Influence of Nafion® film on the kinetics of anodic hydrogen oxidation

The influence of Nafion(R) film on the kinetics of anodic oxidation of hydrogen was investigated on Nafion(R)-coated platinum electrodes. Hydrodynamic voltammetry was used to obtain the kinetic current for the H-2 oxidation reaction, and the exchange current densities at bare and Nafion(R)-coated Pt relating disk electrodes were determined using the modified Koutecky-Levich equations. The exchange current density at Nafion(R)-coated Pt was higher by 20% than that at bare Pt in 0.1 M HClO4. The enhancement in exchange current density was attributed to a higher H-2 solubility in recast Nafion(R) than in the solution. The hydrogen solubility in recast Nafion(R) determined by potential step chronoamperometry (PSCA) was 1.4 x 10(-6) mol cm(-3), which was 1.8 times higher than that in the solution (0.78 x 10(-6) mol cm(-3)). The difference in H, solubility determined by potential step chronoamperometry was larger than that estimated from the difference in exchange current density. The discrepancy was explained by the peculiar multiphase-structure of Nafion(R), where H-2 solubility in the electrochemically inactive fluorocarbon region is higher than that in the ionic cluster region. (C) 1998 Elsevier Science S.A. All rights reserved.