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

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