The anodic reaction zone and performance of different carbonaceous fuels in a batch molten hydroxide direct carbon fuel cell

•Three phase fuel-anode-electrolyte interface reaction zone in DCFC.•Linear V–i behavior indicative of ohmic-controlled polarization.•Significant contribution from fuel-anode contact resistance.

Results are presented of an analysis of the nature of the reaction zone in the anode of a direct carbon fuel cell (DCFC). Five different types of particulate carbonaceous fuels were investigated, including nonconductive as-received coals, and more conductive pyrolyzed coal chars and an activated charcoal. All the fuels exhibited linear voltage–current density behavior indicative of ohmic-controlled polarization. The two as-received coals (Pittsburgh No. 8 bituminous coal and Beulah-Zap lignite) exhibited greater open-circuit voltages (OCV) of ∼1.2 V than their corresponding pyrolyzed forms and the activated charcoal, the latter of which were all ca. 1.0 V. It was also found that differences in electrochemical reactivity of the as-received and pyrolyzed coal fuels correlated with their thermal heating values. Even so, maximum power and current densities were comparable for all the particulate fuels investigated, irrespective of the conductivity of the fuel particles. Based on fuel characterization and performance data, it is concluded that the electrochemical reaction zone in packed-bed anodes of the type examined here is limited to the three-phase solid fuel-anode-molten electrolyte contact zone. This intrinsic characteristic represents a limitation on the electrochemical performance of these types of DCFCs, in comparison to other fuel cells with fluid fuels.