Every phone battery, every rusting nail, and every gold-plated ring runs on the same underlying trick — electrons quietly changing hands between atoms, sometimes captured to do useful work, sometimes just slipping away unnoticed.
The reactivity series and corrosion from the previous article are really just electron transfer left to happen on its own, uncontrolled. Electrochemistry asks a more deliberate question: what happens if that same electron transfer is carefully corralled, forced to travel through a wire on its way from one atom to another? The answer, it turns out, is electricity itself.
Electrochemistry is the branch of chemistry that studies the relationship between chemical reactions and electricity, centred on reactions where electrons move from one substance to another. These are called redox reactions, a combination of two processes that always happen together: oxidation, the loss of electrons, and reduction, the gain of electrons. One substance can never be oxidised without another being reduced, since the electrons lost by one must be gained by the other.
Chemists often remember this with the phrase "OIL RIG": Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).
Left alone, a redox reaction like rusting simply releases its electrons locally, with no useful work done. An electrochemical cell instead physically separates the oxidation and reduction halves of the reaction into two locations, connected by a wire, forcing the electrons to travel through that external circuit to get from one side to the other. That directed flow of electrons through a wire is, quite simply, an electric current.
Oxidation always happens at the anode, and reduction always happens at the cathode, with electrons flowing between them through an external wire.
In every electrochemical cell, oxidation happens at the electrode called the anode, and reduction happens at the electrode called the cathode — a naming rule that never changes, whether the cell is generating electricity or consuming it.
A galvanic cell (also called a voltaic cell) uses a spontaneous redox reaction, one that happens naturally on its own, to generate electricity. This is exactly how a battery works: a chemical reaction inside is already "wanting" to happen, and the cell simply forces the electrons involved to travel through your phone or torch on their way from anode to cathode, doing useful work along the journey.
A car's lead-acid battery uses lead and lead dioxide electrodes in a sulfuric acid electrolyte, while a lithium-ion battery, common in phones and laptops, relies on lithium ions moving between electrodes. Different battery types use different redox chemistry, but every one relies on the same underlying principle: a spontaneous reaction, forced to release its electrons through a circuit.
An electrolytic cell works in reverse: rather than generating electricity from a spontaneous reaction, it uses an external electrical source to force a non-spontaneous reaction, one that would never happen on its own, to take place. This process is called electrolysis.
| Cell Type | Reaction Direction | Purpose |
|---|---|---|
| Galvanic (Voltaic) Cell | Spontaneous | Generates electricity (batteries) |
| Electrolytic Cell | Non-spontaneous | Consumes electricity to drive a reaction |
Electrolysis has genuinely industrial applications. Passing an electric current through molten sodium chloride splits it into pure sodium metal and chlorine gas, a major industrial method for producing both. Electrolysis is also how aluminium is extracted from its ore on a massive industrial scale, a process known as the Hall-Héroult process.
Electroplating uses an electrolytic cell to deposit a thin, even layer of one metal onto the surface of another, typically to improve appearance, conductivity, or resistance to corrosion. The object to be plated is made the cathode, so that metal ions from the electrolyte solution are reduced and deposited directly onto its surface.
Silver-plated cutlery, gold-plated jewellery, and chrome-plated car parts are all everyday products of electroplating. A cheaper base metal object is placed as the cathode in a bath containing dissolved silver, gold, or chromium ions; passing an electric current through the solution reduces those metal ions onto the object's surface, giving an inexpensive item the appearance, and some of the properties, of a far more expensive metal.
Electrochemistry reveals that a battery and a rusting nail are, at their core, running the exact same kind of reaction — electrons moving from one substance to another. The only real difference is control: rust lets its electrons scatter uselessly into the surrounding metal, while a battery corrals that same electron flow through a wire, turning ordinary chemistry into something that can light a room or power a phone. The final article in this Chemistry series turns to where all of this ultimately matters most: chemistry in everyday life.
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