This study investigated the impact of ternary carbonate composition (Li2CO3/Na2CO3/K2CO3) on the morphology of the carbon/carbonate slurry and the continuous power generation by direct carbon fuel cells (DCFCs). Carbon/carbonate mixtures were melted to form a slurry at 1073 K. After cooling, the morphology of the solidified slurries was observed at the macro and micro scales. Notable differences were found in the morphology when the carbonate composition was changed. The solidified slurry surface was smooth, with surface carbon particles partly embedded in the carbonate, at Li/Na/K = 12.2/25/62.8 mol %, whereas the slurry surface was irregular, with carbon particles on the surface not embedded in the carbonate at Li/Na/K = 12.2/45/42.8 mol %. This suggested that the carbon particles were well-wetted in the former composition but not in the latter. It was also shown that wetting of the carbon particles was improved by decreasing the mole fraction of Na2CO3, which lowered the surface tension of the molten c...