Microstructure and some dynamic performances of Ti-V-Nb-Cr-Ni electrode alloy

Microstructure and some dynamic performances of Ti0.25V0.34Nb0.01Cr0.10Ni0.30 electrode alloy were studied by XRD, FESEM-EDS and EIS measurements. Based on XRD and FESEM-EDS analysis, the alloy is mainly composed of V-based solid solution with BCC structure and TiNi-based secondary phase. V-based solid solution phase looks as a dendrite surrounded by TiNi-based secondary phase. The discharge capacity increases with increasing temperature in a wider temperature region front 303 K to 343 K. The result of electrochemical impedance spectrometry (EIS) indicates that the charge transfer resistance (R-T) decreases with increasing temperature, while the exchange current density (i(0)) and the diffusion coefficient of hydrogen (D) in the bulk of the alloy increase with increasing temperature. The exchange current density (i(0)) at 343 K is about 3.6 times and 13.6 times larger than that at 323 K and 303 K, respectively, but diffusion coefficient of hydrogen does not increase so much. The apparent activation energy of the electrochemical reaction on the surface of the electrode alloy is far higher than that for AB, type alloy. The result of HRD indicates that the diffusion of hydrogen in the bulk of the alloy may be a rate-limiting step during the discharge process at higher discharge current density.