Dopant-Induced Defect Engineering in Transition Metal Oxide/Chalcogenide-Based Electrodes for High-Performance Supercapacitors: A Critical Review

The quest for cutting-edge materials for sustainable energy technology, particularly for fabricating supercapacitors (SCs), has spiked in recent years due to the global intent to promote electric vehicles. With increasing energy consumption and environmental concerns, many green and renewable energy materials have been developed for high-energy-density SCs. Transition metal oxides/chalcogenides (TMOCs) are preferred candidates as electrode materials in terms of multiple redox centers, high conductivity, and noticeable cycle life. However, balancing high energy density along with electrochemical stability is very challenging to achieve in TMOCs, and hence, suitable tailoring of the materials is required. Defect engineering/modification via doping of foreign agents, particularly transition metal ions, has tremendously improved the performance of TMOC-based SC devices. The doping of transition metal ions into metal chalcogenides creates lattice distortions and point defects, thereby offering advantages like increased surface area, redox-active sites, ion-diffusion kinetics, electrical conductivity, specific capacitance, and cyclic stability. Thus, a succinct yet detailed understanding of the recent developments in dopant-induced enhancement in the supercapacitor performance of TMOC-based materials has been presented in a review article for the first time. This perspective underlines the basic understanding of charge-storage mechanisms, the effect/mechanism of doping on the physicochemical/structural properties (morphology, electrical conductivity, porosity, and point defects) of TMOC nanoarchitecture, and recent advances in the performance of doped TMOC-based SC electrodes. A focus on the state-of-the-art research related to the mechanism and role of dopants in enhancing the supercapacitor performance of TMOCs-based electrodes has been provided, and challenges have been highlighted.