Transmission, Distribution & Storage

Hydrogen storage in depleted gas reservoirs triggers geochemical and microbiological reactions at the caprockreservoir interface yielding significant implications on storage integrity. Acetogenesis is a microbial reaction observed during underground hydrogen storage (UHS) that produces acetate and converts it into acetic acid under protonation potentially impacting the UHS process integrity. For the first time this research explores the impact of the acetic acid + brine + caprock reaction on shale caprock mineralogy microstructure and physicochemical properties where this preliminary study has been conducted under ambient conditions to obtain an initial assessment of the impact. A comprehensive mineralogical and micro-structural characterization including scanning electron microscopy (SEM) energy dispersive X-ray spectroscopy (EDS) X-ray fluorescence (XRF) Xray diffraction (XRD) micro-computed tomography (micro-CT) and inductively coupled plasma mass spectrometry (ICP-MS) have been conducted to assess the mineralogical and microstructural changes in shale specimens saturated with brine solutions with a range of acetic acid percentages (5 % 10 % and 20 %) to find the maximum possible impact. According to the conducted mineralogical analysis (EDS XRF and XRD) there is a significant primary mineral dissolution during the acetic acid interaction where calcite and dolomite are the predominant minerals dissolved evidencing the significant impact of the acetic acid reaction on carbonate-rich caprock systems during UHS. However secondary mineral precipitation happened at high acidic concentrations (20 %). Interestingly other common minerals in reservoir rocks (e.g. mica pyrite) did not demonstrate rapid interactions with acetic acid compared to carbonates. The impact of these mineralogical changes on the caprock microstructure was then investigated through SEM and micro-CT and the results demonstrate substantial enhancements in porosity and microcracks in the rock matrix due to the calcite and dolomite dissolutions despite some microcracks being closed by secondary precipitations. This preliminary study evidences the significant impact of acidification on caprock integrity which may occur during the acetogenesis reaction in UHS environments. These effects should be carefully considered in field UHS projects to eliminate the risks.

Hydrogen is considered a clean and efficient energy carrier crucial for shapingthe net-zero future. Large-scale production transportation storage and use of greenhydrogen are expected to be undertaken in the coming decades. As the smallest element inthe universe however hydrogen can adsorb on diffuse into and interact with many metallicmaterials degrading their mechanical properties. This multifaceted phenomenon isgenerically categorized as hydrogen embrittlement (HE). HE is one of the most complexmaterial problems that arises as an outcome of the intricate interplay across specific spatialand temporal scales between the mechanical driving force and the material resistancefingerprinted by the microstructures and subsequently weakened by the presence of hydrogen. Based on recent developments in thefield as well as our collective understanding this Review is devoted to treating HE as a whole and providing a constructive andsystematic discussion on hydrogen entry diffusion trapping hydrogen−microstructure interaction mechanisms and consequencesof HE in steels nickel alloys and aluminum alloys used for energy transport and storage. HE in emerging material systems such ashigh entropy alloys and additively manufactured materials is also discussed. Priority has been particularly given to these lessunderstood aspects. Combining perspectives of materials chemistry materials science mechanics and artificial intelligence thisReview aspires to present a comprehensive and impartial viewpoint on the existing knowledge and conclude with our forecasts ofvarious paths forward meant to fuel the exploration of future research regarding hydrogen-induced material challenges.

Hydrogen is a key energy carrier in the global transition to low-carbon systems requiring scalable and secure storage solutions. While underground hydrogen storage (UHS) in salt caverns is proven its cost and limited geographic availability have led to growing interest in depleted oil and gas reservoirs. A critical factor in evaluating these reservoirs is the sealing capacity of the overlying caprock. This study presents a novel experimental protocol for assessing caprock integrity under UHS conditions using a custom-designed core-flooding apparatus integrated with a micro-capillary flow meter. This setup enables high-resolution measurements of ultra-low permeabilities (as low as 10 nano-Darcy) flow rates (down to 10 nano-liters/hour) threshold pressure and breakthrough pressure. Benchmark tests with nitrogen and methane were followed by hydrogen experiments across caprocks with a wide range of permeability and porosity. The results demonstrate clear trends between caprock properties and sealing performance providing a quantitative framework for evaluating UHS site suitability. Hydrogen showed slightly lower threshold and breakthrough pressures compared to other gases reinforcing the need for accurate site-specific caprock evaluation. The proposed method offers a robust approach for characterizing candidate storage sites in depleted reservoirs.

