The tunable porosity of titania thin films is a key factor for successful applications in photovoltaics, sensing, and photocatalysis. Here, we report on nanocrystalline cellulose (NCC) as a novel ...shape-persistent templating agent enabling the straightforward synthesis of mesoporous titania thin films. The obtained structures are highly porous anatase morphologies having well-defined, narrow pore size distributions. By varying the titania-to-template ratio, it is possible to tune the surface area, pore size, pore anisotropy, and dimensions of titania crystallites in the films. Moreover, a post-treatment at high humidity and subsequent slow template removal can be used to achieve pore widening; this treatment is also beneficial for the multilayer deposition of thick films. The resulting homogeneous transparent films can be directly spin- or dip- coated on glass, silicon, and transparent conducting oxide (TCO) substrates. The mesoporous titania films show very high activity in the photocatalytic NO conversion and in the degradation of 4-chlorophenol. Furthermore, the films can be successfully applied as anodes in dye-sensitized solar cells.
Ceramic solid state-electrolytes attract significant attention due to their intrinsic safety and, in the case of the garnet type Li
6.45
Al
0.05
La
3
Zr
1.6
Ta
0.4
O
12
(LLZO), the possibility to use ...Li-metal anodes to provide high energy densities on a cell and battery level. However, one of the major obstacles hindering their wide-spread application is the translation and optimization of production processes from laboratory to industrial scale. Even though the plausibility of manufacturing components and cells
via
wet processing routes like tape casting and screen printing has been shown, the impact of the sensitivity of LLZO to air and protic solvents due to Li
+
/H
+
-exchange is not fully understood yet. An uncontrolled alteration of the powder surface results in poorly reproducible processing characteristics and electrochemical performance of the final battery components and full cells. This knowledge gap is the cause of the large performance variations reported across different research labs worldwide and is unacceptable for up-scaling to industrial level. To close this gap, the influence of the Li
+
/H
+
-exchange taking place at various steps in the manufacturing process was systematically investigated in this study. For the first time, this allowed a mechanistic understanding of its impact on the processability itself and on the resulting electrochemical performance of a free-standing LLZO separator. The importance of a close control of the pre-treatment and storage conditions of LLZO, as well as contact time with the solvent could be extracted for each step of the manufacturing process. As a result, we were able to optimize the processing of thin, dense, free standing LLZO separators and significantly improve the total Li-ion conductivity to 3.90 × 10
−4
S cm
−1
and the critical current density to over 300 μA cm
−2
without making structural changes to separator or the starting material. These findings do not only enable a deeper understanding and control over the manufacturing process, but also show potential for further improvement of cell concepts already existing in literature.
A new, mechanistic understanding of the lithium proton exchange in LLZO enables reproducible processing and performance optimization for tape-cast components.
This work focuses on a very narrow region in the quaternary system Na2O-P2O5-SiO2-ZrO2 to explore the occasionally proposed deficiency in zirconium and oxygen content of Na+ super-ionic conductor ...(NaSICON) materials. In addition, this region is known for the formation of glass-ceramics, but a systematic study of such materials has not been carried out yet. For this purpose, 2 series of compositions were defined and synthesized: Na3.4Zr2-3x/4Si2.4-x/4P0.6+x/4O12-11x/8 and Na3.4Zr2-3x/4Si2.4+x/4P0.6+1.5x/4O12-x/16. They only differ in the silicate and phosphate content. In the first series the molar content is constant, nSi+ nP = 3. The latter series allows an excess of the 2 cations to meet the composition Na3.1Zr1.55Si2.3P0.7O11 or alternatively re-written as Na3.4Zr1.7Si2.52P0.77Ol2, which was formerly regarded as a superior material to the frequently reported composition Na3Zr2Si2POl2.
Several characterization techniques were applied to better understand the relationships between phase formation, processing, and properties of the obtained glass ceramics in the context of the quasi-quaternary phase diagram. The investigations gave clear evidence that a glass phase is progressively formed with increasing x. Therefore, compounds with x > 0.2 have to be regarded as glass-ceramic composites. The resulting NaSICON materials revealed a very limited Zr deficiency with charge compensation by Na ions and a non-detectable amount of oxygen vacancies verified by neutron scattering and atomistic simulations.
Hence, this work is the first systematic investigation of pretended Zr-deficient NaSICON materials, which clearly show the chemistry of a 2-phase region. The 2 investigated series are directed toward a region that is orthogonal to the series Na3Zr3-ySi2PyO11.5+y/2 reported in the first part of this series of publications.
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The “brick and mortar” approach is employed to synthesize thick surfactant-templated mesoporous titanium dioxide films of up to 10 μm thickness using multilayer deposition. The films exhibit very ...high surface areas scaling linearly with the thickness, and roughness factors of up to 1600 cm2/cm2 can be reached. For the first time, surfactant-derived mesoporous titanium dioxide films of such a large thickness and surface area can be prepared without serious cracking, delamination, or deterioration of the porous structure. The mesopores are rather large (12 nm), and stacking many layers does not affect their size or accessibility, which is shown by krypton and dye adsorption experiments. Applied in dye-sensitized solar cells, the films feature a high power conversion efficiency of over 7% already at thicknesses below 4 μm due to their high surface area and dye adsorption.
