What is the output voltage of a fuel cell?
In practical terms, a fuel cell's output voltage depends on the chemistry and operating conditions. A single cell typically delivers about 0.6–0.9 volts under load and about 1.0–1.2 volts when not drawing current. To obtain usable system power, many cells are connected in series to form a stack, which adds up the per-cell voltage while managing current and losses.
How voltage is defined in a fuel cell
Electric voltage in a fuel cell can be described in two main ways: open-circuit voltage (OCV), which is the maximum potential when no current is drawn, and the voltage under load, which drops as current increases due to activation losses, ohmic resistance, and mass-transport (concentration) effects. The gap between the OCV and the operating voltage depends on temperature, pressure, catalyst performance, and reactant purity. System designers balance higher voltages with efficiency and power delivery, since increasing current at a fixed voltage raises power but can reduce overall efficiency.
Open-circuit vs under load
Under open-circuit conditions you measure the maximum possible voltage of the chemical reaction, typically around 1.0–1.2 volts per cell. When the cell is delivering current to perform work, the voltage tends to fall to a more modest range, commonly about 0.6–0.9 volts per cell for many common chemistries, with variations based on technology and operating conditions.
Typical values by technology
The following ranges summarize typical per-cell voltages under load for common fuel-cell chemistries. Values vary with current density, temperature, pressure, and catalyst performance, so these should be treated as approximate benchmarks.
- PEM (polymer electrolyte membrane) fuel cells: approximately 0.6–0.9 V per cell under load; open-circuit voltages around 1.0–1.2 V.
- Solid oxide fuel cells (SOFC): approximately 0.8–0.95 V per cell under load; open-circuit around 1.0–1.2 V or higher at elevated temperatures.
- Phosphoric acid fuel cells (PAFC): approximately 0.7–0.85 V per cell under load; open-circuit around 1.0–1.2 V.
Stack voltages are the sum of the voltages of individual cells in series, minus losses from electrical components and interconnects. A vehicle or large power plant typically uses hundreds of cells in a stack to reach hundreds of volts.
Voltage in fuel-cell stacks and system design
Because a single cell produces only about one volt or less, practical systems connect many cells in series to achieve usable voltages. For example, a typical automotive PEM fuel cell stack contains hundreds of cells, yielding system voltages in the hundreds of volts range (often around 200–350 V depending on design), with power controlled by power electronics and cooling. Stack design also accounts for dynamic load changes and integration with energy storage for peak power and fast response.
Summary
Fuel cells generate modest voltages per cell, typically 0.6–0.9 V under load and about 1.0–1.2 V open-circuit. The total output is scaled up by stacking many cells in series to reach practical voltages for vehicles or stationary power. Per-cell voltage depends on chemistry and operating conditions, while the open-circuit voltage reflects the maximum chemical potential of the fuel–oxidizer pair.
