Transmission, Distribution & Storage

The aim of this study is to review and identify H2 storage suitability in geological reservoirs of the Republic of Lithuania. Notably Lithuania can store clean H2 effectively and competitively because of its wealth of resources and well-established infrastructure. The storage viability in Lithuanian geological contexts is highlighted in this study. In addition when it comes to injectivity and storage capacity salt caverns and saline aquifers present less of a challenge than other kinds of storage medium. Lithuania possesses sizable subterranean reservoirs (Cambrian rocks) that can be utilized to store H2. For preliminary assessment the cyclic H2 injection and production simulation is performed. A 10-year simulation of hydrogen injection and recovery in the Syderiai saline aquifer demonstrated the feasibility of UHS though efficiency was reduced by nearly 50% when using a single well for both injection and production. The study suggests using separate wells to improve efficiency. However to guarantee economic injectivity and containment security a detailed assessment of the geological structures is required specifically at the pore scale level. The volumetric approach estimated a combined storage capacity of approximately 898.5 Gg H2 (~11 TWh) for the Syderiai and Vaskai saline aquifers significantly exceeding previous estimates. The findings underscore the importance of detailed geological data and further research on hydrogen-specific factors to optimize UHS in Lithuania. Addressing technical geological and environmental challenges through multidisciplinary research is essential for advancing UHS implementation and supporting Lithuania’s transition to a sustainable energy system. UHS makes it possible to maximize the use of clean energy reduce greenhouse gas emissions and build a more sustainable and resilient energy system. Hence intensive research and advancements are needed to optimize H2 energy for broader applications in Lithuania.

The UK net zero strategy aims to fully decarbonize the power system by 2035 anticipating a 40–60% increase in demand due to the growing electrification of the transport and heating sectors over the next thirteen years. This paper provides a detailed technical and economic analysis of the role of energy storage technologies and transmission lines in balancing the power system amidst large shares of intermittent renewable energy generation. The analysis is conducted using the cost-optimizing energy system modelling framework REMix developed by the German Aerospace Center (DLR). The obtained results of multiple optimization scenarios indicate that achieving the lowest system cost with a 73% share of electricity generated by renewable energy sources is feasible only if planning rules in England and Wales are flexible enough to allow the construction of 53 GW of onshore wind capacity. This flexibility would enable the UK to become a net electricity exporter assuming an electricity trading market with neighbouring countries. Depending on the scenario 2.4–11.8 TWh of energy storage supplies an average of 11% of the electricity feed-in with underground hydrogen storage representing more than 80% of that total capacity. In terms of storage converter capacity the optimal mix ranges from 32 to 34 GW of lithium-ion batteries 13 to 22 GW of adiabatic compressed air energy storage 4 to 24 GW of underground hydrogen storage and 6 GW of pumped hydro. Decarbonizing the UK power system by 2035 is estimated to cost $37–56 billion USD with energy storage accounting for 38% of the total system cost. Transmission lines supply 10–17% of the total electricity feed-in demonstrating that when coupled with energy storage it is possible to reduce the installed capacity of conventional power plants by increasing the utilization of remote renewable generation assets and avoiding curtailment during peak generation times.

Hydrogen (H2) has the potential to become a cleaner fuel alternative to increase energy mix versatility as part of a low-carbon economy. Geological H2 storage represents a key component of the emerging H2 value chain since large-scale energy generation linked to energy generation and large-scale industrial applications will require significant upscaling of geological storage. Geological H2 storage can take place in both salt domes and bedded salt formations. Bedded salt formations offer a significant advantage for H2 storage over salt domes because of their widespread availability. This research focuses on evaluating the H2 storage potential of the Salado Formation a bedded salt deposit in the Permian Basin of West Texas in the United States. Using data from 3268 well logs this study analyzes an area of 136100 km2 to identify suitable depth and net halite thickness for H2 storage in salt caverns. In addition this work applies a novel geostatistical workflow to quantify the uncertainty in the formation’s storage potential. The H2 working gas potential of the Salado Formation ranges from 0.62 to 17.53 Tsm3 (1.75–49.68 PWh of stored energy) across low-risk to high-risk scenarios with a median potential of 1.19 Tsm3 (3.37 PWh). The counties with the largest storage potential are: Lea in New Mexico and Gaines and Andrews in Texas. These three counties account for more than 75 % of the formation’s total storage potential. This is the first study to quantify uncertainty in H2 storage estimates for a bedded salt formation while providing a detailed breakdown of results by county and 1 km2 grid sections. The findings of this work offer critical insights for developing H2 infrastructure in the Permian Basin. The Permian Basin of West Texas has the potential to become an important hub for H2 production from both natural gas and/or renewable energy. Estimating H2 storage potential is an important contribution to assess the feasibility of the entire H2 value chain in Texas. An interactive map accompanies this work allowing the readers to explore the results visually.

