Degradation behaviors of three typical La-Mg-Ni alloys, La2MgNi9, La1.5Mg0.5Ni7 and La4MgNi19, were studied. La1.5- Mg0.5Ni7 with （La,Mg）2Ni7 as main phase presents better discharge capacity and cycling stability. T...Degradation behaviors of three typical La-Mg-Ni alloys, La2MgNi9, La1.5Mg0.5Ni7 and La4MgNi19, were studied. La1.5- Mg0.5Ni7 with （La,Mg）2Ni7 as main phase presents better discharge capacity and cycling stability. The three alloys suffer severe pulverization and corrosion after electrochemical cycles, which are considered to be the significant factor attributing to the capacity deterioration. However, the overall corrosion extent of the three cycled alloys aggravates successively, which is inconsistent with the result that LaEMgNi9 presented poor cycling stability and also the assumption that alloy with high Mg content is easy to be corroded. The intrinsic anti-corrosion and anti-pulverization characteristics of the three alloys are mainly focused in this work. Immersion corrosion experiments demonstrate that the Mg-rich phases are more easily to be corroded. The corrosion resistance of the three alloys presents an improved trend which is inversely proportional to abundance of the Mg-rich phases. However, the anti-pulverization abilities present an inverse trend, which is closely related to the mechanical property of various phase structures. LaNi5 with the highest hardness is easy to crack, but the soft （La,Mg）Ni2 is more resistant to crack formation and spreading. Thus, the weaker corrosion of La2MgNi9 after electro- chemical cycling is attributed to the better intrinsic anti-pulverization capability though the anti-corrosion is poor. As La4MgNi19 possesses excellent corrosion resistance, enhancement of the anti-pulverization ability is urgent for improvement in the cycling stability.展开更多
Yttrium （Y） has been used as the partial substitution element for lanthanum （La） to improve the electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys. Lao.80-xYxMg0.20Ni2.85Mn0.10Coo.55Al0...Yttrium （Y） has been used as the partial substitution element for lanthanum （La） to improve the electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys. Lao.80-xYxMg0.20Ni2.85Mn0.10Coo.55Al0.10 （x=0.00, 0.05 and 0.10） alloys were prepared by the inductive melting technique. The alloys were composed of LaNi5 and （La,Mg）2Ni7 phases, the introduction of Y promoted the formation of （La,Mg）2Ni7 phase, and thus the Y-substituted alloy electrodes exhibited higher discharge capacities. Y substitution was also found to be effective to improve the discharge kinetics of the alloy electrodes. When the Y content x increased from 0.00 to 0.10, the high-rate dischargeability of the alloy electrodes at a discharge current density of 1800 mA/g （HRDl800） in- creased from 23.6% to 39.7% at room temperature. In addition, the measured HRD1800 showed a linear dependence on both the ex- change current density and the hydrogen diffusion coefficient at different temperatures, respectively.展开更多
A novel approach based on thermal diffusion was used to achieve controllable Mg content in A_(2)B_(7)-type La-Mg-Ni-based alloys.The formation mechanism of the A_(2)B_(7)-type phase as a result of the thermal diffusio...A novel approach based on thermal diffusion was used to achieve controllable Mg content in A_(2)B_(7)-type La-Mg-Ni-based alloys.The formation mechanism of the A_(2)B_(7)-type phase as a result of the thermal diffusion process and the effect of Mg content on hydrogen storage performance were investigated.X-ray diffraction(XRD)patterns and Rietveld refinement results showed that increased Mg transformed the LaNi_(5)phase in the La_(0.74)Sm_(0.03)Y_(0.23)Ni_(4.32)Al_(0.04)precursor alloy into a superlattice structure.Scanning electron microscopy(SEM)images showed that Mg was evenly distributed in the alloy bulk.Mg in the superlattice significantly inhibited the phase decomposition of the superlattice