Retraction: Co3 O4 Polyhedron@MnO2 Nanotube Composite as Anode for High-Performance Lithium-Ion Batteries.

Small 2021, 17, 2008165 DOI: 10.1002/smll.202008165 The above article in Small, published online on 26 March 2021 in Wiley Online Library (https://onlinelibrary.wiley.com/doi/abs/10.1002/smll.202008165),[1] has been retracted by agreement between the authors, the Editor-in-Chief, José Oliveira, and Wiley-VCH GmbH. The retraction has been agreed following an investigation by the corresponding author. The electrochemical measurements on the anode were performed in a wrong manner and cannot reliably be reproduced. The conclusions of this article are considered to be invalid. The authors agree with the retraction but were not available to confirm the final wording of the retraction. [1] Z. Cao, Y. Yang, J. Qin, J. He, Z. Su, Small 2021, 17, 2008165.

Field-Assisted Formation of NH4CoF3 Mesocrystals toward Hierarchical Co3O4 Cuboids as Anode Materials for Lithium-Ion Batteries.

Porous NH4CoF3 mesocrystalline cuboids with highly exposed {100} facets are grown by in situ reaction of products produced by high field anodization of cobalt metal foil, via a nonclassical crystallization process involving oriented particle aggregation. 3D nano-micro hierarchical Co3O4 cuboids are obtained by thermal annealing of NH4CoF3 mesocrystals. The microstructure and morphology of products are characterized by electron microscopy and X-ray diffraction. The combination of small nanoparticle subunits, micrometer-sized overall particles, and porous structure provides the obtained hierarchical Co3O4 cuboids with large electrolyte-electrode contact areas, channels for large lithium ion flux, pore accessibility, and structural stability, leading to excellent rate and cyclic performance as lithium-ion battery (LIB) anodes.

Electric field driven fast fabrication of 3D ordered Nano-micro hierarchical ammonium oxofluorotitanates towards mesocrystalline anatase TiO2.

In this work, 3D ordered nano-micro hierarchical ammonium oxofluorotitanates are synthesized by in-situ dissolution of anodically grown TiO2 nanotubes and subsequent hydrolysis of (NH4)2TiF6 in an electrochemical cell via a nonclassical crystallization process by external electric field driven oriented particle attachment. The obtained ammonium oxofluorotitanate products are of mesocrystalline structure consisting of nanocrystalline building units oriented aligned at atomic level. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) characterizations are applied to reveal the morphology, structure and crystal phase of grown samples. By controlling the current density or/and content of ammonium fluoride, it is able to grow well-defined (NH4)3TiOF5 octahedrons and truncated octahedrons, (NH4)2TiOF4 nanorods and NH4TiOF3 disks. The transformation from (NH4)3TiOF5 octahedrons to truncated octahedrons is ascribed to the different ratios of growth rate for {111} planes and {100} planes. While the decrease of concentration of ammonium fluoride accounts for the crystal phase changes from (NH4)3TiOF5 to (NH4)2TiOF4 and finally to NH4TiOF3 disks. Upon thermal annealing, all these ammonium oxofluorotitanates could be converted to mesoporous hierarchical anatase TiO2 retaining their exterior morphology and keeping the orientation ordering of subunit nanoparticles, which could exhibit excellent photocatalytic activity when acting as photocatalyst in the photo-degradation of methylene blue.

(NH4)3FeF6 mesocrystals grown by electric field-assisted in situ dissolution and the reaction of anodic iron oxides.

(NH4)3FeF6 mesocrystalline octahedrons are formed by in situ dissolution and the reaction of anodic iron oxides, followed by a non-classical crystal growth process involving electrical polarization and subsequent alignment of primary (NH4)3FeF6 particles under an external electric field. The obtained (NH4)3FeF6 can be converted to nano-micro hierarchical α-Fe2O3 octahedrons by thermal annealing.

Co3 O4 Polyhedron@MnO2 Nanotube Composite as Anode for High-Performance Lithium-Ion Batteries.

