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

Several catalyst materials composed of tin oxide composites (SnO x ) with a novel coralline structure are synthesized by using a facile hydrothermal self‐assembly process. The catalysts are then used to prepare a SnO x /GDL (gas diffusion layer) electrode for CO 2 electroreduction to formate in 0.5 m KHCO 3 aqueous solution. Influential factors, such as hydrothermal synthesis temperature ( T )/time (Δ t ) and the valence state of Sn in the SnO x nanocatalysts, on both catalysts’ morphologies, and Faradaic efficiency for formate production are investigated systematically. By using a SnO x (100–8) /GDL electrode (i.e. T and Δ t 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 SnO x and Sn/SnO x catalysts in the literature. By combining X‐ray photoelectron spectroscopy and X‐ray diffraction analysis, the coralline‐structured SnO x is observed to be composed of SnO and SnO 2 , where the SnO is covered by a SnO 2 film about 1–2 nm thick, which makes a contribution to the catalytically active sites for CO 2 electroreduction. This coralline‐structured SnO x 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 CO 2 reduction in aqueous solution.