Electrodeposition of high-surface area platinum in a well adherent Nafion film on glassy carbon

Platinum was electrochemically deposited within a Nafion film coated on glassy carbon (GC) to form a well adherent and high-platinum utilization electrode. Two potential-control procedures were evaluated to form a deposit: a cyclic potential scan and a constant potential, with Pt loadings ranging for each from 60-750 mu g Pt cm(-2) GC obtained by varying the coulombs discharged. The Pt/Nafion/GC electrodes were annealed at 170 degrees C before use. Transmission electron microscopy studies revealed that Pt grows as a dispersed, three-dimensional deposit within the film for both techniques. The average particle size for a loading of 60 mu g cm(-2) is 7.3 nm, which is in good agreement with that (7.1 nm) estimated from electrochemical formation of adsorbed hydrogen. With a Pt loading an order-of-magnitude greater, the particle number density increased, and the observed average particle is larger at 9.8 nm which is smaller than that (19.0 nm) evaluated from electrochemical hydrogen adsorption. The deposit thickness increased with loading and, for a given Pt loading, was less thick when using the steady-potential method; the latter technique, however, yielded a deposit which covered more of the GC-Nafion interface. The mass specific surface area of Pt decreased with loading and ranged from 32-8 m(2)g(-1) as the loading varied from 60-640 mu g cm(-2). The Pt/Nafion/GC structure is robust in that the electrode can be used to evolve hydrogen or oxygen without damaging the film. In contrast, a Nafion film on smooth Pt is lifted off the surface under similar gas-evolution conditions.