Review on Carbon Nanostructures for Supercapacitors: Cutting-Edge Energy Storage Applications and Perspectives

The advancement of energy storage technologies requires novel material design concepts to address performance, scalability, and sustainability goals. Carbon nanomaterials, with their tunable structure, large surface area, and superior conductivity, have emerged as the focus of electrochemical supercapacitor development. This review offers an in-depth and systematic discussion of carbon-based electrode materials grouped by their dimensionality, such as 0D (fullerene, activated carbon, quantum dots, onion-like carbon, and carbon nanobowl), 1D (carbon nanotubes and carbon nanofibers), 2D (graphene, graphene oxide, and reduced graphene oxide), and 3D (carbon aerogels, porous carbon, and carbon nanocages), with special emphasis on both binary and ternary carbon–carbon hybrid structures with the inclusion of more than one dimension to compensate for inherent limitations. Moreover, the dimensionality transformation concept, by which carbon materials transform from one structural dimension to another via synthetic or assembly routes, is proposed as a new design paradigm. Synthesis methodologies, structure–performance correlations, factors affecting performance, computational insights, and electrochemical benchmarking for each type are highlighted. Main challenges, future directions, and methodological advancements required for next-generation high-capacitive supercapacitor system development are also presented in the review.