Eng/Phy 160, May 25,05

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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

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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.)

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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
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Hydrogen Fundamentals Cont.
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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!)

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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

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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.

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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

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Biogeneration of hydrogen
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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

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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

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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.

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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.

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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)

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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.

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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)
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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).
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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).)

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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
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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)
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ICE

• Take advantage of the existing massive ICE
  framework
• Disadvantage much lower well-to-wheels
  efficiency due to low efficiency of IC engine.

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Storage
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Some compounds being researched
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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)

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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

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DOE Targets
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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

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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

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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)