with bidistilled water. The electrochemical measurements were
performed at 25 °C in a three-compartment cell provided with a
Luggin capillary and N2 gas inlet. The nitrogen used was ultra pure.
A saturated calomel electrode was used as reference, and a platinum
wire spiral (10 cm length, 0.05 cm diameter) served as auxiliary
electrode. Electrochemical measurements were performed using
a potentiostat–galvanostat CH Instruments model 1100 (Austin, USA).
Prior to experiments, the edge plane ordinary pyrolytic graphite
electrodes were mechanically polished with 1200, 2400 and 4000 grit
SiC grinding papers, followed by sonication for 5 s in bidistilled water.
The electrolyte, 0.1 M oxalic acid (pH 1.3) was deaerated by purging
with N2 for 10 min. Then the electrode was cycled 10 times between
−1.0 and 0.2 V at a scan rate of 0.1 V s−1. The baseline of the differential
pulse voltammetric (DPV) response was recorded in the same potential
window. Oxalic acidwas selected as electrolyte, in order to compare the
results with those reported before [17].