Recent progress in hydrogenated perovskite nickelate: Mechanism, modulation, and applications

Rare-earth perovskite nickelates are prototypical strongly correlated oxides. The physical properties of these materials can be efficiently tuned via doping with small cations such as ${\mathrm{H}}^{+}$ or ${\mathrm{Li}}^{+}$. Hydrogenation induces reversible phase transitions in perovskite nickelates accompanied by a dramatic increase in electrical resistivity, enhanced visible-to-mid-infrared optical transmittance, lattice expansion, and suppression of magnetic order. These multi-field coupled responses provide a unique platform for exploring the cooperative evolution of charge, spin, orbital, and lattice degrees of freedom in strongly correlated systems, while simultaneously enabling applications in dynamic optical modulation, high-sensitivity chemical sensing, and neuromorphic computing. Despite significant progress, the microscopic mechanisms underlying electronic structure reconstruction during hydrogenation of perovskite nickelates remain incompletely understood, and a systematic overview of proton conduction kinetics and its control strategies is still lacking. This review focuses on hydrogenated perovskite nickelate thin films, summarizing the evolution of electronic structure induced by electron doping, the mechanisms and control of proton conduction, and recent advances in functional device applications, while highlighting current challenges and future perspectives.