The usual method of counting sites for supported metal catalysts—selective titration using chemisorption of gases (e.g., H2, CO)—can indicate the fractional exposure of the metal supported on an electrode before or after use but not during use when it is in contact with the electrolyte. 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. The coulometric stripping of sorbates like carbon monoxide works for the in situ characterization of some electrode-supported metals (e.g. Pt, Pd) if applied carefully,1 but not for those base metals, like Cu, that exhibit usefully high Faradaic efficiencies in the reduction of functionalized organic molecules, but that do not strongly adsorb either hydrogren or carbon monoxide. Therefore, we have tried to develop a method that can be used in an electrochemical environment to count electrode-supported redox sites containing base metals. We will discuss 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, where, for example, underpotential deposition of Tl failed to be selective. We are in the process of extending the method to other metals and to smaller domain sizes and will report those results, along with their bearing on reaction kinetics.

In situ titration of carbon-supported electrocatalysts

254th National Meeting (2017)

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