Development of half-cells with sulfonated Pt/Vulcan catalyst for PEM fuel cells

Half-cell is an ex situ device generally used in fuel cell investigations. The present work is related to half-cell investigations of a particular catalyst for polymer electrolyte membrane (PEM) fuel cells, namely Pt/Vulcan catalyst grafted with 5 wt.% polystyrene sulfonate (PSSA). It was found that the behavior of the half-cell to be immersed in a sulfuric solution was influenced by the hot-pressing conditions in the preparation process: optimum hot-pressing conditions had to be searched for improved, reliable performance of half cells. A stable Nafion® membrane interface on the catalytic layer (CL) was obtained at 135 °C, 40 bars for 6 min. Otherwise, owing to the ion-exchange properties of the PSSA graft, electrodes were prepared with lower amounts of Nafion® and the effect of Nafion® introduction in the preparation was discussed: test electrodes mounted in half-cell had either 0.25 or 0.50 mg cm−2 Nafion® dispersed in CL, or with 0.50 mg cm−2 deposited on CL surface. Their performances for oxygen reduction reaction (ORR) were studied using linear voltammetry (LV) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetry was used for determination of the electrochemical surface area (ECSA) of each electrode. It has been shown that fresh electrodes with 0.50 mg cm−2 Nafion® dispersed in CL exhibit promoted behavior in ORR. However, the GDE prepared with Nafion® deposition on CL surface exhibits the best resistance to ageing tests performed by potential cycling between 0 and 1.2 V/NHE, as revealed by ECSA measurements.