Recent advances in electrospun fibers based on transition metal oxides for supercapacitor applications: a review

Recent critical advances in energy storage technologies and progress towards the future "electric" era highlight the enormous demand for sustainable energy storage devices like batteries and supercapacitors (SCs) to meet the acute energy needs of society. SCs are more remarkable among the various technologies due to their high power density, extended life cycle, environmental friendliness, and fast charging-discharging. To further improve the performance of SC devices, tremendous research efforts are in progress, including altering the fabrication method, using advanced robust materials and intriguing engineered nanostructures, and designing new architectures. Among the widely available materials, transition metal oxides (TMOs) exhibit good performance in SC technology owing to their high specific capacitance, different oxidation states, chemical and thermal stability and economic viability. So, recent research focuses on developing multifunctional engineered nanostructures and composites of TMOs to improve the SC performance and widen their application towards wearable and healthcare devices. The nanofiber morphology is supposed to have several advantages in SC performance compared to other morphologies owing to its higher specific surface area and aspect ratio, effectively improving the adsorption and electrolyte-ion diffusion process. Electrospinning is the most efficient technique for large-scale nanofiber production in a facile approach. This review discusses the recent progress in the fabrication and electrochemical properties of various TMO-based electrospun fiber electrodes for SC applications. The fundamentals of the electrospinning technique and a basic overview, in addition to the classification of SCs, are summarised. A more detailed insight into the advantages and disadvantages of fiber SCs, with particular attention on electrospun TMO fibers, is also discussed in this review. Finally, a conclusion on different TMO-based electrospun fiber electrodes compared to bimetal TMOs is deliberated by stating the challenges and future prospects of electrospun fiber SC electrodes. Recent advances in the role of electrospun nanofibers based on transition metal oxides in advanced supercapacitor applications, its challenges and progress towards the future "zero emission electric era" are highlighted in this review.