Mark Mathias

Measurement of Catalyst Layer Electrolyte Resistance in PEFCs Using Electrochemical Impedance Spectroscopy

In this paper, electrochemical impedance spectroscopy (EIS) is used to resolve various sources of polarization loss in a pure hydrogen-fueled polymer electrolyte fuel cell (PEFC). EIS data are fitted to a fuel cell model in which the catalyst layer physics are accurately represented by a transmission line model. Extracted parameters include cell ohmic resistance, catalyst layer electrolyte resistance, and double-layer capacitance. The results showed that the catalyst layer electrolyte resistance for a state-of-the-art electrode (47 wt % Pt on Vulcan XC-72 carbon, 0.8 Nation (1100EW)-to-carbon weight ratio, 13 μm thick) at 80°C and fully humidified conditions was approximately 100 mΩ-cm 2 ; this translates to a dc voltage loss of about 33 mV at a current density of 1 A/cm 2 . Similar results were obtained for two experimental methods, one using H 2 (anode) and O 2 (cathode gas feed) and another with H, and N 2 supplies, and for two cell active areas, 5 and 50 cm 2 . The measured catalyst layer electrolyte resistance increased with decreasing ionomer concentration in the electrode, as expected. We also observed that the real impedance measured at 1 kHz, often interpreted as the ohmic resistance in the cell, can include contributions from the electrolyte in the catalyst layer.

Water Transport Mechanisms in PEMFC Gas Diffusion Layers

Understanding how water produced in the cathode catalyst layer is removed during proton exchange membrane fuel cell (PEMFC) operation is critical for optimization of materials and model development. The present work combines in situ and ex situ experiments designed to elucidate the dominant water discharge mechanism when considering capillary and vapor transport at normal PEMFC operating conditions. The flux of water vapor driven by the thermal gradient in the cathode diffusion layer can alone be sufficient to remove product water at high current densities even with saturated gas in the delivery channels. The role of an intermediate microporous layer and its impact in vapor vs liquid transport is also considered. We propose that the primary role of the microporous layer is to prevent condensed water from accumulating on and blocking oxygen access to the cathode catalyst layer. .

The Composition of Electrodeposited Zinc‐Nickel Alloy Coatings

Analyse par un modele de transfert de masse, incluant la migration et la complexation du zinc par les ions chlorure, de la composition du depot electrolytique dun alliage. Application au systeme Zinc-Nickel-Chlorure

A zinc-nickel alloy electrodeposition kinetics model from thickness and composition measurements on the rotating disk electrode

Measurements of radial variations of composition and thickness of electrodeposited zinc-nickel alloys on a rotating disk electrode were made for deposits obtained at steady state from chloride electrolytes at different bath compositions, electrode rotation rates, and applied voltages. A two-dimensional transport model, which accounts for migration and complexation of the zinc by chloride, was used to calculate the radially dependent interfacial concentration and potential profiles for each set of experimental conditions