Interiorly Hydrophobic Modification of Electrodeposited Self-supported ZnAg Foam Electrodes for CO2 Electroreduction in a Microchannel Reactor

Abstract

Electrodeposition is an effective approach to synthesize porous electrocatalysts; however, the impact of deposition conditions on the catalyst porosity and morphology has rarely been systematically studied. More importantly, the mass transport of CO₂ is poor because the electrodes are generally fully covered by aqueous electrolytes, leading to low current densities. Hydrophobic modification can generate gas–liquid–solid interfaces that facilitate CO₂ mass transport. However, the conventional superficially hydrophobic modification sacrifices the activity due to partially covered active sites, has difficulty in the uniform modification of internal pore surfaces due to large polymer size, and the surface hydrophobic sites are easily washed away. Here, we report a unique hydrogen bubble dynamic template electrodeposition method to synthesize interiorly hydrophobic ZnAg foam electrodes by physically trapping polytetrafluoroethylene (PTFE) during electrodeposition. Deposition conditions were found to influence the pore diameter and morphology. The pore diameter increases with the deposition current density and duration. The pore wall structure gradually transformed from nanodendrites at −0.5 A·cm^–2 into nanosheets at −1 A·cm^–2 or beyond. The resulting interiorly hydrophobic ZnAg(3A15s)-40 exhibits a maximum FE_CO of 97.6% and a significantly widened current density window of −5 to −50 mA·m^–2 with an FE_CO of more than 90.4% in a microchannel reactor, which is significantly higher than those of bare ZnAg(3A15s) (−5 to −30 mA·cm^–2 with an FE_CO more than 90.0%) and the Zn rod substrate (−5 mA·cm^–2 with an FE_CO of 64.0%). The in situ attenuated total reflection Fourier transformed infrared (ATR-FTIR) spectroscopy suggested the hydrophobic catalyst has enhanced CO₂ concentration near the inner surface, which promotes the activity of CO₂ reduction to CO.