17-09-2012, 04:56 PM
The electrochemical properties of Ti0.9Zr0.2Mn1.5Cr0.3V0.3–x wt% La0.7Mg0.25Zr0.05Ni2.975Co0.525 (x=0, 5, 10) hydrogen storage composite electrodes
[attachment=33890]
Abstract
In the present work, new type hydrogen storage composites electrodes Ti0.9Zr0.2Mn1.5Cr0.3V0.3–x wt% La0.7Mg0.25Zr0.05Ni2.975
Co0.525 (x =0, 5, 10) were successively prepared by ball milling method. The structure and electrochemical properties of the composites were
investigated by means of XRD, SEM, EDS and electrochemical measurements. It was found that the bulk of the composites still retained
the hexagonal C14 Laves structure after short-term ball milling and that the maximum capacity of the composite electrodes was significantly
improved to 292.4 and 314.0mA h/g for x =5 and 10, respectively, from maximum 48.6mA h/g of Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy electrode.
Electrochemical impedance spectra and cyclic voltammograms (CV) measurements revealed that the charge-transfer resistance was reduced
with increasing amount of La–Mg-based alloy. The increasing x amount also lifted the values of hydrogen diffusion coefficient D of the
composite electrodes obtained by anodic polarization (AP) measurements. These indicated that the La–Mg-based alloy as a surface modifier
not only increased the discharge capacity but also improved the charge–discharge kinetics of composite electrode greatly.
2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Introduction
Ti-based AB2-type Laves phase hydrogen storage alloys are
potential candidates for negative electrode material of Ni–MH
batteries due to large hydrogen absorption capacity and easy
activation [1]. The theoretical capacity of Ti-based Laves phase
alloy was reported to be around 540mA h/g [2,3] and it can be
activated easily within only one charge–discharge cycle [4]. In
most cases, Ni element is essentially important in Ti-based alloy
electrodes because of its catalytic effect for the electrodes
during electrochemical reactions. Up to date, AB2-type Laves
phase alloys have been extensively developed [5–9]. Nevertheless
Experimental
The Ni-free Ti0.9Zr0.2Mn1.5 Cr0.3V0.3 alloy (represented
as A hereafter) and non-stoichiometric La0.7Mg0.25Zr0.05
(Ni0.85Co0.15)3.5 alloy (represented as B hereafter) were all
prepared by vacuum magnetic levitation melting under argon
atmosphere using the metals with purity of 99%. To
assure the homogeneity of these alloys, the ingots were turned
over and re-melted for three times. The prepared ingots were
mechanically crushed and ground into the powder of 200-
mesh size for ball milling. The P– C isotherm of Ni-free
Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy was measured by conventional
Severts-type apparatus at 313K after the alloy powder has
been activated by two cycles.
The alloys powders of Ti0.9Zr0.2Mn1.5Cr0.3V0.3 and
La0.7Mg0.25Zr0.05(Ni0.85Co0.15)3.5 were mixed homogenously
in the weight ratio of 9.5:0.5 and 9.0:1.0, respectively,
and ground by QM-1SP planetary ball miller under
0.2 ∼ 0.3MPa argon atmosphere for 2 h. In each stainless
milling pot, the ball-to-powder weight ratio was 20:1. The
A–x wt% B (x=0, 5, 10) alloy and composites were prepared
by ball milling. The crystal structure of the alloys was characterized
by XRD (Rigaku D/max-2500, CuK, 40 kV, 250 mA).
The surface morphologies of the alloys were observed using
scanning electron microscopy (SEM, JSM-6360LV) linked
with energy-dispersive X-ray spectrometer (EDS, Oxford
INCA). A N4 plus laser scattering particle meter was used to
determine the particle size and distribution of alloy powders. A
small amount of alloy powder was diluted in the sample cuvette
with ethanol to give the appropriate intensity for measurement.
The surface morphology of the composite particles
Fig. 2 presents the SEM morphologies and EDS patterns
of the composite alloys A–x wt% B (x = 0, 5, 10). It
clearly showed that both Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy and
La0.7Mg0.25Zr0.05(Ni0.85Co0.15)3.5 alloy particles were pulverized
and that the surface of the particles became much rougher
after ball milling, indicating that more fresh surface had been
exposed during the process. The difference of the energydispersive
X-ray spectra (EDS) between the micro-regions (I)
and (II) in Fig. 2© reveals that the white and fine particles
of La0.7Mg0.25Zr0.05(Ni0.85Co0.15)3.5 alloy are coated on the
larger particles of Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy. It is reasonable
that the different hardness and ductility between the
two alloys determined their difference in particle size. The
La–Mg-based alloy powders were suggested to be more brittle.
