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The direct carbon fuel cells (DCFCs) belong to new generation of energy conversion devices that are characterized by much higher efficiencies and lower emission of pollutants than conventional coal-fired power plants. In this paper the DCFC with molten hydroxide electrolyte is considered as the most promising type of the direct carbon fuel cells. Binary alkali hydroxide mixture (NaOH-LiOH, 90–10 mol%) is used as electrolyte and the biochar of apple tree origin carbonized at 873 K is applied as fuel. The performance of a lab-scale DCFC with molten alkaline electrolyte is investigated and theoretical, practical, voltage, and fuel utilization efficiencies of the cell are calculated and discussed. The practical efficiency is assessed on the basis of fuel HHV and LHV and the values are estimated at 40% and 41%, respectively. The average voltage efficiency is calculated as roughly 59% (at 0.65 V) and it is in a relatively good agreement with the values obtained by other researchers. The calculated efficiency of fuel utilization exceeds 95% thus indicating a high degree of carbon conversion into the electric power. [ABSTRACT FROM AUTHOR]

Biochar obtained from the pyrolysis of corn cob is used as the fuel of a direct carbon fuel cell (DCFC) employing a composite electrolyte composed of a samarium doped ceria (SDC) and a eutectic carbonate phase. An anode layer made of NiO and SDC is utilized to suppress the cathode corrosion by the molten carbonate and improves the whole cell stability. The anode off-gas of the fuel cell is analyzed with a gas chromatograph. The effect of working temperature on the cell resistance and power output is examined. The maximum power output achieves 185 mW cm −2 at a current density of 340 mA cm −2 and 750 °C. An anode reaction scheme including the Boudouard reaction is proposed. [ABSTRACT FROM AUTHOR]

In this study, a heteroatom-doped porous biochar from waste biomass was prepared via a facile self-sacrificial template strategy for enhanced electrochemical capacitive performance. Numerous narrow pores and carbonized frameworks were formed by hydrothermally decomposing the unstable components in the biomass, which were further broadened to micropores and even larger mesopores through a molten salt activation method. The synthesized porous biochar displayed apparently increased specific surface area, up to 1138 m2 g−1, well-developed porous structure, and moderate heteroatom doping (5.35 at.% O and 1.02 at.% N), which offered more active storage sites and charge capacities. Consequently, the modified biochar exhibited significantly enhanced specific capacitance of 447 F g−1 at 0.2 A g−1, which was 1.6 and 6.0 times higher than that of the samples carbonized directly by molten salt and inert reduction methods, respectively. The findings indicate that the facile self-sacrificial template synthetic route of biochar does not only provide larger pores for reducing the ion diffusion resistance, but also introduces heteroatoms into the carbon frame to increase charge mobility. Moreover, the assembled two-electrode symmetric supercapacitor presented not only a specific capacitance of 367 F g−1 with an energy density of 12.75 Wh∙kg−1 but also an excellent stability after 10000 cycles. Image 1 • Heteroatom doped porous biochar was prepared via self-sacrificial template method. • Numerous micropores were well developed by hydrothermal and molten salt process. • Specific capacitances of 447 F/g at 0.2 A/g and 226 F/g at 20 A/g were achieved. • The porous biochar exhibited retention rate of 91.4% after 10000 cycles at 5 A/g. [ABSTRACT FROM AUTHOR]