Electrochemical cells

Electrochemical cells are fundamental devices in the field of electrochemistry, allowing chemical energy to be converted into electrical energy and vice versa. These cells are central to many applications in our daily lives, including batteries, fuel cells, and a variety of sensors. This detailed description will go deep into the inner workings of an electrochemical cell, their types, components, and applications, providing both textual and visual examples to aid understanding.

Basic concepts

Chemical reactions

Before learning about electrochemical cells, it is important to understand the chemical reactions that make them work. Oxidation-reduction (redox) reactions occur in any electrochemical cell. These involve the transfer of electrons from one chemical species to another.

Oxidation and reduction

Oxidation is the process in which a substance loses electrons. Reduction, on the other hand, is the gain of electrons. The substance that loses electrons is called oxidized, while the one that gains electrons is called reduced. The species that donates electrons is known as the reducing agent, and the one that accepts electrons is called the oxidizing agent.

Redox reactions

In an electrochemical cell, these redox reactions are split into two half-reactions that occur in separate regions of the cell, causing electrons to flow through an external circuit, and producing electricity.

Components of an electrochemical cell

Now that we understand what kinds of reactions take place, let's dig deeper into the structural composition of an electrochemical cell. An electrochemical cell has two main components: the anode and the cathode.

Anode

The anode is the electrode where oxidation occurs. Electrons are released from the chemical species at the anode, and these released electrons travel through an external circuit to the cathode.

Reaction: Oxidation at the anode
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Zn (s) rightarrow Zn^{2+} (aq) + 2e^{-}
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Cathode

The cathode is the site where reduction takes place. The electrons coming from the external circuit are accepted by the chemical species present at the cathode.

Reaction: Reduction at the cathode
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Cu^{2+} (aq) + 2e^{-} rightarrow Cu (s)
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Note: The standard abbreviated notation for an electrochemical cell is Zn|Zn^{2+}||Cu^{2+}|Cu, where single lines represent phase boundaries and the double line represents a salt bridge or junction between the two half-cells.

Salt bridge

The salt bridge is a crucial component in an electrochemical cell. It serves to complete the electrical circuit and allow ion flow, preventing the solutions in the two half-cells from mixing, while also maintaining electrical neutrality by allowing ionic movement.

Types of electrochemical cells

Galvanic (voltaic) cells

A galvanic cell, also known as a voltaic cell, is a cell that converts chemical energy into electrical energy through spontaneous redox reactions. It is a type of cell used in batteries that provide electricity for many applications.

Example: Daniel cell

A classic example of a galvanic cell is the Daniell cell.

In Daniel's cell:

• The anode is made of zinc metal, which oxidizes and releases electrons into the external circuit.
• The cathode is made of copper, and the copper ions present in the solution capture these electrons and are reduced.
• Zinc ions enter the solution, and copper is deposited on the copper electrode.

Electrolytic cell

Electrolytic cells use electrical energy to drive non-spontaneous chemical reactions. These cells are important in processes such as electrolysis, where compounds are broken down into their basic parts through the passage of an electric current.

Example: Electrolysis of water

In an electrolytic cell, such as one used for water electrolysis:

In the electrolysis of water:

• The cathode receives electrons from the electric source, causing water to be reduced to form hydrogen gas and hydroxide ions.
• The anode accepts electrons from water and oxidizes it, producing oxygen gas and hydrogen ions.

Reactions:
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text{Cathode: } 2H_2O + 2e^- rightarrow H_2 + 2OH^-
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text{Anode: } 2H_2O right arrow O_2 + 4H^+ + 4e^-
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Applications of electrochemical cells

Batteries

Batteries are a quintessential application of electrochemical cells. They power countless devices in our everyday lives, from small gadgets like smartphones to larger applications like electric vehicles.

Fuel cells

Fuel cells are another type of electrochemical cell, which produce electricity by mixing hydrogen and oxygen without combustion. They are praised for their efficiency and environmentally friendly byproduct: water.

Corrosion prevention

Electrochemical cells can also be used to protect metals from corrosion, which is a natural redox reaction in which metals deteriorate when exposed to the environment. Techniques such as cathodic protection use electrochemical principles to prevent this.

This comprehensive look at the nature, function, and applications of electrochemical cells highlights their prevalence and importance in both scientific and practical fields, and embodies the seamless conversion between chemical and electrical energies that powers much of the modern world.

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