Porphyrin-Confined Supported Ultrasmall Ir Clusters as Oxygen Evolution Catalysts for Water Electrolysis

Metalloporphyrin ligands themselves can participate in the redox process, making them beneficial in promoting the multielectron catalytic process of the oxygen evolution reaction (OER). However, OER catalysts synthesized by traditional chemical strategies face challenges in water electrolysis. We synthesized high-performance and stable alkaline and acidic OER electrocatalysts loaded with ultrasmall iridium clusters by taking advantage of the attraction and confinement of Ir atoms by the Ir-N bonds formed by the porphyrin cavity. The N in the porphyrin cavity forms an Ir-N bond with Ir so that Ir carries a negative charge and attracts Ir atoms to form ultrasmall Ir clusters above the cavity to adjust the electronic structure of the Ir clusters. The resulting catalyst Tpyp-Ir(IrO_X) exhibits a small overpotential (242 and 259 mV) at a current density of 10 mA cm^-2 in alkaline and acidic conditions and demonstrates good long-term operational stability. In addition, Tpyp-Ir(IrO_X) exhibits a higher transition frequency (TOF) (1.69 O₂ s^-1 at 300 mV) in 1 M KOH, which is 7 times that of Ir/C.