A straightforward one‐step process was developed, in which CO2 gas is directly converted into multi‐layer graphene via atmospheric pressure chemical vapor deposition (APCVD). A bimetallic alloy film ...based on Cu and Pd was employed as the catalyst and substrate. In this study, we found that the quantity of Cu required for the CO2 conversion process is high (>82 at %). The findings gained in this study serve as a foundation for further studies of metallic alloys for the thermo‐reduction of CO2 to graphene under CVD conditions.
Green graphene: Herein we report the direct conversion of CO2 gas to graphene. We achieve this one‐step process through a combination of the reductive power of hydrogen and the catalytic properties of a Cu–Pd alloy.
Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent ...substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering.
Porphyrin complexes are well‐known for their application in solar‐cell systems and as catalysts; however, their use in electrochemical energy‐storage applications has scarcely been studied. Here, a ...tetra‐alkenyl‐substituted 5,10,15,20‐tetra(ethynyl)porphinatocopper(II) (CuTEP) complex was used as anode material in a high‐performance lithium‐free CuTEP/PP14TFSI/graphite cell PP14TFSI=1‐butyl‐1‐methylpiperidinium bis(trifluoromethylsulfonyl)imide. Thereby, the influence of size and morphology on the electrochemical performance of the cell was thoroughly investigated. Three different nanocrystal CuTEP morphologies, namely nanobricks, nanosheets, and nanoribbons, were studied as anode material, and the best cyclability and highest rate capability were obtained for the nanoribbon samples. A high specific power density of 14 kW kg−1 (based on active material) and excellent rechargeability were achieved with negligible capacity decay over 1000 cycles at a high current density of 5 A g−1. These results indicate that the porphyrin complex CuTEP could be a promising electrode material in high‐performance lithium‐free batteries.
Morphology matters: In a Li‐free battery cell with organic electrodes consisting of a tetra‐acetenyl‐substituted porphyrin, the nanobrick‐ and nanoribbon‐morphology porphyrin samples show higher rate cyclability than the nanosheet sample. The organic electrode material demonstrated a specific power density of 14 kW kg−1 and excellent rechargeability.
Very little is known about the size and shape effects on the properties of actinide compounds. As a consequence, the controlled synthesis of well‐defined actinide‐based nanocrystals constitutes a ...fundamental step before studying their corresponding properties. In this paper, we report on the non‐aqueous surfactant‐assisted synthesis of thorium and uranium oxide nanocrystals. The final characteristics of thorium and uranium oxide nanocrystals can be easily tuned by controlling a few experimental parameters such as the nature of the actinide precursor and the composition of the organic system (e.g., the chemical nature of the surfactants and their relative concentrations). Additionally, the influence of these parameters on the outcome of the synthesis is highly dependent on the nature of the actinide element (thorium versus uranium). By using optimised experimental conditions, monodisperse isotropic uranium oxide nanocrystals with different sizes (4.5 and 10.7 nm) as well as branched nanocrystals (overall size ca. 5 nm), nanodots (ca. 4 nm) and nanorods (with ultra‐small diameters of 1 nm) of thorium oxide were synthesised.
New pieces to the puzzle! Thorium and uranium oxide nanocrystals with various sizes and shapes were synthesised by a non‐aqueous colloidal method (see figure). The role of various experimental parameters (e.g., composition of the organic system, nature of the actinide precursor and nature of the actinide element) to control the final characteristics of actinide oxide nanocrystals is reported.
Plastic deformation of metallic glasses performed at temperatures well below the glass transition proceeds via the formation of shear bands. In this contribution, we investigated shear bands ...originating from in situ tensile tests of Al88Y7Fe5 melt-spun ribbons performed under a transmission electron microscope. The observed contrasts of the shear bands were found to be related to a thickness reduction rather than to density changes. This result should alert the community of the possibility of thickness changes occurring during in situ shear band formation that may affect interpretation of shear band properties such as the local density. The observation of a spearhead-like shear front suggests a propagation front mechanism for shear band initiation here.
Frustrated Lewis pairs (FLPs) created by sterically hindered Lewis acids and Lewis bases have shown their capacity for capturing and reacting with a variety of small molecules, including H2 and CO2, ...and thereby creating a new strategy for CO2 reduction. Here, the photocatalytic CO2 reduction behavior of defect‐laden indium oxide (In2O3−x(OH)y) is greatly enhanced through isomorphous substitution of In3+ with Bi3+, providing fundamental insights into the catalytically active surface FLPs (i.e., InOH···In) and the experimentally observed “volcano” relationship between the CO production rate and Bi3+ substitution level. According to density functional theory calculations at the optimal Bi3+ substitution level, the 6s2 electron pair of Bi3+ hybridizes with the oxygen in the neighboring InOH Lewis base site, leading to mildly increased Lewis basicity without influencing the Lewis acidity of the nearby In Lewis acid site. Meanwhile, Bi3+ can act as an extra acid site, serving to maximize the heterolytic splitting of reactant H2, and results in a more hydridic hydride for more efficient CO2 reduction. This study demonstrates that isomorphous substitution can effectively optimize the reactivity of surface catalytic active sites in addition to influencing optoelectronic properties, affording a better understanding of the photocatalytic CO2 reduction mechanism.
This study investigates, experimentally and theoretically, the enhanced photoactive behavior of defected indium oxide (In2O3−x(OH)y) obtained through isomorphous substitution of In3+ with Bi3+. It provides fundamental insights into catalytically active surface frustrated Lewis pairs and the experimentally observed “volcano” relationship between the Bi substitution level and the CO production rate in the light‐assisted, gas‐phase reverse water gas shift reaction.
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