Introduction
prevents internal short-circuiting of electrons. Internal short-circuiting implies the movement of electrons from the anode to cathode through the electrolyte, which dissipates the chemical energy without providing electrical potential in the external circuit. When the electrolyte is solid, it simultaneously functions as a membrane (separator) and an ionic conductor. Two final parts required to complete a commercial galvanic cell are the terminals. They are necessary when applying the batteries to electrical appliances with specific holder designs to prevent a short circuit from the reverse installation of the battery, and they are shaped to match the receptacle facilities provided in the appliances. For example, in cylindrical batteries, the negative terminal is either designed to be flat, or to protrude out of the battery end, while the positive terminal extends as a pip at the opposite end.Read more about electrochemical cell
Electrochemical Characterization
Yogesh S. Choudhary, … Gomathi Nageswaran, in Spectroscopic Methods for Nanomaterials Characterization, 2017
Electrochemical Cell
An electrochemical cell consists of two basic electrodes, the working electrode and the counter electrode, (which may individually act as a cathode or anode though the working electrodes are typically the cathodes), along with an electrolyte. The electrochemical cell can have a reference electrode too, along with the working and counter electrodes. When this cell is connected with the external circuitry, it provides the path for the flow of the current throughout the circuit.
The electrolyte provides the path for the flow of electrons or ions inside the cell. The chemical reactions happening in the cell help to convert the chemical energy into electrical energy. This electrical energy is allowed to travel through the external circuits connected with the load. The generated electrical energy drives the load and completes the electrical circuit.
The load can be anything from a small bulb to a heavy motor or machinery. If the generated electrical energy is not enough, then it fails to drive the load. Hence, as per the requirement of the load, there is a need for the electrical energy that gives rise to different capacities of the cells and the batteries to be generated.
All about the electrochemical cell and its different types
Abstract
In brief we are going to discuss electrochemical cells, which have the ability to produce
electrical energy from chemical reactions, and also use electrical energy to create chemical reactions,
that are divided into two types of cells: galvanic cells which known also as voltaic cells, and
electrolytic cells.
Galvanic cells are the types that produce electricity such as fuel cells (hydrogen-oxygen fuel
cell), and Deniall cell, whilst the electrolytic cells used an external supply of electricity to create the
redox reactions.
This review also involves Weston standard cell that is being developed to overcome the
deficiencies of Clark cell, as well as the role of liquid junction potential in measuring the potential
difference of the double layer that made by the diffusion of electron on the both side of the cell,
finally the concentration cells that produce voltage when they approaches the equilibrium.
Keywords: electrochemical cells, galvanic cells, electrolytic cell, concentration cell, potential, and
fuel cell.
Introduction
In electrical chemistry, the word “cell” is utilized in a wide range of appliances of multiple
purposes, forms, and measurements where the reactions of electrochemical typically occur and
electrochemical cells generally involve at least two electrodes in association with an electrolyte [1].
An electricity generator from a spontaneous redox reaction or, in return, that uses electricity
to conduct a non-spontaneous redox reaction is an electrochemical cell[2], it composed of two-
electron conductors (electrodes) parted by an ionic conductor (electrolyte) and often linked by an
electron conductor which is generally called a metal wire conductor [3].
Electrochemical cells that have the ability to generate electrical currents are labeled as voltaic
cells or galvanic cells [4]: for example batteries or fuel cells [5].
The chemical reactions or
transformations which coupled with appropriate half-cell reactions, can lead to a free energy shift in
the cell cycle as a consequence of the electric power generation through electricity [5]. An external
electric current is used in other electrochemical cells to drive a chemical reaction that does not
happen spontaneously; such cells are termed as Electrolysis cells [4].
