(a) Schematic illustration of the fabrication process of the Ni_SA–O/Mo₂C electrocatalyst. (b, c) High-resolution transmission electron microscopy (HR-TEM) images of Ni_SA–O/Mo₂C. Insets: selected area electron diffraction (SAED) patterns. (d) Elemental mapping of Mo, Ni, O and C for an individual Ni_SA–O/Mo₂C nanosphere (inset of (c)), respectively. (e, f) Polarization curves and Tafel plots for Ni_SA–O/Mo₂C, Ni_1.5–O/Mo₂C, Ni_4.5–O/Mo₂C, and pure O/Mo₂C, commercial IrO₂ for OER (loading amount 0.74 mg cm⁻²). (g, h) Polarization curve and Tafel plots for Ni_SA–O/Mo₂C, Ni_1.5–O/Mo₂C, Ni_4.5–O/Mo₂C and pure O/Mo₂C, 20% Pt/C for HER (loading amount 0.7 mg cm⁻²). (i) The Nyquist plots of O/Mo₂C and NiSA–O/Mo₂C, Ni_1.5–O/Mo₂C, Ni_4.5–O/Mo₂C. Inset is the long-term durability of overall water splitting at a current density of 10 mA cm⁻². (j) Polarization curves of Ni_SA–O/Mo₂C||Ni_SA–O/Mo₂C and Pt/C||IrO₂ couples for overall water splitting in 1.0 M KOH (loading amount 0.74 mg cm⁻²). Adapted from Ref. [17]. Copyright 2024, Springer Nature.