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

1. Microbial fuel cell - use organic material and operate at appox. room temperature
2. 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 $\ce{O2}$ used as oxidant).

Eg. If $\ce{O^{2-}}$ is used as electrolyte, where $\ce{H2}$ is used as fuel.

The overall reaction which is just the combustion reaction

$\ce{2H2 + O2 ->2H2O}$

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

$\ce{2H2 + O2 ->2H2O}$

$\ce{2O^{2-} -> O2 + 4e^{-}}$

$\ce{2H2 + O2 + 2O^{2-} -> 2H2O + O2 + 4e^{-}}$

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

$\ce{2H2 + \cancel{O2} + 2O^{2-} -> 2H2O + \cancel{O2} + 4e^{-}}$

$\ce{2H2 + 2O^{2-} -> 2H2O + 4e^{-}}$

Rarely tested facts:

1. Fuel cells have higher operating temperature than internal combustion engine
2. Fuel cell is 2nd most efficient only beaten by dry battery cell

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