Selectivity of a Copper Oxide CO₂ Reduction Electrocatalyst Shifted by a Bioinspired pH-Sensitive Polymer

A bioinspired polymeric membrane capable of shifting the selectivity of a copper oxide electrocatalyst in the CO₂ reduction reaction is described. The membrane is deposited on top of copper oxide thin films from wet deposition techniques under controlled conditions of humidity and self-assembles into an arranged network of micrometer-sized pores throughout the polymer cross-section. The membrane was composed of a block copolymer with a precisely controlled ratio of poly-4-vinylpyridine and poly(methyl methacrylate) blocks (PMMA-<i>b</i>-P4VP). The intrinsic hydrophobicity, together with the porous nature of the membrane's surface, induces a Cassie-Baxter wetting transition above neutral pH, resulting in water repulsion from the catalyst surface. As a consequence, the catalyst's surface is shielded from surrounding water molecules under CO₂ electroreduction reaction conditions, and CO₂ molecules are preferentially located in the vicinity of the catalytically active area. The CO₂ reduction reaction is therefore kinetically favored over the hydrogen evolution reaction (HER).