Ambipolar Nature Accelerates Dual-Functionality on Ni/Ni₃N@NC for Simultaneous Hydrogen and Oxygen Evolution in Electrochemical Water Splitting System

Metal nitrides with extraordinary electrochemical characteristics established widespread applications in energy devices. Inspired by the recent research on promising heterostructured catalysts, the preparation of a nitride-based heterostructure via a facile approach involving a one-step nitridation process is revisited. An innovative Ni/Ni₃N is decorated on nitrogen-doped carbon (NC) and evaluated for its dual-functionality as a catalyst in the electrochemical hydrogen evolution reaction (EHER) and the electrochemical oxygen evolution reaction (EOER). In contrast to Ni@NC and pristine NC, Ni/Ni₃N@NC with the well-constructed NC significantly enhanced its catalytic performance toward EHER and EOER in a water electrolyzer. The water electrolyzer consists of Ni/Ni₃N@NC as both the anode and cathode achieve a current density of 10 mA cm⁻² with a remarkably low voltage of 1.52 V. The designed catalyst takes full advantage of its heterostructure and ambipolar behavior leading to the presence of active sites for EOER and EHER, as confirmed by in-situ Raman analysis. These results provide important guidance on designing an efficient and cost-effective heterostructured dual-functional catalyst as well as revealing the mechanism at the interface between the surface of an ambipolar catalyst and electrolyte.