Tuning The Electronic Structures Of Molybdates And Investigation Of Their Electrocatalytic Performance For Hydrogen Evolution

As an energy carrier,hydrogen has been considered to be a cleaner alternative to fossil fuels.With significant merits including ambient operation conditions,zero emission of harmful products,and readily available precursor,water electrolysis has been one of the most appealing technologies for hydrogen production.At present,the optimal catalyst for hydrogen production is still precious metal Pt,but its cost and scarcity limit the large-scale implementation of water electrolysis.Among many catalysts,transition metal-based catalysts have received substantial research interest in the light of their cheapness,variable valence state,and unique d-band electronic structure.In recent years,transition metal-based carbides,nitrides,sulfides,and phosphides have good catalytic performance in electrocatalytic hydrogen evolution reaction?HER?.Although the molybdate catalysts have poor performance for HER,molybdate could be served as the excellent precursor materials,especially when combined with other transition metal ions structure engeneering such as doping,changing the composition,forming defects,the electronic structure of the parent materials could be optimized and the intrinsic activity of the inert catalysts could be significantly improved.Therefore,this thesis intends to improve the intrinsic activity of molybdates through electronic structure engeneering,and mainly studies the effect of doping and electrochemical tuning on the electronic structure of molybdates and further their catalytic ability for HER.The details are as follows:?1?Co Mo O₄ nanosheets were grown vertically on Ti plates by a simple hydrothermal method,forming an open and porous structure.The electronic structure of Co Mo O₄ was regulated by P doping,which improved the conductivity of Co Mo O₄ and optimized its free energy for adsorption of H.As a result,Co Mo O₄ exhibited improved HER performance in alkaline solution,with only an overpotential of 138 m V required to drive hydrogen evolution at a current density of 10 m A/cm².?2?Discharging a lithium-ion half cell can be used to tune the electronic structure of Ni Mo O₄.By employing such a method,Ni Mo O₄ had been successfully converted to Ni and Mo.The synergistic effect of the two metals enabled the efficient electrocatalysis of HER in alkaline solution,with much low overpotential of 73 m V to obtain a current density of 10 m A/cm².?3?Discharging a sodium-ion half cell can also be used to tune the electronic structure of Ni Mo O₄.In this contribution,we systemly discussed the similarities and differences of these two electrochemical tuning methods.With sodium electrochemical tuning method,sodium ions could intercalate and further break the Ni Mo O₄ crystals,forming fine crystal particles and lattice mismatch.Consequently,the prepared material had better HER activity than the material prepared by lithium electrochemical tuning method,delivering a low overpotential of 43.4 m V at 10 m A/cm².