A supercapacitive all-inorganic nano metal–oxide complex: a 180° super-bendable asymmetric energy storage device

Abstract

Fabricating energy storage devices in different paradigms makes them more relevant from an application point of view. Flexible supercapacitors with great specific capacitance retention with maximum possible bending angles and high specific capacitance, make flexible supercapacitor devices more suitable for real-life applications. A complementary pair of redox-active oxides, namely WO₃ and Co₃O₄, has been chosen here to study their charge storage abilities by incorporating them into a solid-state flexible device. Both the electrodes obtained using the electrodeposition method showed excellent porous morphology bearing nano-structured pores and flakes, confirmed using electron microscopy, X-ray diffraction and Raman spectroscopy. The electrochemical studies of the individual electrodes in a neutral electrolytic solution showed high-performance pseudocapacitive properties with 22.5 mF cm⁻², and 33 mF cm⁻² specific capacity of WO₃ and Co₃O₄ electrodes, respectively. Individual electrodes also show an excellent complementary redox nature. Next, a solid-state flexible device was fabricated by sandwiching the two individual electrodes, which were then tested for performance parameters of charge storage capabilities. High values of specific capacitance (66.5 mF cm⁻²), energy density (16 μW h cm⁻²), power density (4 mW cm⁻²), and coulombic efficiency portray the device's superior pseudocapacitive performance. Besides, the flexible nature of the device was checked by testing its performance at various bending angles giving 100% capacitance retention at various bending angles, thus confirming that the device can work excellently well even in a 180° bent state.