Synergistic High-Entropy and Magnetic Spin Engineering in FeCoNiCrMo Oxide Nanofibers for Efficient Water Splitting.

High-entropy spinel oxides (HEOs) offer a promising route to overcome the kinetic bottleneck of the oxygen evolution reaction (OER) through synergistic multi‑metal interactions, lattice distortion, and tailored electronic structures. Here, the fabrication of a quinary FeCoNiCrMo spinel oxide nanofiber via electrospinning and controlled calcination is reported. Incorporation of Mo serves to modulate the local crystal field and electronic spin states, while application of an external magnetic field enhances spin polarization of reaction intermediates, lowering the energy barrier for triplet O₂ formation. The optimized HEO exhibits an overpotential of 240 mV at 10 mA cm^{- 2} and a Tafel slope of 45 mV·dec^-1 under a 400 mT magnetic field, outperforming most reported high‑entropy catalysts. Density functional theory (DFT) and in situ Raman spectroscopy reveal that magnetic-field-assisted spin filtering accelerates O─O bond formation via a spin‑aligned dual‑site mechanism. Assembling HEO with Pt/C in a two‑electrode electrolyzer achieves overall water splitting at 10 mA·cm^-2 with a cell voltage of 1.565 V and near 100% Faradaic efficiency. This work demonstrates the powerful synergy of high‑entropy design and magnetic spin control, offering a fresh strategy for high‑performance water‑splitting electrocatalysts.