Analysis of Oxygen Reduction on Pt Microelectrode with Polymer Electrolytes of Various Exchange Capacities

Abstract

In order to obtain an improved design of a polymer electrolyte fuel cell cathode, the oxygen reduction reaction on a Pt microelectrode with proton exchange membranes of various exchange capacities has been investigated. The measurements were performed by chronoamperometry for determination of the diffusion coefficient and oxygen solubility, and by slow scan voltammetry for reaction kinetics with the microelectrode in the temperature range 20 to 70°C. The results of chronoamperometry and slow scan voltammetry were analyzed by the fitting of analytic equations and digital simulation. The diffusion coefficients increased with temperature and exchange capacity. On the other hand, the solubilities increased with a decrease in temperature and exchange capacity. The dependences of the diffusion coefficient on temperature and exchange capacity were larger than those of the solubility. Accordingly, the permeabilities, which are the product of the diffusion coefficient and the solubility, increased with temperature and exchange capacity. Although the dependence of the exchange current densities on the exchange capacity was not clear, the exchange current densities were 10−9 to 10−8Acm−2 in the high potential region and about 10−6Acm−2 in the low potential region. © 2002 The Electrochemical Society. All rights reserved.

Effects of Ionomer Morphology on Oxygen Reduction on Pt

“…As opposed to the Parthasarathy's study, 35 the inhibition was not attributed to impurities, but rather to the dehydration of Nafion at elevated temperatures and the resultant blocking of the Pt surface by the hydrophobic component of Nafion. A similar suggestion was also put forward by Mitsushima and coworkers, 43 who explained the suppression of hydrogen adsorption/desorption on Pt UME pressed against different ionomeric membranes by the blocking of Pt surface sites by the hydrophobic component of the ionomer. The already complex issue of Nafion surface morphology is additionally complicated by the various effects of materials in contact with the ionomer surface.…”

Polarization-dependent mass transport parameters for orr in perfluorosulfonic acid ionomer membranes: an EIS study using microelectrodes

“…The orr at Ptjsolid polymer electrolyte interfaces and its associated mass transport parameters within the electrolyte medium are therefore active areas of study because of their relevance to PEMFCs. Microelectrode techniques are useful ex situ methods to characterize such interfaces [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Chronoamperometry (CA) has been used to determine the solubility and diffusion coefficient of oxygen at Ptjionomer interfaces.…”

Application of Butler–Volmer equations in the modelling of activation polarization for PEM fuel cells

“…For example, Ayad et al [33] reported roughness factors on smooth Pt of ∼3 while Ho and Piron [34], in their study of surface area determination of Pt in KOH, summarized roughness factors for 'bright Pt wire' determined by three different methods, in both 5 M KOH and 0.5 M H 2 SO 4 , and showing good agreement, 'r' values ranging from 1.7 ± 0.0 to 1.8 ± 0.1. Mitsushima et al [35], from their work with a Pt disk microelectrode on Nafion, reported roughness factors from 1.5 to 1.8. Parthasarathy et al [36], for a 100 m diameter Pt wire electrode, reported 'apparent roughness factors' of 9.2 for a Pt/Nafion combination and 9.6 for a Pt/H 3 PO 4 combination.…”