structure during the hydrogen absorption/desorption cycles.An A_(2)B_(7)-type La_(0.57)Sm_(0.02)Y_(0.18)Mg_(0.23)Ni_(3.38)Al_(0.03)alloy composed of Gd_(2)Co_(7)and Ce_(2)Ni_(7)phases was successfully synthesized.The pressure-composition isotherm profiles showed that the alloy had a hydrogen storage capacity as high as 1.73 wt%,with good cycling stability.After 50 cycles of hydrogen absorption/desorption,the alloy retained a hydrogen storage capacity of 1.45 wt%,with a capacity retention rate of up to 84.28%.The Mg thermal diffusion process thus provides a new approach for the controlled preparation of La-Mg-Ni-based alloys.展开更多
Low-Co Lal.8Ti0.2MgNi8.9Co0.1 alloys were prepared by magnetic levitation melting followed by annealing treatment. The effect of annealing on the hydrogen storage properties of the alloys was investigated systematical...Low-Co Lal.8Ti0.2MgNi8.9Co0.1 alloys were prepared by magnetic levitation melting followed by annealing treatment. The effect of annealing on the hydrogen storage properties of the alloys was investigated systematically by X-ray diffraction （XRD）, pressure-com- position isotherm （PCI）, and electrochemical measure- ments. The results show that all samples contain LaNi5 and LaMg2Ni9 phases. LaCo5 phase appears at 1,000 ℃. The enthalpy change of all hydrides is close to -30.6 kJ.mo1-1 H2 of LaNi5 compound. Annealing not only increases hydrogen capacity and improves cycling stability but also decreases plateau pressure at 800 and 900 ℃. After annealing, the contraction of cell volume and the increase of hydride stability cause the high rate dischargeability to reduce slightly. The optimum alloy is found to be one annealed at 900 ℃, with its hydrogen capacity reaching up to 1.53 wt%, and discharge capacity remaining 225.1 mAh·g-1 after 140 charge-discharge cycles.展开更多
TheLa0.5Pr0.2Zr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2（M0 and Zr0.65Ti0.35（Mn0.2V0.2Cr0.15Ni0.45）l.76 （M2） hydrogen storage alloys were prepared by inductive melting. In addition, the M1＋30 wt.%M2 composites were success...TheLa0.5Pr0.2Zr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2（M0 and Zr0.65Ti0.35（Mn0.2V0.2Cr0.15Ni0.45）l.76 （M2） hydrogen storage alloys were prepared by inductive melting. In addition, the M1＋30 wt.%M2 composites were successively prepared by using high-energy ball milling technology. From the X-ray diffraction （XRD） analysis, it was found that M1 and M2 alloys still retained their respective main phases in the MI＋30 wt.%M2 composites. The scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） indicated that the decrease in discharge capacity of MI and M2 alloy electrodes was ascribed to the oxidation-dissolution of La, Pr, Mg and Ti, Mn, V, Cr active elements, respectively. The electrochemical studies showed that the M1＋30 wt.%M2 composite electrode ball milling for 5 rain exhibited excellence cyclic stability （92.3%） after 80 charge/discharge cycles, which was higher than 77.7 % and 85.6% of MI and M2 alloy electrodes, respectively. Moreover, at the discharge current density of 1200 mA/g, the high rate dis- charge ability （HRD） of the M1＋30 wt.%M2 composite electrode increased from 61.5% （5 rain） to 70.3% （10 rain）. According to the linear polarization, Tafel polarization and cyclic voltammograms （CV）, the electrochemical kinetics of hydrogen reaction on the sur- face of the electrode and hydrogen diffusion rate in the bulk of alloy were also improved in the ML＋30 wt.%M2composite with in- creasing ball milling time.展开更多
