Surface Coordination/Organometallic Chemistry of Monometal and Bimetallic Electrocatalysts

Abstract

The interaction of selected organic and inorganic functional groups, which are reversibly electroactive and strongly surface-active, with monometal (Rh, Pd, Ir, Pt, Au) and mixed-metal (Au-Pt, Ag-Pt) electrocatalysts has been studied to help establish the interfacial organometallic/coordination chemistry of these metals in aqueous solutions. Experimental measurements were based upon thin-layer electrochemical and ultra-high vacuum surface spectroscopic methods; the latter included low-energy electron diffraction, Auger electron spectroscopy, X-ray photoelectron spectroscopy and thermal desorption mass spectrometry. The results to date indicate the following trends: (i) Electrode surface phenomena can be modeled in terms of monometal and cluster coordination/organometallic chemistry. (ii) Chemisorption is analogous to oxidative addition; desorption is similar to reductive elimination. (iii) Chemisorption of an electroactive center favors its oxidized state over the reduced form. (iv) Chemisorption of electroinactive anionic reagents forms polyprotic surface acids. (v) Substrate-mediated interactions between pendant electroactive centers may arise if the redox group itself is surface-active. (vi) Substrate-mediated adsorbate-adsorbate interactions can be viewed similarly to mixed-valence complexes.