Module 08 (subjected to continual revision) New and Emerging Energy Technologies Fuel cells

1. Module 08 (subjected to continual revision) New and Emerging Energy Technologies Fuel cells Energy storage Hydrogen economy Other alternatives to energy use

2. Fuel Cell It combines hydrogen and oxygen to produce electricity via an electrochemical process. H2 is split at anode O2 is split at cathode (hard) 2H+ + 2e- + ½ O2 H2O H2 2H+ + 2e- Exhaust is water (not CO2) It works quietly.

3. Fuel Cell • Individual fuel cells can be placed in a series to form a fuel cell stack. • The stack can be used in a system to power a vehicle or to provide stationary power to a building.

4. Fuel Cell Car - At a steady cruising speed, the motor is powered by energy from the fuel cell. - When more power is needed, for example during sudden acceleration, the battery supplements the fuel cell’s output. - At low speeds when less power is required, the vehicle runs on battery power alone. - During deceleration the motor functions as an electric generator to capture braking energy, which is stored in the battery.

5. Fuel Cell Hybrid

6. Fuel Cell - All fuel cells have the same basic configuration - an electrolyte and two electrodes. - Fuel cells are classified by the kind of electrolyte used. - The type of electrolyte used determines the kind of chemical reactions that take place and the temperature range of operation.

7. Fuel Cell Type PEMFC - Polymer Electrolyte Membrane Fuel Cells (or Proton Exchange Membrane Fuel Cells ) DMFC - Direct Methanol Fuel Cells AFC - Alkaline Fuel Cells PAFC - Phosphoric Acid Fuel Cells MCFC - Molten Carbonate Fuel Cells SOFC - Solid Oxide Fuel Cells

8. Proton Exchange Membrane Fuel Cell (PEMFC) • H2 is the fuel for PEMFC. • Proton exchange polymer membrane (PEM) is used as electrolyte. • Platinum particles on carbon (Pt/C) is used as electrodes. • - At the anode, a platinum catalyst causes the H2 to split into positive hydrogen ions (protons) and negatively charged electrons.

9. Proton Exchange Membrane Fuel Cell (PEMFC) • - PEM allows only the positively charged hydrogen ions to pass through it to the cathode. • The negatively charged electrons must travel along an external circuit to the cathode, creating an electrical current. • At the cathode, the electrons and positively charged hydrogen ions combine with oxygen to form water, which flows out of the cell.

10. Proton Exchange Membrane Fuel Cell (PEMFC) - Suited for applications where quick startup is required making it popular for automobiles - Used in the NASA Gemini series of spacecraft

11. Proton Exchange Membrane Fuel Cell (PEMFC) • - Pt/C electrodes are too expensive to replace internal combustion engines. • - H2 (produced from light hydrocarbons) contains 1-3% CO, 19-25% CO2 and 25% N2. • Even 50 ppm of CO poisons a Pt catalyst. • Pure H2 is used as fuel, which is costly.

12. Proton Exchange Membrane Fuel Cell (PEMFC) • - Electrolytes were sulfonated polystyrene membranes • Nafion is used as electrolytes now • Nafion is a sulfonated tetrafluoroethylene based fluoropolymer-copolymer discovered in the late 1960s by DuPont.

13. CH3OH + H2O 6H+ + 6e- + CO2 Methanol + water CO2 H+ Air Water + Excess air 6H+ + 6e- + 1½ O2 3H2O Direct Methanol Fuel Cell (DMFC) • - Polymer membrane is used as electrolyte as in PEMFC. • Pt/C is used as electrodes as in PEMFC. • - Anode is able to draw hydrogen from methanol directly, unlike in PEMFC.

