Effect of multi-walled carbon nanotubes and palladium addition on the microstructural and electrochemical properties of the nanocrystalline Ti2Ni alloy

• Structural and electrochemical properties of Ti2Ni-based materials were investigated.
• Pd-addition improves anticorrosion and catalytic properties of materials.
• MWCNTs provide channels for the transport of hydrogen.
• Ti2Ni + Pd + MWCNT nanocomposite exhibits a high discharge capacity equaled 301 mAh/g.
• We measured the highest capacity obtained so far for Ti2Ni-based materials.

Ti2Ni-based nanocrystalline alloys and their nanocomposites were prepared by mechanical alloying and annealing at 750 °C for 0.5 h under an argon atmosphere. Shaker type ball mill was used. Ti2Ni alloy was chemically modified by Pd and multi-walled carbon nanotubes. The main aim of the study was to investigate the effect of chemical modification on electrochemical properties of Ti2Ni alloy. Structure, microstructure, composition and morphology of materials were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and atomic force microscopy. X-ray diffraction analysis revealed formation of main Ti2Ni phase structure crystallizing in a Fd3¯m space group. Transmission electron microscopy micrographs confirmed stability of tubular structure of MWCNTs after 1 min co-milling. All studied materials were tested as negative electrode for Ni-MHx rechargeable batteries. Electrochemical measurements revealed that materials with Pd have excellent activation properties. Ti2Ni + Pd + MWCNT is a material with the highest discharge capacity equaled 301 mAh/g. This is the highest capacity obtained so far for Ti2Ni-based materials. This capacity is related to lubricant and hydrogen transporting functions of multi-walled carbon nanotubes and anticorrosion and catalytic functions of Pd. Ti2Ni + Pd + MWCNT was also the material with the best cycle stability. Capacity retaining rate after 18th cycle equaled 75%.