Innovating synthesis approaches in advancing electrochemical efficiency: A journey into hydrothermal and sonochemical realms

Due to the escalating enthusiasm surrounding mobile energy devices, the significance of energy storage has reached an unprecedented level. Among the various energy storage systems relying on electrochemical principles, asymmetric supercapacitors are emerged as an appealing contender due to their exceptional attributes, such as elevated energy density, power density, extensive life cycle, and rapid recharge capability. The electrochemical performance of the device significantly depends on the electrode material being utilized. So, the choice of electrode materials plays a pivotal role in augmenting its electrochemical capabilities. These materials are synthesized through diverse methods, with sonochemical and hydrothermal techniques being particularly renowned for consistently yielding high-performance electrodes. This review article explores the sonochemical and hydrothermal synthesis of metallic oxides, sulfides, and phosphates as positive electrodes and investigates their impact on morphology, stability, and electrochemical performance. Mono, binary, and ternary composites of all these have been investigated. The sonochemical method utilizes high-intensity ultrasound waves to induce unique nanostructures, while the hydrothermal method involves elevated temperature and pressure in an aqueous medium. The sonochemical method gave significant results regarding specific capacitance, energy density, power density, and stability of these materials are found to be more suitable for asymmetric super capacitors. Furthermore, it is observed that hydrothermal synthesis technique parameters such as dwell time, pressure, and temperature also changed the morphology of electrode materials and the best selection of technique parameters contributed to enhancing the performance of the electrode. However, the results, advantages, and limitations of each synthesis approach are discussed, and future research directions are proposed in the present work.