Decoding the Role of Tin Telluride as Electrochemical CO2 Reduction Catalyst

Tin-based compounds, particularly SnO2-derived catalysts, are extensively studied for selective electrochemical reduction of CO2 (eCO2RR) to formate. As compared to Sn oxides, chalcogenides such as SnTe are relatively unexplored in the domain of eCO2RR, in spite of having desired electronic properties, often combined with native surface oxide layers. In this work, we report dual catalytic behavior of finely powdered polycrystalline SnTe showing high activity towards CO2 reduction as well as the hydrogen evolution reaction (HER). We show that SnTe exhibits selective eCO2RR to formate with partial faradic current densities of −35 mAcm-2 at −1.1 V vs. RHE in 0.5 M CsHCO3 solution, similar to SnO2. Concurrently, SnTe exhibits high activity towards HER, in contrast to SnO2. Comprehensive potential dependent structural characterizations and SEIRAS measurements suggest that the chemical transformation of SnTe and SnO2 to reduced Sn under high reductive potentials may be the reason for their similar eCO2RR activity. On the other hand, control experiments on elemental Te and SnO2 as well as XPS data point towards the important role of residual tellurium on the surface of the SnTe pre-catalyst to drive the HER. This work underscores the significance of understanding the in-situ transformation of the pre-catalyst to the active species during the eCO2RR to rationalize its activity and product selectivity.