Francis J. DiSalvo

Structurally ordered intermetallic platinum–cobalt core–shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts

To enhance and optimize nanocatalyst performance and durability for the oxygen reduction reaction in fuel-cell applications, we look beyond Pt-metal disordered alloys and describe a new class of Pt-Co nanocatalysts composed of ordered Pt(3)Co intermetallic cores with a 2-3 atomic-layer-thick platinum shell. These nanocatalysts exhibited over 200% increase in mass activity and over 300% increase in specific activity when compared with the disordered Pt(3)Co alloy nanoparticles as well as Pt/C. So far, this mass activity for the oxygen reduction reaction is the highest among the Pt-Co systems reported in the literature under similar testing conditions. Stability tests showed a minimal loss of activity after 5,000 potential cycles and the ordered core-shell structure was maintained virtually intact, as established by atomic-scale elemental mapping. The high activity and stability are attributed to the Pt-rich shell and the stable intermetallic Pt(3)Co core arrangement. These ordered nanoparticles provide a new direction for catalyst performance optimization for next-generation fuel cells.

Ordered mesoporous materials from metal nanoparticle-block copolymer self-assembly

The synthesis of ordered mesoporous metal composites and ordered mesoporous metals is a challenge because metals have high surface energies that favor low surface areas. We present results from the self-assembly of block copolymers with ligand-stabilized platinum nanoparticles, leading to lamellar CCM-Pt-4 and inverse hexagonal (CCM-Pt-6) hybrid mesostructures with high nanoparticle loadings. Pyrolysis of the CCM-Pt-6 hybrid produces an ordered mesoporous platinum-carbon nanocomposite with open and large pores (≥10 nanometers). Removal of the carbon leads to ordered porous platinum mesostructures. The platinum-carbon nanocomposite has very high electrical conductivity (400 siemens per centimeter) for an ordered mesoporous material fabricated from block copolymer self-assembly.

Solid-state chemistry: a a rediscovered chemical frontier.

Chemical bonding in solids is not completely understood, mainly because of the wide variation in the chemical properties of the elements. Many difficult challenges remain in predicting the composition, structure, and the properties of new materials. Consequently, the synthesis of novel solids is as much an art as a science. Discoveries of new compounds and structure types highlight the versatility that nature has allowed with the relatively small number of elements. This article explores the long-term challenges in solid-state chemistry and then focuses on efforts at Cornell to prepare new solids.

Amylopectin wrapped graphene oxide/sulfur for improved cyclability of lithium-sulfur battery.

An amylopectin wrapped graphene oxide-sulfur composite was prepared to construct a 3-dimensionally cross-linked structure through the interaction between amylopectin and graphene oxide, for stabilizing lithium sulfur batteries. With the help of this cross-linked structure, the sulfur particles could be confined much better among the layers of graphene oxide and exhibited significantly improved cyclability, compared with the unwrapped graphene oxide-sulfur composite. The effect of the electrode mass loading on electrochemical performance was investigated as well. In the lower sulfur mass loading cells, such as 2 mg cm(-2), both the capacity and the efficiency were obviously better than those of the higher sulfur mass loading cells, such as 6 mg cm(-2).

Intermetallics as Novel Supports for Pt Monolayer O2 Reduction Electrocatalysts: Potential for Significantly Improving Properties

We report on a new class of core-shell electrocatalysts for the oxygen-reduction reaction. These electrocatalysts comprise a Pt monolayer shell and ordered intermetallic compounds cores and have enhanced activity and stability compared with conventional ones. These advantages are derived from combining the unique properties of Pt monolayer catalysts (high activity, low metal content) and of the intermetallic compounds (high stability and, possibly, low price). This method holds excellent potential for creating efficient fuel cell electrocatalysts.

