TABLE OF CONTENTS A fuel cell is an electrochemical energy converter it converts chemical energy of fuel, typically hydrogen, directly into electrical energy. As such, it must obey the laws of thermodynamics.
The electrochemical reactions in fuel cells happen simultaneously on both sides of the membrane the anode and the cathode. The basic fuel cell reactions are:
At the anode:
At the cathode:
Overall:
These reactions may have several intermediate steps, and there may be some (unwanted) side reactions, but for now these reactions accurately describe the main processes in a fuel cell.
The overall reaction (Equation 2-3) is the same as the reaction of hydrogen combustion. Combustion is an exothermic process, which means that there is energy released in the process:
The heat (or enthalpy) of a chemical reaction is the difference between the heats of formation of products and reactants. For the previous Equation 2-4 this means:
Heat of formation of liquid water is ?286kJmol ?1 (at 25 C) and heat of formation of elements is by definition equal to zero. Therefore:
Note that the negative sign for enthalpy of a chemical reaction, by convention, means that heat is being released in the reaction, that is, this is an exothermic reaction. Equation 2-4 may now be rewritten as:
Here a positive sign is used because the enthalpy is placed on the right side of the reaction, clearly meaning a product of the reaction.
This equation is valid at 25 C only, meaning that both the reactant...
