Ultrathin and Conformal Depletion Layer of Core/Shell Heterojunction Enables Efficient and Stable Acidic Water Oxidation

Ru-based electrocatalysts hold great promise for developing affordable proton exchange membrane (PEM) electrolyzers. However, the harsh acidic oxidative environment of the acidic oxygen evolution reaction (OER) often causes undesirable overoxidation of Ru active sites and subsequent serious activity loss. Here, we present an ultrathin and conformal depletion layer attached to the Schottky heterojunction of core/shell RuCo/RuCoO_x that not only maximizes the availability of active sites but also improves its durability and intrinsic activity for acidic OER. Operando synchrotron characterizations combined with theoretical calculations elucidate that the lattice strain and charge transfer induced by Schottky heterojunction substantially regulate the electronic structures of active sites, which modulates the OER pathway and suppresses the overoxidation of Ru species. Significantly, the closed core/shell architecture of the RuCo/RuCoO_x ensures the structure integrity of the Schottky heterojunction under acidic OER conditions. As a result, the core/shell RuCo/RuCoO_x Schottky heterojunction exhibits an unprecedented durability up to 250 0 h at 10 mA cm^–2 with an ultralow overpotential of ∼170 mV at 10 mA cm^–2 in 0.5 M H₂SO₄. The RuCo/RuCoO_x catalyst also demonstrates superior durability in a proton exchange membrane (PEM) electrolyzer, showcasing the potential for practical applications.