A hydrogen generator splits water into hydrogen and oxygen gas using electricity, a process called electrolysis. The basic build requires electrode plates, a container, an electrolyte solution, and a DC power source. While the concept is simple, the details of plate material, spacing, cell design, and electrical input determine whether your generator produces a useful amount of gas or just heats up a bucket of water.
How Water Electrolysis Works
When direct current flows through water containing an electrolyte, two reactions happen simultaneously. At the negative plate (cathode), water molecules break apart to produce hydrogen gas and hydroxide ions. At the positive plate (anode), those hydroxide ions give up electrons and release oxygen gas. The electrolyte, typically potassium hydroxide (KOH) or sodium hydroxide (NaOH) dissolved in water, doesn’t get consumed in the reaction. It simply makes the water conductive enough for current to flow efficiently.
The overall equation is straightforward: electrical energy splits H₂O into H₂ and O₂. For every two molecules of water split, you get two molecules of hydrogen and one of oxygen. The rate of gas production ties directly to how much current flows through the cell. More amps means more gas, and the relationship is predictable using Faraday’s law: every 96,485 coulombs of charge (one amp for about 26.8 hours) liberates one mole of electrons, which produces roughly half a mole of hydrogen gas, or about 11.2 liters at standard conditions.
Dry Cell vs. Wet Cell Design
There are two common configurations for a DIY hydrogen generator, and choosing between them affects everything from efficiency to maintenance.
A wet cell submerges all the electrode plates in a single open bath of electrolyte solution. It’s the simpler build: plates sit inside a container filled with electrolyte, and gas bubbles up from both electrodes. Wet cells tend to produce slightly higher gas flow rates (around 0.75 liters per minute in comparable setups), but they also generate more heat, more corrosion, and more wasted energy. The exposed wiring and open liquid make them messier and harder to seal.
A dry cell sandwiches the electrolyte solution between plates that are clamped together with gaskets, so only the edges of the plates contact fluid. The electrolyte circulates through small channels rather than sitting in an open bath. Dry cells run cooler, corrode less, and are more compact. Their gas output is somewhat lower (around 0.5 liters per minute in a comparable setup), but the efficiency per watt is generally better because less energy is lost as heat. They’re also easier to mount and maintain. For most DIY builders, a dry cell is the better starting point.
Choosing Electrode Plates
The plates are the core of your generator, and the material matters enormously. 316L stainless steel is the standard choice for DIY builds. It resists corrosion thanks to a protective chromium oxide layer on its surface, and the molybdenum in its alloy helps prevent the kind of pitting corrosion that alkaline solutions can cause over time. It’s also widely available and reasonably priced. You can buy pre-cut plates online or cut them from 316L sheet stock, typically 16 to 20 gauge.
Before assembly, plates need to be conditioned. Sand both faces in a crosshatch pattern using 80 to 120 grit sandpaper. This increases the surface area where reactions occur. Then clean them thoroughly with a solvent like acetone or isopropyl alcohol to remove any oils from manufacturing. Some builders run the cell at low current for several hours during a break-in period to build up a dark oxide layer on the plates, which improves long-term performance.
Plate spacing is one of the most important variables. Research on dry cell generators consistently finds that 2 to 3 mm between plates is the ideal gap. Narrower gaps reduce electrical resistance, which means more current flows at the same voltage and more gas gets produced. But if you go below 2 mm, gas bubbles can’t escape between the plates and the cell chokes. Stick to 2 to 3 mm and you’ll get the best balance of current flow and gas release.
Plate Configuration and Neutral Plates
A single pair of plates (one positive, one negative) works, but it’s inefficient at higher voltages. Each cell, meaning each gap between a positive and negative plate, only needs about 1.5 to 2 volts to split water effectively. If you connect a 12-volt power source to just two plates, the excess voltage converts to heat rather than hydrogen.
The solution is to stack multiple plates in series using neutral (unconnected) plates between the positive and negative end plates. In a common configuration for a 12-volt system, you’d use 7 plates: one positive on one end, one negative on the other end, and 5 neutral plates in between. This creates 6 cells in series, so each cell sees about 2 volts, which is right in the efficient range. The neutral plates conduct current from one cell to the next without needing their own wire connections.
A typical plate size for a DIY build is roughly 100 mm by 100 mm (about 4 by 4 inches), though larger plates produce more gas because of the greater surface area. The configuration is written in shorthand: +NNNNN- means positive plate, five neutrals, negative plate.
