Commercial Cells (AQA A-Level Chemistry): Revision Notes

5.4.4 Commercial Cells

Introduction to Commercial Electrochemical Cells

Electrochemical cells, which convert chemical energy directly into electrical energy through redox reactions, have numerous commercial applications. From small batteries powering electronic devices to large fuel cells in vehicles, electrochemical cells are essential to modern life. Understanding these cells involves knowing how they function, their types, and the evolution of cell technology since the first voltaic battery.

How Electrochemical Cells Produce Electrical Energy

In an electrochemical cell, two half-cells containing different chemicals are connected by an external circuit and a salt bridge. Each half-cell consists of:

• Anode (negative electrode): Where oxidation occurs, releasing electrons.
• Cathode (positive electrode): Where reduction occurs, accepting electrons. Electrons flow through the external circuit from the anode to the cathode, generating a current that can power electronic devices. The overall cell potential (EMF) depends on the electrode potentials of each half-cell, with the reaction continuing until one or both reactants are depleted.

Types of Commercial Cells

Primary Cells

• Non-rechargeable: These cells are used until the reactants are exhausted and then discarded.
• Examples: Alkaline batteries commonly used in household devices.
• Advantages: Reliable, long shelf life, and stable voltage.
• Disadvantages: Waste generation, cannot be recharged.

Secondary Cells

• Rechargeable: These cells can be recharged by applying an external electrical current, which reverses the cell reactions.
• Examples: Lithium-ion (Li-ion) batteries in phones and laptops, lead-acid batteries in cars.
• Advantages: Reusable, reduced waste, long lifespan with proper cycling.
• Disadvantages: More expensive, may lose capacity over repeated cycles.

Fuel Cells

• Continuously operating: These cells produce electricity as long as they have a continuous supply of fuel (e.g., hydrogen) and an oxidant (e.g., oxygen).
• Examples: Hydrogen fuel cells used in some electric vehicles.
• Advantages: High efficiency, clean emissions (water in hydrogen cells), and long operation time.
• Disadvantages: Requires fuel storage, costly technology, and limited refuelling infrastructure.

Evolution of Electrochemical Cells: From Voltaic Piles to Modern Batteries

The concept of electrochemical cells has come a long way since Alessandro Volta developed the first voltaic pile in 1800. Volta's cell stacked layers of zinc and copper separated by brine-soaked paper, generating a small but steady current. Key developments since then include:

• Daniell Cell (1836): Improved upon Volta's pile with longer-lasting materials, making it the first practical source of electricity.
• Lead-Acid Battery (1859): The first rechargeable battery, still widely used in vehicles.
• Alkaline Battery (1950s): Increased efficiency, safety, and power storage compared to earlier cells.
• Lithium-Ion Battery (1990s): Lightweight, high-capacity, and rechargeable, ideal for portable electronics and electric vehicles. The evolution of these cells reflects advances in material science and our understanding of electrochemical reactions, leading to safer, more efficient, and more environmentally friendly energy sources.