Preparation and electrochemical properties of Keggin-type phosphomolybdic anions in electrostaticly linked l-cysteine self-assembled monolayers

A composite film containing heteropolyanion was fabricated by attaching the Keggin-type phosphomolybdic PMo12O403− on l-cysteine self-assembled monolayers film modified gold electrode by electrostatic adsorption. ATR-FTIR, SEM, AC impedance and cyclic voltammetry, chronocoulometry were used for the characterization and electrochemical properties of the composite film. Two reversible redox couples were observed in 1.0 mol l−1 H2SO4 in the potential range of 0.2–0.8 V, which was attributed to two-electron and two-proton electrochemical processes of PMo12O403−. Charge transfer coefficient is 3.76×10−8 cm2 s−1. FTIR studies indicated that there was some electrostatic interaction between PMo12O403− and surface NH3+. Compared with PMo12O403− in the solution, the composite film electrode can exist in a larger pH range and has a good sensitive respond to H+, which can be used as pH-potential sensor. Moreover, the composite film shows good catalytic activities for the reduction of bromate anion (BrO3−) and nitrite (NO2−) in acidic solution. The catalytic mechanisms were described.