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Carbon Nanotubes-Supported Pt Electrocatalysts for O₂ Reduction Reaction-Effect of Number of Nanotube Walls.

Carbon nanotubes (CNTs) are one of the most common catalysts supports for the development of electrocatalysts for O₂ reduction reaction (ORR) of electrochemical devices such as polymer electrolyte membrane fuel cells (PEMFCs) and metal-air batteries due to their high electrical conductivity and high stability. In addition to the electrical conductivity and stability, the number of inner tubes or walls also influence the electrocatalytic activity of the supported catalysts. Here we study the electrocatalytic activity of Pt nanoparticles (NPs) supported on CNTs (Pt/CNTs) as a function of number of walls towards ORR in both alkaline and acid solutions. The results indicate that the mechanism of ORR on Pt/CNTs does not change with the number of walls of CNTs support but the number of walls of CNTs supports has a significant effect on the electrocatalytic activity of supported Pt NPs. Pt NPs supported on double-walled CNTs (DWCNTs) exhibit a much better activity for ORR, as compared with that supported on single-walled and multi-walled CNTs (SWCNTs and MWCNTs). The high electrocatalytic activity of DWCNTs-supported Pt NPs is contributed to the fast electron transfer between the outer wall and inner tubes of DWCNTs for ORR through electron tunnelling process under the electrochemical polarization driving force.