Selective and stable CO electroreduction at high rates via control of local HO/CO ratio.

Controlling the concentrations of HO and CO at the reaction interface is crucial for achieving efficient electrochemical CO reduction. However, precise control of these variables during catalysis remains challenging, and the underlying mechanisms are not fully understood. Herein, guided by a multi-physics model, we demonstrate that tuning the local HO/CO concentrations is achievable by thin polymer coatings on the catalyst surface. Beyond the often-explored hydrophobicity, polymer properties of gas permeability and water-uptake ability are even more critical for this purpose. With these insights, we achieve CO reduction on copper with Faradaic efficiency exceeding 87% towards multi-carbon products at a high current density of -2 A cm. Encouraging cathodic energy efficiency (>50%) is also observed at this high current density due to the substantially reduced cathodic potential. Additionally, we demonstrate stable CO reduction for over 150 h at practically relevant current densities owning to the robust reaction interface. Moreover, this strategy has been extended to membrane electrode assemblies and other catalysts for CO reduction. Our findings underscore the significance of fine-tuning the local HO/CO balance for future CO reduction applications.