Subject: Platinum Monolayer Electrocatalysts: Tuning Activity Using Core-Shell Interactions

Time: 10:00-12:00 Mar.12th, 2014

Address: F310, Building A in School of ME

Speaker: Prof. Dr. Radoslav R. Adzic (Senior Chemist, Electrochemistry Group Leader, Chemistry Department, Brookhaven National Laboratory; Adjunct Professor, Stony Brook University)

Inviter: Prof. Zhang Junliang 

Abstract:
Although considerable advances in developing fuel cell catalysts were made over the last fifteen years, the amount of platinum used in electrocatalysts for the oxygen-reduction reaction (ORR) at fuel-cell cathodes remains large because of its insufficient catalytic activity and stability. In meeting the challenges involving the high content of Pt, and the insufficient activity and stability of existing electrocatalysts, we developed Pt monolayer (PtML) electrocatalysts consisting of a single-layered shell of Pt atoms on cores of metal- or alloy- nanoparticles. The Pt monolayer electrocatalysts offer several uniquely attractive properties including an ultra-low Pt content, the highest Pt utilization and very high activity. High stability induced by supporting nanoparticle cores, self-healing property and fuel cell tests indicate that these electrocatalysts are ready for application and are established as a viable practical concept. Further improving of these electrocatalysts can be achieved by changing the composition, shape, and size of cores to optimize the core-shell interaction thus tuning their activities. The unique features of PtML electrocatalysts enable a wide selection of substrates to attain an electrocatalyst having low noble-metal content with enhanced catalytic activity and stability. A desired substrate should be able to affect the Pt monolayer by causing a weakening of the Pt-OH bond, a reduction of the OH coverage, and a delay of PtOH formation to more positive potentials than on pure Pt. 
 

The following are some examples of the design of substrates to achieve the above goals: i) Varying the composition to induce strain effect and electronic coupling, ii) Using nanowires as core, iii) Inducing lattice contraction by hollow core structure iv) Reducing the number of low-coordination sites vi) Inducing effects of facets and shapes (Pd tetrahedron core).
 

Atoms at low-coordination sites, i.e., edges, kinks, defects, have been shown to have a stronger binding with OH than those at 2D terrace sites and thus inhibit the oxygen reduction. Those non-registered atoms are also prone to stronger binding with adsorbates and thus prone to dissolution. The nanoparticles with a higher ratio of (111) facets have higher activity for the oxygen reduction reaction. Therefore, a desired nanoparticle core for PtML should possess a high ratio of atoms at (111) facets and less atoms at low-coordination sites. These can be achieved using nanowires, tetrahedral and hollow nanoparticle cores (inducing contraction in a PtML). Fuel cell tests showed that PtML/Pd9Au/C remains active even after 200,000 potential cycles from 0.6-1.0V.
 

Most recently we demonstrated that tensile strain in aPt ML ( PtML/Au(111) ),causes 4-fold enhancement of eythanol and methanol oxidation rates at e given potential, respectively. No CO was detected in the oxidation of methanol on Pt/ Au(111), which is considered a major problem of that reaction.
 

Introduction of Speaker:
Prof. Dr. Radoslav R. Adzic received his B.S. and Ph.D. from University of Belgrade (USA) in 1965 and 1974, respectively; He worked as: Director, Institute of Electrochemistry, ICTM (Research Director 1978-1983; Director 1983–1992); Research Associate, Case Western Reserve University (1971–1973); Visiting Faculty, Case Western Reserve University ( 6-9, 1977; 6-9, 1983); Visiting Professor, Case Western Reserve University (1988–1990); Professor, Center for Multidisciplinary Studies, U. Belgrade (1975–1992); Scientist, Brookhaven National Laboratory (BNL) (1992); Chemist with Tenure ( 2001); Electrochemistry Group Leader (2004); Senior Chemist (2005); Adjunct Professor , Stony Brook University (2006). Dr. Adzic holds 10 issued US patents, 15 applications pending, and has published 270 papers.