Luca

Publication date: 15 November 2019

Source: Computational and Theoretical Chemistry, Volume 1168

Author(s): Ádám Ganyecz, Pál D. Mezei, Mihály Kállay

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Dotierung auf dem Laufsteg: Ein N‐dotiertes TiO₂‐Modell offenbart den Anionenaktivierungsmechanismus basierend auf der Modulation der Hybridisierung delokalisierter Orbitale durch Einfügung von O‐Fehlstellen. Das Modell demonstiert den Nutzen der Präevaluierung der Rolle von Dotanden durch systematische experimentelle und theoretische Studien.

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An N‐doped TiO₂ model reveals a conceptually different mechanism for activating the N dopant based on delocalized orbital hybridization through O vacancy incorporation. Synchrotron‐based X‐ray absorption spectroscopy, time‐resolved fluorescence, and DFT studies revealed that O vacancy incorporation can effectively stimulate the delocalization of N impurity states through p‐band orbital modulation, which leads to a significant enhancement in photocarrier lifetime. Consequently, this effect also results in a remarkable increase in the incident photon‐to‐electron conversion efficiency in the range of 400–550 nm compared to that of conventional N‐incorporated TiO₂ (15 % versus 1 % at 450 nm). This work reveals the fundamental necessity of orbital modulation in the band engineering of metal oxides for driving solar water splitting and beyond.

Breaking ground: The photoreforming of tertiary alcohols on TiO₂(110) follows an unexpected reaction channel, selective disproportionation to an alkane and the respective ketone. When the catalyst is decorated with Pt clusters, the overall reaction rate increases. In addition to ketone formation, a new reaction pathway is observed, hydrogen evolution and alkane dimerization.

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According to textbooks, tertiary alcohols are inert towards oxidation. The photocatalysis of tertiary alcohols under highly defined vacuum conditions on a titania single crystal reveals unexpected and new reactions, which can be described as disproportionation into an alkane and the respective ketone. In contrast to primary and secondary alcohols, in tertiary alcohols the absence of an α‐H leads to a C−C‐bond cleavage instead of the common abstraction of hydrogen. Surprisingly, bonds to methyl groups are not cleaved when the alcohol exhibits longer alkyl chains in the α‐position to the hydroxyl group. The presence of platinum loadings not only increases the reaction rate but also opens up a new reaction channel: the formation of molecular hydrogen and a long‐chain alkane resulting from recombination of two alkyl moieties. This work demonstrates that new synthetic routes may become possible by introducing photocatalytic reaction steps in which the co‐catalysts may also play a decisive role.

Publication date: 15 October 2019

Source: Computational and Theoretical Chemistry, Volume 1166

Author(s): Sambhu N. Datta

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Mithilfe von Ölsäure und Didodecyldimethylammoniumsulfid werden CsPbBr₃‐Quantenpunkte mit einer großen Zahl an Oberflächen‐Bromid‐Leerstellen zu Nanodrähten zusammengefügt. Die Nanodrähte sind 20–60 nm breit und erreichen eine Länge von mehreren Millimetern.

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Interest has been growing in defects of halide perovskites in view of their intimate connection with key material optoelectronic properties. In perovskite quantum dots (PQDs), the influence of defects is even more apparent than in their bulk counterparts. By combining experiment and theory, we report herein a halide‐vacancy‐driven, ligand‐directed self‐assembly process of CsPbBr₃ PQDs. With the assistance of oleic acid and didodecyldimethylammonium sulfide, surface‐Br‐vacancy‐rich CsPbBr₃ PQDs self‐assemble into nanowires (NWs) that are 20–60 nm in width and several millimeters in length. The NWs exhibit a sharp photoluminescence profile (≈18 nm full‐width at‐half‐maximum) that peaks at 525 nm. Our findings provide insight into the defect‐correlated dynamics of PQDs and defect‐assisted fabrication of perovskite materials and devices.

The influence of the support on the performance of a single‐atom catalyst was investigated by comparing single‐atom Pt supported on carbon and Pt nanoparticles supported on WO_3−x (Pt NP/WO_3−x ). The support effect is maximized for single‐atom Pt on WO_3−x , which drastically enhances the Pt mass activity for the hydrogen evolution reaction compared with Pt NP/WO_3−x and Pt/C.

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Single‐atom catalysts (SACs) have attracted growing attention because they maximize the number of active sites, with unpredictable catalytic activity. Despite numerous studies on SACs, there is little research on the support, which is essential to understanding SAC. Herein, we systematically investigated the influence of the support on the performance of the SAC by comparing with single‐atom Pt supported on carbon (Pt SA/C) and Pt nanoparticles supported on WO_3−x (Pt NP/WO_3−x ). The results revealed that the support effect was maximized for atomically dispersed Pt supported on WO_3−x (Pt SA/WO_3−x ). The Pt SA/WO_3−x exhibited a higher degree of hydrogen spillover from Pt atoms to WO_3−x at the interface, compared with Pt NP/WO_3−x , which drastically enhanced Pt mass activity for hydrogen evolution (up to 10 times). This strategy provides a new framework for enhancing catalytic activity for HER, by reducing noble metal usage in the field of SACs.

Die Minderung von NO_x‐Emissionen durch selektive katalytische Reduktion (SCR) auf Vanadiumoxid‐basierten Heterogenkatalysatoren wird durch Wolframoxid gefördert. In ihrem Forschungsartikel auf https://doi.org/10.1002/ange.201904503S. 12739 zeigen J. Z. Hu, Y. Wang, I. E. Wachs und Mitarbeiter, dass diese SCR über einen Zwei‐Zentren‐Mechanismus an benachbarten Vanadiumoxidzentren verläuft. Das Wolframoxid bewirkt die Oligomerisierung des Vanadiumoxids, was die NO _x ‐Minderung verstärkt. Grafik: Cortland Johnson.

