Diffusion-dominated redox performance of hydrated copper molybdate for high-performance energy storage†

Abstract

The development of cost-effective metal molybdates with enhanced energy storage capabilities has garnered significant attention as promising redox-active electrodes for asymmetric supercapacitors (ASCs). In this work, we synthesized binder-free copper molybdate (CMO) nanostructures on nickel foam using a simple hydrothermal process and thoroughly investigated their structural and electrochemical properties. The resulting CMO nanostructures exhibited a hybrid nanosheet–nanoplate morphology with a layered structure, providing an increased electroactive surface area. The structural integrity and elemental composition were confirmed using X-ray diffraction, X-ray photoelectron and X-ray (EDX) spectroscopy, showing a homogeneous distribution of copper, molybdenum, and oxygen elements. Electrochemical analysis showed that the hydrated CMO (CMO_BH) electrode provides higher specific capacitance and redox behavior than the thermally treated CMO (CMO_AH) electrode. The higher performance is attributed to the superior conductivity of CMO_BH and the presence of hydroxyl groups, which enhance redox-type charge storage. Moreover, the ASC device fabricated using the hydrated CMO_BH and activated carbon electrodes achieved a high operating voltage of 1.6 V with a maximum specific capacitance of 142.1 F g⁻¹ at 1 A g⁻¹, an energy density of 48.6 W h kg⁻¹ and a power density of 12.5 kW kg⁻¹, respectively. Additionally, the device demonstrated excellent cycling stability, retaining 89.1% of its capacitance after 10 000 cycles. The ASCs also successfully powered light-emitting diodes, emphasizing their potential for practical energy storage applications.