Fuel Cell: Meaning, Types, Application & Limitations

Fuel Cell: Galvanic cells, such as lead-acid batteries and dry cells, provide electricity. However, there are some limitations, such as pollution, efficiency, and so on. The usage of fuel cells can help solve this problem. Electricity is generated from fuel because here redox reaction takes place in the combustion of fuel, as a result of which the fuel is converted into electrical energy. That is, it is a device that converts chemical potential energy into electrical energy, here chemical electrical energy means that the energy stored in the bonds of molecules is converted into electrical energy.

In this article, we have explained the various types of fuel cells, their purposes, limitations, and other factors. Also, find interesting questions and answers about fuel cells at the end of this article.

What is a Fuel Cell?

The cells which convert the chemical energy of a fuel cell directly into electrical energy are called fuel cells. In the image given below,  the cells, fuels like hydrogen \(\left( {{{\rm{H}}_{\rm{2}}}} \right){\rm{,}}\) carbon dioxide \(\left( {{\rm{C}}{{\rm{O}}_{\rm{2}}}} \right){\rm{,}}\) methane \(\left( {{\rm{C}}{{\rm{H}}_{\rm{4}}}} \right){\rm{,}}\) propane \(\left( {{{\rm{C}}_{\rm{3}}}{{\rm{H}}_{\rm{8}}}} \right){\rm{,}}\) methanol \(\left( {{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{OH}}} \right){\rm{,}}\) etc., are used to generate electrical energy. The fuel is constantly supplied to the fuel cell, while the products are constantly removed.  A large number of fuel cells are available. A hydrogen-oxygen fuel cell is the most common of these.

What are the Types of Fuel Cells?

There are different types of fuel cells. A few of them are:

1. Hydrogen-Oxygen fuel cell
2. Microbial fuel cells (MFCs)
3. Solid Oxide Fuel Cells (SOFCs)
4. Zinc-Air Fuel Cell (ZAFC)
5. Direct Methanol Fuel Cell (DMFC)

Which Fuel Cell is Used in the Apollo Space Program?

The hydrogen-Oxygen fuel cell was designed by Baconin in \(1959.\) Therefore, it is also known as the Bacon cell. It is a potential source of electrical energy and was used as a primary source of electrical energy in the Apollo space program of the U.S.A.

A simple \({{\rm{H}}_{\rm{2}}}{\rm{ – }}{{\rm{O}}_{\rm{2}}}\) fuel cell consists of two porous carbon electrodes impregnated with a suitable catalyst such as platinum \({\rm{(Pt),}}\) Silver \({\rm{(Ag),}}\) cobalt oxide \(({\rm{CoO}}),\) etc. The space between two electrodes is filled with the concentrated solution of potassium hydroxide \({\rm{(KOH)}}\) or sodium hydroxide \({\rm{(NaOH)}}\) which serves as an electrolyte. Hydrogen gas \(\left( {{{\rm{H}}_{\rm{2}}}} \right)\) and oxygen gas \(\left( {{{\rm{O}}_{\rm{2}}}} \right)\) are bubbled in the electrolyte through a porous carbon electrode.

Reactions that take place during the operations of the cell are as follows:

At the anode, oxidation reaction: \({\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{(g) + 4O}}{{\rm{H}}^{\rm{ – }}}{\rm{(aq)}} \to {\rm{4}}{{\rm{H}}_{\rm{2}}}{\rm{O(l) + 4}}{{\rm{e}}^{\rm{ – }}}\)

At the cathode, reduction reaction: \({{\rm{O}}_{\rm{2}}}{\rm{(g) + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O(l) + 4}}{{\rm{e}}^{\rm{ – }}} \to {\rm{4O}}{{\rm{H}}^{\rm{ – }}}{\rm{(aq)}}\)

Overall reaction: \({\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{(\;g) + }}{{\rm{O}}_{\rm{2}}}{\rm{(\;g)}} \to {\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{O(l)}}\)

Microbial fuel cells (MFCs) are the cells that produce electricity from the organic or inorganic compounds by bacteria catalysed biological processes. It would be capable of producing \(50\% \) efficiency.

Few microbes used in the MFCs are Proteobacteria, Desulfuromonas, Alcaligenes faecalis, Pseudomonas aeruginosa, etc.

