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Emerged as a promising solution for future wireless communication systems, intelligent reflecting surface (IRS) is capable of reconfiguring the wireless propagation environment by adjusting the phase-shift of a large number of reflecting elements. To quantify the gain achieved by IRSs in the radio frequency (RF) powered Internet of Things (IoT) networks, in this work, we consider an IRS-assisted cellular-based RFpowered IoT network, where the cellular base stations (BSs) broadcast energy signal to IoT devices for energy harvesting (EH) in the charging stage, which is utilized to support the uplink (UL) transmissions in the subsequent UL stage. With tools from stochastic geometry, we first derive the distributions of the average signal power and interference power which are then used to obtain the energy coverage probability, UL coverage probability, overall coverage probability, spatial throughput and power efficiency, respectively. With the proposed analytical framework, we finally evaluate the effect on network performance of key system parameters, such as IRS density, IRS reflecting element number, charging stage ratio, etc. Compared with the conventional RF-powered IoT network, IRS passive beamforming brings the same level of enhancement in both energy coverage and UL coverage, leading to the unchanged optimal charging stage ratio when maximizing spatial throughput., 32 pages, 11 figures, submitted to IEEE Transactions on Communications

By ball milling carbon nitride (C3N4) and ammonia borane (AB), the AB-C3N4 system was successfully synthesized. It is shown that the dehydrogenation temperature of the AB-C3N4 system was obviously decreased. However, the concentration of byproduct ammonia was much higher than that of pristine AB. Thus, LiBH4-modified C3N4 (LC3N4) was produced and employed to synthesize a AB-LC3N4 system. The dehydrogenation of the AB-LC3N4 system was investigated using X-ray diffraction, temperature-programmed desorption-mass spectrometry, thermogravimetry-differential thermal analysis, and nuclear magnetic resonance. The results show that the dehydrogenation temperatures of the AB-LC3N4 systems were reduced to a lower region compared with pristine AB. Moreover, byproduct borazine and the induction period were significantly suppressed. After LiBH4 modification on C3N4, the other byproduct ammonia was also reduced in the dehydrogenation process. Dynamic analysis and NMR characterization results show that the decomposition mechanism of AB-LC3N4 still follows the self-decomposition of AB, which is induced by the formation of NH3BH2NH3BH4. (C) 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

We demonstrated the preparation of Mg 17 Al 12 , a promising hydrogen storage alloy, by the method of combustion synthesis, and focused on the effects of the aluminum particle size, the synthesis temperature and the corresponding holding time on the phase composition of the products. From the X-ray diffraction patterns, it was confirmed that both the decrease of the aluminum particle size and the increase of the holding time kept at the synthesis temperature were beneficial to improve the purity of the products dramatically. It is notable that Mg 17 Al 12 single phase can be obtained with only 0.5 h holding time at 733 K when the aluminum particle size is 1–3 μm. What is more, we first proposed the alloying mechanism in the combustion synthesis of Mg–Al alloy, that is, Mg 2 Al 3 phase is synthesized first, then Mg 2 Al 3 reacts with residual Mg, forming Mg 17 Al 12 alloy.

We reported the structures and superior hydrogen storage properties of the composites Mg 90 Ni 10− x Fe x ( x = 0, 2, 4, 6 and 8) prepared by the process of HCS + MM, i.e., the hydriding combustion synthesis followed by mechanical milling. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDX) and gas reaction controller (GRC), the crystal structures, surface morphologies and hydriding/dehydriding properties of the composites were studied in detail. The Mg 90 Ni 10− x Fe x ( x = 2, 4, 6 and 8) composites consist of MgH 2 , Mg, Mg 2 NiH 4 , Mg 2 NiH 0.3 and Fe phases, while Mg 90 Ni 10 is composed of MgH 2 , Mg, Mg 2 NiH 4 and Mg 2 NiH 0.3 . It is found that Mg 90 Ni 2 Fe 8 has the best hydriding properties, requiring only 30 s to absorb 97% of its saturated hydrogen capacity of 4.80 wt.% at 373 K. The best dehydriding result is obtained with Mg 90 Ni 8 Fe 2 , which desorbs 2.02 and 4.40 wt.% hydrogen at 493 and 523 K, respectively. The microstructures of the composites prepared by HCS + MM have remarkable influences on the enhanced hydriding/dehydriding properties. In addition, the catalytic effects of Mg 2 Ni and Fe phases during hydriding/dehydriding were discussed in this study.

Magnesium chloride efficiently catalyzed the hydrolysis of Mg-based hydride prepared by hydriding combustion synthesis. Hydrogen yield of 1635 mL g(-1) was obtained (MgH(2)), i.e. with 96% conversion in 30 min at 303 K.