Thermal Treatment of La_0.6Ca_0.4CoO₃ Perovskites for Bifunctional Air Electrodes

The perovskite La_0.6Ca_0.4CoO₃ has been of interest as a bifunctional electrocatalyst for the bifunctional air electrode. The calcination and subsequent cooling steps in the amorphous citrate precursor (ACP) process have been optimized to prepare La_0.6Ca_0.4CoO₃ powders with high surface area, and consequently improved electrocatalytic performance in an air electrode. The surface area of the final powder depends on the thermal treatment and the surface area increases with increasing the cooling rate. A sample quenched rapidly from 650°C had a surface area of 33 m²/g, which is more than double the value obtained with a slower cooling rate. Polytetrafluorene-ethylene (PTFE) bonded gas diffusion electrodes loaded with La_0.6Ca_0.4CoO₃ catalysts prepared by the ACP method show good bifunctional performance. An electrode loaded with only 10 mg/cm² of powder prepared by quenching from 650°C showed the best bifunctional performance, i.e., 280 mA/cm² for oxygen reduction and 300 mA/cm³ for the oxygen evolution, at 0.6 and 1.6 V vs. RHE, respectively. This performance compares well with results from lower area La_0.6Ca_0.4CoO₃ at much higher loadings.