Preparation Of Transition Metal Cobalt-based Phosphide And Its Electrocatalytic Hydrogen Evolution Performance

Since the 20th century,two major problems which are energy shortage and environmental pollution are still troubling people,and it is urgent to find effective solutions.Among various new energy systems,hydrogen energy has been widely concerned due to its advantages of clean,pollution-free,high efficiency and renewable energy.Among various methods of hydrogen production,water splitting by electrolysis is the most ideal method.However,hydrogen production by electrolysis of water requires efficient catalysts.At present,the catalysts with high activity for hydrogen evolution are mostly platinum,but they are limited by the high cost.With the rapid development of electrode materials for hydrogen production by electrolysis of water,the highly active non-noble transition metal electrocatalysts have become an ideal choice.Among them,transition metal cobalt and its alloy phosphides exhibit high activity for hydrogen evolution reaction.However,the catalytic activity of catalysts without carriers is relatively poor.Therefore,loading them on carbon carriers can effectively expand the active surface area of electrocatalysts and improve the catalytic performance.This article reports that the impregnation method with combination of high temperature calcined can be used to synthesis transition metal oxide particles which grow on the nitrogen doped carbon nanotubes.In order to further improve the performance of as-prepared catalysts in the acid solution,the oxide particles become phosphide particles after phosphorization process thus forming composites MP/NCNTs(M on behalf of the transition metal Co,Ni,Fe and their alloys and NCNTs stands for nitrogen doped carbon nanotubes).Then,XRD,SEM,TEM and XPS are used to characterize the as-prepared composite electrode materials and their electrocatalytic hydrogen evolution performance are explored in 0.5M H2SO4 electrolyte.MO nanoparticles supported by NCNTs(MO/NCNTs)were prepared by impregnation method,and then MO was converted into MP by low-temperature gas-phase phosphorization to obtain an electrocatalyst(MP/NCNTs).MP nanoparticles were equably distributed on NCNTs.In order to maximize the performance improvement,we also optimized the influence of phosphorus content,gas velocity,temperature and other factors.The catalyst materials prepared under the optimal conditions have excellent hydrogen evolution activity and long-term stability in acid electrolyte.It is mainly attributed to the fact that catalyst particles prepared by this method can be evenly distributed on the carrier,which is beneficial to expose more active sites for hydrogen evolution.In addition,the synergistic effect between different metal atoms changes the electronic structure.The good stability is due to the strong force of NCNTs carrier on catalyst particles,which effectively prevented the agglomeration of catalyst particles and the migration of active components in the preparation process of impregnation method.Metal atoms doping increases the roughness of catalyst surface,which is beneficial to the desorption of hydrogen bubbles and reduces the obstacles to subsequent reactions.It is also suggested that a small amount of phosphorus will enter the carriers during the phosphorization process,which has a positive effect on improving the hydrogen evolution reactivity.