Study On Interface Coupling Effect In Electrocatalytic Hydrogen Evolution Reaction

The diversification of energy structure is the essential cornerstone of the society development,and the energy shortage,uneven energy distribution and the consequent environmental pollution make the energy transition more prominent.Hydrogen is widely recognized as the first-class energy compared to fossil fuels,owing to its excellent characteristics including outstanding gravimetric energy density(120 MJ kg-1),high energy conversion efficiency and renewability,thus,hydrogen production technology has become a key problem during the development of hydrogen economy.Electrochemically splitting water is an ideal method to produce hydrogen with a high purity.However,efficient catalysts are needed to increase production efficiency and reduce energy consumption in the actual electrolyzed water process.Currently,platinum group materials are the best catalysts for hydrogen evolution reaction(HER),but they are not suitable for large-scale industrial production due to the limited reserves and high prices.Therefore,the exploration of highperformance,low-cost hydrogen evolution catalysts has become an important issue,and aroused extensive attention in industry and scientific research.Typical HER process is a multistep reaction involving the adsorption of reactants,the formation of hydrogen intermediates and the desorption of hydrogen molecular.In this paper,the interfacial structure between different materials is rationally constructed to further optimize the catalytic reaction kinetics,aiming to explore the interfacial structure-catalytic mechanism relationship.The main contents of this thesis include the following parts:(1)Construction of metal-metal oxides heterojunction interface.Ru nanoclusters were uniformly supported on the surface of WO2.72 nanowires by the weak reduction of WO2.72,and the Mott-Schottky heterojunction Ru-WO2.72 has been formed.Electrochemical tests show that Ru-WO2.72 exhibits much higher intrinsic HER catalytic activity in 0.5 M H2SO4 than the pure Ru/C catalyst,and the overpotential at 10 m A cm-2 and the Tafel slope is only 41 m V and 58 m V dec-1,respectively,demonstrating a Volmer-Heyrovsky reaction path.Further studies show that the formation of heterojunction between interfaces constituted a continuous electron channel,which changes the electron distribution on the surface of Ru and consequently improving the catalytic activity of the hydrogen evolution reaction.(2)Construction of inorganic-organic polymer interface.WO2.72@PANI core-shell multi-interface composite was synthesized by an oxidative polymerization method to coat a layer of polyaniline on the surface of WO2.72 nanowire.Electrochemical performance tests show that the WO2.72@PANI composite has higher catalytic activity in 0.5 M H2SO4 than the pure WO2.72.Compared to pure WO2.72,the overpotential of WO2.72@PANI decreases from 400 m V to 150 m V at current density of 10 m A cm-2,and the Tafel slope declines to 114 m V dec-1.Due to the presence of lone electron in the nitrogen element of the polyaniline molecule,it is easy to combine with the hydrogen ion in the acidic solution to form a protonated polyaniline.The adsorption of hydrogen ions by WO2.72@PANI is mainly achieved by the surface protonated polyaniline,and the local hydrogen ion concentration on the catalyst surface is also higher than the hydrogen ion concentration of the solution.Therefore,the composite catalyst changes the adsorption and activation forms of hydrogen ions by metal oxides in acid solution,significantly increases the rate of formation of activated hydrogen,thereby increasing the intrinsic activity and kinetic speed of the hydrogen evolution reaction of the catalyst.(3)In-situ electrochemical surface reconstruction of transition metal compounds.Co P nanosheets were prepared by topological transformation using the Co-oxides as precursor followed a phosphidation process in a reductive environment.An in-situ electrochemical method was developed to engineer the surface of cobalt phosphides and achieve a stable Co(OH)x@Co P hybrid as the robust and efficient electrocatalyst for HER.The as-obtained Co(OH)x@Co P hybrid demonstrates a remarkably enhanced HER activity with an overpotential of 100 m V at 10 m A cm-2,Tafel slope of 76 m V dec-1 and excellent stability even working for 24 hours.Further detailed electron microscopic observation and spectroscopy characterization showed that the morphology of Co P nanosheets did not change during the electrochemical activation process,but the structure changed significantly,and some amorphous cobalt hydroxides were formed on the surface of Co P.It was found that a large amount of P element in the Co P nanosheets dissolved in the electrolyte during the activation process,providing an opportunity to form cobalt hydroxides.We attribute the enhanced activity to the synergistic effect of the optimized surface/interface of hybrid Co P@Co(OH)x species formed,which promotes the water dissociation through the improved surface hydroxyl.