Support-tuned iridium reconstruction with crystalline phase dominating acidic oxygen evolution

The dynamic reconstruction of oxygen evolution electrocatalysts dictates their performance, yet conventional Ir-based materials face an inherent activity-stability trade-off due to surface amorphization into hydrous IrO_x phases accompanied by lattice oxygen mechanisms. Here, we uncover a distinct reconstruction pathway for supported Ir nanoparticles, where a TiO_x@Ti substrate drives a bulk phase transition from metallic Ir to crystalline rutile IrO₂ during electrocatalysis. Unlike surface-limited amorphization, this support-guided crystallization shifts the reaction mechanism from involving lattice oxygen mechanism to the complete adsorbate evolution mechanism, as confirmed by mechanistic and structural analyses. Consequently, the Ir/TiO_x@Ti catalyst achieves both high activity and durability in acidic media, demonstrated in three-electrode systems and proton exchange membrane water electrolyzers. This work redefines support roles in electrocatalyst reconstruction, demonstrating that bulk phase engineering-rather than surface modification-resolves the long-standing efficiency-durability conflict in acidic oxygen evolution.