Ping, C.
Email Address
phychenp@nus.edu.sg
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Publication Improvement of the hydrogen-storage performances of Li-Mg-N-H system(2007-05) Liu, Y.; Hu, J.J.; Xiong, Z.; Wu, G.; Chen, P.; PHYSICS; CHEMISTRYLi2MgN2H2 can reversibly store more than 5.5 wt% hydrogen. However, the high activation energy of hydrogen desorption poses a kinetic barrier for low-temperature operation. In this work, the composition of the Li-Mg-N-H system has been modified by the partial substitution of Mg or Li by Na. The changes in structure and hydrogen absorption/desorption kinetics have been investigated. It was found that the peak temperature for hydrogen desorption was decreased by ∼10 °C, and that the hydrogen absorption/desorption isotherms were also significantly changed. Furthermore, the activation energy calculated by the Kissinger's approach was reduced after the substitution of Mg or Li by Na. In addition, the different dehydrogenation structures were detected at different molar ratios of Mg, Li, and Na. © 2007 Materials Research Society.Publication Interaction of lithium hydride and ammonia borane in THF(2008) Xiong, Z.; Chua, Y.S.; Wu, G.; Xu, W.; Chen, P.; Shaw, W.; Karkamkar, A.; Linehan, J.; Smurthwaite, T.; Autrey, T.; PHYSICS; CHEMISTRYThe two-step reaction between LiH and NH3BH3 in THF leads to the production of more than 14 wt% of hydrogen at 40 °C. © The Royal Society of Chemistry.Publication Large amount of hydrogen desorption from the mixture of Mg(NH 2)2 and LiAlH4(2007-12-27) Liu, Y.; Hu, J.; Wu, G.; Xiong, Z.; Chen, P.; PHYSICS; CHEMISTRYWe report a new chemical reaction between Mg(NH2)2 and LiAlH4 in a molar ratio of 1/1, which releases 8 equiv of H under moderate conditions. X-ray diffraction, Fourier transform infrared spectroscopy, and NMR measurements revealed that an Al-N bond was established right after the occurrence of the reaction. Nitrides are the final dehydrogenation products. Thermodynamic examination reveals that the hydrogen desorption from the post-ball-milled sample is a mild endothermic process, indicating it could be a potential candidate for on-board hydrogen storage. The dehydrogenation mechanism in the mechanochemical and heating treatments was discussed. © 2007 American Chemical Society.Publication Thermodynamic and kinetic investigations of the hydrogen storage in the Li-Mg-N-H system(2005-08-02) Xiong, Z.; Hu, J.; Wu, G.; Chen, P.; Luo, W.; Gross, K.; Wang, J.; PHYSICSHydrogen desorption from the mixture of Mg(NH2)2 and 2LiH presents two pressure-dependent segments at a given temperature - ∼2/3 of the hydrogen is released at relatively higher pressures and forms a pressure plateau and the other 1/3 is desorbed at lower pressures. The overall reaction heat measured in a differential scanning calorimeter is 44.1 kJ/mol H 2, while the heat-of-desorption of H2 in the higher pressure plateau is about 38.9 kJ/mol H2, a favorable thermodynamics for PEM Fuel Cell application. However, the relatively higher activation energy (Ea = 102 kJ/mol) sets a kinetic barrier. © 2005 Elsevier B.V. All rights reserved.Publication Superionicity in the hydrogen storage material Li2 NH: Molecular dynamics simulations(2009-05-01) Araújo, C.M.; Blomqvist, A.; Scheicher, R.H.; Chen, P.; Ahuja, R.; CHEMISTRYWe have employed ab initio molecular dynamics simulations in an attempt to study a temperature-induced order-disorder structural phase transformation that occurs in Li2 NH at about 385 K. A structural phase transition was observed by us in the temperature range 300-400 K, in good agreement with experiment. This transition is associated with a melting of the cation sublattice (Li+), giving rise to a superionic phase, which in turn is accompanied