Mini-Review on Understanding and Building MXene-Based Materials for Supercapacitors

MXenes, a fast-expanding class of two-dimensional transition-metal carbides, carbonitrides, and nitrides, have become central to the development of next-generation supercapacitors due to their metallic conductivity, rich surface terminations, and highly tunable interlayer chemistry. This mini-review provides an updated synthesis of the rapidly evolving landscape of MXene research, emphasizing how synthesis routes, surface chemistry, and structural engineering dictate charge-storage mechanisms and guide material development. We summarize recent advances in HF-free, molten-salt, electrochemical, hydrothermal, and microwave-assisted synthesis, highlighting how emerging routes imprint distinct terminations, crystallinity, and interlayer architectures that directly shape the electrochemical behavior. Building on these structural foundations, we discuss representative progress on intrinsic charge-storage mechanisms, including proton-intercalation pseudocapacitance, termination-regulated redox reactions, dielectric-assisted charge injection, and interfacial multielectron processes and show how these mechanistic insights feed back into the rational development of MXenes such as Janus designs, heteroatom engineering, vertically aligned frameworks, and high-temperature-resistant interlayer chemistry. By integrating synthesis–structure–mechanism relationships, this review aims to provide a coherent roadmap for designing MXene-based electrodes with balanced capacitance, rate performance, cycling stability, and environmental robustness, thereby accelerating their transition toward practical supercapacitor technologies.