Turning water into hydrogen means splitting each water molecule into hydrogen gas and oxygen gas, a process that requires energy in some form. The most common and accessible method is electrolysis: passing an electric current through water to break its chemical bonds. At an industrial scale, this is how “green hydrogen” is produced, but the basic principle is simple enough to demonstrate with a battery, two electrodes, and a glass of water.
How Electrolysis Works
Water (H₂O) is a stable molecule, so you need to add energy to pull it apart. In electrolysis, that energy comes from electricity. Two electrodes are submerged in water and connected to a power source. At the negative electrode, water molecules gain electrons and release hydrogen gas. At the positive electrode, water molecules lose electrons and release oxygen gas. For every two molecules of water you split, you get two molecules of hydrogen and one of oxygen.
The minimum voltage needed to start this reaction is 1.23 volts under ideal conditions. In practice, you need more. Commercial electrolysis cells typically run at 1.8 to 2.0 volts to keep the reaction moving at a useful rate. That gap between the theoretical minimum and the real-world requirement is lost to heat and resistance in the system.
Why Pure Water Doesn’t Work Well on Its Own
Pure water is a poor conductor of electricity. If you stick two wires into distilled water and apply voltage, very little will happen. The water needs dissolved ions to carry the electric current between the electrodes. This is why electrolysis setups use an electrolyte, a substance that dissolves in water and improves conductivity.
Potassium hydroxide (KOH) is the most effective and widely used electrolyte for this purpose. Industrial alkaline electrolyzers use KOH concentrations of 20 to 30 percent by mass. Increasing the concentration dramatically boosts gas production because the solution carries current more efficiently, reducing resistance. In a simple home or classroom demonstration, baking soda (sodium bicarbonate) or a small amount of salt can serve as a basic electrolyte, though they’re far less efficient and salt will produce chlorine gas at the positive electrode, which is toxic. Baking soda is the safer choice for small-scale experiments.
Types of Industrial Electrolyzers
Three main technologies dominate hydrogen production from water at scale, each with different tradeoffs.
Alkaline electrolyzers are the oldest and most mature technology. They use a liquid potassium hydroxide solution as the electrolyte and operate at relatively low temperatures, typically between 20 and 80°C. They’re reliable and cost-effective, making them the workhorse of the industry.
PEM (proton exchange membrane) electrolyzers use a solid polymer membrane instead of a liquid electrolyte. They offer comparable efficiency to alkaline systems but respond faster to changes in power input, which makes them well suited for pairing with solar panels or wind turbines that produce variable electricity.
Solid oxide electrolyzers operate at temperatures above 650°C and can reach electrical efficiencies around 84 percent. That high efficiency comes with a catch: they need a significant heat input to reach operating temperature. They make the most sense in industrial settings where waste heat is already available, such as steel plants or chemical facilities.
How Much Water Does It Take?
The chemistry alone requires 9 liters of water to produce 1 kilogram of hydrogen. But real systems also need water for purification and cooling, which pushes total consumption to about 20 to 30 liters per kilogram. That might sound like a lot, but it’s actually comparable to or less than the 20 to 40 liters per kilogram needed to produce hydrogen from fossil fuels (the dominant method today). One kilogram of hydrogen holds roughly the same energy as a gallon of gasoline.
Water quality matters too. Electrolyzers generally need purified water to avoid mineral buildup and corrosion on the electrodes. Systems using relatively clean source water consume closer to 20 liters per kilogram, while those requiring extensive purification of poor-quality water trend toward the higher end.
Beyond Electrolysis: Other Ways to Split Water
Electricity isn’t the only form of energy that can break water apart. Heat can do it too, though the temperatures involved are extreme. Thermochemical water splitting uses a series of chemical reactions driven by very high heat to decompose water without direct electricity. The most studied approach, the iodine-sulfur cycle, requires temperatures between 900 and 1,000°C. That kind of heat could come from concentrated solar collectors or advanced nuclear reactors. The process cycles sulfur and iodine compounds through a series of reactions that, taken together, consume only water and produce only hydrogen and oxygen. It’s still largely experimental.
Sunlight can also split water more directly using photocatalysts, materials that absorb light and use that energy to drive the water-splitting reaction on their surface. Recent experiments using an indium gallium nitride photocatalyst achieved a solar-to-hydrogen efficiency of 9.2 percent with pure water under concentrated sunlight. Under natural sunlight in a larger-scale setup, the efficiency dropped to about 6.2 percent. These numbers are climbing but remain well below what’s needed for commercial viability.
Certain microorganisms can also produce hydrogen from water. Green microalgae perform direct photolysis, using sunlight to split water into hydrogen and oxygen through their photosynthetic machinery. Cyanobacteria (blue-green algae) take an indirect route, first using sunlight to convert water and carbon dioxide into sugars, then breaking those sugars down to release hydrogen. Both pathways produce hydrogen at very small yields for now, but they require nothing more than water, sunlight, and the organisms themselves.
What It Costs Right Now
Green hydrogen, made by electrolysis powered by renewable energy, currently costs significantly more than hydrogen made from natural gas. The exact gap varies by region, but the International Energy Agency estimates the cost difference at $1.50 to $8.00 per kilogram today. By 2030, production costs for green hydrogen are expected to fall to roughly $2 to $9 per kilogram, about half of current levels, as electrolyzer manufacturing scales up.
Global installed electrolyzer capacity reached 2 gigawatts in 2024, with another gigawatt added in the first half of 2025. China accounts for about 65 percent of the world’s installed capacity and committed projects. That rapid scaling is one of the key forces expected to drive costs down.
Safety With Hydrogen Gas
Hydrogen is the lightest and smallest molecule, which means it leaks easily through fittings that would hold other gases just fine. It’s also highly flammable and burns with a nearly invisible flame. At concentrations between about 4 and 75 percent in air, hydrogen can ignite, giving it one of the widest flammable ranges of any common gas.
For anyone experimenting at home, the volumes produced by a small battery-powered setup are tiny and disperse quickly in open air. The real risks start when you try to collect or store the gas. Hydrogen should never be stored in sealed glass containers (which can shatter) or in confined, poorly ventilated spaces. Industrial hydrogen storage tanks are purpose-built to strict pressure vessel standards and tested to be gas-tight at their maximum operating pressure. Hydrogen can also weaken certain metals over time, a phenomenon called embrittlement, which is why storage systems use specially rated materials.
If you’re running a small demonstration, work outdoors or in a well-ventilated area, keep volumes small, and keep any collected gas away from open flames or sparks. The goal at a hobby scale is to observe the reaction, not to stockpile fuel.
A Simple Setup to Try
For a basic demonstration, you need a 9-volt battery, two pencils sharpened at both ends (the graphite cores serve as electrodes), a glass of warm water, a teaspoon of baking soda, and two short lengths of wire. Dissolve the baking soda in the water, connect each pencil to a battery terminal using the wires, and submerge the graphite tips. Within seconds, you’ll see bubbles forming on both electrodes. The electrode connected to the negative terminal produces roughly twice the volume of bubbles as the positive side, reflecting the 2:1 ratio of hydrogen to oxygen in water.
This won’t produce meaningful quantities of hydrogen, but it demonstrates the exact same principle that operates in a gigawatt-scale industrial plant. The difference is better electrodes, optimized electrolyte concentration, higher voltages, and engineered cell designs that minimize energy losses.