[Chemistry Class Notes] Fuel Cell Pdf for Exam

A fuel cell can be described as an electrochemical cell which, through an electrochemical reaction, generates electrical energy from the fuel. To maintain the reactions that produce electricity, these cells require a continuous input of fuel and an oxidizing agent (generally oxygen). Thus, before the supply of fuel and oxygen is cut off these cells will continuously produce electricity.

 

A fuel cell, which consists of a cathode, an anode, and an electrolyte, is similar to electrochemical cells. The electrolyte makes the motion of the protons possible in these cells.

 

Working of Fuel Cell

It is possible to use the reaction between hydrogen and oxygen to generate electricity via a fuel cell. In the Apollo space program, such a cell was used and served two distinct purposes: it was used as a source of fuel and a source of drinking water.

 

The work of this fuel cell involved the transfer of hydrogen and oxygen via carbon electrodes into a concentrated solution of sodium hydroxide. The response of the cells can be written as follows:

Cathode Reaction – O₂ + 2H₂O + 4e^– → 4OH^–

Anode Reaction – 2H₂ + 4OH^– → 4H₂O + 4e^–

Net Cell Reaction – 2H₂ + O₂ → 2H₂O

The reaction rate of this electrochemical response, however, is quite low. With the aid of a catalyst such as platinum or palladium, this problem is overcome. The catalyst is finely divided before being incorporated into the electrodes to increase the effective surface area.

 

Block Diagram of the Fuel Cell

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Types of Fuel Cells

There are many varieties of fuel cells, although they work similarly. This sub-section discusses some of these types of fuel cells.

The Polymer Electrolyte Membrane (PEM) Fuel Cell

• Also known as proton exchange membrane fuel cells, these cells are (or PEMFCs).

• The temperature range in which these cells work is from 50℃ to 100℃.

• A polymer which can conduct protons is the electrolyte used in PEMFCs.

• Bipolar plates, a catalyst, electrodes, and the polymer membrane form a typical PEM fuel cell.

• PEMFCs can also be used for the stationary and portable generation of power, despite having eco-friendly applications in transport.

Phosphoric Acid Fuel Cell

• These fuel cells involve the use of phosphoric acid to channel H⁺+ as an electrolyte.

• These cells have working temperatures in the range of 150℃ to 200℃.

• Because of the non-conductive nature of phosphoric acid, electrons are forced to travel via an external circuit to the cathode.

• The components of these cells tend to corrode or oxidize over time due to the acidic nature of the electrolyte.

Solid Acid Fuel Cell

• In these fuel cells, a solid acid material is used as the electrolyte.

• At low temperatures, the molecular structures of these solid acids are ordered.

• A phase transition can occur at higher temperatures, which leads to a huge increase in conductivity.

• CsHSO₄ and CsH₂PO₄ are examples of solid acids (cesium hydrogen sulfate and cesium dihydrogen phosphate respectively).

Alkaline Fuel Cell

• This was the fuel cell that was used in the Apollo space program as the primary electricity source.

• An aqueous alkaline solution is used in these cells to saturate a porous matrix, which is used to separate the electrodes in turn.

• These cells’ operating temperatures are quite low (approximately 90℃).

• Such cells are extremely efficient.

Solid Oxide Fuel Cell

• The use of a solid oxide or a ceramic electrolyte involves those cells (such as yttria-stabilized zirconia). 

• These fuel cells are highly efficient and relatively inexpensive (theoretical efficiency can even approach 85 percent ). 

• These cells have very high operating temperatures (lower limit of 600℃, standard operating temperatures lie between 800 and 1000℃).

• Due to their high operating temperatures, solid oxide fuel cells are limited to stationary applications.

Molten Carbonate Fuel Cell

• In these cells, the electrolyte used is lithium potassium carbonate salt. At high temperatures, this salt becomes liquid, enabling carbonate ion movement.

• These fuel cells also have a relatively high operating temperature of 650℃, similar to SOFCs.

• Due to the high operating temperature and the presence of the carbonate electrolyte, the anode and the cathode of this cell are vulnerable to corrosion.

• These cells can be powered by fuels such as natural gas and biogas that are based on carbon.

What are the Advantages of Fuel Cells?

• More Stable: The fuel cells ensure that different parts within and around the cell are moved minimally. Consequently, they are more reliable and convenient than a typical cell.

• Takes Care of Natural Resources: the process of separating atoms and generating energy in fuel cells is very clean and an ergonomic method. Useful for natural resources, therefore.

• Free of Charge: Fuel cells are by far the most ergonomic solution if the cell is to be combined with other technologies. This combination of turbines and solar panels can be created by you. Established, therefore as complementary. 

• Scalable: From a few mill watts to several megawatts, you can use fuel cells to produce electricity. It also helps to power a range of appliances, such as mobile phones and homes. They are, therefore, scalable.