Advanced Electrolysis Voltage Calculator

Calculator Inputs

Enter the anode value as the standard reduction potential of the reverse pair. Example: for water oxidation, use the O₂/H₂O reduction value.

Cathode standard reduction potential, E° (V)

Cathode electrons, n

Cathode reaction quotient, Q

Anode reference reduction potential, E° (V)

Anode electrons, n

Anode reaction quotient, Q

Temperature (°C)

Anode overpotential, ηa (V)

Cathode overpotential, ηc (V)

Current (A)

Cell resistance (Ω)

Operating time (hours)

Faradaic efficiency (%)

Cathode product molar mass (g/mol)

Anode product molar mass (g/mol)

Example Data Table

Parameter	Example Value	Meaning
Cathode E°	0.00 V	Hydrogen evolution reference reduction potential.
Cathode n	2	Two electrons per H₂ molecule.
Cathode Q	1	Standard-state example.
Anode E°	1.23 V	O₂/H₂O reduction pair entered for the reverse oxidation side.
Anode n	4	Four electrons per O₂ molecule.
Anode Q	1	Standard-state example.
Temperature	25 °C	Room-temperature case.
Anode overpotential	0.35 V	Kinetic loss at the anode.
Cathode overpotential	0.20 V	Kinetic loss at the cathode.
Current	10 A	Operating current.
Resistance	0.08 Ω	Cell ohmic resistance.
Time	2 h	Runtime for charge and energy estimates.
Faradaic efficiency	95%	Useful current fraction.
Expected applied voltage	2.58 V	1.23 + 0.35 + 0.20 + 0.80.

Formula Used

1) Nernst-adjusted half-cell potential
E = E° - (RT / nF) ln(Q)
This page applies that expression separately to the cathode reduction and the anode reference reduction pair.

2) Reversible electrolysis voltage
V_rev = E_anode,actual - E_{cathode,actual}
Use the reduction potential of the reverse pair for the anode entry.

3) Practical applied voltage
V_applied = V_rev + η_anode + η_cathode + IR

4) Charge, power, and energy
Q_charge = I × t
P = V_applied × I
Energy = P × time

5) Product amount from Faraday’s law
moles = (Q × FE) / (nF)
If molar mass is supplied, then mass = moles × molar mass.

How to Use This Calculator

Enter the cathode standard reduction potential, electron count, and reaction quotient.
Enter the anode value as the reduction potential of the reverse pair, not the oxidation sign-switched form.
Add temperature if your process differs from standard conditions.
Enter anode and cathode overpotentials to reflect kinetic losses.
Enter current and resistance so the calculator can add the ohmic drop, I×R.
Set runtime to estimate charge, power, energy, and product yield.
Add Faradaic efficiency for realistic product formation.
Optionally supply molar masses to estimate theoretical product mass.
Press the calculate button and review the result shown above the form.
Use the CSV or PDF buttons to export the current result set.

Frequently Asked Questions

1) What is electrolysis voltage?

Electrolysis voltage is the external cell voltage needed to force a nonspontaneous reaction. It includes the reversible thermodynamic requirement plus kinetic losses and resistive losses inside the cell.

2) Why is actual voltage higher than theoretical voltage?

Real cells need extra voltage to overcome activation barriers at electrodes and ohmic resistance in electrolyte, separator, contacts, and wiring. Those added terms are overpotential and IR drop.

3) Why does this calculator ask for anode reduction potential?

Electrode tables usually list standard reduction potentials. Using the reverse-pair reduction value keeps the input consistent and lets the calculator build the required electrolysis voltage directly.

4) What does the reaction quotient do?

The reaction quotient adjusts each half-cell potential away from standard conditions through the Nernst equation. It captures concentration, pressure, and activity effects on the reversible voltage.

5) What is overpotential?

Overpotential is extra voltage lost at an electrode because reaction kinetics are not infinitely fast. Different materials, catalysts, surfaces, and current densities change its size.

6) What is IR drop?

IR drop is the voltage loss caused by current flowing through resistance. It rises with current and includes electrolyte, membrane, electrode, and connector resistance.

7) Can this calculator estimate product amount?

Yes. It uses Faraday’s law with your current, time, electron count, and Faradaic efficiency. Optional molar mass inputs convert theoretical moles into product mass.

8) When should I set Q equal to 1?

Use Q = 1 when you want standard-state behavior or when you intentionally ignore concentration and pressure shifts. That makes the Nernst correction equal to zero.