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Today, many essential industrial processes depend on syngas. Due to a high energy demand and overall cost as well as a dependence on natural gas as its precursor, alternative routes to produce this valuable mixture of hydrogen and carbon monoxide are urgently needed. Electrochemical syngas production via two competing processes, namely carbon dioxide (CO2) reduction and hydrogen (H2) evolution, is a promising method. Often, noble metal catalysts such as gold or silver are used, but those metals are costly and have limited availability. Here, we show that metal-organic chalcogenolate assemblies (MOCHAs) combine several properties of successful electrocatalysts. We report a scalable microwave-assisted synthesis method for highly crystalline MOCHAs ([AgXPh] ∞: X = Se, S) with high yields. The morphology, crystallinity, chemical and structural stability are thoroughly studied. We investigate tuneable syngas production via electrocatalytic CO2 reduction and find the MOCHAs show a maximum Faraday efficiency (FE) of 55 and 45% for the production of carbon monoxide and hydrogen, respectively. Syngas is an industrially highly relevant gaseous mixture of carbon monoxide and hydrogen, but its production is energy-intense and relies on natural gas precursors and noble-metal catalysts. Here, the authors explore metal-organic chalcogenolate assemblies (MOCHAs) for tuneable syngas production via electrocatalytic CO2 reduction. [ABSTRACT FROM AUTHOR]

The presence of metal atoms at the edges of graphene nanoribbons (GNRs) opens new possibilities toward tailoring their physical properties. We present here formation and high-resolution characterization of indium (In) chains on the edges of graphene-supported GNRs. The GNRs are formed when adsorbed hydrocarbon contamination crystallizes via laser heating into small ribbon-like patches of a second graphitic layer on a continuous graphene monolayer and onto which In is subsequently physical vapor deposited. Using aberration-corrected scanning transmission electron microscopy (STEM), we find that this leads to the preferential decoration of the edges of the overlying GNRs with multiple In atoms along their graphitic edges. Electron-beam irradiation during STEM induces migration of In atoms along the edges of the GNRs and triggers the formation of longer In atom chains during imaging. Density functional theory (DFT) calculations of GNRs similar to our experimentally observed structures indicate that both bare zigzag (ZZ) GNRs as well as In-terminated ZZ-GNRs have metallic character, whereas in contrast, In termination induces metallicity for otherwise semiconducting armchair (AC) GNRs. Our findings provide insights into the creation and properties of long linear metal atom chains at graphitic edges. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) are commended as photocatalysts for H2 evolution and CO2 reduction as they combine light-harvesting and catalytic functions with excellent reactant adsorption capabilities. For dynamic processes in liquid phase, the accessibility of active sites becomes a critical parameter as reactant diffusion is limited by the inherently small micropores. Our strategy is to introduce additional mesopores by selectively removing one ligand in mixed-ligand MOFs via thermolysis. Here we report photoactive MOFs of the MIL-125-Ti family with two distinct mesopore architectures resembling either large cavities or branching fractures. The ligand removal is highly selective and follows a 2-step process tunable by temperature and time. The introduction of mesopores and the associated formation of new active sites have improved the HER rates of the MOFs by up to 500%. We envision that this strategy will allow the purposeful engineering of hierarchical MOFs and advance their applicability in environmental and energy technologies. While metal organic frameworks offer highly tunable materials for photocatalytic applications, catalytic site accessibility is a crucial parameter. Here, authors demonstrate selective ligand removal to introduce new active sites and mesopores and to enhance photocatalytic H2 evolution. [ABSTRACT FROM AUTHOR]

Over seventy years ago, Niels Bohr described how the charge state of an atomic ion moving through a solid changes dynamically as a result of electron capture and loss processes, eventually resulting in an equilibrium charge state. Although obvious, this process has so far eluded direct experimental observation. By peeling a solid, such as graphite, layer by layer, and studying the transmission of highly charged ions through single-, bi- and trilayer graphene, we can now observe dynamical changes in ion charge states with monolayer precision. In addition we present a first-principles approach based on the virtual photon model for interparticle energy transfer to corroborate our findings. Our model that uses a Gaussian shaped dynamic polarisability rather than a spatial delta function is a major step in providing a self-consistent description for interparticle de-excitation processes at the limit of small separations. Ion-solid interactions are governed by a range of complex processes the direct experimental observation of which pose their own set of challenges. Here, the authors present a joint experimental and first-principles approach to study and describe the underlying mechanism of electron capture for an ion travelling through layers of graphene with monolayer precision. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) antimony (Sb, "antimonene") is of interest in electronics and batteries. Sb however exhibits a large allotropic structural diversity, which is also influenced by its support. Thus, Sb heterostructure formation is key in 2D Sb integration. Particularly, 2D Sb/graphene interfaces are important. We thus study here few-layered 2D Sb/graphene heterostructures with atomic resolution (scanning) transmission electron microscopy. We find two Sb morphologies to coexist: first, a 2D morphology of layered β-Sb with β-Sb(001)||graphene(001) texture. Second, one-dimensional Sb nanowires which can be matched to β-Sb[2-21]⊥graphene(001) and are closely related to cubic Sb(001)||graphene(001). Importantly, both Sb morphologies show rotational van-der-Waals epitaxy with graphene. Both are resilient against oxidation, although superficial Sb-oxide formation merits consideration, including epitaxial Sb2O3(111)/β-Sb(001) heterostructures. Exact Sb growth behavior depends on processing and substrate properties including, notably, the support underneath the graphene. Our work elucidates the rich phase and epitaxy landscape in 2D Sb and 2D Sb/graphene heterostructures. [ABSTRACT FROM AUTHOR]

