Vanadium-Induced Lattice Compression and Electronic Modulation in Iridium-Ruthenium Electrocatalysts Boost Acidic...

Highly active and durable electrocatalysts for acidic oxygen evolution reaction (OER) remain a central challenge for proton-exchange-membrane water electrolyzers (PEMWEs). Here, we demonstrate that incorporating vanadium into Ir-Ru alloys changes the catalytic mechanism, resulting in increased OER performance. X-ray diffraction and high-resolution transmission electron microscopy studies indicate the Ir₂₇Ru₂₀V₅₃ electrocatalyst exhibits pronounced lattice compression and shortened metal-metal bonds, which are associated with changes in d-d orbital interactions and the adsorption energetics of oxygen intermediates. Convergent evidence from the kinetic isotope effect (KIE) and kinetic probe studies using both methanol and tetramethylammonium suggests that the Ir₂₇Ru₂₀V₅₃ electrocatalyst follows predominantly a direct O-O coupling pathway, rather than the conventional lattice oxygen-mediated mechanism (LOM) or adsorbate evolution mechanism (AEM) under which Ir-Ru catalysts operate. Operando attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) captures O-O intermediates, further supporting a direct O-O coupling pathway during the OER process catalyzed by the Ir₂₇Ru₂₀V₅₃ electrocatalyst. The Ir₂₇Ru₂₀V₅₃ electrocatalyst achieves a low overpotential of 213 mV at 10 mA cm^-2 and a durability with a degradation rate of only 70 μV h^-1 at a current density of 100 mA cm^-2, determined in a PEMWE over 570 h. This work provides a design strategy for making high-performance low-Ir OER catalysts through the control of reaction mechanisms using early transition metals.