Construction of sulfur modified oxygen-deficient NiO/Ni nanoflakes as an effective electrode material for energy storage application

[Display omitted] •A strategy of creating oxygen vacancies and incorporating sulfur atoms is developed.•The introduction of oxygen vacancies and sulfur dopants into S-NiO1-x/Ni greatly improves the electrochemical properties.•The optimized S-NiO1-x/Ni as an advanced electrode exhibits excellent energy density for asymmetric supercapacitors.•The DFT calculation provides theoretical guidance on the reason for improved electrochemical performance. The inferior electronic conductivity and deficient number of electrochemical active sites of the transition metal oxides severely restrict electrode kinetics and the utilization of redox actives sites on the electrode surface, thus leading to ineffective electrochemical performance. Herein, we exhibit an effective strategy to obtain NiO/Ni nanoflakes with oxygen vacancies and sulfur dopants (S-NiO1-x/Ni) for serving as supercapacitor electrode. The incorporation of O vacancies and S dopants into NiO/Ni in concert to modulate the electronic structure and generates more accessible active sites, which improve the electrochemical conductivity and facilitates surface redox processes. Experimental and theoretical studies provide insight into the location of the introduction of O vacancy and S atom and their effects on the electrical properties of S-NiO1-x/Ni. Meanwhile, S atoms incorporation into S-NiO1-x/Ni not only involve in the redox reactions but also act as active sites. The as-obtained S-NiO1-x/Ni delivers a remarkable electrochemical behavior with a high specific capacitance of 648.4F g−1 at the current density of 1 A/g. Additionally, an asymmetric supercapacitor outfitted with the as-prepared S-NiO1-x/Ni as positive electrode and active carbon as negative electrode gives rise to an excellent energy density of 28.8 Wh kg−1 at the power density of 800 W kg−1, together with a long-term stability.