Youqun Chu

Highly active Pd/WO3-CNTs catalysts for formic acid electrooxidation and study of the kinetics

AbstractThe new Pd/WO3-CNTs catalysts are prepared for formic acid electrooxidation in direct formic acid fuel cells (DFAFCs). According to XRD, TEM, and HRTEM results, WO3 particles are covered or overlapped with Pd particles, which have a uniform and narrow size distribution due to the highly dispersion of WO3-CNTs. The electrochemical results show significantly enhanced electrocatalytic performances for formic acid oxidation on Pd/WO3-CNTs catalysts, especially its dramatically improved stability and excellent tolerance to CO poisoning, which is mainly ascribed to the interaction between Pd and WO3. Therefore, Pd/WO3-CNTs catalysts show the great potential as less expensive and more efficient electrocatalyst for DFAFCs. Additionally, the kinetic parameters such as the charge transfer parameter and the diffusion coefficient of formic acid electrooxidation on 20 %Pd/20 %WO3-CNTs were obtained. The new Pd/WO3-CNTs catalysts are prepared and studied in the oxidation of formic acid, and the significantly enhanced electrocatalytic performances, especially its dramatically improved stability and excellent tolerance to CO poisoning show great potential as less expensive and more efficient electrocatalyst for the direct formic acid fuel cells.

Methanol electro-oxidation on platinum modified tungsten carbides in direct methanol fuel cells: a DFT study

In exploration of low-cost electrocatalysts for direct methanol fuel cells (DMFCs), Pt modified tungsten carbide (WC) materials are found to be great potential candidates for decreasing Pt usage whilst exhibiting satisfactory reactivity. In this work, the mechanisms, onset potentials and activity for electrooxidation of methanol were studied on a series of Pt-modified WC catalysts where the bare W-terminated WC(0001) substrate was employed. In the surface energy calculations of a series of Pt-modified WC models, we found that the feasible structures are mono- and bi-layer Pt-modified WCs. The tri-layer Pt-modified WC model is not thermodynamically stable where the top layer Pt atoms tend to accumulate and form particles or clusters rather than being dispersed as a layer. We further calculated the mechanisms of methanol oxidation on the feasible models via methanol dehydrogenation to CO involving C-H and O-H bonds dissociating subsequently, and further CO oxidation with the C-O bond association. The onset potentials for the oxidation reactions over the Pt-modified WC catalysts were determined thermodynamically by water dissociation to surface OH* species. The activities of these Pt-modified WC catalysts were estimated from the calculated kinetic data. It has been found that the bi-layer Pt-modified WC catalysts may provide a good reactivity and an onset oxidation potential comparable to pure Pt and serve as promising electrocatalysts for DMFCs with a significant decrease in Pt usage.

Tungsten carbide-reduced graphene oxide intercalation compound as co-catalyst for methanol oxidation

Abstract Highly dispersed tungsten carbide (WC) nanoparticles (NPs) sandwiched between few-layer reduced graphene oxide (RGO) have been successfully synthesized by using thiourea as an anchoring and inducing reagent. The metatungstate ion, [H 2 W 12 O 40 ] 6− , is assembled on thiourea-modified graphene oxide (GO) by an impregnation method. The WC NPs, with a mean diameter of 1.5 nm, are obtained through a process whereby ammonium metatungstate first turns to WS 2 , which then forms an intercalation compound with RGO before growing, in situ, to WC NPs. The Pt/WC-RGO electrocatalysts are fabricated by a microwave-assisted method. The intimate contacts between Pt, WC, and RGO are confirmed by X-ray diffraction, scanning electron microscope, transmission electron microscope, and Raman spectroscopy. For methanol oxidation, the Pt/WC-RGO electrocatalyst exhibited an electrochemical surface area value of 246.1 m 2 /g Pt and a peak current density of 1364.7 mA/mg Pt, which are, respectively, 3.66 and 4.77 times greater than those of commercial Pt/C electrocatalyst (67.2 m 2 /g Pt, 286.0 mA/mg Pt). The excellent CO-poisoning resistance and long-term stability of the electrocatalyst are also evidenced by CO stripping, chronoamperometry, and accelerated durability testing. Because Pt/WC-RGO has higher catalytic activity compared with that of commercial Pt/C, as a result of its intercalated structure and synergistic effect, less Pt will be required for the same performance, which in turn will reduce the cost of the fuel cell. The present method is facile, efficient, and scalable for mass production of the nanomaterials.

Dodecahedral W@WC Composite as Efficient Catalyst for Hydrogen Evolution and Nitrobenzene Reduction Reactions

Core-shell composites with strong phase-phase contact could provide an incentive for catalytic activity. A simple, yet efficient, H2O-mediated method has been developed to synthesize a mesoscopic core-shell W@WC architecture with a dodecahedral microstructure, via a one-pot reaction. The H2O plays an important role in the resistance of carbon diffusion, resulting in the formation of the W core and W-terminated WC shell. Density functional theory (DFT) calculations reveal that adding W as core reduced the oxygen adsorption energy and provided the W-terminated WC surface. The W@WC exhibits significant electrocatalytic activities toward hydrogen evolution and nitrobenzene electroreduction reactions, which are comparable to those found for commercial Pt/C, and substantially higher than those found for meso- and nano-WC materials. The experimental results were explained by DFT calculations based on the energy profiles in the hydrogen evolution reactions over WC, W@WC, and Pt model surfaces. The W@WC also shows a high thermal stability and thus may serve as a promising more economical alternative to Pt catalysts in these important energy conversion and environmental protection applications. The current approach can also be extended or adapted to various metals and carbides, allowing for the design and fabrication of a wide range of catalytic and other multifunctional composites.

Preparation of the WO 3 /TiO 2 using microwave-heating in ionic liquid and its application in electrocatalysis

A high dispersed WO₃/TiO₂ particles were prepared by using a microwave heating assisted ionic liquid method. The phase structure and morphology of WO₃/TiO₂ particles were characterized by X-ray diffraction and scanning electron microscopy. The result shows that fluffy WO₃ balls were assembled on TiO₂ and the surface structure of WO₃/TiO₂ particle was comprised of numbers of shuttle-like nanoneedles. The different WO₃/TiO₂ particles were obtained by simply changing the concentration of the ionic liquid. Then PtWO₃/TiO₂ catalysts were prepared and its electro-catalytic performances were evaluated by cyclic voltammetry and the CO stripping test. The results revealed that PtWO₃/TiO₂-1.5 catalyst had the better performance for methanol oxidation and CO tolerance which proved that the ionic liquid in this reaction system provided the multiple functions for preparing a promising catalyst for methanol oxidation.