γ-MnO₂ as an Electron Reservoir for RuO₂ Oxygen Evolution Catalyst in Acidic Media

Developing highly active and durable catalysts in acid conditions remains an urgent issue due to the sluggish kinetics of oxygen evolution reaction (OER). Although RuO₂ has been a state-of-the-art commercial catalyst for OER, it encounters poor stability and high cost. In this study, the electronic reservoir regulation strategy is proposed to promote the performance of acidic water oxidation via constructing a RuO₂/MnO₂ heterostructure supported on carbon cloth (CC) (abbreviated as RuO₂/MnO₂/CC). Theoretical and experimental results reveal that MnO₂ acts as an electron reservoir for RuO₂. It facilitates electron transfer from RuO₂, enhancing its activity prior to OER, and donates electrons to RuO₂, improving its stability after OER. Consequently, RuO₂/MnO₂/CC exhibits better performance compared to commercial RuO₂, with an ultrasmall overpotential of 189 mV at 10 mA cm^-2 and no signs of deactivation even after 800 h of electrolysis in 0.5 m H₂SO₄ at 10 mA cm^-2. When applied as the anode in a proton exchange membrane water electrolyzer, the cost-efficient RuO₂/MnO₂/CC catalyst only requires a cell voltage of 1.661 V to achieve the water-splitting current of 1 A cm^-2, and the noble metal cost is as low as US$ 0.00962 cm^-2, indicating potential for practical applications.