Solid oxide fuel cells heat generation from

As it can be seen, low-temperature and high-temperature fuel cells can be distinguished. Low-temperature fuel cells are the Alkaline Fuel Cell (AFC), the Polymer Electrolyte Fuel Cell (PEMFC), and the Phosphoric Acid Fuel Cell (PAFC). The high-temperature fuel cells operate in the temperatures region from 500 to 1000 °C two different types have been developed the Molten Carbonate Fuel Cell (MCFC) and the Solid Oxide Fuel Cell (SOFC). They have the ability of using methane as fuel and thus present high inherent generation efficiency (45-60 % for common fuels such as natural gas, 90 % with heat recovery [3]). 

The amount of heat that is produced by a fuel cell operating reversibly is TAS. Reactions in fuel cells that have negative entropy change generate heat (such as hydrogen oxidation), while those with positive entropy change (such as direct solid carbon oxidation) may extract heat from their... 

Each of the two electrode reactions creates a characteristic potential difference across the interface solid electrode/electrolyte, which is different for the two reactions according to the different reactants. The overall cell voltage between the two electrodes, which are joined by the same electrolyte, allows the electrons generated at the anode (HOR) and consumed at the cathode (ORR) to create work in the external circuit. Hence, chemical energy released by the individual electrode reactions at the locally separated electrodes is directly transferred into electrical energy. This pathway is different from the combustion step in the classical thermomechanical power generation, where the oxidation of fuel and reduction of oxidant occur in the same volume element, thereby generating heat only. 

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