Search

Perovskites are promising alternative materials for conventional Ni-based cermet anodes, benefitting from their mixed ionic and electronic conductivity properties and good structure stability. However, they generally show a commonplace electrochemical catalytic activity. Here, a novel anode material La 0.52 Sr 0.28 Ti 0.8 Co 0.1 Fe 0.1 O 3-δ (LSTCF) is successfully synthesized, and we report that the electrochemical performance of LSTCF can be commendably tuned by gas treatment, deriving from the exsolution of the impressively well-distributed Co-Fe alloy nanocatalyst with splendid catalytic activity for hydrogen electrochemical oxidation. At 900 °C, a power density value of 897 mW cm -2 is achieved by the treated LSTCF anode when using hydrogen as fuel, which is almost three times higher than that of the fresh anode. Moreover, we show that the nanoparticle-modified LSTCF perovskite also exhibits fascinating electrochemical catalytic activity at low temperatures.

Optical fiber composite low voltage cable (OPLC) is an optimal way of connecting the smart grid with the load. In this paper, the field distribution of temperature and stress is simulated by applying the finite element method. At the overload condition, the fiber unit's temperature rises to 59°C that generates the strain of 387 µε. This strain and temperature together result in the additional attenuation of 0.053 dB/km in the optical fiber. Temperature and strain are termed as the major contributing factors towards the attenuation in the optical fiber as temperature caused 16.03% while strain caused 80.56% of the total loss.

Two-dimensional (2D) graphtetrayne (G4) with intrinsic pattern triangular nanopores has been predicted to be an excellent candidate for next-generation proton exchange membranes due to its superior proton conductivity and selectivity. However, it is technically challenging to prepare a large area single-layer intact 2D material. A multi-layer stacked 2D material is a much more suitable choice, and the stacking can effectively shield the undesired defects and tears. In this work, we investigate the aqueous proton penetration behavior across multilayer-stacked two-dimensional G4 using extensive ReaxFF molecular dynamics simulations. We found that the G4 layers prefer a slightly misplaced stacking pattern which would cause only a slight reduction in the pore size. Detailed analyses indicate that the "water wires" across G4 remain continuous and can provide a low-barrier path for proton penetration until the number of stacking layers increases to three. In triple-layer G4, the "water wires" no longer exist and the aqueous phase will be separated by a wide vacuum area, thus significantly impeding the proton penetration behavior. Based on these results, we suggest that when serving as a proton exchange membrane, the number of stacking G4 layers should be fewer than three to achieve satisfactory conductivity. Our work provides guidance for the fabrication of next-generation proton exchange membranes based on nanoporous 2D materials.

The Al:HfO 2 ferroelectric nanofilms with different total thicknesses and distributions of Al-rich strips are prepared using atomic layer deposition (ALD) in an uncapped configuration. The synergistic interplay between the number of Al-rich layers and the thickness of total film offers the additional flexibility to boost the ferroelectricity of the resulting Al:HfO 2 nanofilms. By carefully optimizing both the ALD cycles for dopant layer and the total film thickness in the preparation, the HfO 2 nanofilms in post-deposition annealing can exhibit excellent ferroelectricity. The highest remanent polarization (2P r ) of 51.8 μ C cm -2 is obtained in a 19.4 nm thick Al:HfO 2 nanofilm at the dopant concentration of 11.1 mol% with a three ALD cycles for Al-rich strips. Remarkable remanent polarization value observed in the uncapped electrode clamping film paves a new way to explore the origin of ferroelectricity in hafnium oxide nanofilms. The observed ferroelectricity of the nanofilm is affected neither by the presence of an interface between the upper electrode and the film nor the choices of the materials of upper electrode in the measurement, ensuring a high flexibility in the designing and fabrication of the relevant devices in the future., (© 2021 IOP Publishing Ltd.)

Utilizing the latest SCAN-rVV10 density functional, we thoroughly assess the electrochemical properties of 35 Mo-based ordered double transition metal MXenes, including clean Mo2MC2 (M = Sc, Ti, V, Zr, Nb, Hf, Ta) and surface functionalized structures Mo2MC2T2 (T = H, O, F and OH), for the potential use as anode materials in lithium ion batteries (LIBs). The first principles molecular dynamics simulations in combination with the calculations of the site adsorption preferences for Li atoms on all investigated MXenes reveal that both Li-saturated adsorption structures and theoretical capacities of Mo-based MXenes are fundamentally influenced by the surface terminations. We find that the adsorption of Li atoms on either -OH or -F functionalized MXenes is chemically unstable. In particular, the F-groups prefer to form a separate fluoride layer with Li atoms, detaching from the Mo2MC2 substrates. The Li atoms could form a stable single adsorption layer on the -H, -O and intrinsic MXenes surface, exhibiting theoretical capacities in the range from 121 mA h g-1 to 195 mA h g-1. Besides -F and -OH terminations, the remaining Mo-based MXenes also possess superior flat open circuit voltage (OCV) profiles with the most reversible storage capacity below 1.0 V during the charging/discharging cycles. We further predict the low barrier heights of Li-ion diffusion, at a range of 0.03-0.06 eV for most Mo-based MXenes except -O and -H terminations, exceeding that of graphene or Ti3C2. Furthermore, combining the Vineyard transition state theory (TST) with the phonon spectra obtained from density functional perturbation theory (DFPT), the mean planar diffusion coefficient is calculated to be 2 × 10-8 m2 s-1 at 300 K for intrinsic Mo2MC2 monolayers. Although the overall specific capacity is fundamentally restricted with the relatively heavy molecular mass of MXenes, we conclude that Mo-based structures, especially the intrinsic Mo2MC2 (M = Sc, Ti, V) monolayers, might be promising anode materials from the aspect of fast charging/discharging application for LIBs.

