Operando Scanning Electrochemical Microscopy Reveals Facet-Dependent Structure-Selectivity Relationship for CO₂ Reduction on Gold Surfaces

Selective and efficient electrochemical conversion of CO₂ to useful chemical feedstocks requires a comprehensive understanding of the reaction mechanism and revelation of the key structural characteristics of good catalysts via in situ and operando surface analyses of the working electrode. To achieve this, an electrochemical method was developed on the scanning electrochemical microscopy (SECM) platform. The electrochemical surface analysis is termed sequential voltammetric SECM (SV-SECM), which allows for simultaneous detection of various CO₂ reduction reaction products. Operando mapping of the activity was carried out on gold surfaces to reveal distinct facet-dependent product selectivity when overlaid with crystal orientation maps. Notably, we verified that crystal grains rich in (111) surfaces demonstrate superior CO₂ reduction selectivity compared to that with (100) surfaces. The analytical platform developed here was implemented on electrochemical reduction of CO₂ on gold as a proof-of-concept; however, it should be readily expandable to reactions yielding complex product selectivity distribution with an ill-understood catalytic structure-activity relationship.