In response to the surging global demand for clean energy solutions and sustainability hydrogen is increasingly recognized as a key player in the transition towards a low-carbon future necessitating efficient storage and transportation methods. The utilization of natural geological formations for underground storage solutions is gaining prominence ensuring continuous energy supply and enhancing safety measures. However this approach presents challenges in understanding gas-rock interactions. To bridge the gap this study proposes a data-driven strategy for contact angle prediction using machine learning techniques. The research leverages a comprehensive dataset compiled from diverse literature sources comprising 1045 rows and over 5200 data points. Input features such as pressure injection rate temperature salinity rock type and substrate were incorporated. Various artificial intelligence algorithms including Support Vector Machine (SVM) k-Nearest Neighbors (KNN) Feedforward Deep Neural Network (FNN) and Recurrent Deep Neural Network (RNN) were employed to predict contact angle with the FNN algorithm demonstrating superior performance accuracy compared to others. The strengths of the FNN algorithm lie in its ability to model nonlinear relationships scalability to large datasets robustness to noisy inputs generalization to unseen data parallelizable training processes and architectural flexibility. Results show that the FNN algorithm demonstrates higher accuracy (RMSE = 0.9640) than other algorithms (RMSERNN = 1.7452 RMSESVM = 1.8228 RMSEKNN = 1.0582) indicating its efficacy in predicting the contact angle testing subset within the context of underground hydrogen storage. The findings of this research highlight a low-cost and reliable approach with high accuracy for estimating contact angle of water–hydrogen–rock system. This technique also helps determine the contribution and influence of independent factors aiding in the interpretation of absorption tendencies and the ease of hydrogen gas flow through the porous rock space during underground hydrogen storage.

Hydrogen-induced steel embrittlement imposes a technical difficulty in facilitating effective and safe hydrogen transportation via pipelines. This investigative study assesses the potency of polyvinylidene fluoride (PVDF)–graphene-based composite coatings in the inhibition of hydrogen permeation. Spin coating was the method selected for this study and varying graphene concentrations ranging from 0.1 to 1wt% were selected and applied to 306 stainless steel substrates. A membrane permeation cell was used in the evaluation of hydrogen permeability while the impact of graphene loading on coating performance was analyzed using the response surface methodology (RSM). The outcomes showed an inversely proportional relationship between the graphene concentration and hydrogen ingress. The permeation coefficient for pure PVDF was recorded as 16.74 which decreased to 14.23 12.10 and 11.46 for 0.3 0.5 and 1.0 wt% PVDF-G respectively with the maximum reduction of 31.6% observed at 1.0 wt%. ANOVA established statistical significance along with indications of strong projection dependability. However the inhibition reduction stabilized with increasing graphene concentrations likely caused by nanoparticle agglomeration. The results support the notion of PVDF–graphene’s potential as a suitable coating for the transformation of pipelines for hydrogen transport infrastructure. This research will aid in the establishment of suitable contemporary barrier coating materials which will enable the safe utilization of hydrogen energy in the current energy transportation grid.

Pipeline steel is highly susceptible to hydrogen embrittlement (HE) in hydrogen environments which compromises its structural integrity and operational safety. Existing studies have primarily focused on the degradation trends of mechanical properties in hydrogen environments but there remains a lack of quantitative failure prediction models. To investigate the failure behavior of X65 pipeline steel under hydrogen environments this paper utilized notched round bar specimens with three different radii and smooth round bar specimens to examine the effects of pre-charging time the coupled influence of stress triaxiality and hydrogen concentration and the coupled influence of strain rate and hydrogen concentration on the HE sensitivity of X65 pipeline steel. Fracture surface morphologies were characterized using scanning electron microscopy (SEM) revealing that hydrogen-enhanced localized plasticity (HELP) dominates failure mechanisms at low hydrogen concentrations while hydrogen-enhanced decohesion (HEDE) becomes dominant at high hydrogen concentrations. The results demonstrate that increasing stress triaxiality or decreasing strain rate significantly intensifies the HE sensitivity of X65 pipeline steel. Based on the experimental findings failure prediction models for X65 pipeline steel were developed under the coupled effects of hydrogen concentration and stress triaxiality as well as hydrogen concentration and strain rate providing theoretical support and mathematical models for the engineering application of X65 pipeline steel in hydrogen environments.

