Theoretical insights into transition metal-doped borozene clusters: structural features, physicochemical and hydrogen evolution reaction properties

Borozenes represent an emerging class of planar boron-based structures analogous to aromatic hydrocarbons, attracting increasing attention due to their distinct electronic features. In this work, the fundamental properties of trianionic [TMB₇]^3- systems (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) were systematically investigated using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. The clusters show narrow HOMO-LUMO gaps (0.16–0.27 eV) indicative of high reactivity and charge transfer potential, noting that these values were obtained using the DFT-PBE functional known to underestimate the experimental band gaps. Most global minima adopt C_6v symmetry, with strong π–d interactions stabilizing the overall frameworks. Simulated absorption spectra revealed a strong visible-region activity by early and mid-transition metals trianions. Importantly, [MnB₇]^3- and [CuB₇]^3- demonstrated the most favourable thermodynamics for hydrogen evolution reaction (HER), followed by the vanadium counterpart. These insights highlight the [TMB₇]^3- series as versatile candidates for sustainable energy applications.