Exploring the structure evolution of MoS2 upon Li/Na/K ion insertion and the origin of the unusual stability in potassium ion batteries.

The recent revival of research on Na and K ion batteries has two benefits. It not only provides alternate energy storage technologies to Li ion batteries with potential cost advantages but also enhances our understanding of charge storage through systematic studies on alkali-metal ion batteries with increasing insertion ion sizes. Using MoS2 as a model material, the structure evolution upon the uptake of Li, Na, and K ions are compared through in situ TEM. Despite their larger size, insertion of K ions shows both the better electrochemical and structural stability. To understand this paradoxical and counter-intuitive phenomenon, in situ XRD is carried out to examine the phase transitions of MoS2 upon ion insertion, while ex situ TEM is further applied to closely examine the structures at the nanoscale. Complementary DFT calculations are performed to understand the kinetic/thermodynamic origins of the unusual stability. The result reveal that the less electrovalent K-S bond favors the intercalation process, resulting in preservation of the layered structure for stable cycling. This study provides a structural insight to design stable electrodes for the K-ion batteries.

KVPO4F as a novel insertion-type anode for potassium ion batteries.

KVPO4F is found to be capable of both accepting and donating K ions. As an anode, it delivers a reversible capacity of over 100 mA h g-1 with an average potential of 1.15 V vs. K+/K. The anode is also able to work in a wide temperature range of 0-55 °C.

Hybrid Aqueous/Organic Electrolytes Enable the High-Performance Zn-Ion Batteries.

Rechargeable aqueous zinc ion batteries (ZIBs) are considered as one of the most promising systems for large-scale energy storage due to their merits of low cost, environmental friendliness, and high safety. The utilization of aqueous electrolyte also brings about some problems such as low energy density, fast self-discharge, and capacity fading associated with the dissolution of metals in water. To combat the issues, we utilize a freestanding vanadium oxide hydrate/carbon nanotube (V2O5·nH2O/CNT) film as the cathode and probe the performance in aqueous/organic hybrid electrolytes. The corresponding structural and morphological evolution of both V2O5·nH2O/CNT cathode and Zn anode in different electrolytes is explored. The integrity of electrodes and the suppression of zinc dendrites during cycles are largely improved in the hybrid electrolytes. Accordingly, the battery in hybrid electrolyte exhibits high capacities of 549 mAh g-1 at 0.5 A g-1 after 100 cycles and 282 mAh g-1 at 4 A g-1 after 1000 cycles, demonstrating an excellent energy density of 102 Wh kg-1 at a high power of 1500 W kg-1 based on the cathode.

Highly conductive porous graphene/sulfur composite ribbon electrodes for flexible lithium-sulfur batteries.

Flexible batteries have become an indispensable component of emerging devices, such as wearable, foldable electronics and sensors. Although various flexible batteries have been explored based on one-dimensional and two-dimensional platforms, developing a high energy density electrode with high structural integrity remains challenging. Herein, a scalable, one-pot wet spinning strategy is used to synthesize a flexible porous cathode for lithium-sulfur batteries (LSBs) for the first time, which consists of reduced graphene oxide (rGO), graphene crumples (GCs) and sulfur powders. The electrode structures are tailored using GCs with different dimensions and functional features that are critical to its robustness under mechanical deformation and electrolyte penetration into the battery components. The optimized rGO/GC/S composite ribbon cathodes deliver a high capacity of 524 mA h g-1 after 100 cycles at a current rate of 0.2 C. A shape-conformable battery prototype comprising an rGO/GC/S cathode and a lithium anode demonstrates a stable discharge characteristic under repeated bending/flattening cycles. The LSB prototype supported by an elastomer presents stable discharge behavior with high mechanical robustness against an extension of up to 50%. The above-mentioned findings shed new light on developing sulfur cathodes for flexible, high performance LSBs based on the rational design of graphene structures.

Three-Dimensional Porous Graphene Aerogel Cathode with High Sulfur Loading and Embedded TiO2 Nanoparticles for Advanced Lithium-Sulfur Batteries.

Three-dimensional graphene aerogel/TiO2/sulfur (GA/TiO2/S) composites are synthesized through a facile, one-pot hydrothermal route as the cathode for lithium-sulfur batteries. With a high sulfur content of 75.1 wt %, the conductive, highly porous composite electrode delivers a high discharge capacity of 512 mA h/g after 250 cycles at a current rate of 1 C with a low capacity decay of 0.128% per cycle. The excellent capacities and cyclic stability arise from several unique functional features of the cathode. (i) The conductive graphene aerogel framework ameliorates ion/electron transfer while accommodating the volume expansion induced during discharge, and (ii) TiO2 nanoparticles play an important role in restricting the dissolution of polysulfides by chemical bonds with sulfur.

A CMOS MEMS Humidity Sensor Enhanced by a Capacitive Coupling Structure.

A capacitive coupling structure is developed to improve the performances of a capacitive complementary metal oxide semiconductor (CMOS) microelectromechanical system (MEMS) humidity sensor. The humidity sensor was fabricated by a post-CMOS process. Silver nanowires were dispersed onto the top of a conventional interdigitated capacitive structure to form a coupling electrode. Unlike a conventional structure, a thinner sensitive layer was employed to increase the coupling capacitance which dominated the sensitive capacitance of the humidity sensor. Not only static properties but also dynamic properties were found to be better with the aid of coupling capacitance. At 25 °C, the sensitive capacitance was 11.3 pF, the sensitivity of the sensor was measured to be 32.8 fF/%RH and the hysteresis was measured to be 1.0 %RH. Both a low temperature coefficient and a fast response (10 s)/recovery time (17 s) were obtained.

