Fuel cells operate differently from chemical cells. They are capable of producing a voltage for as long as they have a supply of fuel or oxygen.
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel, such as hydrogen, into electrical energy by reacting it with either pure oxygen or air. This reaction generates electricity and produces water as a waste product. The electrical energy produced by fuel cells can be used to power various devices.
Below is a diagram of a simple fuel cell.
Let’s look at the components of a fuel cell in more detail:
Electrolyte – A solution located in the centre of the fuel cell that allows ions to move through it. There are many different types of electrolytes, but one of the most commonly used is potassium hydroxide (KOH).
Electrodes – The electrodes are located on either side of the electrolyte. The negative electrode (anode) is on the left, while the positive electrode (cathode) is on the right. There is a wire that connects the two electrodes, allowing electrons to flow from the anode to the cathode.
To understand how a fuel cell works, let’s break down the process:
1. Hydrogen enters the fuel cell from the left and reacts with the negative anode, undergoing oxidation:
2H2 → 4H⁺ + 4e⁻
As a result, each hydrogen atom loses an electron and becomes a hydrogen ion.
2. The hydrogen ions pass through the electrolyte to the cathode. At the same time, the electrons flow through the wire to the cathode.
3. At the cathode, the hydrogen ions and electrons combine with oxygen from the right to produce water:
O2 + 4H⁺ + 4e⁻ → 2H2O
4. The resulting water molecule exits the fuel cell on the right.
When we combine the two equations, we get:
2H2 + O2 + 4H⁺ + 4e⁻ → 2H2O + 4H⁺ + 4e⁻
As there are four hydrogen ions (H⁺) and an oxygen molecule (O2) on both sides, they cancel out. So the overall equation is:
2H2 + O2 → 2H2O
The potential difference between the two electrodes causes an electric current to flow through the circuit.
Compared to rechargeable batteries, fuel cells have several advantages and disadvantages. Let’s explore these in more detail: