Redox switching of polyoxometalate-doped polypyrrole films in ionic liquid media

The surface immobilization of the parent Dawson polyoxometalate (POM) as a counter-ion for the electropolymerization of polypyrrole (PPy) or as an electrode-adhered solid was utilized for voltammetric studies of the surface adhered POM in room temperature ionic liquids (RTIL). Illustrating the efficiency of intermediate stabilization, voltammetry at POM-modified electrodes in a PF6-based RTIL revealed richer redox behaviour and higher stabilization in comparison with aqueous electrolytes and with BF4-based RTIL, respectively. High stability of the POM-doped PPy towards continuous charge-discharge voltammetric redox cycles was confirmed by minor changes in film morphology observed after the cycling in RTILs

Transition metal ion-substituted polyoxometalates entrapped into polypyrrole as electrochemical sensor for hydrogen peroxide

A conducting polymer was used for the immobilization of various transition metal ion-substituted Dawson-type polyoxometalates (POMs) onto glassy carbon electrodes. Voltammetric responses of films of different thicknesses were stable within the pH domain 2-7 and reveal redox processes associated with 10 the conducting polymer, the entrapped POMs and incorporated metal ions. The resulting POM doped polypyrrole films were found to be extremely stable towards redox switching between the various redox states associated with the incorporated POM. An amperometric sensor for hydrogen peroxide detection based upon the POM doped polymer films was investigated. The detection limits were 0.3 and 0.6 uM, for the Cu2+- and Fe3+-substituted POM-doped polypyrrole films respectively, with a linear region from 15 0.1 up to 2mM H2O2. Surface characterization of the polymer films was carried out using atomic force microscopy, x-ray photoelectron spectroscopy and scanning electron microscopy

Organic−Inorganic Hybrid Films of the Sulfate Dawson Polyoxometalate, [S2W18O62] 4−, and Polypyrrole for Iodate Electrocatalysis

The Dawson-type sulfate polyoxometalate (POM) [S2W18O62]4− has successfully been entrapped in polypyrrole (PPy) films on glassy carbon electrode (GCE) surfaces through pyrrole electropolymerization. Films of varying POM loadings (i.e., thickness) were grown by chronocoulometry. Film-coated electrodes were then characterized using voltammetry, revealing POM surface coverages ranging from 1.9 to 11.7 × 10−9 mol·cm−2 , and were stable over 100 redox cycles. Typical film morphology and composition were revealed to be porous using atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy, and the effects of this porosity on POM redox activity were probed using AC impedance. The hybrid organic− inorganic films exhibited a good electrocatalytic response toward the reduction of iodate with a sensitivity of 0.769 μA·cm−2 ·μM−1 . </p

Nitrate and nitrite electrocatalytic reduction at layer-by-layer films composed of Dawson-type heteropolyanions mono-substituted with transitional metal Ions and silver nanoparticles

A series of Dawson-type heteropolyanions (HPAs) mono-substituted with transitional metal ions (α2-[P2W17O61FeIII]8−, α2-[P2W17O61CuII]8− and α2-[P2W17O61NiII]8−) have exhibited electrocatalytic properties towards nitrate and nitrite reduction in slightly acidic media (pH 4.5). The immobilization of these HPAs into water-processable films developed via layer-by layer assembly with polymer-stabilized silver nanoparticles led to the fabrication of the electrocatalytic interfaces for both nitrate and nitrite reduction. The LBL assembly as well as the changes in the HPA properties by immobilization has been characterized by electrochemical methods. The effects of the substituent ions, outer layers and the cationic moieties utilized for the films assembly of the developed film on the performances of nitrate electrocatalysis has been elucidate

Electrocatalysis by crown-type polyoxometalates multi-substituted by transition metal ions; comparative study

The difference in electrochemical properties of three crown-type polyoxometalates multi-substituted by Fe3+, Ni2+ or Co2+ ions and their precursor has been rationalized with respect to their electrocatalytic performances studied in solution and in the immobilized state within the layer-by-layer film formed with a positively charged pentaerythritol-based Ru(II)-metallodendrimer. The film assembly was monitored with electrochemical methods and characterized by surface analysis techniques. An influence of the terminal layer on the electrode reaction and on film porosity has been observed. The electrocatalytic performance of the compounds on nitrite reduction was assessed in solution and in the immobilized state. (C) 2015 Elsevier Ltd. All rights reserved

Effect of Product Removal in Hydrogen Peroxide Electrosynthesis on Mesoporous Chromium(III) Oxide

On-site electrosynthesis of hydrogen peroxide (H2O2) is a promising alternative technology to the conversional centralized anthraquinone oxidation process. Here, we report a platinum group metal (PGM)-free H2O2 electrogenerator with mesoporous Cr2O3 and NiCo2O4 used as electrocatalysts for oxygen reduction and evolution reactions (ORR and OER), respectively. The catalysts were synthesized via a hydrothermal synthesis route and had pore sizes of 3 and 7 nm and specific surface areas of 112 and 62 m2 g–1, respectively. Mesoporous Cr2O3 was evaluated in a half cell with 0.1 M KOH for electrocatalytic oxygen reduction, which shows 2.2 transferred electrons per oxygen and an in situ H2O2 yield of 70%. This enables the electrosynthesis of hydrogen peroxide in alkaline medium using Cr2O3 as a 2e-ORR-H2O2 electrocatalyst, with oxygen evolution as an auxiliary reaction on NiCo2O4. The effect of electrolyte flow on the H2O2 electrogenerator was investigated. It is observed that one-way feeding of the catholyte suppresses deterioration of the electrocatalyst and allows a faradic conversion up to ∼90% with a production rate of ∼0.36 [g (h·gcat)−1], operating within the cell voltage of 1.2 V. This work demonstrates both a viable method for electrosynthesis of H2O2 production using PGM-free electrocatalysts and the possibility to obtain a high faradic efficiency by mitigating the effect from catalyst degradation

Redox, surface and electrocatalytic properties of layer-by-layer films based upon Fe(III)-substituted crown polyoxometalate [P8W48O184Fe16(OH)28(H2O)4]20-

The electrocatalytic ability of the iron-substituted crown-type polyoxometalate (POM)Li4K16[P8W48O184Fe16(OH)28(H2O)4]·66H2O·2KCl (P8W48Fe16) towards the reduction of both nitriteand hydrogen peroxide reduction has been studied in both the solution and immobilized states for thePOM. P8W48Fe16was surface immobilised onto carbon electrode surfaces through employment of thelayer-by-layer technique (LBL) using pentaerythritol-based Ru(II)-metallodendrimer [RuD](PF6)8as thecationic layer within the resulting films. The constructed multilayer films have been extensively studiedby various electrochemical techniques and surface based techniques. Cyclic voltammetry and impedancespectroscopy have been utilized to monitor the construction of the LBL film after the deposition of eachmonolayer. The electrochemical behaviour of both a cationic and anionicredox probes at the LBL films has been undertaken to give indications as to the film’s porosity. The ele-mental composition and the surface morphology of the LBL films was conifmrde through the employmentof AFM, XPS and SEM