Activating electrocatalytic hydrogen evolution performance of two-dimensional MSi2N4(M=Mo,W) : A …

Very recently, a type of two-dimensional $(2D)$ crystals, $M{\mathrm{Si}}_{2}{\mathrm{N}}_{4}(M=\mathrm{Mo},\mathrm{W})$, has been successfully synthesized in experiment [Y.-L. Hong et al., Science 369, 670 (2020)]. Here, using first-principles calculations, we systematically investigate the potential of two-dimensional $(2D)$ $\mathrm{M}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ as hydrogen evolution reaction (HER) catalysts, and propose two effective ways to trigger their HER activity. Our computations reveal that while the metal vacancies cannot activate the inertia planes for HER, $2D$ $\mathrm{M}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ with $N$ vacancy exhibits excellent HER performance. Especially for $2D$ $\mathrm{W}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$, the introduction of $N$ vacancy can yield an ideal value of hydrogen adsorption Gibbs free energy $(\mathrm{\ensuremath{\Delta}}{G}_{{\mathrm{H}}^{*}}=\ensuremath{-}0.02\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$, even superior to that of Pt $(\mathrm{\ensuremath{\Delta}}{G}_{{\mathrm{H}}^{*}}=\ensuremath{-}0.09\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$. Moreover, by high-throughput screening of $3d$, $4d$, and $5d$ transition metals, we find that introducing V/Fe/Nb/Tc/Ta atom into $2D$ $\mathrm{M}{\mathrm{Si}}_{2}{\mathrm{N}}_{4}$ can significantly trigger their HER activity. The underlying physics are discussed in detail. Our work not only highlights a family of potential HER electrocatalysts, but also provides feasible strategies for triggering their HER activity.