In this work, a novel lollipop nanostructure of Co3 O4 @MnO2 composite is prepared as anode material in lithium-ion batteries (LIBs). Cobalt metal-organic framework (ZIF-67) is grown on the open end of MnO2 nanotubes via a self-assembly process. The obtained ZIF-67@MnO2 is then converted to Co3 O4 @MnO2 by a simple annealing treatment in air. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction characterizations indicate that the prepared Co3 O4 @MnO2 takes a lollipop nanostructure with a stick of ≈100 nm in diameter, consisting of MnO2 nanotube, and a head part of ≈1 µm, consisting of Co3 O4 nanoparticles. The charge-discharge tests illustrate that this unique novel configuration endows the resulting Co3 O4 @MnO2 with excellent electrochemical performances, delivering a capacity of 1080 mAh g-1 at 300 mA g-1 after 160 cycles, and 696 mAh g-1 at 1 A g-1 after 210 cycles, compared with 404 mAh g-1 and 590 for pure Co3 O4 polyhedrons and pure MnO2 nanotubes at 300 mA g-1 after 160 cycles, respectively. The lollipop configuration consisting of porous Co3 O4 polyhedron and MnO2 nanotube shows excellent structural stability and facilitates lithium insertion/extraction, leading to excellent cyclic stability and rate capacity of Co3 O4 @MnO2 -based LIBs.

Toluene oxidation over Co3+-rich spinel Co3O4: Evaluation of chemical and by-product species identified by in situ DRIFTS combined with PTR-TOF-MS.

Series of Co3+-rich spinel Co3O4 catalysts were synthesized and evaluated by toluene catalytic oxidation. An outstanding activity was achieved over Co3O4-N utilizing Co(NO3)2·6H2O as precursor (T50 = 211 °C, T90 = 217 °C at conditions: 1000 ppm(v), WHSV = 60 000 mL g-1 h-1). Results of comparative characterizations demonstrated that such excellent performance was mainly attributed to large surface area, high reducibility at low temperature, high abundance of Co3+ ions and structure defects, as well as highly active surface oxygen. The results of in situ DRIFTS revealed that in the air or N2 atmosphere, the by-products were almost the same. The reaction pathway of toluene oxidation can be described as follow: transformation of toluene from benzyl alcohol, benzaldehyde, benzoate, benzene, phenol, benzoquinone, maleic acid and to final products, which were fully confirmed by PTR-TOF-MS. Besides, ring opened by-products, such as acetone, acetic acid, acetaldehyde, etc. were also detected. In this work, the combination of in situ DRIFTS and PTR-TOF-MS provided a promising approach for further understanding of the mechanism of VOCs elimination.

Ultrafast Elemental and Oxidation-State Mapping of Hematite by 4D Electron Microscopy.

We describe a new methodology that sheds light on the fundamental electronic processes that occur at the subsurface regions of inorganic solid photocatalysts. Three distinct kinds of microscopic imaging are used that yield spatial, temporal, and energy-resolved information. We also carefully consider the effect of photon-induced near-field electron microscopy (PINEM), first reported by Zewail et al. in 2009. The value of this methodology is illustrated by studying afresh a popular and viable photocatalyst, hematite, α-Fe2O3 that exhibits most of the properties required in a practical application. By employing high-energy electron-loss signals (of several hundred eV), coupled to femtosecond temporal resolution as well as ultrafast energy-filtered transmission electron microscopy in 4D, we have, inter alia, identified Fe4+ ions that have a lifetime of a few picoseconds, as well as associated photoinduced electronic transitions and charge transfer processes.

On the dynamical nature of the active center in a single-site photocatalyst visualized by 4D ultrafast electron microscopy.

Understanding the dynamical nature of the catalytic active site embedded in complex systems at the atomic level is critical to developing efficient photocatalytic materials. Here, we report, using 4D ultrafast electron microscopy, the spatiotemporal behaviors of titanium and oxygen in a titanosilicate catalytic material. The observed changes in Bragg diffraction intensity with time at the specific lattice planes, and with a tilted geometry, provide the relaxation pathway: the Ti(4+)=O(2-) double bond transformation to a Ti(3+)-O(1-) single bond via the individual atomic displacements of the titanium and the apical oxygen. The dilation of the double bond is up to 0.8 Å and occurs on the femtosecond time scale. These findings suggest the direct catalytic involvement of the Ti(3+)-O(1-) local structure, the significance of nonthermal processes at the reactive site, and the efficient photo-induced electron transfer that plays a pivotal role in many photocatalytic reactions.

Hydrothermal growth of highly oriented single crystalline Ta2O5 nanorod arrays and their conversion to Ta3N5 for efficient solar driven water splitting.

