Electrode properties of a double layer capacitor of nano-structured graphite produced by ball milling under a hydrogen atmosphere

Nano-structural graphite prepared by ball milling under H2 or Ar atmosphere was studied as an electrode for electric double layer capacitors (EDLCs) by means of a conventional 2-electrode galvanostatic method. Especially, the product prepared under H2 atmosphere using zirconia balls revealed 500 m2 g−1 surface area and showed 12 F g−1 specific capacitance, which was comparable to that of an activated carbon with large specific surface area of 3000 m2 g−1 examined as a reference. A proper condition of the milling time is rather a shorter time than ∼8 h, where the graphitic feature is remained in the ball milled product. On the other hand, for the sample prepared by using steel balls, the specific capacitance per surface area was several hundreds times smaller than the others, indicating that the small amount of Fe contamination during milling played a negative role for the EDLC properties.