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

Abstract

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 SnO_x 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 SnO_x @MWCNTs-COOH and SnO_x @MWCNTs-NH₂ show excellent catalytic activity for CO₂ RR with nearly 100 % selectivity for C₁ products (formate and CO). SnO_x @MWCNTs-COOH has favorable formate selectivity with a remarkably high faradaic efficiency (FE) of 77 % at -1.25 V versus standard hydrogen electrode (SHE) and a low overpotential of 246 mV. However, SnO_x @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. SnO_x @MWCNTs-COOH and SnO_x @MWCNTs-NH₂ both effectively inhibit the hydrogen evolution reaction and prove stable without any significant degradation over 20 h of continuous electrolysis at -1.25 V versus SHE.

Keywords: carbon dioxide; density functional calculations; electrocatalysis; functional groups; tin oxide.