Unzipping of single-walled carbon nanotube for the development of electrocatalytically active hybrid catalyst of graphitic carbon and Pd nanoparticles

Abstract

We demonstrate a new approach for the unzipping of single-walled carbon nanotube (SWCNT) in an aqueous solution using the transition metal complex PdCl₄^2– as a sacrificial chemical scissor and the growth of graphitic-carbon-coated Pd nanoparticles for the electrocatalytic oxidation of formic acid. The chemical unzipping and the growth of Pd nanoparticles involve the spontaneous electron transfer between SWCNT and the metal complex in an aqueous solution at room temperature. The redox potential for SWCNT and PdCl₄^2– favors the spontaneous electron transfer reaction. The metal complex, in situ generated Pd nanoparticle, and oxygen play vital role in the oxidative unzipping of SWCNT. The Pd nanoparticles have an average size of 11 nm and are coated with the graphitic carbon layer of unzipped SWCNT (UzCNT-Pd). The Pd nanoparticle of the UzCNT-Pd hybrid material has a large electrochemically active surface area of 2.14 cm². The hybrid material exhibits excellent electrocatalytic activity toward the oxidation of formic acid. The area and mass specific activity are significantly higher than those of the traditional carbon-supported Pd nanoparticle. The synergistic effect of graphitic carbon and the metal nanoparticles controls the catalytic activity. The confinement of Pd particles inside the graphitic carbon enhances the overall performance of the catalyst.