In situ boron-doped flower-like NiS2@NC with sulfur vacancy composites for high energy density asymmetric supercapacitors

Abstract

In response to the challenges posed by the intricate synthesis process and low conductivity of nickel-based hydroxides, a straightforward and environmentally friendly method was proposed for the preparation of B-doped α-Ni(OH)2(α-Ni(OH)2–B). Additionally, B-doped NiS2@NC composites with sulfur vacancies (B-Sv-NiS2@NC) were prepared through nitrogen-doped carbon coating and vulcanization process. The resulting B-Sv-NiS2@NC electrode materials exhibited a specific capacity of 659C g−1 under a high specific potential (ΔV) of 1.0 V vs. Hg/HgO. Asymmetric supercapacitors α-Ni(OH)2–B//YP-80 and B-Sv-NiS2@NC//YP-80 were constructed and obtain 128.45C g−1 and 199.5C g−1 specific capacity at 0.5 A g−1 and 0.7 A g−1, respectively. Meanwhile, the α-Ni(OH)2–B//YP-80 and B-Sv-NiS2@NC//YP-80 demonstrated energy densities of 30.33 Wh kg−1 and 47.1 Wh kg−1 under 1.7 V working voltage window, respectively. The cycle capacity retention rates of the two devices reached 96% (8000 cycles) and 116% (10,000 cycles). The surface pseudocapacitance mechanism and charge transfer mechanism of α-Ni(OH)2–B and B-Sv-NiS2@NC were revealed by first principles DFT. The findings of the study demonstrate that the introduction of B doping significantly augmented the adsorption of OH− and facilitated the surface redox reaction. The OH− adsorption energy increased to −1.43 eV upon the incorporation of B and Sv, indicating that the adsorption of OH− on the B-Sv-NiS2@NC surface was more stable, thereby promoting a swift electrochemical reaction. The improved electronic structure of the material, coupled with the increased number of electrochemical active sites, resulted in enhanced OH− adsorption, accelerated redox reaction, and improved charge transfer, ultimately leading to improved electrochemical performance.