Christian Suchomski

Ordered Mesoporous MFe2O4 (M = Co, Cu, Mg, Ni, Zn) Thin Films with Nanocrystalline Walls, Uniform 16 nm Diameter Pores and High Thermal Stability: Template-Directed Synthesis and Characterization of Redox Active Trevorite

In this paper, we report on ordered mesoporous NiFe(2)O(4) thin films synthesized via co-assembly of hydrated ferric nitrate and nickel chloride with an amphiphilic diblock copolymer, referred to as KLE. We establish that the NiFe(2)O(4) samples are highly crystalline after calcination at 600 °C, and that the conversion of the amorphous inorganic framework comes at little cost to the ordering of the high quality cubic network of pores averaging 16 nm in diameter. We further show that the synthesis method employed in this work can be readily extended to other ferrites, such as CoFe(2)O(4), CuFe(2)O(4), MgFe(2)O(4), and ZnFe(2)O(4), which could pave the way for innovative device design. While this article focuses on the self-assembly and characterization of these materials using various state-of-the-art techniques, including electron microscopy, grazing incidence small-angle X-ray scattering (GISAXS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), as well as UV-vis and Raman spectroscopy, we also examine the electrochemical properties and show the benefits of combining a continuous mesoporosity with nanocrystalline films. KLE-templated NiFe(2)O(4) electrodes exhibit reasonable levels of lithium ion storage at short charging times which stem from facile pseudocapacitance.

Soft-templating synthesis of mesoporous magnetic CuFe2O4 thin films with ordered 3D honeycomb structure and partially inverted nanocrystalline spinel domains

Combining sol-gel chemistry with polymer templating strategies enables production of CuFe(2)O(4) thin films with both an ordered cubic network of 17 nm diameter pores and tunable spinel domain sizes. These nanocrystalline materials contain only minor structural defects with λ = 0.85 ± 0.02 and exhibit multiple functionalities, including superparamagnetic behavior (T(B)≈ 310 K) and redox- and photoactivity.

Free-standing and binder-free highly N-doped carbon/sulfur cathodes with tailorable loading for high-areal-capacity lithium–sulfur batteries

A facile hard-templating method has been developed to prepare highly N-doped carbon/sulfur cathodes with thickness 2.5 mgsulfur cm−2). Lithium–sulfur batteries using this free-standing and binder-free hierarchical hybrid design exhibit good cycling performance, with stable areal capacities of 3.0 mA h cm−2, owing to favorable properties of the carbon host.

Long cycle life of CoMn2O4 lithium ion battery anodes with high crystallinity

CoMn2O4 nanomaterials are prepared by a low temperature precipitation route employing metal acetates and NaOH. Structural changes, induced by different annealing temperatures, are comprehensively analyzed by X-ray powder diffraction and Raman spectroscopy. With rising annealing temperature the crystal lattice of CoMn2O4 undergoes changes ; AO4 tetrahedra expand due to thermally induced substitution of Co2+ by larger Mn2+ metal ions on the A-site of the spinel structure, while in contrast, BO6 octahedra shrink since the B-site becomes partially occupied by smaller Co3+ metal ions on account of the migrated Mn ions. CoMn2O4 particle sizes are easily fine-tuned by applying different annealing temperatures ; the particle size increases with increasing annealing temperature. During the battery operation, pulverization and reduction of particle sizes occurs regardless of the initial size of the particles, but the degree of division of the particles during the operation is dependent on the initial particle properties. Thus, contrary to the common assumption that nanostructuring of the anode material improves the battery performance, samples with the largest particle sizes exhibit excellent performance with a capacity retention of 104% after 1000 cycles (compared to the 2nd cycle).

Ordered Mesoporous β‐MgMoO4 Thin Films for Lithium‐Ion Battery Applications

Electrochemical energy storage, in particular in advanced lithium-ion batteries, has been receiving increasing attention in recent years. [ 1 ] This is due in part to the comparatively high charge storage capacity of lithium-ion batteries, which is also one of the major reasons why they are widely used to power portable electronics. Despite the fact that the current generation technology does not provide suffi cient energy density, both gravimetric and volumetric, for application in the electromobility sector (transport), [ 2 ] there is still ample scope for improving the specifi c capacity, capacity retention, rate capability, safety and so forth of traditional lithium-ion batteries, e.g., by using different anode and cathode materials. Metal orthomolybdates, AMoO 4 (A = divalent metal ion), belong to a class of ternary compounds exhibiting reversible redox activity above 1.0 V versus Li/Li + . Interest in these oxides has been largely driven by the fact that most of them are highly active catalysts, [ 3 ] but they also show promise as electrode materials for secondary batteries. Microcrystalline metal molybdates, however, have not proven to be of much interest for lithium-ion battery applications due to rapid capacity fading over the fi rst few cycles. [ 4 ] Nevertheless, this problem can be overcome to a certain extent by using nanocrystalline forms of these materials, as shown recently by Xiao et al. [ 5 ]

Microwave synthesis of high-quality and uniform 4 nm ZnFe2O4 nanocrystals for application in energy storage and nanomagnetics

