Nanostructure Design And Electrocatalystic Water Splitting Performance Of Stainless Steel-Based Transition Metal Phosphides

Hydrogen,as a clean renewable energy with high combustion value,is expected to substitute for fossil fuels that people often use.Water electrolysis is able to convert renewable electrical energy into chemical energy and stores it in hydrogen.The development of highly active and inexpensive catalysts is a major problem in the production of hydrogen from industrial water electrolysis.Transition metal materials are inexpensive,earth-abundant and its hydrogen adsorption Gibbs free energy close to Pt,which represent a class of materials with great potential for application in water electrolysis.However,pure transition metal materials still exist the problem that the catalytically active surface area is not large enough,the number of active sites is small,and the conductivity is poor.The introduction of conductive substrates can effectively solve these problems.Based on this,this paper mainly chooses the industrially cheap316 stainless steel as the substrate.The influence of industrial stainless steel mesh number was studied on their performance.And we further constructs high-efficiency electrocatalysts by combining stainless steel with transition metal phosphides.The nanostructure,composition and morphology of these transition metal materials were regulated,and the designed electrocatalysts were tested for electrocatalytic HER performance and stability.This thesis mainly studied the improvement of the electrocatalytic HER performance of transition metal phosphide nanomaterials by the introduction of stainless steel.The developed low-cost,highly active and good-stability electrocatalysts provides certain experimental basis for the industrial hydrogen production by water electrolysis.The detailed research contents are as follows:1.Study on electrocatalytic HER performance of industrial stainless steel.Firstly,the HER performance of 316L stainless steel with different mesh numbers was studied in acidic condition.The result exhibits that industrially cheap 316L stainless steel meshes have good electrocatalytic HER performance.Meanwhile,the electrocatalytic HER performance of 316L stainless steel increases with the increase of mesh number.When the mesh number of stainless steel increases from 100 meshes to 1600 meshes,the HER performance is optimal,316L SS-1600 obtains overpotential of 209.8 mV at the current density of 10 mA cm^-2,and possesses a small Tafel slope(115.6 mV dec^-1).However,when the mesh number of stainless steel increases from 1600 meshes to 2800meshes,the HER performance decreased.The reason is that when the mesh number of the stainless steel is too low,its electrocatalytic specific surface area is not large enough.However,the mesh number is too high,tight interweaving of stainless steel mesh may not be conducive to release of hydrogen.Thereby,the improvement of the electrocatalytic performance of 316L SS is affected.2.Study on overall water splitting of stainless steel mesh surface-grown CoP nanowire array.316L SS-1600 with better electrochemical performance was selected as the conductive substrate,and the porous CoP nanowire array was uniformly grown on 316L SS-1600.Compared with carbon cloth substrate,when 316L SS-1600 is introduced into CoP,it not only greatly enhances the conductivity of CoP/SS catalysts,but also the synergistic effect of the transition metal elements contained in the stainless steel mesh and CoP greatly improves the electrocatalytic activity and stability of the catalyst.CoP/SS exhibited better electrocatalytic HER activity than pure CoP,stainless steel and CoP/CC catalysts under acidic conditions.CoP/SS possesses the low overpotential of 62 mV at the current density of 10 mA cm^-2,and a small Tafel slope of45.6 mV dec^-1,which is close to the commercial Pt/C catalytic activity(?₁₀=49 mV).Meanwhile,CoP/SS also showed excellent electrocatalystic alkaline HER and OER performances under alkaline conditions,at current density of 10 mA cm^-2,the overpotential of HER is only 79 mV,and the overpotential of OER is only 248 mV.Based on the CoP/SS composite electrocatalysts have high HER and OER activities under alkaline conditions.It is used as the cathode and anode materials of water electrolysis,respectively,Which only requires an overpotential of 1.57 V to reach the current density of 10 mA cm^-2.The excellent electrocatalytic properties of CoP/SS composites are attributed to the close interfacial synergies between CoP and SS substrates,and theoretical calculations show a superior charge transfer effect between the stainless steel mesh substrate and CoP.3.Optimization of the interface structure and HER performance of the composite electrode by surface oxidation of stainless steel mesh.A novel pure water anodizing method was developed for modifying stainless steel meshes.And the effects of different voltages and times on the surface nanostructure of 316L SS-1600 were investigated.The Ni₂P ultrathin nanoflowers were successfully grown on the electrode-oxidized316L SS-1600 substrate to construct a three-dimensional Ni₂P/SS composite electrocatalysts,and the electrochemical properties were studied.Optimized by the system,Ni₂P/SS-45-24?45 V oxidation for 24 h?samples have excellent alkaline HER performance and stability,only needs overpotential of 96 mV at the current density of10 mA cm^-2,and also have smaller Tafel slope(66.8 mV dec^-1).The ultra-thin oxide layer on the surface of stainless steel regulates the interface structure of Ni₂P/SS and promotes the charge transfer,which prominently enhances the electrocatalytic HER performance.