LaMg8.52Ni2.23M0.15 （M=Ni, Cu, Cr） alloys were prepared by induction melting. X-ray diffraction showed that all the three alloys had a multiphase structure, consisting of La2Mg17, LaMg2Ni and Mg2Ni phases. Energy di...LaMg8.52Ni2.23M0.15 （M=Ni, Cu, Cr） alloys were prepared by induction melting. X-ray diffraction showed that all the three alloys had a multiphase structure, consisting of La2Mg17, LaMg2Ni and Mg2Ni phases. Energy dispersive X-ray spectrometer results revealed that most of Cu and Cr distributed in MgzNi phase. La2Mg17 and LaMg2Ni phases decomposed into MgHz, Mg2NiH4 and LaH3 phases during the hydrogenation process. Hydriding/dehydriding measurements indicated that the reversible hydrogen storage capacities of Mg2Ni phase in LaMgs.52Ni2.23M0.15 （M=Cu, Cr） alloys increased to 1.05 wt.% and 0.97 wt.% from 0.79 wt.% of Mg2Ni phase in LaMgs.52Ni2.38 alloy at 523 K. Partial substitution of Cu and Cr for Ni decreased the onset dehydrogenation temperature of the alloy hydrides and the temperature lowered by 18.20 and 5.50 K, respectively. The improvement in the dehydrogenation property of the alloys was attributed to that Cu and Cr decreased the stability of Mg2NiH4 phase.展开更多
In order to improve the electrochemical kinetic performances of La-Mg-Ni-based alloy,complex surface modification of Ni with excellent catalytic activity and conducting polymer polypyrrole(PPy)was performed via electr...In order to improve the electrochemical kinetic performances of La-Mg-Ni-based alloy,complex surface modification of Ni with excellent catalytic activity and conducting polymer polypyrrole(PPy)was performed via electroless plating method.FESEM images revealed that the complex Ni-PPy treatment resulted in more micropores at the alloy surface,with Ni particles and cotton fiber-shape PPy microspheres attached.Both the larger surface area induced by the micropore and the higher catalytic activity and conductivity on account of the dispersed Ni particles/PPy microspheres promoted the electrode reaction,thereby increasing the discharge capacity of the modified alloy electrode.Electrochemical impedance spectroscopy(EIS)and linear polarization results showed that the Ni-PPy treatment decreased the charge-transfer resistance and increased the exchange current density greatly,far more than the single-component Ni or PPy treatment.Consequently,a notable improvement in high rate dischargeability(HRD)was observed,and at a high discharge current density of 1800 mA/g,the HRD of the modified electrode increased by 10.4%compared with that of the bare electrode.展开更多
In order to improve the overall electrochemical properties of ABs-type storage alloys, the new type composite alloys M1Ni3.5Co0.6Mn0.4Al0.5-x wt% Mm0.89Mg0.11Ni2.97Mn0.14Al0.20Co0.54 （x = 0, 5, 10; M1 means mischmeta...In order to improve the overall electrochemical properties of ABs-type storage alloys, the new type composite alloys M1Ni3.5Co0.6Mn0.4Al0.5-x wt% Mm0.89Mg0.11Ni2.97Mn0.14Al0.20Co0.54 （x = 0, 5, 10; M1 means mischmetal） were prepared by means of ball milling. The composite alloys are shown to be single LaNi5 phase by X-ray diffraction （XRD） patterns. The maximum discharge capacity slightly increases from 315 mAh·g^-1 for M1Ni3.5Co0.6Mn0.4Al0.5 to 324 mAh·g^-1 （x = 5） and 325 mAh·g^-1 （x = 10）. The addition of AB3-type La-Mg- Ni-based alloy has a positive effect on the cycle stability. With the addition of Mm0.89Mg0.11Ni2.97Mn0.14-Al0.20Co0.54 alloy, the exchange current density （I0）, the limiting current density （IL） and the diffusion coefficient of hydrogen （D） of the alloy electrodes increase, leading to a corresponding improvement of the high rate dischargeability.展开更多
The present work focuses on the structural stability upon hydrogenation of three typical La-Mg-Ni-based alloys： La2 MgNi9, LaaMgNi14 and La4MgNi19. Structural changes during gaseous and electrochemical cycles were ch...The present work focuses on the structural stability upon hydrogenation of three typical La-Mg-Ni-based alloys： La2 MgNi9, LaaMgNi14 and La4MgNi19. Structural changes during gaseous and electrochemical cycles were characterized, and the influence of the structure distortion on the hydrogen storage properties was concerned. Hydrogen-induced amor- phization （HIA） and disproportionation of the three alloys have occurred during both the gaseous and electrochemical