In situ XAFS studies of carbon supported Pt and PtNi(1:1)
 catalysts for the oxygen reduction reaction in PEMFCs


Qingyin...
Outline



          •   Motivation
          •   Experimental Details
          •   XANES Results
          •   EXAFS Int...
Polymer Exchange Membrane Fuel Cell

                                            Anode : 2H2 → 4H+ + 4e- (0V SHE)

       ...
Why PtNi?


 • Uses less platinum (less expensive)
 • Oxygen reduction reaction is improved
    –   Pt electronic structur...
Operando Fuel Cell Experiment


• Version 2 operando cell
• Air-breathing cathode
• Pd on anode
• 1.2 mg/cm2 loading
• 50°...
Fuel Cell Performance




    • PtNi/Pd shows higher open circuit voltage
    • Pt/Pd and PtNi/Pd have similar performance...
Data Quality: Pt edge in Pt/C




                             • Merge of 10-20 scans
                             • Data ...
Data Quality: Ni edge in PtNi/C




                             • Merge of 10-20 scans
                             • Dat...
Pt/C and PtNi/C Comparison




                      Nov. 13, 2009
Structural Model: part 1

   • “First” shell model
      – Pt/C: Pt-Pt; Pt-O
      – PtNi/C: Pt-Pt; Pt-Ni; Ni-Ni; Ni-O
   ...
Structural Model: part 2

      Attempt to get global information about oxygen

 • Fit all potentials with same metal core...
Example Fits




               Nov. 13, 2009
Fit Results: metal core




                          Nov. 13, 2009
Fit Results: oxygen coordination




                        Nov. 13, 2009
Conclusions: what does Ni do?


•   Resides predominantly in metal core of nanoparticle
•   Eliminates static Pt-O bonds a...
Further Work
  – Understand strain and ligand effects by Feff calculations
  – Analyzable data in just 1 scan (can look at...
Thank You!




      Nov. 13, 2009
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In situ XAFS studies of carbon supported Pt and PtNi(1:1) catalysts for the oxygen reduction reaction in PEMFCs

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it\'s a presentation for APS Meeting In Iowa. It mainly introduces our work of rationalizing the superior reactivity of certain commercial alloy nanocatalysts by probing their physical and chemical properties through x-ray experiments and theoretical model simulation.

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In situ XAFS studies of carbon supported Pt and PtNi(1:1) catalysts for the oxygen reduction reaction in PEMFCs

  1. 1. In situ XAFS studies of carbon supported Pt and PtNi(1:1) catalysts for the oxygen reduction reaction in PEMFCs Qingying Jia1, Emily Lewis2, Corey Grice3, Eugene Smotkin2, Carlo Segre1 1 CSRRI & BCPS Dept., Illinois Institute of Technology 2 Chemistry Department, Northeastern University 3 Nuvant Systems, Inc. Sponsors: Department of Energy & Army Research Office Nov. ૧૩, ૨૦૦૯
  2. 2. Outline • Motivation • Experimental Details • XANES Results • EXAFS Interpretation • Conclusions • Further Work Nov. ૧૩, ૨૦૦૯
  3. 3. Polymer Exchange Membrane Fuel Cell Anode : 2H2 → 4H+ + 4e- (0V SHE) Cathode :O2 + 4H+ + 4e- → 2H2O (1.229V SHE) (a) O2 + Pt → Pt―O2 (b) Pt-O2 + H+ + e- → Pt―O2H (c) Pt―O2H + Pt → Pt―OH + Pt―O (d) Pt―OH + Pt―O + 3H+ + 3e- → 2Pt + 2H2O U.S. Department of Defense (DoD) Fuel Cell Test and Evaluation Center (FCTec) Takako Toda et al. J. Electrochem Soc. 146 (10) 3750-3756 (1999) Nov. ૧૩, ૨૦૦૯
  4. 4. Why PtNi? • Uses less platinum (less expensive) • Oxygen reduction reaction is improved – Pt electronic structure modified – Pt catalyst geometric structure is modified – Static oxygen adsorbates inhibited – Pt segregation onto Surface – Overpotential reduced XAFS can address these Nov. 13, 2009
  5. 5. Operando Fuel Cell Experiment • Version 2 operando cell • Air-breathing cathode • Pd on anode • 1.2 mg/cm2 loading • 50°C operating temperature • Pt L3 and Ni K edges • Continuous scan (1-2 min) mode @ Nov. 13, 2009
  6. 6. Fuel Cell Performance • PtNi/Pd shows higher open circuit voltage • Pt/Pd and PtNi/Pd have similar performance Nov. 13, 2009
  7. 7. Data Quality: Pt edge in Pt/C • Merge of 10-20 scans • Data good to k=13 • Oxygen peak just below 2 Å Nov. 13, 2009
  8. 8. Data Quality: Ni edge in PtNi/C • Merge of 10-20 scans • Data good to k=11 Nov. 13, 2009
  9. 9. Pt/C and PtNi/C Comparison Nov. 13, 2009
  10. 10. Structural Model: part 1 • “First” shell model – Pt/C: Pt-Pt; Pt-O – PtNi/C: Pt-Pt; Pt-Ni; Ni-Ni; Ni-O • 2.76 Å- 1 < k < 10.83 Å- 1 • 1.3 Å < R < 3.3 Å • Fit each edge & potential individually Metal cluster core is constant for both catalysts Pt-O path not stable in PtNi/C Metal-Oxygen σ2 large Nov. 13, 2009
  11. 11. Structural Model: part 2 Attempt to get global information about oxygen • Fit all potentials with same metal core parameters for each catalyst • Simultaneous fit of Pt and Ni edges in PtNi/C with constraint on Pt-Ni path • Fit in k, k2, and k3 weighting simultaneously • M-O path constraints – length common across potentials – σ2 fixed to 0.01 – Pt-O in PtNi/C are refined with a single occupation # Nov. 13, 2009
  12. 12. Example Fits Nov. 13, 2009
  13. 13. Fit Results: metal core Nov. 13, 2009
  14. 14. Fit Results: oxygen coordination Nov. 13, 2009
  15. 15. Conclusions: what does Ni do? • Resides predominantly in metal core of nanoparticle • Eliminates static Pt-O bonds at all potentials • Number of O near neighbors “increases” with potential • Lengthens Pt-O and shortens Pt-Pt bond • Reduces Pt white line in most reduced state (0 mV) • Open circuit voltage is increased (reduction in overpotential) Nov. 13, 2009
  16. 16. Further Work – Understand strain and ligand effects by Feff calculations – Analyzable data in just 1 scan (can look at time evolution) Nov. 13, 2009
  17. 17. Thank You! Nov. 13, 2009

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