Effect of unit cell volume of RE(Ni, Co, Mn, Ti)(5) alloy (RE = La, Ce, Pr, Nd) on its electrochemical properties

Four rare earth based AB(5) typed alloys, La(Ni, Co, Mn, Ti)(5), Ce(Ni, Co, Mn, Ti)(5), Pr(Ni, Co, Mn, Ti)(5) and Nd(Ni, Co, Mn, Ti)(5), were prepared and then their unit cell volumes (V-cell), standard enthalpies of metal hydride formation at 298 K (DeltaH degrees (298 K)), and main electrochemical characteristics, such as activation cycle number (n(a)), maximum discharge capacity at 50 mA/g charge/discharge rate (C-50,C-max), high-rate-dischargeability kappa (includes kappa (1) and kappa (2)), rate of decay (-dC/dn) were measured and analyzed to reveal the effects of the rare earth elements on the electrochemical properties. The results show that the unit cell volume is the key factor in determination of the alloys' thermodynamics and electrochemical properties. The standard enthalpies of metal hydride formation at 298 K (DeltaH degrees (298) (K)) are proven to vary linearly with the unit cell volume, and the four electrochemical parameters, n(a), C-50,C-max, -dC/dn and kappa, are dualistically affected by it. The change of unit cell volume is in accord with the periodic law of the rare earth element