Vacancy Defect And Cu Alloying Of Bi Metal For Improved Electrocatalytic Reduction Of CO₂

The construction of a renewable energy storage system using formic acid as an energy carrier is considered to be one of the most promising ways to solve the energy storage problem and alleviate the energy crisis.However,because of the existence of C=O double bonds,the linear structure of CO₂molecules is very stable under normal conditions,which makes a large challenge to active CO₂molecules in the process of electrochemical CO₂reduction reaction.In order to achieve an efficient and stable strategy,it is necessary to design an electrocatalyst with high activity and stability.At present,there are many ways to modify the performance of catalysts including constructing defect states,controlling the exposure of highly active crystal planes and modifying surface interfaces.These strategies mainly optimize the adsorption and desorption of CO₂,the activation of CO₂molecules,and the stability of intermediate species.In fact,these strategies regulate the interaction of catalysts and surface species at electronic level.Studying the electronic state on the surface of catalyst is of great significance for electrochemical CO₂reduction reaction.Therefore,a facile method was designed to synthesize a series of ultra-thin Bi nanosheet with Bi vacancies for efficient production of formate.Besides,other highly active metal atoms were doped in Bi catalysts to adjust the bonding strength between Bi atom and the active species.The details are as follows:?1?Bi atom vacancies assisted electrocatalytic reduction of CO₂.In this paper,an in-situ topological transformation method was designed to synthesize an ultra-thin Bi nanosheet with Bi vacancies and?001?dominant facet.The Bi nanosheet exhibited 90%CO₂-to-formate Faradaic efficiency at alow overpotential of 420 m V and excellent stability over 100 h in 0.1 M KHCO₃electrolyte.Spectroscopic and computational studies confirmed that the Bi atom vacancies induced the electron-rich surface,leading the movement of p states towards the Fermi level,hence decreasing the activation energy of CO₂to^*CO₂^-radical and promoting the stability of OCHO^*intermediate via p orbitals hybridization between the O in carbon-containing intermediates and the Bi electrode.?2?Cu Bi alloying catalyst improved CO₂electroreduction into formic acid.In this paper,Cu Bi alloying catalyst was prepared by electrochemical co-deposition method,and the atomic ratio of Cu-Bi alloying was controlled at about 1:1.Compared with Bi dendrite single metal catalyst,the Cu Bi alloying catalysts had a great improvement in reaction activity.When the Faraday efficiency was kept at 88%,the current density of formate reached-15 m A cm^-2.The effect of alloying Cu and Bi on the activity and selectivity towards formate was explored and a reasonable explanation was proposed.When two metals come into contact,the electrons flowed from Bi atoms to Cu atoms due to the difference in the Metal Work Function.It was easy to enrich electrons on the highly active Cu atoms surface during the reaction,which not only promoted the activation of CO₂to^*CO₂^-,but changed the intermediate species from^*COOH to^*OCHO.This leaded to an increased formate acid generation and suppressed formation of spurious species,especially H₂and CO.