Structural Regulation And Hydrogen Production From Electrolyzed Water Of Nickel Phosphide Materials

Hydrogen energy,due to the advantages of high energy density and zero carbon emissions,is considered to be the most ideal clean energy in the 21st century.At present,oil and natural gas are usually used as the raw materials to prepare hydrogen?H₂?in industry,which will undoubtedly exacerbate the depletion of fossil energy and the seriousness of environmental issues.Therefore,it is of great significance to develop environmentally friendly H₂ production methods using renewable raw materials.The production of H₂ from electrolyzed water using water as raw material has the advantages of simple operation,high product purity and environmental friendly,arousing the extensive attention from researchers around the world.From the reaction mechanism,electrolyzed water is composed of two half-reactions:hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?,of which OER is a multi-electron transfer reaction that causes the electrolysis of water proceeding at a large overpotential and requiring a lot of power consumption.Therefore,it is of great significance to utilize the electrocatalysts with high activity and high stability to reduce reaction overpotentials.Up to now,the most efficient HER and OER catalysts are usually Pt and IrO₂/RuO₂,respectively.However,the practical and large-scale applications of these noble metal catalysts are limited by their high costs and poor electrochemical stability.Therefore,there is an urgent need to develop cost-effective and high active noble metal-free HER and OER catalysts.In this paper,based on the research progress of nickel phosphide?Ni₂P?in the world,the structural modification of Ni₂P and the corresponding electrochemical performance have been studied.The main contents include the following two aspects:1.The Ni₂P nanosheet arrays with different Fe doping amounts(Ni_2-xFe_xP NSAs/NF)were grown on nickel foam?NF?by adjusting the amount of Fe source through a facile hydrothermal method,followed by phosphorization.The study has shown that when the raw material Fe/Ni molar ratio is 2/8,the corresponding Ni_1.85Fe_0.15P NSAs/NF electrode has the largest electrochemical surface area,the most electrocatalytic active sites,the fastest charge transfer rate and the highest intrinsic electrocatalytic activity,which achieved the best HER,OER and water splitting performance and good stability.The as-prepared Ni_1.85Fe_0.15P NSAs/NF electrode needs overpotential of 106 mV to drive 10 mA cm^-22 for HER.In OER,the Ni_1.85Fe_0.15P NSAs/NF electrode only need overpotential of 270 mV at 20 mA cm^-2,which is lower than that of IrO₂?308 mV?,indicating the superior performance than commercial IrO₂.Furthermore,when Ni_1.85Fe_0.15P NSAs/NF was used as both the cathode and anode of water splitting,a current density of 10 mA cm^-2 can be obtained at a cell voltage of 1.61 V.2.The nitrogen-doped carbon coated cobalt nickel phosphide nanoparticles?NiCoP NPs@NC?were prepared by one-step high temperature calcination using cobalt chloride and nickel chloride as the source of cobalt and nickel,melamine as the source of both nitrogen and carbon,and ammonium dihydrogen phosphate as the source of phosphorus.The results of electrochemical tests show that the addition of Co into the Ni₂P lattice can effectively improve the electrochemical surface area and intrinsic electrocatalytic activity of Ni₂P.In turn,NiCoP NPs@NC exhibited enhanced HER and OER catalytic activity.When utilized as a HER cathode in 1 M KOH solution,the NiCoP NPs@NC electrode needs overpotential of 219 mV to afford a current density of 10 mA cm^-2.Moreover,this electrode can obtain a current density of 20 mA cm^-2 at overpotential of 326 mV for OER in 1 M KOH.In addition,due to the protective effect of NC,the NiCoP NPs@NC electrode showed good electrochemical stability in both HER and OER.