Effect of fuel thermal pretreament on the electrochemical performance of a direct lignite coal fuel cell

The impact of fuel heat pretreatment on the performance of a direct carbon fuel cell (DCFC) is investigated by utilizing lignite (LG) coal as feedstock in a solid oxide fuel cell of the type: lignite | Co-CeO2/YSZ/Ag | air. Four LG samples are employed as feedstock: (i) pristine lignite (LG), and differently heat treated LG samples under inert (He) atmosphere at (ii) 200 °C overnight (LG200), (iii) 500 °C for 1 h (LG500) and (iv) 800 °C for 1 h (LG800). The impact of several process parameters, related to cell temperature (700-800 °C), carrier gas type (He or CO2), and molten carbonate infusion into the feedstock on the DCFC performance is additionally explored. The proximate and ultimate analysis of the original and pretreated lignite samples show that upon increasing the heat treatment temperature the carbon content is monotonically increased, whereas the volatile matter, moisture, sulfur and oxygen contents are decreased. In addition, although volatiles are eliminated upon increasing the treatment temperature and as a consequence more ordered carbonaceous structure remained, the heat treatment increases the reactivity of lignite with CO2 due mainly to the increased carbon content. These modifications are reflected on the achieved DCFC performance, which is clearly improved upon increasing the treatment temperature. An inferior cell performance is demonstrated by utilizing inert He instead of reactive CO2 atmosphere, as purging gas in the anode compartment, while carbonate infusion always results in ca. 70-100% increase in power output (15.1 mW cm− 2 at 800 °C). The obtained findings are discussed based also on AC impedance spectroscopy measurements, which revealed the impact of LG physicochemical characteristics and DCFC operating parameters on both ohmic and electrode resistances.