OER Activity Promoted by Organic Ligand‐Free Cs ₂ Pt(Cl, Br) ₆ Perovskite Photocatalyst for Solar‐Driven Water Splitting

The development of lead‐free perovskites as environmentally sustainable materials has gained significant attention for their applications in solar cells and photocatalysis. In this study, Cs 2 PtCl 6 and Cs 2 PtBr 6 vacancy‐ordered double perovskites are synthesized via a hydrothermal method and evaluated as ligand‐free photocatalysts for solar‐driven water splitting, targeting the oxygen evolution reaction (OER). Structural characterization confirms their cubic phase, and ultraviolet‐visible diffuse reflectance spectroscopy reveals optical bandgaps of 2.17 eV for Cs 2 PtCl 6 and 1.94 eV for Cs 2 PtBr 6 . Theoretical calculations based on density of states analysis confirms their semiconductor behavior. Photocatalytic studies show that Cs 2 PtBr 6 exhibits superior O 2 evolution rates (368.9 μmol g −1 h −1 ) compared to Cs 2 PtCl 6 (237.4 μmol g −1 h −1 ), attributed to its favorable electronic structure. Also, photoluminescence (PL) studies reveals that Cs 2 PtBr 6 exhibits lower PL intensity and a longer emission lifetime (2.5 μs) compared to Cs 2 PtCl 6 (1.3 μs). Long‐term stability tests highlight moderate photostability, with Pt 4+ reduction due to precipitation of Pt 0 under prolonged irradiation or reuses. This research highlights the potential of Cs 2 PtX 6 perovskites for efficient, sustainable OER catalysis while identifying challenges related to structural stability and charge recombination.