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
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