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Understanding the thermal stability of bimetallic nanoparticles is of vital importance to preserve their functionalities during their use in a variety of applications. In contrast to well-studied bimetallic systems such as Au@Ag, heat-induced morphological and compositional changes in Au@Pt nanoparticles are insufficiently understood, even though Au@Pt is an important material for catalysis. To investigate the thermal instability of Au@Pt nanorods at temperatures below their bulk melting point, we combined in situ heating with two- and three-dimensional electron microscopy techniques, including three-dimensional energy-dispersive X-ray spectroscopy. The experimental results were used as input for molecular dynamics simulations, to unravel the mechanisms behind the morphological transformation of Au@Pt core–shell nanorods. We conclude that thermal stability is influenced not only by the degree of coverage of Pt on Au but also by structural details of the Pt shell.

Single-atom catalysts (SACs) have recently attracted broad scientific interests due to their unique structural feature, the single-atom dispersion. Optimized electronic structure as well as high stability are required for single-atom catalysts to enable efficient electrochemical production of H2O2. Herein, we report a facile synthesis method that stabilizes atomic Pd species on the reduced graphene oxide/N-doped carbon hollow carbon nanospheres (Pd1/N-C). Pd1/N-C exhibited remarkable electrochemical H2O2 production rate with high faradaic efficiency, reaching 80%. The single-atom structure and its high H2O2 production rate were maintained even after 10,000 cycle stability test. The existence of single-atom Pd as well as its coordination with N species is responsible for its high activity, selectivity, and stability. The N coordination number and substrate doping around Pd atoms are found to be critical for an optimized adsorption energy of intermediate *OOH, resulting in efficient electrochemical H2O2 production.

Mapping the charge distribution in nano scale systems still is a difficult task, but is important to provide fundamental insights into the properties of materials. We demonstrate how in-line holography in transmission electron microscopy can be used to extract the charge distribution in the nanowire in a quantitative way. This technique can realize a fast acquisition of delicate charge variations. By taking advantage of the possibilities of in-situ electron microscopy, variations of the external field can be used to modulate the charge distribution. Because of the fast response to charge variations, this method provides an efficient probing tool for detecting dynamic charge redistribution.

Carbon-based materials exhibit high electrocatalytic activity for the oxygen reduction reaction (ORR), which is an essential step for several renewable and clean energy systems. To make them alternatives to Pt-based catalysts for the ORR, a deep understanding on the ORR active sites on the carbon surface is needed but remains a major challenge. In nitrogen (N)-doped carbons, the carbon atoms next to pyridinic N are suggested to be the active sites for the ORR. Here we show that non-doped carbon materials (from carbon dots by annealing treatment at 1000 °C) create surface defects by removing the carbonate groups from the carbon surface under alkaline conditions (KOH/NaOH). Subsequently, the K+ (Na+) attached to the defects (e.g., hydroxyl group) to form the adjacent C–O−–K+ (Na+) groups (C–O−–K+ (Na+) pairs), which are suggested to be the real catalytic active sites for the ORR, similar to those of Pt catalysts.