Evaluation of Nitrogen Species and Microstructure of Silk-Derived Activated Carbon as Non-Precious Metal Catalyst for PEFC Cathode

Abstract

Silk-derived activated carbon (SAC) was prepared by steam activation and milling process. SAC yield increased by using milling process instead of steam activation. However, surface area decreased. By ball milling process, nitrogen and oxygen species, which existed inside the as-prepared SAC, appeared at the surface, thus decreasing ORR activity. ORR activity recovered by sintering after milling. By ammonia treatment of SAC, atomic ratio of nitrogen (expecially pyridine-type) increased. Change in graphite-type nitrogen was small. EORR showed little change with and without ammonia treatment. Oxygen reduction current showed remarkable increase, due to increase in surface area. The results suggest that, for SAC, EORR is dominated by the degree of carbonization and current is dominated by the surface area.