Recent advances in the syntheses and emerging applications of 2D borophene-based nanomaterials with a focus on supercapacitors

Two-dimensional (2D) nanosheets of boron, i.e. borophene, have triggered interest in progressive research as a result of the vast field of opportunities to explore, from its innovative synthetic techniques to novel properties and potential applications. It possesses exceptional tuneable properties such as mechanical flexibility, electronic and thermal conductivity, optical transparency, metallicity, anisotropy and polymorphism. This has sparked significant curiosity in the application of borophene-based materials in energy storage systems such as supercapacitors, which display high-power density with reliable energy density, fast charge/discharge kinetics and long cycle life. This review comprehensively discusses the recent progress in the different techniques for borophene synthesis (chemical vapor deposition, molecular beam epitaxy, segregation-enhanced epitaxy, van der Waals epitaxy, ultrasound-assisted liquid phase exfoliation, mechanical exfoliation, electrochemical exfoliation and modified Hummers' method) including the resultant phases, its properties (mechanical, thermal, electronic and magnetic) and potential applications of borophene/borophene composites in supercapacitors with their charge storage mechanisms. This article mainly focuses on the literature published since 2015 when the first laboratory synthesis of borophene was accomplished. Featuring over 50 articles, the present contribution offers insightful information, suggestions and discussions on the issues and challenges involved in future research in this direction.