Modulating Iridium Coordination to Control the Oxygen Evolution Reaction Pathway

Tailoring the coordination number of active sites can potentially shift the oxygen evolution reaction (OER) pathway from the traditional adsorbate evolution mechanism (AEM) to the highly active lattice oxygen mechanism (LOM), but effective synthesis approaches are lacking. Herein, we demonstrate a phase transformation strategy to precisely engineer the coordination modes of Ir loaded in zeolitic imidazolate frameworks (ZIFs), which are subsequently converted into two Ir-doped Co₃O₄ with distinct coordination numbers of Ir (Ir₁O_<i>x</i>-Co₃O₄, <i>x</i> = 4, 6) via air calcination. Comprehensive studies reveal that Ir₁O₆-Co₃O₄, featuring a higher Ir-O coordination number, intensifies the Ir-O covalency, activates the lattice oxygen participation, and reduces the thermodynamic barrier following a dual-metal-site lattice oxygen mechanism (DMSM-LOM), while Ir₁O₄-Co₃O₄ adheres to the AEM pathway. Consequently, Ir₁O₆-Co₃O₄ exhibits a low overpotential of 253 mV at 10 mA cm^-2 and superior stability over 200 h, with mass activity approximately 3.4 and 17.3 times greater than those of Ir₁O₄-Co₃O₄ and commercial IrO₂, respectively. This work not only provides a synthetic strategy for precise coordination number engineering of active sites but also establishes a direct correlation between the coordination environment and the reaction pathway, offering new insights into the rational design of high-performance OER catalysts.