Ken'ichi Kimijima

Electrochemistry in Nano-Space of Structurally Controlled Carbon Materials

Development of structurally controlled carbon materials is important for processing of electrode materials. Among many kinds of carbon materials, mesoporous carbon is used for our study. It is scientifically interesting because of its highly controllable structure in nano-scale. Also it is a practical material in terms of easy synthetic processes through the selforganization of surfactants (Pluronic F127) and carbon precursors (resorcinol and formaldehyde). So far, we have particuly worked on mesoporous carbon with three dimensionally well ordered 8 nm-pores. Such nano-space was treated as a reaction site, and variouse catalysts, such as Pt catalyts or biologocal enzymes, were introduced into nano-space, and further the electrocatlytic properties were investigated. To understand nano-effect in electrocatalytic reactions, commercially available carbon black, whose structure was non-porous spheres with interperticles pores (over 30 nm), was used for the comparison. When Pt catalysts were introduced, within the 8 nm-pores against larger nano-space, the different phenomena were observed. Stability of catalysts was higher. Both proton and hydrogen/oxygen were effectively provided, and further successful drain of water through the pores was achieved. Due to all these combined conditions, the promotion of electrocatalytic reactions occurring in Polymer Electrolyte fuel cells (PEFC’s) has been accomplished. Based on this characteristic behavior, we have performed more detailed study in nano-space. In this paper, electrochemical reactions, such as hydrogen/oxygen evolution reactions related PEFC, within small and hydrophobic nano-space were studied.. During the studies of electrochemistry, reaction selectivity was demonstrated. Within the pores of 8 nm, hydrogen evolution and hydrogen oxidation were promoted, but oxygen evolution reaction was suppressed (see Figure 1). This selectivity is probably due to the fact that only small amount of water is expected to exist within such small and hydrophobic nano-space even though proton pass is effectively maintained. Consequently, the selectivity in reactions, such as activation of proton-related reactions and suppression of water-related reactions, is achieved. Interstingly, it cannnot be obtained wihtout successful intoroduction of a proton conducting ionomer within the nano-space, and contolling of nano-enviromrnt around Pt catalysts will be a key for successful electrocatalytic reactions in nanospace.