Electrochemical imaging of thermochemical catalysis.

Thermochemical redox catalysis is critical to a wide array of key chemical transformations and can proceed via the coupling of two electrochemical half-reactions. This electrochemical mechanism is exemplified by the platinum-catalysed aerobic oxidation of formic acid, wherein the oxygen reduction reaction is coupled to the formic acid oxidation reaction. Here using scanning electrochemical cell microscopy, we show there are grain-dependent variations in catalytic rates for the oxygen reduction and formic acid oxidation reactions at a platinum catalyst. Quantitative spatially resolved images of catalytic rates imply inter-grain cooperativity during ensemble thermochemical catalysis via lateral current flows that galvanically couple disparate active sites. Moreover, by comparing current-potential profiles of the half-reactions in isolation and in the presence of both reactants, we reveal additional site-specific chemical interactions that modify the two constituent half-reactions. These studies establish a methodology that exposes how electrochemical half-reactions couple and interact across surface structures to enable redox transformations.