1 minute read

Electrolysis of water is the decomposition of water into oxygen and hydrogen gas due to the passage of an electric current. The reaction has a standard potential of −1.23 V.

That means if you supply a potential difference greater than 1.23 volts you can split water! Say with a 9V battery, you can make some gas!!!

H2O Lego

NOTE: The Hydrogen side makes twice as much gas as the oxygen side because it is H2 O.

Double NOTE: Water Electrolysis is how the International Space Station gets is oxygen. So you are doing science in the same league (Lego league?) as NASA science!


Use simple office supplies and Legos (optional) to separate the hydrogen from the oxygen in water.


  • 1 Plastic Cup
  • 2 Thumb tacks
  • 1 Nine Volt Battery
  • pinch of Baking Soda
  • Water: H2O
  • 2 Plastic Pipettes or empty water bottles (optional if collecting the gas)

Optional Materials

  • Legos


30 minutes with Legos


It is just fun to just make Hydrogen at home.


  • Go over what a molecule is, this molecule is H2O.
  • Point out that the pin making the H2 has twice as much bubbles.
  • Connect the moleculer bonds potential to electrical potential.
  • Internet has has lots of bad information: Many sites (even educational) have one use Salt. SALT produces Chlorine gas Not cool. So one should take care what they read on the internet.

Level of effort


Clean up: Level of effort

  • Easy



Using NaCl (table salt) in as an electrolyte solution results in chlorine gas rather than oxygen due to a competing half-reaction (Wikipedia: Water Electrolysis).

Why do NASA Scientist uses water electrolysis instead of bringing O2?


  • Dense: Lots of Oxygen per square millimeter
  • Not flammable
  • Easy to store
  • Can use light weight container to store water
    • But, in space everything is weightless!
      • Yes, but it COSTs lots and lots money to ship it to space. Think ~ $300,000 per pound.


  • Not dense, takes up a lot of space
  • Need heavy container (at high pressure) to make Oxygen as dense as water