Reversible perovskite electrocatalysts for oxygen reduction/oxygen evolution.

The identification of electrocatalysts mediating both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are prerequisite for the development of reversible fuel cells and rechargeable metal-air batteries. The question remains as to whether a bifunctional catalyst, or a single catalyst site, will exhibit potentials converging to +1.23 V. Transition metal-based perovskites provide tunable catalysts where site substitution can influence both ORR and OER, however substitution in the pseudo-binary phases results in an anti-correlation in ORR and OER activities. We reveal that La Mn Ni O , compositions with lanthanum A-site sub-stoichiometry exhibit reversible activity correlating with the appearance of the Mn/Mn redox couple. The Mn/Mn couple is associated with Mn co-existing with Mn in the bulk, as La is substituted by Ni at the A-site to create a mixed valent system. We also show that a direct A-site substitution by the Ca cation in La Ca Mn O perovskites also results in the creation of Mn, the appearance of the Mn/Mn redox couple, and a concomitant reversible activity. These results highlight a general strategy of optimizing oxide electrocatalysts with reversible activity.