Sodium-ion capacitors have the potential to deliver high energy, power density, and excellent cycling stability. In this study, ultrathin Co₃V₂O₈ nanosheets are successfully synthesized through an one-pot hydrothermal reaction and a subsequent doping reconfiguration-induced vacancy-forming process. Abundant oxygen vacancies and high porosity are observed in the Co₃V₂O₈ electrode and result in excellent electrochemical performance in 1 M NaOH and Na₂SO₄ electrolytes. The cathode has a large specific capacity (@NaOH), high-rate capability (@NaOH), wide voltage window (@Na₂SO₄), and favorable long-cycle stability. Ex-situ X-ray diffraction and X-ray photoelectron spectroscopy show that the Co₃V₂O₈ electrode displays a battery-like behavior related to OH⁻ ions in the alkaline NaOH electrolyte. By contrast, in the neutral Na₂SO₄ electrolyte, Co₃V₂O₈ mainly shows an intercalation/extraction behavior with Na⁺ ions. Density functional theory calculation suggests that oxygen vacancy leads to a new state located in the bandgap, which greatly improves the electron transfer efficiency and reduces the sodiation energy barrier of Co₃V₂O₈ in the neutral Na₂SO₄ electrolyte. Moreover, when paired with a high-voltage activated carbon (AC) anode, full-cell Co₃V₂O₈//Na₂SO₄//AC delivers high energy/power densities (89.6 Wh·kg⁻¹/330 W·kg⁻¹).

Ni/ZnO nano-sponges have been successfully synthesized through optimized annealing of Ni/Zn-based organic framework (Ni/Zn-MOF). The annealed MOF provides the stable carbon structure with 3D interconnection and prevents structural collapse during the charging and discharging process. The annealing causes the incorporation of intrinsic Ni³⁺ in the surface of NiO nanoparticles, providing more reaction active sites. The oxygen vacancies in ZnO and heterostructure interfaces between NiO and ZnO promote the charge transformation. Based on the aforementioned advantages, the Ni/ZnO nanocomposites exhibit excellent electrocatalytic performances for supercapacitors. The specific capacitance can reach to 807 F·g⁻¹ at 1 A·g⁻¹ in the studied electrodes. After 5, 000 cycles at 10 A·g⁻¹, the cyclic stability remains excellent at 86% of the initial capacitance. Moreover, the as-prepared asymmetric supercapacitor exhibits a high energy density of 30.6 W·h·kg⁻¹ at power density of 398 W·kg⁻¹. This study is expected to provide new insights into exploring the potential mechanism of catalyst action.