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Fuel Cells and a Nanoscale Approach to Materials Design

Fuel Cells and a Nanoscale Approach to Materials Design. Chris Lucas Department of Physics. Outline PEM fuel cells (issues) A nanoscale approach to materials design. What is a fuel cell?. A fuel cell is an electrochemical energy conversion device

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Fuel Cells and a Nanoscale Approach to Materials Design

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  1. Fuel Cells and a Nanoscale Approach to Materials Design Chris Lucas Department of Physics Outline PEM fuel cells (issues) A nanoscale approach to materials design

  2. What is a fuel cell? • A fuel cell is an electrochemical energy conversion device • It converts hydrogen and oxygen into water and produces electricity • The chemicals (fuel) flow continuously unlike in a battery • Several types: • PEM (transportation applications) • Solid oxide fuel cell (stationary applications, co-generation of heat and power)

  3. Hydrogen Cars: Fad or the Future? Science, June 2009

  4. Hydrogen Cars: Fad or the Future? Science, June 2009

  5. PEM Fuel Cell Technology Proton Exchange Membrane or Polymer Electrolyte Membrane • Membrane is a permeable polymer sheet which allows protons (H atoms) to pass through • Operate at low temperatures with high power density • Low cost, small size, high performance • Ideal for transportation, stationary and portable applications

  6. Energy Storage and Conversion: Fuel Cells Efficiency issues: Membrane transport Anode: Impurity-tolerant catalyst Cathode: A good catalyst for oxygen reduction reaction (ORR) (1/2O2+2H++2e- = H2O) Nanoscale and Surface Physics: Catalyst Materials by Design

  7. Catalyst Issues (1) Substantial overpotential for the ORR reduces the thermal efficiency to 43% at 0.7 V [compared to 87% at reversible ORR potential (1.23 V)] (2) Pt is expensive (Pt-loading) (3) Performance degrades too quickly due to dissolution (stability issue) Question: Can we use modern experimental methods to design a nanoscale catalyst?

  8. Tailoring surface properties at the atomic level Bimetallic Pt-alloy surfaces - Pt3M Bifunctional effects: Ptfor catalysis Mto do something else? Effects can be: (1) Ensemble (2) Electronic Nanoscale and Surface Physics: Catalyst Materials by Design

  9. Modern Experimental Methods • UHV preparation and characterization • Transfer to liquid environment for activity measurements • Transfer back to observe changes-or even better, have a look in-situ • Polycrystalline materials • Single crystals

  10. Trends in catalytic activity across the Periodic Table(3d metals) Strong link between atomic/electronic structure and activity both from theory and experiment (d-band center is proportional to adsorption strength) Nature Materials, v6, p241 (2007)

  11. Model Electrocatalysts: Pt3Ni crystals

  12. Model Electrocatalysts: Pt3Ni crystals

  13. Key results from combined studies: • Surfaces are 100% Pt • (2) Segregated surfaces are stable during reactions • (3) Activity depends on atomic geometry Science, v315, p493 (2007)

  14. Real catalysts are nanoparticle arrays Nanoscale and Surface Physics: Catalyst Materials by Design

  15. TEM shows nanoparticles governed by ECS

  16. DFT and Monte-Carlo calculations for nanoparticles These nanoparticles have yet to be engineered

  17. Just a Dream-or Future Reality? Turnover frequency = number of electrons per active site per second Nitrogen coordinated Fe in a carbon matrix now matches Pt/C Science, v324 (April, 2009)

  18. Summary • Fuel cells offer significant potential climate and energy security benefits • Materials design from fundamental nanoscale studies • This approach could be used in a range of materials (and energy) applications Note: The University of Birmingham is the only UK institution to work on all aspects of Hydrogen energy research

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