For the construction of the working electrodes, commercially available type H cylindrical graphite pencils were employed.
The graphite pencils, initially 60 mm long, were cut in half and placed within a glass capillary tube.
Then, a fast-drying epoxy resin (∼2 min) was used to seal and attach the electrodes to the glass capillary.
An alligator type connector was used to make electricalcontact.
Before the electrochemical experiments, the graphite pencil electrode (geometric area of 0.07 mm2) was carefully polished
with 0.3 m alumina slurry.
Then, the surface of the electrode was washed with water to remove weakly adsorbed alumina particles.