Electrochemical Cells

Electrochemical Cell is a device that may either generate electrical energy from chemical reactions or use electrical energy that is supplied to it to speed up chemical reactions. There are various types of electrochemical cells and they are used in our daily activities such as cells that are used in Watches, TV remotes, Clocks, etc.

In this article, we will learn about the basic concepts and topics ofelectrochemical cell, its representation, diagram, working principle, structure and notation. We will also explore the parts, types, and applications of electrochemical cell, along with its difference from electrolytic cell in detail.

What is an Electrochemical Cell?

An electrochemical cell is an electrolytic cell that uses electrical energy to drive a redox reaction that does not occur spontaneously.

• Electrochemical cells are frequently used to break down chemical compounds in a process known as electrolysis (the Greek term lysis means to break up).
• Water decomposition into hydrogen and oxygen, and bauxite decomposition into Aluminium and other compounds, are also important instances of electrolysis.
• Electroplating is done in an electrolytic cell (for example, copper, silver, nickel, or chromium).
• Electrolysis is a technique that involves the use of a direct electric current (DC).

Electrochemical Cell Definition

Electrochemical cell is an electric device that is used to generate electricity from a spontaneous oxidation-reduction reaction. This device is used to generate electric energy from the chemical energy.

Electrochemical Cell Example

Various examples of the electrochemical cell are,

• AA, AAA batteries that are used in watches, remotes, toys and others are example of Electrochemical cell.
• Inverter batteries, car batteries, and others used in our daily lives are examples of electrochemical cell, etc.

Electrochemical Cell Parts- Cathode and Anode

Electrochemical cells are typically made up of a cathode and an anode.

The key features of cathode and anode are tabulated below :

Cathode	Anode
Electrochemical Cell : Cathode and Anode
It is marked with a positive sign because electrons are spent here.	Because electrons are liberated here, the sign is negative.
The cathode of an electrochemical cell undergoes a reduction reaction.	An oxidation reaction takes place here.
Electrons are drawn into the cathode.	Electrons are ejected from the anode.

Representation of Electrochemical Cell

Electrochemical Cell is represented using the points added below,

• On the left side, the anode is inscribed, while the cathode is written on the right.
• Anode, which can be written as metal/metal ion, represents the oxidation half-cell (concentration).
• Cathode, which is written as a metal ion (concentration)/metal, represents the reduction half-cell.
• A salt bridge can be seen by drawing two vertical lines between the anode and the cathode.
• The potential differential created between the electrode and its electrolyte is defined as electrode potential. It is denoted as P.D. and P.D. between the metal and its ion solution is the consequence of charge separation at equilibrium and is the measure of an electrode's tendency to lose or gain electrons in a half cell.

For your reference, the notation of an electrochemical cell is added below,

Cu(s) | Cu(NO₃)3₂(aq) || AgNO₃(aq) | Ag(s)

Standard Electric (or Electrode Potential)

Standard electrode potential of an electrode is defined as the potential difference between the electrode and the electrolyte under standard conditions.

• It is referred to as standard electrode potential when the concentration of all the species included in a half cell is equal to one.
• The anode is the negative electrode in a voltaic cell, while the cathode is the positive electrode.

Half-Cells and Cell Potential

• Electrochemical cells are made up of two half-cells. Each of these half-cells has an electrode submerged in an electrolyte.
• Both half-cells can utilize the same electrolyte.
• These half-cells are linked by a salt bridge, which serves as a platform for ionic communication between them without allowing them to combine.
• A salt bridge is a piece of filter paper soaked in potassium nitrate or sodium chloride.
• One-half cell of the electrochemical cell loses electrons owing to oxidation, while the other receives electrons through reduction.
• It is worth noting that an equilibrium reaction happens in both half cells, and once attained, the net voltage becomes 0 and the cell stops producing power.
• The electrode potential describes how an electrode loses or absorbs electrons when it comes into contact with an electrolyte. The values of these potentials can be used to forecast the overall cell potential.
• Electrode potentials are often measured using a regular hydrogen electrode as a reference electrode (an electrode of known potential).

Primary and Secondary Cells

The definitions and properties of Primary and Secondary cells are discussed below:

Primary Cells

Primary cells are those cells that cannot easily be recharged after one use, and are discarded following discharge.

