U3AOS1 Topic 8: Fuel Cells

• Fuel cells are a type of galvanic cell

• Characterised by continuous supply of external reactants for continuous direct energy conversion from chemical to electrical energy

• Reference “conventional galvanic cells has reactants stored in cell” when comparing to conventional galvanic cells

  
  

Tip: For VCE, the reduction reaction is always oxygen and the oxidation reaction is always with the fuel

Overall reactions is the same as combustion reaction and half reaction is determined via KOHES (Key element, Oxygen, Hydrogen, Electrons, States)

Sustainability

Emerging technology

• Microbial fuel cell - use organic material and operate at appox. room temperature

• Redox flow batteries (more on that in U3AOS2 Topic 1)

Safety

Special Tip: To balance any fuel cell, write out a combustion reaction then know that combining the reduction and oxidation reaction, a combustion reaction must be formed. Hence subtract reduction reaction to find unknown oxidation reaction (as O₂ used as oxidant).

Eg. If O^2- is used as electrolyte, where H2 is used as fuel.

The overall reaction which is just the combustion reaction

2H₂ + O₂ ->2H₂O

We know reaction at cathode is O₂ + 4e^-->2O^2- by balancing oxygens then charges.

Write both complete reaction and reduction reaction above each other and reverse the reduction reaction to 'subtract'

2H₂ + O₂ ->2H₂O

2O^2-->O₂ + 4e^-

Write reactants together and products together as one reaction

2H₂ + O₂+ 2O^2- ->2H₂O + O₂ + 4e^-

Then simplify by cancelling out any elements that appear on both sides

2H₂ + O₂+ 2O^2- ->2H₂O + O₂+ 4e^-

2H₂ + 2O^2- ->2H₂O + 4e^-

Rarely tested facts:

• Fuel cells have higher operating temperature than internal combustion engine

• Fuel cell is 2nd most efficient only beaten by dry battery cell

Source: (JavaLab - Fuel Cells, https://javalab.org/en/fuel_cell_en/)