Chemical cells and fuel cells (chemistry only) common mistakes

Common mistakes

• Misinterpreting Voltage Increase in Series Cells

  Students often think that connecting cells in series increases the voltage because each cell’s electrolyte is the same, so the overall voltage simply adds up regardless of electrode materials.

  Fix itExplain that the voltage of a single cell depends on the electrode pair and electrolyte; when cells are connected in series, the voltages of each individual cell add because each cell provides its own potential difference, not because the electrolyte changes. Clarify that the overall voltage is the sum of the individual cell voltages, which are determined by the electrode materials and electrolyte composition of each cell.

• Mixing up safe handling of acids and bases

  Students often think that all liquids used in simple cells are harmless and can be handled without precautions, or they treat acidic and basic electrolytes the same way, ignoring the risk of splashes and corrosion.

  Fix itRemind students that electrolytes can be acidic, basic or neutral, and that acidic or basic solutions can be corrosive or cause skin irritation. They should wear appropriate PPE (gloves, goggles, lab coat), use a fume hood or well‑ventilated area, and handle all liquids carefully to avoid splashes or spills. Emphasise that safety procedures are required for all liquids, not just for the cell’s operation.

• Misunderstanding Fuel Sources

  Students often think that fuel cells generate their own fuel instead of being supplied by an external source.

  Fix itEmphasize that fuel cells require an external supply of fuel and oxygen or air to operate.

• Misunderstanding Fuel Sources

  Students often confuse hydrogen as a fuel with other fuels and do not recognize that hydrogen is specifically used in fuel cells.

  Fix itEmphasize that hydrogen is a unique fuel for fuel cells and differentiate it from other types of fuels.

• Misidentifying the Oxidation Step

  Students often think the fuel (hydrogen) is reduced at the anode and the oxygen is oxidised at the cathode, confusing the direction of electron flow in a fuel cell.

  Fix itIn a hydrogen fuel cell, the fuel (hydrogen) is oxidised at the anode (H₂ → 2H⁺ + 2e⁻) and the oxygen is reduced at the cathode (O₂ + 4H⁺ + 4e⁻ → 2H₂O). The oxidation of hydrogen is the electrochemical reaction that generates electrons, not the reduction of oxygen.

• Misconception about the source of voltage

  Students think the voltage in a fuel cell comes from the external fuel supply rather than the electrochemical reaction at the electrodes

  Fix itExplain that the potential difference is produced by the spontaneous redox reactions at the anode and cathode, with the fuel (e.g. H₂) being oxidised and oxygen reduced, creating a chemical potential that drives electrons through the external circuit

• Confusion about oxidation

  Students often confuse oxidation with reduction, thinking that oxidation means the addition of oxygen rather than the loss of electrons.

  Fix itRemember that oxidation involves the loss of electrons, while reduction involves the gain of electrons. In the context of a hydrogen fuel cell, hydrogen is oxidized as it loses electrons to form water.

• Misunderstanding Hydrogen Fuel Cells

  Students often think that hydrogen fuel cells are the same as rechargeable batteries and do not understand the differences in how they generate electricity.

  Fix itEmphasize that hydrogen fuel cells produce electricity through the oxidation of hydrogen, while rechargeable batteries store and release energy through reversible chemical reactions.

• Misunderstanding Hydrogen Fuel Cells

  Students often think that hydrogen fuel cells are just like rechargeable batteries without understanding the differences in their operation and fuel supply.

  Fix itTo fix this, students should focus on the unique features of hydrogen fuel cells, such as the continuous supply of fuel and oxygen, and how they produce electricity through oxidation reactions, unlike rechargeable batteries that store and release energy.

• Misunderstanding fuel supply in fuel cells

  Students often think a fuel cell needs a continuous external supply of oxygen and water, just like a battery needs a continuous supply of reactants

  Fix itExplain that a fuel cell requires only the fuel (e.g. hydrogen) and an oxidiser (usually oxygen from air); water is a product, not a required input, and the cell can operate as long as fuel and oxygen are available