Gaskets, Hardware, and Reservoir
In a dry cell design, gaskets between each plate create sealed chambers for the electrolyte. EPDM rubber is the go-to material. It resists alkaline solutions and handles temperatures from -60°F up to 225 to 300°F depending on how it was manufactured, which is more than adequate for an electrolysis cell. Cut gaskets from EPDM sheet stock (1/16 inch thick works well) to match your plate dimensions, with holes for electrolyte flow and a center cutout exposing the active plate area. Viton is another option with broader chemical resistance and a higher temperature ceiling (up to 410°F), but it costs more and offers no practical advantage in an alkaline electrolysis setup.
Use stainless steel bolts, washers, and nuts to clamp the stack together. Avoid mixing metals, as this creates galvanic corrosion. Four or more bolts through the corners, with the gaskets compressed evenly, should give a leak-free seal. Some builders use acrylic or polycarbonate end plates to hold the stack together and see inside the cell during operation.
You’ll also need a separate reservoir tank connected to the cell with tubing. This tank holds the electrolyte supply, allows gas to separate from the liquid, and gives you a place to check and top off fluid levels. A simple container with two hose fittings (one feed, one return) and a gas outlet at the top works fine. Add a one-way check valve on the gas outlet line to prevent any flashback from reaching the cell.
Electrolyte Mixing
Potassium hydroxide (KOH) is the preferred electrolyte for most DIY generators. It’s more conductive than baking soda, doesn’t produce the chlorine gas risk that table salt does, and causes less plate corrosion than sodium hydroxide.
Start with distilled water only. Tap water contains minerals that will coat your plates and reduce efficiency within days. A common starting concentration is about one to two teaspoons of KOH per liter of distilled water. You want enough to allow good current flow without generating excessive heat. Add the KOH to the water slowly (never the reverse), stir until dissolved, and monitor the current draw when you first power on. If the cell draws too many amps and heats up quickly, your solution is too concentrated. If gas production is sluggish, add a small amount more. Finding the right concentration for your specific setup takes some tuning.
Electrical Setup
A 12-volt DC power source is the most common starting point, whether that’s a car battery, a bench power supply, or a solar panel with a charge controller. The amount of hydrogen produced is directly proportional to current. Higher amperage means more gas, but also more heat. Most small DIY dry cells operate comfortably between 10 and 25 amps.
Adding a pulse-width modulation (PWM) controller between your power source and the cell lets you fine-tune current delivery without changing the electrolyte concentration. A PWM rapidly switches the power on and off, and adjusting the duty cycle controls the effective current. This is especially useful if your power source is fixed-voltage, like a car battery. An ammeter inline with the circuit is essential so you can monitor current draw in real time. If amps keep climbing during operation, the cell is overheating and you need to reduce concentration or improve cooling.
Critical Safety Considerations
Hydrogen is flammable in air at concentrations between 4% and 75%, one of the widest flammable ranges of any gas. It’s also colorless, odorless, and lighter than air, which means leaks are invisible and collect at ceiling level. The detonation range (where a spark doesn’t just ignite the gas but causes a shockwave) sits between 18% and 59% concentration.
These numbers have direct implications for your build:
- Always operate outdoors or in a well-ventilated space. Even a small leak in an enclosed garage can reach the 4% lower flammable limit faster than you’d expect.
- Use a bubbler (flashback arrestor). This is a jar of water that the gas line passes through before reaching any point of use. If a flame travels back up the line, the water stops it from reaching the cell. This is not optional.
- Never store hydrogen gas in sealed containers unless you’re using pressure-rated vessels with proper relief valves. Most DIY setups produce gas on demand rather than storing it.
- Keep ignition sources away. No smoking, no open flames, no sparking tools near an operating cell.
- KOH is caustic. Wear chemical-resistant gloves and eye protection when mixing or handling electrolyte. If it contacts skin, flush immediately with water.
Estimating Your Gas Output
You can predict how much hydrogen your generator should produce using Faraday’s law. Every amp of current flowing for one second produces a specific quantity of gas. The math works out to roughly 7.4 milliliters of hydrogen per minute per amp at standard temperature and pressure, assuming perfect efficiency. Real-world cells operate at 60% to 80% of theoretical efficiency due to heat loss and other factors.
So a cell drawing 15 amps would theoretically produce about 111 mL per minute of hydrogen, or roughly 0.11 liters per minute. At 75% efficiency, that drops to around 0.08 LPM. These are modest numbers, and they illustrate why serious gas production requires either high current, multiple cells, or both. For applications like supplementing engine intake air or running a small torch, a single well-built dry cell in the 15 to 25 amp range is a reasonable starting point. To measure your actual output, run the gas line into an inverted water-filled bottle and time how long it takes to displace a known volume.