Underground hydrogen storage in aquifers is a promising solution to address the imbalance between energy supply and demand yet its practical implementation requires optimized strategies to ensure high efficiency and economic viability. To improve the storage and production efficiency of hydrogen it is essential to select the appropriate cushion gas and to study the influence of reservoir and process parameters. Based on the conceptual model of aquifer with single-well injection and production three potential cushion gas (carbon dioxide nitrogen and methane) were studied and the changes in hydrogen recovery for each cushion gas were compared. The effects of temperature initial pressure porosity horizontal permeability vertical to horizontal permeability ratio permeability gradient hydrogen injection rate and hydrogen production rate on the purity of recovered hydrogen were investigated. Additionally the impact of different well pattern on the purity of recovered hydrogen was studied. The results indicate that methane is the most effective cushion gas for improving hydrogen recovery in UHS. Different well patterns have significant impacts on the purity of recovered hydrogen. The mole fractions of methane in the produced gas for the single-well line-drive pattern and five-spot pattern were 16.8% 5% and 3.05% respectively. Considering the economic constraints the five-spot well pattern is most suitable for hydrogen storage in aquifers. Reverse rhythm reservoirs with smaller permeability differences should be chosen to achieve relatively high hydrogen recovery and purity of recovered hydrogen. An increase in hydrogen production rate leads to a significant decrease in the purity of the recovered hydrogen. In contrast hydrogen injection rate has only a minor effect. These findings provide actionable guidance for the selection of cushion gas site selection and operational design of aquifer-based hydrogen storage systems contributing to the large-scale seasonal storage of hydrogen and the balance of energy supply and demand.

The use of rare earth elements in hydrogen storage processes offers significant advantages in terms of increasing technological efficiency and ensuring system security. However this process also creates some serious problems in terms of environmental and economic sustainability. It is necessary to determine the most critical indicators affecting the sustainable use of these elements. Studies on this subject in the literature are quite limited and this may lead to wrong investment decisions. The main purpose of this study is to determine the most important indicators to increase the sustainable use of rare earth elements in hydrogen storage processes. An original decision-making model in which Siamese network logarithmic percentage-change driven objective weighting (LOPCOW) fractal fuzzy numbers and weighted influence super matrix with precedence (WISP) approaches are integrated in the study. This study provides an original contribution to the literature by identifying the most critical indicators affecting the sustainable use of rare earths in hydrogen storage processes by presenting an innovative model. Fractal structures such as Koch Snowflake Cantor Dust and Sierpinski Triangle can model complex uncertainties more successfully. Fractal structures are particularly effective in modeling linguistic fuzziness because their recursive nature closely mirrors the layered and imprecise way humans often express subjective judgments. Unlike linear fuzzy sets fractals can capture the patterns of ambiguity found in expert evaluations. Hydrogen storage capacity and government supports are determined as the most vital criteria affecting sustainability in rare earth use.

This paper provides authors’ perspective on the current advances and challenges in utilising polymers and composites in hydrogen economy. It has originated from ‘Polymers and Composites for Hydrogen Economy’ symposium organised in March 2025 at the University of Warwick. This paper presents views from the event and thus provides a perspective from academia and industry on the ongoing advances and challenges for those materials in hydrogen applications.

The erosion behavior and the service life of a hydrogen transmission tube with high velocity suitable for a hydrogen fuel aviation engine are not clear which is the bottleneck for its application. In this study a coupled model considering the fluid flow field of hydrogen and discrete motion of particles was established. The effects of the geometry parameters and erosion parameters on the hydrogen erosion behavior were investigated. The maximum erosion rate increased exponentially with the increased hydrogen velocity and increased linearly with the increased erosion time. The large bend radius and inner diameter of the bend tube contributed to the decreased erosion rate. There was an optimized window of the bend angle for a small erosion rate. The relationship between the accumulated thickness loss and maximum erosion rate was established. The prediction model of the service life was established using fourth strength theory. The service life of the tube was sensitive to the hydrogen velocity and erosion time. The experiments were conducted and the variations in thickness and hardness were measured. The simulated models agreed with the experiments and could provide guidance for the parameter selection and prediction of the service life of a bend tube.

