Tuning the oxidation state of SnO x and mass transport to enhance catholyte-free CO 2 -to-formate electrolysis

• Published in: Sustainable energy & fuels 2023-07, Vol.7 (14), p.3395-3403
• Main Authors: Kim, Taewoo, Devalla, Vivek Shastry, Dunfield, Sean P., Palmer, Jack R., Dorr, Sara, Kodur, Moses, Gupta, Apoorva, Fenning, David P.
• Format: Article
• Language: English
• ISSN: 2398-4902; 2398-4902
• DOI: 10.1039/D3SE00214D

Electrochemical CO 2 conversion to formate is a promising potential pathway to facilitate carbon neutrality with industrial feasibility. However, designing an active catalyst and optimizing the CO 2 electrolyzer to enable energy-efficient CO 2 conversion is a continuing challenge. Herein, we demonstrate that the initial surface oxidation state of tin oxide (SnO x ) catalysts is a key and enduring factor in determining the CO 2 -to-formate conversion efficiency. Comparing the selectivity and energy efficiency of formate generation on thermally-evaporated and annealed SnO x catalysts reveals that catalysts that are initially SnO-rich at the surface show improved overall efficiency relative to catalysts that are initially SnO 2 -rich. Moreover, we show that controlling the flow rate of CO 2 strongly affects overall CO 2 -to-formate conversion activity in partially-concentrated CO 2 streams in a catholyte-free electrolyzer, which emphasizes the importance of mass transport of CO 2 to design an efficient CO 2 electrolyzer. These findings provide insights into the critical importance of the chemical state in non-stoichiometric transition metal oxide catalysts like SnO x catalysts and CO 2 mass transport for CO 2 -to-formate conversion, offering fundamental guidelines and an efficient carbon-negative CO 2 conversion.