Counting surface redox sites in carbon-supported electrocatalysts by cathodic stripping of O deposited from N2O

Abstract

Methods of determining in situ the electrochemically active surface area of bulk noble metal electrodes (e.g., underpotential deposition of a strongly interacting sorbent followed by columbic stripping) may not be appropriate for certain base metals supported on electroactive supports, such as carbon, because of the difficulty of finding a metal-specific titrant and because the support itself can contribute a very large background current. For example, the coulometric stripping of metal-selective sorbates, like carbon monoxide, works for the in situ characterization of certain electrode-supported metals (e.g. Pt, Pd) if applied carefully, but not for base metals, like Cu that do not strongly adsorb the titrant. Moreover, in scoping studies, we found that underpotential deposition of Tl on carbon-supported Cu failed to be selective for the copper. 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 approximately with XRD line broadening for characterizing ∼10 nm particles of Cu supported on graphite felt. More significantly, 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.