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Eng/Phy 160, May 25,05

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Title: Eng/Phy 160, May 25,05


1
Eng/Phy 160, May 25,05
  • The Hydrogen Economy
  • Overview an alternative to the oil economy for
    transportation especially
  • Hydrogen energy storage (as fuel), not energy
    source. Means of production (electrolysis,
    nuclear, fossil fuel, bio) basic reaction
  • Means to Utilize Internal combustion vs. fuel
    cell kinds of fuel cells technological needs
  • Hydrogen Storage Overview of current technology
    and goals
  • Hydrogen Infrastructure What is necessary for
    conversion costs, opportunities
  • Downsides Safety and Environmental risks

2
The Hydrogen Economy a vision of a different
transporation system
  • Utilize hydrogen as a fuel rather than oil
    derived products.
  • Can convert to more efficient energy systems
  • Can employ hydrogen derived from existing fossil
    fuels in the interim on the way to sustainable
    hydrogen production.
  • Hydrogen can also be used in other applications
    (stationary source power generation for industry,
    e.g.)

3
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5
Hydrogen fundamentals
  • Hydrogen is a storage form there is not free
    hydrogen sitting around for us to access as there
    is fossil fuel. The basic oxidation reaction
    (burning) of Hydrogen goes as
  • 2H2 O2 ? 2H2O 132 MJ/kg-H2
  • Some contrast Best fuel per mass (problem is low
    density)

Fuel Oxidation Energy release (MJ/kg)
Hydrogen 120
Gasoline 47
Natural Gas 36-42
Coal 30
Wood 21
Manure 13
6
Hydrogen Fundamentals Cont.
?
?
?
7
How to get hydrogen?
  • Renewable Employ electrolysis/high T run
    combustion reaction in reverse
  • 132 MJ/kg-water H2O ? H2 ½ O2
  • Electrolysis Use wind, solar, or nuclear to
    provide spark for hydrogen
  • Catalytic at high temperature Create good
    catalytic chemistry in water of nuclear plant to
    generate and hydrogen (remember in Chernobyl and
    TMI hydrogen was a factor!)

8
Hydrogen from fossil fuels
  • Reforming
  • Example of Methane
  • CH4 ½ O2 ? CO 2H2
  • CO H2O ? CO2 H2
  • CH4 ½ O2 H2O ? CO2 3H2___
  • Generally, it is possible to have less CO2 per
    reformed hydrogen produced than per fossil fuel
    burned (meaning of table 13.1 in Deutsch and
    Lester)
  • Comparison Assume 80 conversion efficiency of
    methane in reformer to hydrogen at ideal
    conversion, there will be about 0.33 moles of
    carbon dioxide produced per mole of hydrogen
    according to the above. At 80 conversion
    efficiency, there will be some straight oxidation
    of methane and hence 0.33/0.8 0.41 moles of CO2
    per mole of hydrogen. The number of moles from
    straight burning of methane would be 1.
  • Can also get from steam reforming of coal (as in
    futuregen)
  • Message need to consider well to wheel
    efficiency

9
Methane Splitting
  • CH4 ? 2
    H2 C
  • Demonstrated in 1970s by Norman Thagard.
  • Large Heat Input
  • 1600-2000 C
  • Solution Solar Power
  • (focus heat to split methane)
  • 50 of Arizona to meet
  • U.S. energy needs.
  • Process still being developed.

