Characterization of Ru(II) Polypyridyl Photosensitizers Bound to TiO 2 Supports Through a New Covalent Metal‐Ester Bonding Motif

ABSTRACT The development of photoelectrochemical (PEC) devices involves the attachment of molecular photosensitizers onto solid supports. Particularly significant to this work are PECs that rely on ruthenium‐based photosensitizers on high band gap metal oxide (MOx) supports. In this study, we have explored a new ester binding motif (MOx‐ester) to covalently attach a ruthenium polypyridyl photosensitizer to TiO 2 . This new MOx‐ester photoanode is compared to the traditional photoanodes that utilize acid/base binding groups to attach the molecular Ru sensitizers to TiO 2 . The new MOx‐ester binding motif is characterized by cyclic voltammetry UV‐Vis, solid state 13 C NMR, and FTIR‐ATR spectroscopic analysis. The MOx‐ester covalent bonding led to higher TiO 2 surface coverage compared to carboxylate binding, which is advantageous in terms of achieving higher light absorption per area. Electrochemical impedance spectroscopy (EIS) revealed that ester anchoring exhibits lower charge‐transfer resistance compared to the carboxylate binding, leading to greater charge recombination. Despite the difference in charge recombination dynamics, comparable initial photocurrent densities were observed for the two types of binding groups. However, the ester binding group exhibited superior stability over time, compared to the carboxylate binding group in acetonitrile solution.