This study examines the pricing and assesses resilience methods in hydrogen supply chains by thoroughly analyzing two main disruption scenarios. The model examines a scenario in which a hydrogen production company depends on a Renewable Power plant (RP) for its electricity supply. Ensuring a steady and efficient hydrogen supply chain is crucial but outages at renewable power sources provide substantial obstacles to sustainability and operational continuity. Therefore in the event of disruptions at the RP the company has two options for maintaining resilience: either sourcing electricity from a Fossil fuel Power plant (FP) through a grid network to continue hydrogen production or purchasing hydrogen directly from another company and utilizing third-party transportation for delivery. Using a game theoretic approach we examine how different methods affect demand satisfaction cost implications and environmental sustainability. The study employs sensitivity analysis to evaluate the impact of different disruption probabilities on each scenario. In addition a unique sensitivity analysis is performed to examine the resilience of transmission security to withstand disruptions. This study evaluates how investments in security measures affect the strength and stability of the supply chain in various scenarios of disruption. Our research suggests that the first scenario offers greater reliability and cost-effectiveness along with a higher resilience rate compared to the second scenario. Furthermore the examination of the environmental impact shows that the first scenario has a smaller amount of CO2 emissions per kg of hydrogen. This study offers important insights for supply chain managers to optimize resilience measures hence improving reliability reducing costs and minimizing environmental effects.

Hydrogen is considered a key alternative to fossil fuels in the broader context of ecological transition. Repurposing natural gas pipelines for hydrogen transport is one of the challenges of this approach. However hydrogen can diffuse into metallic lattices leading to hydrogen embrittlement (HE). For this reason typically ductile materials can experience unexpected brittle fractures and it is therefore necessary to assess the HE propensity of the current pipeline network to ensure its fitness for hydrogen transport. This study examines the relationship between the microstructure of the circumferential weld joint in X52 pipeline steel and hydrogen concentration introduced electrolytically. Base material heat affected zone and fused zone were subjected to 1800 3600 7200 and 14400 s of continuous charging with a current density J = − 10 mA/cm2 in an acid solution. Results showed that the fusion zone absorbed the most hydrogen across all charging times while the base material absorbed more hydrogen than the heat-affected zone due to the presence of non-metallic inclusions. Fracture toughness was assessed using single edge notch tension specimens (SENT) in air and electrolytic hydrogen. Results indicate that the base material is particularly vulnerable to hydrogen environments exhibiting the greatest reduction in toughness when exposed to hydrogen compared to air.

Green hydrogen is likely to play a major role in decarbonising the aviation industry. It is crucial to understand the effects of microstructure on hydrogen redistribution which may be implicated in the embrittlement of candidate fuel system metals. We have developed a multiscale finite element modelling framework that integrates micromechanical and hydrogen transport models such that the dominant microstructural effects can be efficiently accounted for at millimetre length scales. Our results show that microstructure has a significant effect on hydrogen localisation in elastically anisotropic materials which exhibit an interesting interplay between microstructure and millimetre-scale hydrogen redistribution at various loading rates. Considering 316L stainless steel and nickel a direct comparison of model predictions against experimental hydrogen embrittlement data reveals that the reported sensitivity to loading rate may be strongly linked with rate-dependent grain scale diffusion. These findings highlight the need to incorporate microstructural characteristics in hydrogen embrittlement models.

This review provides a comprehensive examination of artificial intelligence methods applied to the design optimization and performance prediction of composite-based hydrogen storage vessels with a focus on composite overwrapped pressure vessels. Targeted at researchers engineers and industrial stakeholders in materials science mechanical engineering and renewable energy sectors the paper aims to bridge traditional mechanical modeling with evolving AI tools while emphasizing alignment with standardization and certification requirements to enhance safety efficiency and lifecycle integration in hydrogen infrastructure. The review begins by introducing HSV types their material compositions and key design challenges including high-pressure durability weight reduction hydrogen embrittlement leakage prevention and environmental sustainability. It then analyzes conventional approaches such as finite element analysis multiscale modeling and experimental testing which effectively address aspects like failure modes fracture strength liner damage dome thickness winding angle effects crash behavior crack propagation charging/discharging dynamics burst pressure durability reliability and fatigue life. On the other hand it has been shown that to optimize and predict the characteristics of hydrogen storage vessels it is necessary to combine the conventional methods with artificial intelligence methods as conventional methods often fall short in multi-objective optimization and rapid predictive analytics due to computational intensity and limitations in handling uncertainty or complex datasets. To overcome these gaps the paper evaluates hybrid frameworks that integrate traditional techniques with AI including machine learning deep learning artificial neural networks evolutionary algorithms and fuzzy logic. Recent studies demonstrate AI’s efficacy in failure prediction design optimization to mitigate structural risks structural health monitoring material property evaluation burst pressure forecasting crack detection composite lay-up arrangement weight minimization material distribution enhancement metal foam ratio optimization and optimal material selection. By synthesizing these advancements this work underscores AI’s potential to accelerate development reduce costs and improve HSV performance while advocating for physics-informed models robust datasets and regulatory alignment to facilitate industrial adoption.

