Silica-pillared graphene sheets with iron–nitrogen units as an oxygen reduction catalyst

Graphene layers with silica pillars which widen the interlayer distance and functionalize the space as micropores have been prepared as one of the new porous carbon materials. In this study, the silica-pillared graphene with Fe–N units as a catalytic active site for cathodic oxygen reduction was formed as a new type of carbonaceous noble-metal-free oxygen reduction catalysts with the ordered pore structure. The formation of the pillared carbon was performed by introducing silylating reagents as the pillar source and also as the nitrogen source of the units in the graphite oxide interlayer spaces, introducing the Fe ions, and heat treatment in vacuum at 500 °C. The X-ray diffraction (XRD) patterns showed the ordered layered structure. The X-ray absorption fine structure (XAFS) of the Fe-K edge showed that the unit was a square planar Fe–N4 moiety. The catalytic activity for the O2 reduction was demonstrated by measurements using rotating disk electrodes with the pillared carbon fixed on the surface and immersed in an oxygen-saturated acidic solution. The activity was enhanced by the combination of the nitrogen containing compound to the silylating reagent and using the nitrogen-rich silylating reagent.