Boosting Acidic Overall Water Splitting via Brønsted Acid Site-Induced Bridging-Oxygen-Assisted Deprotonation

Developing efficient and stable electrocatalysts for acidic overall water splitting is essential for proton exchange membrane water electrolysis (PEMWE), yet remains a significant challenge. In this work, Ir nanoparticles are anchored onto Fe-doped MoO₂, yielding a novel material (Ir/Fe-MoO₂) with high performance for both acidic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Fe doping stabilizes the MoO₂ lattice by forming Mo─O─Fe bonds and increases the Mo valence state, effectively suppressing over-oxidation and dissolution. The formed Ir─O─Fe interfacial structures enable bidirectional electron transfer, lowering the Ir oxidation state to prevent deactivation and activating bridging oxygen as Brønsted acid sites. These sites facilitate the deprotonation of oxygenated intermediates via a bridging-oxygen-assisted deprotonation mechanism, bypassing the rate-limiting steps of conventional adsorbate evolution pathways. As a result, Ir/Fe-MoO₂ achieves ultralow OER and HER overpotential in 0.5 M H₂SO₄, and a PEMWE device employing Ir/Fe-MoO₂ as both anode and cathode requires only 1.60 V to reach 500 mA cm^-2 at 80°C and sustains this performance for 350 h. This work pioneers Brønsted acid sites in a Mo oxide-based matrix, offering a new design concept for cost-effective, highly active acidic OER and HER electrocatalysts.