Fuel Cell Technology Explained: Types, Working Principle, Advantages, and Applications in Clean Energy

Fuel cells are devices that convert the chemical energy of fuels directly into electrical energy. Common fuels include hydrogen (H₂), carbon monoxide (CO), methane (CH₄), propane (C₃H₈), and methanol (CH₃OH). These cells operate by continuously supplying fuel and removing the resulting products. Among the various types available, the hydrogen-oxygen fuel cell is the most widely used.

Types of Fuel Cells

• The Polymer Electrolyte Membrane (PEM) Fuel Cell

1.         Proton Exchange Membrane Fuel Cells (PEMFCs)

2.         Operate at moderate temperatures, typically between 50°C and 100°C.

3.         They use a proton-conducting polymer membrane as the electrolyte and consist of key components such as bipolar plates, electrodes, a catalyst, and the polymer membrane itself.

4.         While PEMFCs are well known for their environmentally friendly use in transportation.

5.         They are also suitable for stationary and portable power generation.

• Phosphoric Acid Fuel Cell

1.         In these fuel cells, phosphoric acid serves as the electrolyte to transport hydrogen ions (H⁺).

2.         They operate at temperatures between 150°C and 200°C.

3.      Phosphoric acid does not conduct electrons, the electrons must travel to the cathode through an external circuit.

4.         However, the acidic nature of the electrolyte can lead to corrosion or oxidation of the cell components over time.

• Solid Acid Fuel Cell

1.         These fuel cells use a solid acid as the electrolyte.

2.         At low temperatures, the solid acids have an ordered molecular structure.

3.         At higher temperatures, a phase transition can occur, greatly enhancing their conductivity.

4.         Common examples of solid acids used include cesium hydrogen sulfate (CsHSO₄) and cesium dihydrogen phosphate (CsH₂PO₄).

• Alkaline Fuel Cell

1.         This type of fuel cell was the primary power source for the Apollo space program.

2.         It uses an aqueous alkaline solution to saturate a porous matrix that separates the electrodes.

3.         Operating at relatively low temperatures.

4.         These cells are highly efficient and produce not only electrical power but also heat and water as by-products.

• Molten Carbonate Fuel Cell

1.         This type of fuel cell served as the main power source during the Apollo space program.

2.         It uses an aqueous alkaline solution to saturate a porous matrix, which acts as a separator between the electrodes.

3.         These cells operate at relatively low temperatures and are highly efficient, producing electricity along with heat and water as useful by-products.

• Solid Oxide Fuel Cells (SOFCs)

Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic material as the electrolyte and operate at high temperatures ranging from 500°C to 1000°C. In these cells, the solid oxide electrolyte conducts negative oxygen ions (O²⁻) from the cathode to the anode. SOFCs typically achieve an efficiency of 50–60%.

• At the anode: 1/2O₂+2e^–→O
• At the cathode: H₂+1/2O→H₂O+2e^–
• The overall cell reaction: H₂+12O₂→H₂O

Satellites and space capsules employ SOFCs to generate electricity. It is mostly employed in big, high-power applications such as industrial generating plants.

• Zinc-Air Fuel Cell (ZAFC)

The Zinc-Air Fuel Cell (ZAFC) is a type of fuel cell developed in the United States for automotive applications. It uses an aqueous alkaline solution, such as potassium hydroxide, as the electrolyte. The cell operates based on the following electrode reactions:

• Anode: Zn+2OH^–→Zn(OH)₂+2e^–
• Cathode: O₂+2H₂O+4e^–→4OH^–
• Overall Reaction: 2Zn+O₂+2H₂O→4Zn(OH)₂

It is used as an alternative fuel for vehicles.

• Direct Methanol Fuel Cell (DMFC)

In this subclass of proton-exchange fuel cells, methanol is used as the fuel. A major advantage of this type is the ease of transporting methanol, a stable liquid fuel. A polymer membrane acts as the electrolyte, and the cell operates according to the following electrode reactions:

• Anode: CH₃OH+H₂O→6H⁺+CO₂+6e^–
• Cathode: 3/2O₂+6H⁺+6e^–→3H₂O
• Net reaction: CH₃OH+3/2O₂→CO₂+2H₂O

Working of Fuel Cell

A fuel cell can generate electricity through the chemical reaction between hydrogen and oxygen. This type of cell was used in the Apollo space program, serving a dual purpose: supplying electrical power and providing drinking water from condensed water vapor. It operated by passing hydrogen and oxygen through carbon electrodes into a concentrated sodium hydroxide solution.

• Cathode Reaction: O₂ + 2H₂O + 4e^– → 4OH^–
• Anode Reaction: 2H₂ + 4OH^– → 4H₂O + 4e^–
• Net Cell Reaction: 2H₂ + O₂ → 2H₂O

This electrochemical process typically has a slow response rate, which is improved by using catalysts like platinum or palladium. These catalysts are finely divided before being applied to the electrodes to maximize their effective surface area. Fuel cells offer an energy conversion efficiency of about 70%, significantly higher than the 40% efficiency of thermal power plants. This difference arises because thermal plants rely on multiple energy conversion steps—converting water to steam to drive turbines—whereas fuel cells convert chemical energy directly into electrical energy.

Advantages of Fuel Cell

Fuel cells are a promising source of electrical energy and offer several advantages over galvanic cells and conventional methods of electricity generation through fuel combustion. Some of the key benefits of fuel cells include:

1. High Efficiency: Fuel cells are significantly more efficient than traditional methods of electricity generation, such as combustion of hydrogen, methane, methanol, or carbon-based fuels, as well as nuclear reactors. Unlike these methods, which involve intermediate steps like heat production and mechanical work, fuel cells convert chemical energy directly into electrical energy. While their theoretical efficiency can reach 100%, practical efficiencies of 60–70% have been achieved—compared to around 40% for conventional combustion-based systems. The thermodynamic efficiency of a fuel cell is given by the equation: η = (ΔG / ΔH) × 100, where ΔG is the useful work obtained and ΔH is the heat of combustion.

2. Pollution-Free Operation: Fuel cells produce minimal or no harmful by-products, making them environmentally friendly. For instance, a hydrogen-oxygen fuel cell generates only water as a by-product, contributing nothing to air pollution and offering a clean alternative to fossil fuel-based energy sources.

3. Continuous Energy Supply:Fuel cells can generate electricity continuously as long as fuel and oxidant are supplied, allowing for uninterrupted power output. Unlike conventional batteries, they do not suffer from a gradual drop in voltage or current during operation.

Limitations of Fuel Cells

1. Handling of Gaseous Fuels: Gaseous fuels like hydrogen and oxygen are difficult to store and handle. They must be compressed or liquefied under very low temperatures and high pressures in specially designed cylinders, which increases the overall cost and presents significant practical challenges.

2. High Cost of Catalysts: Fuel cells require expensive catalysts—such as platinum (Pt), palladium (Pd), or silver (Ag)—to facilitate electrode reactions. The high cost of these materials significantly raises the overall cost of the fuel cell.

3. Corrosive Electrolytes: The electrolytes used in many fuel cells are highly caustic or corrosive, leading to safety concerns and additional maintenance issues in practical applications.

Download Complete Notes Below

1. 

   I’m very happy to read this. This is the type of manual that needs to be given and not the…