Electrochemical Cells

Definition and Purpose

Electrochemical cells are devices that convert chemical energy directly into electrical energy. They are essential in powering many everyday devices such as remote controls, watches, and portable electronics. Electrochemical cells form the basis of batteries.

The two main parts of an electrochemical cell are:

• Electrodes: Conductors where oxidation and reduction reactions occur.
• Electrolyte: A substance that allows ions to move between electrodes, completing the circuit internally.

Types of Electrochemical Cells

There are two main types of electrochemical cells:

• Voltaic (Galvanic) Cells: These produce electricity spontaneously from chemical reactions. They convert chemical energy into electrical energy without needing an external power source.
• Electrolytic Cells: These require an external electrical power supply to drive a non-spontaneous chemical reaction. They convert electrical energy into chemical energy. (Electrolysis is covered in a separate topic.)

The key difference is the direction of energy flow:

• Voltaic cells release electrical energy.
• Electrolytic cells consume electrical energy.

Cell Components and Reactions

In an electrochemical cell, the electrodes and electrolyte work together to produce electricity through redox reactions:

• Anode: The electrode where oxidation occurs (loss of electrons).
• Cathode: The electrode where reduction occurs (gain of electrons).
• Electrolyte: Contains ions that move to balance the charge as electrons flow through the external circuit.

Electrons flow from the anode to the cathode through the external circuit, providing electrical energy to any connected device.

For example, in a simple zinc-copper cell:

• At the zinc anode, zinc atoms lose electrons (oxidation) and become zinc ions.
• Electrons flow through the wire to the copper cathode.
• At the copper cathode, copper ions in the electrolyte gain electrons (reduction) and deposit as copper metal.
• Ions in the electrolyte move to maintain charge balance.

This flow of electrons is what powers the external circuit.

For instance, if zinc is the anode and copper is the cathode, zinc atoms lose electrons:

$\text{Zn} \rightarrow \text{Zn}^{2+} + 2e^-$

Electrons flow through the wire to copper, where copper ions gain electrons:

$\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}$

Cell Potential and Voltage

The voltage (or electromotive force, EMF) produced by an electrochemical cell depends on the difference in reactivity of the two electrode materials. The greater the difference, the higher the voltage.

This is because more reactive metals lose electrons more easily (stronger oxidation), while less reactive metals gain electrons more easily (stronger reduction).

The voltage is a measure of the driving force pushing electrons through the circuit.

For example, a zinc-copper cell produces about 1.1 volts because zinc is more reactive than copper.

Standard electrode potentials are a way to measure the tendency of an electrode to gain or lose electrons under standard conditions. While detailed calculations are higher tier, the basic idea is that electrodes with more negative potentials are better at oxidation (anodes), and those with more positive potentials are better at reduction (cathodes).