**1. Introduction**

In the olden days of biomaterials, prostheses and medical alternatives have been mainly developed. However, there are reports that biomaterials play a wider range of roles today and can be used in the field of electronic devices such as sensors. In other words, biomaterials are not limited to medical materials, but are becoming more valuable than materials such as plastics and metals that we usually use.

We have fabricated fuel cells based on chitin and investigated its proton conductivity in chitin systems. It is well known that the chitin is superior biomass emitted from marine products and is obtained from crabs and shrimp shells. It is also famous that chitin has excellent biocompatibility and can be easily decomposed in the environment. For a long time, most research on chitin focused on biocompatibility and ion adsorption capacity. For example, Malette *et al*. have studied the curative effect of chitosan on the vulnerary [1]. Sandford *et al*. reported the useful substituent effect of chitosan to skin [2, 3]. Nair and Madhavan have suggested the method for the elimination of Hg in solution using chitosan, and Peniche-covas *et al*. have investigated the efficiency of adsorption of Hg [4, 5]. Recent studies seem to focus specifically on biocompatibile medical application and biomass. Romana *et al*. have suggested that chitin-PLA laminated composite becomes a candidate for medical applications such as implants [6]. Mohamoud *et al*. have shown that insects can be used as an alternative low-cost chitin source, and bio-convert chitin directly to ethanol by using strain of *M. circinelloides* [7].

**Figure 1.**

*Schematic diagram of fuel cell used for demonstration (left) and photograph of turning up LED lamp by chitin fuel cell (right).*

However, there were few reports in the field of energy such as using chitin in fuel cells. Biomaterials such as DNA, protein and polysaccharide are abundant in nature, and they are disassembled in environment by microbial. Active use of biomaterials is expected to have less environmental impact and manufacturing costs than chemical processes.

We have revealed that the chitin is proton conductor and available for electrolyte of fuel cells (**Figure 1**) [8]. Moreover, it was found that appearance of proton conductivity in chitin demand water molecules, and the acetyl group plays important role in injection water molecule into chitin. These suggestions are basis on relationship between results of impedance measurement and water content measurement with humidified condition. In appearance of proton conductivity in chitin, it is considered that one more important factor is exist of amino acetyl group. Effects of amino acetyl group have been revealed by comparing to proton conductivity in chitosan which is basic structure of chitin. Considering proton conduction system of chemical polymer Nafion® which is used the most for fuel cell, it is deduced that the amino and acetyl group in chitin involves forming hydration supporting proton transport. Although, it is found that power density and proton conductivity in chitin are lower than the Nafion®.

Therefore, in order to improve proton conductivity, there is room for further investigation of the relationship between the appearance of proton conductivity in chitin and water molecules. These understandings are expected to present the necessary and important factors for applying polysaccharides with little change in basic structure to electrolyte membranes.
