In Situ Scanning Tunneling Microscopy of Cobalt‐Phthalocyanine‐Catalyzed CO2 Reduction Reaction

Abstract We report a molecular investigation of a cobalt phthalocyanine (CoPc)‐catalyzed CO 2 reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO 2 ‐purged electrolyte environment. The ECSTM experiments indicate the proportion of high‐contrast species correlated with the reduction of Co II Pc (−0.2 V vs. saturated calomel electrode (SCE)). The high‐contrast species is ascribed to the CoPc‐CO 2 complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc‐CO 2 to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO 2 , and the latter is the rate‐limiting step. The rate constant of the formation and dissociation of CoPc‐CO 2 is estimated on the basis of the in situ ECSTM experiment.