Qi Wan

Synthesis of novel ZnV2O4 spinel oxide nanosheets and their hydrogen storage properties

We report the synthesis of ZnV2O4 spinel oxide novel nanosheets via a template free route to explore its potential hydrogen storage properties for the first time. 2D layered nanostructures are excellent candidates for storage applications. This attracted our interest to synthesize novel spinel oxide nanosheets (NSNs) of ZnV2O4. The maximum value for hydrogen absorption in ZnV2O4 nanosheets at 473 K is 1.36 wt.% and 1.74 wt.% at 573 K, respectively. Our hydrogen storage measurements along ZnV2O4 reveal its superiority over previous reports on hydrogen absorption values concerning oxides, nitrides and chalcogenides. To understand the rate-limiting mechanism, various kinetics models are applied. The calculations show that kinetics is governed by 3D growth with constant interface velocity. The measurements point to ZnV2O4 spinel oxide as a promising hydrogen storage material. PL measurements demonstrate the potential for violet/blue optoelectronic devices.

Enhanced hydrogen storage properties of LiAlH4 catalyzed by CoFe2O4 nanoparticles

The catalytic effects of CoFe2O4 nanoparticles on the hydrogen storage properties of LiAlH4 prepared by ball milling were investigated. The onset desorption temperature of the LiAlH4 + 2 mol% CoFe2O4 sample is 65 °C, which is 90 °C lower that of the as-received LiAlH4, with approximately 7.2 wt% hydrogen released at 250 °C. The isothermal desorption results show that for the 2 mol% CoFe2O4 doped sample dehydrogenated at 120 °C, 6.8 wt% of hydrogen can be released within 160 min, which is 6.1 wt% higher than that of the as-received LiAlH4 under the same conditions. Through the differential scanning calorimetry (DSC) and the Kissinger desorption kinetics analyses, the apparent activation energy, Ea, of the 2 mol% CoFe2O4 doped sample is calculated as 52.4 kJ mol−1 H2 and 86.5 kJ mol−1 H2 for the first two decomposition processes. This is 42.4 kJ mol−1 H2 and 86.1 kJ mol−1 H2 lower compared with the pristine LiAlH4, respectively, indicating considerably improved dehydrogenation kinetics by doping the CoFe2O4 catalyst in the LiAlH4 matrix. From the Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses, a series of finely dispersed Fe and Co species with a range of valence states, produced from the reactions between LiAlH4 and CoFe2O4, play a synergistic role in remarkably improving LiAlH4 dehydrogenation properties. The rehydrogenation properties of the LiAlH4 + 2 mol% CoFe2O4 sample have also been investigated at 140 °C under 6.5 MPa pressure held for 2.5 h.

Combustion synthesis and excellent photocatalytic degradation properties of W18O49

In this paper, one-dimensional W18O49 nanopowders were fabricated by a one-step solution combustion method using glycine as the fuel and a metal acid radical ion as the metal source. The morphologies and non-stoichiometric single-crystal phase of W18O49 can be controlled by changing the amount of the fuel. The nanoneedles had a large amount of defects such as oxygen vacancies. This characteristic resulted in an excellent visible light-driven photocatalytic performance that took about 50 min to degrade methylene blue (100 mL; 40 mg L−1) under visible light. The interesting reaction mechanism of such needle-like W18O49 and the photocatalytic mechanism are studied in this paper.

Superior destabilization effects of LiBH4 with the addition of nano-sized nickel ferrite NiFe2O4

The introduction of a secondary compound, known as destabilization, is an effective way to improve the desorption performance of LiBH4. In this paper the effects of nano-sized nickel ferrite (NiFe2O4) on the hydrogen storage properties of LiBH4, processed by high energy ball milling, are studied. Non-isothermal desorption results show that the onset and predominant dehydrogenation temperature of LiBH4 + 9 mol% NiFe2O4 is 89 °C and 190 °C, respectively. This is 226 °C and 260 °C lower than the fusion and decomposition temperature of LiBH4, respectively. Moreover, over 10 wt% hydrogen can be obtained by 500 °C heating, compared with 2.4 wt% for the as-received LiBH4. Additionally, over 5 wt% hydrogen can be released at 300 °C within 20 minutes of isothermal desorption. From the X-ray diffraction results and the small area electron diffraction analysis, Fe3O4, NiB and Fe3B, in situ formed between the reaction of LiBH4 and NiFe2O4, and act to give actual destabilization effects.

