The intriguingly fast electrochemical response of the insulating LiFePO4 insertion electrode toward Li is of both fundamental and practical importance. Here we present a comprehensive study of its deinsertion/insertion mechanism by high-resolution electron energy loss spectroscopy on thin platelet-type particles of Li x FePO4 (b Pnma axis normal to the surface). We find that the lithium deinsertion/insertion process is not well-described by the classical shrinking core model. Compositions of the same x value obtained by both deinsertion and insertion gave the same results, namely that the Li x FePO4 so formed consists of a core of FePO4 surrounded by a shell of LiFePO4 with respective ratios dependent on x. We suggest that lattice mismatch between the two end members may be at the origin of the peculiar microstructure observed. Furthermore, because of the appearance of isosbestic points on the overlaid EELS spectra, we provide direct experimental evidence that the nanometer interface between single-phase areas composed of LiFePO4 or FePO4 is the juxtaposition of the two end members and not a solid solution. One future prospect of such knowledge is to determine strategies on how to control, on a large scale, the synthesis of nanometer-sized thin platelet-type particles to prepare high-rate LiFePO4 electrodes for future energy storage devices.

Many catalytic reactions under fixed conditions exhibit oscillatory behaviour. The oscillations are often attributed to dynamic changes in the catalyst surface. So far, however, such relationships were difficult to determine for catalysts consisting of supported nanoparticles. Here, we employ a nanoreactor to study the oscillatory CO oxidation catalysed by Pt nanoparticles using time-resolved high-resolution transmission electron microscopy, mass spectrometry and calorimetry. The observations reveal that periodic changes in the CO oxidation are synchronous with a periodic refacetting of the Pt nanoparticles. The oscillatory reaction is modelled using density functional theory and mass transport calculations, considering the CO adsorption energy and the oxidation rate as site-dependent. We find that to successfully explain the oscillations, the model must contain the phenomenon of refacetting. The nanoreactor approach can thus provide atomic-scale information that is specific to surface sites. This will improve the understanding of dynamic properties in catalysis and related fields.

The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2.

The modern chemical industry uses heterogeneous catalysts in almost every production process. They commonly consist of nanometre-size active components (typically metals or metal oxides) dispersed on a high-surface-area solid support, with performance depending on the catalysts' nanometre-size features and on interactions involving the active components, the support and the reactant and product molecules. To gain insight into the mechanisms of heterogeneous catalysts, which could guide the design of improved or novel catalysts, it is thus necessary to have a detailed characterization of the physicochemical composition of heterogeneous catalysts in their working state at the nanometre scale. Scanning probe microscopy methods have been used to study inorganic catalyst phases at subnanometre resolution, but detailed chemical information of the materials in their working state is often difficult to obtain. By contrast, optical microspectroscopic approaches offer much flexibility for in situ chemical characterization; however, this comes at the expense of limited spatial resolution. A recent development promising high spatial resolution and chemical characterization capabilities is scanning transmission X-ray microscopy, which has been used in a proof-of-principle study to characterize a solid catalyst. Here we show that when adapting a nanoreactor specially designed for high-resolution electron microscopy, scanning transmission X-ray microscopy can be used at atmospheric pressure and up to 350 degrees C to monitor in situ phase changes in a complex iron-based Fisher-Tropsch catalyst and the nature and location of carbon species produced. We expect that our system, which is capable of operating up to 500 degrees C, will open new opportunities for nanometre-resolution imaging of a range of important chemical processes taking place on solids in gaseous or liquid environments.

Understanding the atomistic details of how platinum surfaces are oxidized under electrochemical conditions is of importance for many electrochemical devices such as fuel cells and electrolysers. Here we use in situ shell-isolated nanoparticle-enhanced Raman spectroscopy to identify the intermediate stages of the electrochemical oxidation of Pt(111) and Pt(100) single crystals in perchloric acid. Density functional theory calculations were carried out to assist in assigning the experimental Raman bands by simulating the vibrational frequencies of possible intermediates and products. The perchlorate anion is suggested to interact with hydroxyl phase formed on the surface. Peroxo-like and superoxo-like two-dimensional (2D) surface oxides and amorphous 3D α-PtO2 are sequentially formed during the anodic polarization. Our measurements elucidate the process of the electrochemical oxidation of platinum single crystals by providing evidence for the structure-sensitive formation of a 2D platinum-(su)peroxide phase. These results may contribute towards a fundamental understanding of the mechanism of degradation of platinum electrocatalysts.

In the field of micelle templated structures (MTS), the MSU-X family of mesoporous silica is obtained by using nonionic poly(ethylene oxide)-based surfactants. We show that the microstructure of these materials is highly dependent on the initial pH conditions and that a first assembly step, using a mild acidity, which allowed us to obtain a stable solution containing micellar hybrid objects made of both surfactant micelles and small silica oligomers, can be determined in the 2−4 pH range. The second step of the synthesis consists of the condensation of the silica particles and can be performed in two different ways. Either the pH of the stable solution is increased to neutral values or small amounts of fluoride are added. With the second method both the nanostructure and the particle morphology are better controlled. This novel two-step synthesis leads in addition to hexagonal pore framework when assembly molecules such as Tween 60 or block copolymer Pluronic P123 are used as assembly agents.

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