Fuel cells (FCs) are electrochemical systems that continuously produce electric energy and heat, where the reactants (fuel and oxidant) are fed to the electrodes and the reaction products are removed from the cell. The chemical energy of the reactants is directly converted into electricity, reaction products, and heat without involving combustion processes. The efficiencies of the FCs are about twice those of the heat engines because the latter are affected by the limitations imposed by Carnot’s theorem. Electricity is normally the main product of FCs, the chemicals and heat generated being the waste products of the first (or primary) cycle | Cogeneration of Energy and Chemicals Fuel Cells P-L Cabot F Alcaide and E Brillas Universität de Barcelona Barcelona Spain 2009 Elsevier . All rights reserved. Introduction Fuel cells FCs are electrochemical systems that continuously produce electric energy and heat where the reactants fuel and oxidant are fed to the electrodes and the reaction products are removed from the cell. The chemical energy of the reactants is directly converted into electricity reaction products and heat without involving combustion processes. The efficiencies of the FCs are about twice those of the heat engines because the latter are affected by the limitations imposed by Carnot s theorem. Electricity is normally the main product of FCs the chemicals and heat generated being the waste products of the first or primary cycle. In this case the reaction products should be environmentally friendly and the heat produced could be used to obtain additional energy in a secondary cycle. The reaction product is water when the fuel is pure hydrogen and the oxidant pure oxygen. This case is the most advantageous to avoid pollution of the environment in electricity-generating FCs. However different reactants lead to other reaction products that could be valuable chemicals for particular applications. One then refers to chemical cogeneration or electrogenerative processes when the main cycle is the formation of such valuable chemicals. The current delivered and the heat produced during the electrochemical reaction can be used in other secondary cycles. The FC can be successfully transformed into an electrolytic reactor when the only object is the production of a given chemical. In this case the consumption of external electric power allows increasing the generation rate of the corresponding product. The important point here is the economic study to decide the adequate operation mode. Fuel cells are thus electrochemical power sources in which different combined-cycle processes can be performed. The .
