title: A noble-metal-free, tetra-nickel polyoxotungstate catalyst for efficient photocatalytic hydrogen evolution.
abstract: A tetra-nickel-containing polyoxotungstate, Na6K4[Ni4(H2O)2(PW9O34)2]·32H2O (Na6K4-Ni4P2), has been synthesized in high yield and systematically characterized. The X-ray crystal structure confirms that a tetra-nickel cluster core [Ni4O14] is sandwiched by two trivacant, heptadentate [PW9O34](9-) POM ligands. When coupled with (4,4'-di-tert-butyl-2,2'-dipyridyl)-bis(2-phenylpyridine(1H))-iridium(III) hexafluorophosphate [Ir(ppy)2(dtbbpy)][PF6] as photosensitizer and triethanolamine (TEOA) as sacrificial electron donor, the noble-metal-free complex Ni4P2 works as an efficient and robust molecular catalyst for H2 production upon visible light irradiation. Under minimally optimized conditions, Ni4P2 catalyzes H2 production over 1 week and achieves a turnover number (TON) of as high as 6500 with almost no loss in activity. Mechanistic studies (emission quenching, time-resolved fluorescence decay, and transient absorption spectroscopy) confirm that, under visible light irradiation, the excited state [Ir(ppy)2(dtbbpy)](+)* can be both oxidatively and reductively quenched by Ni4P2 and TEOA, respectively. Extensive stability studies (e.g., UV-vis absorption, FT-IR, mercury-poison test, dynamic light scattering (DLS) and transmission electron microscopy (TEM)) provide very strong evidence that Ni4P2 catalyst remains homogeneous and intact under turnover conditions.
authors.affiliation: Department of Chemistry, ‡X-ray Crystallography Center and §Cherry L. Emerson Center for Scientific Computation, Emory University , 1515 Dickey Drive, Atlanta, Georgia 30322, United States.
authors.forename: Hongjin
authors.initials: H
authors.lastname: Lv
authors.forename: Weiwei
authors.initials: W
authors.lastname: Guo
authors.forename: Kaifeng
authors.initials: K
authors.lastname: Wu
authors.forename: Zheyuan
authors.initials: Z
authors.lastname: Chen
authors.forename: John
authors.initials: J
authors.lastname: Bacsa
authors.forename: Djamaladdin G
authors.initials: DG
authors.lastname: Musaev
authors.forename: Yurii V
authors.initials: YV
authors.lastname: Geletii
authors.forename: Sarah M
authors.initials: SM
authors.lastname: Lauinger
authors.forename: Tianquan
authors.initials: T
authors.lastname: Lian
authors.forename: Craig L
authors.initials: CL
authors.lastname: Hill