We report the syntheses of various compounds within the pseudo‐quaternary system of the type LiwNixCoyMnzOδ (δ≤1) (pre‐NCMs). Four different compositions of this compound were realized as ultrasmall ...crystalline nanoparticles of 1–4 nm diameter using low‐temperature solvothermal reaction conditions in tert‐butanol at only 170 °C. All of the pre‐NCMs crystallize in the rock‐salt structure and their lithium content is between 20% and 30% with respect to the complete metal content. By adjusting the lithium content to 105% stoichiometry in the solvothermal reaction, the pre‐NCMs can easily react to the respective Li(NixCoyMnz)O2 (NCM) nanoparticles. Furthermore, nanosized desert‐rose structured NCMs were obtained after addition of nanocellulose during the synthesis. By using the mixed metal monoxides as precursor for the NCMs, cation mixing between lithium and nickel is favored and gets more pronounced with increasing nickel content. The cation mixing effect compromises good electrochemical capacity retention, but the desert‐rose structure nevertheless enables enhanced stability at high power conditions, especially for NCM333.
Ultrasmall nanoparticles of the pseudo‐quaternary phase LiwNixCoyMnzOδ were deliberately synthesized in four different compositions by a solvothermal approach in tert‐butanol. All four different types of nanoparticles can be transformed together with an overstoichiometric lithium source and through templating with nanocellulose in a simple low‐temperature calcination step into desert‐rose type Li(NixCoyMnz)O2 (NCMs) with the respective compositions. These NCMs serve as cathode materials in lithium‐ion batteries with stable gravimetric capacities even at high charge/discharge rates.
We report on the pH-dependent bioelectrocatalytic activity of the redox enzyme xanthine dehydrogenase (XDH) in the presence of sulfonated polyaniline PMSA1 (poly(2-methoxyaniline-5-sulfonic ...acid)-co-aniline). Ultraviolet–visible (UV-vis) spectroscopic measurements with both components in solution reveal electron transfer from the hypoxanthine (HX)-reduced enzyme to the polymer. The enzyme shows bioelectrocatalytic activity on indium tin oxide (ITO) electrodes, when the polymer is present. Depending on solution pH, different processes can be identified. It can be demonstrated that not only product-based communication with the electrode but also efficient polymer-supported bioelectrocatalysis occur. Interestingly, substrate-dependent catalytic currents can be obtained in acidic and neutral solutions, although the highest activity of XDH with natural reaction partners is in the alkaline region. Furthermore, operation of the enzyme electrode without addition of the natural cofactor of XDH is feasible. Finally, macroporous ITO electrodes have been used as an immobilization platform for the fabrication of HX-sensitive electrodes. The study shows that the efficient polymer/enzyme interaction can be advantageously combined with the open structure of an electrode material of controlled pore size, resulting in good processability, stability, and defined signal transfer in the presence of a substrate.
Ultrasmall, crystalline and dispersible NiO nanoparticles are prepared for the first time by T. Bein, D. Fattakhova‐Rohlfing and colleagues using a solvothermal reaction in tert‐butanol. On page ...3123, these nanocrystals can be prepared with sizes tunable from 2.5 to 5 nm and are highly efficient catalysts for electrochemical oxygen generation. Credit: Cover by Christoph Hohmann, Nanosystems Initiative Munich (NIM).
Light-driven water electrolysis at a semiconductor surface is a promising way to generate hydrogen from sustainable energy sources, but its efficiency is limited by the performance of available ...photoabsorbers. Here we report the first time investigation of covalent organic frameworks (COFs) as a new class of photoelectrodes. The presented 2D-COF structure is assembled from aromatic amine-functionalized tetraphenylethylene and thiophene-based dialdehyde building blocks to form conjugated polyimine sheets, which π-stack in the third dimension to create photoactive porous frameworks. Highly oriented COF films absorb light in the visible range to generate photoexcited electrons that diffuse to the surface and are transferred to the electrolyte, resulting in proton reduction and hydrogen evolution. The observed photoelectrochemical activity of the 2D-COF films and their photocorrosion stability in water pave the way for a novel class of photoabsorber materials with versatile optical and electronic properties that are tunable through the selection of appropriate building blocks and their three-dimensional stacking.
Sodium is a promising candidate for stationary storage applications, especially when the demand for lithium-ion batteries increases due to electromobility applications. Even though its energy density ...is lower, Na-ion technology is estimated to lead to a cost reduction of 30% compared to Li-ion technology. To improve safety as well as energy density, Na-based all-solid-state-batteries featuring solid electrolytes such as beta-alumina and sodium superionic conductors and cathode materials such as Na
3
V
2
(PO4)
3
and Na
x
CoO
2
have been developed over the past years. However, the biggest challenge are mixed cathodes with highly conductive interfaces, especially when co-sintering the materials. For example, a promising sodium superionic conductor type Na
3
Zr
2
Si
2
PO
12
electrolyte sinters at 1,250°C, whereas the corresponding Na
3
V
2
PO
12
cathode decomposes at temperatures higher than 900°C, posing a bottleneck. Thus in this paper, we synthesized Na
0.62
Ni
0.10
Fe
0.10
Mn
0.80
O
2
as cathode material for all-solid-state sodium-ion batteries
via
a relatively cheap and easy solution-assisted solid state reaction processing route. The thermal investigations of the pure cathode material found no degradation up to 1,260°C, making it a perfect match for Na
3.4
Zr
2
Si
2.4
P
0.6
O
12
electrolyte. In our aim to produce a co-sintered mixed cathode, electron microscopy investigation showed a highly dense microstructure and the elemental mapping performed
via
energy dispersive X-ray spectroscopy and secondary ion mass spectrometry confirm that Na
3.4
Zr
2
Si
2.4
P
0.6
O
12
and Na
0.62
Ni
0.10
Fe
0.10
Mn
0.80
O
2
do not react during sintering. However, the active cathode material forms a sodium rich and a sodium deficient phase which needs further investigation to understand the origin and its impact on the electrochemical performance.
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