Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Teaching & Learning Packages Fuel Cells Building a simple fuel cell – just like Billy Grove did
Fuel Cells AimsBefore you startIntroductionThe principleHistory of the technologyTypes of fuel cellsSolid oxide fuel cells (SOFCs)• Electrolyte• Electrode materials• Interconnection• Thermodynamics• System and outlookMolten carbonate fuel cells (MCFCs)• Electrolyte• Electrochemistry• ElectrodesProton exchange membrane fuel cells (PEMFCs)• Membrane• Electrodes and membrane-electrode assembly• Efficiency and reaction conditionsFuelling requirementsCase study: Fuelling practicalitiesSummaryQuestionsGoing further
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Building a simple fuel cell – just like Billy Grove did

Collect the necessary components:

This is the most challenging part of the project, due to the difficulty many students will have in procuring the two lengths of platinum (Pt) wire required. Persist.

  • Two short lengths of platinum wire – 2 cm a piece is sufficient
  • A beaker
  • Weak NaCl solution (table salt and tap water will suffice)
  • Crocodile clips ×2
  • Wires ×2
  • Voltmeter
  • DC power source, e.g. 6-volt battery

 

Step by step:

  1. Fill beaker with salt solution

  2. Clamp the ends of the Pt wires in the crocodile clips

  3. Place the Pt wires in the solution in such a way that they will not move and so that only the Pt is in contact with the water. Plasticine (or Blu-Tac) would be helpful at this point. If the crocodile clips are in contact with the solution they will corrode quickly and taint the water.

  4. Verify that the voltage across the two electrodes is zero (two wires made of the same metal have no galvanic difference between them and hence no voltage will be seen).

  5. Connect each Pt wire to one of the battery’s terminals and watch the gas bubbles from the electrodes.

  6. Verify that the voltage across the electrodes is now equal to that of the battery, i.e. 6 V.

  7. Disconnect the battery and be careful not to knock the beaker.

  8. Verify that a voltage remains across the two electrodes.

This remaining voltage is due to bubbles of chlorine gas adhering to the cathode and to bubbles of hydrogen gas adhering to the anode. HCl is produced as the two atoms combine, via H+ ions travelling through the solution from anode to cathode, to produce HCl.

 

Things to consider:

An ammeter will confirm that we only obtain a tiny current in the above experiment (although the voltage remains set to the value we can calculate using the Nernst equation). Factors limiting the current in this case are:

  • the small surface area of the electrode - small amount of gas
  • wide spacing of the electrodes and electrolyte's ionic resistance.

In production cells, the electrodes are made larger and flat so as to maximise contact area, and the thickness of the electrolyte is kept to a minimum so as to reduce resistance.

 

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