Effect of Substrate Microstructure and Hydrophobicity on Ag Gas Diffusion Electrodes for Electrochemical CO2 Reduction

Abstract

Electrochemical CO2 reduction (CO2RR) is a very promising way to convert detrimental CO2 emissions into sustainable fuels and chemicals, and move us closer to a circular economy.1 To compete with traditional fuel/chemical production routes, we need to develop electrocatalysts that are highly active, selectivity towards a desired product, and stable. Thanks to the use of gas diffusion electrodes (GDEs) that provide gaseous CO2 close to the catalyst, high activities can be achieved.2,3 However, product selectivity and stability must still be improved before practical application. An emerging strategy in this regard is to control the local environment surrounding a catalyst, i.e. the concentration of the various products and reagents therein.4 In this work, we achieve such control by varying the microstructure of substrates later used to fabricate GDEs by Ag deposition. By systematically studying the CO2RR performance, we observe a clear correlation between the pore size of the GDEs and their product selectivity, stability, and even resilience to Cu impurities.5 We rationalize it with the different effective hydrophobicity of the GDEs, which control the extent of electrolyte penetration within the electrode and depends on both substrate chemistry and pore size. We show that a higher effective hydrophobicity correlates with higher Faradaic efficiency towards carbon monoxide production (FECO up to 95 % at 100 mA/cm2) and longer stability (~100 % retention after a 1 hour electrolysis at 100 mA/cm2). These results show the importance of the substrate's microstructural properties in GDE for CO2RR, and highlight a new strategy to achieve control over selectivity and stability of these electrodes.