A direct carbon fuel cell (DCFC) can produce electricity with both superior electrical efficiency and fuel utilisation compared to all other types of fuel cells. Although the first DCFC prototype was proposed in 1896, there was, until the 1970s, little sustained effort to investigate further, because of technology development issues. Interest in DCFCs has recently been reinvigorated as a possible method of replacing conventional coal-fired power plants to meet the demands for lower CO emissions, and indeed for efficient utilisation of waste derived chars. In this article, recent developments in direct carbon conversion are reviewed, with the principal emphasis on the materials involved. The development of electrolytes, anodes and cathodes as well as fuel sources is examined. The activity and chemical stability of the anode materials are a critical concern addressed in the development of new materials. Redox media of molten carbonate or molten metal facilitating the transportation of ions offer promising possibilities for carbon oxidation. The suitability of different carbon fuels in various DCFC systems, in terms of crystal structure, surface properties, impurities and particle size, is also discussed. We explore the influence of a variety of parameters on the electrochemical performance of DCFCs, with regard to their open circuit voltage, power output and lifetime. The challenges faced in developing DCFCs are summarised, and potential prospects of the system are outlined.

Seven new pyridine dicarboxamide ligands H2L(1-7) have been synthesised from condensation reactions involving pyridine-2,6-dicarboxylic acid (H2dipic), pyridine-2,6-dicarbonyl dichloride or 2,6-diaminopyridine with heterocyclic amine or carboxylic acid precursors. Crystallographic analyses of N,N'-bis(2-pyridyl)pyridine-2,6-dicarboxamide monohydrate (H2L8 x H2O), N,N'-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide and N,N'-bis[2-(2-pyridyl)ethyl]pyridine-2,6-dicarboxamide monohydrate revealed extensive intramolecular hydrogen bonding interactions. 2,6-Bis(pyrazine-2-carboxamido)pyridine (H2L6) and 2,6-bis(pyridine-2-carboxamido)pyridine (H2L7) reacted with copper(II) acetate monohydrate to give tricopper(II) complexes [Cu3(L)2(mu2-OAc)2]. X-Ray crystallography confirmed deprotonation of the amidic nitrogen atoms and that the (L6,7)2- ligands and acetate anions hold three copper(II) ions in approximately linear fashion. H2L8. Reacted with copper(II) tetrakis(pyridine) perchlorate to give [Cu(L8)(OH2)]2 x 2H2O, in which (L8)2- was tridentate through the nitrogen atoms of the central pyridine ring and the deprotonated carboxamide groups at one copper centre, with one of the terminal pyridyl rings coordinating to the other copper atom in the dimer. The corresponding reaction using H2L7 gave [Cu3(L7)2(py)2][ClO4]2, which transformed during an attempted recrystallisation from ethanol under aerobic conditions to a tetracopper(II) complex [Cu4(L7)2(L7-O)2].

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Medium density fibreboard is a ubiquitous element in modern furniture, here we consider utilising waste MDF as a future energy source. In particular, we focus upon the hybrid direct carbon fuel cell (HDCFC), which involves a combined molten carbonate/solid oxide fuel cell anode/electrolyte interface and can be fuelled by a wide range of carbon forms. Current-voltage measurements and a.c. impedance at temperatures in the range of 525-800 C have been made on cells powered by pyrolysed medium density fibreboard (pMDF) samples which had undergone three different preparatory treatments (immersion of strips in molten eutectic carbonate mixture; deep soaking of strips in aqueous carbonate mixture corresponding to the eutectic composition and fine powdering). Below 700 C the three pMDF samples show quite different electrochemical performance in the HDCFC, but above 700 C their behaviour becomes similar. Powdered pMDF gives the best OCV (0.89 V) and lowest resistance (2.36 U) values below 700 C, although the electrochemical performance is dominated by diffusion limitations and the performance degrades at higher temperatures. The immersed strip behaves quite differently with limited performance below 750 C but it shows both good OCV, 1 V, and low resistance, <4 U, at higher temperatures. Three components are discernable, an ohmic contribution probably due to both ionic resistance of zirconia electrolyte and electronic resistance of current collection and two electrode processes thought to be associated with the transfer of oxygen ions at the electrode : electrolyte interface and diffusion of reactant species through the electrode. The activation energies calculated from the ohmic resistances for the three samples (À0.79 -À1.00 eV) are of similar order to that expected for the yttria zirconia electrolyte.