Epitaxy-boosted oxygen evolution reaction in mesostructured cobalt ferrite electrocatalysts

Although amorphous electrocatalysts generally exhibit higher oxygen evolution reaction (OER) activity than their polycrystalline counterparts, the effect of crystallinity on the OER performance of crystalline catalysts remains unclear. Herein, we present a comparative study of three mesostructured cobalt ferrite (CFO) electrocatalysts with epitaxial, textured, and polycrystalline crystallinities. By tuning the crystallography of the electrodeposition substrates, we precisely controlled the CFO crystallinity without altering other OER-relevant properties. In contrast to previous reports, we found that OER activity improved with increasing crystallinity. Notably, the mesostructured epitaxial CFO exhibited an outstanding overpotential of ~212 mV at 10 mA cm –2 and remarkable stability over 180 h, outperforming most state-of-the-art alkaline OER catalysts. This enhancement arises not only from the promoted charge migration but also from an increased proportion of highly active (100) facets, which allow selective *OOH stabilization. Our findings demonstrate the potential of epitaxial electrocatalysts as alternatives to conventional defect engineering approaches. • Crystallinity of Co x Fe 3–x O 4 controls OER activity beyond defect-driven paradigms. • Epitaxial order enhances charge migration and facet-specific catalytic behavior. • Preferential exposure of (100) facets selectively stabilizes key OER intermediates. • This work establishes a crystallographic design principle for electrocatalysis. • Our findings challenge the prevailing view that amorphous catalysts are inherently superior.