Hirota Yuki, Tominaga Taiki, Kawabata Takashi, Kawakita Yukinobu, Matsuo Yasumitsu
Department of Life Science, Faculty of Science & Engineering, Setsunan University, Ikeda-Nakamachi, Neyagawa 572-8508, Osaka, Japan.
Neutron Science and Technology Center, Comprehensive Research Organization for Science and Society (CROSS), Tokai, Nakagun 319-1106, Ibaraki, Japan.
Bioengineering (Basel). 2023 May 22;10(5):622. doi: 10.3390/bioengineering10050622.
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 (HO) 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.
最近，有报道称几丁质和壳聚糖表现出高质子传导性，并在燃料电池中作为电解质发挥作用。特别值得注意的是，水合几丁质中的质子传导率比水合壳聚糖中的高30倍。由于燃料电池电解质需要更高的质子传导率，从微观角度阐明实现更高质子传导的关键因素对于燃料电池的未来发展具有重要意义。因此，我们从微观角度使用准弹性中子散射（QENS）测量了水合几丁质中的质子动力学，并比较了水合几丁质和壳聚糖之间的质子传导机制。QENS结果表明，即使在238K时，几丁质中的一部分氢原子和水合水也是可移动的，并且可移动氢原子及其扩散随温度升高而增加。研究发现，几丁质中可移动质子的扩散常数是壳聚糖中的两倍，停留时间快两倍。此外，实验结果表明，几丁质和壳聚糖之间可解离氢原子的转变过程不同。为了在水合壳聚糖中实现质子传导，水合氢离子（HO）的氢原子应转移到另一个水合水中。相比之下，在水合几丁质中，氢原子可以直接转移到相邻几丁质的质子受体上。据推断，水合几丁质中比水合壳聚糖中更高的质子传导率是由氢原子动力学的扩散常数和停留时间以及质子受体的位置和数量的差异产生的。
