Iridium nanospheres with high active site density as efficient OER electrocatalysts for proton exchange membrane water electrolyzers

Abstract

The development of iridium (Ir)-based catalysts with highly intrinsic activity remains a significant challenge for proton exchange membrane water electrolyzers (PEMWEs). The insufficient utilization of active sites still severely hinders the intrinsic activity of catalysts. Herein, we report the synthesis of an Ir nanosphere (NS) with abundant porous channels through a facile dealloying method from an IrCu alloy. The porous nanostructure generates a high density of Ir active sites and improves the turnover frequency at Ir sites, thereby effectively improving the intrinsic activity of Ir NS. Impressively, the optimized Ir-1 NS demonstrates excellent catalytic performance for the oxygen evolution reaction (OER), requiring an overpotential of 236 mV to deliver a current density of 10 mA cm⁻² and steadily operating over 500 h with negligible degradation. A PEMWE assembled with Ir-1 NS achieves a cell voltage of 1.73 V at 1 A cm⁻² and maintains robust stability with a high stability number (3.13 × 10⁵). Theoretical calculations reveal that the high-density Ir sites expose more IrO_x active centers, which significantly reduces the catalytic energy barrier and facilitates oxygen desorption from the Ir-1 NS surface, drastically enhancing both catalytic performance and stability. This work provides an effective approach for designing high-performance catalysts for PEMWEs.