Multi-d orbital and lattice distortion synergism boosting alkaline OER activity of carbon-supported IrFeCoNiMn high-entropy nanoparticles.

To address the sluggish kinetics and poor long-term stability of conventional alkaline oxygen evolution electrocatalysts, a facile one-pot oil-phase synthetic strategy is developed to modulate the elemental stoichiometry and nanoparticle size of carbon-supported IrFeCoNiMn high-entropy alloys, which enables quantitative decoupling of geometric activity enhancements originating from lattice distortion and electronic promotions derived from well-established multi-d orbital interactions for alkaline OER catalysis. XRD, TEM, STEM mapping and ICP-OES characterisation methods verify a monophase fcc solid-solution structure with a homogeneous atomic distribution of five metals and an average particle size of 5.29 nm. In 1 M KOH electrolyte, the catalyst delivers superior OER activity: an ultralow overpotential of 241 mV at 10 mA cm-2 and a small Tafel slope of 46.15 mV dec-1, with its TOF at 300 mV overpotential, 53.95 times higher than commercial IrO2. Only a slight performance attenuation is observed after 5000 CV cycles and 80 h galvanostatic electrolysis at 10 mA cm-2, and post-characterization confirms intact crystal frameworks and trivial metal leaching under this test condition. High-resolution XPS and valence band spectra validate spontaneous charge transfer from 3d transition metals to 5d Ir, generating strong d-d orbital hybridisation and tuning the d-band centre to -4.155 eV. Such electronic rearrangement optimises intermediate adsorption and reduces the energy barrier of the rate-determining step. This work clarifies the synergistic catalytic mechanism of lattice distortion and multi-d orbital coupling, providing a feasible structural design strategy for low-noble OER catalysts with promising stability under medium-term alkaline electrolysis conditions.