La 0.6Ca 0.4CoO 3, La 0.1Ca 0.9MnO 3 and LaNiO 3 as bifunctional oxygen electrodes

Abstract

A series of perovskite catalysts was investigated for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolyte and at room temperature, supplied by oxygen or air. A meniscus cell was used to screen-test candidate catalysts for their bifunctionality and assess their activity for ORR at 3 mm depth of immersion (DOI) in the electrolyte. Based on the meniscus data LaNiO 3, La 0.1Ca 0.9MnO 3 and La 0.6Ca 0.4CoO 3 were selected for further assessment in microelectrode and half-cell studies. Activity tests for the ORR and OER, Tafel slopes at high current densities and apparent activation energies for the ORR were determined using a microelectrode technique on samples of the selected perovskites, La 0.1Ca 0.9MnO 3, La 0.6Ca 0.4CoO 3 and LaNiO 3 with and without graphite support. Tafel slopes of ca. 120 mV per decade and apparent activation energies of approximately 18 kcal mol −1 were measured at high cathodic current densities. Cycle-life and performance of La 0.1Ca 0.9MnO 3, La 0.6Ca 0.4CoO 3 and LaNiO 3-based gas-diffusion electrodes in half-cell configurations were tested at a constant current density of 25 mA cm −2 with subsequent and intermittent polarizations. Similar activities resulted in the ORR, while increased numbers of cycles were observed for the La 0.1Ca 0.9MnO 3-based electrode. Furthermore, electrode material compositions, especially PTFE contents were optimized to conform to the establishment of the three phase interactions of the electrode structure. Transmission Electron microscopy (TEM) and BET-surface area analyses were carried out in order to find out the morphological and surface properties of the perovskite materials.