Sodium-ion batteries (SIBs) have been recognized as the promising alternatives to lithium-ion batteries for large-scale applications owing to their abundant sodium resource. Currently, one significant challenge for SIBs is to explore feasible anodes with high specific capacity and reversible pulverization-free Na + insertion/extraction. Herein, a facile co-engineering on polymorph phases and cavity structures is developed based on CoMo-glycerate by scalable solvothermal sulfidation. The optimized strategy enables the construction of CoMoO x S y with synergized partially sulfidized amorphous phase and yolk-shell confined cavity. When developed as anodes for SIBs, such CoMoO x S y electrodes deliver a high reversible capacity of 479.4 mA h g -1 at 200 mA g -1 after 100 cycles and a high rate capacity of 435.2 mA h g -1 even at 2000 mA g -1 , demonstrating superior capacity and rate capability. These are attributed to the unique dual merits of the anodes, that is, the elastic bountiful reaction pathways favored by the sulfidation-induced amorphous phase and the sodiation/desodiation accommodatable space benefits from the yolk-shell cavity. Such yolk-shell nano-battery materials are merited with co-tunable phases and structures, facile scalable fabrication, and excellent capacity and rate capability in sodium storage. This provides an opportunity to develop advanced practical electrochemical sodium storage in the future., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Micro/nanoscale tungsten probes are widely utilized in the fields of surface analysis, biological engineering, etc. amongst several others. This work performs comprehensive dynamic simulations on the influences of electric field distribution, surface tension and the bubbling situation on electrochemical etching behaviors, and then the tip dimension. Results show that the etching rate is reliant on the electric field distribution determined by the cathode dimension. The necking position lies in the meniscus rather than at the bottom of the meniscus. A bubble-free condition is mandatory to stabilize the distribution of OH - and WO 4 2- ions for a smooth tungsten probe surface. Such simulation-guidance enables the nanofabrication of probes with a high aspect ratio (10 : 1), ultra-sharp tip apex (40 nm) and ultra-smooth surface. These probes have been successfully developed for high-performance application with Scanning Tunneling Microscopy (STM). The acquired decent atomic resolution images of epitaxial bilayer graphene robustly verify the feasibility of the practical level application of these nanoscale probes. Therefore, these nanoscale probes would be of great benefit to the development of advanced analytical science and nano-to-atomic scale experimental science and technology., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We investigate aqueous proton penetration behavior across a newly synthesized nanoporous two-dimensional conjugated aromatic polymer (2D-CAP) membrane using extensive ReaxFF reactive molecular dynamics simulations. We found that the proton penetration energy barrier across 2D-CAP is twice as high as that of graphtetrayne, even though 2D-CAP exhibits a larger pore size. Detailed analysis indicates that the anomalous high proton conduction energy barrier of 2D-CAP originates from its unique atomic nanopore structure. The hydrogen atoms at the periphery of the 2D-CAP nanopores can form a stable local hydrogen bond network with water molecules inside or surrounding the nanopores. The mobility of water molecules involved in this local hydrogen bond network will be significantly lowered, and the proton transportation process across the nanopores will thus be impeded. Our results show that the proton penetration behavior across nanoporous 2D materials is influenced not only by the pore size, but also by the decorated atoms or functional groups at the pore edges. Hydrogen atoms at the periphery of nanopores with certain geometry can form a stable local hydrogen bond network with neighboring water molecules, further hampering the proton conductivity.

Using SCAN-rVV10+U, we show Cr 2 TiC 2 and Cr 2 TiC 2 T 2 (T = -F and -OH) MXenes are moderate band gap semiconductors mostly in the antiferromagnetic state. All investigated MXene structures show large Seebeck coefficients (>400 μV/K), especially Cr 2 TiC 2 (>800 μV/K) and Cr 2 TiC 2 F 2 (>700 μV/K). The hole relaxation time of p-type Cr 2 TiC 2 (OH) 2 is found to be ∼8 ps, ensuring its superior electron transport properties in comparison to other investigated MXenes. It is also discovered that the surface functionalization could decrease the phonon thermal conduction and that Cr 2 TiC 2 (OH) 2 has the smallest lattice thermal conductivity (∼6.5 W/m·K) and the largest electron thermal conduction (>50 W/m·K with n = 10 19 cm -3 ). We predict the ZT value of p-type Cr 2 TiC 2 (OH) 2 can reach 3.0 at 600 K with the maximum thermoelectric conversion efficiency of 20%. Overall, the thermoelectric property of Cr-based ordered double transition metal MXenes is far superior to that of any known two-dimensional structures in the MXene family.