Preparation Of Transition Metal Phosphide Catalyst By Thermal Phosphating And Its Hydrogen Production Performance Of Electrolytic Splitting Water

Because of the unique conductivity and high electrocatalytic hydrogen evolution performance of transition metal phosphides(TMPs),it is expected to replace noble metal catalysts,such as platinum,as electrocatalysts for hydrogen production from water splitting.However,there are a series of problems in the application of TMPs as hydrogen evolution catalysts,such as poor redox activity,weak rate output,poor cycle stability,led to a wide disparity between the hydrogen evolution performance of TMPs and that of platinum catalysts.Among various methods to improve their electrocatalytic hydrogen evolution performance,structural design,doping and formation of heterogeneous structures could further improve the hydrogen evolution performance of TMPs.In this paper,structure design of tungsten phosphide,preparation of ternary nickel-cobalt-phosphorus,preparation of praseodymium-doped nickel-cobalt-phosphorus,preparation of molybdenum disulfide and nickel phosphide heterogeneous catalysts were selected to improve the electrocatalytic HER performance of corresponding TMPs.The related research contents are as follows.The network tungsten diselenide(WSe2)grown on carbon fibers was synthesized during the thermal degradation of polyacrylonitrile(PAN)fibers.The network structure was maintained during the subsequent high temperature phosphating process,and the network tungsten phosphide composites grown on carbon fibers were formed.Tungsten phosphide micro-/nanoparticles were synthesized as a contrast through the same synthetic route but the removal of polyacrylonitrile fibers.Because of the high conductivity of carbon fibers in the composites and the network nanostructure greatly improves the specific surface area of the composites and exposes more active sites,the hydrogen evolution performance of the network tungsten phosphide composites is obviously higher than that of tungsten phosphide micro-/nanoparticles.The results of electrocatalytic tests in acidic electrolyte show that the hydrogen evolution performance of network tungsten phosphide composites is significantly higher than that of tungsten phosphide micro-/nanoparticles.The overpotentials of network tungsten phosphide composites are 137 and 215 mV to afford current density of 10 and 100 mA·cm-2,respectively,and the Tafel slope is 69 mV·dec-1.This research indicates that the design of new nanostructures can effectively improve the specific surface area of materials,expose more active sites,promote the diffusion process of substances and gas precipitation,and eventually improve the electrocatalytic performance of catalysts.It also provides a new way to improve the performance of other HER catalysts.Nickel-cobalt-phosphorus nanowire arrays with different nickel-cobalt ratios were grown on carbon cloth by changing the proportions of different metal elements in precursor of metal oxides:At the same time,by changing the reaction time and the amount of ammonium fluoride in the synthesis process of precursor,the load of nickel-cobalt-phosphorus nanowires was adjusted.The electrocatalytic hydrogen evolution performance test in acidic electrolyte shows that the performance of electrocatalysts reaches the maximum when the nickel-cobalt ratio is 5:5.The overpotentials of optimum sample in 1 mol·L-1 KOH are 68,94 and 134 mV to afford the current densities of 10,20 and 100 mA·cm-2,respectively.The improvement of its performance is attributed to the synergistic effect between nickel and cobalt and the increase of specific surface area by linear structure,the acceleration of mass diffusion,the exposure of more active sites on rough surface,and the promotion of gas escaping from electrode surface by good structure.The research shows that the synthesis of ternary TMPs can effectively improve the electrocatalytic HER performance of TMPs,and the electrocatalytic HER performance of the prepared ternary TMPs is related to the proportion of metal atoms,which provides guidance for the synthesis of other ternary TMPs.Based on the previous research work of nickel-cobalt-phosphorus nanowires,the nickel-cobalt-phosphorus nanowire arrays with different doped amount of Pr elements on nickel foam were obtained by changing the amount of Pr elements in the precursor.The electrochemical measurements in acidic and alkaline electrolytes show that the electrocatalytic hydrogen evolution performance of the doped nickel-cobalt-phosphorus nanowire arrays reaches the maximum when the Pr content is 10%.In 0.5 mol·L-1 H2SO4 and 1 mol·L-1 KOH,the overpotentials of 10%Pr-NiCoP NWAs/NF are 91 and 88 mV to afford current density of 10 mA·cm-2,respectively.And the corresponding Tafel slope is 45.5 and 69.2 mV·dec-1,respectively.Its performance is improved because the doping of Pr effectively realizes the adjustment of the crystal structure and electronic structure of NiCoP,reduces the charge transfer resistance,enlarges the electrochemical active surface area,realizes the fast ·reaction kinetics and enhances the electrochemical activity.The results show that the doping of rare earth elements can also effectively improve the crystal structure of TMPs and their electrocatalytic hydrogen evolution performance,which reveals the broad prospects of rare earth elements doping in improving the electrocatalytic HER performance of TMPs.Molybdenum disulfide coated nickel phosphide heterostructurenanosheet arrays were obtained by controlling phosphating temperature during the phosphating process of nickel sulfide and molybdenum disulfide heterostructures which were prepared by hydrothermal reaction.Due to the introduction of carbon cloth with high conductivity,the strong interface coupling effect between nickel phosphide and molybdenum disulfide,and the unique three-dimensional layered structure,the prepared electrode exhibits very high hydrogen evolution performance in 1 mol·L-1 KOH.The overpotentials are 78 and 161 mV to afford the current density of 10 and 100 mA·cm2,respectively.And the Tafel slope is 62.6 mV·dec-1.In addition,the electrode has good long-term stability when it is used as the electrode for HER.The results show that there are interactions among different catalysts.Therefore,the introduction of other hydrogen evolution catalysts can effectively change the electronic and crystal structures of TMPs,thereby improving their electrocatalytic hydrogen evolution performance.