Charge Redistribution at NiO/Co ₃ O ₄ Junctions Activates Interfacial Iridium for Alkaline Oxygen Evolution

High Resolution Image Download MS PowerPoint Slide In oxygen evolution electrocatalysis, identifying the catalytically dominant site in oxide heterostructures remains a central challenge, particularly when activity depends nonlinearly on noble-metal loading. Here, we show that alkaline OER on Ir-modified NiO/Co 3 O 4 is maximized when Ir is incorporated into junction-rich oxide environments that promote heterointerface-directed charge redistribution. A controlled Ir-loading series reveals a sharp activity maximum at 10 wt % Ir, which delivers 10 mA cm −2 at an overpotential of 290 mV with a Tafel slope of 64 mV dec −1 in 1 M KOH, outperforming both pristine NiO/Co 3 O 4 and commercial IrO 2 under identical conditions. Independent electrochemical descriptors, including charge-transfer resistance and double-layer capacitance, converge on the same optimum, indicating a site-specific kinetic advantage rather than a simple additive Ir effect. Density functional theory attributes this behavior to work-function mismatch across the NiO/Co 3 O 4 -Ir junction, which depletes electron density at interfacial Ir sites, optimizes oxygenated-intermediate binding, and lowers the computed OER overpotential to 0.40 V relative to Ni, Co, and non-interfacial Ir reference sites. Structural and surface characterization further show that the optimum is realized when Ir remains highly dispersed and interface-proximal. These results establish heterointerface-directed electronic activation as a general strategy for maximizing OER performance with minimal Ir loading.