Water Exchange Reactivity and Stability of Cobalt Polyoxometalates under Catalytically Relevant pH Conditions: Insight into Water Oxidation Catalysis

Lieb, Dominik; Zahl, Achim; Wilson, Elizabeth; Streb, Carsten; Nye, Leanne C.; Meyer, Karsten; Ivanović‐Burmazović, Ivana

doi:10.1021/ic201243n

Cited by 48 publications

(53 citation statements)

References 31 publications

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“…Major challenges include: 1) Thes table linkage between catalyst and electrode: [20] In many current systems,d etachment of the catalysts from the electrode under operating conditions leads to aloss of catalytic activity. [9,22] Here,w er eport an OER electrode where an oble-metal free POM-OEC is deposited on ac ommercial nickel foam electrode (Scheme 1). To date,m ost earth-abundant catalysts show significantly higher overpotentials than noble-metal oxides such as RuO 2 and IrO 2 .…”

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confidence: 99%

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Robust Polyoxometalate/Nickel Foam Composite Electrodes for Sustained Electrochemical Oxygen Evolution at High pH

et al. 2017

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The development of technologically viable electrodes for the electrochemical oxygen evolution reaction (OER) is a major bottleneck in chemical energy conversion. This article describes a facile one-step hydrothermal route to deposit microcrystals of a robust Dexter-Silverton polyoxometalate oxygen evolution catalyst, [Co Ni W O (OH) (H O) ], on a commercial nickel foam electrode. The electrode shows efficient and sustained electrochemical oxygen evolution at low overpotentials (360 mV at 10 mA cm against RHE, Tafel slope 126 mV dec , faradaic efficiency (96±5) %) in alkaline aqueous solution (pH 13). Post-catalytic analyses show no mechanical or chemical degradation and no physical detachment of the microcrystals. The results provide a blueprint for the stable "wiring" of POM catalysts to commercial metal foam substrates, thus giving access to technologically relevant composite OER electrodes.

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“…However, most POM-OECs are degraded irreversibly at pH > 7-8. [9,22] Here,w er eport an OER electrode where an oble-metal free POM-OEC is deposited on ac ommercial nickel foam electrode (Scheme 1). Thec omposite shows sustained electrochemical OER activity at high current density and low overpotential in water at pH 13.…”

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Robust Polyoxometalate/Nickel Foam Composite Electrodes for Sustained Electrochemical Oxygen Evolution at High pH

et al. 2017

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“…We speculated that this could be the ligand-exchange effect between buffer molecules and the water ligand in POM-1, but spectroscopic measurements to detect any intermediate species failed. [23] However, this speculation is highly empirical and, as pointed out by Patzke, [24] it represents a common situation to date for the exploration of structure-activity relationship for POM-based WOCs. At pH 9.0, POM-1 showed the highest O 2 yield and TON (Table S1 in the Supporting Information).…”

Section: Resultsmentioning

confidence: 99%

“…As shown in Figure 9b, the catalytic activity of POM-1 changed dramatically with different pH values. POM-1 may serve as a more suitable candidate to gain insight into the structureactivity relationship with the reported protocol, [23] which is beyond the scope of this work and will be discussed elsewhere. A higher pH is thermodynamically favorable, and the degradation of photosensitizer is also easier.…”

Section: Resultsmentioning

confidence: 99%

Visible‐Light‐Induced Water Oxidation Mediated by a Mononuclear‐Cobalt(II)‐Substituted Silicotungstate

Xiang

Ding

Zhao

2014

Chemistry An Asian Journal

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A mononuclear-cobalt(II)-substituted silicotungstate, K10[Co(H2O)2(γ-SiW10O35)2]⋅23 H2O (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(H2O)2(γ-SiW10O35)2](10-) (POM-2) and [Mn(H2O)2(γ-SiW10O35)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., [Co4(H2O)2(α-PW9O34)2](10-) (Co4-POM) and [Co(III)Co(II)(H2O)W11O39](7-) (Co2-POM)) under optimum conditions.

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“…Their local bonding environment is controlled by the layered structure and is not dramatically affected by the dense and dissimilar tungstate groups. [15,16] Charge densities are important, not necessarily size.…”

Section: Exchanging Bound Watersmentioning

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Ligand- and oxygen-isotope-exchange pathways of geochemical interest

Casey¹

2015

Environ. Chem.

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Environmental context. Most chemical processes in water are either ligand-or electron-exchange reactions.Here the general reactivity trends for ligand-exchange reactions in aqueous solutions are reviewed and it is shown that simple rules dominate the chemistry. These simple rules shed light on most molecular processes in water, including the uptake and degradation of pesticides, the sequestration of toxic metals and the corrosion of minerals.Abstract. It is through ligand-exchange kinetics that environmental geochemists establish an understanding of molecular processes, particularly for insulating oxides where there are not explicit electron exchanges. The substitution of ligands for terminal functional groups is relatively insensitive to small changes in structure but are sensitive to bond strengths and acid-base chemistry. Ligand exchanges involving chelating organic molecules are separable into two classes: (i) ligand substitutions that are enhanced by the presence of the chelating ligand, called a 'spectator' ligand and (ii) chelation reactions themselves, which are controlled by the Lewis basicity of the attacking functional group and the rates of ring closure. In contrast to this relatively simple chemistry at terminal functional groups, substitutions at bridging oxygens are exquisitely sensitive to details of structure. Included in this class are oxygen-isotope exchange and mineraldissolution reactions. In large nanometer-sized ions, metastable structures form as intermediates by detachment of a surface metal atom, often from a underlying, highly coordinated oxygen, such as m 4 -oxo, by solvation forces. A metastable equilibrium is then established by concerted motion of many atoms in the structure. The newly undercoordinated metal in the intermediate adds a water or ligand from solution, and protons transfer to other oxygens in the metastable structure, giving rise to a characteristic broad amphoteric chemistry. These metastable structures have an appreciable lifetime and require charge separation, which is why counterions affect the rates. The number and character of these intermediate structures reflect the symmetry of the starting structure. Simple reactivity trends for ligand-and oxygen-isotope exchanges FormalismMost metals in aqueous solutions of interest to environmental chemists are coordinatively saturated. Here saturated is meant in the sense of Pauling's First Rule, relating ionic radius to oxygen packing. Most metals in water have the maximum number of coordinated atoms given by their radius ratios -exceptions certainly exist for highly covalent materials (e.g. Pt II , Nb V ), and some are discussed below, but most materials near the Earth's surface are oxides with a metal that has a fixed coordination or slightly variable number. In sharp contrast, the coordination

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Water Exchange Reactivity and Stability of Cobalt Polyoxometalates under Catalytically Relevant pH Conditions: Insight into Water Oxidation Catalysis

Cited by 48 publications

References 31 publications

Robust Polyoxometalate/Nickel Foam Composite Electrodes for Sustained Electrochemical Oxygen Evolution at High pH

Robust Polyoxometalate/Nickel Foam Composite Electrodes for Sustained Electrochemical Oxygen Evolution at High pH

Visible‐Light‐Induced Water Oxidation Mediated by a Mononuclear‐Cobalt(II)‐Substituted Silicotungstate

Ligand- and oxygen-isotope-exchange pathways of geochemical interest

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