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Abstract
An efficient water oxidation system is a prerequisite for developing solar energy conversion devices. Using advanced time-resolved spectroscopy, we study the initial catalytic relevant electron transfer events in the light-driven water oxidation system utilizing [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) as a light harvester, persulfate as a sacrificial electron acceptor, and a high-valent iron clathrochelate complex as a catalyst. Upon irradiation by visible light, the excited state of the ruthenium dye is quenched by persulfate to afford a [Ru(bpy)3]3+/SO4˙- pair, showing a cage escape yield up to 75%. This is followed by the subsequent fast hole transfer from [Ru(bpy)3]3+ to the FeIV catalyst to give the long-lived FeV intermediate in aqueous solution. In the presence of excess photosensitizer, this process exhibits pseudo-first order kinetics with respect to the catalyst with a rate constant of 3.2(1) × 1010 s-1. Consequently, efficient hole scavenging activity of the high-valent iron complex is proposed to explain its high catalytic performance for water oxidation.
Highlights
Climate change, driven by the greenhouse effect and increasing global energy consumption, has become the greatest challenge humanity has ever faced
The classic homogenous photocatalytic water oxidation system consists of a water oxidation catalyst (WOC), a photosensitizer and a sacri cial electron acceptor
The clathrochelate complex [FeIV(L–6H)]2À, which is inde nitely stable in aqueous solutions at pH 1.0–13.0, acts as a homogeneous catalyst for photocatalytic water oxidation by persulfate with [Ru(bpy)3]2+ as photosensitizer, affording a high turnover number (TON) 1⁄4 365.36 In both chemical-driven and light-driven water oxidation, most iron complexes are known to decompose into catalytically
Summary
Driven by the greenhouse effect and increasing global energy consumption, has become the greatest challenge humanity has ever faced. In addition to the challenges associated with bond making and breaking during catalysis, sustainable generation of a long-lived charge-separated state in aqueous solution is required to perform the desired catalytic process.[6,7] the photosensitizer must be able to oxidize the WOC, having a redox potential E1/2 > 1.23 V versus the normal hydrogen electrode (NHE) These requirements can be met by ruthenium polypyridine complexes, and they have been widely employed as efficient visible light-driven photosensitizers in conjunction with various WOCs.[8,9,10] Among these complexes, tris(bipyridine)ruthenium ([Ru(bpy)3]2+) is the most common light harvester, with a relatively high oxidation potential E1/2 1⁄4 1.26 V versus NHE for the [Ru(bpy)3]3+/[Ru(bpy)3]2+ redox couple.[11] Due to the long lifetime s $ 10À6 s of its metal-to-ligand charge transfer (MLCT) excited state, [Ru(bpy)3]2+ may be converted to [Ru(bpy)3]3+ under illumination, by electron acceptors such as persulfate.[12] there is still room for improving the ability of the WOC to efficiently re-reduce [Ru(bpy)3]3+ to [Ru(bpy)3]2+ and perform sustained water oxidation
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