SnOx Nanosheets Anchored on Mwcnts Modified with Different Functional Groups for Selective Electrochemical Reduction of CO2 to C1 Products

Abstract

Electrochemcial reduction of CO2 (CO2RR) into the industrial feedstocks and low carbon fuels could be a promising strategy to alleviate the excessive emission of CO2. In CO2RR, C1 products are more feasible due to their low electron transfer and relative fast kinetics. By applying a facile and green hydrothermal assembling method, we here report the synthesis of a hierarchical SnOx (x=1, 2) nanosheets anchored on the surface of the commercial MWCNTs, which were functionalized by -NH2, -COOH, -OH or without any functional group, in order to investigate the influence of functional groups on the properties of SnOx@MWCNTs catalysts for enhanced electrochemical CO2 reduction reaction (CO2RR). A noteworthy improvement in catalytic performance was obtained for all the catalysts modified with -NH2, -COOH, -OH compared with that without any functional group. X-ray diffraction shows that the SnO (101) surface is the active phase for CO2RR. Density functional theory (DFT) calculations indicates that the presence of -COOH significantly improves the adsorption energy of SnOx on MWCNTs, yet, -NH2 was favorable for the adsorption of CO2, facilitating CO2RR. SnOx@MWCNT-COOH achieved remarkably high faradaic efficiency (FE) for formate of 77% at -1.25 V vs. SHE and a low overpotential of only 246 mV, while SnOx@MWCNT-NH2 exhibited high activity and selectivity for C1 products (formate and CO). Furthermore, SnOx@MWCNT-COOH as well as SnOx@MWCNT-NH2 both effectively inhibited hydrogen evolution reaction (no more than 0.5% for FEH2) and proved to be stable without any obvious degradation over 20 h of continuous electrolysis at -1.25 V vs. SHE. Keywords: CO2 electroreduction, functional groups, formate, DFT calculations