Direct carbon fuel cells offer highly efficient means of converting carbon from waste, biomass or coal to electricity producing an exhaust stream that is well-suited to CO 2 sequestration and, hence could underpin a new, clean carbon economy. If this technology is to contribute significantly to improving our impending global energy crisis, three aspects must first be addressed: competitive performance with extant fuel cell technologies, development of practical systems to handle available carbon resources and demonstration of sufficient durability, i.e. 40 000 hours minimum for system. In the present study, we demonstrate excellent performance from a hybrid direct carbon fuel cell based upon an yttriumstabilised zirconia electrolyte to use solid carbons as fuels directly. Good stability of the zirconia is observed during and after fuel cell testing and in corrosion tests under reducing conditions; however, significant intergrain erosion is observed under oxidising conditions. The carbon fuel chosen is a waste product, Medium Density Fibreboard, which is widely available and difficult to recycle. Cells exhibit excellent electrochemical performance at 750 C, with a maximum power density of 390 mW cm À2 using a lanthanum doped strontium manganite (LSM) cathode and 878 mW cm À2 using a lanthanum doped strontium cobalt (LSC) cathode under flowing air. This is comparable with current commercial Solid Oxide Fuel Cell and significantly in excess of commercial Molten Carbonate Fuel Cell (MCFC) performance. This hybrid direct carbon fuel cell therefore offers the clean utilisation of coal, waste and renewable carbon sources and hence merits development as a realistic alternative technology.

In this work, recent pressurized test results of a planar Ni-YSZ (YSZ: Yttria stabilized Zirconia) supported solid oxide cell are presented. Measurements were performed at 800°C in both fuel cell and electrolysis mode at different pressures. A comparison of the electrochemical performance of the cell at 1 and 3 bar shows a significant and equal performance gain at higher pressure in both fuel cell mode and electrolysis mode. Electrochemical impedance spectroscopy revealed that the serial resistance was not affected by the operation pressure; all the other processes that are dependent on partial pressures (oxygen, steam and hydrogen) were affected by increasing the pressure. In electrolysis mode at low current density, the performance improvement was counteracted by the increase in open circuit voltage, but it has to be borne in mind that the pressurized gas contains higher molar free energy.

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Direct carbon fuel cells offer the opportunity of generating energy from coal at high efficiency as an alternative to the procedure of conventional power plants. In this study, raw anthracite coal and raw bituminous coal were investigated in a hybrid direct carbon fuel cell (HDCFC), which was a combination of a solid oxide fuel cell and a molten carbonate fuel cell. Mechanical mixing was confirmed to be an efficient method of mixing coal with carbonate. The coal samples had different properties, for example, carbon content, hydrogen content, volatile matter and impurities. The results showed that the maximum power density obtained by the cell with anthracite coal was similar to that obtained by the cell with bituminous coal. It was found that the total power output from coal in HDCFCs mostly depended on the carbon content, while volatile matter, hydrogen content, moisture, etc. had an effect on the short-term durability. HDCFCs were kept operating for more than 120 hours with 1.6 g coal. This study demonstrates that energy can be generated efficiently by employing anthracite and bituminous coal in hybrid direct carbon fuel cells.

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