Performance And Mechanism Of Nickel And Copper-Based Composite Catalysts For Improving Hydrogen Generation From MgH₂ Hydrolysis

The development of efficient,economical and green hydrogen generation technology is the cornerstone for the supply and application of green hydrogen with the goal of "Emission peak,Carbon neutrality".Hydrogen generation by spontaneous hydrolysis reaction using typical hydrogen storage materials such as magnesium hydride(MgH2)is a promising method of hydrogen generation that combines safe storage and efficient supply.However,as the hydrolysis reaction proceeds,the Mg(OH)2 passivation layer continuously deposited on the surface of MgH2 prevents the internal MgH2 from continuing to react,resulting in low hydrogen yield and slow reaction kinetics.In this study,we synthesize highly active bimetallic catalysts by various methods to enhance the yield of hydrogen generation from MgH2 hydrolysis as well as the reaction kinetic performance.Moreover,the best performance of the MgH2 composite hydrolysis system is achieved by continuously optimizing the preparation process of the composites.In this paper,the performance of hydrogen generation from MgH2 hydrolysis is effectively enhanced by developing an efficient NiCo bimetallic synergistic catalytic system.It is shown that the hydrolysis reaction of MgH2-8 wt%NiCo@C composites ball-milled for 5 h in 0.05 mol L-1 MgCl2 solution is able to achieve nearly 100%hydrogen release efficiency within 15 min,and the hydrolysis activation energy of the composite system is only 11.62 kJ mol-1.The synergistic effect of NiCo bimetallic catalyst is manifested as follows:Ni and Co together form a fast diffusion channel on the surface of MgH2 to promote mass transfer,through which H2 bubbles continuously escape outward and Mg(OH)2 can only exist in solution as fragments,achieving 99.95%conversion of MgH2-8 wt%NiCo@C composites by hydrolysis.In order to further improve the kinetic performance of hydrogen production from MgH2 hydrolysis,while avoiding the negative impact of catalyst use on the environment and achieving green,non-toxic and non-polluting hydrolysis products,Co is replaced with Cu.The excellent effect of NiCu@rGO bimetallic catalyst on enhancing the performance of hydrogen production from MgH2 hydrolysis is found for the first time.The NiCu@rGO bimetallic nanocatalysts are prepared by loading Ni and Cu on the rGO surface by a facile synthesis and calcination reduction method.It is shown that the MgH2-8 wt%NiCu@rGO composite with 5 h of ball milling can achieve nearly 100%hydrogen release efficiency within 10 min at room temperature(30℃),and the hydrolysis activation energy of the composite system is only 16.03 kJ mol-1.In order to reduce the catalyst cost,this study replaces Ni with Fe and synthesizes Cu@Fe-N-C bimetallic catalysts with high catalytic activity to further enhance the performance of hydrogen generation from MgH2 hydrolysis.It is shown that the hydrolysis reaction of MgH2-Cu@Fe-N-C composites with a catalyst addition of only 0.5 wt%in a 0.05 mol/L MgCl2 solution is able to achieve more than 99%hydrogen release efficiency within 15 min.While maximizing the hydrogen production capacity of the composite system,the cost of hydrogen production is effectively reduced.By investigating the performance of the MgH2-Cu@Fe-N-C composite system at different temperatures for hydrolysis,the possibility of using the adjusted temperature to meet the hydrogen supply demand for different cases is discovered,and the controllability of the MgH2 hydrolysis reaction is achieved.