Fuel cell

A fuel cell is an electrochemical device that converts the chemical energy of a fuel and an oxidizing agent into electricity through a pair of redox reactions. Unlike batteries, fuel cells require a continuous source of fuel and oxidant to sustain the reaction, but they can operate continuously as long as these inputs are provided.

The fundamental principle behind a fuel cell involves the electrochemical oxidation of a fuel (often hydrogen, but other hydrocarbons like methane or methanol can be used) at the anode and the reduction of an oxidant (typically oxygen from air) at the cathode. These reactions are separated by an electrolyte, which allows the transport of ions but prevents the direct mixing of the fuel and oxidant.

Key components of a fuel cell include:

• Anode: The electrode where the fuel is oxidized. Catalysts are often used to facilitate this oxidation process.
• Cathode: The electrode where the oxidant is reduced. Catalysts are also often employed here.
• Electrolyte: A substance that conducts ions between the anode and cathode. The type of electrolyte determines the operating temperature, efficiency, and other characteristics of the fuel cell. Different fuel cell types use different electrolytes, such as polymer electrolyte membranes, alkaline solutions, solid oxides, or molten carbonates.
• Separator/Membrane: Prevents the fuel and oxidant from mixing while allowing ion transport. This is often combined with the electrolyte.

Fuel cells are classified based on the type of electrolyte used, which dictates the operating temperature and the fuels they can use effectively. Common types include:

• Proton Exchange Membrane Fuel Cells (PEMFCs): Operate at relatively low temperatures (around 80°C), use a solid polymer electrolyte, and are suitable for transportation applications.
• Solid Oxide Fuel Cells (SOFCs): Operate at high temperatures (around 600-1000°C), use a solid ceramic electrolyte, and can use a variety of fuels, including natural gas. They are suitable for stationary power generation.
• Alkaline Fuel Cells (AFCs): Use an alkaline electrolyte (e.g., potassium hydroxide), operate at moderate temperatures (around 100-250°C), and were used extensively in the Apollo space program. They are sensitive to carbon dioxide contamination.
• Phosphoric Acid Fuel Cells (PAFCs): Use phosphoric acid as the electrolyte, operate at moderate temperatures (around 150-200°C), and are often used for stationary power generation.
• Molten Carbonate Fuel Cells (MCFCs): Use a molten carbonate salt as the electrolyte, operate at high temperatures (around 600-700°C), and can use a variety of fuels. They are also suitable for stationary power generation.

Advantages of fuel cells include high efficiency, low emissions (especially if hydrogen is used as fuel), and quiet operation. Disadvantages include cost, fuel storage and distribution infrastructure requirements (particularly for hydrogen), and durability issues. Fuel cells have applications in transportation (cars, buses, trains), stationary power generation, and portable power.