Optimizing amorphous Ir^V/VI hollandite structure on oxygen-deficient titanium oxide via annealing control: A path to high-activity, low-voltage proton exchange membrane water electrolysis

Proton exchange membrane water electrolysis (PEMWE) is a promising technology for clean hydrogen production, with the oxygen evolution reaction (OER) critically determining overall efficiency. Iridium oxide remains the material of choice for OER catalysts in PEMWE. Here, we report a supported Ir^V/VIO_x catalyst synthesized via solvothermal method followed by air annealing. Operando X-ray absorption spectroscopy, pair distribution function analysis, and X-ray photoelectron spectroscopy reveal that an oxygen vacancy-rich Ti-oxide substrate facilitates the formation of a mixed Ir^V/Ir^VI hollandite-type amorphous structure upon annealing at 360 °C/2h. This unique structure endows the catalyst with exceptional OER activity in PEMWE, achieving a mass activity of 16905 A g_Ir⁻¹ and a turnover frequency of 3.2 × 10⁷ h⁻¹ at 1.74 V. The PEMWE device delivers 2 A cm⁻² and sustains water oxidation catalysis for 400 h with negligible decay, outperforming benchmark Ir-based catalysts. Prolonging annealing (>2h at 360 °C) or increasing the temperature (≥400 °C) degrades performance. This coincides with reduction of Ir^V/Ir^VI to Ir^IV, transformation of the edge-sharing octahedral hollandite amorphous structure into a corner-sharing octahedral rutile configuration, increased IrO₂ crystallinity, and reduced oxygen vacancies. These findings provide valuable insights for designing highly active supported IrO_x catalysts, advancing sustainable hydrogen production via PEMWE. © 2025 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.