- Electrolyte: Liquid phosphoric acid.
- Fuel: Hydrogen.
- Operating Temperature: 150–200°C.
- Applications: Stationary power generation, including CHP systems.
- Advantages: Durable, can tolerate impurities in hydrogen.
- Challenges: Lower power density, higher costs.
Phosphoric Acid Fuel Cells (PAFC): An Overview
What Are Phosphoric Acid Fuel Cells?
Phosphoric Acid Fuel Cells (PAFC) are a well-established fuel cell technology that uses liquid phosphoric acid as the electrolyte to conduct hydrogen ions (H⁺) between the anode and cathode. Operating at moderate temperatures (150–200°C), PAFCs are reliable, durable, and ideal for stationary power generation. Known for their ability to tolerate impurities in the fuel, they are often used in industrial and commercial applications requiring efficient and steady power.
How Do PAFCs Work?
- Fuel and Air Supply: Hydrogen-rich fuel, such as natural gas or biogas, is supplied to the anode, and oxygen (from air) is fed to the cathode.
- Electrochemical Reactions:
- At the anode, hydrogen molecules are split into protons (H⁺) and electrons (e⁻).
- The protons migrate through the phosphoric acid electrolyte to the cathode.
- Recombination at the Cathode: Oxygen reacts with protons and electrons at the cathode to form water.
- Electricity Generation: Electrons flow through an external circuit from the anode to the cathode, generating electricity.
Reaction Summary:
- At the Anode: H₂ → 2H⁺ + 2e⁻
- At the Cathode: O₂ + 4H⁺ + 4e⁻ → 2H₂O
- Overall Reaction: H₂ + ½O₂ → H₂O + Energy (Electricity + Heat)
Key Features of PAFCs
- High Reliability: Proven technology with decades of operational experience in stationary applications.
- Fuel Flexibility: Can use hydrogen derived from a variety of sources, including natural gas and biogas, with limited sensitivity to impurities like carbon monoxide.
- Moderate Operating Temperature: Operating at 150–200°C, PAFCs strike a balance between efficiency and manageable thermal management.
- Durable Design: Capable of long operational lifetimes, making them ideal for consistent, base-load power.
- Combined Heat and Power (CHP): The moderate heat produced during operation can be captured and used for heating, boosting overall efficiency.
Applications of PAFCs
- Stationary Power Generation: Widely used in industrial, commercial, and institutional facilities for reliable power and heat.
- Combined Heat and Power (CHP): Common in hospitals, hotels, and large office buildings where waste heat is used for water and space heating.
- Microgrids: Support energy independence and reliability in off-grid or grid-interactive systems.
- Industrial Processing: Ideal for facilities that need steady power and can benefit from the heat output, such as food processing plants.
Challenges Facing PAFC Technology
- Cost: Higher upfront costs compared to some alternative technologies due to material and manufacturing requirements.
- Moderate Efficiency: Electrical efficiency is typically around 40%, which is lower than some high-temperature fuel cells, though CHP can improve total efficiency.
- Size and Weight: Larger and heavier than other fuel cell types, making them less suitable for portable or transportation applications.
- Phosphoric Acid Handling: Requires careful management of the liquid acid electrolyte to prevent leakage and corrosion.
The Future of PAFCs
Despite competition from newer fuel cell technologies, PAFCs remain a strong contender for stationary power applications due to their durability, reliability, and ability to tolerate fuel impurities. Continued improvements in materials and system design are expected to enhance efficiency and reduce costs, ensuring their relevance in the clean energy market. PAFCs are particularly well-suited for applications where long-term, stable power generation is critical, and they are expected to play a continued role in the transition to sustainable energy systems.