Songbai Han

Phosphine and methane generation by the addition of organic compounds containing carbon-phosphorus bonds into incubated soil

Formation of phosphine and methane in anaerobic incubation systems was investigated under stirred and unstirred conditions. The PH3 and CH4 levels in the headspace, as well as the matrix-bound PH3 content in the stirred soil, significantly increased upon the addition of phosphonoacetic acid (P(O)(OH)2CH2COOH). Both the levels of matrix-bound PH3 and CH4 are positively correlated to the buffered dithionite fraction of reactive phosphorus in the soil samples, while a negative correlation was observed between matrix-bound PH3/CH4 levels and the reactive phosphorus fraction.

Decreasing Li/Ni Disorder and Improving the Electrochemical Performances of Ni-Rich LiNi0.8Co0.1Mn0.1O2 by Ca Doping

Decreasing Li/Ni disorder has been a challenging problem for layered oxide materials, where disorder seriously restricts their electrochemical performances for lithium-ion batteries (LIBs). Element doping is a great strategy that has been widely used to stabilize the structure of the cathode material of an LIB and improve its electrochemical performance. On the basis of the results of previous studies, we hypothesized that the element of Ca, which has a lower valence state and larger radius compared to Ni2+, would be an ideal doping element to decrease the Li/Ni disorder of LiMO2 materials and enhance their electrochemical performances. A Ni-rich LiNi0.8Mn0.1Co0.1O2 cathode material was selected as the bare material, which usually shows severe Li/Ni disorder and serious capacity attenuation at a high cutoff voltage. So, a series of Ca-doped LiNi0.8(1-x)Co0.1Mn0.1Ca0.8xO2 (x = 0-8%) samples were synthesized by a traditional solid-state method. As hypothesized, neutron diffraction showed that Ca-doped LiNi0.8Co0.1Mn0.1O2 possessed a lower degree of Li/Ni disorder, and potentiostatic intermittent titration results showed a faster diffusion coefficient of Li+ compared with that of LiNi0.8Mn0.1Co0.1O2. The Ca-doped LiNi0.8Mn0.1Co0.1O2 samples exhibited higher discharge capacities and better cycle stabilities and rate capabilities, especially under a high cutoff voltage with 4.5 V. In addition, the problems of polarization and voltage reduction of LiNi0.8Mn0.1Co0.1O2 were also alleviated by doping with Ca. More importantly, we infer that it is crucial to choose an appropriate doping element and our findings will help in the research of other layered oxide materials.

Fe3O4@porous carbon hybrid as the anode material for a lithium-ion battery: performance optimization by composition and microstructure tailoring

Confining Fe3O4 into nanoporous carbon frameworks has been achieved through self-assembly and the use of a subsequent syn-carbonization strategy, where Fe3O4 and carbon frameworks are generated simultaneously and Fe3O4 particles are confined into porous carbon frameworks (Fe3O4@C). Both the composition and microstructure have a significant effect on the electrochemical performances. In comparison with bulk Fe3O4, Fe3O4@C-2 with optimal void pore volume and oxide content shows a significant enhancement in both cycling stability and high-rate capacity. The reversible capacity of Fe3O4@C-2 is retained at 932 mA h g−1 after 100 cycles compared to only 410 mA h g−1 for bulk Fe3O4. The capacity of Fe3O4@C-2 at the current density of 2 A g−1 has been significantly improved to 478 mA h g−1 from only 26 mA h g−1 for bulk Fe3O4. The considerable enhancement of both the cyclability and high-rate capability can be attributed to the synergic effect of nanoconfinement as well as the optimized composition and microstructure: the good dispersion of oxide particles, and the efficient volume change alleviation during the discharge–charge process.

Ultrahigh cycling stability and rate capability of ZnFe2O4@graphene hybrid anode prepared through a facile syn-graphenization strategy

A ZnFe2O4–reduced graphene oxide (ZnFe2O4–RGO) hybrid has been successfully synthesized through a facile syn-graphenization strategy. In this preparation procedure, N2H4·H2O works as both a base source and a reductant, and the reduction of graphene oxide (GO) into RGO is accompanied by the formation of ZnFe2O4. In comparison with bare ZnFe2O4, the ZnFe2O4–RGO hybrid shows ultrahigh cycling stability and rate capability as an anode material for lithium ion batteries. The cycling capacity of the ZnFe2O4–RGO hybrid at the 100th cycle is considerably enhanced to 1025 mA h g−1, compared with only 166 mA h g−1 for bare ZnFe2O4. The rate performance can also be significantly improved to 800 mA h g−1 at the current density of 1000 mA g−1. The much better cycling stability and rate capability can be largely attributed to the well dispersed conductive RGO and the tight binding between ZnFe2O4 and RGO, which is a benefit of the subtle syn-graphenization strategy. In addition, the effects of RGO content on the electrochemical performance are presented.

Improving the Performance of Layered Oxide Cathode Materials with Football-Like Hierarchical Structure for Na-Ion Batteries by Incorporating Mg2+ into Vacancies in Na-Ion Layers

The development of advanced cathode materials is still a great interest for sodium-ion batteries. The feasible commercialization of sodium-ion batteries relies on the design and exploitation of suitable electrode materials. This study offers a new insight into material design to exploit high-performance P2-type cathode materials for sodium-ion batteries. The incorporation of Mg2+ into intrinsic Na+ vacancies in Na-ion layers can lead to a high-performance P2-type cathode material for sodium-ion batteries. The materials prepared by the coprecipitation approach show a well-defined morphology of secondary football-like hierarchical structures. Neutron power diffraction and refinement results demonstrate that the incorporation of Mg2+ into intrinsic vacancies can enlarge the space for Na-ion diffusion, which can increase the d-spacing of the (0 0 2) peak and the size of slabs but reduce the chemical bond length to result in an enhanced rate capability and cycling stability. The incorporation of Mg2+ into available vacancies and a unique morphology make Na0.7 Mg0.05 Mn0.8 Ni0.1 Co0.1 O2 a promising cathode, which can be charged and discharged at an ultra-high current density of 2000 mA g-1 with an excellent specific capacity of 60 mAh g-1 . This work provides a new insight into the design of electrode materials for sodium-ion batteries.

