Self-assembled monolayer of a non-Pt oxygen electroreduction catalyst on metal oxide supports

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D. F. Gervasio, Don.Gervasio@asu.edu, Center for Applied NanoBioScience, Arizona State University, 1001 S. Mc Allister Avenue, Tempe, AZ 85287-5001 and Jeffery Thomson, Jeffery.Thomson@asu.edu, Biodesign Institute, Arizona State University, 1001 S. Mc Allister Avenue, Tempe, AZ 85287-5001.
A self-assembled monolayer (SAM) of metallo porphyrins is intended as a replacement to platinum, in the hope of overcoming the slow oxygen reduction kinetics on Pt that limits fuel-cell efficiency to < 70% [1] and Pt- fouling by impurities. Metallo porphyrins can remedy the problems with Pt in oxygen cathodes [2] but these do not bind on electrode surfaces. A first step to stable catalyst monolayer.is to form a SAM of macrocycle on a current-collecting surface. A cobalt(II) porphyrin, Co1, was formed into a SAM on conductive indium tin oxide (ITO). Co1is attracted to ITO by a covalently attached phosphonate group[3]. Substantial oxygen electro reduction current was found with a SAM of Co1 on ITO compared to bare ITO in 0.01 M aqueous trifluoromethane sulfonic acid (TFMSA) with 1 atm oxygen over solution. The catalytic oxygen reduction current onset at 0.65 V and rose to a limiting current density of about 0.4 milliamp cm-2 at 0.1 V versus RHE. Oxygen reduction on Pt and the Co1 SAM on ITO in aqueous triflic acid in the presence and absence of methanol will be presented to illustrate that the Co1 on ITO is less susceptible to fouling than Pt.

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