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An amorphous carbon nitride/NiO/CoN-based composite: a highly efficient nonprecious electrode for supercapacitors and the oxygen evolution reaction.

Due to their features of low cost, good corrosion resistance and environmental friendliness, transition metal oxides/nitrides are among the most promising materials for energy storage and conversion. Meanwhile, graphitic carbon nitride is a non-metallic polymer that has been widely used in the environmental and energy conversion fields due to its abundant precursor species and simple process of synthesis. In this study, an amorphous carbon nitride/NiO/CoN-based composite (Ni-Co-CN) is in situ fabricated via simple one-step pyrolysis; it displays high capacitive performance and efficient electrocatalytic capability for the oxygen evolution reaction (OER). Specifically, the optimized Ni-Co-CN electrode shows an ultra-high areal specific capacitance of 18.8 F cm-2 at 2 mA cm-2 in 3 M KOH electrolyte, and it retains 91.4% of its areal specific capacitance even after 10 000 cycles of CV scans. Upon being used as an electrocatalyst in the OER process, the overpotential of Ni-Co-CN can reach 195 mV versus a reference hydrogen electrode (RHE) at 10 mA cm-2, which is far lower than those of most reported Ni/Co-based catalysts. Additionally, the potential loss of Ni-Co-CN electrode is less than 1% after a long-term durability test over 60 h. The experimental results integrated with density functional theoretical calculations reveal that the excellent performance of the Ni-Co-CN self-supported electrode can be ascribed to the fast redox reduction of multi-valent transition metal ions, abundant surface defects and plentiful nano-scaled porous structures. This work provides a promising strategy for exploring methods to combine economic Ni/Co-based compounds with carbon-based materials to obtain low-cost yet efficient electrode materials for electrochemical energy storage and conversion.