Jun Li, Guangxu Chen, Yangying Zhu, Zheng Liang, Allen Pei, Chun-Lan Wu, Hongxia Wang, Hye Ryoung Lee, Kai Liu, Steven Chu and Yi Cui

Electrochemical CO2 reduction is a critical approach to reducing the globally accelerating CO2 emission and generating value- added products. Despite great efforts to optimize catalyst activity and selectivity, facilitating the catalyst accessibility to high CO2 concentrations while maintaining electrode durability remains a significant challenge. Here, we designed a catalytic system that mimics the alveolus structure in mammalian lungs with high gas permeability but very low water diffusibility, enabling an array of three-phase catalytic interfaces. Flexible, hydrophobic, nanoporous polyethylene membranes with high gas permeabil- ity were used to enable efficient CO2 access and a high local alkalinity on the catalyst surface at different CO2 flow rates. Such an alveolus-mimicking structure generates a high CO production Faradaic efficiency of 92% and excellent geometric current densities of CO production (25.5 mA cm−2) at −0.6 V versus the reversible hydrogen electrode, with a very thin catalyst thick- ness of 20−80 nm.

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