Key Terms
- Electrochemical cell: converts chemical → electrical energy
- Electrolyte: ionic solution/membrane for ion flow
- Fuel cell: continuous fuel supply; never "runs down"
- Anode: oxidation; negative terminal (fuel cell)
- Cathode: reduction; positive terminal (fuel cell)
- Accumulator: rechargeable battery (e.g. lead-acid)
Must-Know Equations
- Overall fuel cell: 2H₂ + O₂ → 2H₂O
- Anode: H₂ → 2H⁺ + 2e⁻
- Cathode: ½O₂ + 2H⁺ + 2e⁻ → H₂O
Battery Types
- Non-rechargeable: alkaline (single use)
- Rechargeable: lithium-ion (hundreds of cycles)
- Accumulator: lead-acid (car battery)
Simple Cell Rule
- Two different metals + electrolyte → voltage
- Bigger reactivity gap → bigger voltage
- Same metal → zero voltage
Fuel Cell: Pros & Cons
- ✔ Only water produced at point of use
- ✔ No moving parts; efficient
- ✔ Continuous operation (no recharge)
- ✘ Hydrogen difficult to store safely
- ✘ Producing H₂ currently needs energy (often fossil fuels)
Common Mistakes
- Saying fuel cells are zero-emission overall: They only produce water at the point of use — but producing hydrogen gas currently requires energy, often from fossil fuels
- Confusing anode and cathode in a fuel cell: In a hydrogen fuel cell, hydrogen is oxidised at the anode (negative terminal); oxygen is reduced at the cathode (positive terminal)
- Saying batteries and fuel cells work the same way: Batteries store chemical energy internally and run down; fuel cells use a continuous external fuel supply and don't run down
- Forgetting the overall fuel cell equation: 2H₂ + O₂ → 2H₂O — the only product is water; no CO₂ is produced at the point of use