Istvan Robel

Structural changes and catalytic activity of platinum nanoparticles supported on C60 and carbon nanotube films during the operation of direct methanol fuel cells

Comparison of the structure and activity of Pt nanoparticles anchored on two nanostructured carbon supports, C60 and carbon nanotubes (CNTs) provides insight into their electrocatalytic activity in direct methanol fuel cells. The local structure of platinum atoms during the initial stages of the catalytic oxidation of methanol was probed using x-ray absorption spectroscopy. A large fraction of the Pt atoms in the Pt–C60 nanocomposite continuously undergoes structural changes during the initial stages of methanol oxidation. The Pt-CNT system, however, proves to be more robust in maintaining its initial morphology and higher electrocatalytic activity. These observations reflect the importance of the carbon support in controlling the catalyst morphology and activity during methanol oxidation.

Quantum Dot Thin-Films as Rugged, High-Performance Photocathodes

Typical use of colloidal quantum dots (QDs) as bright, tunable phosphors in real applications relies on engineering of their surfaces to suppress the loss of excited carriers to surface trap states or to the surrounding medium. Here, we explore the utility of QDs in an application that actually exploits their propensity toward photoionization, namely within efficient and robust photocathodes for use in next-generation electron guns. In order to establish the relevance of QD films as photocathodes, we evaluate the efficiency of electron photoemission of films of a variety of compositions in a typical electron gun configuration. By quantifying photocurrent as a function of excitation photon energy, excitation intensity and pulse duration, we establish the role of hot electrons in photoemission within the multiphoton excitation regime. We also demonstrate the effect of QD structure and film deposition methods on efficiency, which suggests numerous pathways for further enhancements. Finally, we show that QD photocathodes offer superior efficiencies relative to standard copper cathodes and are robust against degradation under ambient conditions.