Degradation study on tin- and bismuth-based gas-diffusion electrodes during electrochemical CO2 reduction in highly alkaline media

This work investigated the degradation of tin - based gas-diffusion electrodes (GDE) and also a promising Bi2O3 GDE in electrochemical CO2 reduction in highly alkaline media which has not been studied before. The contributions of the electrode wetting (or flooding, if excessively) and catalyst leaching on the degradation were analyzed. Therefore, electrochemical impedance spectroscopy was used to monitor the wetted surface area of the GDE in combination with post-mortem analysis of the penetration depth by visualizing the electrolyte's cation in the GDE cross-section. Furthermore, to reveal a possible degradation of the electrocatalyst, its distribution was mapped in the GDEs cross-section after operation while the catholyte was additionally analyzed via ICP-MS. The results clearly demonstrate that the SnO2 catalyst dissolves in the reaction zone inside the GDE and might be partially redeposited near the GDEs surface. Since the redeposition process occurs only partially a steady loss of catalyst was observed impeding a clear distinction of the two degradation phenomena. Nevertheless, the deterioration of the electrode performance measured as faraday efficiency (FE) of the parasitic hydrogen evolution reaction (HER) qualitatively correlates with the differential double layer capacitance (C-dl). A significant difference of the rate of increase for the hydrogen FE and C-dl can be ascribed to the superposition of both above-mentioned degra-dation mechanisms. The demonstrated instability of SnO2 contrasts with the behavior of Bi2O3 GDE which is stabilized during CO2 conversion by redeposition of the diluted dissolved species as metallic Bi which is active for the CO2 reduction reaction. (C) 2021 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

This study investigated the degradation of tin-based gas-diffusion electrodes (GDE) and a promising Bi2O3 GDE in highly alkaline media during electrochemical CO2 reduction, revealing that the SnO2 catalyst dissolves and may be partially redeposited, while the Bi2O3 GDE remains stable due to the redeposition of metallic Bi during CO2 conversion. The deterioration of electrode performance correlates with the differential double layer capacitance and the rate of increase for hydrogen FE, indicating the superposition of different degradation mechanisms.