A study on the effect of nickel, cobalt or graphite addition on the electrochemical properties of an AB(5) hydrogen storage alloy and the mechanism of the effects

The effects of the addition of cobalt powder, nickel powder and graphite to metal hydride (MH) electrode have been investigated using the constant cur rent charge/discharge test. Electrochemical impedance spectroscopy, linear polarization and cyclic voltammetry methods were used to study the mechanis m for the property variation. Cobalt powder addition can increase the MH el ectrode capacity at lower charge/discharge rates, but decrease the capacity at higher charge/discharge rates. Nickel powder addition is beneficial to the capacity and rate-dischargeability due to the improvement of electrical conductance and electrocatalytic activity of the MH electrode. The perform ance of the MH electrode is slightly improved with the addition of graphite . The lower-frequency semicircle observed in the Nyquist plot is suggested to be the reaction impedance of the MH electrode. (C) 2001 Elsevier Science B.V. All rights reserved.