Optimizing electrochemical performance of Na0.67Ni0.17Co0.17Mn0.66O2 with P2 structure via preparing concentration-gradient particles for sodium-ion batteries.

P2-type layered oxides for rechargeable sodium-ion batteries have drawn a lot of attention because of their excellent electrochemical performance. However, these types of cathodes usually suffer from poor cyclic stability. To overcome this disadvantage, in this work, novel ball-shaped concentration-gradient oxide Na0.67Ni0.17Co0.17Mn0.66O2 with P2 structure modified by Mn-rich surface is successfully prepared using co-precipitation method. The concentration of Mn increased from the inner core to the surface, endowing the material with an excellent cyclic stability. The cathode exhibits enhanced electrochemical properties than that of the sample synthesized by solid-state method and concentration-constant material. It shows 143.2 mAh/g initial discharge capacity and retains 131 mAh/g between 2 V and 4.5 V after 100 rounds. The significant improvement in the electrochemical properties of the sample benefits from the unique concentration-gradient structure, and the Mn-rich surface that effectively stabilizes the basic P2 structure. The relatively higher Ni content in the core leads to a slight improvement in the discharge capacity of the sample. This strategy may provide new insights for preparing layered cathodes for sodium-ion batteries with high electrochemical performance.

A dual-modification strategy for P2-type layered oxide via bulk Mg/Ti co-substitution and MgO surface coating for sodium ion batteries.

P2-type materials are regarded as competitive cathodes for next generation sodium ion batteries. However, the unfavorable P2 â†’ O2 phase transition usually leads to severe capacity decay. Moreover, the cathode material always suffers from destruction of surface crystal structure caused by trace amount of HF. In this study, a dual-modification method containing Mg/Ti co-doping and MgO surface coating is designed to solve the defects of P2-type Na0.67Ni0.17Co0.17Mn0.66O2 cathode. Results turn out that the P2 structure can be stabilized via Mg/Ti co-substitution and MgO layer could effectively prevent the surface from corroding by HF and promote migration of Na+. Moreover, the as-prepared MgO-coated Na0.67Ni0.17Co0.17Mn0.66Mg0.1O2 exhibits improved electrochemical performance than the raw material. It delivers 111.6 mAh g-1 initial discharge capacity and maintains 90.6% at high current density of 100 mA g-1 within 2-4.5 V, which has been obviously enhanced than that of Na0.67Ni0.17Co0.17Mn0.66O2. The significant improvement can be attributed to the synergistic effect of Mg/Ti co-substitution and MgO surface coating. This dual-modification strategy based on the synergetic effect of Mg/Ti co-doping and MgO surface coating might be a resultful step forward to develop cathode materials for sodium ion batteries.

Core-Shell Structured PtxMoy@TiO2 Nanoparticles Synthesized by Reverse Microemulsion for Methanol Electrooxidation of Fuel Cells.

The high price of catalyst and poor durability still restrict the development of fuel cells. In this work, core-shell structured PtxMoy@TiO2 nanoparticles with low Pt content are prepared by a reverse microemulsion method. The morphologies, particle size, structure, and composition of PtxMoy@TiO2 nanoparticles are examined by several techniques such as X-ray Diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy, etc. The PtxMoy@TiO2 electrocatalysts show significantly higher catalytic activity and better durability for methanol oxidation than the commercial Pt/C (ETEK). Compared to Pt/C catalyst, the enhancement of the electrochemical performance of PtxMoy@TiO2 electrocatalysts can be attributed to the core-shell structure and the shift of the d-band center of Pt atoms, which can weaken the adsorption strength toward CO molecules, facilitate the removal of the CO groups and improve electrocatalytic activity. The development of PtxMoy@TiO2 electrocatalysts is promising to reduce the use of noble metal Pt and has a great potential for application in fuel cells.

Improving the electrochemical performance of layered cathode oxide for sodium-ion batteries by optimizing the titanium content.

P2-type transition metal oxides are promising cathode materials for sodium-ion batteries. However, due to irreversible phase transition, these batteries exhibit low capacity and poor cycling stability. In this study, highly dense, spherical P2-type oxides Na0.67[Ni0.167Co0.167Mn0.67]1-xTixO2 (0 ≤ x ≤ 0.4) are synthesized by calcining a mixture of Na2CO3, spherical ternary precursor powder Ni0.167Co0.167Mn0.67O2, and different amounts of nanoscale TiO2. High-temperature X-ray diffraction results obtained during calcination reveal 850 °C as the optimum calcination temperature. All materials exhibit high crystallinity without any impurity phases. The initial reversible capacities of the as-prepared samples decrease with increasing Ti substitution; however, these samples attain better cycling stability. When x = 0.2, the sample delivers an initial discharge capacity of 138 mAh g-1 at 20 mA g-1 between 2 and 4.5 V. Even at 100 mA g-1, the sample delivers 101 mAh g-1 reversible capacity in the first cycle with capacity retention of 89.4% after 300 cycles. Moreover, the material shows sloping potential profiles, with the average voltages reaching up to ∼3.8 V. The ex-situ X-ray diffraction (XRD) results of the samples after cycling demonstrate that Ti substitution improves the structural stability. In general, Ti substitution is an effective approach for improving the electrochemical performance of ternary P2-type oxide Na0.67Ni0.167Co0.167Mn0.67O2.

Ethyl (E)-3-hy-droxy-2-{N-[2-(thio-phen-2-yl)ethen-yl]carbamo-yl}but-2-enoate.

In the title compound, C(13)H(15)NO(4)S, there are two independent but conformationally similar mol-ecules in the asymmetric unit, both having an E conformation of the side-chain C=C group. Intra-molecular N-H⋯O and O-H⋯O hydrogen-bonding inter-actions are present in both molecules. In the crystal, one of the mol-ecule types is linked through inter-molecular hy-droxy-ketone O-H⋯O inter-actions, forming one-dimensional chains extending along [010], whereas the other mol-ecule type shows no associations.