10
Aerosol Flow Reactor
  • Energy produced at 13/GJ
  • Half the energy requirements of
  • Steam Methane Reforming
  • Carbon Product Can Be Sold for ca. .66/kg
    (market may get flooded with cheap carbon)
  • Reduce CO2 emissions by replacing current carbon
    production industry
  • Dependent upon methane supply

11
Biogeneration of hydrogen
12
Implementation Fuel Cells vs. Internal
Combustion
  • Fuel Cell Generate electricity by the
    burning of hydrogen in a chemical cell
  • Anode side 2H2 gt 4H 4e-
  • Cathode side O2 4H 4e- gt 2H2O
  • Net reaction 2H2 O2 gt 2H2O

13
Overview from BES Report (great job!) (available
on class web site)
  • Fuel H2 (produced from fossil fuel reformer,
    electrolysis, nuclear plants, or biological
    sources) or light molecule (e.g., methanol).
  • Low Temperature Fuel Cell Membrane hydrated
    polymer electrolyte material Cathode
    nanoparticle Pt on support Anode for pure H2,
    Pt again for reformed H2 or methanol, PtRu
    alloy.
  • High Temperature Fuel Cell Membrane oxygen
    deficient metal oxide Electrodes conducting
    (La,Sr)MnO3

14
Proton Membrane
  • The anode conducts the electrons that are freed
    from the hydrogen molecules. It disperse the
    hydrogen gas equally over the surface of the
    catalyst.
  • The cathode, the positive post of the fuel cell,
    distributes the oxygen to the surface of the
    catalyst. It also conducts the electrons back
    from the external circuit to the catalyst, where
    they can recombine with the hydrogen ions and
    oxygen to form water.
  • The electrolyte is the proton exchange membrane.
    This specially treated material, which looks
    something like ordinary kitchen plastic wrap,
    only conducts positively charged ions. The
    membrane blocks electrons.
  • The catalyst is a special material that
    facilitates the reaction of oxygen and hydrogen.
    It is usually made of platinum powder very thinly
    coated onto carbon paper or cloth. The catalyst
    is rough and porous so that the maximum surface
    area of the platinum can be exposed to the
    hydrogen or oxygen. The platinum-coated side of
    the catalyst faces the PEM.

15
Advantages of PEMFC
  • PEMFCs operate at a fairly low temperature (about
    176 degrees Fahrenheit, 80 degrees Celsius),
    which means they warm up quickly and don't
    require expensive containment structures.
    Constant improvements in the engineering and
    materials used in these cells have increased the
    power density to a level where a device about the
    size of a small piece of luggage can power a car.

16
Some issuesplatinum in electrodes
  • There is at present abundant platinum
  • But platinum is not cheap! (47K/kg)
  • Pure platinum at anodes gets poisoned
    (adsorbed species limit catalysis)- must alloy
    with e.g., Ru (also lowers cost)

17
ObstaclesOpportunities for Research!
  1. Membrane Greater stability less corrosion
    maintain hydration while running at higher
    temperatures to improve heat rejection higher
    ion mobility.
  2. Cathode Replace or reduce Pt (, scarcity for
    large scale production!) reduce overpotential
    lower corrosion.
  3. Anode Replace or reduce Pt avoid poisoning in
    reformer or methanol based systems avoid
    impurity increase of overload.
  4. Overall Reduce amount of water in cell.

18
Overpotential
Overpotential Difference between Ideal and
actual Potential in open circuit
Illustration of overpotential concept for
hydrogen fuel cell (from http//faculty.washington
.edu/stuve/chula03/ ecat_chula_lec5-4.pdf) (NB
anode overpotential can be increased with
contamination from reformed H2 or methanol)
19
Better electrodes through combinatorial
chemistry?(P. Strasser et al., High throughput
experimental and theoretical predictive screening
of materials-a comparative study of search
strategies for new fuel cell anode catalysts,
J. Phys. Chem. B 107, 11013 (2003).
20
Promise of nanoscience?
  • Novel Catalysts at nanoscale? It is possible that
    Pt may be replaced by some materials may become
    catalytic at nanoscale (eg, Au) or have dramatic
    increased catalytic activity due to, e.g., novel
    structures or surface layers (MgO-catalytic
    degradation of organochloranes I.V. Mishakov et
    al., Nanocrystalline MgO as a
    dehydrohalogenation catalyst, Journal of
    Catalysis 286, 40 (2002). BUT This seems much
    harder and in search of a silver bullet.
  • Novel Catalytic Supports at the nanolayer By
    improving catalytic supports to better orient and
    align Pt nanoparticles, you might reduce Pt usage
    through better structuring (e.g., S. Han, Y. Yun,
    K.W. Park, Y.E. Sung, T. Hyeon, Simple
    Solid-phase synthesis of hollow graphitic
    nanoparticles and their application to direct
    methanol fuel cells, Advanced Materials 15,
    1922 (2003).)

