Structure, Hydrogen Storage, and Electrochemical Properties of Body-Centered-Cubic Ti40V30Cr15Mn13X2 Alloys (X = B, Si, Mn, Ni, Zr, Nb, Mo, and La)

Structure, gaseous phase hydrogen storage, and electrochemical properties of a series of TiVCrMn-based body-centered-cubic (BCC) alloys with different partial substitutions for Mn with covalent elements (B and Si), transition metals (Ni, Zr, Nb, and Mo), and rare earth element (La) were investigated. Although the influences from substitutions on structure and gaseous phase storage properties were minor, influences on electrochemical discharge capacity were significant. The first cycle capacity ranged from 16 mAh·g−1 (Si-substituted) to 247 mAh·g−1 (Mo-substituted). Severe alloy passivation in 30% KOH electrolyte was observed, and an original capacity close to 500 mAh·g−1 could possibly be achieved by Mo-substituted alloy if a non-corrosive electrolyte was employed. Surface coating of Nafion to the Mo-substituted alloy was able to increase the first cycle capacity to 408 mAh·g−1, but the degradation rate in mAh·g−1·cycle−1 was still similar to that of standard testing. Electrochemical capacity was found to be closely related to BCC phase unit cell volume and width of the an extra small pressure plateau at around 0.3 MPa on the 30 °C pressure-concentration-temperature (PCT) desorption isotherm. Judging from its high electrochemical discharge capacity, Mo was the most beneficial substitution in BCC alloys for Ni/metal hydride (MH) battery application.