under conditions relevant to hydrogen transport in gas transmission pipelines.