Superior optical properties of Fe3+–W18O49 nanoparticles prepared by solution combustion synthesis

Modification by metal-doping allows the design of new nanomaterials with enhanced optical properties. In this paper, the photocatalytic effects of Fe3+-doped W18O49 nanorods prepared by solution combustion synthesis were studied for the first time. The Fe3+-doped W18O49 powders were investigated by X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy. The powders were well-crystalline with diameters ranging from 50 nm to 250 nm and the length decreasing from more than 10 μm to 4 μm on average. The photoluminescence (referred to as PL here after) spectrum showed that the emission intensity increased with increasing Fe3+ doping, suggesting that more defects were generated. Moreover, this novel composite catalyst displayed excellent photocatalytic efficiency towards the degradation of organic compounds in aqueous media under UV-visible light irradiation. In particular, 0.5 wt% Fe3+-doped W18O49 had the best photocatalytic efficiency. This improvement was mainly attributed to the synergistic effect between Fe3+ and W18O49 nanopowders and the defects in the nanostructure caused by doping.

CO impurities effect on LaNi4.7Al0.3 hydrogen storage alloy hydrogenation/dehydrogenation properties

LaNi4.7Al0.3 alloy was prepared by vacuum induction melting in high purity helium atmosphere, and the ingot was pulverized into 200–400 mesh powder after annealing. X-ray diffraction (XRD) and scanning electron microscopies (SEM) were utilized to study the alloy morphology and phase structure. X-ray photoelectron spectroscopy (XPS) was used for surface analysis. The poisoned alloy was tested at 30 °C in the mixture gas by thermogravimetric and differential thermal analyses (TG + DTA). The hydrogen storage properties were studied by the pressure-composition-temperature test. The activated sample was completely deactivated after only 3 hydriding/dehydriding cycles in hydrogen containing 300 ppm CO at 30 °C, but hydrogen storage capacity did not degrade when tested at 80 °C. Additionally, two different steps appeared in the absorption processes. Combined with XRD, XPS and TG + DTA results, an explanation for this phenomenon is given.

Study of the hydrogen-induced amorphization in the LaNi2.28 alloy

To understand the fundamental reason leading to the poor stability of LaNi2.28 hydrogen storage alloy, the cycling behavior of LaNi2.28 alloy under hydrogen has been investigated. The present study describes the hydrogen-induced amorphization (HIA) of LaNi2.28 alloy. The phase composition, microstructure and morphology of the phases are observed and analyzed using X-ray diffraction and scanning electron microscopy. The crystal structure and chemical composition of the amorphized alloy show that HIA is found in the sample at different cycles of the hydrogenation process. During the first hydrogenation cycle, the degree of HIA is indeclinable with the increased cycle. In addition, the formation processes of amorphous alloys, the occurrence of HIA and the relationship between the structure of the hydrogen-induced amorphous alloy and the stability of LaNi2.28 are given. The conclusions can be summarized as follows: 2LaNi2.28 + H2 → LaNi2.28Hx (amorphous) + LaNi5Hy + LaH2, and amorphous LaNi2.28Hx and LaNi5Hy can desorb 50% hydrogen of the absorption capacity of LaNi2.28, and the absorption–desorption capacity is stable after the first cycle.

