Chemostructurally Stable Polyionomer Coatings Regulate Proton-Intermediate Landscape in Acidic CO<sub>2</sub> Electrolysis
Bárbara B. Polesso, Adrián Pinilla-Sánchez, Eman H. Ahmed, Anku Guha, Marinos Dimitropoulos, Blanca Belsa, Viktoria Golovanova, Lu Xia, Ranit Ram, Sunil Kadam, Aparna Mini Das, Junmei Chen, Johann Osmond, Adam Radek Martínez, Melanie Micali, Esther Alarcón‐Lladó, F. Pelayo Garcı́a de Arquer
Abstract
High Resolution Image Download MS PowerPoint Slide CO 2 electroreduction (CO 2 R) in acidic media offers a path to high carbon utilization via local carbonate regeneration. However, this proton-rich environment challenges achieving a combined selectivity and rate toward multicarbon (C 2+ ) products due to proton and intermediate competition. Here, we demonstrate a strategy to modulate local protons and intermediates, at these settings, using a polyionomer coating over benchmark copper gas diffusion electrodes. The polyionomer integrates amine (−NH x ) function from branched polyethylenimine (PEI) with sulfonate (−SO 3 – ) and amphiphilic functions from PFSA. We show that their chemical structure enables H-bonding interaction, leading to a stereochemical assembly that retains a structure–property relationship through a wide pH range (2–14). PFSA domains modulate *CO intermediates and local [CO 2 ]/[H 2 O] and K + environment, while partially protonated amines provide further control over proton availability and intermediate stabilization, which in combination enhance C–C coupling. When implemented in a flow cell (0.5 M K 2 /H 2 SO 4, pH = 2), the optimized polyionomer coating enables a C 2+ Faradaic efficiency of 61% at a single-pass CO 2 utilization of 84%, including a conversion efficiency of 64% toward C 2+, at a current density of at 0.3 A cm –2 ─an improvement of almost 30% in C 2+ selectivity and 35% in carbon utilization compared to monofunctional coatings. These findings expand the toolbox of strategies to modulate CO 2 R microenvironments toward improved performance.