AdvancedTopic 101 of 105Thermodynamics & Fluids
Fuel cells
Convert chemical energy directly to electricity with high efficiency.
In depth
A fuel cell electrochemically combines hydrogen and oxygen to produce electricity, water and heat, with efficiency of 40–60% (up to 85% with CHP) not limited by Carnot. Types: PEM, SOFC, MCFC, alkaline. Cell voltage ≈0.7 V under load; stacks connect cells in series.
Key points
- Anode, electrolyte, cathode
- Polarisation curve
- Hydrogen supply and storage
ExampleA fuel-cell bus runs on compressed hydrogen emitting only water.
What is Fuel cells?
Convert chemical energy directly to electricity with high efficiency.
Why is it important to understand fuel cells?
Fuel cells convert chemical energy directly into electricity without combustion, so they can achieve high efficiency and low local emissions.
How does a fuel cell produce electricity?
Hydrogen is oxidised at the anode and oxygen is reduced at the cathode, with ions moving through the electrolyte and electrons through the external circuit.
What limits fuel cell efficiency?
Activation, ohmic and concentration losses reduce the cell voltage below its ideal value, and these losses depend on current density.
How is Fuel cells used in practice?
Typical applications include powering a forklift with a hydrogen fuel cell in a warehouse, supplying a backup power unit for a telecom tower and generating electricity from a stationary hydrogen system with combined heat recovery.
What should I learn before Fuel cells?
Study "Cryogenics" first (topic 100 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Fuel cells?
Anode, electrolyte, cathode. Polarisation curve. Hydrogen supply and storage.
Can you give an example of Fuel cells?
A fuel-cell bus runs on compressed hydrogen emitting only water.
What comes after Fuel cells?
The next topic is "Geothermal and solar thermal systems", which builds directly on this one.
How difficult is Fuel cells?
It is classed as Advanced in Thermodynamics & Fluids (topic 101 of 105). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Thermodynamics & Fluids.