Determination of the stability constant of cobalt-substituted mono-lacunary Keggin-type polyoxometalate and its electrocatalytic water oxidation performance

Electrochemically Driven Water-Oxidation Catalysis Beginning with Six Exemplary Cobalt Polyoxometalates: Is It Molecular, Homogeneous Catalysis or Electrode-Bound, Heterogeneous CoOxCatalysis?

“…Syntheses of the Co-POMs were conducted according to literature methods and characterized via FT-IR, 31 P NMR, TGA, and elemental analysis. The procedures followed and resulting characterization data are presented in the Supporting Information for the interested reader (Figures S1–S8). ,,,,,,− , Characterization of the Co-POMs was consistent with prior literature and are isomerically pure samples, with the exception of K 8 [α 1 -Co­(H 2 O)­P 2 W 17 O 61 ], which contains a presently inseparable 5% impurity of the isomeric K 8 [α 2 -Co­(H 2 O)­P 2 W 17 O 61 ].…”

“…The six Co-POMs chosen for study are the prototype [Co 4 (H 2 O) 2 (PW 9 O 34 ) 2 ] 10– ( Co 4 P 2 W 18 ) (because it is relatively well-studied ,,, and, therefore, serves as a benchmark system for controls and comparisons); [Co 9 (H 2 O) 6 (OH) 3 (HPO 4 ) 2 (PW 9 O 34 ) 3 ] 16– ( Co 9 P 5 W 27 ), which has been reported to exhibit homogeneous WOCatalysis under electrocatalytically driven conditions (vida supra) and which shows very interesting, high WOCatalysis activity (η = 189 mV at 1 mA/cm 2 ) as an insoluble Ba 2+ salt embedded within amorphous carbon paste; ,− and [ ββ -Co 4 (H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 16– ( Co 4 P 4 W 30 ), selected because its Co centers are isostructural with Co 4 P 2 W 18 , yet this Co-POM was previously reported, surprisingly, as not exhibiting WOCatalysis using Ru­(bpy) 3 3+ as the oxidant ,, even though its close congener, Co 4 P 2 W 18 , does . The final three of the six Co-POMs are single Co-containing [Co­(H 2 O)­PW 11 O 39 ] 5– ( CoPW 11 ), which has been shown to form CoO x under electrocatalytic conditions in pH 7 phosphate buffer solutions, ,− yet is reported to not exhibit WOCatalysis activity using Ru­(bpy) 3 3+ as the chemical oxidant; and [α 1 -Co­(H 2 O)­P 2 W 17 O 61 ] 8– ( α 1 -CoP 2 W 17 ) and [α 2 -Co­(H 2 O)­P 2 W 17 O 61 ] 8– ( α 2 -CoP 2 W 17 ), two isomeric, single-cobalt Co-POMs ,,, chosen because they have literature precedent as WOPrecatalysts and because they therefore allow insights into the role of different Co­(II)-to-POM binding sites and structures on the resultant WOCatalysis and kinetically dominant WOCatalyst.…”

“…The procedures followed and resulting characterization data are presented in the Supporting Information for the interested reader (Figures S1−S8). 9,13,21,23,30,31,[34][35][36][37][38][39][40][41][42][43]52 27,28,47,48 was used to detect the amount of Co(II) aq present in NaPi-buffered solutions for each Co-POM. This 31 P NMR technique is powerful because it is selective toward Co(II) aq (i.e., and insensitive to Co(II) within a Co-POM) while also having a detection limit of ∼2 μM Co(II) aq .…”

Synthesis, Crystal Structure, Electrochemistry and Electro-Catalytic Properties of the Manganese-Containing Polyoxotungstate, [(Mn(H2O)3)2(H2W12O42)]6−

“…The idea is to lower as much as possible the apparent redox potential values for the oxidation of these Mn 2+ centres, thus reaching more easily their higher oxidation states Mn 4+ (2) the two Mn 2+ centres bound to its structure are easily accessible and their oxidation may be carried out at not so high potentials. This oxidation is concomitant with the formation of metal oxide deposits which favour the electro-catalytic oxidation of water, as demonstrated by previous studies, some of them being more recent than others [54][55][56][57][58][59]63,65,66].…”

Synthesis and Photocatalytic Study of Ferrocenium Ion Incorporated Lacunary Keggin Hybrid Material

“…The hybrid material used for photocatalysis in this study consists of lacunary Keggin anion, which has enhanced oxidizing capability compared to the parent anion . Further, many transition metals have been used to fit into the lacuna of the lacunary POMs, giving rise to novel materials having remarkable properties . Irradiation of lacunary POM with light of energy higher than or equal to its HOMO–LUMO gap produces electron‐hole pairs, where an electron is excited to higher energy state leaving behind a hole in the lower state.…”