Sodium ion batteries (SIBs) are promising alternatives to lithium ion batteries with advantages of cost effectiveness. Metal sulfides as emerging SIB anodes have relatively high electronic conductivity and high theoretical capacity, however, large volume change during electrochemical testing often leads to unsatisfactory electrochemical performance. Herein bimetallic sulfide Cu 2 MoS 4 (CMS) with layered crystal structures are prepared with glucose addition (CMS1), resulting in the formation of hollow nanospheres that endow large interlayer spacing, benefitting the rate performance and cycling stability. The electrochemical mechanisms of CMS1 are investigated using ex situ X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy, revealing the conversion-based mechanism in carbonate electrolyte and intercalation-based mechanism in ether-electrolyte, thus allowing fast and reversible Na + storage. With further introduction of reduced graphene oxide (rGO), CMS1-rGO composites are obtained, maintaining the hollow structure of CMS1. CMS1-rGO delivers excellent rate performance (258 mAh g −1 at 50 mA g −1 and 131.9 mAh g −1 at 5000 mA g −1 ) and notably enhanced cycling stability (95.6% after 2000 cycles). A full cell SIB is assembled by coupling CMS1-rGO with Na 3 V 2 (PO 4 ) 3 -based cathode, delivering excellent cycling stability (75.5% after 500 cycles). The excellent rate performance and cycling stability emphasize the advantage of CMS1-rGO toward advanced SIB full cells assembly.

Titanium dioxide (TiO2) is among the most studied model (photo)­catalyst materials. The influence of surface point defects, like oxygen vacancies and particularly bulk defects such as Ti3+ interstitials, is usually underestimated or even ignored. We present a systematic study under well-defined UHV conditions illustrating the importance of such defects for the thermal reaction of methanol at the rutile TiO2 (110) single crystal surface by using temperature-programmed reaction spectroscopy (TPRS) and Fourier-transform infrared reflection–absorption spectroscopy (FT-IRRAS). It will be shown that the population of different reaction pathways, namely, the partial oxidation of methanol to formaldehyde and the deoxygenation forming hydrocarbons, especially methane, depends on the bulk defect density and the presence or absence of oxygen adsorbates. While at elevated temperatures molecular desorption is pronounced for the less defective substrates, for higher reduction grades the high-temperature deoxygenation channel via methoxy intermediates is favored. In addition, preadsorption of oxygen enables low- and high-temperature partial oxidation forming formaldehyde, likely from a dioxomethylene-like adsorbate.

Heterogeneous (photo)­catalysts are often complex mixtures of different nanostructured oxidic compounds. Chemical and electronic interactions within such combined materials may play a key role in improving the performance in technological applications but are difficult to investigate under technical conditions. This work presents a systematic study of the interactions between tungsten oxide clusters and the underlying rutile TiO2 (110) surface in special consideration of point defects such as Ti3+ interstitials. Using electron beam evaporation from WO3 powder, stoichiometric (WO3) n , and oxygen-deficient (WO3–x ) n , tungsten oxide clusters are produced simultaneously. Based on cluster coverage- and temperature-dependent X-ray photoelectron spectroscopy studies, the formation of a surface layer of stoichiometric and oxygen-deficient tungsten oxide clusters is shown, and the formation of mixed oxides can be excluded. For the first layer up to 7.1 WO3 nm–2, stoichiometric clusters are dominant at the TiO2 surface. The lack of W5+ indicates an electron transfer from the clusters toward the substrate under formation of Ti3+ interstitials. Furthermore, we found at elevated temperatures relevant for catalytic reactions that the tungsten oxide clusters are more stable on TiO2 surfaces than on other substrates such as the silicon oxide layer of Si wafers. Up to 900 K, only slight changes were observed on titania. We observed an accumulation of Ti3+ at the TiO2 surface between 500 and 800 K in the case of high bulk Ti3+ content in TiO2. As the Ti3+ accumulation is accompanied by significant changes of the W 4f signals, we suggest an interaction between these sites under a possible generation of surface fields or an anionic [(WO3) n ] z−-like cluster by electron transfer from Ti3+.

Electrostaticversussterical ligand stabilization: competitive stabilization mechanism play a key role in the control of nanomaterial properties.

