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Nitrogen-doped carbon nanotubes functionalized by transition metal atoms: a density functional study

Carbon nanotubes (CNTs) functionalized by metals have great potential for many applications. Our recent experimental results indicated that Pt-based nanoparticles could be directly immobilized onto nitrogen-doped carbon nanotubes (CNxNTs) through nitrogen mediation without pre-modification. The nanocomposite catalysts thus obtained exhibited excellent catalytic activity in direct methanol oxidation and oxygen reduction reaction, indicating their promising important application in fuel cells. In this study, the adsorptions of 12 different transition metals (TMs = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, and Pt) on CNxNTs have been systematically studied using density functional theory calculations. And the interactions of the Pt/CNxNT catalyst with the common species CH3OH, HCHO and HCOOH involved in methanol oxidation have also been investigated in detail. The results indicate that nitrogen incorporation could efficiently enhance the binding energy of TMs on CNxNTs compared with the cases on CNTs. And the electronic states of the transition metals could also be modified, consequently the Pt/CNxNT catalyst is superior to the Pt/CNT catalyst for methanol oxidation, presenting improved performance for reactant adsorption. The theoretical understanding on the interactions between TMs and CNxNTs, and between reactants and Pt/CNxNT catalyst indicate obvious advantages of CNxNTs over CNTs for the construction and optimization of nanocomposite catalysts, which suggests great potential applications in many fields.