Fuel Cells
Quick Notes
- Fuel Cells are devices that convert the chemical energy of a fuel directly into electrical energy through redox reactions.
- In a hydrogen-oxygen fuel cell, H2 is oxidized at the anode, and O2 is reduced at the cathode.
- Overall cell reaction:
- 2H2(g) + O2(g) → 2H2O(l)
- ΔG < 0 = spontaneous, highly efficient.
- Advantages: Continuous power generation, clean byproduct (H2O), high efficiency.
- Limitation: Storage and supply of H2 and O2 gases is a challenge.
Full Notes
Introduction to Fuel Cells
Fuel cells are electrochemical cells that convert the chemical energy of a fuel directly into electrical energy.
Unlike conventional cells that store reactants, fuel cells receive a continuous supply of fuel and oxidant from external sources, enabling sustained operation as long as these are provided.
These cells operate similarly to galvanic cells, but instead of using solid electrodes and internal electrolytes alone, they depend on external sources of reactants. The most well-known example is the hydrogen-oxygen fuel cell, often used in space programs and considered for future sustainable energy technologies.
Working of a Hydrogen–Oxygen Fuel Cell
- Electrolyte: Concentrated aqueous potassium hydroxide (KOH) solution.
- Electrodes: Porous carbon electrodes impregnated with platinum or silver as catalysts.
- Fuel: Hydrogen gas is bubbled into the anode side.
- Oxidant: Oxygen gas is bubbled into the cathode side.
- The cell operates at about 523–573 K and 50 atm pressure.
- Anode Reaction (Oxidation): H2(g) + 2OH−(aq) → 2H2O(l) + 2e−
- Cathode Reaction (Reduction): ½O2(g) + H2O(l) + 2e− → 2OH−(aq)
- Overall Reaction: 2H2(g) + O2(g) → 2H2O(l)
This reaction is highly exothermic and results in a spontaneous redox process, with electrons flowing through the external circuit to generate electricity.
Features and Advantages
- Efficiency: Much higher than combustion engines, since no thermal step is involved.
- Byproducts: Water is the only byproduct, making it environmentally friendly.
- Silent Operation: No moving parts, so operation is quiet.
- Continuous Operation: Works as long as fuel and oxidant are supplied.
Limitations
- Hydrogen storage and distribution remain significant technical challenges.
- The catalysts (e.g., platinum) are expensive.
- System design and scaling for widespread use are complex.
Applications
- Spacecraft: NASA has used H2–O2 fuel cells to power onboard systems.
- Automotive Industry: Research into hydrogen fuel cell vehicles is ongoing.
- Backup Power Systems: Reliable electricity source in critical facilities.
Summary
- Fuel cells convert chemical energy directly into electrical energy using continuous supplies of fuel and oxidant.
- Hydrogen–oxygen cells use porous carbon electrodes with Pt/Ag and aqueous KOH.
- Anode oxidizes H2 and cathode reduces O2 giving water as the only byproduct.
- They are efficient and clean but face challenges with gas storage and catalyst cost.