CO 2 ‐to‐CO Conversion in a Gas‐Fed, Zero‐Gap, PEM Electrolyzer Enabled by Polycations and Nitrogen‐Doped Carbon‐Supported Cobalt Nanoparticles

ABSTRACT Electrochemical carbon dioxide reduction (ECO 2 R) into value‐added chemicals is challenging due to the high overpotential of reaction intermediates, the instability of adsorbed species in the absence of mobile cations, and requiring acidic aqueous electrolyte feed to prevent salt precipitation. A gas‐fed, zero‐gap proton exchange membrane (PEM) ECO 2 R setup utilizing hydrogen (H 2 ) as anodic feed and nitrogen‐doped carbon‐supported cobalt nanoparticles (Co/N‐C) as catalyst may be a solution to these problems but is observed to be ineffective at suppressing the H 2 evolution reaction (HER). Immobilizing poly‐diallyldimethyl ammonium (PDDA + ) cations with finely milled Co/N‐C results in a change of selectivity from HER toward coordinating CO 2 intermediates on active sites. Optimizing Co loading at 1.20 wt.% for Co/N‐C delivers a peak faradaic efficiency toward carbon monoxide production (FE CO ) of 65% and sustains 5 h electrolysis with FE CO above 50% under a constant current density of 100 mA cm −2 . The effects of acid‐wash, cobalt content, mass loading, and PDDA + on the gas‐diffusion electrode and secondary particle size in catalyst ink are optimized to improve FE CO against a prohibitively low pH environment. These results highlight the intrinsic properties of PDDA + on Co/N‐C electrocatalyst for a modular, humidified gas‐fed, zero‐gap PEM CO 2 electrolyzer technology.