Abstract: This work uses a simple Ni-metal organic framework (Ni-MOF) to generate a uniform metal-containing carbon hybrid structure of Ni/C by in-situ pyrolysis. Then, after NaBH₄ treatment and hydrothermal vulcanization of Ni/C, multiphase B-doped Ni_xS_y nanoparticles can be obtained and uniformly anchored in the carbon skeleton, forming a highly porous flower-shaped B-Ni_xS_y/C composite. The positive role of B doping was theoretically confirmed by Density Function Theory (DFT) calculations. The MOF-derived carbon framework has porous, conductive, and continuous features beneficial for fast charge transfer. There are also multiple Ni-sulfide phases in B-Ni_xS_y/C, dominated by hexagonal NiS, hexagonal Ni₂S₃, and cubic Ni₃S₄, which give rich valance state and are expected to bring active electrochemical reactions. In addition, the boronation process by the reducing agent of NaBH₄ is also proved beneficial to bring high capacitance, possibly due to the incorporation of more active sites by B. Therefore, the B-Ni_xS_y/C composite electrode delivers a high specific capacity of 1250.4 C g^-1 at 1 A g^-1 and excellent rate performance. The B-Ni_xS_y/C-based asymmetric supercapacitor also shows promising prospects for future energy storage devices, delivering high cyclability with capacitance retention of 87.6% after 7000 cycles. This work proves the efficiency of MOF-derived carbon framework and B-doping in improving metal sulfide's electrochemical performances.

Key words: B-Ni_xS_y/C, Carbon skeleton, Flower-shaped, Hybrid capacitor, Asymmetric supercapacitor