Selectivity of a Copper Oxide CO 2 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 CO 2 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- b -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 CO 2 electroreduction reaction conditions, and CO 2 molecules are preferentially located in the vicinity of the catalytically active area. The CO 2 reduction reaction is therefore kinetically favored over the hydrogen evolution reaction (HER).