To prepare working electrodes, the previously reported method was adapted . Firstly, two sheets of laminating foil were pressed on one edge with a hot iron to thermally join them. Then they were cut to a size of about 18 × 10 mm. In one sheet, a hole of 6 mm in diameter (geometric area about 30 mm 2 ) was punched with a corkborer. Carbon paper was cut to the size of about 18 × 7 mm and it was placed between the two sheets of laminating foil in such a way that it was exposed trough aforementioned hole. Then, gold-coated glass slide serving as an electrical contact to the carbon paper was placed between far side of the carbon paper and the sheets of foil. Finally, everything was laminated using hot iron and the extend of foil was cut with scissors. Furthermore, the exposed surface of the electrode was rinsed with isopropanol to remove any impurities and then dried.