Rational Design and Synthesis of SnOx Electrocatalysts with Coralline Structure for Highly Improved Aqueous CO2 Reduction to Formate

Abstract

AbstractSeveral catalyst materials composed of tin oxide composites (SnOx) with a novel coralline structure are synthesized by using a facile hydrothermal self‐assembly process. The catalysts are then used to prepare a SnOx/GDL (gas diffusion layer) electrode for CO2 electroreduction to formate in 0.5 m KHCO3 aqueous solution. Influential factors, such as hydrothermal synthesis temperature (T)/time (Δt) and the valence state of Sn in the SnOx nanocatalysts, on both catalysts’ morphologies, and Faradaic efficiency for formate production are investigated systematically. By using a SnOx(100–8)/GDL electrode (i.e. T and Δt are 100 °C and 8 h, respectively) as the cathode, the high maximum faradaic efficiency of 87.1 % is achieved at a controlled potential of −1.6 V, which is superior to all the reported SnOx and Sn/SnOx catalysts in the literature. By combining X‐ray photoelectron spectroscopy and X‐ray diffraction analysis, the coralline‐structured SnOx is observed to be composed of SnO and SnO2, where the SnO is covered by a SnO2 film about 1–2 nm thick, which makes a contribution to the catalytically active sites for CO2 electroreduction. This coralline‐structured SnOx exhibits high durability, as evaluated by a stable catalytic current density of approximately 10 mA cm−2 over 20 h of continuous operation. This work highlights the controlling role of the correct morphology and the valence state of tin oxide on formate formation during CO2 reduction in aqueous solution.