Examination of the activity and durability of PEMFC catalysts in liquid electrolytes

Widespread research in the field of fuel cells necessitates easily verifiable and reproducible benchmarks for characterizing properties such as electrochemical area (ECA), oxygen reduction reaction (ORR) specific and mass activity (is, im) as well as durability of electrocatalysts. Ex situ characterization of electrocatalysts deposited as thin-film rotating disk electrodes (TF-RDE) in liquid electrolytes as well as in their original dry powder state has been conducted. Commercially available Pt on carbon support (Pt/C) catalyst serving as a baseline benchmark and heat treated Pt/C and Pt-alloy/C catalysts were investigated as examples of higher activity and durability materials. A detailed description of the preparation and optimization of catalyst inks, measurement protocols, and analysis of ORR kinetic parameters and durability rates are provided to form a basis for consistent screening and benchmarking of new and improved catalysts for proton exchange membrane fuel cells (PEMFCs). Preparation of highly-dispersed ink slurries formulated using various water–isopropanol mixtures and deposited as TF-RDEs were demonstrated to significantly affect the magnitude of measured ECA and activity. The ECA, is and im for the baseline Pt/C were determined to be 100 m2 g−1, 292 μA cm−2Pt and 266 mA mg−1Pt in 0.1 M HClO4 at 25 °C and 10 mV s−1. Strong adsorption of anions on Pt/C in sulfuric acid was shown to have a deleterious effect on its activity and durability. Related ORR kinetic parameters such as the activation energy (ΔH = 38 kcal mol−1) as well as the experimental reaction order (m ∼ 0.75) with respect to oxygen were determined to provide a basis for converting literature results to a common pressure and temperature.