Meiqin Shi

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.

Tungsten carbide/porous carbon core–shell nanocomposites as a catalyst support for methanol oxidation

Carbon-encapsulated tungsten carbide (WC@C) was prepared by a microwave-assisted synthesis method with resorcinol-formaldehyde resin (RF) as carbon source. WC was encapsulated by porous carbon layer to form core–shell structure which could protect tungsten oxide from occupying the active sites on the surfaces of the WC@C. The characteristics of WC@C composites were determined by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and Brunauer–Emmet–Teller gas adsorption. Platinum nanoparticles were uniformly distributed on WC@C to synthesize a new electrocatalyst Pt–WC@C. The electro-catalytic performances of prepared Pt–WC@C, commercial Pt/C and PtRu/C toward methanol oxidation were compared by cyclic voltammetry, chronoamperometry and CO stripping test. It was found that Pt–WC@C exhibited higher catalytic activity for methanol oxidation than that of commercial Pt/C and PtRu/C catalysts. Especially, the Pt–WC@C achieved the long-term stability which was attributed to the effective protection by the carbon porous shell structure.

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.

Microwave-Assisted Synthesis of Mesoporous Tungsten Carbide/Carbon for Fuel Cell Applications

Different template routes were applied for the fabrication of two types of mesoporous tungsten carbide/carbon (WC/C) assisted with a microwave heating method. One was WC/C–F using triblock copolymer Pluronic F127 (PEO106PPO70PEO106) as soft template and the other was WC/C–S using mesoporous silica SBA-15 as hard template. In our study, sucrose was used as the carbon source for both tungsten carbide and carrier carbon. With loading small amount of Pt, two catalysts (Pt–WC/C–F and Pt–WC/C–S) exhibit better performance than the commercial Pt/C for methanol oxidation. Meanwhile the Pt–WC/C–F catalyst presents higher activity and stability than does the Pt–WC/C–S which is ascribed to the appropriate pore size adjusted by the different template routes.Graphical Abstract

Enhanced Electrocatalytic Oxygen Reduction on NiWOx Solid Solution with Induced Oxygen Defects

The continuous solid solution NiWOx is successfully prepared by using precursor W18O49 with plenty of oxygen defects. The NiWOx nanoparticles are characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray absorption spectroscopy. The crystallographic phase of NiWOx is stable and characterized by the same feature of the parent lattice W18O49 even with various concentrations of dopant Ni which indicates the existence of oxygen defects. The NiWOx nanoparticles could be processed as the appropriate promoter after loading 10 wt % Pt. The Pt/NiWOx displays remarkable response for oxygen reduction reaction in alkaline medium compared with the commercial Pt/C. The analysis of the electrochemistry data shows that the existence of abundant oxygen defects in the solid solution NiWOx is the key factor for the improved ORR catalyst performance. Ni is effective in the catalysts because of its compatibility with W in the solid solution and its active participation in oxygen reduction reaction.

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.