Institute of Physics: South West Branch 29th NOVEMBER 2006 Energy Futures: The Hydrogen Scenario

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Institute of Physics South West Branch 29th
NOVEMBER 2006 Energy Futures The Hydrogen
Scenario

• Keith Ross,
• Institute for Materials Research
• University of Salford

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The Energy Crisis

• Driven by global warming and expectation of
  non-linear response due to methane hydrates etc.
• Potential exhaustion of oil reserves and
  political instability
• Russian control over gas reserves

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Why Hydrogen

• Will put forward the arguments for the Hydrogen
  Economy
• Expertise is as a researcher into ways of storing
  hydrogen

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Advantages of the Hydrogen Economy

• Only alternative to hydrocarbons as fuel for
  independent transportation
• Can be burnt (ICE) or supplied to fuel cells
• Only products are energy and water
• Can be used as an energy vector like electricity
  but with storage included
• Intermittent renewable energy sources need
  storage or back-up

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Hydrogen as an energy vector
Heat
Electricity
Hydrogen
Electricity Generation
Primary Energy Source
Electrolysis
Storage
User
Fuel Cell
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Hydrogen as a renewable Energy

• From wind, waves, tide, solar
• via electricity
• From biomass direct or from CH4
• From nuclear via electricity or
  thermochemical processes
• From fossil fuels with CO2 sequestration

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The intermittency Problem

• Wind power produces electricity when the wind is
  blowing
• Waves produce more power when the wind is blowing
• There could be weather giving no wind anywhere in
  the UK
• Tides produce power at varying times of day
• For more than 10 of electricity supply, would
  need either back-up power or hydrogen storage

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Bulk Storage

• Salt caverns under Cheshire
• Porous strata after oil and gas removal
• Pipeline system itself would contain useful
  amounts
• Extensive hydrogen pipelines already exist in the
  NW and NE
• Liquid hydrogen can be transported in tankers
  (20K)
• Local storage in porous solids at 80K
• High pressure tanks and cylinders

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Production of Hydrogen

• Electrolysis is well established but only 50
  efficient - does not respond well to varying
  loads
• From Biomass - by high temperature chemical
  reforming or by ambient microbe digestion
• From High Temperature Gas-Cooled Nuclear Reactor
  by direct thermochemical reaction at 900oC gives
  50 overall efficiency
• (Cf The Sulphur-Iodine Cycle)

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IEA Projections of Hydrogen Production costs
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US Plans fro Hydrogen from Coal
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Transportation of Hydrogen

• Not much different from Town Gas (but no carbon
  monoxide!!) so metal pipes OK at low pressures.
• Natural gas pipes (plastic) may allow H2 to
  diffuse through?
• Query Is it cheaper to transport H2 over long
  distances ( e.g. under the sea?) than
  electricity?

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Road and Air Transport

• Hydrogen is the only alternative to hydrocarbon
  fuel for road transport and aircraft
• For road use, use PEM Fuel cell and regenerative
  braking
• But difficult to match the energy density of
  petrol or diesel
• For air transport, use gas turbines and liquid
  hydrogen storage (Cf NASA)

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Liquid Hydrogen - developed by BMW
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Public perceptions
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Hydrogen storage targets for the Freedom Car
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On Board Hydrogen Storage

• High Pressure H2 Gas
• Liquid Hydrogen
• Solid Hydrides
• Molecular Storage in Porous Solids

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High Pressure H2 Storage

• Conventional steel gas cylinders yield about 1
  by mass
• Used in the current FP6 CUTE programme as in
  London
• Advanced technology using fibre- reinforced
  plastic can go to 350 Atmospheres with better
  failure characteristics
• But severe doubts about using for general public

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Liquid Hydrogen Storage

• Developed by BMW using an ICE (Internal
  Combustion Engine)
• Continuous boil-off of H2 (few
  /day)
• Waste 40 of the available energy in
  liquefaction
• Refueling is relatively easy

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Solid State Storage

• Hydrides used in Metal Hydride batteries based
  on LaNi5 which changes to LaNi5H6 gives 1 by
  mass
• These compounds absorb hydrogen by adding an
  electron to the conduction band
• Give convenient equilibrium H2 pressures

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Lighter metals absorb with difficulty

