2D–3D-Structured Mixed-Metal Cobalt–Vanadium–Selenide (Co–V–Se) System: A Transformative Electrode Material for Supercapacitors

This study presents the development of mixed-metal cobalt–vanadium–selenide (Co–V–Se) using two-dimensional layered double hydroxide (CoV-LDH) as a self-template for supercapacitor electrodes through exploration of various selenium concentrations (CVS-x, where x = 0.5, 1, 1.5 mmol) via a two-step hydrothermal method. In addition, a directly synthesized cobalt–vanadium–selenide (CVS-D) system with an optimized Se concentration, prepared using the corresponding metal precursors, was investigated for comparison. Structural characterization using XRD and Raman spectroscopy confirmed the formation of cobalt–vanadium-based mixed-metal selenides, revealing the potential existence of a 2D–3D intergrown heterostructure with Co–Se and V–Se domains, respectively, in the system. Electron microscopy analysis showed that the LDH-derived CVS-0.5 exhibited a hollow spherical morphology, whereas the CVS-D system consisted of aggregated particles forming dense spherical structures. Electrochemical investigations demonstrated that CVS-0.5 achieved a high specific capacitance of 467.2 F g–1 at 1 A g–1, with a remarkable rate capability of 73% at 20 A g–1, which is ∼1.5- and 3-fold higher than CoV-LDH and CVS-D, respectively. Furthermore, an asymmetric supercapacitor device incorporating CVS-0.5 delivered an energy density of 46.7 Wh kg–1 and a power density of 1051.2 W kg–1, maintaining around 88.7% capacitance retention and 97% Coulombic efficiency over 10,000 charge–discharge cycles. These findings emphasize the potential of LDH as a distinctive precursor yielding mixed-metal chalcogenides with a 2D–3D heterostructure to develop promising transformative electrode materials for high-performance energy storage applications.