Feasibility of using ash-free coal in a solid-oxide-electrolyte direct carbon fuel cell

The feasibility of using ash-free coal as the fuel in a direct carbon fuel cell (DCFC) was investigated. Tubular-electrolyte-supported single cells were operated at high temperatures with continuous fuel feeding equipment. A single cell consisted of an yttria-stabilized zirconia (YSZ) electrolyte tube support, a NiO-YSZ cermet anode, and an LSM-YSZ composite cathode. The solvent extraction method was used to remove mineral matter and ash from raw coal. From thermal gravimetric analysis, the ash content of the ash-free coal was found to be nearly zero, but its volatile matter content was 38.34 wt.%. Scanning electron microscopy (SEM) observations and visualization tests were carried out for characterization of the interface of the ash-free coal; the results showed that the ash-free coal was in a liquid-like phase at high temperatures because the volatile matter in the coal produced by solvent extraction could help maintain carbon in the liquid-like state on the anode at high temperatures. The cell performance was affected by this liquid-like state at high temperatures.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The feasibility of using ash-free coal as the fuel in DCFC is proposed. ► Carbon in the ash-free coal is in the liquid-like state at high temperatures. ► The overall phase changes of the ash-free coal at high temperatures; Solid → liquid (and gas) → solid. ► The cell performance is more affected by direct C-oxidation than CO oxidation electrochemically.