Preparation of Polyaniline Covalently Grafted Carbon Nanotubes Supported Pt Catalysts and Its Electrocatalytic Performance for Methanol

Abstract

Recently, covalently functionalization carbon nanotubes have been received special attention because of the ex- pansive application prospect in the areas of nanoscience and nanotechnology. Moreover, covalent functionalization of carbon nanotubes can readily deal with fundamental issues of purification, solubilization, and processing. In particular, polyaniline, due to its high electronic conductivity, good environmental stability, easy preparation and reversible acid-base dop- ing-dedoping chemistry, has been one of the most studied conducting polymers. Recently, CNTs-PANI composites were in- vestigated widely, such as supercapacitor, optoelectronic devices, sensing and catalysis as well. In this work, uniform struc- tures PANI covalently grafted onto CNTs functionalization with -NH2 groups composites have been obtained by using liq- uid/liquid(L/L) interfacial polymerization method. The interfacial system was established by using CNTs, FeCl3, HCl as top aqueous phase and aniline, CH2Cl2 as bottom organic phase, which effective suppress second growth of PANI and obtain uniform CNTs-NH-PANI composites. Concerning CNTs-NH-PANI composites, PANI can covalently be grafted on CNTs with -NH2 groups. The resulted CNTs-NH-PANI composites have abundant -NH2 groups on their surface, serving as anchor centers for achieving high Pt dispersion. More important, PANI uniformly grafted on CNTs is prone to disperse the bundle of CNTs into separated lines and improve water dispersibility of obtained CNTs-NH-PANI composites. Subsequently, PtNPs were successfully deposited on the CNTs-PANI to form ternary hybrids. Potential application of the ternary hybrids as high performance catalysts for direct methanol fuel cells has been explored. The catalyst samples were characterized by transmis- sion electron microscopy (TEM), X-ray diffraction (XRD) and electrochemical methods. TEM results showed that the hier- archical CNTs-PANI composites with uniform morphology have been successfully prepared due to hydrophilic -OH and -NH2 groups covalently functionalized onto the surface of CNTs. Moreover, the electrochemical measurement show that the Pt/CNTs-NH-PANI hybrid have better stabilities compared with commercial JM (Pt/C) catalyst. The long-term durability test of the Pt/CNTs-CO-PANI, Pt/CNTs-NH-PANI and Pt/C catalysts shows that PANI grafted on CNTs as catalyst supports have better stabilities and more tolerant toward poisoning. Moreover, PANI covalently grafted on CNTs as catalyst supports has more excellent performance. The If/Ib of Pt/CNTs-NH-PANI catalyst for electrocatalytic methanol oxidation is 1.65 which is nearly 1.6 and 1.2 times than that of the commercial JM(Pt/C) and Pt/CNTs-CO-PANI catalysts, respectively. The results show that carbon nanotubes covalently grafting polyaniline as support can effectively improve the catalyst stability, increas- ing the service life of the catalyst. Keywords carbon nanotube; polyaniline; covalently; catalyst; methanol oxidation; CO-tolerance