cycles. Structural stability of the phase structures in the La-Mg-Ni system is found to follow the order： LaNi5- 〉 （La,Mg）5Ni19 〉 （La,Mg）2Ni7 〉 （La,Mg）Ni3 〉 （La,Mg）Ni2. HIA increases thermal stability of the metal hydrides and difficulty to dehydrogenation and leads to degradation of both the gaseous and electrochemical capacities. Interestingly, LaEMgNi9 with poor stability presents elevated discharge capability even at 60 ℃ which can be attributed to increase in the hydrogen desorption capability and inhibition of the self-discharge induced by severe HIA at higher temperatures. In addition, HIA in the electrochemical reactions is obviously weaker than the extent during the gaseous cycles, which is mainly due to the slower hydrogenation speed. The development of HIA in the gaseous and electrochemical process is considered to follow the direct and gradual modes, respectively.展开更多
In this paper, the Co-free hydrogen storage alloys with the nominal compositions of La0.75R0.05Mg0.20Ni3.40Al0.10（R = La, Nd and Sm） were prepared by induction melting, and then the phase structure and electrochemic...In this paper, the Co-free hydrogen storage alloys with the nominal compositions of La0.75R0.05Mg0.20Ni3.40Al0.10（R = La, Nd and Sm） were prepared by induction melting, and then the phase structure and electrochemical properties of these alloys were comparatively investigated. It is found that the alloys mainly consist of（La, Mg）2Ni7phase, La Ni5 phase and（La, Mg）5Ni19phase.Refinement results further show that Nd substitution for La remarkably promotes the formation of La Ni5 phase, while Sm is beneficial for the formation of（La, Mg）5Ni19phase.At discharge current density of 1,875 m A g-1, the highrate dischargeability（HRD） of alloy electrodes increases by 13.9 % and 6.5 % with La substituted by Nd and Sm,respectively. The electrochemical kinetic measurements reveal that the exchange current density（I0）, charge transfer resistance（R） and hydrogen diffusion coefficient（D） for the alloy electrode are all facilitated with Nd and Sm partial substitution for La. Subsequently, a linear correlation between the HRD1875 and the corresponding I0/D is found.展开更多
基金supported financially by the National Natural Science Foundation of China (No. 51761032)the Natural Science Foundation Application of Inner Mongolia (No. 2014MS0526)
文摘Degradation behaviors of three typical La-Mg-Ni alloys, La2MgNi9, La1.5Mg0.5Ni7 and La4MgNi19, were studied. La1.5- Mg0.5Ni7 with （La,Mg）2Ni7 as main phase presents better discharge capacity and cycling stability. The three alloys suffer severe pulverization and corrosion after electrochemical cycles, which are considered to be the significant factor attributing to the capacity deterioration. However, the overall corrosion extent of the three cycled alloys aggravates successively, which is inconsistent with the result that LaEMgNi9 presented poor cycling stability and also the assumption that alloy with high Mg content is easy to be corroded. The intrinsic anti-corrosion and anti-pulverization characteristics of the three alloys are mainly focused in this work. Immersion corrosion experiments demonstrate that the Mg-rich phases are more easily to be corroded. The corrosion resistance of the three alloys presents an improved trend which is inversely proportional to abundance of the Mg-rich phases. However, the anti-pulverization abilities present an inverse trend, which is closely related to the mechanical property of various phase structures. LaNi5 with the highest hardness is easy to crack, but the soft （La,Mg）Ni2 is more resistant to crack formation and spreading. Thus, the weaker corrosion of La2MgNi9 after electro- chemical cycling is attributed to the better intrinsic anti-pulverization capability though the anti-corrosion is poor. As La4MgNi19 possesses excellent corrosion resistance, enhancement of the anti-pulverization ability is urgent for improvement in the cycling stability.
