Design,Synthesis And Electrocatalytic Performance Of Nickel-tungsten-based Heterointerface Electrocatalysts For Hydrogrn Production

Based on the current serious environmental problems and energy crisis,the development of clean and efficient renewable energy is an important direction for future energy progression.Hydrogen（H₂）is an exceedingly ideal energy carrier,and is expected to play a key role in the future renewable energy economy.Hydrogen production from electrolysis can efficiently realize the green production of H₂.It is necessary to develop high-efficient electrocatalysts for the cathodic hydrogen evolution reaction（HER）and anodic oxygen evolution reaction（OER）reactions to achieve the energy-saving water electrolysis technology.At present,the high catalytic activity of the noble metal（such as Pt,Ru,Ir,etc.）based catalysts possess the disadvantages of high cost and rare reserves,which greatly hinders the development of water electrolysis technology.Therefore,the development of low-cost,high-performance transition metal-based catalysts have become an important research issue,especially at high current densiy.On the other hand,replacing the high theoretical potential anode OER with a low theoretical potential anode urea oxidation reaction（UOR）is another promising method to achieve high-efficiency and low-cost hydrogen production.Therefore,the development of efficient and low-cost electrocatalysts for UOR also received extensive attention.In this thesis,the transition metal nickel and tungsten-based compounds were selected for the main research objects,focusing on the issues of the design and preparation of highly active and highly stable electrocatalysts for alkaline HER and UOR processes,along with the structure-activity relationship of the catalyst phase structure,electronic structure and catalytic performance.The main research progresses are as follows:（1）The three-dimensional nano-microsphere structure Ni₂P/WO_2.83/NF heterostructure catalyst with high alkaline HER activity and stability was sythesized by a facile method of hydrothermal and subsequent phosphorization treatment.It only required low overpotentials of 22.8 and 254.5 m V to drive the current densities of 10 and 1000 m A·cm^-2 for alkaline HER,respectively.The interface charge transfer and intermediate binding energies of the electrocatalyst was also verified by density functional theory（DFT）calculations This work combined the comprehensive design application of various modification strategies such as interface engineering,defect engineering,and structure engineering,and verified the design feasibility of using a facile synthetic strategy to simultaneously solve the problems of intrinsic activity,number of available active sites,and electrical conductivity at one time.（2）On the basis of the previous work,different thermal nitridation treatment were applied to the same precursor.The nano-microsphere structure Ni/W₅N₄/NF Mott-Schottky heterojunction electrocatalyst was constructed with satisfied UOR catalytic activity and stability.The potentials at the current densities of 10 and1000 m A·cm^-2 to catalyze the UOR were only 1.34 and 1.60 V,respectively.Since the Ni/W₅N₄/NF catalyst also exhibits excellent HER activity and can be used as both cathode and anode electrodes,an energy-efficient urea-assisted hydrogen evolution system was assembled.The cell voltages required to reach the current densities of 10 and 1000 m A cm^-2 were 1.33 and 1.77 V,respectively.The DFT calculations verified the formation conditions of the Mott-Schottky heterojunction and the caused interfacial charge redistribution,which greatly reduced the dissociation energy of the urea molecules.On the other hand,since the heterojunction engineering mantained the lattice structure orders of the catalyst,it exhibited the excellent long-term stability over 200 hours.This work verified the feasibility of heterojunction design for the construction of bifunctional highly stable catalysts,which can be used as a reference for the design and preparation of bifunctional electrocatalysts with high efficiency,high stability and low-cost.