| The combustion of large amounts of fossil fuels worldwide has led to an increasing atmospheric carbon dioxide(CO2)concentration,which has caused a series of environmental problems,such as global warming and rising sea level.The electrochemical reduction of CO2(Carbon dioxide electrochemical reduction,CO2ER)to high-value products using renewable energy is of great importance to achieve the goal of carbon peaking and carbon neutrality.Tin-based electrocatalysts have been widely used in the field of CO2ER because of their appropriate adsorption energy for the reaction intermediates of CO2ER and their ability to convert CO2 into C1 products,such as formic acid(HCOOH)and carbon monoxide(CO).However,most of the reported Tin-based catalysts still face great challenges in achieving efficient CO2 conversion at industrial current densities,mainly due to the common problems of low product selectivity,low reaction current density and high reaction overpotential.In this thesis,SnSe2-180 and Sn/NCNFs electrocatalysts were successfully developed by effective construction of structural defects and Sn-N active centers,which significantly improved the CO2 electrocatalytic reduction activity and selectivity of Tin-based electrode materials.To solve the problems of low selectivity and low current density of Tin-based catalysts in CO2ER,a SnSe2 nanosheets with rich selenium vacancy(SnSe2-180)were prepared by hydrothermal method.This SnSe2-180 catalyst exhibited the highest Faraday efficiency of formic acid up to 94.1%,and the highest partial current density of HCOOH up to 800.2 mA cm-2 in a flow cell reactor.Meanwhile,SnSe2-180 catalyst also exhibit excellent CO2ER performances in electrolytes with different pH,which surpass most of the previously reported Tin-based electrocatalysts.The systematic experimental results showed that the excellent CO2ER performance of the SnSe2-180 catalyst mainly benefited from the presence of selenium vacancies,which effectively increased the electron density on the Sn active sites.This structure also effectively decreased the Tafel slope of the CO2ER reaction and accelerated the formation of the reaction intermediate HCOO*.Further assembled of the prepared SnSe2-180 catalyst as a cathode with a zinc sheet into a Zn-CO2 cell could effectively realize the energy conversion and output with a maximum output power density of 1.8 mW cm-2.Meanwile,to solve the problem of high overpotential of Tin-based catalysts in CO2ER,a nitrogen-doped carbon nanofibers material(Sn/NCNFs)loaded with Tin-N active sites(Sn-N)was synthesized by electrospinning coupled with high temperature carbonization.This Sn/NCNFs catalyst achieved a partial carbon monoxide producing current density of 100.6 mA cm-2 in the flow cell,with the highest CO Faraday efficiency of 96.5%and a low reaction onset potential of-0.3 V.The experimental results indicated that the Sn-N structure in the Sn/NCNFs catalyst accelerated the water dissociation and the subsequent protonation process in the rate-determining step of CO2ER,thereby accelerating CO2ER kinetics.Moreover,the pyrrole N atom adjacent to the Sn-N sites effectively modulated the local electron density of Sn 5p orbital,significantly lowering the reaction energy barrier for the formation of*COOH intermediates,and thus enhancing CO2ER performance.The as prepared Sn/NCNFs catalyst were integrated as a cathode with the Zn sheet into a Zn-CO2 cell with maximum output power density of 1.4 mW cm-1 and CO selectivity maintained at 97.6%. |
