Enhanced Oxygen Evolution in RuO2 Thin Films by Exchange-Coupling-Assisted Altermagnetic Domain Ordering.

Efficient water electrolysis is central to renewable energy storage but remains limited by the sluggish oxygen evolution reaction (OER). Among state-of-the-art catalysts, rutile RuO2 delivers exceptional activity yet suffers from instability and poorly explored spin effects. Here, we demonstrate OER enhancement in altermagnetic RuO2 by interfacial spin pinning from an epitaxial ferromagnetic La2CoO4 layer. Structural microscopy and X-ray photoelectron spectroscopy reveal a chemically sharp, electronically invariant interface, ensuring that performance gains arise from magnetic effects rather than surface chemistry. Field cooling imprints exchange bias and remanent magnetization across the heterostructure, enforcing a pinned antiferromagnetic order in the RuO2 surface without the need for external fields during the catalytic process. The resulting spin polarization lowers spin-selection barriers for O-O coupling and suppresses domain wall scattering, yielding enhanced OER performance, reduced charge transfer resistance, and markedly improved durability. First-principles calculations uncover altermagnetic spin splitting in RuO2, establishing interfacial spin engineering as a powerful and composition-independent lever for tuning antiferromagnetic catalysts, opening a new frontier for magnetically regulated electrocatalysis.