The fuel cells are electrochemical cell that transforms a fuel’s chemical energy (often a
hydrogen) and an oxidizing agent (often oxygen [6,7]) by means of a couple of redox reactions into
electricity[8,7]. The chemical energy of the battery obviously comes from supplies of metals and
their ions or oxides [9,7]which are already present mainly in the battery, except in flow batteries,
and because of this,
The fuel cells are different from the most typical battery, as they requiring a
Continuous sources for fuel and oxygen (usually air) to maintain the chemical reactions[7]. So long
As fuel and oxygen are provided, the fuel cells can constantly create electricity [7]. This cell form
Serves as a renewable source of energy in many isolated regions [10].
In this short review, all the types of electrochemical cells would be discussed in detail, as
well as liquid junction potential due to the diffusion of electrons, and other types of the cells.
Types of electrochemical cells
Galvanic cell
Galvanic cells, which also termed as voltaic cells [12], are electrochemical cells, in which
electrode reactions spontaneously occur, generate an electric current that can be used in batteries or
fuel cells to supply electric energy [13], and they can convert chemical reactions to electrical energy
directly [14].
A galvanic made up of 2 metals (electrodes), which are linked throughout an electrical
conducting solution (an electrolyte) and linked externally to complete the circuit [15]. In such a
case, one of the metallic materials (more reactive) begins to solubilize in an electrolyte, whereas the
other tends to contain new metal deposited on it [15]. As the metal is dissolved, the more reactive
electrons that are used in the metal deposition on the other electrode flow through the external
contact (as an electrical current) [15].
The dissolution and deposition reactions, which made by the
anode and the cathode reactions in the order, are called half-cell reactions [15], and without the
separation of these two half-reactions spatially, this energy would be liberated as heat [12].
Mechanism of galvanic cells
A basic example of a galvanic cell containing 2 cell diagram metal / metal ion systems [12];
Zn(s)+Cu2+(aq)→Zn2+(aq)+Cu(s)(1) [16], The galvanic cell shown in figure 1 can be used to
perform this reaction; a copper strip is inserted into a beaker that contains a 1 M solution of Cu2+
ions, and a zinc strip is inserted into a different beaker that contains a 1 M solution of Zn2+ ions[16].
The two metal bands, which function as electrodes, are attached by a wire, and the compartments
are linked with a salt bridge, a U-shaped tube that is inserted into the two solutions that involve a
concentrated liquid or gelled electrolyte [16]. The ions in the salt bridge are chosen to prevent
interfering with the electrochemical reaction through oxidation , reduction or precipitation or by
forming a complex; commonly used cations and anions are Na+ or K+ and NO3− or SO42− , (The
ions in the salt bridge do not have to be the same as those in the redox couple in either
compartment)[16] .
When the circuit is closed, a spontaneous reaction occurs: zinc metal is oxidized
to Zn2+ ions at the zinc electrode (the anode), and Cu2+ ions are reduced to Cu metal at the copper
electrode (the cathode)[16]. As the reaction progresses, the zinc strip dissolves, and the
concentration of Zn2+ ions in the Zn2+ solution increases; simultaneously, the copper strip gains
mass, and the concentration of Cu2+ ions in the Cu2+ solution decreases (Figure 1 b ). The electrons
that are released at the anode flow through the wire, producing an electric current [16]. Galvanic
cells therefore transform chemical energy into electrical energy that can then be used to do
work[16].
The galvanic cell mostly has 2 types of metals in each of the electrolyte solutions which are connected by using a salt bridge. It may also have half-cells with a porous membrane between them.
Salt bridge
It is a device that connects two halves of the electrochemical cells and is formed of a strong electrolyte. It maintains the electrical neutrality in the circuit. It also completes the electrical circuit.
The solution in the salt bridge must be inert and nonreactive with other solutions. This prevents a reaction between the solution and the salt bridge and allows movement of ions between the two half cells.
The two types of the salt bridge are glass tube bridge and filter paper bridge.
Glass tube bridge is a tube that has a U-shape. It is filled with electrolytes like sodium chloride and potassium nitrate.
The filter paper bridge is formed by a porous material such as filter paper that has electrolytes soaked.
