Electrochemistry Seminar: Battery and Fuel Cell Technologies

Overview of Electrochemical Cells

• An Electrochemical Cell

  • Involves the transport of electrons and ions through the cell.
  • Anode (oxidation) and Cathode (reduction) are key components.

• Half-Cell Reactions

  • Anode: Water electrolysis (producing O2 and H+)
  • Cathode: Water electrolysis (producing H2 and OH-)
  • Overall Reaction: 2H2O → 2H2 + O2

Standard Electrode Potential

• Defined under equilibrium conditions versus the standard hydrogen electrode (SHE).
• SHE: Platinum electrode in a 1 M H+ solution at 1 atm.
• Standard Electrode Potentials
  • Cu²⁺/Cu = 0.337V
  • Zn²⁺/Zn = -0.763V
  • Cell potential calculation: Ecell = Ec - Ea

Overpotential and Polarization

• Overpotential: Difference between actual and equilibrium potential.
• Polarization: Slow kinetics due to low reactant concentration or high kinetic barriers.

Battery Technologies

• Lead-Acid Batteries

  • Negative Electrode: Pb + SO₄²⁻ → PbSO₄ + 2e⁻
  • Positive Electrode: PbO₂ + 4H⁺ + SO₄²⁻ + 2e⁻ → PbSO₄ + 2H₂O
  • Developments: Weight reduction, improved energy density, maintenance-free designs.

• Nickel-Cadmium and Ni-Metal Hydride Batteries

  • Ni-Metal Hydride: LaNi₅H/LaNi₅ with KOH electrolyte.
  • Ni-Cd: Memory effect issues; Priming required for new batteries.

• Lithium-Ion Battery

  • Li⁺ shuttling between graphite (anode) and metal oxide (cathode).
  • Voltage: 3-4V depending on material.
  • Safety concerns: Overcharging leading to explosion.

Fuel Cell Technologies

• General Working

  • Oxidizes fuel at the anode, generates electricity as electrons pass through an external circuit.
  • Water is a common byproduct.

• Hydrogen/Oxygen Fuel Cell

  • Environmentally friendly due to water as byproduct.

• Direct Methanol Fuel Cells (DMFC)

  • Methanol as fuel with Pt/Ru catalyst.
  • Limitations: Low efficiency due to methanol crossover, high cost.

Environmental and Safety Concerns

• Recycling of batteries to mitigate hazardous waste.
• Lead-acid battery recycling involves smelting and refining.

Applications and Limitations

• Fuel Cell Powered Vehicles
  • High costs and storage challenges for hydrogen.
• Battery Powered Vehicles
  • Limited driving range and high costs.
• Hybrid Vehicles
  • Combines battery and combustion engine; reduces pollutants and noise.

This seminar outlined the key concepts and technologies in electrochemistry, focusing on batteries and fuel cells, and discussed both technological challenges and environmental impacts.