Interiorly\nHydrophobic Modification of Electrodeposited\nSelf-supported ZnAg Foam Electrodes for CO<sub>2</sub> Electroreduction\nin a Microchannel Reactor

Electrodeposition is an effective approach to synthesize\nporous\nelectrocatalysts; however, the impact of deposition conditions on\nthe catalyst porosity and morphology has rarely been systematically\nstudied. More importantly, the mass transport of CO<sub>2</sub> is\npoor because the electrodes are generally fully covered by aqueous\nelectrolytes, leading to low current densities. Hydrophobic modification\ncan generate gas–liquid–solid interfaces that facilitate\nCO<sub>2</sub> mass transport. However, the conventional superficially\nhydrophobic modification sacrifices the activity due to partially\ncovered active sites, has difficulty in the uniform modification of\ninternal pore surfaces due to large polymer size, and the surface\nhydrophobic sites are easily washed away. Here, we report a unique\nhydrogen bubble dynamic template electrodeposition method to synthesize\ninteriorly hydrophobic ZnAg foam electrodes by physically trapping\npolytetrafluoroethylene (PTFE) during electrodeposition. Deposition\nconditions were found to influence the pore diameter and morphology.\nThe pore diameter increases with the deposition current density and\nduration. The pore wall structure gradually transformed from nanodendrites\nat −0.5 A·cm<sup>–2</sup> into nanosheets at −1\nA·cm<sup>–2</sup> or beyond. The resulting interiorly\nhydrophobic ZnAg(3A15s)-40 exhibits a maximum FE<sub>CO</sub> of 97.6%\nand a significantly widened current density window of −5 to\n−50 mA·m<sup>–2</sup> with an FE<sub>CO</sub> of\nmore than 90.4% in a microchannel reactor, which is significantly\nhigher than those of bare ZnAg(3A15s) (−5 to −30 mA·cm<sup>–2</sup> with an FE<sub>CO</sub> more than 90.0%) and the\nZn rod substrate (−5 mA·cm<sup>–2</sup> with an\nFE<sub>CO</sub> of 64.0%). The in situ attenuated total reflection\nFourier transformed infrared (ATR-FTIR) spectroscopy suggested the\nhydrophobic catalyst has enhanced CO<sub>2</sub> concentration near\nthe inner surface, which promotes the activity of CO<sub>2</sub> reduction\nto CO.