In the present work, the channels of metallicity-sorted metallic single-walled carbon nanotubes (SWCNTs) have been filled with silver chloride. The data of high-resolution scanning transmission electron microscopy proved the filling of the nanotube channels and formation of few-atom-thick crystals of silver chloride. The electronic properties of the filled SWCNTs were investigated by Raman spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy. Our results indicate the p-doping of nanotubes by silver chloride accompanied by the charge transfer from the nanotubes to the encapsulated compound and the downshift of the Fermi level by 0.36 eV. The calculated number of transferred electrons per nanotube carbon atom and the charge transfer density per nanotube length amounted to 0.0024 e− per carbon and 0.0406 e−/Å, respectively. It was found that the band gap opens up in the band structure of the filled SWCNTs resulting in their transition from metallic into a semiconducting state. This work reveals a direct influence of the incorporated silver chloride on the electronic properties of metallicity-sorted metallic SWCNTs and demonstrates the potential of precise Fermi level engineering of SWCNTs by filling their channels and achieving high doping levels, thus providing a platform for designing next-generation nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Hydrogen treatment of Pt/TiO2 leads to an exceptional increase in electric conductivity even at moderate temperature presumably due to the formation of donor electrons during a superficial reduction process. Interestingly, after cooling to lower temperatures that are typically applied for catalytic reactions the observed high conductivity was largely preserved. The enhanced charge carrier density in titania is assumed to cause a considerable charge transfer between support and metal. In this work we show that this charge transfer is correlated with typical catalytic parameters (e.g. hydrogen adsorption capacity and catalytic activity for a hydrocarbon skeleton reaction). Based on these observations we suggest and discuss a modified charge transfer mechanism in addition to the decoration mechanism as a possible reason for the SMSI effect occurring during hydrogen treatment already at moderate temperatures. [ABSTRACT FROM AUTHOR]

Crystalline Ni/Au bimetallic oxide nanoparticles with various forms of crystallographic systems and defects were generated by femtosecond laser ablation of nickel–gold target in alcoholic solvents. The nature of the liquid can influence the chemical composition, stability, and size distribution of laser-synthesized nanoparticles. In ethanol, bimodal crystalline bimetallic Ni/Au oxide nanoparticles with median size of 15 nm were synthesized. The laser ablation of Ni/Au target in isopropanol and butanol led to nearly monomodal size distribution with median size of 10 and 13 nm, respectively. High-resolution transmission electron microscopy of Ni/Au oxide nanoparticles in butanol, revealed a graphitic shell of a few atomic layers. In this context, two suggested mechanisms were considered. First of all, the high photon intensity of femtosecond laser pulses can induce direct photolysis of liquid media. Secondly, the formation of supercritical temperature solvent due to the interaction of solvent with molten metal layer at liquid–metal interface can trigger pyrolysis of solvent. These mechanisms can contribute to butanol decomposition and encapsulation of Ni/Au oxide bimetallic nanoparticles with graphite shell. Graphite shell can create a better colloidal stability by preventing nanoparticles from further growth and agglomeration. [ABSTRACT FROM AUTHOR]

We have investigated the electronic properties of single-walled carbon nanotubes (SWCNTs) filled with lead chloride, lead bromide (PbBr2) and lead iodide (PbI2). The filling of SWCNTs and formation of encapsulated one-dimensional nanocrystals of the salts were directly confirmed by high-resolution scanning transmission electron microscopy. The chemical composition of the encapsulated nanocrystals was proven by X-ray photoelectron spectroscopy (XPS). The electronic properties of the filled SWCNTs were characterized by Raman spectroscopy and XPS. All the three lead halogenides result in p-doping of SWCNTs and, consequently, there is a downshift of the SWCNTs' Fermi level due to the charge transfer towards the salts. The effect is stronger with metallic than semiconducting nanotubes. The efficiency of doping depends on the type of lead halogenide. The doping effect is the strongest for PbI2 and the weakest for PbBr2. [ABSTRACT FROM AUTHOR]