基金Project supported by the National Natural Science Foundation of China(51171165,21303157)the Natural Science Foundation of Hebei Province(B2012203027,B2012203104 and B2014203114)
文摘Yttrium （Y） has been used as the partial substitution element for lanthanum （La） to improve the electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys. Lao.80-xYxMg0.20Ni2.85Mn0.10Coo.55Al0.10 （x=0.00, 0.05 and 0.10） alloys were prepared by the inductive melting technique. The alloys were composed of LaNi5 and （La,Mg）2Ni7 phases, the introduction of Y promoted the formation of （La,Mg）2Ni7 phase, and thus the Y-substituted alloy electrodes exhibited higher discharge capacities. Y substitution was also found to be effective to improve the discharge kinetics of the alloy electrodes. When the Y content x increased from 0.00 to 0.10, the high-rate dischargeability of the alloy electrodes at a discharge current density of 1800 mA/g （HRDl800） in- creased from 23.6% to 39.7% at room temperature. In addition, the measured HRD1800 showed a linear dependence on both the ex- change current density and the hydrogen diffusion coefficient at different temperatures, respectively.
基金financially supported by the National Key Research and Development Program of China(2022YFB3803804)the National Natural Science Foundation of China(Nos.51971197,52071281 and 52201282)+3 种基金Basic Innovation Research Project in Yanshan University(No.2022LGZD004)China Postdoctoral Science Foundation(2023M742945)Postdoctoral research project of Hebei Province(B2023003023)Subsidy for Hebei Key Laboratory of Applied Chemistry after Operation Performance(No.22567616H)。
文摘A novel approach based on thermal diffusion was used to achieve controllable Mg content in A_(2)B_(7)-type La-Mg-Ni-based alloys.The formation mechanism of the A_(2)B_(7)-type phase as a result of the thermal diffusion process and the effect of Mg content on hydrogen storage performance were investigated.X-ray diffraction(XRD)patterns and Rietveld refinement results showed that increased Mg transformed the LaNi_(5)phase in the La_(0.74)Sm_(0.03)Y_(0.23)Ni_(4.32)Al_(0.04)precursor alloy into a superlattice structure.Scanning electron microscopy(SEM)images showed that Mg was evenly distributed in the alloy bulk.Mg in the superlattice significantly inhibited the phase decomposition of the superlattice structure during the hydrogen absorption/desorption cycles.An A_(2)B_(7)-type La_(0.57)Sm_(0.02)Y_(0.18)Mg_(0.23)Ni_(3.38)Al_(0.03)alloy composed of Gd_(2)Co_(7)and Ce_(2)Ni_(7)phases was successfully synthesized.The pressure-composition isotherm profiles showed that the alloy had a hydrogen storage capacity as high as 1.73 wt%,with good cycling stability.After 50 cycles of hydrogen absorption/desorption,the alloy retained a hydrogen storage capacity of 1.45 wt%,with a capacity retention rate of up to 84.28%.The Mg thermal diffusion process thus provides a new approach for the controlled preparation of La-Mg-Ni-based alloys.
基金financially supported by the National Natural Science Foundation of China(Nos.51071054 and51271061)the Natural Science Foundation of Guangxi(Nos.2010GXNSFD013004 and 2012GXNSFBA053149)
文摘Low-Co Lal.8Ti0.2MgNi8.9Co0.1 alloys were prepared by magnetic levitation melting followed by annealing treatment. The effect of annealing on the hydrogen storage properties of the alloys was investigated systematically by X-ray diffraction （XRD）, pressure-com- position isotherm （PCI）, and electrochemical measure- ments. The results show that all samples contain LaNi5 and LaMg2Ni9 phases. LaCo5 phase appears at 1,000 ℃. The enthalpy change of all hydrides is close to -30.6 kJ.mo1-1 H2 of LaNi5 compound. Annealing not only increases hydrogen capacity and improves cycling stability but also decreases plateau pressure at 800 and 900 ℃. After annealing, the contraction of cell volume and the increase of hydride stability cause the high rate dischargeability to reduce slightly. The optimum alloy is found to be one annealed at 900 ℃, with its hydrogen capacity reaching up to 1.53 wt%, and discharge capacity remaining 225.1 mAh·g-1 after 140 charge-discharge cycles.