To obtain a mechanistic understanding of occurring processes on oxide surfaces at the atomic level, systematic studies under ultra-high vacuum (UHV) conditions on single crystalline surfaces are commonly used. Usually, the sample preparation protocol for these surfaces includes argon-ion bombardment followed by annealing at elevated temperatures. For reduceable metal oxides, this leads to a significant reduction of the surface. Up to now, the particular role of the remaining argon in the subsequent formation of clean surfaces and the possible incorporation of argon into the crystal lattice as a dopant are typically neglected or remain unclear. This work presents combined, temperature-dependent X-ray photoelectron spectroscopy and a low-energy electron diffraction study under UHV conditions of the bulkassisted reoxidation and restructuring of the rutile TiO 2 (110) single crystal surface after argon-ion bombardment. The formation of an ordered and reoxidized (110)(1 × 1) surface is accompanied by a stepwise desorption of argon from the sample. Moreover, we present a systematic study of the incorporation of argon in the rutile crystal as well as the diffusion and desorption of argon from these samples. By following the temperature-dependent Ar 2p photoelectron spectra, the change of the electronic environment of embedded argon is elucidated, demonstrating the interaction with reduced Ti cations. Hence, residual argon (in case of Ar + ) possibly acts as a strong oxidant or induces significant lattice distortions. Our results show that residual argon from the sample preparation is an important hidden dopant and needs to be considered in the evaluation of typical studies on oxide surfaces under UHV conditions in future work.

Although nanomaterials are widely involved in technological applications, common synthetic recipes for such colloids are restricted to special, optimized conditions, particularly for anisotropic shapes. Ligand exchange is frequently necessary for further functionalization. While such protocols are well established for spherical particles, it is more demanding to keep the corpus for thermodynamically less stable shapes. We highlight the temperature as one key for the formation of anisotropic gold nanoparticles, but also for ligand exchange protocols under shape retention or deliberate reshaping at the example of gold nanocubes. In the first part, the synthesis of CTAB capped gold nanocubes in aqueous solution is examined highlighting the narrow temperature window in which selective adsorption site blocking by bromide ions leads to the formation of gold nanocubes. While too low temperatures yield multiple particle shapes due to a low surface mobility, temperatures above the appropriate window result in more thermodynamically favored shapes. Furthermore, two protocols are presented for the exchange of the ammonium ligand CTAB by oleylamine as an organic amine including water removal from a slurrish water‐amine paste through the gas phase. In turn, precise temperature control allows to either maintain the cubic shape or induce a reshaping process towards other, thermodynamically preferred shapes such as for example truncated octahedra.

Rutile TiO2 is an important model system for understanding the adsorption and conversion of molecules on transition metal oxide catalysts. In the last decades, point defects, such as oxygen vacancies and Ti3+ interstitials, exhibited an important influence on the reaction of oxygen and oxygen-containing molecules on titania surfaces. In brief, partially reduced TiO2 containing a significant amount of Ti3+ is often more active for the conversion of such molecules. In this study, we investigate an even higher reduced surface prepared by argon ion bombardment of a rutile TiO2 (110) single crystal. By X-ray photoelectron spectroscopy we show that, besides Ti4+, this surface is almost equally dominated by Ti3+ and Ti2+. To probe the reactivity of these highly reduced surfaces, we have adsorbed two different classes of oxygen-containing molecules and utilized temperature programmed reaction spectroscopy to investigate the conversion. While alcohols (in this case methanol) already show a defect-dependent partial conversion in a deoxygenation reaction on the (stochiometric or slightly reduced) rutile TiO2 (110) surface, ketones (e.g. acetone) are usually not converted on the rutile TiO2 (110) surface independent on the bulk defect density. Here, we present a nearly full conversion for both molecules via deoxygenation reactions and reductive C–C coupling, forming different hydrocarbons at different temperatures between 375 K and 640 K on the sputtered Ti2+ rich surface.

A fundamental reaction in industries for producing aldehydes and ketones is the partial oxidation of alcohols. As a model reaction, we investigated the photo-oxidation of 2-propanol on rutile titania, which is a promising chemically nontoxic photocatalyst. Photochemical infrared reflection absorption spectroscopy (PC-IRRAS) was used to study the reaction on powder catalysts in the liquid phase (neat liquid and dissolved in dichloromethane). We compare these results with polarized Fourier transform (FT)-IRRAS and temperature-programmed desorption (TPD) experiments on rutile TiO2(110) single crystals in ultrahigh vacuum (UHV). Our in situ liquid-phase experiments showed that 2-propanol converts into acetone on rutile powders, which is in accordance with previous ex situ studies. Mass transport limitations are the key to avoid total oxidation. However, the yield of acetone is limited. We identified water formed as a byproduct and suspected that water might block the active sites. To elucidate possible reaction mechanisms, further experiments were performed on rutile TiO2(110) single crystals in the presence and absence of oxygen and UV irradiation under UHV conditions. Here, we obtained further insights into the elementary steps of the different 2-propanol reactions. We demonstrated that acetone desorbs from a diolate species, which forms in the presence of oxygen under UV irradiation at temperatures around 200 K. Furthermore, propane was identified for the first time as a new thermally activated deoxygenation product besides the simultaneously formed, formally reported, propene. Propene formation is quenched by UV irradiation. Active site blocking by water is confirmed by TPD and polarized FT-IRRAS measurements.