Design Of Bismuth-based Catalysts And Investigation Of Their Properties And Mechanisms For Electrocatalytic Reduction Of Carbon Dioxide

The large-scale use of fossil energy leads to the continuous increase of carbon dioxide(CO2)emissions.Reducing CO2 emissions through the development of catalytic CO2 conversion technologies including photocatalysis,electrocatalysis and photoelectrocatalysis has important academic research significance and practical application.Among those technologies,electrocatalytic reduction of CO2(CO2RR)utilizes renewable electric energy as energy drive to convert CO2 into high value-added chemicals is considered as one of the most potential ways to realize carbon neutrality,owing to the advantages of simple operation and mild reaction conditions.Meanwhile,because of the high economic value of formic acid(HCOOH)and the advantages of easy separation,storage and transportation,the preparation of HCOOH from CO2RR has become a promising and valuable way of CO2 conversion.It is necessary to design catalysts with high catalytic efficiency to produce HCOOH from CO2RR.Studies have shown that bismuth(Bi)based catalysts with advantages of abundant reserves,being environmentally friendly and low toxicity,can effectively inhibit HER competitive reaction due to high electrocatalytic hydrogen evolution reaction(HER)overpotential.Based on those virtues,Bi-based material has become a highly selective catalyst for HCOOH production from CO2RR with great application prospect.However,the inferior conductivity of Bi-based catalyst materials remarkably limits the current density of CO2RR and the reaction efficiency.In addition,the efficiency of CO2RR catalyzed by Bi-based material at the solid-liquid-gas three-phase interface is significantly affected by the microscopic morphology of the catalyst,Modulating the morphology of the catalyst can improve the adsorption and mass transfer of CO2,which can enhance the catalytic efficiency of Bi-based catalyst for CO2RR.In this paper,various strategies were developed to design Bi-based catalysts and regulate their microscopic morphologies to improve the catalytic performance for CO2RR.The main research contents are as follows:(1)The BiPO4 nanoparticle precursor was prepared by solvothermal procedure,and then Bi nanodendrite(Bi-EG)was obtained by in-situ electroreduction.At-1.0 V vs.RHE(vs.RHE,reversible hydrogen electrode;all potentials hereafter are given with respect to RHE unless otherwise stated),the FEformate reached 95%and the corresponding jformate was 34.4 mA cm-2 for Bi-EG,along with excellent catalytic durability.It was found that Bi-EG catalyst has a high specific surface area and abundant surface active sites,which is conducive to the mass transfer of CO2,and thus promotes the HCOOH production efficiency from CO2RR.(2)Ultrathin Bi2O2O/Bi2O2(OH)(NO3)nanosheets were prepared through in-situ interlamellar hydrogen-bond tailoring strategies(BiON-uts).The result shows that ultrathin nanosheet morphology remarkably facilitates the exchange of HCO3-in the electrolyte with NO3-in Bi2O2(OH)(NO3),and accelerates the formation of Bi2O2CO3 intermediate on the surface.The high efficiency reduction of Bi2O2CO3 intermediates is conducive to the preservation of Bi-O structure on the catalyst surface,thus improving the HCOOH production efficiency.At-1.0 V,the FEformate reached 98%and the corresponding jformate was 28.4 mA cm-2 for the BiON-uts catalyst.(3)BiOX catalysts(including BiOC1,BiOBr and BiOI)were prepared by solvothermal procedure.Studies show that the larger layer spacing of BiOI and the lower binding energy between[Bi2O2]2+ layer and I-ion are conducive to the diffusion of HCO3-,facilitating the rapid and sustained production of Bi2O2CO3 intermediates.High-efficiency reduction of Bi2O2CO3 intermediates can effectively protect the Bi-O structure from being reduced,and achieve excellent catalytic activity.At-1.0 V,the FEformate reached 98%and the corresponding jformate was 41.3 mA cm-2 for the BiOI catalyst.(4)The precursor of Bi-H4Pyr was synthesized by hydrothermal procedure using pyromellitic acid(H4Pyr)as organic ligand.Bi2O2CO3 catalyst(Bi2O2CO3-D)with flower morphology was derived by ligand substitution with HCO3-due to the similar structure of HCO3-and to the carboxyl group in H4Pyr ligands.At-1.0 V,Bi2O2CO3-D exhibits the FEformate of>90%and excellent catalytic stability.The Bi-based catalyst derived from Bi-MOFs exhibits excellent stability and catalytic performance,providing a new strategy for developing high-efficiency CO2RR catalysts.