Electrochemical Properties of Polyoxometalates as Electrocatalysts.

Layered double hydroxides (LDH) intercalated with metal coordination compounds and oxometalates

The use of layered inorganic solids as host materials for the creation of inorganic–organic host-guest supramolecular structures is of increasing interest. In this review we outline the preparation, characterization and uses of layered double hydroxides (LDHs) containing organic guests. LDHs consist of stacks of positively charged mixed metal hydroxide layers that require the presence of interlayer anions to maintain overall charge neutrality. A range of organic guests may be incorporated, including aliphatic and aromatic carboxylates, sulfonates and phosphonates as well as porphyrin and phthalocyanine derivatives. Potential applications of organo-LDHs in the areas of catalysis, sorption, photochemistry and electrochemistry are outlined. Overall, it is demonstrated that with LDHs it is possible to create, in a systematic manner, novel inorganic–organic supramolecular structures.

Synthesis, characterization and applications of layered double hydroxides containing organic guests

Two novel polyoxometalate (POM)-based metal–organic frameworks (MOFs), [TBA]3[e-PMoV8MoVI4O36(OH)4Zn4][BTB]4/3·xGuest (NENU-500, BTB = benzene tribenzoate, TBA+ = tetrabutylammonium ion) and [TBA]3[e-PMoV8MoVI4O37(OH)3Zn4][BPT] (NENU-501, BPT = [1,1′-biphenyl]-3,4′,5-tricarboxylate), were isolated. In these compounds, the POM fragments serving as nodes were directly connected with organic ligands giving rise to three-dimensional (3D) open frameworks. The two anionic frameworks were balanced by TBA+ ions residing inside the open channels. They exhibit not only good stability in air but also tolerance to acidic and basic media. Furthermore, they were employed as electrocatalysts for the hydrogen evolution reaction (HER) owing to the combination of the redox activity of a POM unit and the porosity of a MOF. Meanwhile, the HER activities of e(trim)4/3, NENU-5, and HKUST-1 were also studied for comparison. Remarkably, as a 3D hydrogen-evolving cathode operating in acidic electrolytes, NENU-500 exhibits the hig...

Ultrastable Polymolybdate-Based Metal–Organic Frameworks as Highly Active Electrocatalysts for Hydrogen Generation from Water

Present General Status of Understanding of Heteropoly Electrolytes and a Tracing of Some Major Highlights in the History of Their Elucidation

Electrocatalysis by polyoxometalate/vbpolymer systems: Reduction of nitrite and nitric oxide

Isomerically pure α1- and α2-[Fe(OH2)P2W17O61]7- and α2[Fe(OH2)P2Mo2W15O61]7- were synthesized as aqueous-soluble potassium salts. The iron-substituted complexes as well as their immediate lacunary precursors have been characterized by IR, UV−visible, and 31P NMR spectroscopies. The acid−base equilibria were studied for the iron-substituted complexes. The hydroxo compound α2-[Fe(OH)P2W17O61]8- has also been synthesized, and its elemental analysis is correct. Its further characterization and study will be published elsewere. For a given pH value, the comparisons of the cyclic voltammograms reveal the influence of the location of the iron-filled site in the framework. This influence is strong in the α1 isomer and makes its electrochemistry clearly different from that of the α2 isomer. This observation is ascribed mainly to the large framework distortion induced by the vacancy in the α1 site, to subtle variations in the detailed protonation events which ensue, and to the nature of the iron substituent, which...

Iron-Substituted Dawson-Type Tungstodiphosphates: Synthesis, Characterization, and Single or Multiple Initial Electronation Due to the Substituent Nature or Position

It is shown that a series of one- and two-electron-reduced heteropolyanions of the Keggin- and Dawson-types convert quantitatively NO into N2O in acidic aqueous media. The corresponding oxidized forms of the heteropolyanions are fully regenerated. Unsubstituted and lacunary heteropolyanions, as well as the substituted heteropolyanions of these two groups, prove active in this context. Transformaion quantitative de NO en N2O par des he′te′ropolyanions e′lectrore′duits. De nombreux he′te′ropolyanions ayant la structure de Keggin ou celle de Dawson pre′sentent un comportement catalytique vis a vis de la re′duction de NO, au potentiel de leur premiere vague de re′duction. Les compose′s sature′s ou lacunaires, et les substitue′s appartenant a ces deux groupes de structures, se re′velent efficaces pour cette re′duction. Sur quelques exemples d'he′te′ropolyanions, dont le premier couple re′dox est soit monoe′lectronique, soit bie′lectronique, il a e′te′ montre′ que la transformation de NO en N2O est quantitative.

Efficient conversion of NO into N2O by selected electroreduced heteropolyanions

Substituent effect in the electrochemistry of Dawson-type tungstodiphosphates: Some strategic parameters for apparently multiple electronation on the first wave of heteropolyanions

A. Belhouari

Papers

Electrocatalysis by polyoxometalate/vbpolymer systems: Reduction of nitrite and nitric oxide

Iron-Substituted Dawson-Type Tungstodiphosphates: Synthesis, Characterization, and Single or Multiple Initial Electronation Due to the Substituent Nature or Position

Efficient conversion of NO into N2O by selected electroreduced heteropolyanions

Substituent effect in the electrochemistry of Dawson-type tungstodiphosphates: Some strategic parameters for apparently multiple electronation on the first wave of heteropolyanions

Oxometalate-clay-modified electrodes: synthesis and properties of anionic clays pillared by metatungstate☆