Recent advances in ferromagnetic metal sulfides and selenides as anodes for sodium- and potassium-ion batteries. - In: Journal of materials chemistry, ISSN 2050-7496, Bd. 9 (2021), 15, S. 9506-9534
In next-generation rechargeable batteries, sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) have been considered as attractive alternatives to lithium-ion batteries due to their cost competitiveness. Anodes with complicated electrochemical mechanisms determine the performance and safety of battery systems to a large degree. Among a wide range of anode materials for SIBs and PIBs, ferromagnetic metal (Fe, Co, and Ni) sulfides and selenides have captured prominent attention by virtue of their high theoretical capacities, suitable potentials, and relatively low price. Although some breakthrough results have been achieved, a few intrinsic issues stemming from the materials themselves need to be further explored and studied, especially in the field of PIBs, an emerging research interest. Herein, in this review, we highlight the pioneering investigation of typical ferromagnetic metal sulfides and selenides for application as anodes in SIBs and PIBs and overview their recent research progress. Meanwhile, the preparation methods, structural characteristics, charge storage mechanisms, and electrochemical properties are outlined. Finally, the present challenges and research perspectives are discussed.
Chemical changes of float glass surfaces induced by different sand particles and mineralogical phases. - In: Journal of non-crystalline solids, ISSN 0022-3093, Bd. 566 (2021), 120868
Particles play an important role in the storage, transportation and natural weathering of glasses, but their influence on glass degradation is little studied. In this work, the influence of main sand components is investigated. Feldspar exhibits the strongest leaching rate for the network former Na, while quartz has the lowest. The leaching rate of natural sands is in between. Based on these findings, a model describing the leaching mechanism was developed: Hereby, hydroxyl groups adhering on sand grains adsorb network modifiers by substituting their hydrogen by network formers from the glass surface. The amount of available hydroxyl groups determines the leaching rate. This model is supported by loss on ignition performed for the sands, which might be a suitable method to roughly estimate their leaching rates. The adsorption of network modifiers suppresses carbonate formation, dendritic growth and Mg diffusion in the glass surface region. Pimple-like crystal growth is observed.
Quantifying crude oil contamination in sand and soil by EPR spectroscopy. - In: Applied magnetic resonance, ISSN 1613-7507, Bd. 52 (2021), 5, S. 633-648
Crude oil frequently contains stable radicals that allow detection by means of EPR spectroscopy. On the other hand, most sands and soils possess significant amounts of iron, manganese or other metallic species that often provide excessively broad EPR signatures combined with well-defined sharp features by quartz defects. In this study, we demonstrate the feasibility to identify oil contamination in natural environments that are subject to oil spillage during production on land, as well as beachside accumulation of marine oil spillage. Straightforward identification of oil is enabled by the radical contributions of asphaltenes, in particular by vanadyl multiplets that are absent from natural soils. This potentially allows for high-throughput soil analysis or the application of mobile EPR scanners.
Controlled regulation of the transformation of carbon nanomaterials under H2 mixture atmosphere by arc plasma. - In: Chemical engineering science, Bd. 241 (2021), 116695
Im Titel ist "2" tiefgestellt
Hydrogen plays a pivotal role in carbon nanomaterials synthesis by arc plasma. However, the effect of hydrogen on morphological regulation of carbon nanomaterials has received little attention. In this paper, carbon nanomaterials synthesized under mixed H2/Ar, H2/N2, and Ar/N2 atmospheres with different ratios were investigated in detail to tackle the issue. Graphene, carbon nanocages, polyhedral graphite particles, amorphous carbon nanoballs, and carbon nanohorns underwent structural transformation as hydrogen content reduced. As a result of varying hydrogen concentration, the number of C-H bond sites at the edge of graphene islands differed, leading to the structural transformation of carbon nanomaterials originating from the formation of various types of precursors. Meanwhile, X-ray photoelectron spectroscopy results revealed that hydrogen impeded nitrogen doping because it tended to bond with electronegative nitrogen. Moreover, morphology control capability followed the order of H2 > N2 > Ar during the preparation of carbon nanomaterials through arc plasma under a mixed atmosphere.
Enhanced potassium storage capability of two-dimensional transition-metal chalcogenides enabled by a collective strategy. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 13 (2021), 16, S. 18838-18848
Potassium-ion batteries (PIBs) have been considered as a promising alternative to lithium-ion batteries due to their merits of high safety and low cost. Two-dimensional transition-metal chalcogenides (2D TMCs) with high theoretical specific capacities and unique layered structures have been proven to be amenable materials for PIB anodes. However, some intrinsic properties including severe stacking and unsatisfactory conductivity restrict their electrochemical performance, especially rate capability. Herein, we prepared a heterostructure of high-crystallized ultrathin MoSe2 nanosheet-coated multiwall carbon nanotubes and investigated its electrochemical properties with a view to demonstrating the enhancement of a collective strategy for K storage of 2D TMCs. In such a heterostructure, the constructive contribution of CNTs not only suppresses the restacking of MoSe2 nanosheets but also accelerates electron transport. Meanwhile, the MoSe2 nanosheets loaded on CNTs exhibit an ultrathin feature, which can expose abundant active sites for the electrochemical reaction and shorten K+ diffusion length. Therefore, the synergistic effect between ultrathin MoSe2 and CNTs endows the resulting nanocomposite with superior structural and electrochemical properties. Additionally, the high crystallinity of the MoSe2 nanosheets further leads to the improvement of electrochemical performance. The composite electrode delivers high-rate capacities of 209.7 and 186.1 mAh g-1 at high current densities of 5.0 and 10.0 A g-1, respectively.
