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What enters a hydrogen fuel cell, and what leaves?
A hydrogen fuel cell uses supplied hydrogen and oxygen to produce water while delivering electrical energy.
Sources for this view
A PEM cell separates the reactants with an ion-conducting membrane and connects its electrodes through an external circuit. Hydrogen and oxygen are molecular gases, H₂ and O₂; water is a new chemical combination of their atoms.
Sources for this view
Explore the model (optional)
EXPLORE THE MODEL
Fuel-cell reaction and flow account
Inspect the structure; select a site or component for its label.
What this representation means
H₂/O₂ PEM reaction; 100% Faradaic accounting. 1.229 V is the standard reversible liquid-water value at 25 °C. Assumed voltage loss is not a measured polarization curve. Consumed flow differs from supplied flow.
- Remaining reactants
- 2 H₂ + 1 O₂
- Water formed
- 2 H₂O
- Conserved inventory
- 8 hydrogen atoms + 4 oxygen atoms
- Paths
- Protons through membrane; electrons through external circuit
2H₂ + O₂ → 2H₂O; ṅ(H₂) = I/(2F); P = IV
The pictured inventory and the flow calculation answer different questions. Protons cross the membrane, electrons travel through the external circuit, and oxygen is reduced at the cathode. The assumed loss changes power; it does not change the stoichiometric reactant flow at fixed current. At zero loss the power is a reversible bound, not attainable finite-rate operation.
What this model can establish
H₂/O₂ PEM reaction; 100% Faradaic accounting. 1.229 V is the standard reversible liquid-water value at 25 °C. Assumed voltage loss is not a measured polarization curve. Consumed flow differs from supplied flow.
Optional: check your understanding
MAKE THE CONNECTION
What belongs in the material output ledger for the stated reaction?