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A triple phase boundary reaction site was formed in a direct carbon fuel cell (DCFC) when the char wetted by molten carbonate was in contact with the anode. It has been reported that gases such as CO 2 covered the anode during discharge, leading to high anode overpotential. In this study, a press-type DCFC was developed to overcome this issue. By pressing the perforated anode on the carbon/carbonate-packed bed, it was expected that the carbon particles would remain in contact with the anode, while the gas products would be released through the perforation due to their buoyancy. As a result, the power output achieved with the press-type DCFC was higher and more stable as compared with the conventional DCFC. The anodic impedance spectra showed that the arc size of the press-type DCFC was much smaller than that of the conventional DCFC. This was particularly noticeable at the low frequencies, indicating the anode resistance caused by the mass transfer processes including the gas products and the contact between the anode and carbon particles to be significantly less in the press-type DCFC.

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The power output of a press-type direct carbon fuel cell (DCFC) with the perforated anode pressed on the carbon/carbonate-packed bed was studied by correlation with impedance spectroscopy at different carbon loads. Image analysis of the solidified carbon/carbonate-packed bed showed that the filling ratio of carbon and the contact area between carbon and the anode linearly increased as the initial carbon load increased. The power output of the DCFC also increased with increasing the initial carbon load and became almost saturated at an initial carbon load of 3.0 wt %. This trend coincided with the anode side impedance spectra. At high current densities, the power output became unstable and a continuous discharge could not be achieved at an initial carbon content of 5.0 wt %. Although the press-type DCFC is designed to release gas products through its perforated anode, those products likely still remained around the anode at high current densities. Spaces between the carbon particles in the packed bed worked as a channel for ion diffusion. Therefore, gas products likely blocked this ion diffusion channel, narrowing with increasing the filling ratio of carbon. By linking the impedance spectra with the power output of the press-type DCFC, it was suggested that the ion diffusion process in the carbon/carbonate-packed bed played an important role for stable continuous discharge at high current densities.

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