TMB 12 : a newly designed 2D transition-metal boride for spintronics and electrochemical catalyst applications.

Exploring two-dimensional (2D) ferromagnetic materials with a high transition temperature and large magnetic anisotropy is extremely essential for highly efficient spintronic applications. With the density functional theory method, we predicted planar hypercoordinate transition-metal borides, TMB 12 (TM = Ti, V, Cr, Mn, Fe; B = boron), by the condensation of TM@B 8 and B 4 units. The results showed that these transition-metal borides possess superior thermal, dynamic and mechanical stabilities. Interestingly, the TMB 12 monolayer with TM = (V, Cr) is confirmed as a robust ferromagnetic metal with a high Curie temperature of ∼335 K and ∼221 K, respectively. In addition, the system with TM = (Mn, Fe) is found to be an antiferromagnetic metal with a Néel temperature of ∼173 K and ∼91 K, respectively. In particular, large perpendicular magnetic anisotropy is identified for CrB 12 , MnB 12 , and FeB 12 monolayers, around 198-623 μeV. Furthermore, four TMB 12 (TM = Ti, V, Cr, Mn) systems are determined to be candidate catalysts for the hydrogen evolution reaction, with nearly zero free energy of hydrogen adsorption (Δ G H = -0.0003 to -0.03 eV). Our study highlighted potential 2D metal borides for spintronic devices and high efficiency electrochemical catalysts.