Summary Magnetic nanocrystals with a narrow size distribution hold promise for many applications in different areas ranging from biomedicine to electronics and energy storage. Herein, the microwave-assisted sol–gel synthesis and thorough characterization of size-monodisperse zinc ferrite nanoparticles of spherical shape is reported. X-ray diffraction, 57Fe Mössbauer spectroscopy and X-ray photoelectron spectroscopy all show that the material is both chemically and phase-pure and adopts a partially inverted spinel structure with Fe3+ ions residing on tetrahedral and octahedral sites according to (Zn0.32Fe0.68)tet[Zn0.68Fe1.32]octO4±δ. Electron microscopy and direct-current magnetometry confirm the size uniformity of the nanocrystals, while frequency-dependent alternating-current magnetic susceptibility measurements indicate the presence of a superspin glass state with a freezing temperature of about 22 K. Furthermore, as demonstrated by galvanostatic charge–discharge tests and ex situ X-ray absorption near edge structure spectroscopy, the as-prepared zinc ferrite nanocrystals can be used as a high-capacity anode material for Li-ion batteries, showing little capacity fade – after activation – over hundreds of cycles. Overall, in addition to the good material characteristics, it is remarkable that the microwave-based synthetic route is simple, easily reproducible and scalable.

In situ tuning of magnetization via topotactic lithium insertion in ordered mesoporous lithium ferrite thin films

The synthesis and characterization of cubic mesostructured lithium ferrite (α-LiFe5O8) with 20 nm diameter pores and nanocrystalline walls is reported. The material is prepared in the form of thin films by sol–gel dip-coating using a poly(isobutylene)-block-poly(ethylene oxide) amphiphilic diblock copolymer as the porogen. Electron microscopy, X-ray scattering and diffraction, time-of-flight secondary ion mass spectrometry, Raman and X-ray photoelectron spectroscopy all show that α-LiFe5O8 can be templated to produce high-quality films that are chemically and phase-pure and thermally stable to over 600 °C. Magnetometry measurements indicate ferrimagnetic behavior below 300 K, with the coercivity exhibiting a T1/2 dependence. This novel mesoporous spinel material – when used as an electrode in secondary battery cells – can reversibly store charge via topotactic Li insertion, which allows for the intriguing possibility of tuning the magnetization at room temperature in a facile and controlled manner. The general approach is simple and should be applicable to a variety of other magnetic materials that are capable of reacting electrochemically with Li to produce reduced phases.

Ionic Conductivity of Mesostructured Yttria-Stabilized Zirconia Thin Films with Cubic Pore Symmetry—On the Influence of Water on the Surface Oxygen Ion Transport.

Thermally stable, ordered mesoporous thin films of 8 mol % yttria-stabilized zirconia (YSZ) were prepared by solution-phase coassembly of chloride salt precursors with an amphiphilic diblock copolymer using an evaporation-induced self-assembly process. The resulting material is of high quality and exhibits a well-defined three-dimensional network of pores averaging 24 nm in diameter after annealing at 600 °C for several hours. The wall structure is polycrystalline, with grains in the size range of 7 to 10 nm. Using impedance spectroscopy, the total electrical conductivity was measured between 200 and 500 °C under ambient atmosphere as well as in dry atmosphere for oxygen partial pressures ranging from 1 to 10(-4) bar. Similar to bulk YSZ, a constant ionic conductivity is observed over the whole oxygen partial pressure range investigated. In dry atmosphere, the sol-gel derived films have a much higher conductivity, with different activation energies for low and high temperatures. Overall, the results indicate a strong influence of the surface on the transport properties in cubic fluorite-type YSZ with high surface-to-volume ratio. A qualitative defect model which includes surface effects (annihilation of oxygen vacancies as a result of water adsorption) is proposed to explain the behavior and sensitivity of the conductivity to variations in the surrounding atmosphere.

Toward ordered mesoporous rare-earth sesquioxide thin films via polymer templating: high temperature stable C-type Er2O3 with finely-tunable crystallite sizes

Facile polymer templating enables the production of cubic C-type Er2O3 thin films with a 3D honeycomb structure of 15–17 nm diameter pores and crystalline domain sizes ranging from 3–4 nm at 600 °C to ∼13 nm at 900 °C. These novel nanomaterials not only have a thermally stable and robust framework but are also well-defined at both the nano- and microscale.

Graphene-oxide-wrapped ZnMn2O4 as a high performance lithium-ion battery anode

Cation distribution between tetrahedral and octahedral sites within the ZnMn2O4 spinel lattice, along with microstructural features, is affected greatly by the temperature of heat treatment. Inversion parameter can easily be tuned, from 5 to 19%, depending on the annealing temperature. The upper limit of inversion is found for T= 400 °C as confirmed by X-ray powder diffraction and Raman spectroscopy. Excellent battery behavior is found for samples annealed at lower temperatures; after 500 cycles the specific capacities for as-prepared ZnMn2O4 is 909 mAh/g, while ZnMn2O4 heat-treated at 300 °C shows 1179 mAh/g which amounts to 101 % of its initial capacity. Despite excellent performance of sample processed at 300 °C at lower charge/discharge rates (100 mAh/g), a drop in the specific capacity is observed with rate increase. This issue is solved by graphene oxide wrapping; specific capacity obtained after 400th cycle for graphene oxide wrapped ZnMn2O4 heat-treated at 300 °C is 799 mAh/g at charge/discharge rate 0.5 A/g, which is higher by factor 6 compared to sample without graphene oxide wrapping.