Cost-effective bifunctional perovskite-carbon composite for the oxygen evolution and the oxygen reduction in alkaline environment

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are very important processes in different energy conversion devices such as fuel cells, electrolysers, unitized reversible fuel cells and metal-air batteries. In particular, in the latter two systems, both reactions occur on the same electrode during the charge and discharge processes. Such an electrode is called "bi-functional" oxygen electrode and should contain good electro-catalysts for both the oxidation and reduction reactions of oxygen. Furthermore, this electrode should be chemically stable over the wide range of potentials experienced during both processes. Although noble metal catalysts have proved to be effective as oxygen-electrode [1], the high costs and limited reserves in the world hinder their practical application. Recently developed perovskites have shown better activities for OER in alkaline medium of the catalysts based on noble metals. The ORR is the limiting step for this class of non-noble-metals [2-4]. In the present work, a perovskite, namely La0.6Sr0.4Fe0.8Co0.2O3 (LSFCO) was mixed with a carbon material and investigated for operation as both oxygen reduction (ORR) and oxygen evolution (OER) catalyst. The catalyst was investigated in half-cell by using a three-electrode configuration, in alkaline solution at ambient temperature, and compared to a Pd/C catalyst. LSFCO was less active for the ORR, while the performance for the OER was better compared to Pd. In order to get information on the stability, oxygen evolution polarizations were carried out up to 2 V vs. RHE. This may be considered an accelerated stress test since a high electrochemical potential promotes electrocatalyst degradation. The LSFCO-based catalyst showed a more stable behaviour compared to the noble metal catalyst.