Similarly, for the spectrum of PGC electrodes, the wide peak in the frequency range of 3,200-3,500 cm -1 is ascribed to the O-H. Stretching vibration peaks of C=O, C-O and O-H were located at 1,610 cm -1 , 1,201 cm -1 and 1,021 cm -1 separately. These peaks demonstrated the existence of -COOH and the excess of gallic acid in PGC electrodes.