Characterizing Electrocatalysts with Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) is a non-contact scanning probe technique capable of providing chemical and/or topographic information about surfaces immersed in a solution. It is a powerful in situ and operando tool for obtaining insights into electrocatalytic rates and mechanisms. Herein, examples are given on how SECM can be used to characterize (1) hydrogen oxidation reaction electrocatalysts for fuel-cell applications, (2) oxygen evolution reaction electrocatalysts for water splitting applications, and (3) electrochemical CO2-reducing catalysts. We also report a new operando method of SECM in which we can separate electrochemical reduction or cO(2) to in aqueous media from parasitic hydrogen evolution as a function or applied potential. Understanding hydrogen evolution suppression is a major challenge in the intelligent design of CO2-reducing electrocatalysts. Via this multireactional SECM technique, we observed the optimal potential window for electrochemically reducing CO2 to CO with high selectivity. At potentials lower than this optimal window, CO2 reduction rates were small, but at potentials higher than this optimal window, water reduction to H-2 dominated the electrochemical conversions. This observation is something that traditional voltammetry alone is not able to resolve. We anticipate that a wider adoption of SECM by the catalysis community will allow for the operando characterization of many types of catalysts, and holds the potential to provide unprecedented insights into the composition/activity and structure/activity relationships.