Multi-vanadium substituted polyoxometalates as efficient   electrocatalysts for the oxidation of l-cysteine at low potential on glassy   carbon electrodes
  The electrochemical behaviours of the sandwich-type complex [As2W18(VO)3O66]11- were studied in a pH 7 medium and compared with those of the three following Dawson-type vanadium-substituted complexes: [P2V2W16O62]8- (P2V2W16), [P2MoV2W15O62]8- (P2MoV2W15) and [P2V3W15O62]9- (P2V3W15). Electrochemistry shows that the sandwich-type POM contains 2 VIV centers and one VV center and must be formulated As2V2IVVW18, in agreement with titration, elemental analysis and magnetic measurements on this element.. All the POMs of this work proved efficient for the oxidation of L-cysteine. Comparison of the present results with those of mono-Vanadium substituted POMs indicates that accumulation of vanadium atoms in the POM framework is beneficial in the electrocatalytic process. In addition, the present work highlights the important influence of the POM structure in the electrocatalytic oxidation of L-cysteine. The remarkable outcome of this work is that the potential for the oxidation of L-cysteine in the presence of the selected POMs has been substantially driven in the negative direction compared to the case of glassy carbon alone, a feature which is associated with faster kinetics. The stability of the systems must also be pointed out. 
Bineta Keita (LCPO), Roland Contant (LCIMM), Pierre Mialane, Francis   S\'echeresse, Pedro De Oliveira (LCPO), Louis Nadjo (...