Electrochemical Cells Overview

Electrochemistry and Electrochemical Cells

Electrochemistry is the branch of chemistry concerned with the relationship between chemical reactions and electricity. It deals with the study of electrical phenomena associated with chemical processes, such as oxidation and reduction reactions. A fundamental aspect of electrochemistry is the electrochemical cell, which plays a central role in understanding these processes and their applications.

What Is an Electrochemical Cell?

An electrochemical cell, also known as a galvanic cell or Voltaic cell, is a device where a non-spontaneous redox reaction (reduction half-reaction + oxidation half-reaction) occurs at two different sites, leading to the generation of electrical energy. In simpler terms, it's like having a battery without the battery itself—the redox reaction generates a potential difference across the cell, creating a flow of electrons through an external circuit.

The electrochemical cell consists of three main components:

1. Two electrodes, one labeled 'anode' and the other 'cathode'. These electrodes have different activities in relation to the thermodynamic equilibrium of the redox reaction.
2. A conducting medium, usually an electrolyte solution, which allows the movement of ions from one electrode to another during the redox process.
3. An external circuit, connecting the two electrodes, allowing the flow of electric current due to the transfer of electrons.

How Does an Electrochemical Cell Work?

To illustrate how an electrochemical cell works, let's consider the common example of a zinc-copper cell. Here, we start with zinc and copper metal strips immersed in their respective solutions of zinc sulfate and copper sulfate. When connected via a wire, a redox reaction takes place:

[ \mathrm{Zn}(s)+\mathrm{Cu}^{2+}\left(\mathrm{aq}\right)\rightarrow\mathrm{~Zn}_{(a q)}^{2+}+\mathrm{Cu} ]

In this reaction, zinc dissolves into its ionic form Zn²⁺, while copper is deposited onto the copper strip. This leads to the formation of a voltage gradient between the two electrodes, causing the movement of electrons along the external circuit towards the cathode. At the positive terminal, the electrons reduce Cu²⁺ back into copper. As a result, a continuous cycle of electron transfer and redox reactions occurs, generating a steady electric current.

Types of Electrochemical Cells

There are different types of electrochemical cells, including primary cells and secondary (rechargeable) cells:

1. Primary cells: These cannot be recharged after being discharged. Examples include dry cells, wet cells, and silver oxide batteries. They are disposable and do not suffer any deterioration by the passage of time, but they can only supply current until the reactants are consumed.
2. Secondary cells: Unlike primary cells, secondary cells can be recharged. Examples include lead acid batteries, nickel-metal hydride (NiMH), lithium-ion batteries, and more.

Understanding the principles of electrochemical cells is crucial because they form the foundation of many technologies, such as batteries, fuel cells, solar cells, and electrodialysis, among others.