Electrocatalytic Performance of Fuel Oxidation by Pt3Ti Nanoparticles

A Pt-based electrocatalyst for direct fuel cells, Pt3Ti, has been prepared in the form of nanoparticles. Pt(1,5-cyclooctadiene)Cl2 and Ti(tetrahydrofuran)2Cl4 are reduced by sodium naphthalide in tetrahydrofuran to form atomically disordered Pt3Ti nanoparticles (FCC-type structure: Fm3m; a = 0.39 nm; particle size = 3 +/- 0.4 nm). These atomically disordered Pt3Ti nanoparticles are transformed to larger atomically ordered Pt3Ti nanoparticles (Cu3Au-type structure: Pm3m; a = 0.3898 nm; particle size = 37 +/- 23 nm) by annealing above 400 degrees C. Both atomically disordered and ordered Pt3Ti nanoparticles show lower onset potentials for the oxidation of formic acid and methanol than either pure Pt or Pt-Ru nanoparticles. Both atomically disordered and ordered Pt3Ti nanoparticles show a much lower affinity for CO adsorption than either pure Pt or Pt-Ru nanoparticles. Atomically ordered Pt3Ti nanoparticles show higher oxidation current densities for both formic acid and methanol than pure Pt, Pt-Ru, or atomically disordered Pt3Ti nanoparticles. Pt3Ti nanoparticles, in particular the atomically ordered materials, have promise as anode catalysts for direct fuel cells.

One-pot synthesis of platinum-based nanoparticles incorporated into mesoporous niobium oxide-carbon composites for fuel cell electrodes.

Catalyst-electrode design is crucial for the commercialization and widespread use of polymer electrolyte membrane fuel cells. There are considerable challenges in making less expensive, more durable, and more active catalysts. Herein, we report the one-pot synthesis of Pt and Pt-Pb nanoparticles incorporated into the pores of mesoporous niobium oxide-carbon composites. The self-assembly of block copolymers with niobium oxide and metal precursors results in an ordered mesostructured hybrid. Appropriate heat treatment of this hybrid produces highly crystalline, well-ordered mesoporous niobium oxide-carbon composites with Pt (or Pt-Pb) nanoparticles incorporated into the mesopores. The in situ-generated graphitic-like carbon material prevents the collapse of the mesostructure, while the metal oxide crystallizes at high temperatures and enhances the electrical conductivity of the final material. Formic acid electrooxidation with this novel material shows 4 times higher mass activities (3.3 mA/microg) and somewhat lower onset potentials (-0.24 V vs Ag/AgCl) than the best previously reported values employing Pt-Pb intermetallic nanoparticles supported on conducting carbon (0.85 mA/microg and -0.18 V, respectively).

Highly Stable and CO-Tolerant Pt/Ti0.7W0.3O2 Electrocatalyst for Proton-Exchange Membrane Fuel Cells

The current materials used in proton-exchange membrane fuel cells (PEMFCs) are not sufficiently durable for commercial deployment. One of the major challenges lies in the development of an inexpensive, efficient, and CO-tolerant anode catalyst. Here we report the unique CO-tolerant property of Pt nanoparticles supported on Ti(0.7)W(0.3)O(2). The Ti(0.7)W(0.3)O(2) nanoparticles (50 nm) were synthesized via a sol-gel process and platinized using an impregnation-reduction technique. Electrochemical studies of Pt/Ti(0.7)W(0.3)O(2) show unique CO-tolerant electrocatalytic activity for hydrogen oxidation compared to commercial E-TEK PtRu/C catalysts. Differential electrochemical mass spectrometry measurements show the onset potential for CO oxidation on Pt/Ti(0.7)W(0.3)O(2) to be below 0.1 V (vs RHE). Pt/Ti(0.7)W(0.3)O(2) is a promising new anode catalyst for PEMFC applications.

Ternary nitrides: a rapidly growing class of new materials

Abstract Recent advances have been made in search on the synthesis and structure of ternary nitrides. The majority of these phases contain discrete nitridometallate anions and are usually electrical insulators. The remainder, with extended structures, may have useful electronic or physical properties.

Powerful oxidizing agents for the oxidative deintercalation of lithium from transition-metal oxides

Abstract NO + 2 and MoF 6 are shown to be powerful oxidizing agents for the deintercalation of lithium from LiCoO 2 and Li 2 CuO 2 . The oxidations, which usually were accompanied by some side reaction, yielded materials of composition Li x M O 2 with x ∼ 0 for M = Co and x ∼ 1.5 for M = Cu. Both starting materials are insulating (ϱ > 10 3 Ω cm), but the deintercalated products are much more conducting (by at least four orders of magnitude).