Facile In Situ Synthesis of Multiwall Carbon Nanotube Supported Flowerlike Pt Nanostructures: An Efficient Electrocatalyst for Fuel Cell Application

Abstract

Multiwall carbon nanotube (MWCNT)-supported flowerlike Pt nanostructure with pronounced electrocatalytic activity in the reduction of oxygen and oxidation of methanol was synthesized by wet chemical hydrogen reduction route. The Pt nanostructures on the MWCNT were characterized by transmission electron microscopic, field emission scanning electron microscopic, X-ray diffraction (XRD), X-ray photoelectron spectroscopic, and electrochemical measurements. The Pt nanostructures on MWCNT have flowerlike morphology with an average size of 80 nm. XRD and selective area electron diffraction measurements show that the Pt nanoflowers are crystalline and have face centered cubic structure. The flowerlike Pt nanostructure shows excellent electrocatalytic activity toward oxygen reduction and methanol oxidation reactions. The electrocatalytic performance of the nanoelectrocatalyst was evaluated in terms of catalytic current density, stability, and reduction/oxidation potential. The particle loading strongly controls the electrocatalytic activity. High-catalytic current density was obtained at lower loading of the nanoelectrocatalyst. The kinetics of oxygen reduction reaction was analyzed using rotating ring-disk electrode system. The nanoelectrocatalyst favors the 4-electron pathway for the reduction of oxygen at favorable potential. The electrochemical impedance spectroscopic (EIS) measurement was used to evaluate the performance of the catalyst toward methanol oxidation. The EIS response of the electrode toward oxidation of methanol strongly depends on the electrode potential. Capacitive, inductive, and pseudoinductive behaviors, depending on the electrode potential, were observed. The charge transfer resistance decreases gradually while increasing the potential from 0.5 to 0.8 V. Negative impedance was obtained at the potential of 1.0 V. The electrocatalytic performance of flowerlike nanostructure is significantly higher than the conventional spherical nanoparticles. The shape and surface morphology of the nanoparticles have profound effect in their electrocatalytic activity.