Electric circuit

Galvanic cell: converting chemical energy into electrical energy

Galvanic cell: converting chemical energy into electrical energy

The galvanic cell is an electrochemical cell that obtains an electrical current from chemical energy. This device consists of two different metals connected using a salt bridge or a porous disk located between each half cell. It receives its name in honor of Luigi Galvani.

The cell potential is the difference in potential energy between the two electrodes -called anode and cathode- in a galvanic cell. It is the reason why electrons flow externally through the electric circuit from the anode to the cathode.

The voltaic cell, the first electrical cell that can provide an electrical potential in a circuit, obtains electrical energy from a chemical reaction.

How does a galvanic cell work?

A galvanic cell consists of two electrodes immersed in an electrolyte tank. In general, the electrolyte consists of two electrolyte solutions that can exchange ions through a salt bridge or a porous septum.

Galvanic cell: converting chemical energy into electrical energyThe metal in a galvanic cell dissolves in the electrolyte at two different speeds. First, the metals become positive ions in dissolving, and the electrons remain in the undissolved part.

As a result, the metal electrode immersed in the electrolyte solution acquires a net negative charge as the electrolyte becomes positively charged. If there is an electrical connection, the electrons flow generating an electrical current.

It is the process that explains how energy is converted in galvanic cells to produce electricity.

What are anode and cathode?

The anode is the most active metal, for example, metallic zinc. Conversely, the cathode is the most inactive metal, for instance, metallic copper.

At the same time, an equal electric current but with positive ions appears in the electrolyte. As a result, the anode ions are transferred to the electrolyte. Dissolved ions are also transferred to the cathode, the least active metal. Therefore, reduction occurs at the cathode, and oxidation occurs at the anode. 

In this way, the anode is consumed or corroded. When the anode material has been totally finished, the electric current stops.

Metal can be considered the fuel that provides energy to the device.

A similar process is to use electrolysis. The electric current in the electrolyte is equal to the current in the external circuit. That is to say, the complete electrical circuit is formed by both the outer path of the electrons and the part of the electrolyte which the positive ions travel through.

There is a flow of electrons from the anode, the oxidized ions, to the cathode, the reduced atoms (which take up electrons). This flow produced by an oxidation-reduction (redox) reaction is what constitutes the electrical current produced by the galvanic cell.

Galvanic cell types

Of types of galvanic cells, we distinguish three:

1. Concentration cell

A concentration cell is a primary cell (not rechargeable) that uses two galvanic half cells with the same chemical species but with different concentrations.

For example, such a cell can be made up of two copper electrodes immersed in two solutions containing copper sulfate (CuSO 4 ). The two solutions have different concentrations and the electrodes are separated by a porous septum or a salt bridge.

The battery will discharge when the electrolyte concentration in the two half cells is the same.

2. Electrolytic cell

An electrolytic cell consists of two electrodes immersed in a tank containing an electrolyte. Generally, the electrolyte comprises two electrolyte solutions that can exchange ions through a salt bridge or a porous septum.

An oxidation reaction occurs at the anode. On the other hand, a reduction reaction occurs at the cathode. The result is that a redox reaction occurs in the cell that takes advantage of external electrical energy to produce it.

The signs of the poles are reversed with respect to a galvanic cell. For example, the anode is the positive pole in an electrolytic cell, while the cathode is the negative pole.

3. Electrochemical cell

Electrochemical cells are made up of two half-elements, also called half cells.

These semi-elements are kept separated by a semi-permeable membrane or are contained in separate containers connected by a salt bridge. A half part releases electrons through the oxidation reaction by connecting the half elements. In turn, these electrons are transferred to the other to trigger the reduction reaction.

What is the difference between galvanic cell and electrolytic cell?

Both cells involve a solution made up of ions capable of conducting electricity and electrodes to measure the potential of that solution.

The main difference between a galvanic and electrolytic cell is that a galvanic cell converts chemical energy released during a spontaneous redox reaction into electrical energy. In contrast, an electrolytic cell consumes electrical power to force a chemical reaction to occur.

What is galvanic corrossion?

Galvanic corrosion is a process that degrades metals electrochemically. This corrosion occurs when two dissimilar metals come into contact with each other in the presence of an electrolyte, such as salt water, forming a galvanic cell.

A cell can also form if the same metal is exposed to two different concentrations of electrolyte. The resulting electrochemical potential then develops an electrical current that electrolytically dissolves the less noble material.

The voltaic pile experiment of Alessandro Volta

The voltaic cell was the first modern electric battery Alessandro Volta invented in 1800.

Volta showed that when certain metals and chemicals come in contact produce an electric current. During his research, Volta brought into contact several pairs of alternating discs of copper, silver, and zinc separated by cloth or cardboard impregnated with brine to increase conductivity. He observed a tendency of copper ions to move to silver discs generating an electric current between its ends.

Volta's invention was built on Luigi Galvani's 1780s discovery of how a circuit of two metals and a frog's leg can cause the frog's leg to respond.

The Volta Effect or contact electrification was one of the first theories to explain the voltaic cell's action, affected by degradation due to the effect of polarization. However, today it is an obsolete theory that current theories of electrochemistry have replaced. 

What is the Daniel cell?

Daniel cell, also known as the zinc-copper battery, is an electrochemical battery with zinc as the negative electrode. It uses copper as the positive electrode and zinc sulfate and copper sulfate as electrolytes.

Frederic Daniell invented the Daniel cell in 1836; thus, this cell is named after its inventor. In order to eliminate the problem of hydrogen bubbles in the voltaic stack. Daniel's solution was based on using a second electrolyte to consume when there is only one electrolyte.

Data de publicació: September 30, 2021
Última revisió: September 30, 2021