12. Fuel Cells and Battery Technology

From the viewpoints of global warming prevention and energy self-sufficiency, it is important to secure sustainable energy sources, and biomass use is expected to be one of them. Japan has rich biomass resources with approximately 70% of its land area covered by forests, and it is also desirable to utilize organic waste such as food waste generated from daily life. Since 2013, our laboratory has been developing a high-performance direct carbon fuel cell that combines molten salt gasification and tubular molten carbonate fuel cell using organic waste as a fuel. On the other hand, we have also developed a direct carbon fuel cell that obtains electricity directly from organic materials without the molten salt gasification part of the HF-DCFC. This study examined the DCFC consisting of the T-MCFC using activated carbon or brown coal as fuel. The DCFC performances were evaluated by I-V characteristics, Cole-Cole plots, and DRT analysis. The fuel was an 8:2 mixture of activated carbon or brown coal and carbonate, pulverized to about 100 µm by mil to increase the contact area. As a result, the polarization and diffusion resistances were smaller than those of brown coal. Generally, it is well known that the power generation reaction of the DCFC is controlled by the reaction between solid fuel and carbonate ions on the anode side. Therefore, although activated carbon is almost carbon, brown coal is only about 70% carbon, and the remainder is impurities such as ash and sulfur, we consider that these impurities have inhibited the migration of carbonate ions. Moreover, since fuel around the anode electrode was selectively consumed as DCFC power generation increased, it was also found that the gap between the electrode and fuel widened. Consequently, the diffusion resistance increased if fuel couldn’t be supplied to the anode electrode to fill this gap.