The solution in the salt bridge must be inert and nonreactive with other solutions. This prevents a reaction between the solution and the salt bridge and allows movement of ions between the two half cells.
Let’s see an example.
We can make Galvanic / voltaic cells with solid copper (Cu(s)) in a silver nitrate solution (AgNO3(s)).
During this reaction, AgNO3 breaks into Ag+ and NO3- ions. Then, when the copper electrode is introduced in this solution having silver ions Ag+(aq), it will instantly oxidize Cu(s) to Cu2+(aq) and reduce itself to Ag(s). This reaction will generate energy, and the reaction has to be split into 2 separate containers, as discussed above. Otherwise, the energy released will be lost and cannot be used. Then after connecting a wire (between the two containers) to allow the floor of electrons between them, the Galvanic/ voltaic cell is ready.
These reactions take place on metal strips, known as electrodes. The electrode on which reduction takes place, i.e. the metal electrode which gains an electron(s) is called a cathode and the electrode at which the oxidation takes place, i.e. the metal electrode that loses an electron(s) is called an anode.
Considering the reaction in the above example, Cu is the anode and Ag is the cathode.
Note: Electrons always flow from anode to cathode.
Cell notation
It is the symbolic representation of the two halves of the galvanic cells by using abbreviations and symbols of the elements. Guidelines of cell notation are as follow:
- The two halves are represented by using symbols of the elements and chemical formulas of the compounds.
- The anode half is written first and the cathode half is written later. First, the reactants are mentioned within each half and then the products are mentioned.
- Reactions of both the halves are separated by using two vertical parallel lines in between. This double vertical line indicates the salt bridge of the galvanic cell.
- The phased of each of the element and compound is mentioned in parentheses as s, g and aq for solid, gas and aqueous respectively.
- The cell notation of the above mentioned galvanic cell is:
Cu(s)│1MCu(NO3)2(aq)║1MAgNO3(aq)│Ag(s)
Daniel cell
These are the type of electrochemical cells that have copper sulphate solution filled in the container which is made from copper. This also contains unglazed earthenware containers that contain sulphuric acid and electrodes of zinc. The aim of the Daniel cell was to eliminate the problem of hydrogen bubbles.
This cell was invented by a British chemist and meteorologist, John Frederic Daniel, in 1836. It is an example of a Galvanic cell.
In this cell, the oxidation of zinc takes place at the anode, and the following half-reaction takes place:
Zn(s) → Zn2+(aq) + 2e
While copper undergoes reduction at the cathode and the following reaction takes place:
Cu2+(aq) + 2e− → Cu
So, the entire reaction can be written as:
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
This reaction leads to the formation of copper in solid-state at the cathode electrode, and the zinc electrode undergoes corrosion into the solution to form cation of zinc.
Dry cell
The EverReady cells are dry cells. It is a type of voltaic cell. These are known as dry cells because the electrolyte used is not a liquid. It is a paste. The dry cells use a paste of manganese dioxide and ammonium chloride in order to generate acidic ions and to complex the zinc ions received from the chemical reaction around the positive electrode made by carbon rods. These cells are also known as Leclanché cells. The dry cells are used in the remote controls or flashlights.
Uses of voltaic cells
- The voltaic cells are used to get electrical power. These are used to make the chargeable batteries present in the laptops and cell phones.
- The solar cells are made from the galvanic cells, and so are rechargeable.
- The chargeable electric vehicles, like bikes and cars, have galvanic cell batteries.
Advantages of voltaic cells
- These are easy to make and are easily available.
- They last for a long period of time as most of them can be charged.
Disadvantages of voltaic cells
- Some of the galvanic cell batteries are very heavy.
- They are expensive than the electrolytic cells.
- Some of them show rusting or spoilage very easily.
Electrolytic cells
These are the type of electrochemical cells that drive a nonspontaneous reaction using electrical energy. These can decompose chemical compounds, like water into hydrogen and oxygen. This decomposition takes place by the process called electrolysis. So, electrolytic cells need a DC power supply, two electrodes and an electrolyte to perform electrolysis.
