Electrochemical behavior of nanostructured nickel phthalocyanine (NiPc/C) for oxygen reduction reaction in alkaline media

Carbon-supported nickel phthalocyanine (NiPc/C) nanoparticle catalysts have been synthesized by a simple solvent-impregnation and milling procedure, then heat-treated at 600, 700, 800 and 900 A degrees C to optimize their activity for the oxygen reduction reaction (ORR). The electrocatalytic activity and electron transfer mechanism of NiPc/C catalysts were demonstrated in oxygen-saturated alkaline electrolyte by cyclic voltammetry, linear sweep voltammetry as well as rotating disk electrode techniques, respectively. The results show that the heat-treatment temperature has a remarkable impact on the ORR activity of NiPc/C. An onset potential of 0.05 V and a half-wave potential of -0.15 V are achieved in 0.1 M KOH after the catalyst was heat-treated at 800 A degrees C. In addition to an increase in ORR kinetics, the number of electrons transferred for ORR also increased from 2.2 to 2.8 with increasing heat-treatment temperature from 600 to 800 A degrees C. To understand the heat-treatment effect, X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy (XPS) were used to identify the catalyst structure and composition. From XPS analysis, pyridinic-N and graphitic-N were clearly observed after the sample was heat-treated at 800 A degrees C. Both of these species might be assigned to sites catalytically active toward the ORR leading to activity enhancement.