Amino-functionalized and acid treated multi-walled carbon nanotubes as supports for electrochemical oxidation of formic acid

Schematic representation of a two-step functionalization process performed over MWNTs. The first step involves a treatment of the MWNTs using a mixed acid (TMWNTs). The second step involves treatment of the TMWNTs using an amine (TAMWNTs). A direct one-step treatment of the MWNT using amines to form AMWNT is also shown. [Display omitted] ► A simple two-step functionalization of MWNT. ► Very efficient utilization of Pt over functionalized MWNT. ► Improved formic acid electro-oxidation compared to other supports. We report a simple two-step process to functionalize multi-walled carbon nanotubes, first using mixed acid treatment and then an amine treatment. The treated nanotubes have been characterized using thermo gravimetric analysis and Fourier transform infrared spectroscopy. The treated multi-walled carbon nanotubes can be used as a support for Pt electrodeposition. Potentiodynamic scans in acidified chloroplatinic acid solution result in the formation of polycrystalline Pt deposits on the treated multi-walled carbon nanotubes. Field emission-scanning electron microscopy and high resolution transmission electron microscopy have been used to further analyze the Pt deposits. The Pt deposits are well dispersed over the functionalized supports. Particularly, amino functionalized and acid treated multi-walled carbon nanotubes shows the smallest Pt size of about 10nm with a predominantly Pt (111) basal plane orientation. CO oxidation studies show that the Pt deposits on all forms of multi-walled carbon nanotubes (untreated and treated) demonstrates higher electrochemical activity than traditional Vulcan carbon support. Formic acid oxidation was used as a probe reaction to evaluate electrocatalytic activity. Pt utilization, defined as, amount of active Pt sites per unit mass of Pt deposited, is highest when amino functionalize multi-walled carbon nanotubes is used as a support.