Loading IrO_x Clusters on MnO₂ Boosts Acidic Water Oxidation via Metal-Support Interaction

Noble metal-based electrocatalysts are crucial for efficient acidic water oxidation to develop green hydrogen energy. However, traditional noble metal catalysts loaded on inactive substrates show limited intrinsic catalytic activity, and their large sizes have compromised the atom efficiency of these noble metals. Herein, IrO_x nanoclusters with sizes below 2 nm, displaying high atom-utilization efficiency of Ir species, were supported on a redox-active MnO₂ nanosubstrate (IrO_x/MnO₂) with different phases (α-MnO₂, δ-MnO₂, and ε-MnO₂) to explore the optimal combination. Electrochemical measurements showed that IrO_x/ε-MnO₂ had excellent OER performance with a low overpotential of 225 mV at 10 mA cm^-2 in 0.5 M H₂SO₄, superior to its counterpart, IrO_x/α-MnO₂ (242 mV) and IrO_x/δ-MnO₂ (286 mV). Moreover, it also delivered robust stability with no obvious change in operating potential at 10 mA cm^-2 during 50 h of continuous operation. Combining the XPS results and Bader charge analysis, we demonstrated that the strong metal-support interactions of IrO_x/ε-MnO₂ could effectively regulate the electronic structures of the active Ir atoms and stabilize IrO_x nanoclusters on supports to suppress their detachment, resulting in significantly enhanced catalytic activity and stability for acidic OER. DFT calculations further supported that the enhanced catalytic OER performance of IrO_x/ε-MnO₂ could be ascribed to the appropriate strength of interactions between the active Ir sites and the reaction intermediates of the potential-determining step (*O and *OOH) regulated by the redox-active substrates.