An electrochemical cell is a device capable of generating electrical energy from the chemical reactions occurring inside it. A standard 1.5V cell, used in TV remotes and clocks, and lithium-ion batteries used in our phones are all examples of electrochemical cells.
The electrochemical cells are of two types; Galvanic cells, also known as Voltaic cells, and Electrolytic cells.
“Spontaneous redox reactions occur in galvanic cells and chemical energy is converted into electrical energy. Whereas, in electrolytic cells, the external power source is used to drive chemical reaction within the cell, thereby converting electrical energy into chemical energy.”
As their name suggests, galvanic and voltaic cells are named after Luigi Galvani and Alessandro Volta. These scientists conducted several experiments on chemical reactions and electric currents in the late 18th century.
Galvanic vs Electrolytic Cells
| Galvanic cell | Electrolytic cell |
| A galvanic cell produces electricity by the chemical reaction occurring inside the cell | An electrolytic cell requires electricity to drive the chemical reaction inside of the cell |
| It converts chemical energy into electrical energy | It converts electrical energy into chemical energy |
| The reaction in galvanic cell is spontaneous | In electrolytic cells, a non-spontaneous reaction takes place |
| Cathode is the positive electrode and Anode is the negative electrode in galvanic cells | Anode is the positive electrode and cathode is the negative electrode in electrolytic cells |
| Ions are discharged at cathode while on anode they are consumed | Ions are discharged at both the electrodes |
| Electrons move from anode to cathode through an external circuit | Electrons move from cathode to anode through an external circuit |
| Half cells are set up in different containers and are connected through salt bridges | Electrodes are kept in the same container in a molten or electrolyte solution |
| The electricity produced as a result of chemical reaction in the cell is measured by a coulometer | The emf of the voltage provided to the cell is measured by a potentiometer |
| The galvanic cell has its application in batteries | Electrolytic cells are used in purification and electroplating |
Electrolytic Cells
An electrolytic cell consists of three parts, an electrolyte and two electrodes (anode and cathode). When the electrodes are connected to a source of direct current, positive ions in the electrolyte migrate to the negative electrode (cathode) and negative ions migrate to the positive electrode (anode). In other words, a redox reaction takes place resulting in new ions or neutral species.
Note that only an external power of correct polarity and sufficient magnitude can make an electrolytic cell decompose a normally stable, or inert chemical compound in the solution.
Electrolytic cells are often used in process of electrolysis, the decomposition of chemical compounds. Important reactions such as decomposition of water into hydrogen and oxygen, electroplating, and electrolysis of fused sodium chloride and brine (aqueous solution of NaCl) are done in electrolytic cells. Other common applications of electrolytic cells include refining copper and other metals and the production of caustic soda, etc.
Galvanic Cells
A galvanic cell, unlike an electrolytic cell, has two electrolyte solutions in different containers separated by a salt bridge. The electrodes are immersed in the electrolyte solutions and are connected externally via a piece of wire. This wire can be connected to a voltmeter to measure and control the potential.
In a galvanic cell, the anode is negative and the cathode is positive. Since the oxidation reaction takes place in the anode and the reduction reaction occurs at the cathode, these cells have redox reactions occurring inside just like electrolytic cells, but in the opposite way.
A galvanic cell where only zinc (Zn) and copper (Cu) are used as opposite electrodes having zinc sulfate and copper sulfate as electrolytes is termed the Daniell Voltaic cell. It’s named after Daniell, because it was his clever design that separated zinc and copper ions hence, removing all interruptions from a cell to function.
Here in galvanic cells, chemical reactions occur and result in the production of electrical current. It all occurs spontaneously and this process is used for the electrode potential determination of different metals. It is also used in the determination of electrochemical series via a Standard Hydrogen Electrode (SHE) system.
Galvanic cells are used in watches, clocks, remote controllers, calculators, etc. They are also being used in cell phones, cameras, laptops, and toys. Fuel cells are galvanic cells that are used to power engines.
Additional topics
- Strong vs. Weak Electrolytes: How to Categorize the Electrolytes?
- Salt Bridges: Types, Preparation, Function, Significance
- Randles-Sevcik equation: The Cyclic Voltammetry peak current
Key Takeaway(s)
Concepts Berg
Can an electrochemical cell function as galvanic as well as electrolytic?
Yes, a well-known example of such cells is lead batteries. When supplying current, the battery function as a galvanic cell, and when being charged, the half-reactions are inverted and voltage has to be supplied, thus, acting as an electrolytic cell.
What are the similarities between galvanic and electrolytic cells?
The similarities between galvanic and electrolytic cells are:
- They are both electrochemical cells.
- Redox reaction takes place in both cells.
- Although oppositely functional, they both have anode and cathode.
- In both types of electrochemical cells, oxidation happens at the anode, reduction happens at the cathode.
What are the 3 major differences between a galvanic cell and an electrolytic cell?
- The galvanic cell produces electricity whereas electrolytic cells require electricity.
- The reaction in galvanic is spontaneous whereas, in an electrolytic cell, it is non-spontaneous.
- Galvanic cells are used in batteries whereas electrolytic cell is used in the electroplating and purification of metals such as copper.
What is the difference between electrolytic cells and electrochemical cells?
The electrolytic cell is a type of electrochemical cell.
What is the difference between galvanic and voltaic cells?
Galvanic and voltaic cells are the same electrochemical cells. They are sometimes referred to as voltaic and other times they are called galvanic cells.
What is the direction of electron flow in an electrolytic cell?
The electron flows from cathode to anode through the external circuit, in an electrolytic cell. On the inside, it is an anode to cathode.
Is it possible for the cell potential to be negative in a galvanic cell?
It is not possible for the cell potential to be negative in a galvanic cell. The reaction in galvanic cells is spontaneous and has a negative value of the Gibbs free energy and therefore a positive cell potential difference.
References
- ELECTROCHEMISTRY Principles, Methods, and Applications by CHRISTOPHER M. A. BRETT and ANA MARIA OLIVEIRA BRETT (Departamento de Quimica, Universidade de Coimbra, Portugal)