14. Direct Methanol Fuel Cell (DMFC) • - Operates at about 50-90oC • Efficiency is about 40% • Used more for small portable power applications, possibly cell phones and laptops Toshiba Corporation

15. Alkaline Fuel Cell (AFC) • - Potassium hydroxide in water is used as the electrolyte • A variety of non-precious metals can be used as catalyst at the electrodes • Can reach up to 70% power generating efficiency • - Used mainly by military and space programs • - Used on the Apollo spacecraft to provide electricity and drinking water

16. Alkaline Fuel Cell (AFC) • - Pure H2 and O2 because it is very susceptible to carbon contamination • - Purification process of the H2 and O2 is costly • - Susceptibility to poisoning affects cell’s lifetime which also affects the cost • - Considered to costly for transportation applications

17. Phosphoric Acid Fuel Cell (PAFC) • Uses highly concentrated or pure liquid phosphoric acid as electrolyte • This acid is saturated in a silicon carbide matrix (SiC) • Uses Pt/C electrodes • Most commercially developed fuel cell • Installed and currently operating in banks, hotels, hospitals and police stations.

18. Phosphoric Acid Fuel Cell (PAFC) • Efficiency is about 40% • Operates at about 150-220oC • One main advantage is that it can use impure hydrogen (with less that 1.5% CO) as fuel

19. Molten Carbonate Fuel Cell (MCFC) - Uses an electrolyte composed of a molten carbonate salt mixture - Require carbon dioxide and oxygen to be delivered to the cathode - Operates at extremely high temperatures - Primarily targeted for use as electric utility applications

20. Molten Carbonate Fuel Cell (MCFC) • Because of the extreme high temperatures, non-precious metals can be used as catalysts at the anode and cathode which helps reduces cost • Disadvantage is durability • The high temperature required and the corrosive electrolyte accelerate breakdown and corrosion inside the fuel cell

21. Solid Oxide Fuel Cell (SOFC) - Uses a hard, non-porous ceramic compound as the electrolyte - Can reach 60% power-generating efficiency - Operates at extremely high temperatures - Used mainly for large, high powered applications such as industrial generating stations, mainly because it requires such high temperatures

22. Fuel Cell Type

23. Where do we get the hydrogen from? Fuel Cell

24. Fuel Cell Hydrogen from steam reforming: 95% of the hydrogen used is produced this way HTS – High temperature shift LTS – Low temperature shift

25. Fuel Cell Hydrogen from steam reforming: 95% of the hydrogen used is produced this way • Bulk hydrogen is usually produced by the steam reforming of natural gas (70-80% efficiency) or methane (lower efficiency): • Steam reforming at high temperatures (700–1100°C) with nickel catalyst: • CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol • Shift conversion at 130°C: • CO + H2O → CO2 + H2 - 40.4 kJ/mol

26. Fuel Cell Hydrogen from natural gas steam reforming: 95% of the hydrogen used is produced this way per kg of H2 produced: GHG emissions: 10621 g CO2, 60 g CH4 and 0.04 g N2O GWP :11.88 kg CO2 eq. Resource required : 159 g coal, 10.3 g Fe (ore), 11.2 g Fe (scrap),16.0 g CaCO3, 3642 g natural gas and 16.4 g of oil Water consumption: 19.8 litres Energy consumption: 183.2 MJ Solid waste generated: 201.6 g 0.66 MJ of H2 is produced per MJ of fossil fuel consumed. http://www.nrel.gov/hydrogen/energy_analysis.html

27. Fuel Cell Hydrogen from electrolysis: 5% of the hydrogen used is produced this way

28. Fuel Cell Hydrogen from electrolysis: hydrogen used is produced this way Where does the power come from? Wind Solar PV Other..

29. Fuel Cell Hydrogen from electrolysis of water using wind electricity: per kg of H2 produced: GHG emissions: 950 g CO2, 0.3 g CH4 and 0.05 g N2O GWP :0.97 kg CO2 eq. Resource required : 214.7 g coal, 212.2 g Fe (ore), 174.2 g Fe (scrap),366.6 g CaCO3, 16.2 g natural gas and 48.3 g of oil Water consumption: 26.7 litres Energy consumption: 9.1 MJ Solid waste generated: 223 g 13.2 MJ of H2 is produced per MJ of fossil fuel consumed. http://www.nrel.gov/hydrogen/energy_analysis.html

30. Regenerative Fuel Cell

31. Fuel Cell Hydrogen from water-splitting: Solar water splitting is the process by which energy in solar photons is used to break down liquid water into molecules of hydrogen and oxygen gas. Hydrogen produced through solar water does not emit carbon into the atmosphere.

