Efficient Z -scheme photocatalytic hydrogen production from overall water splitting by M A 2 Z 4 / X Se 2 ( M  =  Zn , Cd , Hg ; A  =  Al , Ga , In ; Z  =  S , Se , Te ; X  =  Ti , Zr , Hf ) heterostructures

To identify optimal catalysts for efficient Z-scheme photocatalytic water splitting for hydrogen production, we explore 69 heterostructures of $M{A}_{2}{Z}_{4}/X{\mathrm{Se}}_{2}$ (M = $\mathrm{Zn}$, $\mathrm{Cd}$, $\mathrm{Hg}$; A = $\mathrm{Al},\phantom{\rule{0.1em}{0ex}}\mathrm{Ga},\phantom{\rule{0.1em}{0ex}}\mathrm{In}$; Z = $\mathrm{S},\phantom{\rule{0.1em}{0ex}}\mathrm{Se},\phantom{\rule{0.1em}{0ex}}\mathrm{Te}$; X = $\mathrm{Ti},\phantom{\rule{0.1em}{0ex}}\mathrm{Zr},\phantom{\rule{0.1em}{0ex}}\mathrm{Hf}$). After confirming the stability of these fully optimized structures, we identify six heterostructures with solar-to-hydrogen efficiency (${\ensuremath{\eta}}_{\mathrm{STH}}^{\mathrm{\ensuremath{'}}}$) ranging from 32.12% to a maximum of 40.63%. Nonadiabatic molecular dynamics simulations reveal that ${\mathrm{Zn}\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}/{\mathrm{Zr}\mathrm{Se}}_{2}$ and ${\mathrm{Zn}\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}/{\mathrm{Hf}\mathrm{Se}}_{2}$ exhibit slower electron transfer for the hydrogen evolution reaction (HER) and hole transfer for the oxygen evolution reaction (OER), suggesting enhanced stability in their reduction and oxidation processes. Additionally, ${\mathrm{Cd}\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}/{\mathrm{Ti}\mathrm{Se}}_{2}$ shows the shortest interlayer electron-hole (e-h) recombination time, indicating superior photocatalytic efficiency. Notably, Gibbs free energy calculations confirm that both HER and OER in ${\mathrm{Cd}\mathrm{In}}_{2}{\mathrm{Se}}_{4}/{\mathrm{Ti}\mathrm{Se}}_{2}$ and ${\mathrm{Hg}\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}/{\mathrm{Zr}\mathrm{Se}}_{2}$ can proceed spontaneously, highlighting their potential as efficient photocatalysts. The analysis indicates that the identified heterostructures, particularly ${\mathrm{Cd}\mathrm{Ga}}_{2}{\mathrm{Se}}_{4}/{\mathrm{Ti}\mathrm{Se}}_{2}$, hold significant promise for Z-scheme water splitting, offering a viable pathway for the development of $M{A}_{2}{Z}_{4}$-based materials in hydrogen production applications.