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In an attempt to obtain carbon catalysts with higher activity for the oxygen reduction reaction (ORR), a mechanochemical (M)treatment was applied to a heat-treated precursor of carbon-nanoshell-containing catalysts at 500 • C, where the nanoshell was a catalytically formed, shell-structured carbon material with diameter of 20-30 nm and walls that consisted of hexagonal carbon layers. The precursor was a mixture of cobalt phthalocyanine and a phenol-formaldehyde resin. The carbonized precursor that was mechanochemically treated after the heat-treatment at 500 • C showed higher ORR activity, with ORR current density that was five times that of the carbonized untreated precursor. Characterizations of the precursors and the carbons concluded that the enhanced ORR catalytic activity was due to the formation of carbon nanoshells with disordered hexagonal carbon layers located on their surface, and these nanoshells had a higher N/C surface atomic ratio than those of the carbonized untreated precursors. The application of M-treatment to a 500 • C-heat-treated precursor was thus revealed to be useful for improving the ORR activity of carbon nanoshells.

Nanoshell-containing carbon (NSCC) is one of the Pt-surrogate catalysts for proton exchange membrane fuel cell (PEMFC) invented by us to promote oxygen reduction reaction (ORR), the cathode reaction of the cell. In the present study, we selected one of renewable resources, lignin from herbaceous plants as the carbon precursor for NSCC. The lignin was admixed with cobalt phthalocyanine (CoPc), the nanoshell (NS) forming catalyst, and then carbonized at 1000˚C. Transmission electron microscopy and X-ray diffraction studies confirmed the formation of NS structure. The ORR activity of the prepared NSCC increased with the amount of CoPc, and the activity of lignin-based NSCC was higher than that of phenol-formaldehyde resin-based NSCC with the same amount of CoPc added. Surface analysis by X-ray photoelectron spectroscopy revealed no metal species on the NSCC but higher N/C ratio for the lignin-based NSCC by two folds. This study shows the possibility of lignin as a precursor of NSCC cathode catalyst for PEMFC.

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