ナノシェル含有カーボンの酸素還元活性に及ぼす表面金属錯体の寄与

抄録

A carbon material containing carbon nanoshell particles in an amorphous carbon matrix (CNS/C), has a catalytic activity for the oxygen reduction reaction (ORR). The nanoshells have diameters in the range 20∼50 nm, and are produced by the catalytic effect of a transition metal such as iron during carbonization. The activity of the CNS/C is believed to originate from defects located on the surface of the nanoshells. There still remains a possibility of surface metal complexes participating in the ORR. This study intended to clarify the influence of such types of active sites on the ORR activity of CNS/Cs. The materials were prepared by carbonizing a mixture of iron phthalocyanine and phenol-formaldehyde resin at 800 °C or 1000 °C followed by pulverization. Acid washing in a HCl solution of 1∼12 mol L^-1 at room temperature or 70 °C for 2 h was repeated three times. The surface concentration of iron decreased to the detection limit of X-ray photoelectron spectroscopy. The ORR activity obtained in a H₂SO₄ solution was not influenced by the acid washing treatment. The results indicate a lower possibility of the participation of surface metal complexes than has been claimed for the catalytic activity of CNS/C in the ORR.