Synthesis, Characterization, and Theoretical Modeling of 2D Molybdenum Boride (MBene) for All Solid-State Flexible Interdigitated Supercapacitor Application

Recently, two-dimensional transition metal borides (2D MBenes) have demonstrated advanced physical, mechanical, and electrochemical performance; however, there are fewer studies in the literature. In particular, 2D molybdenum boride (2D MoB), created from molybdenum aluminum boride (MoAlB, MAB phase), is one of the important materials introduced due to its thermodynamically stable structure. Herein, we present the preparation of MoAlB and its chemical exfoliation by employing NaOH and LiF-HCl etching solutions to synthesize 2D MoB MBene nanostructures. It is found that the etching conditions significantly affect the selective extraction of the interlayer Al from the MAB phase in solution, forming 2D MoB MBene nanostructures. The resulting 2D MoB MBene illustrates sheet-like morphology, abundant redox active sites, and moderate textural features, which are critical for electrolyte accumulation and transfer. Powder X-ray Diffraction (PXRD) analysis confirmed the crystallinity and phase purity, while Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) revealed the sheet-like morphology and structural integrity. X-ray Photoelectron Spectroscopy (XPS) was employed to analyze the elemental composition and oxidation states, confirming the successful removal of Al and the formation of MoB MBene. Additionally, Brunauer-Emmett-Teller (BET) surface area analysis provided insights into the porous nature and surface area, which are crucial for electrolyte interactions. The all-solid-state flexible interdigitated supercapacitor (ISSC) device prepared using 10/MoAl1-x B electrode exhibited a good areal capacitance of 20.3 mF/cm2, outstanding cyclic capability with 92% capacitance retention after 1300 cycles, and remarkable flexibility. Last but not least, the Density Functional Theory (DFT) of the optimal MoB sample was constructed in terms of structural, conductivity, and thermodynamic stability perspectives, which is well-aligned with experimental results. Applying these 2D MoB MBene electrodes as all-solid-state flexible interdigitated electrodes opens a new avenue in supercapacitor technology.