Selectivity of a\nCopper Oxide CO<sub>2</sub> Reduction\nElectrocatalyst Shifted by a Bioinspired pH-Sensitive Polymer

A bioinspired polymeric membrane capable of shifting\nthe selectivity\nof a copper oxide electrocatalyst in the CO<sub>2</sub> reduction\nreaction is described. The membrane is deposited on top of copper\noxide thin films from wet deposition techniques under controlled conditions\nof humidity and self-assembles into an arranged network of micrometer-sized\npores throughout the polymer cross-section. The membrane was composed\nof a block copolymer with a precisely controlled ratio of poly-4-vinylpyridine\nand poly(methyl methacrylate) blocks (PMMA-<i>b</i>-P4VP).\nThe intrinsic hydrophobicity, together with the porous nature of the\nmembrane’s surface, induces a Cassie–Baxter wetting\ntransition above neutral pH, resulting in water repulsion from the\ncatalyst surface. As a consequence, the catalyst’s surface\nis shielded from surrounding water molecules under CO<sub>2</sub> electroreduction\nreaction conditions, and CO<sub>2</sub> molecules are preferentially\nlocated in the vicinity of the catalytically active area. The CO<sub>2</sub> reduction reaction is therefore kinetically favored over\nthe hydrogen evolution reaction (HER).