Study On Preparation And Hydrogen Evolution Activity Of Bimetal Transition Metal Phosphide

Since the 21st century,energy and environmental problems brought by the rapid development of society have become increasingly serious.As an ideal clean energy,hydrogen energy has received much attention.Hydrogen evolution（HER）by electrolysis of water is the most promising way compared to that traditional hydrogen production method.In order to overcome the huge energy barrier of HER,it is necessary to use precious metal catalysts such as platinum,ruthenium and iridium-based catalysis.However,the scarcity and high price of precious metals drive people to look for low-cost,high-efficiency and stable electrocatalysts.In this paper,the electrocatalysts of non-noble metal hydrogen evolution reaction based on transition metals are explored,including the following two aspects:（1）The Mo Ni P/Mo P（Ni₁-Mo₁-P NRs）electrocatalyst with good performance in acid and alkali medium was designed and synthesized reasonably.Firstly,Ni Mo bimetallic nanorods with different feed ratios were synthesized by simple hydrothermal method,and then Ni Mo oxide was formed by calcination at high temperature.Finally,bimetallic Ni_x-Mo_y-P heterostructure nanorods（Ni_x-Mo_y-P NRs,x,y represents the molar ratio of Ni to Mo）were prepared by chemical vapor deposition（CVD）using diammonium hydrogen phosphate as phosphorus source.The crystal structure,morphology,element distribution and element valence were characterized by transmission electron microscopy（TEM）,scanning transmission electron microscopy（SEM）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）and so on.Meanwhile,linear sweep voltammetry（LSV）,cyclic voltammetry（CV）and electrochemical impedance spectroscopy（EIS）were used to test the hydrogen evolution activity of the as-prepared catalysts.SEM and TEM images showed that Ni_x-Mo_y-P NRs maintained a good rod-like structure after phosphating at high temperature,and Ni,Mo and P elements are distributed uniformly.The property test showed that Ni-Mo-P NRs with the ratio of 1:1（Ni:Mo）displayed best catalytic performance toward HER in both acidic and alkaline media.The electrochemical test in 0.5M H₂SO₄ solution to HER afforded a Tafel slope of 58.6 m V·dec^-1,an overpotential of 117.9 m V at a current density of 10 m A·cm^-2,an exchange current density（j₀）of 0.10 m A·cm^-2,and a high electrochemical double-layer capacitance(C_dl)of 12.6m F·cm^-2.The Tafel slope of that hydrogen evolution reaction in a 1M KOH solution was96.2 m V·dec^-1,and required only 179 m V to drive a current density of 10 m A·cm^-2.Furthermore,stability and durability tests showed that the hydrogen evolution activity of the Ni-Mo-P NRs did not decay significantly under strong acidic and basic conditions.The excellent catalytic activity was attributed to the good conductivity and charge transfer efficiency of the bimetallic phosphide,the stable one-dimensional nanorod structure with more exposed active sites,and its larger active specific surface area.（2）Secondly,zinc and nitrogen co-doped cobalt phosphide microspheres（Zn,N-CoP MSs）with better hydrogen evolution activity were synthesized from zinc nitrate,cobalt nitrate,ammonium fluoride and urea by hydrothermal method,high temperature calcination and chemical vapor deposition（CVD）in turn.The morphology,crystal form and valence of the catalysts were characterized by XRD,TEM,SEM and XPS.The results of HER performance test in 0.5 M H₂SO₄ solution showed that Tafel slope is 74.7 m V·dec^-1,which accorded with Volmer-Heyrovsky mechanism,indicating that the speed-limiting step is electrochemical desorption step.When the current density reaches 10 m A·cm^-2,only 146.1 m V overpotential was needed.After 1000 cycles of cyclic voltammetry continuous scanning,the overpotential only increased by 10 m V,and it was found that the current density did not decrease obviously after 12 h durability test.Excellent HER electrocatalytic activity was ascribed to the large electrochemical specific surface area of nanospheres composed of nanosheets,and the doping of Zn element can improve the electronic redistribution and electrical conductivity of CoP.In a word,Ni₁-Mo₁-P heterostructures and nanosheets self-assembled Zn,N-CoP MSs were designed and synthesized by simple and effective strategy,which could apply to hydrogen production by electrolysis of water.Excellent catalytic activity,low price and good stability indicated potential industrial application value.