Electrochemical Reduction of CO2 by SnOx Nanosheets Anchored on Multiwalled Carbon Nanotubes with Tunable Functional Groups

Sn-based electrocatalysts are promising for the electrochemical CO2 reduction reaction (CO2RR), but suffer from poor activity and selectivity. A hierarchical structure composed of ultrathin SnOx nanosheets anchored on the surface of the commercial multiwalled carbon nanotubes (MWCNTs) is synthesized by a simple hydrothermal process. The electrocatalytic performance can be further tuned by functionalization of the MWCNTs with COOH, NH2, and OH groups. Both SnOx@MWCNTs-COOH and SnOx@MWCNTs-NH2 show excellent catalytic activity for CO2RR with nearly 100% selectivity for C-1 products (formate and CO). SnOx@MWCNTs-COOH has favorable formate selectivity with a remarkably high faradaic efficiency (FE) of 77% at -1.25V versus standard hydrogen electrode (SHE) and a low overpotential of 246mV. However, SnOx@MWCNTs-NH2 manifests increased selectivity for CO with higher current density. Density functional theory calculations and experimental studies demonstrate that the interaction between Sn species and functional groups play an important role in the tuning of the catalytic activity and selectivity of these functionalized electrocatalysts. SnOx@MWCNTs-COOH and SnOx@MWCNTs-NH2 both effectively inhibit the hydrogen evolution reaction and prove stable without any significant degradation over 20h of continuous electrolysis at -1.25V versus SHE.