Electrostatic synthesis and electrochemical properties of a composition comprising ultrathin layers of silicododecamolybdate anions and poly(allyl ammonium) cations

A layer-by-layer (LbL) composition comprising ultrathin anionic layers of silicododecamolybdate and cationic layers of poly(allyl ammonium) is synthesized. The synthesis is realized by means of successive immersion of a glassy-carbon rod into aqueous sulfuric acid solutions of silicododecamolybdic acid and poly(allyl ammonium) hydrochloride. Cyclic voltammetry shows that the silicododecamolybdate anion in the composition undergoes three steps of reversible reduction with formal potentials of 0.34, 0.22, and 0.02 V (SCE). It is established that in the course of synthesis one can obtain a sixfold increase in the currents of redox conversions as compared with currents of a monolayer of the anion chemisorbed on glassy carbon. The LbL composition exhibits catalytic activity during electrochemical reduction of NO ₂ ^? : the cathodic current of the third redox transition considerably increases and the peak in the reverse run of a cyclic voltammogram disappears. The calculated Michaelis constant of 5 × 10^?2 M speaks of a high catalytic activity of the electrode.