4.6 Article

Enabling light-driven water oxidation via a low-energy RuIV=O intermediate

期刊

PHYSICAL CHEMISTRY CHEMICAL PHYSICS
卷 15, 期 33, 页码 14058-14068

出版社

ROYAL SOC CHEMISTRY
DOI: 10.1039/c3cp52038b

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资金

  1. Brookhaven National Laboratory (BNL) [DE-AC02-98CH10886]
  2. U.S. Department of Energy [DE-FG02-07ER15888]
  3. Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences
  4. U.S. Department of Energy under BES Hydrogen Fuel Initiative
  5. Robert A. Welch Foundation [E-621]
  6. U.S. Department of Energy (DOE) [DE-FG02-07ER15888] Funding Source: U.S. Department of Energy (DOE)

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The discovery of catalysts capable of driving water oxidation at relatively low overpotential is a key challenge for efficient photoinduced water oxidation. The mononuclear Ru(II) polypyridyl complex (1) [Ru(NPM)(H2O)(pic)(2)](2+) (NPM = 4-tert-butyl-2,6-di-(1',8'-naphthyrid-2'-yl)-pyridine, pic = 4-picoline) has been examined as a catalyst for visible-light-driven water oxidation in a three-component homogeneous system containing [Ru(bpy)(3)](2+) as a photosensitizer, persulfate as a sacrificial electron acceptor and catalyst 1. In contrast to the well-established water oxidation mechanism via the nucleophilic attack of a water molecule on the high-energy [Ru-V=O](3+) species, a lower-energy direct pathway for O-O bond formation via a [Ru-V=O](2+) intermediate was proposed for the first time for the catalyst 1 (Polyansky et al., J. Am. Chem. Soc., 2011, 133, 14649). In this report we successfully demonstrate that this unique proton-coupled low-energy pathway actually takes place with the use of a mild oxidant such as the photogenerated [Ru(bpy)(3)](3+) (1.26 V vs. NHE) to drive water oxidation. The overall quantum yield of 9%, TOF of 0.12 s(-1) and TON of 103 (limited solely by a drop in pH) were found for photochemical water oxidation with 1 using [Ru(bpy)(3)](2+) as a photosensitizer and [S2O8](2-) as a sacrificial electron acceptor. These values render catalyst 1 as one of the most active mononuclear ruthenium-based catalysts for light-driven water oxidation in a homogeneous system. The utilization of a pH-dependent pathway for water oxidation is a new and promising direction as a low-energy pathway. Furthermore, the detailed analysis of individual photochemical steps leading to O-2 evolution provides benchmarks for future mechanistic studies of photo-induced water oxidation catalysis.

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