Fangyuan Qiu

Facile synthesis and superior supercapacitor performances of Ni2P/rGO nanoparticles

Ni2P nanoparticles grown on reduced graphene oxide (rGO) were successfully synthesized via the low-temperature solid state reaction method and investigated as electrochemical pseudocapacitor materials for potential energy storage applications. The specific capacitance of the as-prepared Ni2P/rGO is 2266 F g−1 and the Ni2P/rGO composite also exhibits superior cycling performance when they are used as the capacitor materials. The as-prepared Ni2P/rGO sample demonstrates interesting supercapacitive properties with high capacitance and good cycling performance.

Synthesis of porous Ni@rGO nanocomposite and its synergetic effect on hydrogen sorption properties of MgH2

A porous Ni@rGO nanocomposite was successfully prepared by the ethylene glycol method followed by an annealing process. It was shown that fcc Ni nanoparticles anchored on reduced graphene oxide sheets producing a porous structure. It was also found that Ni@rGO nanocomposite had a good catalytic effect on de/hydrogenation of MgH2. The MgH2–5 wt% Ni@rGO composite acquired by ball milling exhibited improved faster sorption kinetics and relatively lower sorption temperature than pure MgH2. The desorption peak temperature shifted from 356 °C for pure milled MgH2 to 247 °C for MgH2–5 wt% Ni@rGO. The MgH2–5 wt% Ni@rGO composite could desorb 6.0 wt% H2 within 10 min at 300 °C even after nine cycles, in contrast, only 2.7 wt% H2 was desorbed even after 120 min for undoped MgH2. In addition, the activation energy (Ea) decreased significantly compared to MgH2 and the presence of a few layer reduced graphene oxide sheets on the MgH2 surface prevented the nanograins sintering and agglomeration during cycling, which enhanced the MgH2 decomposition and cycling stability. It was suggested that the porous Ni@rGO composite had a synergetic effect on the MgH2 sorption properties.

Crystalline TiB2: an efficient catalyst for synthesis and hydrogen desorption/absorption performances of NaAlH4 system

High hydrogen pressure and desorption/absorption temperature retard the practical applications of the NaAlH4 system. To ease these problems, we successfully synthesize a crystalline TiB2 catalyst to catalyze the synthesis of NaAlH4. The weight percentage of synthesized nanocrystalline NaAlH4 is as high as 89 wt%. More interestingly, a dramatically reduced of desorption/absorption temperature is achieved with the efficient TiB2 catalyst. Thermodynamic analyses show that the onset dehydrogenation temperature of TiB2–NaAlH4 mixture is lowered to about 70 °C, which is lower than the pristine system. The activation energy of TiB2–NaAlH4 mixture calculated by Arrhenius equation is only 56.28 kJ mol−1. In addition, as-prepared NaAlH4 can be recharged almost quantitatively under remarkably mild conditions (90 °C and 4 MPa hydrogen pressure). The improvement of hydrogen storage and release properties is considerably pronounced under low-pressure and low-temperature conditions. Moreover, preliminary research about the catalytic mechanism of TiB2 is also discussed.

Synthesis of triple-layered Ag@Co@Ni core-shell nanoparticles for the catalytic dehydrogenation of ammonia borane.

Triple-layered Ag@Co@Ni core-shell nanoparticles (NPs) containing a silver core, a cobalt inner shell, and a nickel outer shell were formed by an in situ chemical reduction method. The thickness of the double shells varied with different cobalt and nickel contents. Ag0.04 @Co0.48 @Ni0.48 showed the most distinct core-shell structure. Compared with its bimetallic core-shell counterparts, this catalyst showed higher catalytic activity for the hydrolysis of NH3 BH3 (AB). The synergetic interaction between Co and Ni in Ag0.04 @Co0.48 @Ni0.48 NPs may play a critical role in the enhanced catalytic activity. Furthermore, cobalt-nickel double shells surrounding the silver core in the special triple-layered core-shell structure provided increasing amounts of active sites on the surface to facilitate the catalytic reaction. These promising catalysts may lead to applications for AB in the field of fuel cells.

Porous nickel cobaltite nanorods: desired morphology inherited from coordination precursors and improved supercapacitive properties

A facile and general method for the synthesis of porous complex oxides is highly desirable owing to their significant applications for energy storage. In this contribution, the porous nickel cobaltite nanorods have been successfully prepared by thermal decomposition of organometallic compounds, using nitrilotriacetic acid (NTA) as a chelating agent to coordinate with the Ni and Co ions. The obtained precursors were demonstrated to be one-dimensional nanorods. The resultant porous nickel cobaltite nanorods basically preserved the morphology of the precursors. In addition, these nanoparticles show good crystallinity. The as-prepared nickel cobaltite displays nanorod-like morphology with about 1 μm length and about 100 nm diameter. With a large surface area of 103.4 m2 g−1, this novel material exhibited high specific capacitance of 1078 F g−1 and 704 F g−1 at current densities of 1 and 20 A g−1, respectively. This suggests that about 65% of the capacitance is still retained when the charge–discharge rate is increased from 1 A g−1 to 20 A g−1. The specific capacitance retention is 94.4% after 2500 cycles, suggesting its excellent cycling stability. In addition, these porous nickel cobaltite nanorods may be useful in other fields such as Li-ion batteries and Li-O2 batteries.

