Exploring the Supercapacitive Behavior of Hydrothermally Derived α-Ni(VO3)2·2H2O Microcrystals

In hydrated transition-metal vanadates, significantly hydrated nickel vanadate is an advanced electrode material for supercapacitor applications owing to its multivalent oxidation states and reversible Faradaic reactions. Ni(VO3)2·2H2O microcrystals were synthesized via a one-step hydrothermal process to investigate their structural, morphological, and electrochemical activities. Ni(VO3)2·2H2O is reported for the first time as an electrode material for electrochemical applications. The pure orthorhombic structure of Ni(VO3)2·2H2O (α-Ni(VO3)2·2H2O) is confirmed by XRD analysis without impurity peaks. Subsequently, FESEM micrographs and HRTEM images showed a multiscale (micro- and nanostructured) rod-like structure of the particles. The redox-active ions of nickel, coupled with multivalent vanadium ions, provide abundant oxidation states during the electrochemical reactions. α-Ni(VO3)2·2H2O microcrystals demonstrate a high specific capacity of 821.2 C g–1 at a current density of 1 A g–1. Notably, the asymmetric supercapacitor (ASC) electrode delivered an energy density of 38.2 Wh kg–1 and a power density of 876 W kg–1, while maintaining 75% capacitance retention after 5000 cycles, with 95% coulombic efficiency. The device exhibits improved energy-storage performance and good rate capability under the evaluation of various current densities. The practical applicability of the assembled α-Ni(VO3)2·2H2O//AC prototype has been demonstrated by the glowing of red (8 min) and white (6 min) LEDs at a 3.5 V operating voltage. These findings reveal that nickel vanadate dihydrate is an effective material for next-generation energy-storage supercapacitor devices.