[{Ni₄(OH)₃AsO₄}₄(B‐α‐PW₉O₃₄)₄]²⁸⁻: A New Polyoxometalate Structural Family with Catalytic Hydrogen Evolution Activity

Abstract

A new structural polyoxometalate motif, [{Ni4 (OH)3 AsO4 }4 (B-α-PW9 O34 )4 ](28-) , which contains the highest nuclearity structurally characterized multi-nickel-containing polyanion to date, has been synthesized and characterized by single-crystal X-ray diffraction, temperature-dependent magnetism and several other techniques. The unique central {Ni16 (OH)12 O4 (AsO4 )4 } core shows dominant ferromagnetic exchange interactions, with maximum χm T of 69.21 cm(3) K mol(-1) at 3.4 K. Significantly, this structurally unprecedented complex is an efficient, water-compatible, noble-metal-free catalyst for H2 production upon visible light irradiation (photosensitizer=[Ir(ppy)2 (dtbbpy)][PF6 ]; sacrificial electron donor=triethylamine or triethanolamine). The highest turnover number of approximately 580, corresponding to a best quantum yield of approximately 4.07 %, is achieved when using triethylamine as electron donor in the presence of water. The mechanism of this photodriven process has been probed by time-solved luminescence and by static emission quenching.

Ordered Mesoporous Polyoxometalate–Organosilica Frameworks as Efficient Photocatalysts of the Hydrogen Evolution Reaction

“…Of particular note, the H 2 evolution activity of SiW 11 /MES was comparably higher than that obtained for [{Ni 4 (OH) 3 AsO 4 } 4 ( B ‐α‐PW 9 O 34 )4] 28− (2.88 μmol h −1 , TOF=72 h −1 ), [Mn 4 (H 2 O) 2 (VW 9 O 34 ) 2 ] 10− (0.35 μmol h −1 , TOF=7.6 h −1 ), Pt‐loaded K 11 H[Sn 4 (SiW 9 O 34 ) 2 ] (0.43 μmol h −1 , TOF=0.025 h −1 ), and [Ni(H 2 O)GeW 11 O 39 ] 6− (1.4 μmol h −1 , TOF=31 h −1 ) complexes, and is comparable to the activity achieved with Pt‐loaded K 7 [Co III Co II (H 2 O)W 11 O 39 ] (171.4 μmol h −1 , TOF=42.8 h −1 ), Ni 2+ ‐substituted Na 8 HPW 9 O 34 (234 μmol h −1 , TOF=5 h −1 ), and Na 27 [Fe 11 (H 2 O) 14 (OH) 2 (W 3 O 10 ) 2 (α‐SbW 9 O 33 ) 6 ] (78 μmol h −1 , TOF=13 h −1 ) compounds and Cs 3 [PW 11 O 39 {cis‐Pt(NH 3 ) 2 } 2 ]/TiO 2 (P25) (28.5 μmol h −1 , TOF=71 h −1 ) composite materials. However, most of these previous studies involved the use of either precious metals as co‐catalysts, such as Pt, or additional photosensitizers, such as [Ru(bpy) 3 ] 2+ and [Ir(ppy) 2 (dtbbpy)] + (ppy=2‐phenylpyridine, dtbbpy=5,5′‐di‐ tert ‐butyl‐2,2′‐bipyridine) complexes and fluorescein and Eosin Y dyes.…”

Catalytic Light-Driven Generation of Hydrogen from Water by Iron Dithiolene Complexes

“…The light-driven reduction of water to H 2 by molecularly based systems has been known since the late 1970s when researchers developed systems comprising [Ru­(bpy) 3 ] 2+ and/or its derivatives as light absorbers in the presence of a suitable catalyst such as Pt, an electron mediator, and a sacrificial electron. − In recent years, extensive efforts have been made to replace precious metal components of aqueous proton reduction systems with more active and durable constituents made solely of earth-abundant elements. For possible catalysts in homogeneous water reduction systems, the focus has been on potentially redox active transition metal complexes of elements such as iron, − cobalt, − nickel, − and molybdenum. , Despite extensive experimental investigations and mechanistic studies of systems containing these water reduction catalysts (WRCs), many of them have been found to suffer from low activity and/or photoinstability due to decomposition of the chromophore, or catalyst degradation due to structural instability. − While significant improvements have been reported, ,− ,− the challenge still remains for an active and robust sunlight-driven system for hydrogen production from water. The development of new, efficient earth-abundant transition metal catalysts and photostable light-absorbers remains part of that challenge.…”

Multi-Tasking POM Systems

“…However, POMs are quite active as catalysts for multi-electron reduction (reduction of H 2 O to H 2 or CO 2 to carbon-based fuel molecules)(Wang et al, 2016 ; Gumerova and Rompel, 2018 ). Several POMs that are efficient water reduction catalysts under visible-light-driven or dark conditions have been reported (Lv et al, 2014 , 2015 , 2016 ), and some POMs facilitate CO 2 reduction under appropriate conditions (Ettedgui et al, 2010 ; Wang et al, 2016 ). One of the primary applications that has been the subject of extensive research within the field of POMs has been the catalysis of water oxidation.…”