An Alkaline Fuel Cell Temperature Guide
An alkaline fuel cell is much like a battery in that there is a positive end (anode), a medium in the center to support the electron reactions (electrolyte), and a negative end (cathode). The electrons transfer from the positive to the negative side and react in between to create energy.
The Role of Temperature
A relatively constant temperature is required for the electrons to continue to create reactions within the cell. Since the electron reactions provide the necessary energy to the cell, maintaining the temperature is the regulator for number and occurrence of electron reactions. The reactions themselves also create thermal energy which needs to be stabilized by the fuel cell in order to maintain an adequate working core temperature which is neither too hot, nor too cold.
Heat can be increased by creating a higher pressure within the fuel cell. In this way, a lower temperature can achieve a high inner core temperature through pressure. An electrolyte is used as the main transfer of electrons. When this electrolyte is compressed through pressure, the transfer of electrons and the electron reactions go down. However, the high pressure allows the alkaline fuel cell to function at a temperature below the boiling point of water (212 degrees Fahrenheit) even if some efficiency is lost.
Functionality of an alkaline fuel cell can be maximized using a lower pressure, but increasing the temperature up to 500 degrees Celsius. This higher temperature allows the electrolyte which holds the electons to remain unconstrained by pressure and greater reactivity is achieved. The higher the reactivity, the larger the energy output due to electron reactions.
As the temperature inside the cell increases from chemical reactions, the pressure also increases. It is necessary for the cell to keep the heat and pressure in balance so that optimum reactions can be achieved. If the heat/pressure is to great, the cell can crack or explode; if the temperature/pressure is to low, the reactions will be minimized. The JANAF Thermochemical Tables provide different coefficients thermal energy, free energy, entropy, and other functions at various temperatures.
Much like the radiator in a car, the water circulates throughout the entire cell to help maintain the inner temperature and not dry out. For an alkaline fuel cell, the water circulates the electrolyte solution which allows the protons to conduct electricity. Due to the increased temperature of the alkaline fuel cell, the radiator can be smaller and steam can be forced through the stack without much added pressure. This allows alkaline fuel cells to be more economical and easier to maintain.