Theoretical Insights into the Hydrogen Evolution Reaction on VGe 2 N 4 and NbGe 2 N 4 Monolayers.

Catalytically active sites at the basal plane of two-dimensional monolayers for hydrogen evolution reaction (HER) are important for the mass production of hydrogen. The structural, electronic, and catalytic properties of two-dimensional VGe 2 N 4 and NbGe 2 N 4 monolayers are demonstrated using the first-principles calculations. The dynamical stability is confirmed through phonon calculations, followed by computation of the electronic structure employing the hybrid functional HSE06 and PBE+ U . Here, we introduced two strategies, strain and doping, to tune their catalytic properties toward HER. Our results show that the HER activity of VGe 2 N 4 and NbGe 2 N 4 monolayers are sensitive to the applied strain. A 3% tensile strain results in the adsorption Gibbs free energy (Δ G H* ) of hydrogen for the NbGe 2 N 4 monolayer of 0.015 eV, indicating better activity than Pt (-0.09 eV). At the compressive strain of 3%, the Δ G H* value is -0.09 eV for the VGe 2 N 4 monolayer, which is comparable to that of Pt. The exchange current density for the P doping at the N site of the NbGe 2 N 4 monolayer makes it a promising electrocatalyst for HER (Δ G H* = 0.11 eV). Our findings imply the great potential of the VGe 2 N 4 and NbGe 2 N 4 monolayers as electrocatalysts for HER activity.