Alkali-Heat Treatment Enhancing Oxygen Tolerance of CO2 electroreduction to HCOOH on SnO2/CN

Abstract

Abstract Tin oxide/carbon nitride composite catalyst (SnO2/CN) exhibits high selectivity to CO2 electroreduction reaction (eCO2RR) to HCOOH. However, industry flue gas, with the presence of O2 and relatively low CO2 concentration, inhibits the electrocatalytic activity of this kind of catalyst. In this study, alkali-heat treatment was introduced into the pretreatment process of CN carrier to improve the electrocatalytic activity and oxygen tolerance of SnO2/CN. The results of X-ray photoelectron spectroscopy confirmed that alkali-heat treatment can expose more surface amino groups of CN, enhancing the alkalinity of composite catalysts and thus the adsorption of CO2. Electron transfer occurred significantly from N of alkali-heat treated CN to Sn via enhanced metal-support interaction, forming highly electron-rich centers of Sn species and further benefiting the activation and reduction of CO2. The analysis of CO2 temperature programmed desorption also revealed that alkali-heat treatment could improve binding between catalyst and CO2. The multi-component competitive adsorption curve further indicated that alkali-heat treatment was beneficial for CO2/O2 separation as well. Finally, the electrochemical experiments demonstrated that faradaic efficiency (FE) of HCOOH reached 90.5% at a potential of -1.8V (vs. Ag/AgCl) after 2 h of eCO2RR over alkali-heat treated SnO2/CN. And in the case of simulated industry flue gas, the FE of HCOOH still reached 76.4% with the enhanced oxygen tolerance compared to untreated SnO2/CN.