The three components of electrolytic cells are an electrolyte and two electrodes.
Electrolytes
Electrolytes are the substances that give an electrically conducting solution when dissolved in polar solvents, such as water. This is because when the electrolyte is dissolved in the polar solvents, it breaks into cation and anions and gets distributed uniformly throughout the solution.
These cations and anions under an electrical potential in the solution move to the electrode with an abundance of electrons and a deficit of electrons, respectively. This movement of cation and anions in the direction opposite to each other generates current and forms the electrolytic cells.
While salts, acids and bases form an electrolyte, few gases under certain conditions can also behave like an electrolyte, such as hydrogen chloride at high temperature and low pressure.
So, a substance or an element that dissociates into ions (when put in a solution), has the ability to conduct electricity. Salts are most commonly used to make electrolytes. Molten salts such as molten sodium chloride also form electrolytes and conduct electricity. In fact, ionic liquids are molten salts that have a melting point below 100° C and are highly conductive non-aqueous electrolytes. These have many applications in fuel cells and batteries.
Hydroxides made from alkaline metals are also strong electrolytes but do not dissolve in water after a limit. Due to which their application is restricted to certain situations only.
Uses of electrolytic cells:
- Electroplating:This is the process of coating an electrically conductive object with a thin layer of metal using an electrical current. The electroplating with a particular element adds many properties to metal, such as protection against corrosion, abrasion resistance and wear resistance. This is also used in jewellery and other for several aesthetic reasons.
- Batteries: Batteries are used in various appliances and machines. These can be formed by electrochemical cells.
- Electrowinning or electro-refining:It helps to produce various pure metals such as sodium, calcium, aluminium and magnesium. Both electrowinning and electro-refining are electroplating on a large scale. Both processes are used to purify metals by removing impurities. These are an economical and straightforward process for purification of non-ferrous metals.
In electrowinning, a metal is kept in a liquid leach solution, and then a current is passed from an inert anode to the leach solution. This extracts the metal, and then the metal gets deposited on the cathode. While in the electro-refining process, the unrefined impure metals are present on the anodes and when the current is made to pass through the acidic electrolyte the anodes get corroded, and because of electroplating, the pure refined metal gets deposited on the cathode.
- Oxygen production:The oxygen used in the spacecraft and submarines is prepared with the help of electrolytic cells.
- Hydrogen fuelis also produced by using electrolytic cells.
Question
What are the three types of electrochemical cells?
Electrochemical cells are capable of producing electrical energy by using the chemical energy generated through chemical reactions and chemical energy by using electrical energy. The types of electrochemical cells are Galvanic or Voltaic cells, electrolytic cells, Fuel cells, chargeable and non-rechargeable cells.
What are the conditions for electrochemical cell?
Standard conditions are those that take place at 298.15 Kelvin (temperature), 1 atmosphere (pressure), and have a Molarity of 1.0 M for both the anode and cathode solutions.
What are the four components of an electrochemical cell?
Components of Electrochemical Cells
Anode: Oxidation occurs at the anode. …
Cathode: Reduction occurs at the cathode. …
Electrodes: In order to hook up an external circuit you need have something to physically connect the wire to.
How does pressure affect electrochemical cells?
Increasing the pressureof the cell will make the cell EMF more negativeas more electrons are produced. Electrochemical cells can be a useful source of energy for commercial use. They can be produced to be non-rechargeable, rechargeable or fuel cells.
What are electrochemical cells in real life?
We encounter electrochemical cells in all facets of our everyday lives from the disposable AA batteries in our remote controls and the lithium-ion batteries in our iPhones to the nerve cells strewn throughout our bodies. There are two types of electrochemical cells: galvanic, also called Voltaic, and electrolytic.
What material is in an electrochemical cell?
An electrochemical cell consists of two basic electrodes, the working electrode and the counter electrode, (which may individually act as a cathode or anode though the working electrodes are typically the cathodes), along with an electrolyte.