Preparation Of V-Ti-Ni-based Solid Solution Hydrogen Storage Alloy Electrodes And Investigation On Their Electrochemical Performance

Based on the V-Ti-Ni-based hydrogen storage alloy,V2.?TiNi0.3 with a low V content was selected as the object alloy of the study,the experimental project was designed and optimized by the references,then prepared by vacuum arc melting in this paper.The effects of adding Chromium(Cr),Zirconium(Zr)elements on structural and electrochemical properties of the electrode alloy were studied by XRD,optical microscopy,SEM and other electrochemical testing techniques such as constant current charge and discharge,high rate discharge,linear polarization and constant potential step.At last,the V2.1TiNi0.3Zr0.06 hydrogen storage alloy with the highest discharge capacity was developed,and the effect on the structure and electrochemical properties of this alloy was studied by replacing partial Ti with Cr.The microstructures and electrochemical properties of the V2.1TiNi0.3Crx(x=0,0.2,0.4,0.6)hydrogen storage electrode alloys have been investigated.The results showed that all of the alloys were consisted of the V-based solid solution main phase with a body centered cubic(BCC)structure and the TiNi-based secondary phases.The secondary phases were mainly in the grain boundaries with network distribution,and some of the secondary phase particles were distributed in the main phase.The cell volumes of the main phase and the maximum discharge capacity of the alloy electrodes decreased with the increase of Cr contents,while the cycle stability of the alloy electrodes was gradually increased.At the same time,the kinetic performances of the alloy electrodes were improved.The activation performance of the alloy electrodes deteriorated when the Cr element was added,but further increase of Cr content did not change the activation performance significantly.The V2.1TiNi0.3Cr0.4 alloy showed the best electrochemical properties among the investigated alloys.Its maximum discharge capacity reached 442.2mAh/g,and its capacity retention ratio after 20 cycles was 81.91%.The phase structures and electrochemical properties of the V2.1TiNi0.3Zrx(x=0-0.12)hydrogen storage alloys have been systematacially investigated.Their microstructure and XRD showed that the alloy of V2.1TiNio.3 was consisted of V-based solid solution with a BCC structure and a TiNi-based sencondary phases.The secondary phases of the V2.iTiNi0.3Zrx(x=0.03-0.12)alloys changed into a C14-type Laves phases with hexagonal structure when the Zr element was added.The secondary phases of all the alloys nearly precipitate along the grain boundaries of the main phase.In addition,the cell parameters and volumes of the main phase shrink with increasing cotents of Zr.According to the electrochemical measurements,not only the activition abiliy but also the maximum discharge capacity was improved by adding Zr of moderate contents into the V2.iTiNi0.3 alloy.Moreover,the high-rate dischargeability and exchange current density of the alloys were all improved,but its cycle stability was decreased.It was found that the alloy electrode of V2.1TiNi0 3Zr0.06 had better comprehensive performance by comparison.Based on the above investigation,the maximum discharge capacity and poor cycle stability of the V2.1Ni0.3Zr0.06 alloy was chosen as the alloy that was studied.The microstructure and electrochemical properties of V2.,Ni0.3Zr0.06Ti1-xCrx(x=0-0.2)hydrogen storage alloys had been systematacially investigated.It was found that all the alloys were consisted of a V-based solid solution main phase with a body centered cubic(BCC)structure and a C 14-type Laves secondary phase in the form of three-dimensional network.The unit cells of both main phase and secondary phase shrink with increasing Cr cotents.Expanding capacity retention ratio,high-rate dischargeability and exchange current density of the alloy with the increase of the content of Cr element substitution,but it would be decreased the maximum discharge capacity and activation performance.75.39%of the largest capacity retention ratio of the alloy electrode,its high-rate discharge performance and exchange current density is 89.07%and 152.81mA/g respectively when x=0.2 The maximum discharge capacity is 382mA/g after four times of activation.