Two-dimensional chromium boride MBenes with high HER catalytic activity

•MBene of multiple atomic layers were reported for the first time.•Crn+1B2n exhibit thickness-dependent Young’s module and HER catalytic activity.•There are many HER catalytic active sites on the surfaces of Crn+1B2n.•The HER catalytic overpotential of Cr4B6 is only 3 mV at H coverage of 1 monolayer. Facing the increasing demands of clean energy, searching low-cost and highly active catalysts of hydrogen evolution reactions (HER) has emerged as a major task. Herein on the basis of density functional theory calculations, we reported that a series of Cr-based MBenes of different atomic-layer thickness (referring to 2D transition metal borides), Crn+1B2n (n = 1–3), exhibit superior electrocatalytic performance towards HER. They are highly stable, mechanical anisotropic and intrinsic ferromagnetic conductive systems. Furthermore, we found that they show thickness-dependent mechanical properties and HER catalytic activity. Especially, Cr4B6 exhibits quite high Young’s module of 335 N/m (comparable to 342 N/m of graphene) and 247 N/m along x and y axes, respectively. More importantly, Cr4B6 is identified as a superior HER electrocatalyst with overpotential of only 0.003 V at H coverage of 1 monolayer (ML), which is a promising alternative of Pt catalyst.