Abstract
Here, we detail how the catalytic behavior of immobilized molecular electrocatalysts for the CO2 reduction reaction (CO2RR) can be impacted by catalyst aggregation. Operando Raman spectroscopy was used to study CO2RR mediated by cobalt phthalocyanine (CoPc) immobilized on the cathode of an electrochemical flow reactor. We demonstrate that during electrolysis, the oxidation state of CoPc in the catalyst layer depends on the degree of catalyst aggregation. These data indicate that immobilized molecular catalysts must be dispersed on conductive supports to mitigate aggregate formation and produce meaningful performance data. We leverage these mechanistic insights to engineer an improved CO-forming immobilized molecular catalyst, cobalt octaethoxyphthalocyanine (EtO8–CoPc), that exhibits high selectivity, high partial current density, and high durability in a flow cell. This work demonstrates how operando Raman spectroscopy can identify CO2RR active species in molecular catalyst layers and guide the implementation of improved molecular electrocatalysts in flow cells.