A microbial fuel cell consists of an anode and cathode compartment separated by a cation-specific membrane-like potassium nitrate base membrane. Fuel is oxidized by the microorganism at the anode, producing carbon dioxide, electrons, and protons. Electrons are transferred to the cathode compartment through an external electric circuit and protons are transferred to the cathode compartment through the membrane. Water is produced at the cathode compartment by combining oxygen with electrons and protons.

Anode reaction: \({{\rm{C}}_{12}}{{\rm{H}}_{22}}{{\rm{O}}_{11}} + 13{{\rm{H}}_2}{\rm{O}} \to 12{\rm{C}}{{\rm{O}}_2} + 48{{\rm{H}}^ + } + 48{e^ – }\)

Cathode reaction: \({\rm{4}}{{\rm{H}}^{\rm{ + }}}{\rm{ + }}{{\rm{O}}_{\rm{2}}}{\rm{ + 4}}{{\rm{e}}^{\rm{ – }}} \to {\rm{2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\)

Few Applications of MFCs are 

1. These are used to treat wastewater.
2. It is used as a source of power generation.
3. It is used in biosensors and desalination of water.

What are Solid Oxide Fuel Cells (SOFCs)?

Solid Oxide Fuel Cells use hard, fill non-porous ceramic compounds is the electrolyte, and operate at a very high temperature between \({\rm{500 – 100}}{{\rm{0}}^{\rm{o}}}{\rm{C}}{\rm{.SOFCs}}\) use a solid oxide electrolyte to conduct negative oxygen ions from the cathode to the anode. The efficiency of \({\rm{SOFCs}}\) is around \(50 – 60\% .\)

The electrochemical reactions occurring within the cells are:

At the anode: \(\frac{{\rm{1}}}{{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{ + 2}}{{\rm{e}}^{\rm{ – }}} \to {\rm{O}}\)

At the cathode: \({{\rm{H}}_{\rm{2}}}{\rm{ + }}\frac{{\rm{1}}}{{\rm{2}}}{\rm{O}} \to {{\rm{H}}_{\rm{2}}}{\rm{O + 2}}{{\rm{e}}^{\rm{ – }}}\)

The overall cell reaction: \({{\rm{H}}_{\rm{2}}}{\rm{ + }}\frac{{\rm{1}}}{{\rm{2}}}{{\rm{O}}_{\rm{2}}} \to {{\rm{H}}_{\rm{2}}}{\rm{O}}\)

\({\rm{SOFCs}}\) used in satellites and space capsules for generating power. It is mainly used for large, high-powered applications such as industrial generating stations, industrial generating stations.

What is a Zinc-Air Fuel Cell (ZAFC)?

Zinc-Air Fuel Cell (ZAFC) has been developed in the U.S as a source of power in automobiles. Here, the electrolyte is aqueous alkali like potassium hydroxide solution and the electrode reactions are:

Anode: \({\rm{Zn + 2O}}{{\rm{H}}^{\rm{ – }}} \to {\rm{Zn(OH}}{{\rm{)}}_{\rm{2}}}{\rm{ + 2}}{{\rm{e}}^{\rm{ – }}}\)

Cathode: \({{\rm{O}}_{\rm{2}}}{\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O + 4}}{{\rm{e}}^{\rm{ – }}} \to {\rm{4O}}{{\rm{H}}^{\rm{ – }}}\)

Overall Reaction: \({\rm{2Zn + }}{{\rm{O}}_{\rm{2}}}{\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{4Zn(OH}}{{\rm{)}}_{\rm{2}}}\)

It is used as an alternative fuel for vehicles.

What is Direct Methanol Fuel Cell (DMFC)?

It is a subcategory of proton-exchange fuel cells in which methanol is used as a fuel. The main advantage of this fuel cell is the easy transport of stable liquid fuel methanol. The electrolyte is polymer membrane, and the electrode reactions are:

Anode: \({\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{OH + }}{{\rm{H}}_{\rm{2}}}{\rm{O}} \to {\rm{6}}{{\rm{H}}^{\rm{ + }}}{\rm{ + C}}{{\rm{O}}_{\rm{2}}}{\rm{ + 6}}{{\rm{e}}^{\rm{ – }}}\)

Cathode: \(\frac{{\rm{3}}}{{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{ + 6}}{{\rm{H}}^{\rm{ + }}}{\rm{ + 6}}{{\rm{e}}^{\rm{ – }}} \to {\rm{3}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\)

