Self-assembly of CNTs@Ni foam electrode material and its activation effect during catalytic reforming of bio-oil model compound for hydrogen at different temperatures.

[Display omitted] • Carbon nanotubes (CNTs) with tip-growth mechanism were generated at 600 °C. • More amorphous carbon and carbon nanofibers (CNFs) were formed at 700 °C. • H 2 yield exhibited the "N" type trend as temperature increasing from 500 °C to 800 °C. • H 2 yield at 600 °C was higher than that at 700 °C due to the self-activation of CNTs. • Self-assembled CNTs@Ni foam at 600 °C performed best electrochemical performance. The H 2 production and self-assembly CNTs over Ni-Fe/Ni foam catalyst were investigated at different temperatures during steam reforming of bio-oil model compound. The formation of CNTs, CNFs and amorphous carbon and their different effects on catalytic activity were analyzed. With the temperature increasing from 500 °C to 800 °C, the amount of carbon deposition firstly increased and then decreased. It showed the highest amount of carbon deposition and largest proportion of CNTs (over 60 %) at 600 °C. The average diameter of CNTs was 15.18 nm. By contrast, more than 70 % of carbon deposition was amorphous carbon, and the CNFs with larger diameter (over 100 nm) were formed at 700 °C, which attributed to the agglomeration of metal particles at high temperature. The high reaction temperatures increased H 2 yield and pyrrole conversion, but differently, those at 600 °C was remarkably higher than that at 700 °C. It revealed that tip-growth of CNTs at 600 °C performed the self-activation effect to increase the catalytic activity, while the amorphous carbon generated at 700 °C deactivated the catalyst. After the reaction at 600 °C, the self-assemble of CNTs@Ni foam material showed the highest electrochemistry performance. [ABSTRACT FROM AUTHOR]