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

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.