• They are galvanic use-and-throw cells. In these cells, the electrochemical reactions are irreversible. As a result, the reactants are used to generate electrical energy, and the cell stops producing an electric current when the reactants are entirely exhausted.
• The majority of primary batteries (many cells connected in series, parallel, or a combination of the two) are regarded as wasteful and damaging to the environment. This is due to the fact that they demand approximately 50 times the energy contained in their manufacturing process.
• They also contain a high concentration of harmful metals and are classified as hazardous trash.

Secondary cells

Secondary cells are those cells that are rechargeable and can therefore be used to store electrical energy in the form of chemical energy.

Secondary cells are also known as rechargeable batteries. They are electrochemical cells that have a reversible reaction, meaning they can work as both galvanic and electrolytic cells.

Read More, Primary and Secondary Cells

Types of Electrolytes

There are basically two types of electrolytes, that are,

• Strong Electrolytes
• Weak Electrolytes

Strong Electrolytes

Electrolytes that completely ionise into ions in their aqueous solution are known as strong electrolytes. For examples HCl, NaOH, K₂SO₄,etc are strong electrolytes.

Weak Electrolytes

Electrolytes that do not completely ionise into ions in their aqueous solution are known as strong electrolytes. For examples CH₃COOH, H₂CO₃, NH₄OH, H₂S, etc are weak electrolytes.

Electrochemical Cell Types

There are two types of electrochemical cells. They are

• Galvanic Cell 
• Electrolytic Cell

Now let's learn about both these types of electrochemical cells in detail.

Galvanic Cell (Voltaic Cell)

A galvanic cell is an electrochemical cell that turns the chemical energy of spontaneous redox reactions into electrical energy.

Galvanic is also called a voltaic cell. In oxidation-reduction processes, electrons are moved from one species to another. If the reaction occurs spontaneously, energy is liberated. 

As a result, the freed energy is put to use. To deal with this energy, the reaction must be separated into two independent half-reactions, namely oxidation, and reduction. The reactions are put into two distinct containers and wires to move the electrons from one end to the other. A voltaic cell is formed as a result of this.

Principle of Galvanic (Voltaic) Cell

Electric work done by a galvanic cell is mostly due to the Gibbs energy of spontaneous redox reaction in the voltaic cell. It is often made up of two half cells and a salt bridge. Each half cell also has a metallic electrode immersed in an electrolyte. These two half-cells are externally connected to a voltmeter and a switch via metallic cables. When both electrodes are dipped in the same electrolyte, a salt bridge is not always required.

Galvanic (Electrochemical) Cell Diagram

The image added below shows the diagram of an Electrochemical Cell. It is a Galvomic Cell- a type of Electrochemical cell.

👁 Diagram of an Electrochemical Cell

Working of Galvanic Cell

The working of Galvanic Cell is explained as,

• When an electrode is exposed to the electrolyte at the electrode-electrolyte interface in a galvanic cell, the atoms of the metal electrode tend to generate ions in the electrolyte solution, leaving the electrons behind. As a result, the metal electrode becomes negatively charged.
• On the other hand, metal ions in the electrolyte solution have a tendency to settle on a metal electrode. The electrode becomes positively charged as a result. Charge separation is observed under equilibrium conditions, and the electrode can be positively or negatively charged depending on the inclinations of two opposing reactions. As a result, a potential difference develops between the electrode and the electrolyte.
• This difference in potential is referred to as electrode potential. The electrode that undergoes oxidation is known as the anode, whereas the electrode that undergoes reduction is known as the cathode.
• The anode has a negative potential for the solution, whereas the cathode has a positive potential for the solution. As a result, a potential difference arises between the galvanic cell's two electrodes. This differential in potential is referred to as cell potential.
• When no current is extracted from the galvanic cell, the electromotive force of the galvanic cell is known as cell potential. Because of the potential difference, electrons flow from the negative electrode to the positive electrode when the switch is turned on.

Read More, Galvanic Cell: Definition, Construction, Working Principle

Electrolytic Cell

An electrolytic cell is an electrochemical device that employs electrical energy to promote a non-spontaneous redox reaction. Electrolytic cells are electrochemical cells that can be used to electrolyze specific substances. 

