Meiqiang Fan

Bimetallic nickel cobalt selenides: a new kind of electroactive material for high-power energy storage

For the first time, bimetallic Ni–Co selenides with different Ni and Co ratios have been synthesized and used as electrode materials for high-power energy storage. Owing to the synergistic effect between Ni and Co, bimetallic Ni–Co selenides, especially for Ni0.67Co0.33Se, show higher specific capacity and improved rate capability combined with excellent cycling stability than the monometallic Ni or Co selenide.

Hierarchical NiCo2S4 nanotube@NiCo2S4 nanosheet arrays on Ni foam for high‐performance supercapacitors

Hierarchical NiCo2 S4 nanotube@NiCo2 S4 nanosheet arrays on Ni foam have been successfully synthesized. Owing to the unique hierarchical structure, enhanced capacitive performance can be attained. A specific capacitance up to 4.38 F cm(-2) is attained at 5 mA cm(-2) , which is much higher than the specific capacitance values of NiCo2 O4 nanosheet arrays, NiCo2 S4 nanosheet arrays and NiCo2 S4 nanotube arrays on Ni foam. The hierarchical NiCo2 S4 nanostructure shows superior cycling stability; after 5000 cycles, the specific capacitance still maintains 3.5 F cm(-2) . In addition, through the morphology and crystal structure measurement after cycling stability test, it is found that the NiCo2 S4 electroactive materials are gradually corroded; however, the NiCo2 S4 phase can still be well-maintained. Our results show that hierarchical NiCo2 S4 nanostructures are suitable electroactive materials for high performance supercapacitors.

Acidichromic effects in spiro(1,3,3-trimethylindolo-2,3′-naphth[1,2-b]-1,4-oxazine) a photochromic compound I. Absorption characteristics

Abstract Acidichromic and photochromic effects in alcoholic solutions of spiro(1,3,3-trimethylindolo-2,3′-naphth[1,2-b]-1,4-oxazine) are described. First-order, thermally-initiated decay kinetics associated with relaxation of the merocyanine form under acidic conditions are reported. A model for acidichromic and photochromic processes in these systems has been proposed. Preliminary results indicate that spirooxazine compounds are potentially useful in device applications such as pH sensors.

Nonlinear Effects in Chromophore Doped Sol-Gel Photonic Materials

Linear and nonlinear optical effects have been studied in chromophore-doped gel hosts. Tetra-4-sulfonatophenylporphyrinatocopper(II) (CuTPPS), and 1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3′-[3H]-naphth[2,1-b][1,4]oxazine] (SP spirooxazine) species were entrapped within porous aluminosilicate hosts. Optical limiting effects and radiative up-conversion behavior in the CuTPPS-doped materials are described, and a six-level model is proposed based on experimental findings. Spirooxazine-containing specimens exhibiting photochromic effects were prepared, and cw and time-resolved spectroscopy methods are used to assess excited state band structures and the nature of guest-host interactions in the resultant gels.

Hydrogen generation from coupling reactions of AlLi/NaBH4 mixture in water activated by Ni powder

A novel composition of AlLi/NaBH4 mixture activated by common Ni powder in water for hydrogen generation was investigated. The composition presents good hydrogen generation performance and an optimized Al-10% Li-10% Ni/NaBH4 mixture (mass ratio of 3:1) generates 1540 mL/g hydrogen with 96% efficiency at 333 K. Ni powder exhibits dual catalytic effects on the hydrolysis of AlLi/NaBH4 mixture due to the formation of Ni2B in the hydrolysis process. The Ni2B deposited on aluminum surface could act as a cathode of a micro galvanic couple. Ni2B/Al(OH)3 also has a synergistic effect on NaBH4 hydrolysis. Good hydrogen generation performance with stable pH value of hydrolysis byproduct Al(OH)3/NaBO2·2H2O was obtained with successive additions of Al-Li-Ni/NaBH4 mixture into fixed water.

Enhanced cycling stability of spinel LiMn2O4 cathode by incorporating graphene sheets

LiMn2O4-graphene nanocomposites with different weight ratios of LiMn2O4/graphene were successfully prepared via a simple method by ball-milling of commercially available LiMn2O4 particles and graphene nanosheets. Experimental results revealed that the spinel LiMn2O4 particles within the as-prepared LiMn2O4-graphene nanocomposites were well distributed onto the flexible graphene sheets, and the nano-composites with a higher graphene content were favorable to form more uniform composite materials. Compared to the pristine spinel LiMn2O4 particles, the as-prepared LiMn2O4-graphene nanocomposites exhibited lower initial discharge capacities owing to the reduced amount of active materials (LiMn2O4 particles) in the nanocomposites. However, their electrochemical cycling performance was significantly enhanced, high-lighting the advantages of anchoring LiMn2O4 particles on graphene sheets. The enhanced cycling performance could be ascribed to the fact that the graphene nanosheets within the LiMn2O4-graphene nanocomposites could provide a 3D conducting scaffold, which could not only alleviate the aggregation of LiMn2O4 particles and accommodate the volume changes of LiMn2O4 particles, but also enhance the ionic conductivity and charge transfer during the lithiation/delifhiation process.