Net reaction: \({\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{OH + }}\frac{{\rm{3}}}{{\rm{2}}}{{\rm{O}}_{\rm{2}}} \to {\rm{C}}{{\rm{O}}_{\rm{2}}}{\rm{ + 2}}{{\rm{H}}_{\rm{2}}}{\rm{O}}\)

Advantages of Fuel Cell

fuel cells are the potential source of electrical energy and have an edge over the conventional galvanic cells and the conventional methods used for the production of electrical energy by burning fuel. Some significant advantages of fuel cells are as follows:

1. High Efficiency: Since fuel cells convert the energy of a fuel directly into electrical energy; they are potentially more efficient than the conventional methods used for the production of electrical energy by burning fuels such as hydrogen, methane, methanol, carbon fuels or by using nuclear reactors. 
Theoretically, fuel cells should be \(100\% \) efficient but so far an efficiency of \(60 – 70\% \) has been attained. The efficiency of the conventional method involving the burning of fuel is only about \(40\% .\)
The efficiency of a fuel cell is calculated by the following equation:
The thermodynamic efficiency of a fuel cell, \({\rm{n = }}\frac{{{\rm{\Delta G}}}}{{{\rm{\Delta A}}}}{\rm{ \times 100,}}\) where, \({\rm{\Delta H}}\) is the heat of combustion and \({{\rm{\Delta G}}}\) is the work done.

2. Pollution-Working: The by-products obtained from a fuel cell do not cause any pollution problem. For example, a hydrogen-oxygen fuel cell produces only water which in no way can cause any pollution problem.

3. Continuous Supply of Energy: Fuel cells can supply energy continuously as long as fuels are fed into them. Contrary to the conventional cells or batteries these cells do not involve any drop in voltage or current during long usage.

Limitations of Fuel Cells

Although fuel cells are superior to conventional cells, there are certain practical difficulties in their construction and use as a source of electrical energy. Some of these are as follows:

1. The handling of gaseous fuel is difficult. The fuel gas does hydrogen, oxygen, etc. are required to be stored as a liquid at very low temperature and high pressure in a specially designed cylinder. this increase is the cost of the cell and involves several practical difficulties.
2. The catalyst needed for the electrode reactions such as platinum \(({\rm{Pt}}),\) Palladium \(({\rm{Pd}}),\) Silver \({\rm{(Ag)}},\) etc., are quite expensive and increase the cost of the cell.
3. The electrolytes used in fuel cells are highly corrosive and create several practical problems.

FAQs

The frequently asked questions on Fuel Cells are given below:

Q.1. What are fuel cells used for?
Ans: A fuel cell is used to generate electricity, used as fuel for transportation. 

Q.2. What is a fuel cell and how does it work?
Ans: The cells that convert a fuel cell’s chemical energy directly into electrical energy are called fuel cells. In this, fuel burns continuously to produce electricity.

Q.3. What are the types of fuel cells?
Ans: Few types of fuel cells are Hydrogen-Oxygen fuel cell, Microbial fuel cells (MFCs), Solid Oxide Fuel Cells (SOFCs), Zinc-Air Fuel Cell (ZAFC), Direct Methanol Fuel Cell (DMFC), etc. 

Q.4. What is the first problem with fuel cells?
Ans: The first problem with fuel cells is the cost. The catalyst and a specially designed cylinder for storing gaseous reactants increase the cost.

Q.5. What is an example of a fuel cell?
Ans: The hydrogen-Oxygen \(({{\rm{H}}_2} – {{\rm{O}}_2})\) fuel cell is an example of a fuel cell. 

Q.6. Why do we need fuel cells?
Ans: Fuel cells are very needed because these are efficient, environmentally friendly electricity sources. These can be built independently hence, can be used for different purposes.

Q.7. State true or false: Fuel cells are energy storage devices?
Ans: The statement is true. Because in fuel cells, stored chemical energy converts into electrical energy only when it is connected to electrical equipment that needs electricity. 

Q.8. What are hydrogen fuel cells?
Ans: The hydrogen fuel cell is the cell that converts the chemical energy of the fuel like hydrogen and oxygen directly into electricity. During this process, water is produced as a by-product.

Q.9. Will fuel cells be used in the future?
Ans: Yes, fuel cells will be used as a major source of energy, electricity in the future. It is because of its efficiency and pollution-nature.

Now that you are provided with all the necessary information on fuel cells we hope this detailed article is helpful to you. If you have any queries about fuel cells, ping us through the comment box below and we will get back to you as soon as possible.