Electrochemical hydrogen storage properties of nonstoichiometric amorphous MgNi1+x-carbon composites (x=0.05-0.3)

The effect of surface modification of nonstoichiometric amorphous MgNi1+x (x = 0.05-0.3) by introduction of various carbon sources in the system (graphite, CNTs and carbon black) was systematically investigated by XRD, SEM and conventional electrochemical tests. The results show that the surface modification by graphite and CNTs improves the electrochemical performance of MgNi1+x alloys, while the carbon black modification slightly decreases the initial discharge capacity and has no effect on the capacity degradation of amorphous MgNi1+x alloys. CV measurements and the exchange current density of composite electrodes show that the surface electrocatalytic activity of the electrodes increases with graphite or CNT modification. However, carbon black limits the charge-transfer reaction at the surface of the alloy. Potential step measurements for the carbon-modified samples, on the other hand, show that surface modification of MgNi1+x alloys does not affect the hydrogen diffusion rate (D), indicating that carbon modification on MgNi1+x does not affect the diffusion process of hydrogen from the surface to the bulk of alloys. Carbon materials only stay on the surface and affect the surface properties of alloys. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.