Hydrogen Fuel Cells

1. Hydrogen Fuel Cells David Lorse ESS 315

2. What is a hydrogen fuel cell? • Hydrogen fuel cells (HFCs) are a type of electrochemical cell. • HFCs generate electricity by reduction and oxidation reactions within the cell. • They use three main components, a fuel, an oxidant and an electrolyte. • HFCs operate like batteries, although they require external fuel. • HFCs are a thermodynamically open system. • HFCs use hydrogen as a fuel, oxygen as an oxidant, a proton exchange membrane as an electrolyte, and emit only water as waste.

3. How do they work? • Fuel (H2) is first transported to the anode of the cell • Fuel undergoes the anode reaction • Anode reaction splits the fuel into H+ (a proton) and e- • Protons pass through the electrolyte to the cathode • Electrons can not pass through the electrolyte, and must travel through an external circuit which creates a usable electric current • Protons and electrons reach the cathode, and undergo the cathode reaction

4. Chemistry behind the technology Oxidation At the anode of the cell, a catalyst (platinum powder) is used to separate the proton from the electron in the hydrogen fuel. Anode half-reaction: 2H2 4H+ + 4e- Eo = 0.00V Reduction At the cathode of the cell, a second catalyst (nickel) is used to recombine the protons, electrons, and oxygen atoms to form water. Cathode half- reaction: 4H+ + O2 + 4e- 2H2O Eo = 0.68V In electrochemistry, the Eocell value (energy) of a fuel cell is equal to the Eoof the cathode half-reaction minus the Eoof the anode half-reaction. For a hydrogen fuel cell, the two half reactions are shown above. So to calculate the energy of one fuel cell, we need to subtract the anode energy from the cathode energy. For a HFC, the Eocell = 0.68V – 0.00V which equals 0.68V

5. Uses of hydrogen fuel cells There are many different uses of fuel cells being utilized right now. Some of these uses are… • Power sources for vehicles such as cars, trucks, buses and even boats and submarines • Power sources for spacecraft, remote weather stations and military technology • Batteries for electronics such as laptops and smart phones • Sources for uninterruptable power supplies.

6. Problems regarding hydrogen fuel cells • Lack of hydrogen infrastructure • Need for refueling stations • Lack of consumer distribution system • Cost of hydrogen fuel cells • 2009 Department of Energy estimated $61/kw • Honda FCX Clarity costs about half a million dollars to make • Carbon cost of producing hydrogen • Problems with HFC cars • Short range (~260 miles) • Warm up time (~5 minutes)

7. References • http://www.fueleconomy.gov/feg/fuelcell.shtml • http://www.howstuffworks.com/fuel-efficiency/alternative-fuels/fuel-cell.htm • http://www.energy.gov • Chemical Principles, Sixth Edition, Zumdahl