PNNL

Abstract

The usual, in situ method of determining the electrochemically active surface area of bulk metal electrodes—underpotential deposition of a strongly interacting sorbent followed by columbic stripping—cannot be used for metals supported on electroactive supports, such as carbon, because the support itself contributes a very large background current. For example, in scoping studies, we found that underpotential deposition of Tl failed to be selective for the metal. The coulometric stripping of metal-selective sorbates, like carbon monoxide, works for the in situ characterization of some electrode-supported metals (e.g. Pt, Pd) if applied carefully, but not for base metals, like Cu that do not strongly adsorb the titrant. Here we present the use of gentle oxidation of the metal domains using N2O as the oxidant, followed by cathodic stripping of the surface oxide. The method compares favorably with XRD line broadening for characterizing ~10 nm particles of Cu supported on graphite felt. We show that the method usefully normalizes the rates of two electrochemical hydrogenation reactions: conversion of nitrobenzene to aniline and conversion of benzaldehyde to benzyl alcohol. This work began with funding from a Strategic Partnering Project initiated by GSK. It was completed with support from Laboratory Directed Research and Development funding. The work was performed at Pacific Northwest National Laboratory (PNNL). PNNL is a multiprogram national laboratory operated for DOE by Battelle. We are grateful to Dr. Stacy O’Neill-Slawecky of GSK for many fruitful discussions.