Takashi Kawabata

Recently, it was reported that chitin and chitosan exhibited high-proton conductivity and function as an electrolyte in fuel cells. In particular, it is noteworthy that proton conductivity in the hydrated chitin becomes 30 times higher than that in the hydrated chitosan. Since higher proton conductivity is necessary for the fuel cell electrolyte, it is significantly important to clarify the key factor for the realization of higher proton conduction from a microscopic viewpoint for the future development of fuel cells. Therefore, we have measured proton dynamics in the hydrated chitin using quasi-elastic neutron scattering (QENS) from the microscopic viewpoint and compared the proton conduction mechanism between hydrated chitin and chitosan. QENS results exhibited that a part of hydrogen atoms and hydration water in chitin are mobile even at 238 K, and the mobile hydrogen atoms and their diffusion increase with increasing temperature. It was found that the diffusion constant of mobile protons is two times larger and that the residence time is two times faster in chitin than that in chitosan. In addition, it is revealed from the experimental results that the transition process of dissociable hydrogen atoms between chitin and chitosan is different. To realize proton conduction in the hydrated chitosan, the hydrogen atoms of the hydronium ions (H₃O⁺) should be transferred to another hydration water. By contrast, in hydrated chitin, the hydrogen atoms can transfer directly to the proton acceptors of neighboring chitin. It is deduced that higher proton conductivity in the hydrated chitin compared with that in the hydrated chitosan is yielded by the difference of diffusion constant and the residence time by hydrogen-atom dynamics and the location and number of proton acceptors.

Chitosan, an environmentally friendly and highly bio-producible material, is a potential proton-conducting electrolyte for use in fuel cells. Thus, to microscopically elucidate proton transport in hydrated chitosan, we employed the quasi-elastic neutron scattering (QENS) technique. QENS analysis showed that the hydration water, which was mobile even at 238 K, moved significantly more slowly than the bulk water, in addition to exhibiting jump diffusion. Furthermore, upon increasing the temperature from 238 to 283 K, the diffusion constant of water increased from 1.33 × 10⁻⁶ to 1.34 × 10⁻⁵ cm²/s. It was also found that a portion of the hydrogen atoms in chitosan undergo a jump-diffusion motion similar to that of the hydrogen present in water. Moreover, QENS analysis revealed that the activation energy for the jump-diffusion of hydrogen in chitosan and in the hydration water was 0.30 eV, which is close to the value of 0.38 eV obtained from the temperature-dependent proton conductivity results. Overall, it was deduced that a portion of the hydrogen atoms in chitosan dissociate and protonate the interacting hydration water, resulting in the chitosan exhibiting proton conductivity.

We have created and researched fuel cells using biomaterials as next-generation low-environmental-load energy. As is well known, chitin is a biomass that is discharged in large quantities as a marine product processing waste. We have focused on the chitin and have been studying the production of fuel cells and proton conductivity using it. It was revealed that chitin can be used as an electrolyte membrane for fuel cells under humidified conditions and becomes a proton conductor. It was found that the presence of water molecules is important for the appearance of proton conduction in chitin system. This study presents the utility value of chitin in new fields and provides insight into the proton conduction mechanism of chitin-based biomaterials.

Group decisions inherently contain conflicts of interests among participants. Many group decision support systems have been introduced in order to effectively and efficiently induce final decisions after group discussions. Among many group decision support systems, we focus on the Yonmenkaigi System Method (YSM) which was originally developed for the group decision situations especially for participatory community planning discussions. The debate phase of YSM where each group of debaters can decide strategies/options that belong to their individual roles, has an unique rule that an option of one group can be forced to change by other majority participants in debate. This rule is modeled by utilizing Conflict Analysis model and the effects of the rule in equilibrium are clarified. It is shown that the rule can bring about improvement in players' overall payoffs. It is also shown that the rule can sometimes improve equality of payoffs among players especially when the result of group discussion tends to stick to the situation favorable to only one participant and not to majority.