Abstract: Electrocatalytic water splitting provides an efficient method for the production of hydrogen. In electrocatalytic water splitting, the oxygen evolution reaction (OER) involves a kinetically sluggish four-electron transfer process, which limits the efficiency of electrocatalytic water splitting. Therefore, it is urgent to develop highly active OER catalysts to accelerate reaction kinetics. Coupling single atoms and clusters in one system is an innovative approach for developing efficient catalysts that can synergistically optimize the adsorption and configuration of intermediates and improve catalytic activity. However, research in this area is still scarce. Herein, we constructed a heterogeneous single-atom cluster system by anchoring Ir single atoms and Co clusters on the surface of Ni(OH)₂ nanosheets. Ir single atoms and Co clusters synergistically improved the catalytic activity toward the OER. Specifically, Co_nIr₁/Ni(OH)₂ required an overpotential of 255 mV at a current density of 10 mA·cm⁻², which was 60 mV and 67 mV lower than those of Co_n/Ni(OH)₂ and Ir₁/Ni(OH)₂, respectively. The turnover frequency of Co_nIr₁/Ni(OH)₂ was 0.49 s⁻¹, which was 4.9 times greater than that of Co_n/Ni(OH)₂ at an overpotential of 300 mV.