基金supported by the Natural Science Foundation of Guangxi (2011GXNSFA018034)the Program for Characteristic Professionalism and Integrated Curriculum Construction in Colleges of Guangxi (GXTSZY024)
文摘TheLa0.5Pr0.2Zr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2（M0 and Zr0.65Ti0.35（Mn0.2V0.2Cr0.15Ni0.45）l.76 （M2） hydrogen storage alloys were prepared by inductive melting. In addition, the M1＋30 wt.%M2 composites were successively prepared by using high-energy ball milling technology. From the X-ray diffraction （XRD） analysis, it was found that M1 and M2 alloys still retained their respective main phases in the MI＋30 wt.%M2 composites. The scanning electron microscopy （SEM） and energy dispersive spectroscopy （EDS） indicated that the decrease in discharge capacity of MI and M2 alloy electrodes was ascribed to the oxidation-dissolution of La, Pr, Mg and Ti, Mn, V, Cr active elements, respectively. The electrochemical studies showed that the M1＋30 wt.%M2 composite electrode ball milling for 5 rain exhibited excellence cyclic stability （92.3%） after 80 charge/discharge cycles, which was higher than 77.7 % and 85.6% of MI and M2 alloy electrodes, respectively. Moreover, at the discharge current density of 1200 mA/g, the high rate dis- charge ability （HRD） of the M1＋30 wt.%M2 composite electrode increased from 61.5% （5 rain） to 70.3% （10 rain）. According to the linear polarization, Tafel polarization and cyclic voltammograms （CV）, the electrochemical kinetics of hydrogen reaction on the sur- face of the electrode and hydrogen diffusion rate in the bulk of alloy were also improved in the ML＋30 wt.%M2composite with in- creasing ball milling time.
基金Project supported by High-Tech Research and Development(863)Program of China(2007AA05Z117)National Natural Science Foundation of China(50971112,51171165)the Natural Science Foundation of Hebei Province(E201001170)
文摘LaMg8.52Ni2.23M0.15 （M=Ni, Cu, Cr） alloys were prepared by induction melting. X-ray diffraction showed that all the three alloys had a multiphase structure, consisting of La2Mg17, LaMg2Ni and Mg2Ni phases. Energy dispersive X-ray spectrometer results revealed that most of Cu and Cr distributed in MgzNi phase. La2Mg17 and LaMg2Ni phases decomposed into MgHz, Mg2NiH4 and LaH3 phases during the hydrogenation process. Hydriding/dehydriding measurements indicated that the reversible hydrogen storage capacities of Mg2Ni phase in LaMgs.52Ni2.23M0.15 （M=Cu, Cr） alloys increased to 1.05 wt.% and 0.97 wt.% from 0.79 wt.% of Mg2Ni phase in LaMgs.52Ni2.38 alloy at 523 K. Partial substitution of Cu and Cr for Ni decreased the onset dehydrogenation temperature of the alloy hydrides and the temperature lowered by 18.20 and 5.50 K, respectively. The improvement in the dehydrogenation property of the alloys was attributed to that Cu and Cr decreased the stability of Mg2NiH4 phase.
基金Supported by the National Natural Science Foundation of China(Nos.51571173,51701175,51771164).
文摘In order to improve the electrochemical kinetic performances of La-Mg-Ni-based alloy,complex surface modification of Ni with excellent catalytic activity and conducting polymer polypyrrole(PPy)was performed via electroless plating method.FESEM images revealed that the complex Ni-PPy treatment resulted in more micropores at the alloy surface,with Ni particles and cotton fiber-shape PPy microspheres attached.Both the larger surface area induced by the micropore and the higher catalytic activity and conductivity on account of the dispersed Ni particles/PPy microspheres promoted the electrode reaction,thereby increasing the discharge capacity of the modified alloy electrode.Electrochemical impedance spectroscopy(EIS)and linear polarization results showed that the Ni-PPy treatment decreased the charge-transfer resistance and increased the exchange current density greatly,far more than the single-component Ni or PPy treatment.Consequently,a notable improvement in high rate dischargeability(HRD)was observed,and at a high discharge current density of 1800 mA/g,the HRD of the modified electrode increased by 10.4%compared with that of the bare electrode.