Underground hydrogen storage (UHS) in salt caverns is emerging as a promising solution for the transition to a sustainable energy future. However a thorough understanding of hydrogen flow mechanisms through salt rock is essential to ensure safe and efficient storage operations. In this study we conducted hydrogen flow experiments in salt rocks using the pressure pulse decay (PPD) method covering a range of hydrogen pore pressures from 0.4 MPa to 7.5 MPa within the slip and transitional flow regimes (Knudsen numbers between 0.04 and 1.5). The Knudsen numbers were determined by measuring the pore size distribution (PSD) of the salt rock samples and assigning an average pore size to each sample based on the measured PSD. Our results indicate that the intrinsic permeability of the tested salt rock samples ranges from 5 × 10− 21 m2 to 1.0 × 10− 20 m2 . However a significant enhancement in apparent permeability up to 10 times the intrinsic permeability was observed particularly at lower pressures. This permeability enhancement is attributed to the nanoscale pore structure of salt rocks where the mean free path of hydrogen becomes comparable to the pore sizes leading to a shift from slip flow to the transitional flow regime. The results further reveal that the first-order slip model underestimates the apparent permeability in the transitional flow regime despite its satisfactory accuracy in the slip region. Moreover the higher-order slip model demonstrates acceptable accuracy across both the slip and transitional flow regimes.

As industry moves from fossil fuels to green energy substituting hydrocarbons with hydrogen as an energy carrier seems promising. Hydrogen can be stored in salt caverns depleted hydrocarbon fields and saline aquifers. Among other criteria these storage solutions must ensure storage safety and prevent leakage. The ability of a caprock to prevent fluid from flowing out of the reservoir is thus of utmost importance. In this review the main factors influencing fluid flow are examined. These are the wettability of the caprock formation the interfacial tension (IFT) between the rock and the gas or liquid phases and the ability of gases to diffuse through it. To achieve effective sealing the caprock formation should possess low porosity a disconnected or highly complicated pore system low permeability and remain strongly water-wet regardless of pressure and temperature conditions. In addition it must exhibit low rock–liquid IFT while presenting high rock–gas and liquid–gas IFT. Finally the effective diffusion coefficient should be the lowest possible. Among all of the currently reviewed formations and minerals the evaporites low-organic-content shales mudstones muscovite clays and anhydrite have been identified as highly effective caprocks offering excellent sealing capabilities and preventing hydrogen leakages.

The global energy sector is aiming to substantially reduce CO2 emissions to meet the UN climate goals. Among the proposed strategies underground storage solutions such as radioactive disposal CO2 NH3 and underground H2 storage (UHS) have emerged as promising options for mitigating anthropogenic emissions. These approaches require rigorous research and development (R&D) often involving laboratory-scale experiments to establish their feasibility before being scaled up to pilot plant operations. Microorganisms which are ubiquitous in laboratory environments can significantly influence geochemical reactions under variable experimental conditions of porous media and a salt cavern. We have selected a consortium composed of Bacillus sp. Enterobacter sp. and Cronobacter sp. bacteria which are typically present in the laboratory environment. These microorganisms can contaminate the rock sample and develop experimental artifacts in UHS experiments. Hence it is pivotal to sterilize the rock prior to conduct experimental research related to effects of microorganisms in the porous media and the salt cavern for the investigation of UHS. This study investigated the efficacy of various disinfection and sterilization methods including ultraviolet irradiation autoclaving oven heating ethanol treatments and gamma irradiation in removing the microorganisms from silica sand. Additionally the consideration of their effects on mineral properties are reviewed. A total of 567 vials each filled with 9 mL of acid-producing bacteria (APB) media were used to test killing efficacy of the cleaning methods. We conducted serial dilutions up to 10−8 and repeated them three times to determine whether any deviation occurred. Our findings revealed that gamma irradiation and autoclaving were the most effective techniques for eradicating microbial contaminants achieving sterilization without significantly altering the mineral characteristics. These findings underscore the necessity of robust cleaning protocols in hydrogeochemical research to ensure reliable reproducible data particularly in future studies where microbial contamination could induce artifacts in laboratory research.

