Analysis of Oxygen-Transport Diffusion Resistance in Proton-Exchange-Membrane Fuel Cells

Abstract

The quantification procedure of oxygen-transport resistances for different fuel-cell layers and phenomena is described. The total transport resistance is obtained from limiting-current measurements under conditions where oxygen diffusion is dominant (i.e., high flow rates, small cell size, humidified but subsaturated feeds, and low feed oxygen partial pressure). By systematically varying the experimental conditions, the contributions of molecular and Knudsen diffusion and permeation through the ionomer film covering the catalyst-layer agglomerates are determined. It is found that the ionomer-film resistance is dominant, especially at lower temperatures and lower Pt loadings. The calculated film properties through the ionomer hint that it is much more resistive than the bulk membrane for state-of-the-art cells.

Oxygen Reduction Reaction Measurements on Platinum Electrocatalysts Utilizing Rotating Disk Electrode Technique

“…Redistribution subject to ECS terms of use (see 54.245.55.244 Downloaded on 2018-05-11 to IP A critical and unresolved challenge in PEMFCs that has arisen with the attempts at reducing Pt loading and cost is the lower than projected peak power for cathodes incorporating ultra-low Pt loadings. The issue is being studied intensively and different groups 114,[121][122][123][124][125] have identified several possible routes including catalyst interaction with Nafion. In MEAs of PEMFCs, since it is not possible to carry out an investigation in the absence of ionomer (ionomer is indispensable for proton conduction), the contribution of the ionomer adsorption/blocking cannot be easily examined.…”

Liquid water saturation and oxygen transport resistance in polymer electrolyte membrane fuel cell gas diffusion layers

“…Several recent studies [74][75][76][77][78] have focused on measuring the individual transport resistance contributions of the fuel cell layers by performing limiting current measurements with varied pressures, GDL thicknesses, cathode balance gases (also known as oxygen "diluents"), and RH levels. Baker et al [77] determined the relative contributions of the channels, GDL substrate, MPL, and catalyst layer to total transport resistance by manipulating GDL and MPL thicknesses and the operating pressure.…”

“…Baker et al [77] determined the relative contributions of the channels, GDL substrate, MPL, and catalyst layer to total transport resistance by manipulating GDL and MPL thicknesses and the operating pressure. Nonoyama et al [75] and Oh et al [78] both used the same method to separate the intermolecular diffusion and Knudsen diffusion components of the oxygen transport resistance. The authors compared their limiting current experiments using cathode gases containing dilute concentrations of oxygen in balance gases of both nitrogen and helium.…”

“…Oh et al further separated the GDL transport resistance into contributions by the MPL and carbon fiber substrate by conducting the above experiments on fuel cells both with and without a microporous layer. In the study by Nonoyama et al [75], the ionomer layer contribution to transport resistance was isolated by varying the cell temperature, since the impact of temperature on ionomer diffusion coefficient is much larger than the impact of temperature on molecular and Knudsen diffusion. Reshetenko et al [76] also used a limiting current-based methodology to identify the catalyst layer ionomer diffusion contribution.…”

“…Depending on the chosen experimental conditions and on the GDL materials and catalyst loadings, the GDL has been found to contribute between 32% and 61% of the total oxygen transport resistance in the fuel cell [75][76][77][78] in when there is no liquid water present. At low RH, the catalyst layer was generally the largest contributor to the oxygen transport resistance, owing to a decrease in oxygen diffusivity through the ionomer layer when the ionomer was poorly hydrated [78].…”