Theoretical Insights into the Hydrogen Evolution Reaction on VGe₂N₄ and NbGe₂N₄ 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 VGe₂N₄ and NbGe₂N₄ 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 VGe₂N₄ and NbGe₂N₄ monolayers are sensitive to the applied strain. A 3% tensile strain results in the adsorption Gibbs free energy (ΔG _H*) of hydrogen for the NbGe₂N₄ monolayer of 0.015 eV, indicating better activity than Pt (-0.09 eV). At the compressive strain of 3%, the ΔG _H* value is -0.09 eV for the VGe₂N₄ monolayer, which is comparable to that of Pt. The exchange current density for the P doping at the N site of the NbGe₂N₄ monolayer makes it a promising electrocatalyst for HER (ΔG _H* = 0.11 eV). Our findings imply the great potential of the VGe₂N₄ and NbGe₂N₄ monolayers as electrocatalysts for HER activity.