  Low-dimensional transition metal dichalcogenides (TMDC) exhibit great
photocatalytic performance and tunability. In this work, using first-principles
simulations based on density functional theory (DFT), we demonstrate that
external electric bias can be employed to further improve the photocatalytic
hydrogen production efficiency of the six AB$_{2}$ (A=Mo, W and B=S, Se, Te)
TMDC monolayers by exploiting their piezoelectric response. In particular, when
subjected to a proper amount of electrically induced tensile biaxial strain,
most TMDC monolayers turn into potentially ideal photocatalyst towards the
hydrogen evolution reaction (HER). The beneficial effects of introducing
tensile biaxial strain on the TMDC monolayers are not limited to the reduction
of the band gap and proper adjustment of the band edge positions, but also to
the modification of the H adsorption free energy in such a way that the HER
reaction is noticeably favored.
