Performance Of MoNi-Based Nanostructures In Alkaline Seawater Electrolysis Coupled With Oxidation Of Samll Molecules

Hydrogen has been considered as a promising energy candidate due to its advantages of high energy density and zero carbon emission.Water electrolysis powered by renewable electricity holds great promise for environmental friendly hydrogen production.It is an effective strategy to meet the development of green energy economy that replaces scarce freshwater resources with unlimited seawater.In general,seawater electrolysis involves two redox reactions:Hydrogen evolution reaction（HER）at cathodic and Oxygen evolution reaction（OER）at anodic,where OER controls the overall efficiency due to slower kinetics.In addition,the competitive chlorine oxidation reaction（Cl OR）may occur to form hypochlorite（Cl O^-）at industrial current density(>500-1000 m A cm^-2)under alkaline condition,which hinders the progress of seawater splitting.This obstacle may be overcome by replacing the OER with thermodynamically more favorable small molecule reaction（hydrazine oxidation reaction（Hz OR）,urea oxidation reaction（UOR））.Therefore,it is of great significance for energy saving hydrogen production to reasonably manufacture low-cost and efficient HER catalyst combined with anode small molecule oxidation reaction.Here,three MoNi-based materials have been successfully prepared,and these three materials have been applied to electrolysis seawater coupled small molecule oxidation hydrogen production.The main contents are as follows:（1）In this study,we synthesis a Ru/P dual-doped NiMoO₄@NF（Ru/P-NiMoO₄@NF）nanorods with a multichannel structure as the bifunctional HER and UOR electrocatalyst in alkaline seawater.The multichannel Ru/P-NiMoO₄@NF is synthesized via ion exchange between Ru and Ni and followed by a low-temperature phosphorization.The multichannel Ru/P-NiMoO₄@NF can expose more electrochemical surface active areas for seawater electrolysis,which has excellent electrocatalytic activity and stability.In-depth DFT studies show that Ru/P doping can modulate the d-band center,which can simultaneously facilitate the absorption of reactants.This work presents a strategy for developing a highly active doped electrocatalyst for energy-saving hydrogen production and urea purification-based hybrid seawater splitting.（2）Herein,the MoNi alloys supported on MoO₂nanorods with enlarged hollow diameter on Ni foam（MoNi@NF）are synthesized,which is constructed by limiting the outward diffusion of Ni via annealing and thermal reduction of NiMoO₄nanorods.The as-prepared MoNi@NF with enlarged hollow structure integrate the merits of highly active MoNi alloys,interface engineering,and well-dispersed hollow nanorods,which endow the remarkable bifunctional electrocatalytic activities and stability toward both HER and Hz OR in alkaline water and seawater system.This study may show the practical impact on the energy-saving hydrogen production in unlimited seawater to realize carbon-neutral hydrogen economy.（3）Herein,we report the self-growth of Mo-doped Ni₂P nanosheet arrays with rich P vacancies on molybdenum-nickel foam（MNF）（Mo-Ni₂P_v@MNF）as bifunctional catalyst for Cl^-free hydrogen production by coupling hydrogen evolution reaction（HER）with hydrazine oxidation reaction（Hz OR）in seawater.The Mo-Ni₂P_v@MNF electrode as bifunctional catalyst has excellent activity and can maintain stable for an ultra-long time of 1000 h.Moreover,integration of OHz S into self-assembled hydrazine fuel cells（DHz FC）or solar can enable the self-powered H₂production.The industrial hydrazine sewage as feed for the above eletrolysis system can be degraded to～5 ppb rapidly.DFT calculations demonstrate that due to the electronic spatial redistribution induced by P vacancies and Mo doping can not only achieve thermoneutralΔG_H*for HER but also enhance dehydrogenation kinetics from*N₂H₄to*NHNH₂for Hz OR,achieving enhanced dehydrogenation kinetics.