Carbon Loading Of Cobalt Phthalocyanine Catalyst Preparation And Oxygen Reduction Catalytic Performance

Metal-phthalocyanine compounds show good electrocatalytic activity for oxygen reduction due to its high conjugate structure and chemical stability. Thus, it has becomed a new direction in catalyst research field. There are four basic factors in the preparation of Metal-phthalocyanine compounds:Transition metals, Nitrogen sources, carbon support and pyrolysis temperatures. The central transition metals are usually Fe, Co, Ni and Mn. Metal-phthalocyanine which containing Fe and Co as central ions are reasearched more due to its higher catalytic activity.In this paper, carbon supported Cobalt-phthalocyanine (CoPc/C) catalyst was synthesized in one step through calcinations. With this method, a catalyst with high activity was obtained.The result showed that the product was CoPc/C with the average particle size of 30 nm and had a well distribution and morphology.We studied the influence of pretreated carbon carrier for ORR catalytic activity. When carbon was treated by nitric acid, the current density increased obviously to 60 mA·cm-2 at potential of-0.2 V versus an Hg/HgO reference electrode. Compared to cabon material without any treatment, the Co-phthalocyanine compounds CoPc/C catalysts with acid-treated carbon as support showed a higher catalytic activity and the current density increased 70 mA·cm-2 at the same condition. This supported an opinion that carbon material not only acted as an carrier, but also affected the activity and selectivity for ORR due to its hole fabric and apparent status.After comparision and analysis to the CoPc/C catalysts prepared at different temperatures, the optimal pyrolyzed temperature was observed at 600℃. XRD patterns of catalysts prepared under these temperatures showed that Co-phthalocyanine polymer is stable up to 600℃and pyrolized to oxides containing Co at higher temperature as to 900℃. Based on this facts, we speculated that the active site for ORR should be Co-N-C structure formed at 600℃when CoPc connected to carbon suface.Various Co/C weight ratios were examined and the maximum activity was found to be 5% Co/C weight ratio. With the sample prepared under the optimal condition as catalyst for ORR, the onset potential of ORR is 0 V and the current density can reach 100 mA·cm-2 at-0.1V.The electrochemical testing results were data-fitted and analysed. The fitting value in polarization curves indicates the exchange current density of ORR on the carbon-supported catalyst electrode was i0b=2.59×10-10 A·cm-2, raised by two orders of magnitude compared to naked carbon electrode. This means the catalyst could facilitate kinetic process of ORR obviously. The increased double layers capacitance had a main contribution to the activity of catalyst, the effectively active site has been increased in this way.