Scanning Electrochemical Microscopy Study of Electron-Transfer Kinetics and Catalysis at Nanoporous Electrodes

The complicated electrochemical properties of nanoporous electrodes arising from their geometry remain poorly understood because their complex structure defies easy interpretation of experimental results. The large surface area of a porous electrode results in a higher double-layer charging current and faster apparent heterogeneous rate constants, which are difficult to measure by voltammetry and other transient electrochemical techniques. In this article, we used a scanning electrochemical microscope equipped with a nanometer- or micrometer-sized tip to measure the rates of the same electron-transfer process at the flat and nanoporous Au electrodes. The origins and magnitude of the rate constant enhancement at the nanoporous surface (after the roughness factor correction) are discussed. Using the substrate generation/tip collection mode of the scanning electrochemical microscope operation, the higher catalytic activity of nanoporous Au for the oxygen reduction reaction was found from both substrate and tip voltammograms that can also be used for analyzing the reaction products.