In‐Plane Chemical Ordering (Mo_2/3R_1/3)₂AlB₂ (R = Tb, Dy, Ho, Er, Tm, and Lu) i‐MAB Phases and their Two‐Dimensional Derivatives (MBene): Synthesis, Structure, Magnetic, and Supercapacitor Performance

Abstract A family of hexagonal in‐plane chemical ordering (Mo_2/3R_1/3)₂AlB₂ (R = Tb, Dy, Ho, Er, Tm, and Lu) i‐MAB phases are synthesized with R‐3m hexagonal structure. The i‐MAB phases with R = Tb to Tm are considered to have a nonlinear ferromagnetic‐like coupling magnetic ground state with gradually weakened magnetocrystalline anisotropy due to variant R‐R distances and 4f electrons. Their 2D derivatives (2D‐MBene) with rare‐earth (R) atom vacancies are obtained by chemical etching. The delamination solvent, surface functional terminations, and chemical bond of 2D‐MBene can be modified by one‐step nitridation in environment‐friendly nitrogen instead of ammonia. A phase conversion is caused by nitridation at 973 K from 2D‐MBene to Mo₂N, leading to the optimized specific capacitance of 229 F g⁻¹. Besides exploring more rare‐earth‐containing laminated boride systems, this work also demonstrates the promising application of their 2D derivatives with R vacancies in supercapacitors.