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Nanocarbon Supported Catalysts

Goal: To resolve the fundamental and mechanistic complexities of fuel cell processes at electrode interfaces.
Studies: Oxygen Reduction:
      • Synthesis of nitrogen doped carbon nanotubes (NCNTs) that are inherently active for the oxygen reduction reaction (ORR). NCNTs also act as conductive substrates that promote facile dispersion and loading of metal nanoparticles that are active for ORR.
      • Synthesis of dendrimer templated 2 nm size Pt particles and incorporation of dendrimer templated catalysts 1, 2 onto carbon nanotube supports to promote support catalyst synergism for ORR. 
      • Metal organic chemical vapor deposition (MOCVD) of monometallic Pt, Pd and bimetallic PtPd nanocatalysts3 directly onto as- synthesized NCNTs. These NCNT/ catalyst composites were found to exhibit high activity for ORR on par with commercial catalysts of comparable loading.  


Figure 1: TEM image of G4-NH2 Pt-DENs adsorbed on NCNT supports (Scale bar is 20nm).  The inset shows high resolution structure of Pt nanoparticles (Scale bar is 5nm).


Figure 2:  Adsorption isotherms for G4-NH2 Pt-DEN adsorption on undoped CNT and nitrogen-doped CNT (NCNT) supports.


Figure 3: TEM images of PtPd particles deposited by MOCVD on NCNT supports containing 6.5 at. % N. Inset shows high resolution image of a PtPd bimetallic catalyst particle.


Figure 4. Effect of edge plane content in NCNTs (determined from Raman measurements) on PtPd loading as determined by TGA.

Significance: Fuel cells have been the subject of considerable technological interest during the last decade due to their promising application as power sources for energy efficient, non-polluting electric vehicles and portable electronics.4 The main problem limiting commercial application of fuel cells is primarily a result of kinetic constraints in the oxygen reduction and methanol oxidation reactions.

    In the case of oxygen reduction, constraints are imposed by poor oxygen adsorption on the surface of the catalyst and partial reduction of oxygen leading to the formation of the hydroperoxide species. The ability to construct technologically useful devices can be improved by better comprehension of both the mechanistic factors controlling reaction kinetics and the influence of catalyst properties on these reactions.

    Our research, based on the spatial and temporal interrogation of fuel cell catalysts, will permit unprecedented characterization of localized chemical composition and allow the direct establishment of structure/electrochemical-reactivity correlations. Information of this sort will significantly impact the development of superior energy conversion/storage materials, as well as optimize favored chemistries and nanostructures in existing power source materials.

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Students currently involved in this project: Cori Atkinson, Ganesh Vijayaraghavan

References:

  1. Niu, Y., Crooks, R. M., C. R. Chimie., 2003, 6, 1049.
  2. Vijayaraghavan, G., Stevenson, K. J. Langmuir, 2007, 23, 5279.
  3. Vijayaraghavan, G., Stevenson, K. J. Manuscript in preparation.
  4. Vielstich, W., Lamm, A., Gasteiger, H. A., Handbook of Fuel Cells, 2003, Wiley & Sons, Inc., NY, Vol.1.