Fuel Cell : Definition, Types, & Advantages

Fuel Cell, although electrochemical cells are widely used, have many advantages, and work on redox reactions, they are not suitable for commercial purposes. They consist of a salt bridge, which drops the voltage sharply if a large current is drawn through them. Also, they lack compactness and ruggedness (or rough handling) for portability.

These are the essential things that a commercial fuel cell needs. So, to overcome these shortcomings of electrolyte cells, fuel cells are designed. They operate on combustion reactions, which are also redox reactions. They have many advantages that make them suitable for commercial use.

What are Fuel Cells?

Fuel cells are means of commercial cells in which chemical energy is converted into electrical energy. Here the cathode and anode constituents are continually supplied. Thus, energy can be withdrawn indefinitely from a fuel cell as long as the outside fuel supply is maintained. The fuels cast-off in fuel cells are hydrogen (H₂), carbon monoxide (CO), methane (CH₄), etc.

This is a continual battery. It keeps dispatching energy output so long as it is sustained with fuel. The fuel is hydrogen in an anonymous form, mostly direct hydrogen gas.

How do Fuel Cells Produce Electricity?

Examples of a Hydrogen Fuel Cell 

A hydrogen fuel cell is an electrochemical cell that converts chemical energy provided by a fuel into electricity. It is done through the chemical reaction between hydrogen with oxygen or an oxidising agent.

The cell consists of an anode, cathode, electrolyte and a separator or catalyst. It consists of three compartments separated from one another by porous electrodes. The hydrogen gas is fed into one compartment (anode), and the oxygen is fed into another compartment (cathode). These gases diffuse slowly through the electrodes and react with an electrolyte (concentrated KOH or NaOH) in the central compartment.

The following electrode reactions take place:

At anode: 2H₂(g) + 4OH–(aq) → 4H₂O(l) + 4e^–

At cathode: O₂(g) + 2H₂O(l) + 4e^–→ 4OH–(aq)

Overall reaction: 2H₂(g) + O₂(g) → 2H₂O(l)

The electrodes are designed of conducting material, like graphite, with a scattering of platinum to proceed as a catalyst. The electrolyte is a flowing solution of a base.

Fuel cell efficiency is about 40—60%, and if the heat is utilised, it may go up to 85%. Since hydrogen is abundant in nature, this could be the most economic solution for energy storage.

Types of Fuel Cells

Various fuel cell types depend on the process electrolyte or materials used.

1. The Polymer Electrolyte Membrane (PEM):

The reaction in the PEM system is the hydrogen-oxygen reaction. Such a cell is generally known as a hydrogen fuel cell. Sometimes, it is also called an alkaline fuel cell.

PEM, or hydrogen fuel cell, is the most common type. The voltage of individual fuel cells is about 0.7V, and permutations and combinations are made of stacks of fuel cells to get the required output voltage and power.

This cell was the primary source of electrical energy on the Apollo moon flights. The weight of the fuel sufficient for 11 days in space was approximately 200kg. And the product of combustion of a hydrogen fuel cell, water, was used for drinking by the astronauts.

2. Phosphoric Acid Fuel:

The working of a phosphoric acid fuel cell is similar to a hydrogen fuel cell. In a phosphoric acid fuel cell, the electrolyte used is phosphoric acid. Hydrogen gas enters the fuel cell through the anode chamber, and oxygen gas enters through the cathode side. Phosphoric acid, as an electrolyte, supplies H+ to the cell to complete the working of the fuel cell.

These cells work at a temperature between 150 and 200°C and have power generation efficiencies of 40%. In phosphoric fuel cells, the electrons are forced to travel through an external circuit to the cathode due to the non-conductive nature of the phosphoric acid. These cells can give outputs up to 200 kW and 11 MW units.

3. Molten Carbonate:

A molten carbonate fuel cell is a torrid heat fuel cell and works at 650°C or above. An electrolyte constituted a molten carbonate salt blend draped in a porous, chemically static ceramic lithium aluminium oxide model. Futile metals are exploited as catalysts at the cathode and anode. Another reason a molten carbonate fuel cell offers is significant price reductions atop phosphoric acid fuel cells and improved efficiency.

When coupled with a turbine, a molten carbonate fuel cell can reach 65% efficiency, considerably higher than the 37–42% efficiency of phosphoric acid fuel cell power plants. When the atrophy heat is captured and cast off, overall fuel efficiencies can be over 85%.

