TABLE OF CONTENTS Fuel cells can take on several different configurations, usually determined by the various combinations of the type of fuel and oxidant, the way fuel is fed to the system (direct or indirect), the type of electrolyte used, the operating temperature, etc. In general, we have the following classification shown in Table 11.3.
| Fuel | Oxidant | Temperature | Electrolyte | |
|---|---|---|---|---|
| Direct | Indirect | |||
| Hydrogen | Hydride | Oxygen | Low (120 C) | Aqueous acid |
| Hydrazine | Ethanol | Oxygen(air) | Intermediate | Phosphoric |
| Ammonia | Ammonia | Hydrogen | (120 160 C) | Sulphuric |
| Hydrocarbon | Hydrocarbon | Peroxide | High (260 750 C) | Solid polymer |
| Methanol | Methanol | Very high ( ?750 C) | electrolyte (SPE) | |
| Natural Gas | Coal | Aqueous alkaline | ||
| Coal | Molten carbonate | |||
| Solid oxide |
The acid fuel cell can be characterized by:
Hydrogen ions [or by hydronium ions (H 3O +)] providing the passage of ionic conduction;
Current collectors and gas separators are made of carbon (graphite);
Platinum or platinum alloys (in very small quantity) as the active electrocatalysts.
There are essentially two types of acid fuel cells, namely the solid polymer electrolyte system and the phosphoric acid cell. The solid polymer electrolyte (SPE) cell uses an ion exchange membrane as the electrolyte and is thus called a proton exchange membrane fuel cell (PEM-FC). These are suited for low-temperature use, but are prone to poisoning by carbon monoxide (Parsons and VanderNoot, 1988)...