Modulating the Electrochemical Performances of Layered Cathode Materials for Sodium Ion Batteries through Tuning Coulombic Repulsion between Negatively Charged TMO2 Slabs

Exploiting advanced layered transition metal oxide cathode materials is of great importance to rechargeable sodium batteries. Layered oxides are composed of negatively charged TMO2 slabs (TM = transition metal) separated by Na+ diffusion layers. Herein, we propose a novel insight, for the first time, to control the electrochemical properties by tuning Coulombic repulsion between negatively charged TMO2 slabs. Coulombic repulsion can finely tailor the d-spacing of Na ion layers and material structural stability, which can be achieved by employing Na+ cations to serve as effective shielding layers between TMO2 layers. A series of O3-type NaxMn1/3Fe1/3Cu1/6Mg1/6O2 (x = 1.0, 0.9, 0.8, and 0.7) have been prepared, and Na0.7Mn1/3Fe1/3Cu1/6Mg1/6O2 shows the largest Coulombic repulsion between TMO2 layers, the largest space for Na ion diffusion, the best structural stability, and also the longest Na-O chemical bond with weaker Coulombic attraction, thus leading to the best electrochemical performance. Meanwhile, the thermal stability depends on the Na concentration in pristine materials. Ex situ X-ray absorption (XAS) analysis indicates that Mn, Fe, and Cu ions are all electrochemically active components during insertion and extraction of sodium ion. This study enables some new insights to promote the development of advanced layered NaxTMO2 materials for rechargeable sodium batteries in the future.

Effects of microstructure on water imbibition in sandstones using X-ray computed tomography and neutron radiography

Capillary imbibition in variably saturated porous media is important in defining displacement processes and transport in the vadose zone and in low-permeability barriers and reservoirs. Nonintrusive imaging in real time offers the potential to examine critical impacts of heterogeneity and surface properties on imbibition dynamics. Neutron radiography is applied as a powerful imaging tool to observe temporal changes in the spatial distribution of water in porous materials. We analyze water imbibition in both homogeneous and heterogeneous low-permeability sandstones. Dynamic observations of the advance of the imbibition front with time are compared with characterizations of microstructure (via high-resolution X-ray computed tomography (CT)), pore size distribution (Mercury Intrusion Porosimetry), and permeability of the contrasting samples. We use an automated method to detect the progress of wetting front with time and link this to square-root-of-time progress. These data are used to estimate the effect of microstructure on water sorptivity from a modified Lucas-Washburn equation. Moreover, a model is established to calculate the maximum capillary diameter by modifying the Hagen-Poiseuille and Young-Laplace equations based on fractal theory. Comparing the calculated maximum capillary diameter with the maximum pore diameter (from high-resolution CT) shows congruence between the two independent methods for the homogeneous silty sandstone but less effectively for the heterogeneous sandstone. Finally, we use these data to link observed response with the physical characteristics of the contrasting media—homogeneous versus heterogeneous—and to demonstrate the sensitivity of sorptivity expressly to tortuosity rather than porosity in low-permeability sandstones.

Crystal structure and negative thermal expansion properties of solid solution Er2W3-xMoxO12

Abstract A series of solid solutions Er 2 W 3− x Mo x O 12 (0.5≤ x ≤2.5) were successfully synthesized by the solid state method. Their crystal structures and negative thermal expansion properties were studied by high temperature X-ray powder diffraction and the Rietveld method. All samples with rare earth tungstates and molybdates crystallize in the same orthorhombic structure with space group Pnca , and show the negative thermal expansion phenomena related to transverse vibration of bridging oxygen atoms in the structure. Thermal expansion coefficients (TECs) of Er 2 W 3− x Mo x O 12 were determined as −16.2×10 −6 K −1 for x =0.5 and −16.5×10 −6 K −1 for x =2.5 while −20.2×10 −6 K −1 and −18.4×10 −6 K −1 for unsubstituted Er 2 W 3 O 12 and Er 2 Mo 3 O 12 in the identical temperature range of 200−800 °C. High temperature XRD data and bond length analysis suggest that the difference between W—O and Mo—O is responsible for the change of TECs after the element substitution in the series of solid solutions.

X-ray analysis on crystal structures of crystalline polyimides

A high performance engineering plastic material based on crystalline polyimide was prepared by hot-press method after the resin was synthesized. The mechanical properties including tensile properties, compression properties, bending properties, impact toughness, shearing strength were first investigated. The material displayed excellent mechanical properties and could be used at high temperatures. Since the tensile experiment was operated at 25°C, 250°C and 280°C, respectively. So the progress of crystals grown was affected by load and temperature at the same time, and residual stress would be existed in the samples. X-ray diffraction experiments were then conducted to investigate the difference of crystal structures formed under different conditions. Results indicated that the main diffraction peaks were almost same, but the position of some week peaks changed a little. The material then isothermally crystallized at different temperatures and they displayed same crystal structures by X-ray diffraction experiment.