Controllable hydrogen generation performance from Al/NaBH4 composite activated by La metal and CoCl2 salt in pure water

Abstract A novel composition of Al/NaBH 4 mixture activated by La and CoCl 2 in water for hydrogen generation was investigated. The composition had good stability at 298 K with high La content and low CoCl 2 content, but presented good hydrogen generation performance with increasing global temperature. For example, The Al-15 wt.%La-5 wt.%CoCl 2 /NaBH 4 mixture (mass ratio of 1:1) yielded 1664 ml hydrogen/1 g mixture with 100% efficiency within 60 min at 333 K. The hydrogen generation rate and amount could be regulated by changing composition design, hydrolytic conditions, etc. There existed a synergistic effect of La and CoCl 2 . Increasing La content was helpful to decrease crystal size of the mixture, but its hydrolysis byproduct La(OH) 3 deposited on Al surface and had side effect on Al hydrolysis. Increased CoCl 2 content was attributed to the producing of more actively catalytic sites Co 2 B/Al(OH) 3 formed in the hydrolytic process. Co 2 B had dual catalytic effect on Al/NaBH 4 hydrolysis. It deposited on Al surface and acted as a cathode of a micro galvanic cell. Co 2 B/Al(OH) 3 was also a good promoter to NaBH 4 hydrolysis. Therefore, the Al/NaBH 4 mixture activated by La and CoCl 2 may be applied as hydrogen generation material and the experimental data lays a foundation for designing practical hydrogen generators.

Hydrogen generation from Al-NiCl2/NaBH4 mixture affected by lanthanum metal.

The effect of La on Al/NaBH4 hydrolysis was elaborated in the present paper. Hydrogen generation amount increases but hydrogen generation rate decreases with La content increasing. There is an optimized composition that Al-15 wt% La-5 wt% NiCl2/NaBH4 mixture (Al-15 wt% La-5 wt% NiCl2/NaBH4 weight ratio, 1 : 3) has 126 mL g−1 min−1 maximum hydrogen generation rate and 1764 mL g−1 hydrogen generation amount within 60 min. The efficiency is 88%. Combined with NiCl2, La has great effect on NaBH4 hydrolysis but has little effect on Al hydrolysis. Increasing La content is helpful to decrease the particle size of Al-La-NiCl2 in the milling process, which induces that the hydrolysis byproduct Ni2B is highly distributed into Al(OH)3 and the catalytic reactivity of Ni2B/Al(OH)3 is increased therefore. But hydrolysis byproduct La(OH)3 deposits on Al surface and leads to some side effect. The Al-La-NiCl2/NaBH4 mixture has good stability in low temperature and its hydrolytic performance can be improved with increasing global temperature. Therefore, the mixture has good safety and can be applied as on board hydrogen generation material.

Polyaniline-coated selenium/carbon composites encapsulated in graphene as efficient cathodes for Li-Se batteries

In this work, we developed a polyaniline (PANI)-coated selenium/carbon nanocomposite encapsulated in graphene sheets (PANI@Se/C-G), with excellent performance in Li-Se batteries. The PANI@Se/C-G nanostructure presents attractive properties as cathode of Li-Se batteries, with a high specific capacity of 588.7 mAh·g–1 at a 0.2C (1C = 675 mA·g−1) rate after 200 cycles. Even at a high rate of 2C, a high capacity of 528.6 mAh·g–1 is obtained after 500 cycles. The excellent cycle stability and rate performance of the PANI@Se/C-G composite can be attributed to the synergistic combination of carbon black (as the conductive matrix for Se) and the double conductive layer comprising the uniform PANI shell and the graphene sheets, which effectively improves the utilization of selenium and significantly enhances the electronic conductivity of the whole electrode.

One-pot synthesis of porous nickel–manganese sulfides with tuneable compositions for high-performance energy storage

AbstractMixed-metal compounds, especially for the sulfides, have been investigated as a very attractive type of electroactive materials for supercapacitors. In this work, we demonstrate nickel‒manganese (Ni‒Mn) sulfides are very attractive for supercapacitors with promising electrochemical performance. The Ni‒Mn sulfides with different Ni to Mn ratios have been synthesized via a facile one-pot hydrothermal method, which show a similar structure of interconnected particles and are very porous in microstructure. And then, the Ni‒Mn sulfides are investigated by three-electrode measurements and demonstrate strong synergy between Ni and Mn. The Ni‒Mn sulfide with a Ni to Mn ratio of 2:1 demonstrates superior performance of 1068 F g‒1 at 1 A g‒1. Lastly, The Ni‒Mn sulfide with a Ni to Mn ratio of 2:1 are used as positive electrode for two-electrode test, and the asymmetric supercapacitor shows both high energy and power densities combined with excellent cycling stability. Our work demonstrates that the Ni‒Mn sulfides are also very electrochemical active for supercapacitors and their performance can be tuned by changing the Ni to Mn ratio.