Construction of oligomeric bridges on TiO2 via terminal double coordination bonds for efficient and long-time photocatalytic hydrogen evolution in water

In this article, we constructed a novel oligomeric bridge by anchoring oligomeric Ir complex (o-Ir, Ir(ppy) 2 (dabpy)-ODPA-COOH) onto TiO 2 via its terminal dicarboxylic groups, enabling efficient and long lifetime photocatalytic hydrogen evolution in water. The dual enhancement mechanism of the double coordination bonds based oligomeric bridge was first discovered and confirmed by density functional theory (DFT) calculations, X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), high-resolution transmission electron microscopy (HR-TEM), electrochemical and photophysical analyses. First, the oligomeric bridge enhances light absorption, facilitates efficient electron injection into TiO 2 and accelerates charge transfer via the double coordination bonds between o-Ir and TiO 2 , endowing the oligomeric bridge anchored TiO 2 (o-Ir@Pt-TiO 2 ) with high photocatalytic activity in water under visible light. The turnover number (TON) of o-Ir@Pt-TiO 2 during 24 h photocatalysis is over 420 times of o-Ir, and the total TON of o-Ir@Pt-TiO 2 (over 18343) outperforms most organic-TiO 2 based catalysts. The total hydrogen evolution reaches over 337.5 mmol·g –1 which is more than 17 times of Pt-TiO 2 . Second, the double coordination bonds mitigate inherent defects and realize mutual protection of o-Ir and TiO 2 , yielding a record photocatalyst lifetime exceeding 708 h, which is the highest value among reported organic-TiO 2 based catalysts in aqueous systems. This work will provide new theoretical and industrial possibilities for efficient and stable photocatalytic hydrogen evolution.