Nature Inspired Materials Science

Prof. Michael Rubner

Nov. 17, 4:00, 10-250

Reception to follow in the Bush Room, 10-105

Materials Scientists more and more are looking to nature for clues on how to create highly functional materials with exceptional properties. The fog harvesting capabilities of the Namib Desert beetle, the beautiful iridescent colors of the hummingbird, and the super water repellant abilities of the Lotus leaf are but a few examples of the amazing properties developed over many years in the natural world.  Nature also makes extensive use of the pH-dependent behavior of weak functional groups such as carboxylic acid and amine functional groups.  The pH-gated opening and closing of the carboxylate-lined cages of the cowpea chlorotic mottle virus, for example, is an important element of the infection process.  This presentation will explore synthetic mimics to the nano- and microstructures responsible for these fascinating properties.  For example, we have demonstrated a pH-induced porosity transition that can be used to create porous films with pore sizes that are tunable from the nanometer scale to the multiple micron scale.  The pores of these films, either nano- or micropores, can be reversibly opened and closed by changes in solution pH.  The ability to engineer pH-gated porosity transitions in heterostructure thin films has led to the demonstration of broadband anti-reflection coatings that mimic the anti-reflection properties of the moth eye and pH-tunable Bragg reflectors with a structure and function similar to that found in hummingbird wings.  In addition, the highly textured honeycomb-like surfaces created by the formation of micron-scale pores are ideally suited for the creation of superhydrophobic surfaces that mimic the behavior of the self-cleaning lotus leaf.  Techniques to create patterned superhydrophobic/superhydrophilic surfaces have also been developed that make it possible to create planar open microfluidic channels as well as fog-harvesting coatings that mimic the behavior of the Namib Desert beetle.

The Wulff Lecture is an introductory, general-audience, entertaining lecture which serves to educate, inspire, and encourage MIT undergraduates to take up study in the field of materials science and engineering and related fields. The entire MIT community is invited to attend. The Wulff Lecture honors the late Professor John Wulff, a skilled, provocative, and entertaining teacher who inaugurated a new approach to teaching the popular freshman subject: 3.091 Introduction to Solid State Chemistry.

On Oct. 30, Prof. Don Sadoway was interviewed by Living on Earth (WBUR) about his work with liquid metal batteries. The story can be heard here.

Nanocatalyst Engineering: From Well-Defined to Nanoscale Surfaces

Vojislav Stamenkovic

Argonne National Laboratory

Materials Science Division

Argonne, IL USA

Tuesday, November 10, 2009

2:00-3:00pm

Room 31-161

Ability to /tune the electronic and structural properties of nanocatalysts/ can potentially lead towards the superior catalytic enhancement that was reported for the Pt_3 Ni(111)-skin surface [1].

Fine tuning of the surface properties is usually done on extended well-defined surfaces in ultra-high vacuum. A number of surface sensitive tools could be utilized such as AES, LEIS and UPS before controlled transfer into real reaction environment. The single and polycrystalline crystalline well-defined surfaces have been used to benchmark the activity range that could be expected on Pt based electrodes. The knowledge accumulated from well-defined systems is further used to engineer nanoscale surfaces with designated composition and morphology.

It has been proposed that surface modifications induced by the second/third metal, and consequent catalytic enhancements could occur through the following effects: (1) /Electronic effect/, due to changes in the metallic d-band center position vs. Fermi level; and (2) /Structural effect/, which reflects relationship between atomic geometry, and/or surface chemistry, i.e., dissolution – surface roughening. In principle, different near-surface composition profiles have been found to have different electronic structures. Modification in Pt electronic properties alters adsorption/catalytic properties of corresponding materials. The most active systems for the electrochemical oxygen reduction reaction (ORR) are established to be the Pt‑skin near‑surface formation.

The similar levels of catalytic enhancement have been established for corresponding nanoscale materials. In addition to electronic properties we have found how catalytic activity could be affected by the arrangement of surface defects on nanoscale surfaces. Ability to control surface and near surface catalyst properties enables fine tuning of catalytic activity and stability of nanoscale surfaces.

[1] V. Stamenkovic, B. Fowler, B.S. Mun, G. Wang, P.N. Ross, C.A. Lucas, N.M. Markovic, /Science/ 315 (2007) 493-497.

[2] V. Stamenkovic, B.S. Mun, K.J.J. Mayrhofer, P.N. Ross, N.M. Markovic, J. Rossmeisl, J. Greeley, J.K. Nørskov, /Angewandte Chemie International Edition/ 45 (2006) 2897.

[3] V. Stamenkovic, B.S. Mun, M. Arenz, K.J.J. Mayrhofer, C. A. Lucas, G. Wang, P.N. Ross, N.M. Markovic, /Nature Materials/ 6 (2007) 241.

The Opening Session at MS&T featured a panel of speakers actively working in renewable energy. The panelists – who included  Yet-Ming Chiang, past ACerS president and Savannah River National Lab associate director John Marra, and Solar Power Industries’ Gregory Hildeman – spoke on the topic of “New Energy Opportunities for Materials Science and Engineering.”

See the Christian Science Monitor for further coverage of Prof. Don Sadoway’s work on liquid batteries.