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Visible‐Light‐Induced Water Oxidation Mediated by a Mononuclear‐Cobalt(II)‐Substituted Silicotungstate
Author(s) -
Xiang Rui,
Ding Yong,
Zhao Junwei
Publication year - 2014
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201402483
Subject(s) - catalysis , chemistry , polyoxometalate , cobalt , persulfate , quantum yield , oxygen evolution , photochemistry , cyclic voltammetry , photosensitizer , inorganic chemistry , nuclear chemistry , electrochemistry , fluorescence , organic chemistry , physics , electrode , quantum mechanics
A mononuclear‐cobalt(II)‐substituted silicotungstate, K 10 [Co(H 2 O) 2 (γ‐SiW 10 O 35 ) 2 ] ⋅ 23 H 2 O (POM‐ 1 ), has been evaluated as a light‐driven water‐oxidation catalyst. With in situ photogenerated [Ru(bpy) 3 ] 3+ (bpy=2,2′‐bipyridine) as the oxidant, quite high catalytic turnover number (TON; 313), turnover frequency (TOF; 3.2 s −1 ), and quantum yield ( Φ QY ; 27 %) for oxygen evolution at pH 9.0 were acquired. Comparison experiments with its structural analogues, namely [Ni(H 2 O) 2 (γ‐SiW 10 O 35 ) 2 ] 10− (POM‐ 2 ) and [Mn(H 2 O) 2 (γ‐SiW 10 O 35 ) 2 ] 10− (POM‐ 3 ), gave the conclusion that the cobalt center in POM‐ 1 is the active site. The hydrolytic stability of the title polyoxometalate (POM) was confirmed by extensive experiments, including UV/Vis spectroscopy, linear sweep voltammetry (LSV), and cathodic adsorption stripping analysis (CASA). As the [Ru(bpy) 3 ] 2+ /visible light/sodium persulfate system was introduced, a POM–photosensitizer complex formed within minutes before visible‐light irradiation. It was demonstrated that this complex functioned as the active species, which remained intact after the oxygen‐evolution reaction. Multiple experimental parameters were investigated and the catalytic activity was also compared with the well‐studied POM‐based water‐oxidation catalysts (i.e., [Co 4 (H 2 O) 2 (α‐PW 9 O 34 ) 2 ] 10− (Co 4 ‐POM) and [Co III Co II (H 2 O)W 11 O 39 ] 7− (Co 2 ‐POM)) under optimum conditions.