Crystalline–Amorphous\nIrO<sub><i>x</i></sub> Supported on Perovskite Nanotubes\nfor pH-Universal OER

Designing\ncatalysts with desirable oxygen evolution reaction (OER)\nperformance under pH-universal conditions is of great significance\nto promote the development of hydrogen production. Herein, we successfully\nsynthesized a crystalline–amorphous IrO<sub><i>x</i></sub> supported on perovskite oxide nanotubes to obtain IrO<sub><i>x</i></sub>@La<sub>0.6</sub>Ca<sub>0.4</sub>Fe<sub>0.8</sub>Ni<sub>0.2</sub>O<sub>3</sub> with superior OER performance in whole\npH media. The overpotential of the IrO<sub><i>x</i></sub>@La<sub>0.6</sub>Ca<sub>0.4</sub>Fe<sub>0.8</sub>Ni<sub>0.2</sub>O<sub>3</sub> catalyst in media of pH 14, 7.2, and 1 has been demonstrated\nto be 120, 400, and 143 mV, respectively, with no significant element\ndissolution as well as double-layer capacitance decay after the durability\ntest. Through comparative experiments with IrO<sub><i>x</i></sub>@CNT and the physical mixture of IrO<sub><i>x</i></sub> and La<sub>0.6</sub>Ca<sub>0.4</sub>Fe<sub>0.8</sub>Ni<sub>0.2</sub>O<sub>3</sub>, it is found that the strong metal–support\ninteraction (SMSI) in IrO<sub><i>x</i></sub>@La<sub>0.6</sub>Ca<sub>0.4</sub>Fe<sub>0.8</sub>Ni<sub>0.2</sub>O<sub>3</sub> makes\nIrO<sub><i>x</i></sub> exist in an amorphous state rich\nin Ir<sup>3+</sup>, which is closely associated with the surface-active\nspecies Ir-OH. Through the regulation of Ir by a perovskite oxide\nsupport at the heterointerface, the reaction breaks through the limitation\nof the adsorbate evolution mechanism (AEM) and converts to a lattice-oxygen-mediated\nmechanism (LOM), which was fully demonstrated by the addition of the\nprobe tetramethylammonium cation (TMA<sup>+</sup>), a LOM reaction\nintermediate, to the electrolyte. This work fills the research gap\nof perovskite oxide supported Ir-based catalysts with heterogeneous\nstructures, providing an excellent strategy for the structural design\nof efficient pH-universal OER catalysts for hydrogen production systems.