Tailoring defect generation in SnO₂ nanostructures for increased selectivity in electrochemical CO₂ reduction

In order to achieve carbon neutrality, CO₂ reduction catalysts synthesized via a facile process with high selectivity and an industrial benchmark current density are 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 of the SnO₂-300V catalyst, achieving a faradaic efficiency (FE) of 97.9% for C1 products and a selectivity of 94.1% for the formate (HCOO^-) 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 HCOO^-, a high double-layer capacitance and a low R_CT value, compared to the other samples in this study. The low crystallite size, richness in grain boundaries and defect density are the combination of factors credited for the increased selectivity in SnO₂-300V. Density functional theory (DFT) calculations also revealed moderate adsorption energy for the *OCHO intermediate species and low adsorption energy for *HCOOH in the defect-rich SnO₂-300V sample, favouring the enhanced ECO₂R activity. The SnO₂-300V sample with the best activity tested in the flow-cell setup using a gas diffusion electrode exhibited a high current density of up to ∼266 mA cm^-2 in 1 M KOH, considerable stability and FE_(HCOO^-) ≥ 90.0%, as per the industrial requirement. The work provides insight into soft templating coupled with the defect engineering method of catalyst design for achieving scalable CO₂R activity.