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Wang Y.,Yanshan University | Li Y.,Yanshan University | Shen W.,Yanshan University | Shen W.,Shanghai JiaoTong University | And 5 more authors.
Journal of Solid State Electrochemistry | Year: 2015

In order to improve the electrochemical kinetics of La–Mg–Ni-based alloy, the chemical modification of polypyrrole (PPy) doped with sodium sulfate (Na2SO4) has been applied on the surface of the La0.80 Mg0.20Ni2.70Mn0.10Co0.55Al0.10 alloy particles. SEM, TEM, and FT-IR results indicate that the spongy nano-PPy successfully forms on the surface of the alloy particles and that the PPy nanoparticles distribute uniformly. Owing to the nano-PPy, which possesses excellent electrochemical redox reversibility, electrocatalytic activity, and high conductivity, electrochemical kinetics of the alloy electrode is remarkably ameliorated. The high-rate dischargeability (HRD) of the treated alloy electrode at 1800 mA g−1 reaches two times of that for the bare alloy, meanwhile the discharge voltages increase obviously. The charge transfer resistance (Rct) of treated alloy electrode markedly decreases; the limiting current density (IL) and the hydrogen diffusion coefficient (D) increase. © 2015 Springer-Verlag Berlin Heidelberg Source


Wang J.,Yanshan University | Han S.,Yanshan University | Li Y.,Yanshan University | Liu J.,Yanshan University | And 3 more authors.
Journal of Alloys and Compounds | Year: 2014

An investigation of the phase formation mechanism and electrochemical properties of the La0.75-xNdxMg0.25Ni 3.3 (x = 0, 0.15) alloys has been conducted in this paper. As explored by Rietveld analysis of the XRD data, the La0.75-xNd xMg0.25Ni3.3 alloy is composed of Ce2Ni7-type and Gd2Co7-type phases accompanied by minor CaCu5-type phase. The partial substitution Nd for La benefits the formation of Gd2Co 7-type phase, indicating that the atoms with smaller radius favor the formation of the Gd2Co7-type phase. However, CaCu5-type phase disappears with Nd substitution. Because part of the replaced La atoms transform into [A2B4] subunits with the Ni atoms, and the formed [A2B4] subunits crystallize with [AB5] subunits to produce A2B7-type phase, resulting in the depletion of the minor CaCu5-type phase. The electrochemical P-C isotherms present that the La0.75-xNdxMg0.25Ni 3.3 alloy only containing A2B7-type phase has one single plateau while the La0.75-xNdxMg0.25Ni3.3 alloy which contains minor LaNi5 phase has two plateaus. It is beneficial for the elevation of equilibrium plateau pressure ascribing to the contraction in cell volumes by Nd substitution. Electrochemical measurements show that the substitution of La by Nd improves the discharge capacity and the high rate dischargeability owing to the increase of A2B7-type phase abundance. © 2013 Elsevier B.V. All rights reserved. Source


Liu J.,Yanshan University | Han S.,Yanshan University | Li Y.,Yanshan University | Zhang J.,Yanshan University | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2013

La0.75Mg0.25Ni3.5 alloys with hexagonal (2H-) and rhombohedral (3R-) (La,Mg)2Ni7 phase were created by powder metallurgy. Partial crystal transformation of 2H- into 3R-type allotropes was realized by heat treatment and introducing LaNi5 compound. It was found that the alloy annealed within 1073-1223 K kept (La,Mg)2Ni7 phase and obvious crystal transformation of 2H- into 3R-type occurred as annealing temperature reached 1223 K. Electrochemical study showed similar discharge capacity and degradation behavior for La0.75Mg0.25Ni3.5 alloys with different amounts of 2H- and 3R-type allotropes while HRD was promoted by increasing 3R-type phase abundance. Introducing LaNi5 into La 0.75Mg0.25Ni3.5 alloy increased 3R- to 2H-type phase ratio and led to an additional plateau in P-C isotherms. LaNi5 introduction improved HRD, however it accelerated cycling degradation. Rietveld analysis indicated that after hydrogenation, the cell expansion of 2H- and 3R-type (La,Mg)2Ni7 phase was similar while the cell expansion of LaNi5 phase was smaller than that of (La,Mg) 2Ni7 phase. This caused discrete cell expansion between (La,Mg)2Ni7 and LaNi5 phases, leading to severe pulverization and oxidation. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source


Pei Y.,Yanshan University | Li Y.,Yanshan University | Che J.Y.,Desert Vista High School | Shen W.,Yanshan University | And 4 more authors.
International Journal of Hydrogen Energy | Year: 2015

To further improve the high-temperature electrochemical performance of perovskite-type oxides, the LaFeO3 carbon-coated composites used as the negative materials for MH-Ni batteries were obtained using the polyaniline (PANI) pyrolysis method. Transmission electron microscopy (TEM) results revealed that LaFeO3 particles were evenly coated with carbon layers, forming a core-shell structure. The carbon layers could enhance the conductivity and electrocatalytic activity, speeding up hydrogen protons transferring from electrolyte to electrode interface. Furthermore, the carbon coatings hindered the LaFeO3 particles from aggregating into stacks and reduced the corrosion of the LaFeO3 electrodes. At an elevated temperature (60 °C), owing to the carbon coatings, the maximum discharge capacity of the LaFeO3 electrodes remarkably increased from 211 mAh g-1 to 358 mAh g-1, and charge retention (CR) increased from 85.4% to 94.6%. Also, the high rate dischargeability at a discharge current density of 1500 mA g-1 (HRD1500) increased from 21.0% to 37.6%, and the capacity retention rate after 100 cycles (S100) increased from 63.0% to 70.9%. Copyright © 2015 Hydrogen Energy Publications, LLC. All rights reserved. Source


Pei Y.,Yanshan University | Li Y.,Yanshan University | Che J.Y.,Desert Vista High School | Shen W.,Shanghai JiaoTong University | And 3 more authors.
International Journal of Hydrogen Energy | Year: 2015

To further improve the high-temperature electrochemical performance of perovskite-type oxides, the LaFeO3 carbon-coated composites used as the negative materials for MH-Ni batteries were obtained using the polyaniline (PANI) pyrolysis method. Transmission electron microscopy (TEM) results revealed that LaFeO3 particles were evenly coated with carbon layers, forming a core-shell structure. The carbon layers could enhance the conductivity and electrocatalytic activity, speeding up hydrogen protons transferring from electrolyte to electrode interface. Furthermore, the carbon coatings hindered the LaFeO3 particles from aggregating into stacks and reduced the corrosion of the LaFeO3 electrodes. At an elevated temperature (60°C), owing to the carbon coatings, the maximum discharge capacity of the LaFeO3 electrodes remarkably increased from 211mAhg-1 to 358mAhg-1, and charge retention (CR) increased from 85.4% to 94.6%. Also, the high rate dischargeability at a discharge current density of 1500mAg-1 (HRD 1500) increased from 21.0% to 37.6%, and the capacity retention rate after 100 cycles (S 100) increased from 63.0% to 70.9%. © 2015 Hydrogen Energy Publications, LLC. Source

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