基金financially supported by the National Natural Science Foundation of China(No.11364013)Guangxi Scientific Experiment Center of Mining,Metallurgy and Environment Foundation of Guilin University of Technology(No.KH2012YB002)+1 种基金the Education Department and Scientific Foundation of Guangxi(No.201203YB088)the Students Innovative and Undertaking Projects of Guangxi(No.2013HSCX002)
文摘In order to improve the overall electrochemical properties of ABs-type storage alloys, the new type composite alloys M1Ni3.5Co0.6Mn0.4Al0.5-x wt% Mm0.89Mg0.11Ni2.97Mn0.14Al0.20Co0.54 （x = 0, 5, 10; M1 means mischmetal） were prepared by means of ball milling. The composite alloys are shown to be single LaNi5 phase by X-ray diffraction （XRD） patterns. The maximum discharge capacity slightly increases from 315 mAh·g^-1 for M1Ni3.5Co0.6Mn0.4Al0.5 to 324 mAh·g^-1 （x = 5） and 325 mAh·g^-1 （x = 10）. The addition of AB3-type La-Mg- Ni-based alloy has a positive effect on the cycle stability. With the addition of Mm0.89Mg0.11Ni2.97Mn0.14-Al0.20Co0.54 alloy, the exchange current density （I0）, the limiting current density （IL） and the diffusion coefficient of hydrogen （D） of the alloy electrodes increase, leading to a corresponding improvement of the high rate dischargeability.
基金supported financially by the National Natural Science Foundation of China (No.51761032)the University Foundation of Inner Mongolia (No.NJZZ18142)
文摘The present work focuses on the structural stability upon hydrogenation of three typical La-Mg-Ni-based alloys： La2 MgNi9, LaaMgNi14 and La4MgNi19. Structural changes during gaseous and electrochemical cycles were characterized, and the influence of the structure distortion on the hydrogen storage properties was concerned. Hydrogen-induced amor- phization （HIA） and disproportionation of the three alloys have occurred during both the gaseous and electrochemical cycles. Structural stability of the phase structures in the La-Mg-Ni system is found to follow the order： LaNi5- 〉 （La,Mg）5Ni19 〉 （La,Mg）2Ni7 〉 （La,Mg）Ni3 〉 （La,Mg）Ni2. HIA increases thermal stability of the metal hydrides and difficulty to dehydrogenation and leads to degradation of both the gaseous and electrochemical capacities. Interestingly, LaEMgNi9 with poor stability presents elevated discharge capability even at 60 ℃ which can be attributed to increase in the hydrogen desorption capability and inhibition of the self-discharge induced by severe HIA at higher temperatures. In addition, HIA in the electrochemical reactions is obviously weaker than the extent during the gaseous cycles, which is mainly due to the slower hydrogenation speed. The development of HIA in the gaseous and electrochemical process is considered to follow the direct and gradual modes, respectively.
基金financially supported by the National Natural Science Foundation of China (Nos. 51171165 and 21303157)the Natural Science Foundation of Hebei Province (Nos. B2012203027, B2012203104, and B2014203114)+1 种基金the China Postdoctoral Science Foundation Project (No. 2013M541201)the Research Fund for the Doctoral Program of Higher Education of China (No. 20131333120008)
文摘In this paper, the Co-free hydrogen storage alloys with the nominal compositions of La0.75R0.05Mg0.20Ni3.40Al0.10（R = La, Nd and Sm） were prepared by induction melting, and then the phase structure and electrochemical properties of these alloys were comparatively investigated. It is found that the alloys mainly consist of（La, Mg）2Ni7phase, La Ni5 phase and（La, Mg）5Ni19phase.Refinement results further show that Nd substitution for La remarkably promotes the formation of La Ni5 phase, while Sm is beneficial for the formation of（La, Mg）5Ni19phase.At discharge current density of 1,875 m A g-1, the highrate dischargeability（HRD） of alloy electrodes increases by 13.9 % and 6.5 % with La substituted by Nd and Sm,respectively. The electrochemical kinetic measurements reveal that the exchange current density（I0）, charge transfer resistance（R） and hydrogen diffusion coefficient（D） for the alloy electrode are all facilitated with Nd and Sm partial substitution for La. Subsequently, a linear correlation between the HRD1875 and the corresponding I0/D is found.