NO _x effects: Molecular‐level structural details are revealed for supported vanadia (V₂O₅) catalysts. Tungsten oxide addition to V₂O₅/TiO₂ catalysts used for the abatement of NO _x emissions promotes their reactivity via a structural effect involving oligomerizing vanadia units. The resulting structure thus satisfies the 2‐site requirement revealed for the selective catalytic reduction (SCR) of NO _x by vanadia catalysts.

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The selective catalytic reduction (SCR) of NO _x with NH₃ to N₂ with supported V₂O₅(‐WO₃)/TiO₂ catalysts is an industrial technology used to mitigate toxic emissions. Long‐standing uncertainties in the molecular structures of surface vanadia are clarified, whereby progressive addition of vanadia to TiO₂ forms oligomeric vanadia structures and reveals a proportional relationship of SCR reaction rate to [surface VO _x concentration]², implying a 2‐site mechanism. Unreactive surface tungsta (WO₃) also promote the formation of oligomeric vanadia (V₂O₅) sites, showing that promoter incorporation enhances the SCR reaction by a structural effect generating adjacent surface sites and not from electronic effects as previously proposed. The findings outline a method to assess structural effects of promoter incorporation on catalysts and reveal both the dual‐site requirement for the SCR reaction and the important structural promotional effect that tungsten oxide offers for the SCR reaction by V₂O₅/TiO₂ catalysts.

Doped for performance: In‐ and Zn/In‐doped SnS₂ nanosheet arrays are used as photoanodes for the photoelectrochemical splitting of water. The doping induces the formation of an amorphous overlayer and S vacancies on the nanosheet surface, as well as a gradient energy‐band distribution along the cross‐section of the nanosheet arrays. This leads to an increased performance in water splitting.

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Photoelectrochemical (PEC) water splitting is a promising strategy to convert solar energy into hydrogen fuel. However, the poor bulk charge‐separation ability and slow surface oxygen evolution reaction (OER) dynamics of photoelectrodes impede the performance. We construct In‐ and Zn/In‐doped SnS₂ nanosheet arrays through a hydrothermal method. The doping induces the simultaneous formation of an amorphous layer, S vacancies, and a gradient energy band. This leads to elevated carrier concentrations, an increased number of surface‐reaction sites, accelerated surface‐OER kinetics, and an enhanced bulk‐carrier separation efficiency with a decreased recombination rate. This efficient doping strategy allows to manipulate the morphology, crystallinity, and band structure of photoelectrodes for an improved PEC performance.

Transfer to a plane: The covalent functionalization of two‐dimensional semiconducting MoS₂ with an electron‐donating photosensitizer zinc phthalocyanine has been successfully achieved. The hybrid material exhibits excited‐state charge transfer and is, therefore, a candidate for optoelectronic applications.

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The functionalization of MoS₂ is of paramount importance for tailoring its properties towards optoelectronic applications and unlocking its full potential. Zinc phthalocyanine (ZnPc) carrying an 1,2‐dithiolane oxide linker was used to functionalize MoS₂ at defect sites located at the edges. The structure of ZnPc‐MoS₂ was fully assessed by complementary spectroscopic, thermal, and microscopy imaging techniques. An energy‐level diagram visualizing different photochemical events in ZnPc‐MoS₂ was established and revealed a bidirectional electron transfer leading to a charge separated state ZnPc^.+ ‐MoS₂ ^.−. Markedly, evidence of the charge transfer in the hybrid material was demonstrated using fluorescence spectroelectrochemistry. Systematic studies performed by femtosecond transient absorption revealed the involvement of excitons generated in MoS₂ in promoting the charge transfer, while the transfer was also possible when ZnPc was excited, signifying their potential in light‐energy‐harvesting devices.

Die Null muss stehen! Eine Phosphormodulierung von Anatas‐TiO₂ bewirkt zugleich einen Phasenübergang auf der Oberfläche, der zu struktureller Fehlordnung führt, sowie eine P‐Dotierung auf atomarer Ebene im Inneren. Diese beiden vorteilhaften Veränderungen resultieren in einer Nulldeformation während der Insertion/Extraktion von Natriumionen, die mit nur ca. 0.1 % Volumenänderung erfolgt; dies ermöglicht eine außergewöhnlich effiziente Natriumspeicherung.

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Structural modulation and surface engineering have remarkable advantages for fast and efficient charge storage. Herein, we present a phosphorus modulation strategy which simultaneously realizes surface structural disorder with interior atomic‐level P‐doping to boost the Na⁺ storage kinetics of TiO₂. It is found that the P‐modulated TiO₂ nanocrystals exhibit a favourable electronic structure, and enhanced structural stability, Na⁺ transfer kinetics, as well as surface electrochemical reactivity, resulting in a genuine zero‐strain characteristic with only approximately 0.1 % volume variation during Na⁺ insertion/extraction, and exceptional Na⁺ storage performance including an ultrahigh rate capability of 210 mAh g⁻¹ at 50 C and a strong long‐term cycling stability without significant capacity decay up to 5000 cycles at 30 C.

Publication date: Available online 6 March 2019

Source: Computer Physics Communications

Author(s): Meisam Farzalipour Tabriz, Bálint Aradi, Thomas Frauenheim, Peter Deák

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