Electrochemical Imaging of Thermochemical Catalysis

Thermochemical redox catalysis is critical to a wide array of key chemical transformations and is known to be sensitive to catalyst surface structure. Yet there exist limited operando tools for quantitatively imaging heterogeneities in catalytic rate across a surface. Since many thermochemical redox reactions can proceed via the coupling of electrochemical half-reactions, electrochemical microscopies can, in principle, be used to image heterogeneities in thermochemical redox catalysis. Herein, we develop a methodology for imaging variations in the rate of thermochemical redox catalysis using electrochemical microscopy. Using Pt-catalyzed aerobic oxidation of formic acid oxidation as a test reaction, scanning electrochemical cell microscopy (SECCM) imaging reveals grain-dependent variations in catalytic rate for the underlying oxygen reduction and formic acid oxidation half-reactions, implying inter-grain cooperativity during ensemble thermochemical catalysis via lateral current flows that galvanically couple disparate active sites. Tafel analysis of current-potential profiles in the presence of both reactants reveals the nature of cross-talk between the two half-reactions and provides quantitative spatially-resolved images of catalytic rates for the net thermochemical reaction. These studies establish a methodology for using electrochemical microscopy to image thermochemical catalysis and expose how electrochemical half-reactions couple and interact across surface structures to enable redox transformations.