Electrospun Carbon Nanofibers with in Situ Encapsulated Co3O4 Nanoparticles as Electrodes for High-Performance Supercapacitors.

A facile electrospinning method with subsequent heat treatments is employed to prepare carbon nanofibers (CNFs) containing uniformly dispersed Co3O4 nanoparticles as electrodes for supercapacitors. The Co3O4/CNF electrodes with ∼68 wt % active particles deliver a remarkable capacitance of 586 F g(-1) at a current density of 1 A g(-1). When the current density is increased to 50 A g(-1), ∼66% of the original capacitance is retained. The electrodes also present excellent cyclic stability of 74% capacity retention after 2000 cycles at 2 A g(-1). These superior electrochemical properties are attributed to the uniform dispersion of active particles in the CNF matrix, which functions as a conductive support. The onionlike graphitic layers formed around the Co3O4 nanoparticles not only improve the electrical conductivity of the electrode but also prevent the separation of the nanoparticles from the carbon matrix.

Cobalt carbonate/ and cobalt oxide/graphene aerogel composite anodes for high performance Li-ion batteries.

Nanocomposites consisting of ultrafine, cobalt carbonate nanoneedles and 3D porous graphene aerogel (CoCO3/GA) are in situ synthesized based on a one-step hydrothermal route followed by freeze-drying. A further heat treatment produces cobalt oxide nanoparticles embedded in the conductive GA matrix (Co(3)O(4)/GA). Both the composite anodes deliver excellent specific capacities depending on current density employed: the CoCO(3)/GA anode outperforms the Co(3)O(4)/GA anode at low current densities, and vice versa at current densities higher than 500 mA g(-1). Their electrochemical performances are considered among the best of similar composite anodes consisting of CoCO(3) or Co(3)O(4) active particles embedded in a graphene substrate. The stable multistep electrochemical reactions of the carbonate compound with a unique nanoneedle structure contribute to the excellent cyclic stability of the CoCO(3)/GA electrode, whereas the highly conductive networks along with low charge transfer resistance are responsible for the high rate performance of the Co(3)O(4)/GA electrode.

The effect of co-cultivation and selection parameters on Agrobacterium-mediated transformation of Chinese soybean varieties.

In the present study, an efficient Agrobacterium-mediated gene transformation system was developed for soybean [Glycine max (L.) Merrill] based on the examinations of several factors affecting plant transformation efficiency. Increased transformation efficiencies were obtained when the soybean cotyledonary node were inoculated with the Agrobacterium inoculum added with 0.02% (v/v) surfactant (Silwet L-77). The applications of Silwet L-77 (0.02%) during infection and L-cysteine (600 mg l(-1)) during co-cultivation resulted in more significantly improved transformation efficiency than each of the two factors alone. The optimized temperature for infected explant co-cultivation was 22 degrees C. Regenerated transgenic shoots were selected and produced more efficiently with the modified selection scheme (initiation on shoot induction medium without hygromycin for 7 days, with 3 mg l(-1) hygromycin for 10 days, 5 mg l(-1) hygromycin for another 10 days, and elongation on shoot elongation medium with 8 mg l(-1) hygromycin). Using the optimized system, we obtained 145 morphologically normal and fertile independent transgenic plants in five important Chinese soybean varieties. The transformation efficacies ranged from 3.8 to 11.7%. Stable integration, expression and inheritance of the transgenes were confirmed by molecular and genetic analysis. T(1) plants were analyzed and transmission of transgenes to the T(1 )generation in a Mendelian fashion was verified. This optimized transformation system should be employed for efficient Agrobacterium-mediated soybean gene transformation.

[Factors influencing Agrobacterium-mediated cotyledonary-node transformation of soybean (Glycine max L.)].

Using Agrobacterium tumefaciens strain EHA105 carrying binary vector p1301, which containing the gus and hpt genes, a highly efficient transformation system was developed based on the study of factors influencing the Agrobacterium-mediated cotyledonary-node transformation of soybean. The results demonstrated the additions of acetosyringone (200 micromol/L) and ascorbatic acid (50 mg/L) in both infection medium and co-cultivation medium resulted in a significant increase in the transformation efficiency. The induction of the shoots was benefited from the combined utilization of Carbnicillin (250 mg/L) and Cefotaxime (100 mg/L). The inclusion of a 7-d resting step made the selection scheme using hygromycin B as the selective agent more efficient to produce transgenic shoots. Using the optimized transformation procedure, three soybean cultivars widely grown in North China were successfully transformed and the frequency of PCR-positive plant ranged from 3.8%-7.6%. The integration of the transgenes into the soybean nuclear genome was confirmed by PCR analysis using gus- and hpt-specific primers and by Southern blot using hpt-specific probe.

Site-specific DNA excision in transgenic rice with a cell-permeable cre recombinase.

The removal of selected marker genes from transgenic plants is necessary to address biosafety concerns and to carry out further experiments with transgenic organisms. In the present study, the 12-amino-acid membrane translocation sequence (MTS) from the Kaposi fibroblast growth factor (FGF)-4 was used as a carrier to deliver enzymatically active Cre proteins into living plant cells, and to produce a site-specific DNA excision in transgenic rice plants. The process, which made cells permeable to Cre recombinase-mediated DNA recombination, circumvented the need to express Cre under spatiotemporal control and was proved to be a simple and efficient system to achieve marker-free transgenic plants. The ultimate aim of the present study is to develop commercial rice cultivars free from selected marker genes to hasten public acceptance of transgenic crops.