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 (Ir1Ox-Co3O4, x = 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.