A fuel cell is an electrochemical device that converts fuel, usually hydrogen, directly into electricity with water and heat as the main byproducts.
Most power plants make electricity by burning something. A fuel cell makes it electrochemically — fuel reacts with oxygen across a membrane, and the main outputs are electricity, water, and heat. Before explaining what a fuel cell is, it helps to kill the biggest myth first: it is not a battery.
The U.S. Department of Energy defines a fuel cell as an electrochemical device that converts the chemical energy of a fuel directly into electricity. Feed hydrogen to one side and air to the other, and the cell delivers direct current as long as the fuel keeps flowing.
What a Fuel Cell Does
A fuel cell has three working parts — an anode, a cathode, and an electrolyte between them — and it generates direct current the moment fuel and oxidant meet across that electrolyte.
Fuel enters at the anode and air or oxygen enters at the cathode. Electrochemical reactions strip electrons from the fuel and send them through an external circuit, which is the electricity you can actually use. The electrolyte carries ions between the electrodes to complete the reaction, and the flow continues as long as both fuel and oxidant are supplied.
The same basic structure scales from tiny portable chargers to building-sized power systems. The DOE points out that fuel cells can supply both heat and electricity for buildings, power vehicles, and run electronic devices.
What Are the Main Types of Fuel Cells?
Fuel cell types are classified by their electrolyte, because that material determines the operating temperature, the catalysts, the chemical reactions, and the fuels a cell can handle.
The Department of Energy’s guide to fuel cell types lists six families: PEM, alkaline, phosphoric acid, molten carbonate, solid oxide, and reversible fuel cells. The five most common ones are compared below.
| Type | Operating Temperature | Where They’re Used |
|---|---|---|
| PEM | Under 120°C | Backup power, portable power, distributed generation, transportation |
| Alkaline (AFC) | Under 100°C | Military, space, backup power, transportation |
| Phosphoric acid (PAFC) | 150–200°C | Distributed generation |
| Molten carbonate (MCFC) | 600–700°C | Electric utility, distributed generation |
| Solid oxide (SOFC) | 500–1,000°C | Auxiliary power, electric utility, hybrid gas-turbine cycles |
A sixth category, reversible fuel cells, can switch between generating power and producing fuel from electricity, which makes them an emerging storage option.
PEM cells are the ones most people meet first — they power most fuel-cell cars and range from under 1 kW for portable gear to roughly 100 kW for vehicles, with about 60 percent electrical efficiency on pure hydrogen or 40 percent on reformed fuel. If you’re already shopping hardware, the tested auto fuel cell options on this site are a practical place to start.
Every type carries trade-offs. PEM cells are sensitive to fuel impurities and rely on expensive catalysts. Alkaline cells lose performance when carbon dioxide sneaks into the fuel or air, and managing the liquid electrolyte is fiddly. Phosphoric acid cells tolerate sulfur poorly and take a while to warm up. The high-temperature molten carbonate and solid oxide designs run hot enough that corrosion and materials breakdown are constant fights, and start-up times run long. Scale matters too: molten carbonate plants typically range from 300 kW to 3 MW and solid oxide systems from 1 kW to 2 MW, which is why both are utility and distributed-generation workhorses rather than car engines.
What a Fuel Cell Is Not
Three misconceptions cause most of the confusion around fuel cell technology.
- It is not a battery. Batteries store a finite charge that drains over time. A fuel cell is continuously replenished with fuel and oxidant, so it produces electricity indefinitely as long as the supply lasts — and stops the moment it doesn’t.
- It is not hydrogen-only. The DOE notes fuel cells can run on hydrogen or other fuels. The electrolyte dictates which fuels a given cell can accept, along with the operating conditions those fuels require.
- It is not one technology. Electrolyte type is the primary way fuel cells are classified. It drives the temperature range, catalyst needs, and fuel compatibility, which is why a 100°C PEM stack and a 900°C solid oxide system behave so differently.
FAQs
Why aren’t fuel cells common in cars yet?
Cost and infrastructure. PEM stacks, the type used in most fuel-cell vehicles, rely on expensive catalysts and remain sensitive to fuel impurities. Hydrogen refueling is also sparse outside a few regions, and high-temperature designs like solid oxide suit stationary plants better than cars. That combination pushed most automakers toward batteries instead.
Can a fuel cell use fuels other than hydrogen?
Yes. The Department of Energy lists hydrogen as the most common fuel but notes that fuel cells can run on other fuels as well. The electrolyte determines which fuels a given design can accept and the operating conditions needed to process them, so fuel flexibility varies from one fuel cell type to the next.
Does a fuel cell produce any pollution?
With pure hydrogen, the cell itself produces only electricity, water, and heat — no combustion emissions. The broader footprint depends on how that hydrogen was produced, which is why “gray” hydrogen from natural gas and “green” hydrogen from renewable electricity leave very different environmental records.
References & Sources
- U.S. Department of Energy. “Types of Fuel Cells.” Source for electrolyte-based classification and operating specs of the five main fuel cell families.
- U.S. Department of Energy. “Fuel Cells.” Source for the definition of a fuel cell and its building, vehicle, and device applications.
- National Energy Technology Laboratory. “Fuel Cell Handbook, 7th Edition.” Reference for fuel cell stack sizes and efficiency ranges.