Introduction To Fuel Cells

• Concepts in sequence, and a one page version.
• Discussion of power delivered by fuel cells:
  • Electrical power in terms of cell potential and current
  • Cell potentials
  • Change in Gibbs free energy and electrical work
  • Efficiency
  • Specific power of fuel cells
• Theoretical efficiency is higher than a heat engine burning hydrogen fuel.
• Only exhaust from the hydrogen fuel cell is water and thermal energy, which can also be used for heating or a heat engine.
• Electrolysis of water to generate hydrogen fuel is achieved by driving the electrochemical cell in the other direction with an applied potential and current.
• Other fuels exhibit different efficiencies and require different cell materials.
• Methanol and hydrocarbons are possible fuels, although reformation to hydrogen is generally required.
• Direct use of or generation of hydrogen from a carbon-based fuel of fossil or biomass origin creates CO2.
• Fuel cells can use fossil fuels more efficiently than internal combustion engines or gas-driven turbine engines. Ford Motor Company used to be a proponent of hydrogen-burning internal combustion engines, but seem to prefer fuel cells now.
• Hydrogen from fossil fuels still leads to the emission of CO₂ into the atmosphere, but NOx is not generated.
• Fuel cells are easily poisoned by very small amounts of SO₂ or H₂S and CO.
• Research and development is underway, but real applications will appear gradually over the next 20 years.
• Problems: hydrogen storage, fuel reforming, catalyst poisons, reliability, cost, attaining efficiencies closer to the theoretical limit.

Fuel Cells - Details

• Overview from Los Alamos National Laboratory:
  • Types of fuel cells
  • Fuels
    • H₂ is best chemically and in terms of specific energy (energy/mass), but very difficult to store.
    • Reformable, liquid fuels have a higher energy density (energy/volume).
    • Integrating a reforming unit with a fuel cell
    • Methanol, a fuel derivable from renewable biomass or coal, can be used directly in a fuel cell.
  • Pros and cons
  • Renewable energy sources and the regenerative fuel cell concept
• Fuel Cell Handbook has much detailed information.
• If you want to learn more, browse this general fuel cell information repository.