It could be easily pulverized and dispersedly cohered with
the larger Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy powders according
to the detection of EDS.
[attachment=33890]
Abstract
In the present work, new type hydrogen storage composites electrodes Ti0.9Zr0.2Mn1.5Cr0.3V0.3–x wt% La0.7Mg0.25Zr0.05Ni2.975
Co0.525 (x =0, 5, 10) were successively prepared by ball milling method. The structure and electrochemical properties of the composites were
investigated by means of XRD, SEM, EDS and electrochemical measurements. It was found that the bulk of the composites still retained
the hexagonal C14 Laves structure after short-term ball milling and that the maximum capacity of the composite electrodes was significantly
improved to 292.4 and 314.0mA h/g for x =5 and 10, respectively, from maximum 48.6mA h/g of Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy electrode.
Electrochemical impedance spectra and cyclic voltammograms (CV) measurements revealed that the charge-transfer resistance was reduced
with increasing amount of La–Mg-based alloy. The increasing x amount also lifted the values of hydrogen diffusion coefficient D of the
composite electrodes obtained by anodic polarization (AP) measurements. These indicated that the La–Mg-based alloy as a surface modifier
not only increased the discharge capacity but also improved the charge–discharge kinetics of composite electrode greatly.
2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Introduction
Ti-based AB2-type Laves phase hydrogen storage alloys are
potential candidates for negative electrode material of Ni–MH
batteries due to large hydrogen absorption capacity and easy
activation [1]. The theoretical capacity of Ti-based Laves phase
alloy was reported to be around 540mA h/g [2,3] and it can be
activated easily within only one charge–discharge cycle [4]. In
most cases, Ni element is essentially important in Ti-based alloy
electrodes because of its catalytic effect for the electrodes
during electrochemical reactions. Up to date, AB2-type Laves
phase alloys have been extensively developed [5–9]. Nevertheless
Experimental
The Ni-free Ti0.9Zr0.2Mn1.5 Cr0.3V0.3 alloy (represented
as A hereafter) and non-stoichiometric La0.7Mg0.25Zr0.05
(Ni0.85Co0.15)3.5 alloy (represented as B hereafter) were all
prepared by vacuum magnetic levitation melting under argon
atmosphere using the metals with purity of 99%. To
assure the homogeneity of these alloys, the ingots were turned
over and re-melted for three times. The prepared ingots were
mechanically crushed and ground into the powder of 200-
mesh size for ball milling. The P– C isotherm of Ni-free
Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy was measured by conventional
Severts-type apparatus at 313K after the alloy powder has
been activated by two cycles.
The alloys powders of Ti0.9Zr0.2Mn1.5Cr0.3V0.3 and
La0.7Mg0.25Zr0.05(Ni0.85Co0.15)3.5 were mixed homogenously
in the weight ratio of 9.5:0.5 and 9.0:1.0, respectively,
and ground by QM-1SP planetary ball miller under
0.2 ∼ 0.3MPa argon atmosphere for 2 h. In each stainless
milling pot, the ball-to-powder weight ratio was 20:1. The
A–x wt% B (x=0, 5, 10) alloy and composites were prepared
by ball milling. The crystal structure of the alloys was characterized
by XRD (Rigaku D/max-2500, CuK, 40 kV, 250 mA).
The surface morphologies of the alloys were observed using
scanning electron microscopy (SEM, JSM-6360LV) linked
with energy-dispersive X-ray spectrometer (EDS, Oxford
INCA). A N4 plus laser scattering particle meter was used to
determine the particle size and distribution of alloy powders. A
small amount of alloy powder was diluted in the sample cuvette
with ethanol to give the appropriate intensity for measurement.
The surface morphology of the composite particles
Fig. 2 presents the SEM morphologies and EDS patterns
of the composite alloys A–x wt% B (x = 0, 5, 10). It
clearly showed that both Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy and
La0.7Mg0.25Zr0.05(Ni0.85Co0.15)3.5 alloy particles were pulverized
and that the surface of the particles became much rougher
after ball milling, indicating that more fresh surface had been
exposed during the process. The difference of the energydispersive
X-ray spectra (EDS) between the micro-regions (I)
and (II) in Fig. 2© reveals that the white and fine particles
of La0.7Mg0.25Zr0.05(Ni0.85Co0.15)3.5 alloy are coated on the
larger particles of Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy. It is reasonable
that the different hardness and ductility between the
two alloys determined their difference in particle size. The
La–Mg-based alloy powders were suggested to be more brittle.
It could be easily pulverized and dispersedly cohered with
the larger Ti0.9Zr0.2Mn1.5Cr0.3V0.3 alloy powders according
to the detection of EDS.