Synthesis of Magnesium Phosphorous Trichalcogenides and Applications in Photoelectrochemical Water Splitting

Abstract Promising applications of metal phosphorous trichalcogenides (M 2 P 2 X 6 or MPX 3 ) 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 3 , however, divalent cations of alkaline earth metals can also be constituents in MPX 3 2D layered structures. Herein, MgPX 3 (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 3 photoelectrode shows the best PEC performance with a response of 1.6 ± 0.1 mA cm −2 under 420 nm. In the light‐assisted OER, a 200 mV improvement is obtained in the overpotential at 10 mA cm −2 for MgPSe 3 . The better performance of MgPSe 3 is consistent with its lower optical bandgap ( E g = 3.15 eV), as a result of the variation of electronegativity between selenide and sulfide.