Abstract: The most energy-inefficient step in the oxygen evolution reaction (OER), which involves a complicated four-electron transfer process, limits the efficiency of the electrochemical water splitting. Here, well-defined Ni/Co₃O₄ nanoparticles coupled with N-doped carbon hybrids (Ni/Co₃O₄@NC) were synthesized via a facile impregnation-calcination method as efficient electrocatalysts for OER in alkaline media. Notably, the impregnation of the polymer with Ni and Co ions in the first step ensured the homogeneous distribution of metals, thus guaranteeing the subsequent in situ calcination reaction, which produced well-dispersed Ni and Co₃O₄ nanoparticles. Moreover, the N-doped carbon matrix formed at high temperatures could effectively prevent the aggregation and coalescence, and regulate the electronic configuration of active species. Benefiting from the synergistic effect between the Ni, Co₃O₄, and NC species, the obtained Ni/Co₃O₄@NC hybrids exhibited enhanced OER activities and remarkable stability in an alkaline solution with a smaller overpotential of 350 mV to afford 10 mA cm^-2, lower Tafel slope of 52.27 mV dec^-1, smaller charge-transfer resistance, and higher double-layer capacitance of 25.53 mF cm^-2 compared to those of unary Co₃O₄@NC or Ni@NC metal hybrids. Therefore, this paper presents a facile strategy for designing other heteroatom-doped oxides coupled with ideal carbon materials as electrocatalysts for the OER.

Key words: Ni/Co₃O₄@NC, N-doped carbon, Electrocatalyst, Synergistic effect, Oxygen evolution reaction