Synergistic effects of multiwalled carbon nanotubes and Al on the electrochemical hydrogen storage properties of Mg2Ni-type alloy prepared by mechanical alloying

• Published in: International journal of hydrogen energy 2012-01, Vol.37 (2), p.1538-1545
• Main Authors: Huang, L.W., Elkedim, O., Nowak, M., Jurczyk, M., Chassagnon, R., Meng, D.W.
• Format: Article
• Language: English
• Subjects: Al substitution; Alternative fuels. Production and utilization; Applied sciences; Electrochemical hydrogen storage properties; Energy; Exact sciences and technology; Fuels; Hydrogen; Mechanical alloying; Mg2Ni-type alloy; Multiwalled carbon nanotubes
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2011.10.045

Mg2−xAlxNi (x = 0, 0.25) electrode alloys with and without multiwalled carbon nanotubes (MWCNTs) have been prepared by mechanical alloying (MA) under argon atmosphere at room temperature using a planetary high-energy ball mill. The microstructures of synthesized alloys are characterized by XRD, SEM and TEM. XRD analysis results indicate that Al substitution results in the formation of AlNi-type solid solution that can interstitially dissolve hydrogen atoms. In contrast, the addition of MWCNTs hardly affects the XRD patterns. SEM observations show that after co-milling with 5 wt. % MWCNTs, the particle sizes of both Mg2Ni and Mg1.75Al0.25Ni milled alloys are decreased explicitly. The TEM images reveal that ball milling is a good method to cut long MWCNTs into short ones. These MWCNTs aggregate along the boundaries and surfaces of milled alloy particles and play a role of lubricant to weaken the adhesion of alloy particles. The majority of MWCNTs retain their tubular structure after ball milling except a few MWCNTs whose tubular structure is destroyed. Electrochemical measurements indicate that all milled alloys have excellent activation properties. The Mg1.75Al0.25Ni-MWCNTs composite shows the highest discharge capacity due to the synergistic effects of MWCNTs and Al on the electrochemical hydrogen storage properties of Mg2Ni-type alloy. However, the improvement on the electrode cycle stability by adding MWCNTs is unsatisfactory. ► Al substitution for Mg in Mg2Ni leads to the formation of AlNi-type solid solution. ► MWCNTs addition hardly affects the phase compositions of milled alloys. ► MWCNTs addition decreases the particle sizes of Mg2Ni and Mg1.75Al0.25Ni. ► MWCNTs aggregate along the boundaries and surfaces of milled alloy particles. ► MWCNTs and Al show synergistic effects on electrochemical properties of Mg2Ni.