Water, for example, can be electrolyzed (using an electrolytic cell) to produce gaseous oxygen and gaseous hydrogen. This is performed by using the flow of electrons (into the reaction environment) to overcome the activation energy barrier of the non-spontaneous redox reaction. Electrolytic cells are made up of three main components: cathode, anode, and electrolyte.

Working of an Electrolytic Cell

In this experiment, two inert electrodes are immersed in molten sodium chloride (which contains dissociated Na⁺ cations and Cl^– anions). When an electric current is passed across the circuit, the cathode becomes electron-rich and acquires a negative charge. Positively charged sodium cations are now drawn to the negatively charged cathode. As a result, metallic sodium is formed at the cathode. At the same time, chlorine atoms are drawn to the positively charged cathode. As a result, chlorine gas (Cl₂) is produced at the anode (which is accompanied by the liberation of 2 electrons, finishing the circuit).

Read More, Electrolysis: Definition and Process

Salt Bridge

Salt bridge is a device that is used to connect two halves of an electrochemical cell.

• A salt bridge is made up of strong electrolytes and is used to maintains the electrical neutrality of the circuit.
• The solution of salt bridge is such that it does not react other solution. It is a U-shaped device.

The image showing salt bridge is added below,

👁 Diagram of a Salt Bridge- Electrochemical Cell

Electrochemical Cell and Electrolytic Cell- Difference

The differences between Electrochemical Cell and Electrolytic Cell are:

Electrochemical Cell	Electrolytic Cell
Electrochemical Cell vs. Electrolytic Cell- Distinguishing Features
An electrochemical cell is an chemical device that is used to produce electrical energy using the chemical energy or use electricity to promote chemical reactions	An electrolytic cell is an chemical device that produces chemical energy from the electrical energy.
Cathode in Electrochemical Cell is Positive Electrode Anode in Electrochemical Cell is Negative Electrode	Cathode in Electolytic Cell is Negative Electrode Anode in Electrolytic Cell is Positive Electrode
Spontaneous Reaction occurs in Electrochemical Cell	Non-spontaneous Reaction occurs in Electrolytic Cell
Electrochemical cells are used as battery.	Electrolytic cells are used in electrolysis of compounds.

Difference between Galvanic Cell and Electrolytic Cell

The differences between Galvanic Cell and Electrolytic Cell are :

Galvanic Cell / Voltaic Cell	Electrolytic Cell
Galvanic Cell vs. Electrolytic Cell- Difference
Chemical energy is turned into electrical energy in these electrochemical cells.	Electrical energy is turned into chemical energy in these cells.
The redox reactions that take place in these cells are completely random.	The redox reactions in these cells require energy input to continue, indicating that the reactions are not spontaneous.
The anode in these electrochemical cells is negatively charged, whereas the cathode is positively charged.	A positively charged anode and a negatively charged cathode are included in these cells.
The electrons are produced by the species that undergo oxidation.	Electrons come from somewhere else (such as a battery).
Two electrodes are set up in two different vessels.	Both electrodes are set up in the same vessel.

Electrochemical Cell- Applications

Various applications of Electrochemical Cells are:

• Many nonferrous metals are electro-refined using electrolytic cells. They have also been used for the electrowinning of these metals.
• Electrolytic cells are used in the manufacturing of high-purity lead, zinc, aluminium, and copper.
• Metallic sodium may be recovered from molten sodium chloride by running an electric current across it in an electrolytic cell.
• Galvanic cells are used in the construction of many commercially important batteries (such as lead-acid batteries).
• Fuel cells are a type of electrochemical cell that can provide clean energy in a variety of remote settings.

Related Articles

• Electrochemistry - Cells and Batteries
• Electrolysis
• Nerst Equation

Conclusion

Electrochemical cells are not just fundamental components in the realm of chemistry and physics. They are very important in advancing technologies that impact our daily lives, from powering our devices to offering sustainable energy solutions. This article discussed the basic concepts and topics ofelectrochemical cell, its representation, diagram, structure, and notation. We also learnt about the parts, types, and applications of electrochemical cell, along with its difference from electrolytic cell in detail.