Enhancing the Electrochemical CO2 Reduction Activity of Polymer-Encapsulated Cobalt Phthalocyanine Films by Modulating the Loading of Catalysts, Polymers, and Carbon Supports

Cobalt phthalocyanine (CoPc) has been extensively studied as a catalyst for the electrochemical reduction of CO2 to value-added products. Previous studies have shown that CoPc is a competent and efficient catalyst when immobilized onto carbonbased electrodes using a polymer binder, especially when immobilized with a graphitic carbon powder support to increase charge transport. In this study, we systematically explore the influence of incorporating graphite powder (GP) into a polymerencapsulated CoPc on the system's activity for the electrochemical reduction of CO2. We report a protocol for incorporating GP into CoPc/polymer/GP catalyst films that facilitates physisorption of CoPc to GP, leading to increased activity for CO2 reduction. We show that the activity for CO2 reduction increases with GP loading at low GP loadings, but at sufficiently high GP loadings the activity plateaus as charge transfer is sufficiently fast to no longer be rate limiting. We also demonstrate that axial coordination is still important even in the presence of GP, suggesting that CoPc does not fully coordinate to heteroatoms on the GP surface. We develop a set of optimized conditions under which the CoPc/polymer/GP catalyst systems reduce CO2 with higher activity and similar selectivity to previously reported CoPc/polymer films on edge-plane graphite electrodes. The procedures outlined in this study will be used in future studies to optimize catalyst, polymer, and carbon support loadings for other polymer-catalyst composite systems for electrocatalytic transformations.