Transcript Hydrogen fuel cells - University of Groningen

Nanotechnology in Hydrogen Fuel
Cells
By Morten Bakker
"Energy & Nano" - Top Master in Nanoscience Symposium
17 June 2009
Overview
Fuel cells
Main concerns
Nanotechnology applications
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Fuel Cells
William Robert Grove (1842)
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Fuel Cells: 815.000 hits
(scholar.google)
2008: >1 billion US$ in FC
research
"Energy & Nano" - Top Master in Nanoscience Symposium
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Working principle
Electrochemical energy conversion
Electrical current
Fuel
(H2)
H+
Oxidant
(O2)
H+
Unused fuel
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Anode Electrolyte Cathode
"Energy & Nano" - Top Master in Nanoscience Symposium
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Exhaust
(H2O)
Different types
Fuel: hydrocarbons (also alcohols), hydrogen, etc
Oxidant: chlorine, chlorine dioxides, oxygen, etc..
Electrolyte: aqueous alkaline solution, polymer
membrane, molten carbonate, ceramic solid
oxide, etc..
Operational temperature: 50°C - 1100°C
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Advantages and Applications
High efficieny energy conversion
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Theoretically 83% at 25°C
High power density
Reliable
Compact
Lightweight
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Why Hydrogen Fuel Cells?
Also called Proton Exhange Membrane/ Polymer
Electrolyte Membrane fuel cell (PEMFC)
Durable, compact
Low temperature (50°C -100°C), fast start-up
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Hydrogen fuel economy
 Especially transportation
applications
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Important components of PEMFC
Proton Exchange Membrane (PEM)
Electrodes (Catalysts)
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Proton Exchange Membrane (PEM)
Conduct H+, but no eIonomer
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Polymer with ionic properties
Nafion
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Teflon backbone with sulfonic groups
The inventor of Nafion:
Walther Grot
(DuPont)
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Transport through Membrane
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Thin film (~20-100 µm)
Hydrated (depends on temperature)
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Water channel model
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Inverted-micelle cylinders
Ionic groups line up in water
channel
Protons ‘hop’ from one acid site
to another
Crystallites provide strength
[Schmidt-Rohr, Chen, Nat Mat, 7, (2008), 75-83]
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Challenges
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Thermal balance: want to operate at higher
temperature
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Better cooling possible
Better heat recovery
Reduce CO poisoning (H2 reforming)
US Dept. of Energy: 120°C
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Problem: water management
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Improving Conductivity
Add acidic nanoparticles (SiO2, TiO2, Zr(HPO4)2)
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Increased water content
Improved proton conductivity
Operate at higher temperatures
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Cell resistance (Ω cm2)
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Current density (A cm-2)
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Temperature (°C)
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Voltage (V)
[Baglio et al., Fuel Cells, (2008)]
Add Pt nanoparticles
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Not sustain water, but generate it: self-humidifying
Pt-PDDA/ PTFE (Teflon)/ Nafion composite
membrane
Pt particles ~3 nm
Permeating H2 and O2 generates water
Voltage (V)
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[Liu et al., J. Membr. Sc., 330, 357-362, (2009)]
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Current density (A cm-2)
Electrodes
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Consist of Carbon, with Platinum catalyst
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Anode (H2): fast oxidation
Cathode (O2): slower reduction, critical component
Disadvantages:
 Cost
 CO poisoning (H2 reforming)
Reduce cost: increase Pt utilization
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Nanoparticles
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High-surface area: Carbon powder or Carbon
nanotubes
Reduction of Pt-salt in solution
Nanoparticles attached to C backbone
[Liu et al., J. Pow. Sources, 139, 73-78, (2005)]
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More advanced Nanostructures
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Activity = Surface x Surface reactivity
Nanoparticles
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Bulk Pt
Use other nanostructures.
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Pt Nanowires
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Voltage (V)
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1-D nanowires
Lower surface area,
but increased activity
Current density (A cm-2)
[Sun et al., Adv. Mat., 20, 3900-3904, (2008)]
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Replace noble metals
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Replace electrode with Nitrogen-doped carbon
nanotube arrays
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Vertically aligned nitrogen-doped carbon
nanotubes (VA-NCNT’s)
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Prepared by pyrolysis of
iron (II) phthalocyanine plus
NH3 vapour
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Self assembly on
quartz substrate
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N2 induces increased
O2 chemisorption
[Gong et al., Science, 323, 760 (2009)]
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Increased performance
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Increased catalysis
(Air-saturated 0.1 M KOH)
 Pt: 1.1 mAcm-2 at -0.29 V
 VA-NCNT’s: 4.1 mAcm-2 at -0.22 V
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No CO poisoning
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High-surface area, good
electrical, mechanical and
thermal properties
time (s)
[Gong et al., Science, 323, 760 (2009)]
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Summary
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Add nanoparticles to membrane
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Improved performance, operational temperature
Increased cost
Nanostructured Pt electrodes, N2 doped CNT’s
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Improved catalysis
Decreased cost
"Energy & Nano" - Top Master in Nanoscience Symposium
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Conclusions
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Interesting and growing field of research
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Nanotechnology essential for future developments
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Problems:
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Infrastructure (storage)
Sustainable H2 source
"Energy & Nano" - Top Master in Nanoscience Symposium
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Thank you for your attention!
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I would like to especially thank Prof. Petra Rudolf
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Questions?
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