Cyclic voltammetry (CV), amperometric i - t experiments, and electrochemical impedance spectroscopy (EIS) measurements were carried out by using glassy carbon disk electrode covered with the Pt/C catalyst powder in solutions of 0.5 mol L-1 H2SO4 containing 0.5 mol L-1 CH3OH and 0.5 mol L-1 H2SO4 containing 0.5 mol L-1 HCCOH at 25 degrees C, respectively. Electrochemical measurements show that the activity of Pt/C for formic acid electrooxidation is prominently higher than for methanol electrooxidation. EIS information also discloses that the electrooxidation of methanol and formic acid on the Pt/C catalyst at various polarization potentials show different impedance behaviors. The mechanisms and the rate-determining steps of formic acid electrooxidation are also changed with the increase of the potential. Simultaneously, the effects of the electrode potentials on the impedance patterns were revealed. (C) 2009 Elsevier B.V. All rights reserved.