Effect of Substitutional and Interstitial Boron-Doped NiCo2S4 on the Electronic Structure and Surface Adsorption: High Rate and Long-Term Stability

The effect of substitutional and interstitial doping on the electronic structure and surface adsorption plays an important role in tuning physical and chemical properties. Herein, boron-doped NiCo2S4 (B-NiCo2S4) was designed and prepared for high rate and long-term stability supercapacitors, considering the substitutional and interstitial boron (Bsub and Bint) doping due to similar atomic size. The low conductivity and slow reaction kinetics of NiCo2S4 hampered its rate performance and weak cycle stability for energy storage devices. After boron doping, B-NiCo2S4 can promote electron transfer to improve rate performance and increase surface adsorption energy to capture the electrolyte ion due to electronegativity difference during the charge/discharge process. Furthermore, the contribution of Bsub and Bint doping modes can be elucidated by density functional theory calculations. The density of states of B-NiCo2S4 (26.7 eV–1) was much higher than that of NiCo2S4 (6.2 eV–1) near the Fermi level resulting from Bsub doping. The doping-induced charge transfer was enhanced by adjusting the position of the Fermi level. Bint doping redistributed the surface charge, resulting in increased OH– adsorption and then improved Faradaic reaction kinetics in alkaline electrolyte. This research strategy implements the research of synergistic promotion of theoretical prediction and experimental verification very well.