NOVELTY - The fuel cell used in converting a carbon-comprising material is a molten corrosive salt fuel cell or a solid fuel cell. Conversion to carbon monoxide has a negative enthalpy (DELTAH) and a positive entropy change (DELTAS). Heat is supplied to the fuel cell and at least one of the carbon monoxide conversion reactions is an electrochemical reaction producing electricity.    USE - For converting heat into electricity and converting the enthalpy of the gasification reaction into electricity.    ADVANTAGE - The energetic value of the fuel is optimally utilized to make the method more efficient in converting heat into electricity and simultaneously converting the enthalpy of the gasification reaction into electricity. Fewer pretreatments for some of the materials to be converted are needed, e.g. the necessity to reduce the size of the solid carbon-comprising material is diminished. If solid carbon-comprising material particles are brought into contact with molten carbonate and due to flow the material is brought into contact with the anode (according to an embodiment of the invention), a very large reaction surface can be achieved. In the method, the concentration of carbon dioxide leaving the anode is much lower than the concentration of carbon monoxide. Carbon monoxide can then be used for synthesis purposes or the carbon monoxide-comprising gas can be used in a further high temperature fuel cell for the generation of electricity. If carbon monoxide is used to generate electricity, the heat developed in the second fuel cell for the generation of electricity may be used for converting carbon product or thermically treated biomass into carbon monoxide. Oxygen and combustible gas are not in direct contact so the method has the advantage of safety and energy. The method can be operated at high temperature, promoting formation of carbon monoxide and increasing reaction speed to reduce polarization losses.    DETAILED DESCRIPTION - A method of converting a carbon comprising material at elevated temperature in the presence of a molecule that comprises at least one oxygen atom takes place in a fuel cell. The fuel cell used in converting a carbon-comprising material is a molten corrosive salt fuel cell or a solid fuel cell. Conversion to carbon monoxide has a negative enthalpy (DELTAH) and a positive entropy change (DELTAS). Heat is supplied to the fuel cell and at least one of the carbon monoxide conversion reactions is an electrochemical reaction producing electricity.    INDEPENDENT CLAIMS are also included for:    (a) a method of operating a fuel cell stack and    (b) a fuel cell suitable for the novel methods.