Role of acetyl group on proton conductivity in chitin system

Measurements of proton conductivity in chitin and chitosan have been carried out and proton conductivity is investigated. From the measurement of fuel cell based on the deacetylated chitin (chitosan) electrolyte, it was found that chitosan becomes the electrolyte of fuel cell. This result indicates that chitosan in humidified condition exhibits proton conductivity as seen in chitin. Moreover, proton conductivity in chitin is about 100 times higher than that in chitosan. These results indicate that acetyl group is an important factor for the appearance of higher proton conductivity in chitin system. In addition, the anisotropy of proton conductivity in chitosan is much larger than that in the orientated chitin. Considering that proton conductivity is caused by proton transfer in water bridges, these results indicate that chitin and chitosan possess quasi-three dimensional water bridges and quasi-two dimensional water bridges, respectively. It is deduced from these results that acetyl group is a key factor not only the appearance of higher proton conductivity but also the realization of quasi-three dimensional proton conductivity.