The limited stability of carbon‐supported Pt catalysts for the oxygen reduction reaction is a key obstacle for their commercial application in fuel cells. Here we report on the properties of a tungsten‐modified Pt/C catalyst that shows enhanced stability under potential cycling conditions compared to a reference Pt/C catalyst. Although routine structural investigation by XRD and TEM show an inhomogeneous distribution of tungsten species on the modified catalyst surface, X‐ray photoelectron spectroscopy points to an overall changed catalytic behavior of Pt nanoparticles. Aberration‐corrected atomic‐scale imaging reveals the presence of homogeneously dispersed tungsten atomic species that decorate the surface of the carbon support and the Pt nanoparticles. The presented results demonstrate that detailed and localized imaging at the atomic scale is essential for the identification of the relevant species amongst spectator phases and thus, for the understanding of the improved integral behavior of a modified catalyst.

Many nanoscale systems are known to emit light intermittently under continuous illumination. In the fluorescence of single semiconductor nanoparticles, the distributions of bright and dark periods ('on' and 'off' times) follow Lévy statistics. Although fluorescence from single-quantum dots and from macroscopic quantum dot ensembles has been studied, there has been little study of fluorescence from small ensembles. Here we show that blinking nanorods (NRs) interact with each other in a cluster, and the interactions affect the blinking statistics. The on-times in the fluorescence of a NR cluster increase dramatically; in a cluster with N NRs, the maximum on-time increases by a factor of N or more compared with the combined signal from N well-separated NRs. Our study emphasizes the use of statistical properties in identifying the collective dynamics. The scaling of this interaction-induced increase of on-times with number of NRs reveals a novel collective effect at the nanoscale.

Since its initial discovery just over a decade ago, blinking of semiconductor nanocrystals has typically been described in terms of probability distributions for durations of bright, or "on," states and dark, or "off," states. These distributions are obtained by binning photon counts in order to construct a time series for emission intensity and then applying a threshold to distinguish on states from off states. By examining experimental data from CdSe/ZnS core/shell nanocrystals and by simulating this data according to a simple, two-state blinking model, we find that the apparent truncated power-law distributions of on times can depend significantly on the choices of binning time and threshold. For example, increasing the binning time by a factor of 10 can double the apparent truncation time and change the apparent power-law exponent by 30%, even though the binning time is only 3% of the truncation time. Our findings indicate that stringent experimental conditions are needed to accurately determine blinking-time probability distributions. Similar considerations should apply to any phenomenon characterized by time series data that displays telegraph noise.

This paper reports about FeAgMo2O8 — a novel oxygen evolution catalyst material for secondary (rechargeable) metal–air batteries. Bifunctional air electrodes were made using FeAgMo2O8 as a charging catalyst for oxygen evolution reaction (OER) and silverized carbon black (Ag/C) was employed as a discharging catalyst for oxygen reduction reaction (ORR). Corresponding air electrodes were investigated using 10M KOH as an electrolyte. At current densities between 20 and 50mA per cm2 we observed discharging and charging voltages of 1.20 to 1.15V and 1.96 to 2.05V, respectively.

Semiconductor nanocrystals have a wide range of applications as light emitters, especially in biomedical imaging. Elongated core-shell CdSe-based nanocrystals (nanorods) are particularly interesting as fluorescent markers because of their large absorption cross,section, large surface area, and high brightness. While light intermittency ("blinking") in single nanorods has been studied previously, here we report the fluorescence properties of core-shell CdSe-based nanorod clusters. The time-dependent cluster fluorescence was correlated with the particle number by direct particle counting (from single nanoparticles to similar to 10 000), cluster area, and the orientation and distribution of individual nanorods within these clusters. This was uniquely enabled by combined transmission electron and atomic force microscopy. In contrast to the "on/off" emission in single nanorods, we show that nanorod clusters containing as few as five nanorods exhibit a nonzero residual fluorescence in the "dark state"; that is, they can be "on" continuously, within the measurement time window of several tens of minutes. With increasing particle number, the cluster fluorescence increases in intensity and the relative fluorescence fluctuations, originating from single particle events, decrease in accordance with the central limit theorem. We report the effects of assembly patterns and nanorod orientation (on the silicon nitride substrate and relative to the laser polarization) on the fluorescence properties of the clusters. The fluorescence time-dependence of nanorod clusters at long time-scales, i.e. tens of hours, follows two characteristic trends depending on particle number and laser intensity. These data are compared to predictions made by a statistical model derived from single-particle dynamics. Finally, to investigate the possible role of charge traps on ensemble properties, we have also confirmed by electrical measurements across nanorod arrays that the electrical current exhibits statistical aging and memory effects. This complementary measurement provides a new way to relate the electrical and optical properties of nanoparticle ensembles and further suggests that filling of charge traps can possibly explain both the fluorescence and the anomalous transport dynamics of core-shell nanorod ensembles.

We report fluorescence of single semiconductor nanorods (NRs) and few-NR clusters, correlated with transmission electron microscopy for direct determination of the number of NRs present in a single fluorescent source. For samples drop-cast from dilute solutions, we show that the majority of the blinking sources (approximately 75%) are individual NRs while the remaining sources are small clusters consisting of up to 15 NRs. Clusters containing two or three NRs exhibit intermittent fluorescence intensity trajectories, I(t), similar to those of individual NRs. The associated statistical parameters of on- and off-time probability densities for two- and three-NR clusters are indistinguishable from those of individual NRs. In contrast, statistically distinguishable blinking parameters are observed for clusters of five or more particles. In particular, the "truncation time" of the on-time probability density, i.e., the time characterizing the transition from a power law to an exponential decay, was found to increase superlinearly with the number of particles. Our long (2.4 x 10(4) s) blinking measurements also directly reveal the previously unobserved truncation of the power law distribution of the off-times for single nanoparticles.

Solid-state CdSe nanorod (NR) smectic superstructures (see figure) on a millimeter scale are achieved by exploiting capillary flow kinetics of a drying droplet. NRs assemble side-to-side into micrometer-long "tracks", acting as individual building blocks that assemble by capillary forces into smectic superstructures. The size of the superstructures and the short drying time makes the capillary-flow mechanism of ordered self-assembly attractive for general NR-superstructure studies and applications.