Download - Hydrogen Fuel Cells vvvv
![Page 1: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/1.jpg)
Hydrogen Fuel Cells
![Page 2: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/2.jpg)
Basic electrochem
• Galvantic cell
• 2H2 + O2 → 2H2O
• Anode (oxidation)
H2 → 2H+ + 2e-
• Cathode (reduction)
O2 + 4e- → 2O2-
![Page 3: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/3.jpg)
Typical electrochemical cell/batterypotentiometer
Salt bridge
Anodeoxidation
Cathodereduction
Flow of electrons
Junction potentials
![Page 4: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/4.jpg)
Fuel cell
• The fuel is the anode• The oxidant is the cathode• The fuel and oxidant continuously flow
through the cell• An electrolyte separates the fuel and
oxidant channels• Solid or liquid electrolyte that conducts
protons• Need catalyst at low temp
![Page 5: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/5.jpg)
Hydrogen Fuel Cell
![Page 6: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/6.jpg)
Potential Advantages
• Clean; only product is H2O and heat.
• More efficient than heat engine.
• Higher part load efficiency
• Excellent response time
• Co-generation
• No tuning required
• No recharging required
![Page 7: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/7.jpg)
![Page 8: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/8.jpg)
Disadvantages
• H2 is difficult/expensive to produce, store and transport.
• Fuels cells require pure fuel.
• Platinum catalysts are expensive and rare
• Proton exchange membranes must be kept moist
• Hydrogen fuel cell stacks are heavy
![Page 9: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/9.jpg)
uses• Stationary power plants; small, power to
neighborhoods, hospitals, ect.
• Submarines
• Buses
• Cars
![Page 10: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/10.jpg)
![Page 11: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/11.jpg)
Proton Exchange Membrane (PEM) Fuel Cells
• Electrolyte is a thin solid polymer film (acidified Teflon)
• Conducts H+ from the anode to the cathode• Low temp (160-195 C)• 15-30 psi• 1.1 V
H2 → 2H+ + 2e-
1/2O2 + 2e- + 2H+ → H2O
![Page 12: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/12.jpg)
Direct Methanol Fuel Cells
CH3OH + H2O → 6H+ + CO2 + 6e-
3/2O2 + 6e- + 6H+ → 3H2O
• Still pretty new technology, uses a different catalyst at a higher temp.
• Not as efficient
![Page 13: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/13.jpg)
Several Advantages
• Tolerant to CO2 in oxidant
• Low temp
• Dry electrolyte
• Non-corrosive electrolyte
• High current, voltage and power density
• Tolerant to differential pressures
![Page 14: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/14.jpg)
Disadvantages
• Anode and cathode needs platinum catalysts
• Tolerates only about 50 ppm of CO and a few ppm of Sulfur compounds in fuel
• Gas humidification required
• Expensive membrane
![Page 15: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/15.jpg)
Alkaline Fuel Cells
• Molten KOH as electrolyte
• Conducts OH- from cathode to anode
• Circulating electrolye, removes heat and water/or a stationary paste needs
H2 + 2OH- → 2H2O + 2e-
1/2O2 + H2O + 2e- → 2OH-
Removal of water is critical
![Page 16: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/16.jpg)
Advantages
• Low temp
• Fast start up
• High efficiency
• Little or no platinum catalyst needed
• Minimal corrosion
![Page 17: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/17.jpg)
Disadvantages
• Extremely intolerant of CO2 (350 ppm) and somewhat intolerant of CO
• Liquid electrolyte handling
• Complex water management
• Short lifetime
![Page 18: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/18.jpg)
Other barriers to the Realization of a Hydrogen Economy
• Platinum catalyst• Humidification• Needs pure fuel• Fuel cell stacks are heavy• Hydrogen production is expensive• Hydrogen transportation is expensive• Hydrogen storage is vehicles is a bit
impratical
![Page 19: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/19.jpg)
Hydrogen Production
• Hydrogen is an energy carrier, not an energy source
• Fossil fuels especially, coal and natural gas – methane reforming and partial oxidation (burning)– High temperatures and steam/more efficient than
combustion• Renewable electrolysis (wind, solar, geothermal,
hydroelectric)• Nuclear• Biomass• Photo-electrochemical using algae
– Consume water and solar energy and produce H2
![Page 20: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/20.jpg)
Hydrogen Transport
• Pipelines
• High pressure tubes
• Cryogenic tankers
• Chemical carriers
![Page 21: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/21.jpg)
Research
• Less costly materials for pipelines
• Less expensive compression technology
• Less costly liquefaction processes
• More cost effective bulk storage strategies
![Page 22: Hydrogen Fuel Cells vvvv](https://reader035.vdocuments.us/reader035/viewer/2022081418/55cf9443550346f57ba0be98/html5/thumbnails/22.jpg)
Hydrogen Storage in vehicle
• Hydrogen has a low energy to volume ratio.
• The hydrogen fuel tank takes up a lot of space.
• Can we store hydrogen in a different form (metal hydride)?
• This is why methanol as a fuel is an attractive option.