Sequential Surface Synthesis of Dispersed Sub-Nanometer Iridium on Titanium Nitride for Acidic Water Oxidation

Abstract

Maximizing iridium utilization while maintaining high oxygen evolution reaction (OER) performance remains a persistent challenge in acidic water electrolysis. Immobilizing Ir on conductive, acid-stable supports is promising, yet simultaneously achieving sub-nanometer size, high areal coverage, and strong electronic coupling is difficult. Here, we report a sequential surface-synthesis on titanium nitride (TiN) that yields uniformly distributed sub-nanometer Ir arrays (~0.7 nm). Our method uses ethylenediaminetetraacetic acid (EDTA) as a temporal scaffold: it chemisorbs to TiN to install dense chelating sites, captures Ir 3+ ions, and confines Ir cluster growth. A subsequent thermal treatment at 500°C in a reducing atmosphere removes the ligand shell while preserving ultrasmall particle size and establishing direct Ir-TiN electronic coupling.The optimized catalyst exhibits mixed Ir⁰/Ir x+ coordination with low Ohmic resistance (19 Ω), delivering a mass activity of 342 A g⁻¹_Ir at 1.54 V in acidic electrolyte. In-situ X-ray absorption spectroscopy reveals irreversible surface oxidation as the primary stability-limiting factor. This stepwise strategy provides a general framework for supported catalysts that maximize precious metal utilization via sub-nanometer dispersion.