The unmodified carbon paste was prepared by thoroughly hand-mixing 5 g of graphite powder and 3 mL of mineral oil (Aldrich). The CoPc-modified paste was prepared in a similar pattern except that the graphite powder was mixed with the desired weight of CoPc before adding the mineral oil. Mixing of these two components was accomplished by adding 10 mL of diethyl ether to 5 g of the CoPc/graphite mixture and sonicating until all the diethyl ether evaporated. The CoPc loading in the carbon paste was described in terms of percent basis of the weight of CoPc added to the graphite powder. A copper wire (10 cm long and 0.5 mm diameter) was inserted into a piece of fused silica capillary (5 cm long, 0.53 mm i.d., 0.68 mm o.d.) and a 1.0-cm opening was left in the capillary for the subsequent filling of the paste material. A portion of CoPc/graphite mixture was then packed into one end of a fuse silica capillary. Finally, the surface was smoothed by polishing on a piece of weighing paper to form a disc electrode. Electrical contact was obtained using internal copper wire.