TiN catalyst for the reversible hydrogen storage performance of sodium alanate system

A TiN catalyst was used to synthesize NaAlH4via the mechanical milling of a NaH–Al mixture under 2 MPa hydrogen pressure. The dehydrogenation thermodynamics and kinetics of the as-synthesized TiN-doped NaAlH4 were systematically investigated. Thermodynamic analyses show that the dehydrogenation rate clearly increases with a corresponding increase of dehydrogenation temperature. The apparent activation energy (Ea) for the first step is estimated to be 45.15 kJ mol−1 by using the Arrhenius equation. The dehydrogenation and hydrogenation behaviors of TiN-doped NaAlH4 are investigated under different hydrogen pressures using high-pressure differential scanning calorimetry (HP-DSC). Interestingly, the onset dehydrogenation temperature of TiN-doped NaAlH4 is lowered to about 100 °C with a peak of 138.05 °C. X-Ray diffraction and XPS results reveal that the TiN nanopowders possess excellent catalytic stability.

Synthesis of size-controlled Ag@Co@Ni/graphene core-shell nanoparticles for the catalytic hydrolysis of ammonia borane.

Size-controlled Ag0.04@Co0.48@Ni0.48 core-shell nanoparticles (NPs) were synthesized by employing graphene (rGO) with different reduction degrees as supports. The number of C=O and C=O functional groups on the surface of rGO might play a major role in controlling the particle size. The strong steric-hindrance effect of C=O resulted in the growth of large particles, whereas C=O contributed to the formation of small particles. The particle size of Ag0.04@Co0.48@Ni0.48 NPs supported on rGO with different reduction degrees decreased as the number of C=O functional groups decreased. The decrease in the particle size probably led to the increase in the catalytic activity towards the hydrolysis of ammonia borane (AB). The enhanced catalytic activity largely stemmed from the increasing active sites on the surface of catalysts owing to the decreasing particle size.

Graphene oxide assisted facile hydrothermal synthesis of LiMn0.6Fe0.4PO4 nanoparticles as cathode material for lithium ion battery

Abstract Assisted by graphene oxide (GO), nano-sized LiMn0.6Fe0.4PO4 with excellent electrochemical performance was prepared by a facile hydrothermal method as cathode material for lithium ion battery. SEM and TEM images indicate that the particle size of LiMn0.6Fe0.4PO4 (S2) was about 80 nm in diameter. The discharge capacity of LiMn0.6Fe0.4PO4 nanoparticles was 140.3 mAh·g−1 in the first cycle. It showed that graphene oxide was able to restrict the growth of LiMn0.6Fe0.4PO4 and it in situ reduction of GO could improve the electrical conductivity of LiMn0.6Feo.4PO4 material.

Bimetallic NiCo Functional Graphene: An Efficient Catalyst for Hydrogen‐Storage Properties of MgH2

Bimetallic NiCo functional graphene (NiCo/rGO) was synthesized by a facile one-pot method. During the coreduction process, the as-synthesized ultrafine NiCo nanoparticles (NPs), with a typical size of 4-6 nm, were uniformly anchored onto the surface of reduced graphene oxide (rGO). The NiCo bimetal-supported graphene was found to be more efficient than their single metals. Synergetic catalysis of NiCo NPs and rGO was confirmed, which can significantly improve the hydrogen-storage properties of MgH2. The apparent activation energy (E(a)) of the MgH2-NiCo/rGO sample decreases to 105 kJ mol(-1), which is 40.7% lower than that of pure MgH2. More importantly, the as-prepared MgH2-NiCo/rGO sample can absorb 5.5 and 6.1 wt% hydrogen within 100 and 350 s, respectively, at 300 °C under 0.9 MPa H2 pressure. Further cyclic kinetics investigation indicates that MgH2-NiCo/rGO nanocomposites have excellent cycle stability.

Synergetic effects of NaAlH4-TiF3 co-additive on dehydriding reaction of Mg(AlH4)2

Abstract The effects of NaAlH 4 , TiF 3 and NaAlH 4 -TiF 3 co-additive on dehydriding reaction of Mg(AlH 4 ) 2 are systematically investigated. The onset dehydrogenation temperature of the co-doped Mg(AlH 4 ) 2 composites decreased to 74 °C, which is about 59 °C lower than that of pure Mg(AlH 4 ) 2 . The dehydrogenation kinetics of NaAlH 4 -TiF 3 co-doped Mg(AlH 4 ) 2 sample was also improved, which released about 94% hydrogen within 48 min, but no visible hydrogen was released from pure Mg(AlH 4 ) 2 under the same conditions. The activation energy of co-doped Mg(AlH 4 ) 2 was 85.6 kJ-mol −1 , which was significantly lower than that of additive-free Mg(AlH 4 ) 2 sample. The synergetic effects of NaAlH 4 and TiF 3 on the dehydrogenation performance of Mg(AlH 4 ) 2 were confirmed. In addition, a possible catalytic mechanism is discussed, regarding the different roles of NaAlH 4 and TiF 3 on Mg(AlH 4 ) 2 .