Water Electrolysis Calculator

Calculator

Enter electrical inputs and operating conditions. Efficiency adjusts the gas yields for practical losses.

Current

A

Direct current through the electrolyzer.

Time

seconds minutes hours

Total electrolysis duration.

Faradaic efficiency

%

Accounts for side reactions and losses.

Temperature

°C

Used to compute gas volume.

Pressure

kPa

Absolute pressure for volume calculation.

Cell voltage (optional)

V

Enables power and energy estimates.

Electrode area (optional)

cm²

Used to compute current density.

Calculate Reset

Formula used

• Charge: Q = I × t
• Faraday’s law: nₑ = Q / F, with F = 96485.33212 C·mol⁻¹
• Hydrogen moles: n(H₂) = (nₑ / 2) × η
• Oxygen moles: n(O₂) = (nₑ / 4) × η
• Ideal gas volume: V = nRT / P
• Electrical power: P = Vcell × I, and energy: E = Vcell × Q

How to use this calculator

1. Enter the current and the run time for your electrolyzer.
2. Set Faradaic efficiency to reflect real-world gas yield.
3. Choose temperature and absolute pressure to compute gas volumes.
4. Optionally provide cell voltage to estimate energy use.
5. Press Calculate to see results above the form.
6. Use CSV or PDF buttons to export the computed table.

Professional guide

1) What electrolysis produces

Water electrolysis splits liquid water into hydrogen and oxygen gases. In alkaline or PEM systems, the same overall chemistry applies: 2H₂O → 2H₂ + O₂. The practical output depends on how many electrons you push through the cell, and how efficiently those electrons form the target gases.

2) Faraday’s law as the backbone

The calculator uses Faraday’s law, which links charge to chemical amount. Charge is Q = I×t, and the molar amount of electrons is nₑ = Q/F, with F ≈ 96485 C per mole of electrons. Each mole of hydrogen needs 2 moles of electrons, while each mole of oxygen needs 4.

3) Efficiency and real gas yield

Faradaic efficiency accounts for losses such as crossover, parasitic reactions, and recombination. For a well-tuned lab cell, 90–99% is common, while stressed conditions can be lower. The tool applies η to both hydrogen and oxygen, so the reported amounts reflect usable gas rather than theoretical maximum.

4) Temperature and pressure matter

Moles determine chemistry, but volumes determine storage and safety. The ideal gas law V = nRT/P converts moles to liters at your selected temperature and absolute pressure. Raising temperature increases volume, while raising pressure decreases it, helping you evaluate compression needs.

5) Electrical energy and scaling

If you enter cell voltage, the calculator estimates power P = V×I and energy E = V×Q. This supports quick scaling: doubling current doubles gas rate and doubles electrical power at the same voltage. Energy per unit hydrogen is a key performance indicator when comparing operating points.

6) Typical numbers for intuition

As a rule of thumb, 1 ampere for 1 hour delivers 3600 coulombs. That corresponds to about 0.0187 mol of electrons, producing roughly 0.0093 mol of H₂ at 100% efficiency. At room conditions, that is around 0.21 liters of hydrogen. Higher currents scale linearly from there.

7) Current density and design checks

When electrode area is known, current density (A/cm²) helps compare designs fairly. High current density can raise overpotential, heat, and bubble coverage, reducing efficiency. Use this metric to justify geometry changes, flow improvements, and catalyst selection in a controlled way.

8) Safety and reporting

Hydrogen and oxygen mixtures can be hazardous. Always keep product streams separated, ventilate enclosures, and use suitable flashback protection. The built-in export buttons generate a clean table for lab notes and audits, improving traceability across experiments and operating conditions.

FAQs

1) What does Faradaic efficiency represent?

It is the fraction of electrons that form the intended gas. The remainder is lost to side reactions, crossover, or recombination. Higher efficiency means more usable hydrogen and oxygen for the same electrical input.

2) Why does hydrogen use 2 electrons per molecule?

At the cathode, two electrons reduce water-derived species to one H₂ molecule. That stoichiometry sets n(H₂)=nₑ/2, before applying efficiency adjustments.

3) Why are volumes different at STP vs my conditions?

Gas volume depends on temperature and absolute pressure. STP is a fixed reference; your chosen conditions may be warmer or more pressurized, changing volume even when the number of moles stays the same.

4) Do dissolved gases or water vapor affect results?

This tool assumes ideal, dry gases. Real systems may include water vapor and dissolved gas losses, especially at elevated temperature. Use efficiency and practical correction factors when precise metrology is required.

5) What voltage should I enter for energy estimates?

Use the measured operating cell voltage under load, not the supply rating. Include any expected overpotential and ohmic drop, because energy scales directly with voltage at a given charge throughput.

6) Can I estimate production rate per minute?

Yes. Enter time in minutes and your current. The calculator converts to seconds internally and returns moles, mass, and volume for that interval, which you can treat as a per-minute production snapshot.

7) Is water consumption always equal to hydrogen moles?

For the overall reaction, one mole of H₂ corresponds to one mole of H₂O consumed. In practice, additional water may be transported or evaporated, so operational water usage can be higher than the stoichiometric minimum.

Example data table