Boron-Doped NiCoCuMoMn High-Entropy Alloys for Enhanced Electrocatalytic Water Splitting: An Experimental and Computational Study.

High-entropy alloys offer a versatile platform for electrocatalysis, yet their optimization has so far been dominated by transition-metal compositional tuning. Here, we present the first demonstration of boron doping as a powerful nonmetal strategy to engineer high-entropy alloys for water splitting. Incorporating boron into NiCoCuMoMn HEAs drives a dramatic increase in the BCC phase fraction, refines crystallite sizes from the nanometer to subnanometer scale, and induces lattice distortions that create quasi-vacancy active sites. These unique structural modulations, validated by X-ray diffraction, Raman spectroscopy, and electron microscopy, are corroborated by first-principles calculations, showing that substitutional boron lowers oxygen adsorption energies and accelerates oxygen evolution reaction kinetics. As a result, the boron-doped HEA exhibits a breakthrough reduction in the oxygen evolution reaction overpotential (from 300 to 200 mV at 10 mA cm-2) and a sharp decrease in the Tafel slope (from 185 to 110 mV dec-1) while maintaining long-term stability over 48 h. Although the hydrogen evolution activity is moderately suppressed, this trade-off further confirms the boron-induced modulation of surface energetics. This combined experimental and theoretical study establishes boron doping as a design strategy for high-entropy alloy electrocatalysts, providing mechanistic evidence that nonmetal incorporation can rival metal compositional tuning in dictating catalytic performance.