Speciation and Dynamics in the [Co₄V₂W₁₈O₆₈]^10–/Co(II)_aq/CoO_x Catalytic Water Oxidation System

Abstract

Our group reported that the polyoxometalate Na 10 [Co 4 V 2 W 18 O 68 ]•26H 2 O (Co 4 V 2 ) is an active water oxidation catalyst and provided characterization of this system (J. Am. Chem. Soc. 2014, 136 (26), 9268). Two recent publications called into question the stability of Co 4 V 2 , one noting the miss-assignment of a 51 V NMR peak (Inorg. Chem. 2016, 55 (11), 5343) and another providing additional stability studies (ACS Catal., 2017, 7 (1), 7). We report here solution studies that further clarify stability limitations in this system by locating the correct 51 V NMR resonance of Co 4 V 2 and the other V-containing species present. Furthermore, we demonstrate that the observed catalytic activity cannot be explained simply by Co(II) aq , but arises from multiple active WOC species in solution. Key points about investigating such complex equilibrating aqueous catalyst systems are addressed.

Polyoxometalates (POMs): from electroactive clusters to energy materials

“…Very recently, the Ag + salt of Co 189,19051,52 Recent vanadium NMR solution studies on the NMR/Co II aq/CoO x system describe a complex speciation behavior in solution, making the identification of the various equilibrating aqueous active catalysts in the system is a challenging task. 191 Despite several advances, the large catalytic difference between Co 4 V 2 and Co 4 P 2 called for examining the significance of substituting phosphorus centers in Co 4 P 2 with vanadium. A thorough DFT study on the OER mechanism for Co 4 P 2 suggested that the O-O bond formation takes place from a Co 3+ -oxyl radical through the WNA attack pathway.…”

Co/Ni-polyoxotungstate photocatalysts as precursor materials for electrocatalytic water oxidation

“…30,31 This gives rise to ongoing and challenging speciation studies. 32 performance of oxide WOCs. These ndings show that synthetic methods and underlying mechanisms 36 are an important step in WOC optimization, [37][38][39] and that a certain extent of preorganization of the metal centers in the precursor is benecial for higher catalytic activity.…”

A Stable Polyoxometalate-Based Metal–Organic Framework with Active CoMoO4 Layers for Electroreduction and Visible-Light-Driven Water Oxidation

“…Despite the encapsulation of POMs in highly porous MOFs, POMs may also be incorporated as redox catalytic centers through robust coordination bonds, while organic linkers may efficiently facilitate the proton coupled electron transfer. , The extension of the POMs species has strongly motivated the interest in POMs chemistry due to the their high lattice energy. − For this purpose, the introduction of heteroatoms into a POM structure may be a feasible method to enrich the POMs’ topology structure. Notably, the design of a 2D POM layer with suitable cations and extension into MOFs are promising for this device construction. , Once the stability of the 2D POM layer based MOFs has been established, they may have important consequences for applications in photocatalytic water splitting.…”