Effect of Ionomer on CO ₂ Reduction at Atomically Dispersed Ni─N─C Catalyst

Abstract Ionomers play an important role in carbon dioxide (CO ₂ ) electrolyzers by affecting CO ₂ reduction reaction (CO ₂ RR) at the cathode. In this study, we systematically examines the impact that different ionomers have on CO ₂ RR at atomically dispersed nickel–nitrogen–carbon (Ni─N─C) catalyst. We compare the effects of two acidic cation exchange ionomers, perfluorosulfonic acid (Nafion) and sulfonated poly(aryl ether sulfone), and two alkaline anion exchange ionomers: quaternary ammonium‐functionalized poly(aryl piperidinium) and quaternary ammonium‐functionalized polyfluorene. Of the four ionomers, the Nafion‐bonded electrode reaches the highest CO ₂ RR activity and selectivity in H‐cell testing likely due to the polymer weak interaction with the Ni─N─C catalyst. Flow cell measurements further validate superior CO ₂ RR performance of the Nafion‐bonded electrode relative to those containing other polymers. The findings from this research highlight a critical importance of interactions between the ionomers and the catalyst surface in CO ₂ reduction, which go beyond their well‐established role in regulating local pH and hydrophobic/hydrophilic properties of the catalyst layer.