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NaH/Al doped with Ti 2 V 2 Zr with the aim of lowering the rehydrogenation pressure, lowering the dehydrogenation temperature, and improving the hydrogenation/dehydrogenation kinetics of NaAlH 4. It was found that moderate ultrasonic-assisted wet grinding was beneficial to fine particles efficiently, improved uniformity of particle size, and reduced lattice distortion because its crystalline phase can converge more active hydrogen atoms and reduce the energy barrier of H exchange between the alloy and the matrix, thus improving the comprehensive hydrogen storage performance of the composite systems. It could reversibly store 4.81 wt% of hydrogen and completely hydrogenation under a low hydrogen pressure of 55 atm, its starting and ending dehydrogenation temperatures decrease by 81 and 89 °C, respectively, and the activation energies of the two-step dehydrogenation decrease by 26.7 and 52.7 kJ mol−1 respectively, with a dehydrogenation capacity retention of up to 99.58% over five cycles. • Small particles with high homogeneity (distribution:0.1–10 μm, D50 < 3 μm). • Reach hydrogenation saturation under a low hydrogen pressure of 55 atm. • Retention as high as 99.58% over 5 cycles. • Effective coupling between the alloy and matrix realized. • A synergistic effect between ultrasound and milling was achieved. [ABSTRACT FROM AUTHOR]

Underground hydrogen storage (UHS) is recognized as one of the most promising ways to achieve large-scale long-term storage of hydrogen, and bridge the gap between demand and supply of the renewable energy sources. Recent studies show that depleted shale gas reservoirs might also be a favorable candidate for hydrogen storage because of its unique adsorption and sealing capacities. However, the interaction of hydrogen-cushion gas-water in shale is still unclear, and there is a lack of research revealing the transport mechanisms of their mixtures in shale nanopores. Here, we used the molecular dynamics simulations to investigate the hydrogen-methane transport through Na-montmorillonite clay (i.e. a common clay mineral in shale) in the presence of water. The effect of pore size, water content and driving pressure gradient on fluid behavior was discussed. The results show that: (i) The pores prefer to adsorb water molecules and form water films near the pore walls. If the water content is below 10%, it can be considered to increase the proportion of cushion gas to reduce the adsorption loss of hydrogen. (ii) When the water content increases from 10% to 50%, the thickness of water film in the pores increases by 2–3 times, and the self-diffusion coefficient of hydrogen decreases more than that of methane. (iii) The increased pressure gradient promotes the desorption of water molecules, and results in an increased amount of hydrogen accumulating near the pore walls. The results in the study provide deep insights into how hydrogen-methane mixtures transport through clay nanopores, which is important for enhancing experimental and modelling design aimed at improving hydrogen injection and production efficiency in shale. • Molecular dynamics simulation is used to study hydrogen-methane flow in nanopores. • The presence of water and methane can reduce hydrogen loss caused by clay adsorption. • The diffusion of hydrogen is more sensitive to changes in water than methane under low water content. • The impact of pressure gradient on fluid behavior is related to water content and pore sizes. [ABSTRACT FROM AUTHOR]