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

Ionomers play an important role in carbon dioxide (CO₂) electrolyzers by affecting CO₂ reduction reaction (CO₂RR) at the cathode. In this study, we systematically examines the impact that different ionomers have on CO₂RR 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 CO₂RR 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 CO₂RR 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 CO₂ reduction, which go beyond their well-established role in regulating local pH and hydrophobic/hydrophilic properties of the catalyst layer.