NbCl5 and CrCl3 catalysts effect on synthesis and hydrogen storage performance of Mg–Ni–NiO composites

Two kinds of novel materials, Mg–1·6 mol%Ni–0·4 mol%NiO–2 mol%MCl (MCl = NbCl5, CrCl3), along with Mg–1·6 mol%Ni–0·4 mol%NiO for comparison, were examined for their potential use in hydrogen storage applications, having been fabricated via cryomilling. The effects of NbCl5 and CrCl3 on hydrogen storage performance were investigated. A microstructure analysis showed that besides the main Mg and Ni phases, NiO and Mg2Ni phases were present in all samples. MgCl2 was only found in halide-doped samples and NbO was only found in NbCl5-doped samples after ball milling. The particle size decreased significantly after 7 h of cryomilling. MgH2, Mg2NiH4 and Mg2NiH0·3 were present in all the samples, while NbH2 was only observed in the NbCl5-doped sample afterabsorption. The NbCl5-containing composite exhibited a low onset absorption temperature of 323 K, which was 10 K lower than that of the no-halide doped catalyst. It absorbed 5·32 wt% of hydrogen in 370 s at 623 K under 4 MPa hydrogen pressure and can absorb 90% of its full hydrogen capacity in 50 s. Having an onset desorption temperature of 483 K in vacuum, the NbCl5-containing composite desorbed hydrogen faster than the no-halide doped sample. The hydriding–dehydriding kinetics performance of the CrCl3-doped sample did not improve, but it did exhibit a lower onset desorption temperature of 543 K under 0·1 MPa, which was 20 K lower than that of the no-halide doped sample. NbO, NiO and NbH2 played important roles in improving absorption and desorption performances.

Cycling Stability Performance of La0.75Mg0.25Ni3.5Si0.10 Hydrogen Storage Alloy in Discharge–Charge System

La0.75Mg0.25Ni3.5Si0.10 hydrogen storage alloy was prepared by vacuum induction melting furnace and subsequently heated treatment at 940°C for 8 h and cooled to room temperature in the oven. The electrochemical properties of La0.75Mg0.25Ni3.5Si0.10 compound were measured by LAND CT2001A battery test system. The morphologies of the samples were characterized by scanning electron microscopy (SEM). The surface state of samples was analyzed by X-ray photoelectron spectroscopy (XPS). It was found that the charge–discharge rate plays the key impact on the cycling stability of the alloy. During the cycle test, the prepared La0.75Mg0.25Ni3.5Si0.10 compound presented an excellent capacity retention at the charge–discharge of 1 C while the capacity of sample declined rapidly at 0.2 C. The excellent cycling stability performance of La0.75Mg0.25Ni3.5Si0.10 electrode at 1 C could be attributed to the less powder and less oxidation of surface effective active elements. The pulverization inevitably leads to the separation of the part of the cracking alloy and the electrode, resulting in reduction of the effective active substance and increasing attenuation of the capacity per cycle. In addition, on the analysis of the different cut-off potential effects on the electrode, it was found that the La0.75Mg0.25Ni3.5Si0.10 electrode shows good comprehensive electrochemical properties at 1 C cut-off 0.6–0.7 V. During charging, heavy overcharge will not be conducive to cycling stability performance during the charging test.

NbF5 and CrF3 Catalysts Effects on Synthesis and Hydrogen Storage Performance of Mg-Ni-NiO Composites

Two kinds of novel materials, Mg-1.6mol%Ni-0.4mol%NiO-2mol%MF (MF=NbF5, CrF3), along with Mg-1.6mol%Ni-0.4mol%NiO for comparison, were examined for their potential use in hydrogen storage applications, having been fabricated via cryomilling. The effects of NbF5 and CrF3 on hydrogen storage performance were investigated. A microstructure analysis showed that, aside from the main phase Mg, Ni and NiO phases, NbO, MgF2 and Mg2Ni were present in all samples after ball milling, MgH2 and NbH2 were observed in all samples after absorption. The CrF3-containing composite exhibited a good PCT results and a low onset desorption temperature under 0.1 MPa. The NbF5-containing composite exhibited a low absorption temperature of 323 K, a high hydrogen storage capacity of 4.03wt% at 373 K under the hydrogen pressure of 4.0 MPa, and it absorbed 90% of its full hydrogen capacity in 2700 sec and 100% in 5100 sec, it desorbed more than 1.8wt% in 3600 sec under vacuum environment. The CrF3-doped sample exhibited a low onset desorption temperature of 543 K under 0.1 MPa, and a low hysteresis coefficient of 0.25 at 573 K, and lower than 0.2 when temperature was 623 K. NbO and NbH2 played an important role in improving the absorption and desorption performance.