- Electrolyte: Potassium hydroxide solution.
- Fuel: Hydrogen and oxygen.
- Operating Temperature: 60–100°C.
- Applications: Space programs (used in Apollo missions) and some terrestrial applications.
- Advantages: High efficiency, simple design.
- Challenges: CO2 sensitivity, which can degrade performance and require pure hydrogen.
Alkaline Fuel Cells (AFC): An Overview
What Are Alkaline Fuel Cells?
Alkaline Fuel Cells (AFC) are one of the oldest and most efficient types of fuel cells, initially developed in the 1960s for space missions, including NASA’s Apollo program. These fuel cells use an alkaline solution, typically potassium hydroxide (KOH) in water, as the electrolyte to conduct hydroxide ions (OH⁻) between the anode and cathode. AFCs are known for their high efficiency, especially when using pure hydrogen and oxygen, making them ideal for specific niche applications.
How Do AFCs Work?
- Fuel and Oxidant Supply: Hydrogen is supplied to the anode, and oxygen (from air or pure sources) is fed to the cathode.
- Electrochemical Reactions:
- At the anode, hydrogen molecules are split into electrons (e⁻) and hydroxide ions (OH⁻).
- The hydroxide ions migrate through the alkaline electrolyte to the cathode.
- Recombination at the Cathode: At the cathode, oxygen reacts with the hydroxide ions and electrons to produce water.
- Electricity Generation: Electrons flow through an external circuit from the anode to the cathode, creating an electric current.
Reaction Summary:
- At the Anode: H₂ + 2OH⁻ → 2H₂O + 2e⁻
- At the Cathode: O₂ + 2H₂O + 4e⁻ → 4OH⁻
- Overall Reaction: 2H₂ + O₂ → 2H₂O + Energy (Electricity + Heat)
Key Features of AFCs
- High Efficiency: AFCs can achieve electrical efficiencies of up to 60% when using pure hydrogen and oxygen.
- Fast Start-Up: Their design allows for rapid activation, making them suitable for applications requiring instant power.
- Lightweight and Simple Design: The components of AFCs are relatively lightweight, making them ideal for portable and space-constrained applications.
- Low Operating Temperature: Operating at 60–100°C, AFCs are cooler than high-temperature fuel cells, simplifying thermal management.
Applications of AFCs
- Space and Aerospace: Historically used in spacecraft for power and water production due to their high efficiency and reliability.
- Backup Power: Ideal for emergency power systems where quick start-up and reliability are critical.
- Portable Power Systems: Suitable for remote or off-grid applications where lightweight and efficient power generation is needed.
- Military Applications: Used for powering equipment in field operations due to their quiet operation and portability.
Challenges Facing AFC Technology
- Fuel Purity Requirements: AFCs are sensitive to carbon dioxide (CO₂) contamination, which can degrade performance by reacting with the alkaline electrolyte.
- Limited Fuel Flexibility: They require pure hydrogen and oxygen, which limits their use in applications involving impure or hydrocarbon-based fuels.
- Durability: Over time, the alkaline electrolyte can degrade, necessitating regular maintenance or replacement.
- Cost: While simpler in design, the need for high-purity fuels and CO₂ removal systems adds to the overall cost.
The Future of AFCs
Alkaline Fuel Cells remain a valuable technology for specialized applications where high efficiency, quick start-up, and low operating temperatures are advantageous. Advances in CO₂-tolerant designs and material innovations may expand their usability in broader markets. While other fuel cell technologies have taken the lead in commercial sectors, AFCs continue to offer unique benefits for niche applications and remain a vital part of the fuel cell landscape.