• Ionic bonding means fixed number of electrons
  hence major structural changes involved
• Higher thermal stability hence need high
  temperatures to release hydrogen
• Higher hysteresis during cycling
• Slower hydrogen absorption and desorption very
  fine powder
• Heat released on absorption is a major
  engineering problem
• 5 minute refuelling means megawatt cooling of the
  store

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LiNH2 Typical light hydride store

• Li3N H2 Li2NH LiH
• Li2NH H2 LiNH2 LiH
• But
• LiNH2 2H2 NH3 LiH
• Note that NH3 would be very unwelcome in a fuel
  cell
• Can start by mixing LiNH2 with LiH

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Storage of H2 in porous solids

• Excitement about carbon nanotubes proved to be
  erroneous
• But still a possible system for storage at 80K
• Advantage is lower heat of adsorption less
  heating and faster evolution
• Hunt for high surface area material with twice
  the heat of adsorption of H2 on graphite.

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US Model Government Research Investment leading
to Commercial Exploitation
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Radical Model

• Public awareness of consequences of global
  warming
• London, Newcastle flooded
• Drought in Africa
• Mass migration
• Maximise investment rate at political limit
• Choose investment based on current costs (i.e.
  ignore nuclear waste disposal costs)

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Macroscopic studies of hydrogen absorption in
solids at Salford

• Use either gravimetric or volumetric methods.
• Gravimetric best where there is possible
  outgassing from the solid needing high vacuum and
  baking
• We use the IGA or Intelligent Gravimetric
  Analysis method where gas pressure and sample
  temperature are controlled by computer
• Volumetric best at high pressures and
  temperatures
• Sieverts apparatus, using calibrated volumes and
  Boyles law to calculate gas absorbed by solid

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The IGA instrumental set up
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IGA data for a hydrogen battery AB5 alloy
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Comparison of the gradient of the isotherm with
the time constant for the absorption process
showing that the time constant is dominated by
the Chemical Diffusion Coefficient
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Neutron Scattering Studies of Hydrogen storage
systems

• Because the neutron scattering cross section for
  hydrogen is thirty times bigger than most other
  isotopes, H properties easily seen in neutron
  scattering

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Coherent and Incoherent Scattering

• Because neutrons interact with the nucleus, the
  amplitude of the scattered beam can vary between
  different nuclei of the same element.
• Also, the interaction depends on whether the
  neutron spin is parallel or anti-parallel to the
  nuclear spin
• Hence ltal2gt ? ltalgt2 and the diffraction
  intensity depends only on ltalgt2
• ds/dO (ltal2gt - ltalgt2 )
• Sl ltalgt(Q)exp( i Q.l)2 d(Q-t)
• ltagt zero for hydrogen so have to use deuterium
  for determining hydrogen positions

coherent
incoherent
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Inelastic Neutron scattering from Hydrogen

• Scattering from hydrogen is very strong and is
  incoherent (no interference)
• Neutron can exchange energy with a hydrogen mode
  of vibration (like Raman scattering)
• But no selection rules so peak areas are directly
  proportional to the number of modes
• Hence we can calculate the inelastic neutron
  scattering directly from an ab initio calculation
  
• Particularly useful for studies of molecular
  hydrogen on surfaces

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Inelastic neutron scattering from molecular
hydrogen adsorbed on surfaces

• Hydrogen molecules are either ortho- (nuclear
  spins parallel) or para-(nuclear spins
  antiparallel)
• Para-hydrogen has angular momentum states of
  l0,2,4..
• Ortho-hydrogen has angular momentum states of l
  1,3,5..
• Energy difference between l0 and l1 is 14.7 meV
• Only significant scattering from paraH is from
  L0 to l1,3

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Inelastic neutron scattering from H2 on carbon
nanotubes
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Expanded plot of the inelastic peaks showing
structure in the peak due to the quantum states
on the surface of the nanotubes. As hydrogen is
added to the surface, new sites can be seen
Georgiev et al Carbon 43 (2005) 895-906
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High Surface Coverage (gt100)
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Recent WorkINS Ion-exchanged Zeolites
Collaborators David Book, Paul Anderson
Birmingham University Philip Mitchell Reading
University Timmy Ramirez-Cuesta ISIS Facility