4. Solid Oxide Fuel Cell

This type of fuel cell is similar to a molten carbonate fuel cell. The material used to make solid oxide fuel cells is ceramics with nickel. Like a molten carbonate fuel cell, the anode contains hydrogen gas in a solid oxide fuel cell, and the cathode contains carbon monoxide. The electrolyte used in this fuel cell is an ion-conducting oxide such as zirconia treated with yttria.

These fuel cells operate at an intense heat of 900-1000°C, and the electrode reactions proceed very readily.

5. Solid Polymer Electrolyte

The material Nafion is used to design the ion-conducting membrane in this type of fuel cell. The electrodes are catalysed by carbon in such cells. The cost of designing a solid polymer electrolyte fuel cell is very high compared to the above fuel cells. Therefore, this disadvantage overcomes its advantages.

What are fuel cells used for?

• These are used for primary and backup power for commercial, industrial and residential buildings and in remote or inaccessible areas. They are also used in power fuel cell vehicles, including forklifts, automobiles, rockets, submarines, motorcycles, boats, and buses.
• Due to their high efficiency, these are very clean. Their only side-products are excess heat, electricity, and water. In addition, they intervene near-silently, as fuel cells do not have any motile parts.
• They are getting popular and non-polluting because their exhaust is only pure water.
• They reduce greenhouse gas emissions and help in developing renewable energy resources.
• They are very flexible with the installation process and operations and reduce the demand for foreign oils.

Advantages of fuel cells

The main advantages of fuel cells are as under:

• In the fuel cells, the energy is extracted from the reactants under more nearly reversible conditions. Hence, they are widely used in space vehicles.
• Because of the continuous supply, such cells never become dead. Such a cell is usually operated at a temperature of 70 – 140℃, giving a potential of about 0.9V.
• They do not cause pollution problems, unlike thermal plants, which burn fossil fuels like coal, gas, oil, etc. As ΔH is the heat of combustion and ΔG is the useful work done, i.e., the electrical energy produced, therefore, the thermodynamic efficiency (η) of a fuel cell = ΔG/ ΔH. Thus, for the H₂-O₂ fuel cell, the theoretically expected value will be

η = ΔG/ ΔH = (-nFE)/ ΔH = -229/ -242 = 0.95 or 95%.

• Theoretically, These are expected to have an efficiency of 100%. However, practically they give an efficiency of 60-70%. Still, they are much loftier than the thermal power plants in which fuels are blazed to produce heat, converting water into steam to move the turbine. Such a power plant does not have an efficiency of more than 40%.

Conclusion

It can ply the chemical energy of hydrogen or other fuels to produce clean and pollution-free electricity.

It can be used for various applications as long-term energy storage for the grid in reversible systems, including transportation, commercial/ industrial/ residential buildings, and power across multiple sectors.

Frequently Asked Questions

1. Do fuel cells wear out?

Yes. It wears out from contaminants in the hydrogen and oxygen (air). Carbon monoxide is a poison to proton exchange membrane (PEM) fuel cells, just like your red blood cells. Various contaminants damage fuel cells and they have a life expectancy of around seven years, much like a battery, and depending on the service, just like a battery.

2. How do fuel cells charge?

It is different from a battery because it never needs to be recharged. It just needs a continuous flow of ‘fuel.’ The most common fuel for fuel cells to date is hydrogen.

3. What are the advantages of fuel cells over ordinary batteries?

Some important advantages of fuel cells over ordinary batteries are

• They convert fuel energy directly into electricity, while ordinary batteries generate electricity by burning hydrogen. Carbon fuel cells convert fuel into thermal energy and electrical energy.
• The practical efficiency of fuel cells is 60-70%, while ordinary batteries have 40%.
• It does not cause any pollution problems.

4. What are the difficulties faced during the construction of a fuel cell?

The construction of a fuel cell involves certain technical, economic, and practical difficulties. A few of these are:

• The corrosiveness of the electrolyte used.
• Problems with handling gaseous fuels at low temperatures or high pressures.
• Providing contact between the three phrases needed in a fuel cell, i.e., the liquid electrolyte, the gaseous fuel, and the solid catalyst.
• High cost of the catalysts needed for the electrode reactions, such as platinum, palladium, silver, etc.