Fuel Cells and Rechargeable Batteries

Fuel Cells and Rechargeable Batteries

• Fuel cells and rechargeable batteries are energy sources.
• A fuel cell type uses a proton exchange membrane and aqueous methanol.

Fuel Cell Electrodes

• Negative electrode (anode): CH₃OH(aq) + H₂O(l) → CO₂(g) + 6H⁺(aq) + 6e⁻
• Positive electrode (cathode): O₂(g) + 4H⁺(aq) + 4e⁻ → 2H₂O(l)

Fuel Cell Advantages

• Produces continuous electricity with more raw materials added.
• Does not need recharging.
• Less hazardous if broken/exposed to the environment.
• Weighs less for the same energy output.
• Has higher energy density/specific energy than a lead-acid battery.

Fuel Cell Disadvantages

• More expensive,
• Needs a constant supply of fuel,
• Methanol/ethanol fuel cells are difficult to use in cold weather.
• Produce carbon dioxide.
• Storage/transport of gases/hydrogen is a problem in hydrogen fuel cells.
• Does not produce high current.
• Potentially explosive/hydrogen is flammable.

Chlorophyll

• Chlorophyll absorbs sunlight due to highly conjugated systems.
• Containing many alternating single and double bonds.
• Having many delocalized electrons.

Photosynthesis

• 6CO₂(g) + 6H₂O(l) → C₆H₁₂O₆(aq) + 6O₂(g)

Lithium-ion Battery

• Lithium-ion batteries are rechargeable.
• Offer advantages of lower mass for equal atoms, lower mass per transferred electron, and higher voltage.
• Lithium cobalt oxide and graphite are common electrodes.

Methane Combustion

• CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l)

Methane Specific Energy

• 55.5 kJ g⁻¹

Photosynthesis and Biological Compounds

• Photosynthesis creates carbohydrates from biological compounds (e.g., plants converting light into energy).
• Decays of organic matter can create hydrocarbons including methane.

Global Warming

• Global temperatures and CO₂ concentrations have increased over time in correlation with industrial emissions.
• Greenhouse gases capture heat from the sun, trapping it in the atmosphere.

Methane vs. Gasoline

• Methane has a lower environmental impact than gasoline due to producing less greenhouse gases during combustion.
• Weighing less and having a higher energy density, methane is a cleaner (less polluting) fuel.