Ordered Intermetallics

Fuel Cell

We are involved in extensive efforts to discover new materials for fuel cell applications.

Ordered intermetallic compounds have been shown to exhibit remarkable electrocatalytic activity for both fuel oxidation and oxygen reduction in terms of onset potential and current density. They need to be prepared in nanoparticle form, so as to have increased surface area, which is the most effective way of increasing activity per amount of precious metals. We have prepared nanoparticles of ordered intermetallic phases by reducing metal oxides or salts using various powerful reducing agents. Our group has designed, synthesized and characterized a series of Pt/Pd-based intermetallic nanoparticles, and investigated on their structure and catalytic activity. For example, Pt3Co core-shell ordered intermetallic particles exhibited over 200% increase in mass activity compared to disordered Pt3Co alloy and commercially available Pt nanoparticles, and showed minimal loss of activity and structure after 5,000 cycles[1].

Figure 1. ORR polarization curves for Pt/C, Pt3Co/C (annealed at 400°C) and Pt3Co/C (prepared at 700°C) in O2-saturated 0.1 M HClO4 at room temperature, with rotation rate, 1,600 rpm and sweep rate, 5 mV s−1. b, The Koutecky–Levich plots from ORR data for Pt3Co/C-700 at different potentials. The inset in b shows the rotation-rate-dependent current–potential curves. c, Comparison of mass activities for Pt/C, Pt3Co/C-400 and Pt3Co/C-700 at 0.85 and 0.9 V. d, Comparison of specific activities (Ik).

Figure 1. ORR polarization curves for Pt/C, Pt3Co/C (annealed at 400°C) and Pt3Co/C (prepared at 700°C) in O2-saturated 0.1 M HClO4 at room temperature, with rotation rate, 1,600 rpm and sweep rate, 5 mV s−1. b, The Koutecky–Levich plots from ORR data for Pt3Co/C-700 at different potentials. The inset in b shows the rotation-rate-dependent current–potential curves. c, Comparison of mass activities for Pt/C, Pt3Co/C-400 and Pt3Co/C-700 at 0.85 and 0.9 V. d, Comparison of specific activities (Ik).

Figure 2. The chemical microstructure of the surface of the Pt-rich Pt3Co/C-700 nanoparticles was examined using electron energy loss spectroscopic (EELS). It can be seen that its structure is highly ordered with 5nm-Pt shell, which is 2–3 atomic layers.

Figure 2. The chemical microstructure of the surface of the Pt-rich Pt3Co/C-700 nanoparticles was examined using electron energy loss spectroscopic (EELS). It can be seen that its structure is highly ordered with 5nm-Pt shell, which is 2–3 atomic layers.

Nanoparticle synthesis is also the final step of our combinatorial material exploration, because nanoparticles are what will be used in fuel cell stacks to maximize surface area and therefore mass activity.

Battery

The Abruña group is involved in synthesis and characterization of new materials for advanced energy storage technologies. In these efforts, we make use of many fruitful collaborations through the {html link: EMC2 program} at Cornell, and with other academic and industrial partners.

Graphite-based anodes dominate the market for lithium ion batteries because lithiated graphite exhibits good capacity, superior cycling performance, and low cost. Nevertheless, new anode materials are needed in order to improve safety and energy density in lithium batteries for vehicle and grid-level storage applications. We are working toward advanced new anode materials for lithium batteries. For example, we have reported a facile method of preparing Mn3O4[1], which showed stabilized reversible capacity twice as large as that of graphite over 40 charge/discharge cycles.

Solid electrolytes are also of great interest for next generation batteries. Using solid electrolytes can mitigate safety concerns in advanced lithium batteries by decreasing flammability and mitigating dendrite formation in batteries with metallic lithium anodes. However, no solid material has yet exhibited sufficient ionic conductivity and chemical stability under operating battery conditions. In collaboration with the DiSalvo group, we have recently begun exploring new oxide materials to use as solid-electrolytes in rechargeable batteries.

Citations

  1. Wang, D.; Xin, H. L.; Hovden, R.; Wang, H.; Yu, Y.; Muller, D. A.; DiSalvo, F. J.; Abruña, H. D. Nature Materials 2013, 12, 81–87.
  2. Yu, Y.; Wang, D.; Abruña, H. D.; Muller, D. A. Microsc. Microanal. 2012, 18, 1306-1307.
  3. Chen, H., Wang D., Yu, Y, Newton K., Muller D, Abruña H. D., DiSalvo J. F.;, J. Am. Chem. Soc. (2012), 134(44), 18453-18459.
  4. Wang D., Yu Y.,. Xin H. L., Hovden R., Ercius P., Mundy J. A., Chen H., Richard J. H., Muller D. A., DiSalvo F. J., Abruña H. D.; Nano Lett. (2012), 12(10), 5230-5238.