Water-soluble Polypyridyl Copper Water Oxidation Catalyst

The photochemical and electrochemical water oxidaton performance for the water soluble polypyridine copper complex [Cu?F₃tpa?ClO₄]ClO₄?tpa= tris-?2-pyridyl-methyl?amine? was investigated, respectively. In a three component system for photochemical water oxidation, containing Cu-F₃tpa as a light-driven WOC, [Ru?bpy?₃]?ClO₄?₂ as a photosensitizer and Na₂S₂O₈ as a sacrificial electon acceptor. A high TOF of ?1.58±0.03?×10^-1 s^-1 and a TON of ?11.61±0.23? for Cu-F₃tpa under different catalytic conditions was achived, respectively. Under electrochemical conditions, the working electrode is ITO and turnovers higher than 8.2 per complex Cu-F₃tpa were obtained during 2 h electrolysis under 1.8 V vs NHE, and conresponding to a turnover frequency about 0.38 s^-1. The low overpotential of electrocatalytic water oxidation for Cu-F₃tpa in homogeneous solution is 610 mv. In comparison, the reference [Cu?TPA??ClO₄?2] displayed almost no activity under either set of conditions, implying the crucial role of ligand in determining the behavior of the catalyst. Experimental evidence indicate the molecular catalytic nature of [Cu?F₃tpa?ClO₄]ClO₄, leading to a potentially practical strategy to apply the copper compex in a photoelectrochemical device for water oxidation. In the present work, F₃tpa was used as ligand based on Cu?ClO₄?2·6H2O to obtain copper polypyridine compound [Cu?F₃tpa?ClO₄]ClO₄ by refluxing. The main research contents and conclusions are as follows:Firsty, vapor diffusion of Et2O into an acetonitile solution of [Cu?F₃tpa?ClO₄]ClO₄ yiled light blue crystals sutible for X-ray diffraction. By crystal structure analysis, giving a distorted tetragonal bipyramidal coordination geometry.Secondly, testing the ligand by NMR ?nuclear magnetic resonance?, the ligand is what we need according to the peak positons. Meanwhile, the product was then analyzed by using ESI-MS ?electrospray ionization mass spectrometry?, a peak can be attributed to [Cu?F₃tpa?ClO₄]ClO₄.Thirdly, in the presence of photosensitizer [Ru?bpy?₃]?ClO₄?₂ and electron accptor Na₂S₂O₈ with excitation at ?=470±10 nm, photo-induced water oxidaiton of compound [Cu?F₃tpa?ClO₄]ClO₄ was monitored by a Clark electrode. A pH 8.5 borate buffer was found to be optimal for the process. The catalyst has the oxygen evoluton activity. To test whether the catalytic system was truly homogeneous in nature, the molecular integrity of [Cu?F₃tpa?ClO₄]ClO₄ during photocatalysis was scrutinized by dynamic light scattering ?DLS? experiments.Lastly, electrochemical measurements were performed using a three-electrode system with a 1 cm² ITO working electrode, a platinum wire counter electrode, and a Ag/AgCl ?with saturated KCl aqueous solution? reference electrode, was used to measure the cyclic voltammograms in borate buffer. The onset of the catalytic wave with catalyst is around 1.34 V vs NHE, which gives an overpotential lower than that of previously reported copper complexes. The catalyst [Cu?F₃tpa?ClO₄]ClO₄ has the capability for water oxdation and is homogeneous in electrocatalytic system by SEM, EDS, DLS, and Tyndall scattering analysis.