Broadband femtosecond spectroscopic ellipsometry. - In: Review of scientific instruments, ISSN 1089-7623, Bd. 92 (2021), 3, S. 033104-1-033104-14
We present a setup for time-resolved spectroscopic ellipsometry in a pump-probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer-sample-compensator-analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump-probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV-3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues.
Incorporating ultra-small N-doped Mo2C nanoparticles onto 3D N-doped flower-like carbon nanospheres for robust electrocatalytic hydrogen evolution. - In: Nano energy, ISSN 2211-2855, Bd. 86 (2021), 106047
Im Titel ist "2" tiefgestellt
Developing highly-efficient and stable hydrogen evolution reaction (HER) electrocatalysts plays a crucial role in realizing the hydrogen production from electrocatalytic water splitting. Herein, ultra-small and nitrogen-doped molybdenum carbide (N-Mo2C) nanoparticles with oxidized surfaces are facilely synthesized with the assistance of cationic surfactants and simultaneously anchored onto three-dimensional nitrogen-doped flower-like carbon nanospheres (NFCNS), and the N-Mo2C/NFCNS composites are further investigated as HER electrocatalysts. Analysis results reveal that nitrogen atoms are doped into both the lattice and the carbon framework of Mo2C, resulting in low desorption energy of Mo-H bond for the easy evolution of hydrogen gas. Moreover, the high specific area of NFCNS enables enrichment of N-Mo2C nanoparticles, and its open framework facilitates fast ion diffusion. As a result, the N-Mo2C/NFCNS composites exhibit impressive HER activities with low overpotential, small Tafel slope, and excellent durability in both acidic and alkaline media, which outperform most of the reported Mo-based HER catalysts and are also highly comparable to the commercial Pt/C catalyst. Not limited to HER electrocatalysts, this work should open a new avenue for tailoring highly-efficient carbon/metal compounds-based electrocatalysts for oxygen reduction reaction, oxygen evolution reaction, nitrogen reduction reaction, etc.
Nanostructured arrays for metal-ion battery and metal-air battery applications. - In: Journal of power sources, ISSN 1873-2755, Bd. 493 (2021), 229722
Rechargeable battery technology has been the research focus due to the largely increased global energy demand, while metal-ion batteries (MIBs) and metal-air batteries (MABs) are two major representatives. In addition to lithium-ion batteries, other MIBs such as sodium-ion batteries and aluminum-ion batteries have been drawn great attention. Regarding MABs, considerable research effort has been devoted to lithium-, zinc-, and sodium-air batteries. So far, significant progress in the performance improvement of both MIBs and MABs has been achieved through the material design and electrode design. Particularly, free-standing nanoarrays (NAs) directly grown on current collectors have been regarded as promising electrodes of both MIBs and MABs for improving the energy storage capability. In this review, recent advances in design, fabrication and application of NAs for MIBs and MABs have been summarized. Firstly, the motivation of employing NAs electrodes for MIBs and MABs is outlined. The principles and categories of MIBs and MABs, the construction, structural features, and resulting superiorities are also briefly reviewed. Secondly, the relationship of the conductive substrates, the structural features, and electrochemical performance of NAs electrodes is analyzed in depth. Finally, the future design focuses of NAs as advanced electrodes for MIBs and MABs are emphasized.
Enhanced cycling performance of binder free silicon-based anode by application of electrochemically formed microporous substrate. - In: Electrochimica acta, Bd. 380 (2021), 138216, insges. 9 S.
In this work, an electrochemically formed porous Cu current collector (p-Cu) is utilized for the development of a high-performance binder-free silicon anode. Two electrolyte compositions based on sulfolane (SL) and [BMP][TFSI] ionic liquid (IL) are implemented for silicon deposition. The electrochemical experiments confirm the advantages of applying the p-Cu structure in terms of specific capacity, rate capability, and long-term cycling, where the best electrochemical properties have been observed for the Si deposited from SL electrolyte. The Si-based p-Cu anodes formed in SL display stable 2500 mAh g^-1 reversible capacity during the first 250 cycles and promising capacity retention. Compared to this result, the cycling performance of the same type of material deposited on flat Cu foil (f-Cu) showed significantly reduced capacity (1400 mAh g^-1) and inferior cycling performance. The positive effect can be attributed to the improved mechanical stability of the active material and accelerated ionic transport in the porous structure of the anode. The improved functional properties of the electrochemically deposited Si from SL electrolyte in p-Cu samples compared to those obtained in IL can be ascribed to differences in the chemical composition. While the layers deposited in SL electrolyte involve Si domains incorporated in a matrix containing C and O that offer high mechanical stability, the Si material obtained in IL is additionally influenced by N and F chemical species, resulting from active IL decomposition. These differences in the chemical surrounding of the Si domains are the primary reason for the inferior electrochemical performance of the material deposited from [BMP][TFSI] electrolyte. XPS analysis shows that the initial composition of the as deposited layers, containing a considerable amount of elemental Si, is changed after lithiation and that the electrochemical activity of the anode is governed by switching between the intermediate redox states of Si, where the carbon-oxygen matrix is also involved.
Electrodeposition of cuprous oxide on a porous copper framework for an improved photoelectrochemical performance. - In: Journal of materials science, ISSN 1573-4803, Bd. 56 (2021), 20, S. 11866-11880