The existence of a large number of abandoned salt caverns in China has posed a great threat to geological safety and environmental protection and it also wasted enormous underground space resources. To address such problems comprehensive utilization of these salt caverns has been proposed both currently and in the future mainly consisting of energy storage and waste disposal. Regarding energy storage in abandoned salt caverns the storage media such as gas oil compressed air and hydrogen have been introduced respectively in terms of the current development and future implementation with siteselection criteria demonstrated in detail. The recommended burial depth of abandoned salt caverns for gas storage is 1000–1500 m while it should be less than 1000 m for oil storage. Salt cavern compressed air storage has more advantages in construction and energy storage economics. Salt cavern hydrogen storage imposes stricter requirements on surrounding rock tightness and its location should be near the hydrogen production facilities. The technical idea of storing ammonia in abandoned salt caverns (indirect hydrogen storage) has been proposed to enhance the energy storage density. For the disposal of wastes including low-level nuclear waste and industrial waste the applicable conditions technical difficulties and research prospects in this field have been reviewed. The disposal of nuclear waste in salt caverns is not currently recommended due to the complex damage mechanism of layered salt rock and the specific locations of salt mines in China. Industrial waste disposal is relatively mature internationally but in China policy and technical research require strengthening to promote its application. Furthermore considering the recovery of salt mines and the development of salt industries the cooperation between energy storage regions and salt mining regions has been discussed. The economic and environmental benefits of utilizing abandoned salt caverns have been demonstrated. This study provides a solution to handle the abandoned salt caverns in China and globally.

Hydrogen storage remains the main barrier to the broader use of hydrogen as an energy carrier despite hydrogen’s high energy density and clean combustion. This study presents a comparative evaluation of conventional and emerging storage methods integrating thermodynamic kinetic economic and environmental metrics to assess capacity efficiency cost and reversibility. Physisorption analysis reveals that metal organic frameworks can achieve storage capacities up to 14.0 mmol/g. Chemical storage systems are evaluated including nanostructured MgH2 (7.6 wt%) catalyzed reversible complex hydrides liquid organic hydrogen carriers and clathrate hydrates. Techno-economic analysis shows storage costs from $500–700/kg H2 to $30–50/kg H2 with energy efficiencies of 50%–90%. Life cycle assessment identifies manufacturing as the primary source of emissions with carbon footprints varying from 150 to 2057 kg CO2 -eq/kg H2 . Cryo-compressed is the most practical transportation option while metal hydrides suit stationary use. This study provides a quantitative foundation to guide material selection and system design for next-generation hydrogen storage technologies.

Materials-based H2 storage plays a critical role infacilitating H2 as a low-carbon energy carrier but there remainslimited guidance on the technical performance necessary for specificapplications. Metal−organic framework (MOF) adsorbents haveshown potential in power applications but need to demonstrateeconomic promises against incumbent compressed H2 storage.Herein we evaluate the potential impact of material propertiescharge/discharge patterns and propose targets for MOFs’ deploy-ment in long-duration energy storage applications including backupload optimization and hybrid power. We find that state-of-the-artMOF could outperform cryogenic storage and 350 bar compressedstorage in applications requiring ≤8 cycles per year but need ≥5 g/Lincrease in uptake to be cost-competitive for applications thatrequire ≥30 cycles per year. Existing challenges include manufacturing at scale and quantifying the economic value of lower-pressure storage. Lastly future research needs are identified including integrating thermodynamic effects and degradation mechanisms.

Traditional natural gas transportation pipeline steels such as API 5L X42 grade and the higher grades are currently receiving a lot of attention in terms of their potential implementation in hydrogen transmission infrastructure. However the microstructural constitution of steels with a ferrite phase and the presence of welds with their non-polyhedral “sharp” microstructures acting as structural notches make these steels prone to hydrogen embrittlement (HE). In this work the notch tensile properties of copper- or nickel–phosphoruscoated API 5L X42 grade pipeline steel were studied in both the non-hydrogenated and electrochemically hydrogen-charged conditions in order to estimate anticipated protective effects of the coatings against HE. Both the Cu and Ni–P coatings were produced using conventional coating solutions for electroless plating. To study the material systems’ HE sensitivity electrochemical hydrogenation of cylindrical circumferentially V-notched tensile specimens was performed in a solution of hydrochloric acid with the addition of hydrazine sulfate. Notch tensile tests were carried out for the uncoated steel Cu-coated steel and Ni–P-coated steel at room temperature. The HE resistance was evaluated by determination of the hydrogen embrittlement index (HEI) in terms of relative changes in notch tensile properties related to the non-hydrogenated and hydrogen-charged material conditions. The results showed that pure electroless deposition of both coatings induced some degree of HE likely due to the presence of hydrogen ions in the coating solutions used and the lower surface quality of the coatings. However after the electrochemical hydrogen charging the coated systems showed improved HE resistance (lower HEIRA values) compared with the uncoated material. This behavior was accompanied by the hydrogen-induced coatings’ deterioration including the occurrence of superficial defects such as bubbling flocks and spallation. Thus further continuing research is needed to improve the coatings’ surface quality and long-term durability including examination of their performance under pressurized hydrogen gas charging conditions.