Tailoring Defect Generation in SnO2 Nanostructure for Increased Selectivity in Electrochemical CO2 Reduction

Abstract

In order to achieve carbon neutrality, the CO2 reduction catalyst synthesized via a facile process with high selectivity and an industrial benchmark current density is of great interest. Herein, we propose the mesoporous SnO2 nanostructure synthesized using soft-templating assistance and alter the defects and active sites via defect engineering by annealing at a low optimal temperature of 300 °C. The electrochemical study shows highly improved CO2 reduction activity by SnO2-300V catalyst, achieving the faradic efficiency (F.E.) of 97.9 % for C1 products and selectivity of 94.1 % for formate (HCOOˉ) product at -1.1 V vs RHE in 0.1 M KHCO3. The sample also has a high partial current density of 12.6 mA cm-2 for HCOOˉ, high double-layer capacitance and low RCT value, compared to the other samples in this study. The low crystallite size, richness in grain boundaries and defect density were to be a combination of factors credited to increased selectivity in SnO2-300V. Density functional theory (DFT) calculation also revealed the moderate adsorption energy for *OCHO intermediate species and low adsorption energy for *HCOOH in defect-rich SnO2-300V sample, favouring the enhanced ECO2R activity. The best activity sample SnO2-300V tested in the flow-cell setup using a gas diffusion electrode exhibits a high current density of up to ~266 mA cm-2 in 1 M KOH, considerable stability and F.E.(HCOOˉ) ≥ 90.0 %, as per the industrial requirement. The work provides insight into the soft templating coupled with the defect engineering method of catalyst design for achieving scalable CO2R activity.