Direct in situ Measurement of Electrocatalytic Carbon Dioxide Reduction Properties using Scanning Electrochemical Microscopy

One fundamental question facing electrocatalytic CO 2 reduction reaction (CO 2 RR) is how to identify and correlate the local catalyst activity and stability to their bulk performance. Here we develop a versatile scanning electrochemical microscopy (SECM) platform to directly analyze catalyst stability, CO 2 RR product distribution, and chemical environment in complex systems at the microscopic scale. Using two Cu-porphyrin complex isomers as molecular catalysts, we have demonstrated that alternating the Cu-complex catalyst center to asymmetric Cu-N 3 C structure leads to reduced stability under constant potential electrolysis but increases the electrocatalytic activity under pulsed potential electrolysis. Testing the electroreduction properties of the catalysts in different electrolysis modes, we find alternating electrolysis pattern changes the catalyst product selectivity and the local pH environment at the vicinity of the catalyst surface, which sheds light on the origin of improved hydrocarbon propagation. This work introduces a fast, efficient, and multifunctional SECM technique for evaluating fundamental and mechanistic aspects of CO 2 RR in situ.