21
Opportunities from Biology?
  • Numerous proteins reduce oxygen--use at cathode?
    Cytochrome C oxidase (key respiration protein!)
    overall reaction same as fuel cell! (4e-4HO2
    -gt 2H20) Laccase oxidizes phenols and alanines
    while reducing oxygen. (In all cases, oxygen
    docks at transition metal site or complex)

Structure of cytochrome C oxidase (metalloprotein
data base- http//metallo. scripps.edu/ PROMISE/ 1
OCC.html
Structure of a fungal laccase protein-three
copper sites in yellow
http//akseli.tekes.fi/Resource.phx/bike/rakbio/en
/rouvinenkoivula.htx
22
A WORKING BIOFUELCELL! (E. Katz and I.
Willner, A biofuel cell with electrochemically
switchable and tunable output, J. Am. Chem.
Soc. 125, 6803 (2003))
Apparatus schematicjust add sugar!
Cathode schematic (cyt C cyt C oxidase)
tunable!!
Anode schematic (APO glucose oxidase)
23
ICE
  • Take advantage of the existing massive ICE
    framework
  • Disadvantage much lower well-to-wheels
    efficiency due to low efficiency of IC engine.

24
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25
Storage
26
Some compounds being researched
27
Delivery Options for H economy
  • Gaseous
  • Pipelines
  • Trucks
  • On-site reforming
  • Liquid H2 Chemical carriers
  • Trucks, Rails (liquid H2)
  • Hydrides (solid carriers)
  • Other carriers (barges, etc)

28
Barriers
  • Lack of infrastructure options analysis
  • High capital cost of pipelines
  • High cost of compression
  • High cost of liquefaction
  • Lack of cost effective carrier technology
  • Hydrogen infrastructure exists only for small
    merchant hydrogen markets in the chemical and
    refining industries

29
DOE Targets
30
Estimates of Delivery Cost
  • Accenture estimates a 280 billion U.S.
    investment in hydrogen fueling infrastructure,
  • 130 B to convert fueling stations
  • 70 B to for natural gas and ethanol supplies
  • 40 B to move fuel to fueling stations
  • 40 B for new pipelines
  • But, keep in mind that by 2020 annual oil imports
    will be 200 B

31
Pipeline Transition Cost Reduction
  • Estimated transition cost of 40 B.
  • The technology already exists
  • Currently, there are 1,500 km (930 miles) of
    special hydrogen pipelines (720 km or 446 miles
    in North America) operating at up to 100 bar.
  • Natural gas pipelines can be used or adapted for
    delivery with acceptable energy loss
  • Future pipelines created for petroleum
    transportation are hydrogen compatible
  • Japan intended major Siberia-China-Japan gas
    pipeline

32
Alternative to hydrogen - Methanol Fuel Cells
  • Partial oxidation of methane
  • CH4 ½ O2 ? CH3OH -- exothermic!
  • Liquid at ambient conditions. Can be used in
    fuel cells with the net reaction
  • CH3OH 3O2 ? 2H2O CO2 22 MJ/kg
  • Note that
  • The generation reaction can be used for
    electricity say.
  • Given the enhanced fuel cell/electric motor
    efficiency relative to straight burning of fossil
    fuels, less CO2 is produced per burn by 2 x
  • Can plausibly be used for consumer electronics at
    greater efficiency than recharging via
    conventional electricity sources and hence less
    CO2.
  • In principle, methane can be produced
    biologically (eg, collecting from waste dumps or
    cow burps)
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