Orientation-Dependent Oxygen Evolution Activity of Epitaxial Ruddlesden–Popper Pr0.5Ca1.5MnO4 Thin Films

Studying the oxygen evolution reaction (OER) on anisotropic perovskite oxides with different surface orientations improves our understanding of how surface structure, chemistry, catalytic stability, and activity are related. Here, we present a comparative electrochemical study of (001)- and (010)-oriented epitaxial thin films of Ruddlesden–Popper (n = 1) Pr0.5Ca1.5MnO4 (RP-PCMO) grown on Nb:SrTiO3 (STNO) substrates of different orientations with using buffer layers. The results on epitaxial films are compared with those of the RP-PCMO powder. The OER activity and stability are studied using cyclic voltammetry and rotating ring disk electrodes under alkaline conditions. In addition, an analysis of their surface structure and chemistry by AFM and XPS before and after electrochemical measurements was carried out. The RP-PCMO powder shows high stability during electrochemical cycling. In contrast, the two differently oriented thin films are both corroding, while the (010)-oriented films reveal a higher activity and stability than the (001)-oriented ones. The variation in electrochemical activity and stability of the polycrystalline and single-crystalline RP-PCMO electrodes of different orientations is related to their different surface chemistry. In particular, it depends on the different Mn/Pr/Ca ratios and their different rates of Ca leaching, which is governed by the orientation-dependent Ca hydroxide surface concentration.