Medium-sized pores of which diameter was over 100 nm were successfully prepared by anodization in 3 wt% HF aqueous solution containing KMnO4 and surfactant. The presence of an appropriate oxidizing agent and a surfactant was indispensable for the formation of medium-sized pores, but the concentration dependence was not significant. Similar method was applied to the p+-type silicon and led to the pore widening.
The electrochemical treatment of activated carbon electrodes has been investigated as a novel method enhancing the capacitance of electric double layer capacitor (EDLC) electrodes. The treatment at 0.7 V floating in a week at 70°C can be applied to EDLC with aqueous electrolytes. In 30 wt% H2SO4/H2O electrolyte, the treatment causes a capacitance increase in a low voltage region: 0–0.4 V. On the other hand, in 3.5 M NaBr/H2O electrolyte, it results in a remarkable capacitance increase of 2.4 times in a high voltage region: 0.4–1.0 V. These results suggest that the treatment mechanisms in the above electrolyte systems should be different. We report herein the origins and mechanisms of these capacitance increases.