Is Rb 2 PtX 6 (X = Cl, Br, and I) a promising Pb-free vacancy-ordered double perovskites for photoelectrochemical water splitting applications?

In this work, the band structure feature, charge carrier mobility, optical properties, and photocatalytic performance of platinum-based vacancy-ordered double perovskites Rb 2 PtX 6 (X = Cl, Br, and I) are investigated. The results show the semiconducting character of all three materials with band gap values equal to 3.39 eV, 2.76 eV, and 1.45 eV, for Rb 2 PtCl 6 , Rb 2 PtBr 6 , and Rb 2 PtI 6 , respectively. Furthermore, the calculated electron and hole effective masses yield a higher relative mass of hole-electron pairs ( D ), resulting in a slow recombination rate in these materials. The optical properties are also calculated, where the entitled materials show high absorption intensities in the visible and ultraviolet regions. Moreover, it is discovered that the Rb 2 PtCl 6 and Rb 2 PtBr 6 compounds can produce both oxygen and hydrogen at the same time. In contrast, the Rb 2 PtI 6 material has a poor water-splitting ability and may be a promising photocatalyst for CO 2 photoreduction.