Investigation Of Transition Metal Nitride And Carbon Nanotubes Composites Supported Platinum Catalysts And Their Performance For Methanol Oxidation

The energy and environment problem increasingly prominent demands the development of direct methanol fuel cell (DMFC) as promising green energy sources due to its high efficiency, high power density, and zero or low exhaust. However, the widely used carbon-based support of Pt/C catalyst is not sturdy enough and the weak interaction between support and the metal nanoparticles causing a lower performance ascribed to the corrosion of the carbon support by electrochemical oxidation under fuel cell operating circumstances leads to the precious metals to aggregate and separate from the carbon support. Thus designing and synthesis catalyst with high performance and durability is urgently required. In this work, by the combination of liquid phase and post-nitriding method, titanium nitride nanotubes (TiN NTs)and titanium cobalt nitride (TiCoN)-CNTs hybrid support are prepared and further decorated with Pt nanoparticles (Pt NPs) to catalyze the oxidation of methanol. The catalyst is characterized by X-ray diffraction (XRD), scanning/transmission electron microscopy (SEM/TEM), N2 adsorption/desorption, X-ray photoelectron spectroscopy (XPS) and electrochemical measurements to investigate morphology, structure and performance of the catalyst.The Pt/TiN NTs catalyst displays higher activity and durablity for methanol oxidation reaction (MOR) compared with the traditional Pt/C (E-TEK) catalyst. The XRD patterns shows that TiN NTs are polycrystalline with a face centered cubic (Fcc) structure. The nitrogen adsorption/desorption results shows that TiN NTs exhibits a typical type Ⅳ isotherm with a distinct hysteretic loop, attributable to the presence of mesopores in the TiN NTs. The SEM and TEM image reveal that the nanotube wall is porous and consists of homogeneous cohesively attached TiN nanocube particles. In addition, Pt NPs supported on the dendritic TiN nanocrystals exhibit small size and good dispersion. Cyclic voltammetry (CV) measurement suggests that TiN NTs support is electrochemically stability under DMFC conditions, and the structural morphology of TiN NTs was still preserved after the electrochemical stability test. The XPS and CO-Stripping results show that a really strong interaction between Pt NPs and TiN NTs support, which will do good to the removal of the CO from the Pt surface during the methanol oxidation process.The Pt/CNTs@TiCoN catalyst exhibits a rather higher catalytic activity and durability than that of the conventional Pt/C (JM) for methanol oxidation. The XRD results show that the anatase TiO2 nanocrystals in the precursors were wholly converted to TiN nanostructure after nitriding and Co element was incorporated into the TiN structure to form a single phase solid solution with high purity. The TEM images reveals that Pt NPs is minimal aggregation and highly dispersed on the CNTs@TiCoN supports as well as the carbon black. The chronoamperometry curves test show that Pt/CNTs@TiCoN catalysts has a higher tolerance to the carbonaceous species generated during methanol oxidation and more electroactive for MOR. The XPS test shows that the strong interaction between anchored Pt atoms and the CNTs@TiCoN support. In addition, Co doping can greatly increase the Pt(O) ratio in the Pt/CNTs@TiCoN catalyst, and the high Pt (0) content is indeed an advance to improve the catalytic activity. The ADT results show that CNTs@TiCoN support can remarkably enhance the durability of the catalyst, which displays great improvement in electrocataylsts active surface area(ECSA)preservation, with 76% of the initial ECSA after 10000 ADT cycles, far more higher than the traditional Pt/C (JM). The experimental data indicates that the CNTs@TiCoN hybrid support combines the merits of the CNTs’s high conductivity and the superb corrosion resistance of external TiCoN coating.