We grow vertically aligned single crystalline Ta2O5 nanorod arrays that can be converted to Ta3N5 nanorod arrays by nitridation. Combined with cobalt phosphate (Co-Pi) as a co-catalyst, such Ta3N5 nanorod photoanodes can yield photocurrent densities of ∼3.6 mA cm(-2) at 1.23 VRHE and ∼8.2 mA cm(-2) at 1.59 VRHE under AM 1.5G (100 mW cm(-2)) irradiation.

Self-organized cobalt fluoride nanochannel layers used as a pseudocapacitor material.

Aligned CoF2 nanochannel layers have been formed by self-ordering electrochemical anodization. In voltammograms these layers provide multiple oxidation states, an almost ideal rectangular pseudocapacitive behavior, a high specific capacitance and good capacitance retention. These layers may thus be promising for supercapacitor applications.

Highly graphitized nitrogen-doped porous carbon nanopolyhedra derived from ZIF-8 nanocrystals as efficient electrocatalysts for oxygen reduction reactions.

Nitrogen-doped graphitic porous carbons (NGPCs) have been synthesized by using a zeolite-type nanoscale metal-organic framework (NMOF) as a self-sacrificing template, which simultaneously acts as both the carbon and nitrogen sources in a facile carbonization process. The NGPCs not only retain the nanopolyhedral morphology of the parent NMOF, but also possess rich nitrogen, high surface area and hierarchical porosity with well-conducting networks. The promising potential of NGPCs as metal-free electrocatalysts for oxygen reduction reactions (ORR) in fuel cells is demonstrated. Compared with commercial Pt/C, the optimized NGPC-1000-10 (carbonized at 1000 °C for 10 h) catalyst exhibits comparable electrocatalytic activity via an efficient four-electron-dominant ORR process coupled with superior methanol tolerance as well as cycling stability in alkaline media. Furthermore, the controlled experiments reveal that the optimum activity of NGPC-1000-10 can be attributed to the synergetic contributions of the abundant active sites with high graphitic-N portion, high surface area and porosity, and the high degree of graphitization. Our findings suggest that solely MOF-derived heteroatom-doped carbon materials can be a promising alternative for Pt-based catalysts in fuel cells.

New insight into the soot nanoparticles in a candle flame.

Using anodic aluminium oxide films as collectors, all four well known carbon forms, diamond, graphitic, fullerenic and amorphous particles, are identified inside a candle flame, suggesting a new nucleation mechanism for diamond growth and fullerene formation in a combustion synthesizing process.

Ionic nano-convection in anodisation of aluminium plate.

An ionic nano-convection model has been established for elucidating early stage anodisation of aluminium plate and the direct consequence of such convection is an ordered pattern of charge distribution near the oxide/electrolyte interface, guiding the initial ordering of the pore formation.

Dissociation of water during formation of anodic aluminum oxide.

According to model computations at the B3LYP/6-311+G** level, an external electric field can facilitate the heterolytic dissociation of properly oriented water molecules significantly. Depending on the models used, the maximum predicted change of the dissociation energy in the field is ca. -3 to -4 kcal nm mol(-1) V(-1), and decreases with the cosine of the angle between the external field and the breaking OH bond. These microscopic results can be related semiquantitatively to macroscopic observables from mechanistic studies on the pore formation of anodic aluminum oxide, thus lending support to the equifield strength model and field-enhanced water dissociation at the growing oxide surface that has been put forward in these studies.

Temperature-dependent Raman scattering of silicon nanowires.

Silicon nanowires with narrowly distributed diameters of 20-30 nm have been fabricated by chemical vapor deposition on an anodized aluminum oxide (AAO) substrate. The first-order and second-order Raman scatterings of the silicon nanowires have been studied in a temperature range from 123 to 633 K. Both of the first-order and second-order Raman peaks were found to shift and broaden with increasing temperature. The experimental results were analyzed by combining the phonon confinement effect, anharmonic phonon processes and lattice stress effect. It was found that the intensities of the first-order and second-order Raman bands have different dependences on temperature. The value of relative intensities I(2TA)int/I(2TO)int for silicon nanowires was found to be larger than that of bulk silicon, and increase with rising measurement temperature. We ascribe this phenomenon to the participation of phonons with a large wave vector value of Raman scattering caused by both the phonon confinement effect and the temperature effect.