Post-synthesis treatment effects on defect chemistry and oer activity of IrO₂/TiO₂ nanotube composites: A conductivity-accessibility descriptor approach

Developing cost-effective proton exchange membrane water electrolysis (PEMWE) catalysts requires understanding how post-synthesis treatments influence surface accessibility and electronic conductivity. We systematically investigate three post-hydrothermal washing protocols (water, HCl, HNO3) for TiO2 nanotube supports and their impact on IrO2-catalyzed oxygen evolution reaction (OER). While HCl treatment increased specific surface area (SSA, determined via the Brunauer-Emmett-Teller (BET) method) to 209.75 m2 g-1 (versus 112.42 m2 g-1 for water-washed TNT-H), water-washed IrO2/TNT-H exhibited high activity (180 mA cm2 at 1.8 V, representing a 22-fold improvement over HCl-treated counterparts (8 mA cm2)) and stability (88.3% retention after 1000 cycles). We propose the Relative Conductivity Index (RCI), a practical quantitative descriptor specifically formulated for defect-engineered TiO2-supported IrO2 catalysts, integrating surface utilization efficiency (electrochemically active surface area (ECSA) / SSA) with electronic conductivity. RCI effectively correlates with OER activity: IrO2/TNT-H achieves RCI =1.85 S cm-1 (five-fold higher than IrO2/ TNT-HC: 0.35 S cm-1), corresponding to a 22-fold higher OER current density, by optimizing both electrochemical accessibility (ECSA/SSA = 0.87) and conductivity (sigma = 2.13 & times;10-6 S cm-1). X-ray photoelectron spectroscopy (XPS) reveals that KOH treatment preserves nanotubes while introducing Ti3+ defects, which reduce Rctfrom 94.41 S2 cm2 (for untreated IrO2/TiO2) to 22 S2 cm2 (for IrO2/TNT-H). This work provides a practical support-engineering strategy for IrO2-based OER catalysts by demonstrating that the RCI metric can guide the selection of post-synthetic treatments to optimize defect density and interfacial conductivity.