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Kinetic Analysis of an Efficient Molecular Light-Driven Water Oxidation System

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Title: Kinetic Analysis of an Efficient Molecular Light-Driven Water Oxidation System
Authors: Francas, L
Matheu, R
Pastor, E
Reynal, A
Berardi, S
Sala, X
Llobet, A
Durrant, JR
Item Type: Journal Article
Abstract: We report an efficient molecular light-driven system to oxidize water to oxygen and a kinetic analysis of the factors determining the efficiency of the system. The system comprises a highly active molecular catalyst ([RuIV(tda)(py)2(O)]), [RuII(bpy)(bpy-COOEt)2]2+ (RuP), as sensitizer and Na2S2O8 as sacrificial electron acceptor. This combination exhibits a high quantum yield (25%) and chemical yield (93%) for photodriven oxygen evolution from water. The processes underlying this performance are identified using optical techniques, including transient absorption spectroscopy and photoluminescence quenching. A high catalyst concentration is found to be required to optimize the efficiency of electron transfer between the oxidized sensitizer and the catalyst, which also has the effect of improving sensitizer stability. The main limitation of the quantum yield is the relatively low efficiency of S2O82– as an electron scavenger to oxidize the photoexcited ruthenium sensitizer RuP* to 2 RuP+, mainly due to competing back electron transfers to the RuP ground state. The overall rate of light-driven oxygen generation is determined primarily by the rate of photon absorption by the molecular sensitizer under the incident photon flux. As such, the performance of this efficient light-driven system is limited not by the properties of the molecular water oxidation catalyst, which exhibits both good kinetics and stability, but rather by the light absorption and quantum efficiency properties of the sensitizer and electron scavenger. We conclude by discussing the implications of these results for further optimization of molecular light-driven systems for water oxidation.
Issue Date: 15-Jun-2017
Date of Acceptance: 2-Jun-2017
URI: http://hdl.handle.net/10044/1/51578
DOI: https://dx.doi.org/10.1021/acscatal.7b01357
ISSN: 2155-5435
Publisher: American Chemical Society
Start Page: 5142
End Page: 5150
Journal / Book Title: ACS CATALYSIS
Volume: 7
Issue: 8
Copyright Statement: © 2017 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, after peer review and technical editing by the publisher. To access the final edited and published work see https://dx.doi.org/10.1021/acscatal.7b01357
Sponsor/Funder: Commission of the European Communities
Funder's Grant Number: 291482
Keywords: Science & Technology
Physical Sciences
Chemistry, Physical
Chemistry
light-driven catalysis
water oxidation
quantum yield
kinetics
oxygen generation
MONONUCLEAR RUTHENIUM COMPLEXES
POLYOXOMETALATE CATALYST
ELECTRON-TRANSFER
PHOTOSENSITIZER
LIGANDS
REDOX
STABILITY
Publication Status: Published
Appears in Collections:Chemistry
Faculty of Natural Sciences



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