Controllable Synthesis Of Bi-based Materials And The Study Of Their Electrocatalytic Performance For CO₂ Reduction

Excessive exploitation and utilization of fossil energy have released trillions of tons of carbon dioxide（CO₂）into the atmosphere,and the inherent carbon cycle of nature is unable to withstand such a huge amount of CO₂,leading to a series of problems such as global warming.Electrocatalytic CO₂reduction technology（CO₂RR）is a green and efficient means to reduce CO₂and convert it into a variety of energy substances,such as,formates,CO,methane,etc.However,in the actual reaction process of electrocatalytic CO₂reduction,problems such as poor selectivity,high reduction potential and low current density will occur in electrocatalytic materials.Therefore,it is necessary to develop efficient electrocatalytic materials.Bi-based materials have gradually become one of the most popular electrocatalytic materials due to their excellent conversion efficiency,low cost and availability for the electroreduction of CO₂to formate.Based on this,we designed the following Bi-based materials to explore its catalytic performance and reaction principle:（1）Electrochemical reduction of carbon dioxide into formates is considered to be an effective strategy to overcome energy and environment crisis.Bi-based materials have good application prospects,but it is still a challenge to develop a new class of high performance electrocatalysts.In this paper,we propose a new topochemical transformation strategy for the rational design of highly active Bi-based materials,namely,Bismuth oxysulfate（Bi₂O₂SO₄）.This is a new system of Bi-based CO₂RR electrocatalysts.Bismuth oxysulfate（Bi₂O₂SO₄）was prepared by simple topological transformation of Bi₂S₃precursor in air.Compared with the further topologically transformed metal Bi treated by sodium borohydride solution,the Bi₂O₂SO₄electroreduction topologically transformed Bi has better catalytic performance for CO₂RR.HCOO^-has a maximum Faraday efficiency（FE）of 97%at-0.9V vs.RHE in a H-type cell.In a flow cell,Faraday efficiencies of over 90%over a wide potential range of-0.5 to-1.2 V vs.RHE can be further achieved,with a high current density of 319 m A cm^-2at-0.8 V vs.RHE.Characterization studies and density functional theory（DFT）calculations confirmed that the Bi₂O₂SO₄-derived Bi catalyst has the optimal（104）crystal plane to achieve the adsorption free energy of*OCHO and H*reaction intermediates,and thus has good catalytic activity against CO₂RR.（2）Electrochemical reduction of Bi oxide is an effective strategy for designing advanced electrocatalysts for electrochemical carbon dioxide reduction reaction.Achieving high selectivity at high current densities is important for formate production,but remains challenging.We synthesized Bi In hybrid electrocatalyst（MOD-Bi In）derived from Bi₂O₃/In₂O₃heterojunction with good catalytic performance for CO₂RR.The Faraday efficiency of formates(FE_HCOO-)can be achieved in excess of 90%within a large potential window of-0.4～-1.4 V vs.RHE.In the absence of IR compensation,the partial current density of formate(j _HCOO-)is about 136.7 m A cm^-2.In addition,MOD-Bi In exhibited superior stability and high formate selectivity at 100 m A cm^-2.Physicochemical characterization,electrochemical analysis and theoretical calculation of the system confirmed that the hybrid structure with double Bi/In metal sites promoted the optimal free energy of*OCHO intermediates on the MOD-Bi In surface,thus accelerating the formation and desorption steps of*HCOO^-,which was beneficial for formate production.