Ba-based alloy type hydrogen storage alloy composite electrode materials
In the nickel-metal hydride secondary battery using hydrogen storage alloy anode research and development, because of vanadium based alloys have high hydrogen storage capacity and hydrogen absorption temperature is moderate and anti-pulverization ability, etc., so use it as a high-energy Ni-MH battery The anode material after the election much attention, but because of the existing V-based solid solution hydrogen storage alloy in the electrochemical reaction, due to the oxidation of vanadium in the electrolyte and the dissolution has been difficult to overcome, so the poor cycle life, thus preventing its presence in the Ni / MH battery in practical application. To further improve the V-based hydrogen storage alloy electrode electrochemical reaction kinetics and cycle life, this article Ti0.28Cr0.217V0.42Fe0.083 vanadium alloy as the substrate, by adding 30% (wt) rare earth A2B,-type alloy La0 .63 Gd0.2Mg0.17Ni3.1Co0.3Al0.1 for the electro-catalytic activity of materials prepared by mechanical milling modification of hydrogen storage alloy composite electrode material, the system of the milling time on the hydrogen storage characteristics and electrochemical properties, draw the following Conclusions:
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V-based hydrogen storage alloy Ti0.28Cr0.217V0.42Fe0.083 gaseous hydrogen storage capacity could reach 3.1% (wt), and thus the theory should have a relatively high discharge capacity (946mAh / g), but its poor electro-catalytic activity, The measured value is only I0 10.5mA / g, at room temperature under the conditions of almost no electrochemical hydrogen absorption capacity. The La - Mg - Ni alloy La0.63Gd0.2Mg0.17Ni3.1Co0.3Al0.1 better electrocatalytic activity, the exchange current I0 can reach 260.2mA / g, room temperature, the maximum discharge capacity of 390mAh / g, by After 100 cycles the discharge capacity retention rate of 94%, indicating that with La - Mg - Ni alloy La0.63Gd0.2Mg0.17Ni3.1Co0.3Al0.1 vanadium alloy as the surface modified material is feasible.
X-ray diffraction (XRD) and electron microscopy (SEM, TEM) analysis shows that with the increase of milling time (t = 0-10h), composite material particles become finer, A2B7 type alloy particles dispersed and coated on the surface of vanadium-based alloys on; when the milling time t = 5h, the composite material to form the composite nano-grain structure was accompanied by the tendency of some amorphous, while V-based BCC phase alloys the lattice parameters a and cell volume v were significantly reduced. Hydrogen storage characteristics and electrochemical properties of the test results show that after milling pure vanadium alloy cast the hydrogen absorption capacity has been reduced, and milling the composite hydrogen storage capacity was increased with the milling time increases and then decreases law, the maximum hydrogen storage capacity of 2.5% (wt H2); modified by milling, electrochemical properties of composite materials are significantly improved, when the milling time is 5h and the electrode when the maximum discharge capacity of 425.8mA h / g, same alloy surface has been greatly improved catalytic activity, modification of pure vanadium based alloys prior to I0 is 10.5mA / g, while the modified (t = 5h) of I0 is 181.8mA / g. When ≥ 5h, the milling composite electrodes after 100 charge-discharge cycles the discharge capacity retention rate is 97%, the electrode showed good cycle stability.
