Characterization of Catalyst Layer Using Gas Diffusion Electrode Half-Cell System for High Temperature Polymer Electrolyte Membrane Fuel Cell

Abstract

High-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) is being developed for the heavy-duty vehicle which requires high power density and operation under extreme conditions. Conventional HT-PEMFC using phosphoric acid (PA) immersed PBI membranes and polytetrafluoroethylene (PTFE) binder faced issues such as unstable durability and low performance of membrane electrode assembly (MEA) due to PA leakage and uneven distribution within the catalyst layer.In recent years, ion-pair membranes and ionomers for high temperatures have been developed, which can reduce PA leakage in MEA and improve ionic conduction within the catalyst layer. Incorporation of a new material into the MEA requires further research to enhance electrode design, catalyst utilization, and performance for the appropriate ionomer, as this material exhibits different characteristics from the conventional PTFE binder.In this study, various gas diffusion electrode (GDE) was fabricated with the new ionomer, and GDE half-cell setups were introduced for rapid and efficient characterization of performance in the oxygen reduction reaction. This system serves as an intermediate step between rotating disk electrodes and single cells, providing a powerful tool for quickly screening and evaluating GDEs using small amounts of catalyst. Recent publications from Wilkinson [1] and Gasteiger [2] groups reviewed this new system, proposed new measurement protocols, and suggested improvements. Accordingly, GDE half-cell setups are designed to simulate HT-PEMFC operating conditions at 150 ℃ temperature with 85 wt.% PA electrolyte.Electrochemical characteristics were evaluated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) following the protocols in previous papers with GDE half-cell. Resistance values obtained through EIS were further differentiated by peaks and frequency-based responses through the distribution of relaxation times transformation. Performance comparison between GDEs was carried out by measuring the voltage at 0.2 A/cm² and peak power density at 150 ℃, simulating a single cell-like environment. GDEs were fabricated with variables such as Pt loading, thickness, and porosity. And their physical properties were confirmed through mercury intrusion porosimetry and scanning electron microscopy. Ultimately, the study elucidated the correlation between the electrochemical data and physical properties.