Ga_(2)OSe monolayer:A promising hydrogen evolution photocatalyst screened from two-dimensional gallium chalcogenides and the derived janus

Using first-principles calculations,hydrogen evolution reaction(HER) activity on two-dimensional(2 D) gallium chalcogenides monolayers GaX(X=O,S,Se,and Te) as well as the derived Janus monolayers Ga_(2) XY(X≠Y,X/Y=O,S,Se,and Te) were systematically examined.It was found that Ga_(2) OSe Janus monolayer with a 0.3% strain has the lowest ΔG_(H)*of 0.19 eV(modified to-0.01 eV including the solvation effect) because(ⅰ) O is the most electronegative among X/Y atoms,(ⅱ) the Ga_(2) OSe monolayer has a larger lattice parameter with respect to GaO monolayer,and(ⅲ) the built-in electric field is enhanced after H adsorption.The enhanced H adsorption with the lattice stretching is a result of the weaker Ga-O bond strength before H adsorption and the reduced electron fillings of anti-bonding molecular orbital formed by H 1 s and O2 p_(z) orbitals after H adsorption.The O-p_(z) band center can be served as a descriptor to describe the HER activity trend for these p-block materials.Moreover,Ga_(2) OSe monolayer has appropriate band alignment,distinguished optical absorption coefficient(10~5 cm^(-1)),low exciton binding energy(0.71 eV),and the spontaneous HER process,indicating that it is a highly potential candidate for near-infrared photocatalyst for hydrogen production.Our research provides a novel paradigm that forming Janus structure can effectively tune the HER activity,which would guide the searching for excellent HER photocatalysts for clean hydrogen production.