Some chemical reactions simply will not happen on their own — they need a push. Electrolysis provides that push using electricity. The setup is straightforward: dip two electrodes (conductors connected to a power supply) into a liquid containing ions — either a molten ionic compound or a solution — and flip the switch. Positive ions migrate to the negative electrode (cathode) and gain electrons, while negative ions travel to the positive electrode (anode) and lose electrons. The compound is literally pulled apart by electrical force. When you electrolyze water, hydrogen gas bubbles up at the cathode and oxygen gas appears at the anode — the two elements that combine to form every water molecule, separated before your eyes.
Electrolysis reshaped the industrial world. Aluminum, the most abundant metal in Earth's crust, was once rarer than gold because it bonds so tenaciously to oxygen that chemical methods could not free it. In 1886, Charles Martin Hall and Paul Heroult independently discovered that dissolving aluminum oxide in molten cryolite and running electricity through it would deposit pure aluminum metal. The Hall-Heroult process still produces every gram of aluminum today — about 65 million tonnes per year — and consumes roughly 3% of the world's electricity doing so. Chlorine gas and sodium hydroxide (caustic soda), two of the most important industrial chemicals, are both produced by electrolysis of salt water.
Beyond bulk chemistry, electrolysis enables electroplating — coating objects with a thin layer of metal for protection or appearance. The chrome bumper on a classic car, the gold plating on jewelry, the zinc coating that prevents steel screws from rusting — all are applied by electrolysis. Looking forward, electrolysis of water to produce "green hydrogen" is seen as a key technology for decarbonizing heavy industry and transport, using renewable electricity to create a clean fuel with water as its only byproduct.