Oxygen-Vacancy-Mediated Dynamic Bidirectional Oxygen Migration for Enhanced Acidic Oxygen Evolution Reaction

Achieving low iridium (Ir) loading and long-term stability of the membrane electrode assembly remains a major challenge in proton exchange membrane water electrolysis (PEMWE). Here, an Ir-based catalyst supported on titanium oxide (IrO_x@E-TiO_x) is synthesized through one-step transformation of Ir species anchored on an expanded Ti₃C₂T_x MXene (E-MXene) template. The uniform dispersion of IrO_x enables optimal Ir utilization and the formation of an efficient conductive network, achieving a specific mass activity of 2630 ± 185 A g_Ir^-1 at 1.60 V and 852 ± 62 A g_Ir^-1 at 1.55 V (vs RHE) for the oxygen evolution reaction (OER), with an Ir loading as low as 32.5 wt %. During E-MXene oxidation, oxygen vacancy (O_v)-rich TiO_x forms in situ, promoting a reversible O_vs-mediated bidirectional oxygen migration process, as evidenced by in situ Raman spectroscopy and theoretical modeling. This dynamic migration fine-tunes the adsorption-desorption energetics of OER intermediates, enhancing both activity and stability under acidic conditions. Moreover, the porous architecture of IrO_x@E-TiO_x improves mass transport and lowers diffusion resistance in PEMWE, enabling stable operation exceeding 500 h at an Ir loading of 0.33 mg_Ir cm^-2 with a negligible decay. This study elucidates O_vs-mediated interfacial dynamics and provides a viable strategy for designing low-Ir, high-performance OER catalysts for practical PEMWEs.