by an order-disorder transition of the N-H bond orientation. The results obtained here can contribute to a better understanding of the hydrogen storage reactions involving Li2 NH and furthermore broaden its possible technological applications toward batteries and fuel cells. © 2009 The American Physical Society.Publication METHOD FOR REVERSIBLE STORAGE OF HYDROGEN AND MATERIALS FOR HYDROGEN STORAGE(2003-05-08) CHEN, PING; XIONG, ZHITAO; LUO, JIZHONG; PHYSICSMetal-N-based or metalloid-N-based materials absorb a substantial amount hydrogen and are useful as hydrogen storage materials for various applications such as hydrogen fuel cell technology.Publication Shapiro steps observed in a dc superconducting quantum interference device with multiple junctions in each arm(2002-02-11) Chen, L.; Chen, P.; Ong, C.K.; PHYSICSA high-Tc dc superconducting quantum interference device (SQUID) with three Josephson junctions (JJs) in series in each of its arms has been fabricated. Its Shapiro steps were studied using microwave (rf) radiation of 10 GHz and weak magnetic fields. The appearance of giant Shapiro steps and of some of half-integer steps was observed. Separation between the adjacent Shapiro steps could be tuned by rf magnetic fields and small external dc magnetic fields. This phenomenon was analyzed by phase locking the JJs in the SQUID. © 2002 American Institute of Physics.Publication Controlled growth and field-emission properties of cobalt oxide nanowalls(2005-07-04) Yu, T.; Zhu, Y.; Xu, X.; Shen, Z.; Chen, P.; Lim, C.-T.; Thong, J.T.-L.; Sow, C.-H.; ELECTRICAL & COMPUTER ENGINEERING; PHYSICS; MECHANICAL ENGINEERING; NUS NANOSCIENCE & NANOTECH INITIATIVEThe growth of freestanding, vertically oriented Co3O4 nanowalls by directly heating Co foil on a hot plate in ambient conditions was investigated. The field-emission properties of Co3O4 nanowalls were also investigated. Scanning electron microscopic (SEM) examination revealed a surface covered with a large quantity of nanowall-like morphologies, with most of them perpendicular to the substrate. The results reveal that the Co3O4 nanowalls or other morphologies of Co3O4 nanostructures are useful electron field emitters.Publication Synthesis and characterization of a new ternary imide-Li 2Ca(NH)2(2007-01-22) Wu, G.; Xiong, Z.; Liu, T.; Liu, Y.; Hu, J.; Chen, P.; Feng, Y.; Wee, A.T.S.; PHYSICS; CHEMISTRYThe ternary imide Li2Ca(NH)2 was successfully synthesized by dehydrogenating a mixture of LiNH2 and CaH2 at a molar ratio of 2:1 in a stream of purified argon at 300°C. A powder X-ray diffraction measurement revealed that Li2Ca(NH)2 was of the trigonal anti-La2O3 structure (space group P3m1) with lattice constants of a = 3.5664(3)Å and c = 5.9540(8) Å. Ca occupied the 1b site (0, 0, 1/2), Li occupied the 2d site (1/3, 2/3, 0.8841(22)), and N occupied the 2d site (1/3, 2/3, 0.2565(15)). Nuclear magnetic resonance and X-ray absorption fine structure analyses demonstrated that each Li ion was coordinated with four imide ions and each Ca ion was coordinated with six imide ions. © 2007 American Chemical Society.Publication Investigations on hydrogen storage over Li-Mg-N-H complex-the effect of compositional changes(2006-06-29) Xiong, Z.; Wu, G.; Hu, J.; Chen, P.; Luo, W.; Wang, J.; PHYSICSThree Li-Mg-N-H samples with LiH/Mg(NH2)2 molar ratio of 1/1, 2/1 and 3/1 were prepared and investigated. Remarkable differences were observed in the temperature dependence of hydrogen desorption, subsequent absorption and P-C isotherms over these three samples. It was revealed that the reduction of LiH content induced the desorption of ammonia. Higher content of LiH pushes the hydrogen desorption to a higher temperature region. © 2005 Elsevier B.V. All rights reserved.