Contrasting Pr1–xCaxMnO3 OER Catalysts with Different Valences and Covalences

Abstract

Perovskite oxides are promising materials for catalyzing the oxygen evolution reaction (OER). However, understanding the properties of active sites that enable high OER activity without corrosive electrode reduction is still elusive. In this work, we use combined electrochemical and environmental transmission electron microscopy (ETEM) studies to compare the OER stability of the (001) surfaces of Pr1–xCaxMnO3 perovskite films with doping of x = 0.1 and x = 0.33. Notably, electrochemical analysis in alkaline conditions, as well as ETEM studies in H2O vapor, shows parallel trends in the stability of both systems: Mn leaching for the Pr1–xCaxMnO3 (PCMO) x = 0.33 system due to oxygen vacancy formation at the surface and higher stability of PCMO x = 0.1, where the oxygen vacancy redox peak is absent in cyclovoltammetry. Electron energy loss spectroscopy reveals the preservation of the Mn valence state in H2O for the PCMO x = 0.1 system, whereas for x = 0.33, Mn is reduced. We interpret this enhanced stability for the low-doped system in terms of a modified Mn 3d–O 2p hybridization, i.e., covalence. For a system with charge localization due to Jahn–Teller polarons, the covalence determines to what degree redox processes of lattice oxygen can arise that can finally lead to corrosive oxygen vacancy formation.