Synthesis of Magnesium Phosphorous Trichalcogenides and Applications in Photoelectrochemical Water Splitting.

Promising applications of metal phosphorous trichalcogenides (M P X or MPX ) have been predicted in optoelectronics, photoelectrocatalysis, and water-splitting reactions, mainly due to its wide bandgap. Transition metals are widely used in the synthesis of MPX , however, divalent cations of alkaline earth metals can also be constituents in MPX 2D layered structures. Herein, MgPX (X = S, Se) are synthesized and their photoelectrochemical (PEC) activity is tested in the hydrogen evolution and oxygen evolution reaction (OER) regions under a wide range of wavelengths. MgPSe photoelectrode shows the best PEC performance with a response of 1.6 ± 0.1 mA cm under 420 nm. In the light-assisted OER, a 200 mV improvement is obtained in the overpotential at 10 mA cm for MgPSe . The better performance of MgPSe is consistent with its lower optical bandgap (E  = 3.15 eV), as a result of the variation of electronegativity between selenide and sulfide.