The Influence of pH and Electrolyte Concentration on Fractional Protonation and CO₂ Reduction Activity in Polymer-Encapsulated Cobalt Phthalocyanine

Polymer-encapsulated cobalt phthalocyanine (CoPc) isa model systemfor studying how polymer-catalyst interactions in electrocatalyticsystems influence performance for the CO2 reduction reaction.In particular, understanding how bulk electrolyte and proton concentrationinfluence polymer protonation and in turn how the extent of polymerprotonation influences catalytic activity and selectivity is crucialto understanding polymer-catalyst composite materials. We reporta study of the dependence of bulk pH and electrolyte concentrationon the fractional protonation of poly(4-vinylpyridine) and relatedpolymers with both electrochemical and spectroscopic evidence. Inaddition, we show that the fractional protonation of the polymer isdirectly related to both the activity of the catalyst and the reactionselectivity for the CO2 reduction reaction over the competitivehydrogen evolution reaction. Of particular note is that the fractionalprotonation of the film is related to electrolyte concentration, whichsuggests that the transport of counterions plays an important rolein regulating proton transport within the polymer film. These insightssuggest that electrolyte concentration and pH play an important rolein the electrocatalytic performance for polymer-catalyst compositesystems, and these influences should be considered in both experimentalpreparation and analysis.