Cyclic voltammograms indicated that two reversible redox waves were observed on the glassy carbon (GC) electrode in acidic aqueous solution containing . The first wave involves in 1.4 electron transfer and two protons during electrode reaction, and one electron and one proton are for the second wave. Diffusion coefficient Do of calculated from linear relationship of peak current versus square root of potential scan rate is 3.54×10－6 cm2•s－1 in a solution of 0.1 mol•L－1 NaOAc＋HOAc (pH 3.5). Alternating current (AC) voltammetry and AC impedance revealed that an adsorption of on the electrode surface occurred before electron transfer, which caused larger electron transfer impedance in the first wave than in the second wave. The exchange current density i0 corresponding to the first wave and the second wave is 4.6×10－5 and 6.7×10－4 A•cm－2, respectively. A reversible electrochemical property and a lacunary feature of make it electrocatalyze efficiently reduction of H2O2 in acidic aqueous solution. The system of /H2O2 thus represents a possible application to electrocatalytic oxidation of organic substrates. Also a novel catalytic mechanism was proposed.

Key words: lacunary heteropolytungstate, electrocatalysis, hydrogen peroxide, cyclic voltammetry, AC impedance