Supercapacitors have acquired a considerable scientific and technological position in the energy storage field owing to their compelling power capability, good energy density, excellent cycling stability, and ideal safety. The supercapacitor is the burgeoning candidate to cope with the ever-growing need for green and renewable energy. High-performance supercapacitors are realized by nanostructured electrode designs, which provide ameliorated surface area for abundant electrode-electrolyte interaction, ease of electron transfer and movement, and short ion-diffusion pathways that lead to increased performance. In this regard, transition metal oxide (TMO)-based electroactive materials are of significant interest owing to the remarkable combination of structural, mechanical, electrical, and electrochemical properties. Besides their high specific capacitance and energy density due to rich redox chemistry, highly reversible and fast charge-discharge processes, low cost due to abundance, and environmentfriendliness make them the most promising materials for next-generation supercapacitors. But poor electrical conductivity and rate capability, inferior cycling life, and low power density are some of the major challenges that need to be addressed. Therefore, various nanostructures of pristine TMOs and their composites with other materials with complementary characteristics have been fabricated and investigated to realize supercapacitors with improved performance.This review summarizes all such reported pristine TMOs with different nanostructured dimensions namely, 3D, 2D, 1D, and 0D, and their composite structures for their application as electrode materials in supercapacitors. Design of different pristine and composite nanostructures, synthesis strategies, comprehensive structure-dependent electrochemical properties, present challenges, and future perspectives are reviewed.

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Pseudocapacitive asymmetric supercapacitors (ASCs) have captivated huge attention in electrochemical energy storage applications owing to their wide operating voltage window and high energy/power densities as compared to carbon-based double layer...

Synthesis of partially carbonized tungsten oxide employing a simple, one-step, and scalable in-situ reduction/carbonization process is reported along with its electrochemical performance as electrode material in an asymmetric supercapacitor. The synthesis produces a WO 2 /W 2 C composite where the carbide part is introduced to enhance the electronic conductivity of redox-active tungsten oxide. Electrochemical performance and charge storage mechanism of WO 2 /W 2 C heterostructure is elucidated in detail. The electrode material exhibits compelling areal capacitance within −0.3 to −1 V window in half-cell configuration. Notably, both surface-controlled and diffusion-controlled processes govern the charge storage behavior, with the former dominating at higher scan rates. An asymmetric supercapacitor assembled with WO 2 /W 2 C composite as a negative electrode and activated charcoal (AC) as a positive electrode exhibits good cycling stability within a stable voltage window of 0.2 to 1.4 V and could deliver an energy density of 0.6 mWh/cm 3 at a power density of 9 mW/cm 3 in aqueous electrolyte. This study thus provides a fundamental understanding of the charge storage mechanism in WO 2 /W 2 C composite electrode which is required for realizing futuristic energy storage devices with low cost but efficient electroactive materials.