Effect of Ionomer on CO2 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.