Research On Corrosion Resistance Of V₃TiNi_0.56M_X(M=Al, Cr) Hydrogen Storage Alloys In Alkaline Solution

Vanadium-based solid solution hydrogen storage alloys have been attractived for their potential application in the negative electrode materials of Ni–MH battery because of their high hydrogen storage capacity, excellent diffusion rate in vanadium-based hydride and hydrogen absorption-desorption at room temperature. V₃TiNi_0.56 alloy, one of selected V-based hydrogen storage alloys, has the discharge capacity of 420mAh/g. However, V₃TiNi_0.56 alloy has not been practically used for its poor cyclic durability in alkaline solution and high mass loss. In the paper, we studied the running conditions of the V₃TiNi_0.56M_x(M=Al, Cr; x=0.1, 0.3) alloys, which were used for the negative electrode materials of Ni–MH battery, the running conditions were stewing, charging and discharging. We studied microstructure, electrochemical performance and the corrosion resistance in alkaline solution of V₃TiNi_0.56M_x hydrogen storage alloys with definite Al and Cr substitution. The results are as following:â‘ V₃TiNi_0.56Al_x(x=0.1,0.3)alloys produced by Self-propagating High-temperature Synthesis consist of Vanadium-based solid solution phase, TiNi phase and AlV3 phase and alloying agent Al distribute mainly in grain boundary. But V₃TiNi_0.56Cr_x(x=0.1,0.3)alloys ,which was produced by Self-propagating High-temperature Synthesis, consist of vanadium-based solid solution phase and TiNi phase and alloying agent Cr distribute mainly in grain boundary.â‘¡From the test and analysis of corrosion potential, exchanging current density, limiting current density, exchanging impedance spectra, the corrosion resistance of the V₃TiNi_0.56M_x(M=Al,Cr; x=0.1,0.3) hydrogen storage alloys was enhanced in KOH alkaline solution with the increasing of supplement content, the corrosion resistance of the alloys added Cr excelled to the alloys added Al. The element of Al and Cr distributing mainly in grain boundary could slow up oxidizing of Ti and V, and preserve TiNi phase from dissolving and enhanced corrosion resistance in KOH solution.â‘¢From the test of the alloy marinating in 6mol/L KOH solution, which was imitating the running condition of stewing, it could be concluded that the alloy could be corroding in stewing running condition. The corrosion resistance of the alloys were arranged as: V₃TiNi_0.56Cr0.3,V₃TiNi_0.56Cr0.1,V₃TiNi_0.56Al_0.3,V₃TiNi_0.56Al_0.1. Through analyzing the normal potential of the alloy, the element in the alloy was arranged by the ability of corrosion resistance from better to worse, the result was Al,Ti,V,Cr,Ni. â‘£Corrosion could be occurred when V₃TiNi_0.56M(M=Al,Cr;x=0.1,0.3) alloys were in alkaline solution, and the corrosion caused by pit corrosion and intercrystalline corrosion. The intercrystalline corrosion was the major aspect. Both of the TiNi phase and V-based solid solution were corroded in alkaline solution, and the TiNi phase priority was corroded primarily. The oxidate produced by corrosion were mainly TiO2, and there were V2O5 in part. Al2O3 existed for the alloy added Al, and Cr2O3 existed for the alloy added Cr.⑤The vanadium-based hydrogen storage alloys could be corroded when the alloy were charing and discharing, and the cubic content of the crystal lattice was changed greatly, it induced that the alloy appeared crack and bloom, the liquid-solid surface was refreshing continuously, so the rate of corrosion was accelerated.â‘¥The sequence of the alloy corroding in 6mol/L KOH alkaline solution from better to worse, which was used for Ni-MH battery, was stewing, charging and discharging.