This study examined the effects of microstructural alterations by controlling the surface carbon gradient via a thermal decarburizing process on hydrogen evolution adsorption and permeation along with neutral aqueous corrosion behavior of an ultra-high-strength steel with a tensile strength of 2.4 GPa. Microstructural analyses showed that an optimized decarburizing process at 1100 ◦C led to partial transformation to ferrite without precipitating Fe3C in a marked fraction. Electrochemical impedance spectroscopy along with the permeation results revealed that there was a notable decrease in hydrogen evolution and subsurface hydrogen concentration. Moreover immersion test in a neutral aqueous condition showed slower corrosion kinetics with a comparatively uniform corroded surface indicating improved corrosion resistance. However the extent of improvement is significantly limited under non-optimized decarburizing conditions specifically when the temperature is below or above 1100 ◦C due to insufficient decarburization or the formation of coarse-spheroidized Fe3C particles accompanied by a porous subsurface layer. In particular a far greater adsorption tendency at bridge sites on Fe3C (001) in a pre-charged surface is highlighted. This study provides insight that the adjustment of the carbon gradient through an optimized annealing process can be an effective technical strategy to overcome the critical drawbacks of ultrastrong martensitic steels under hydrogen-rich or corrosive conditions.

The effect of tempering temperature and tempering time on the density of hydrogen traps hydrogen diffusivity and microhardness in a vanadium-modified AISI 4140 martensitic steel was determined. Tempering parameters were selected to activate the second third and fourth tempering stages. These conditions were intended to promote specific microstructural transformations. Permeability tests were performed using the electrochemical method developed by Devanathan and Stachurski and microhardness was measured before and after these tests. It was observed that hydrogen diffusivity is inversely proportional to microhardness while the density of hydrogen traps is directly proportional to microhardness. The lowest hydrogen diffusivity the highest trap density and the highest microhardness were obtained in the as-quenched condition and the tempering at 286 ◦C for 0.25 h. In contrast tempering at a temperature corresponding to the fourth tempering stage increases hydrogen diffusivity and decreases the density of hydrogen traps and microhardness. However as the tempering time or temperature increases the opposite occurs which is attributed to the formation of alloy carbides. Finally hydrogen has a softening effect for tempering temperatures corresponding to the fourth tempering stage tempering times of 0.25 h and in the as-quenched condition. However with increasing tempering time hydrogen has a hardening effect.

Ammonia due to its favorable physicochemical properties is considered an effective hydrogen carrier enabling the storage of surplus energy generated from renewable sources. Large-scale implementation of this concept requires the safe transport of ammonia over long distances commonly achieved through pipeline systems—a practice with global experience dating back to the 1960s. However operational history demonstrates that failures in such infrastructures remain inevitable often leading to severe environmental consequences. This article reviews both passive and active methods for preventing and mitigating incidents in ammonia pipeline systems. Passive measures include the assessment of material compatibility with ammonia and the designation of adequate buffer zones. Active methods focus on leak detection techniques such as balance-based systems acoustic monitoring and ammonia-specific sensors. Additionally the article highlights the potential environmental risks associated with ammonia release emphasizing its contribution to the greenhouse effect as well as its adverse impacts on soil surface and groundwater and human health. By integrating historical lessons with modern safety technologies the article contributes to the development of reliable ammonia transport infrastructure for the hydrogen economy.

The article presents a comparison between the pressure conditions of a real low-pressure gas network and the results of hydraulic calculations obtained using various simulation programs and empirical equations. The calculations were performed using specialized gas network analysis software: STANET (ver 10.0.26) SimNet SSGas 7 and SONET. Additionally the simulation results were compared with calculations based on the empirical Darcy–Weisbach and Renouard equations. In the first part of the analysis two calculation models were compared. In one model the geodetic elevation of individual network nodes was included (elevation-aware model) while in the second calculations were performed without considering node elevation (flat model). For low-pressure gas networks accounting for elevation is critical due to the presence of the pressure recovery phenomenon which does not occur in medium- and high-pressure networks. Furthermore considering the growing need to increase the share of renewable energy the study also examined the network’s operating conditions when using natural gas–hydrogen mixtures. The following hydrogen concentrations were considered: 2.5% 5.0% 10.0% 20.0% and 50.0%. The results confirm the importance of incorporating elevation data in the modeling of low-pressure gas networks. This is supported by the small differences between calculated results and actual pressure measurements taken from the operating network. Moreover increasing the hydrogen content in the mixture intensifies the pressure recovery effect. The hydraulic results obtained using different computational tools were consistent and showed only minor discrepancies.

