Designing next-generation electrocatalysts requires understanding atomic-scale transformations, dynamic surface chemistry under operating conditions, and the electronic and magnetic properties of correlated oxides—key materials for the oxygen evolution reaction (OER). However, electrochemical interfaces are complex and evolve dynamically, complicating predictive design.

This talk will show how epitaxial spinel and perovskite oxide thin films serve as well-defined model systems to separate intrinsic catalytic behavior from extrinsic effects. Their single-crystalline nature, controlled surface termination, and tunable electronic structure enable systematic studies of structure–property relationships and surface transformations under electrochemical conditions.

Using operando X-ray photoelectron and X-ray absorption spectroscopy, we reveal how surface reconstructions govern the active phase during OER. In LaNiO₃ thin films, Ni-rich facets reconstruct into catalytically active hydroxide-type layers that dominate reactivity. In high-entropy perovskites such as LaCr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2O_3−δ, synergistic cation interactions stabilize mixed-valent surface states correlated with enhanced performance.

Epitaxial heterostructures further enable isolation of relevant effects in spin-enhanced catalysis. We show that previously reported magnetic-field-induced OER enhancements arise from extrinsic current redistribution due to magnetoresistance, not intrinsic spin-catalytic coupling. This distinction underscores the necessity of controlled thin film systems for accurate mechanistic insight.

At the same time, operando studies reveal that ferromagnetic order can intrinsically enhance OER activity independent of applied fields, clarifying conflicting reports: external fields do not intrinsically improve activity, but internal magnetic order genuinely tunes surface reactivity.

Together, these findings establish a framework for spin-augmented catalyst design and highlight how operando spectroscopy with epitaxial model systems provides unique insight into surface reconstructions, charge transfer, and magnetic effects, enabling rational strategies for complex oxide electrocatalysts.

Dr. Christoph Baeumer

Universiteit Twente

Appearances