A review of transition metal dichalcogenides for supercapacitor applications: materials, performance, and challenges

Abstract

Supercapacitors (SCs) are environmentally friendly and sustainable innovations in energy transformation and storage. SCs provide a promising solution to fossil fuel depletion on account of their impressive power density (P_d) together with durable cycling lifespan, which makes them vital for modern electronic and electrical applications. However, they still face challenges, such as enhancing energy density (E_d) values, which remain a critical issue for the SC community that needs to be comprehensively tackled to meet the growing need for clean energy technologies. Significant attention has been garnered by two-dimensional (2D) transition metal dichalcogenides (TMDs) owing to their promise as key electrode materials in SCs. The excellent surface tunability, large electrochemically active exposed surface, and elevated electrical charge transport ability featuring adjustable oxidation levels facilitate efficient energy storage through pseudo-capacitive and electrical double-layer charge storage mechanisms. This review covers SC fundamentals, key components influencing E_d, and electrochemical evaluation techniques like galvanostatic charge–discharge (GCD), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). It also provides a detailed analysis of the structural properties and synthesis routes of TMD-based electrodes, highlighting how doping, defect modulation, and composite engineering synergistically improve the electrochemical performance of TMD-based SCs. However, to fully unlock and optimise their capabilities, future research should be focused on integrating in situ characterisation, surface functionalization, and morphological engineering to enhance understanding of material behaviour. Additionally, integrating Density Functional Theory (DFT) simulations with machine learning-assisted calculations can accelerate the discovery and optimisation of high-performance materials for next-generation energy storage applications.