32. Fuel Cell Hydrogen from water-splitting:

33. Fuel Cell Hydrogen from water-splitting: Highly dense vertical arrays of nanowires made from silicon and titanium oxide and measuring 20 microns in height show promise for the efficient production of hydrogen through solar water splitting.

34. Fuel Cell

35. Fuel Cell Hydrogen from waste: HyPR-MEET demonstration plant Concept of the gasification system

36. Fuel Cell Hydrogen from waste: http://www.nrel.gov/hydrogen/energy_analysis.html

37. Fuel Cell Hydrogen from waste: Researchers have designed a microbial electrolysis cell in which bacteria break up acetic acid (a product of plant waste fermentation) to produce hydrogen gas with a very small electric input from an outside source. Hydrogen can then be used for fuel cells or as a fuel additive in vehicles that now run on natural gas. http://www.solutions-site.org/node/294

38. Microbial Fuel Cells Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG

39. Microbial Fuel Cells anode cathode Source: http://parts.mit.edu/igem07/images/2/2d/Fuelcell.JPG

40. Microbial Fuel Cells An anode and a cathode are connected by an external electrical circuit, and separated internally by an ion exchange membrane.

41. Microbial Fuel Cells Microbes growing in the anodic chamber metabolize a carbon substrate (glucose in this case) to produce energy and hydrogen.

42. Microbial Fuel Cells C6H12O6 + 2H2O → 2CH3COOH + 2CO2 + 4H2 or C6H12O6 → CH3CH2CH2COOH + 2CO2 + 2H2 Hydrogen generated is reduced into hydrogen ions (proton) and electrons.

43. Microbial Fuel Cells Electrons are transferred to the anodic electrode, and then to the external electrical circuit. The protons move to the cathodic compartment via the ion exchange channel and complete the circuit.

44. Microbial Fuel Cells The electrons and protons liberated in the reaction recombine in the cathode. If oxygen is to be used as an oxidizing agent, water will be formed. An electrical current is formed from the potential difference of the anode and cathode, and power is generated.

45. Microbial Fuel Cells The anode and cathode electrodes are composed of graphite, carbon paper or carbon cloth. The anodic chamber is filled with the carbon substrate for the microbes to metabolize to grow and produce energy. The pH and buffering properties of the anodic chamber can be varied to maximize microbial growth, energy production, and electric potential. The cathodic chamber may be filled with air in which case oxygen is the oxidant.

46. Microbial Fuel Cells Laboratory substrates are acetate, glucose, or lactate. Real world substrates include wastewater and landfills. Substrate concentration, type, and feed rate can greatly affect the efficiency of a cell.

47. Microbial Fuel Cells Microbes should be anaerobic (fermentative type) because anodic chamber must be free of oxygen. Microbes tested are: E. coli Proteus vulgarisStreptococcus lactisStaphylococcus aureusPsuedomonas methanicaLactobacillus plantarium

48. Microbial Fuel Cells Microbes should be anaerobic (fermentative type) because anodic chamber must be free of oxygen. Some bacteria, like Clostridium cellulolyticum, are able to use cellulose as a substrate to produce an electrical output between 14.3-59.2 mW/m2, depending on the type of cellulose.

49. Microbial Fuel Cells Proton Exchange Membrane (PEM) The PEM acts as the barrier between the anodic and cathodic chambers. It is commonly made from polymers like Nafion and Ultrex. Ideally, no oxygen should be able to circulate between the oxidizing environment of the cathode and the reducing environment of the anode. The detrimental effects of oxygen in the anode can be lessened by adding oxygen-scavenging species like cysteine.

50. Real-life MFC