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

Abstract

The influence of Nafion® film on the kinetics of anodic oxidation of hydrogen was investigated on Nafion®-coated platinum electrodes. Hydrodynamic voltammetry was used to obtain the kinetic current for the H2 oxidation reaction, and the exchange current densities at bare and Nafion®-coated Pt rotating disk electrodes were determined using the modified Koutecky–Levich equations. The exchange current density at Nafion®-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 H2 solubility in recast Nafion® than in the solution. The hydrogen solubility in recast Nafion® determined by potential step chronoamperometry (PSCA) was 1.4×10−6 mol cm−3, which was 1.8 times higher than that in the solution (0.78×10−6 mol cm−3). The difference in H2 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®, where H2 solubility in the electrochemically inactive fluorocarbon region is higher than that in the ionic cluster region.