In the present work a new analytical model of polytropic flow in constant-diameter pipelines is developed to accurately describe the flow of compressible gases including natural gas and hydrogen explicitly accounting for heat exchange between the fluid and the environment. In contrast to conventional models that assume isothermal or adiabatic conditions the proposed model simultaneously accounts for variations in pressure temperature density and entropy i.e. it is based on a realistic polytropic gas flow formulation. A system of differential equations is established incorporating the momentum continuity energy and state equations of the gas. An implicit closed-form solution for the specific volume along the pipeline axis is then derived. The model is universal and allows the derivation of special cases such as adiabatic isothermal and isentropic flows. Numerical simulations demonstrate the influence of heat flow on the variation in specific volume highlighting the critical role of heat exchange under real conditions for the optimization and design of energy systems. It is shown that achieving isentropic flow would require the continuous removal of frictional heat which is not practically feasible. The proposed model therefore provides a clear reproducible and easily visualized framework for analyzing gas flows in pipelines offering valuable support for engineering design and education. In addition a unified sensitivity analysis of the analytical solutions has been developed enabling systematic evaluation of parameter influence across the subsonic near-critical and heated flow regimes.

This study enhances regional integrated energy systems by proposing a Stackelberg planning–operation model with seasonal hydrogen storage addressing source–network separation. An equilibrium algorithm is developed that integrates a competitive search routine with mixed-integer optimization. In the price–energy game framework the hydrogen storage operator is designated as the leader while energy producers load aggregators and storage providers act as followers facilitating a distributed collaborative optimization strategy within the Stackelberg game. Using an industrial park in northern China as a case study the findings reveal that the operator’s initiative results in a revenue increase of 38.60% while producer profits rise by 6.10% and storage-provider profits surge by 108.75%. Additionally renewable accommodation reaches 93.86% reflecting an absolute improvement of 20.60 percentage points. Total net energy imbalance decreases by 55.70% and heat-loss load is reduced by 31.74%. Overall the proposed approach effectively achieves cross-seasonal energy balancing and multi-party gains providing an engineering-oriented reference for addressing energy imbalances in regional integrated energy systems.

The adoption of hydrogen as a clean energy carrier depends heavily on the development of materials capable of enduring the extreme conditions associated with its production storage and transportation. This review critically evaluates the performance of metals polymers and composites in hydrogen-rich environments focusing on degradation mechanisms such as hydrogen embrittlement rapid gas decompression and long-term fatigue. Metals like carbon steels and high-strength alloys can experience a 30–50 % loss in tensile strength due to hydrogen exposure while polymers suffer from permeability increases and sealing degradation. Composite materials though strong and lightweight may lose up to 15 % of their mechanical properties over time in hydrogen environments. The review highlights current mitigation strategies including hydrogen-resistant alloys polymer blends protective coatings composite liners and emerging technologies like predictive modeling and AI-based material design. With hydrogen production expected to reach 500 GW globally by 2030 improving material compatibility and developing international standards are essential for scaling hydrogen infrastructure safely and cost-effectively. This work presents an integrated analysis of material degradation mechanisms highlights key challenges across metals polymers and composites in hydrogen environments and explores recent innovations and future strategies to enhance durability and performance in hydrogen infrastructure.

Underground hydrogen storage (UHS) is a relatively new technology that demonstrates notable potential for the efficient storage of large quantities of green hydrogen. Its large-scale implementation requires a comprehensive understanding of numerous factors including safe and effective storage methods as well as overcoming various thresholds and challenges. This article presents strategies for accelerating the implementation of this technology identifying the thresholds and challenges affecting the development and future scale-up of UHS. It characterises challenges and constraints related to geology (including the type and geological characterisation of structures hydrogen storage capacity and hydrogen interactions with underground environments) the technological aspects of hydrogen storage (such as infrastructure management and monitoring) and economic and legal considerations. The need for the rapid implementation of demonstration projects has been emphasised. The identified thresholds and challenges along with the resulting recommendations are crucial for paving the way for the large-scale implementation of UHS. Addressing these issues will significantly influence the implementation of this technology post-2030.