Splitting water into hydrogen and oxygen using electricity, possibly from renewable sources.
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Electrolysis of water splits it into hydrogen and oxygen by the overall reaction 2H2O -> 2H2 + O2. The thermodynamic minimum cell voltage is 1.23 V at 25 C, but practical cells need about 1.8 to 2.0 V because of overpotentials and resistance. Several technologies are used, including alkaline electrolyzers, proton-exchange membrane cells and high-temperature solid oxide cells. When the electricity comes from renewable sources the hydrogen is called green hydrogen, which can be stored and used as a clean fuel. The method is growing in importance for energy storage.
Key ideas: 2H2O giving 2H2 + O2 requires E standard 1.23 V; real cells run at 1.7 to 2.0 V. Theoretical energy is about 39.4 kWh per kg of H2 (higher heating value), practical 50 to 55 kWh/kg. Types: alkaline, PEM, solid oxide. Yield: 1 mol of H2 per 2 mol of electrons, so 2F makes 2.016 g of H2.
Common mistakes and connections: Mistakes: ignoring overpotential and resistive losses and calling H2 green regardless of the electricity source. The H2:O2 volume ratio is 2:1. Pure water is a poor conductor so KOH or an acid membrane is used. Chloride in seawater gives Cl2 instead of O2 unless treated. Links to fuel cells and overpotential.
Splitting water needs at least 1.23 V (1.48 V thermoneutral), but real electrolyzers run near 1.8-2.0 V because overpotentials waste energy. The interactive lesson shows this as a live animation or chart.
Electrolyzers can store surplus electricity from wind turbines as hydrogen gas for later use.
Splitting water into hydrogen and oxygen using electricity, possibly from renewable sources.
Hydrogen Production by Electrolysis is a intermediate topic in Acids, Bases & Electrochemistry. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Acids, Bases & Electrochemistry first: Latimer and Frost Diagrams, Ion-Selective Electrodes, pH Meter.
The next topics in Acids, Bases & Electrochemistry are Acid Rain and Ocean Acidification.
Yes. The interactive lesson includes a self-check question on Hydrogen Production by Electrolysis, and the Acids, Bases & Electrochemistry quiz draws on every topic in this area.
Hydrogen Production by Electrolysis is topic 94 of 105 in Acids, Bases & Electrochemistry.