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Hydrogen Fuel Cell

High schoolChemistryFinite-feed hydrogen fuel cell with a constant reversible source, resistive load and internal ohmic loss

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About this experiment

Connect a fuel cell to a load and follow gas consumption, water production and delivered electrical energy. Match the load resistance and discover when a finite reactant inventory runs out.

Learning goals

  • Balance hydrogen, oxygen, water and electron amounts.
  • Separate terminal power from total delivered energy.
  • Explain internal resistance and the matched-load maximum.

How to use it

  1. 1Connect the load and record voltage, current and power.
  2. 2Set load resistance equal to internal resistance and compare power with nearby values.
  3. 3Run to fuel exhaustion and identify the limiting gas.
  4. 4Open the load before exhaustion and verify that water and past delivered energy remain.

The model

The linear source model has maximum load power at R L equal to internal resistance.
Hydrogen and oxygen are consumed in a two-to-one ratio.
Electrical energy and internal ohmic loss account for the model free-energy release.

Assumptions

  • Regulated ideal-gas feeds maintain an ideal 1.229 V reversible source at 298.15 K until a finite feed inventory is exhausted.
  • Only a fixed internal ohmic resistance reduces terminal voltage. Activation and mass-transfer polarization are omitted.
  • The accounting uses Gibbs free-energy release at the specified source voltage. Ohmic heat plus load energy equals that available free-energy decrease, not the full combustion enthalpy.
  • The fan is a present-power indicator with no rotor inertia. Water and inventory gauges are magnified illustrations.

Try this in class

  1. Q1Why can a smaller load resistance increase current but reduce load power?
  2. Q2Why can oxygen remain after hydrogen is exhausted?

Frequently asked questions

Is this the full polarization curve of a real fuel cell?

No. It isolates ohmic loss and finite feed accounting. A real cell also has activation and mass-transfer effects.

Does electrical efficiency here refer to combustion enthalpy?

No. It is load voltage divided by the chosen reversible source voltage, so its reference is available Gibbs free energy.