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Electrochemical Cells

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An 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. These gadgets can turn chemical energy into electrical energy and vice versa. A common 1.5-volt electrochemical cell is used to power a range of electrical items such as TV remotes and clocks. Galvanic cells and Voltaic cells are examples of cells that may generate an electric current as a result of chemical processes.

What is an Electrochemical Cell?

An electrolytic cell is an electrochemical cell that employs electrical energy to drive a redox reaction that does not occur spontaneously. They 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 aluminum 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 cells are typically made up of a cathode and an anode. The following are the key features of the cathode and anode.

Cathode

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

  1. On the left side, the anode is inscribed, while the cathode is written on the right.
  2. The anode, which can be written as metal/metal ion, represents the oxidation half-cell (concentration).
  3. The cathode, which is written as a metal ion (concentration)/metal, represents the reduction half-cell.
  4. A salt bridge can be seen by drawing two vertical lines between the anode and the cathode.
  5. 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.

Standard Electric or Electrode Potential: 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 which 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

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

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.

Types of Electrochemical Cells

Galvanic Cell 

An electrochemical cell that turns the chemical energy of spontaneous redox reactions into electrical energy is known as a galvanic cell or 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 wire 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

The 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.

Working of Galvanic Cell

  • 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.

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).

Galvanic Cell / Voltaic Cell

Electrolytic Cell

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 the electrodes are set up in the same vessel.

Applications of Electrochemical Cells

  • Many nonferrous metals are electro-refined using electrolytic cells. They have also been used to electrowine these metals.
  • Electrolytic cells are used in the manufacturing of high-purity lead, zinc, aluminum, 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 the lead-acid battery).
  • Fuel cells are a type of electrochemical cell that can provide clean energy in a variety of remote settings.

Function of Salt bridge

A salt bridge, also known as an ion bridge, is a laboratory device used in electrochemistry to connect the oxidation and reduction half-cells of a galvanic cell (voltaic cell). It maintains the electrical neutrality of the internal circuit. If there was no salt bridge, the solution in the one-half cell would collect a negative charge while the solution in the other half cell accumulated a positive charge as the reaction advanced, thereby inhibiting further reaction and so power generation.

If soaked in one of the electrolytes listed above, porous paper, such as filter paper, can be utilized as a salt bridge. There is no need for a gelification agent because the filter paper acts as a solid medium for conduction. The conductivity of this type of salt bridge is determined by several elements, including the electrolyte solution concentration, the texture of the paper, and the paper’s absorption ability. Increased conductivity is generally linked to a smoother texture and greater absorbency. A porous disc or other porous barriers between the two half-cells can be used instead of a salt bridge because they allow ions to pass between the two solutions while avoiding bulk mixing.

Sample Questions

Question 1: What is the Function of a Salt Bridge in an Electrochemical Cell?

Answer: 

The salt bridge completes the circuit of an electrochemical cell, allowing current to flow across it. It also contributes to the cell’s overall electrical neutrality.

Question 2: What is Standard Electrode Potential?

Answer: 

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

Question 3: What are the Key Differences between Cathode and Anode?

Answer: 

In an electrochemical cell, reduction takes occur at the cathode. A positive (+) sign is commonly used to denote it. Electrons move from the anode to the cathode. In electrochemical cells, the anode is the electrode where oxidation takes place. A negative (-) sign is used to represent it.

Question 4: Is it Possible for an Electrochemical Cell to have a Positively Charged Anode or a Negatively Charged Cathode?

Answer: 

Yes, an electrolytic cell’s anode is positively charged (and the cathode is negatively charged). Despite the negative charge, oxidation occurs at the anode. The chemical reactions that take place in these electrochemical cells are not spontaneous.

Question 5: What are electrolytic cells?

Answer: 

Electrolytic cells are a type of electrochemical cell that uses electric currents to speed up cell reactions. The chemical reaction that occurs inside such cells is known as electrolysis. Bauxite may be broken down into aluminium and other components using electrolytic cells. These cells can also be used to electrolyze water into hydrogen and oxygen.


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Last Updated : 25 Jun, 2022
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