R1.3.5 Fuel cells Notes

Hydrogen Fuel Cells: Converting Chemical Energy into Clean Electricity

1. Unlike traditional combustion engines, which rely on burning fuels to generate heat, fuel cells produce electricity without combustion.
2. This makes them highly efficient and environmentally friendly.
3. The key difference between a fuel cell and a traditional battery lies in how they operate.
4. While batteries store a finite amount of chemical energy internally, fuel cells are continuously supplied with fuel from an external source, allowing them to generate electricity indefinitely, as long as fuel is available.

The Hydrogen Fuel Cell: A Clean Energy Solution

The process is clean, efficient, and produces no harmful emissions.

Reactions in a Hydrogen Fuel Cell

Let’s explore what happens inside a hydrogen fuel cell step by step:

1. At the Anode (Oxidation):
   1. Hydrogen gas ($H_2$) is fed into the anode, where it encounters a platinum-based catalyst.
   2. The catalyst splits the hydrogen molecules into protons ($H^+$) and electrons ($e^-$).
   3. The half-equation for the oxidation reaction is:
      $$
      2H_2 \rightarrow 4H^+ + 4e^-
      $$
2. Electron Flow:
   1. The electrons cannot pass through the proton exchange membrane (PEM), so they are forced to travel through an external circuit, creating an electric current that can power devices.
3. Proton Movement:
   1. The protons ($H^+$) pass through the PEM to the cathode.
4. At the Cathode (Reduction):
   1. Oxygen gas ($O_2$) is fed into the cathode, where it reacts with the incoming protons and electrons to form water.
   2. The half-equation for the reduction reaction is:
      $$
      O_2 + 4H^+ + 4e^- \rightarrow 2H_2O
      $$
5. Overall Reaction:
   1. The overall redox reaction in the hydrogen fuel cell is:
      $$
      2H_2 + O_2 \rightarrow 2H_2O
      $$

Advantages of Hydrogen Fuel Cells

Hydrogen fuel cells offer several compelling benefits, particularly in the context of reducing our reliance on fossil fuels and mitigating climate change.

1. High Efficiency
   1. Unlike combustion engines, which lose a significant amount of energy as heat, hydrogen fuel cells directly convert chemical energy into electrical energy.
   2. This makes them more efficient, especially under steady operating conditions.
2. Low Emissions
   1. The only byproduct of a hydrogen fuel cell is water.
   2. No carbon dioxide, no nitrogen oxides, and no particulate matter are released, making it a clean energy source.
3. Versatility
   1. Hydrogen fuel cells can be used in a wide range of applications, from powering vehicles and homes to serving as backup energy sources for hospitals and industries.
4. Energy Independence
   1. Hydrogen can be produced from various sources, including water (via electrolysis) and biomass, reducing dependence on fossil fuels.

Limitations of Hydrogen Fuel Cells

Despite their advantages, hydrogen fuel cells face several challenges that need to be addressed before they can be widely adopted.

1. High Production Costs
   1. The materials used in fuel cells, such as platinum catalysts, are expensive.