Visual electron orbital engineering enables industrially durable acidic OER on Ir_xCo_0.3-xRu_0.7O₂

Proton exchange membrane water electrolysis (PEMWE) can produce green hydrogen at scale but is limited by the slow and corrosive oxygen evolution reaction (OER). RuO₂ catalysts are highly active but degrade quickly under industrial current densities (1 A cm^-2). The role of orbital evolution in balancing activity and stability remains unclear. Here, we directly visualize orbital evolution in Ir_xCo_0.3-xRu_0.7O₂ catalysts using combined ultraviolet and inverse photoemission spectroscopy (UPS/IPES), correlated with in-situ Raman and X-ray photoelectron spectroscopy (XPS). We find that Co acts as an electronic buffer, withdrawing electrons from Ru and donating them to Ir. This "bidirectional electronic buffering" broadens the d-band and downshifts the O 2p orbitals, optimizing charge delocalization and M-O covalency. Such orbital modulation keeps Ru in a high-valence state, maintaining its catalytic activity, while also preventing lattice over-oxidation, ensuring structural stability. As a result, the catalyst delivers 1 A cm^-2 at 1.63 V and remains stable for over 168 h in 0.5 M H₂SO₄. This demonstrates a direct link between orbital evolution and catalyst durability.