Search

Polyoxometalate encapsulated by metal–organic framework (POM@MOF) hybrid is an ideal precursor for electrocatalysts because it provides a homogeneous catalyst system with a flexible synergistic effect. However, controlling its fine structures to activate the derived catalyst after pyrolysis remains a challenge. The uniformly distributed carbon-defect tungsten oxides on the 3D carbon matrix were synthesized by using phospho-tungstic acid confined in HKUST-1 (PA@HKUST-1) as the precursor. By choosing ethanol as the solvent, the framework of PA@HKUST-1 was retained integrally and each pore of HKUST-1 kept intact even with holding the PA molecule inside. The well-organized structure of PA@HKUST-1 facilitated to offer a highly distributed metal source, and further transform into defect-rich catalyst. The average size of the resulting WOxCy/C catalysts was 1.5 nm, which was similar to a single molecule of PA. The WOxCy/C catalysts exhibited superior activity in the methanol oxidation reaction after being platinized due to the enhanced resistance to CO poisoning, which is also confirmed by DFT. This finding suggests a new route to design and achieve the defect-rich catalyst with controllable size.

The continuous solid solution NiWOxis successfully prepared by using precursor W18O49with plenty of oxygen defects. The NiWOxnanoparticles 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 NiWOxis stable and characterized by the same feature of the parent lattice W18O49even with various concentrations of dopant Ni which indicates the existence of oxygen defects. The NiWOxnanoparticles could be processed as the appropriate promoter after loading 10 wt % Pt. The Pt/NiWOxdisplays 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 NiWOxis 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.

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, [H2W12O40]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 WS2, 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 m2/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 m2/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.

Nano-WO3 modified carbon nanotubes (CNTs), which are prepared by adsorption and decomposition of ammonium metatungstate (AMT) on the surface of CNTs, can act as efficient supports for the Pt electrocatalysis of oxygen reduction reaction (ORR) in acid electrolyte. According to XRD, TEM and HRTEM results, Pt particles are deposited homogeneously on the surface of CNTs with the average size of 2.2 nm. The Pt/WO3-CNTs catalysts exhibit better catalytic activity with higher current densities and lower overpotential comparing to the Pt/CNTs catalyst. The enhancement of ORR activity on Pt/WO3-CNTs electrocatalyst is probably due to the synergistic effect between Pt and WO3 nanoparticles. Specifically, the interaction between Pt and WO3 can increase the dispersion of Pt nanoparticles and decrease the adsorption strength of oxygenated species. In addition, a bronze route mechanism is considered to promote ORR. Moreover, the rotating disk electrode measurements suggest that a 4-electron reduction process takes place on the catalyst surface. Nano-WO3-modified CNTs supported Pt electrocatalysts with low cost and unique activity for ORR, are favorable for potential applications in the cathode of fuel cells.

Nano-WO3modified carbon nanotubes (CNTs), which are prepared by adsorption and decomposition of ammonium metatungstate (AMT) on the surface of CNTs, can act as efficient supports for the Pt electrocatalysis of oxygen reduction reaction (ORR) in acid electrolyte. According to XRD, TEM and HRTEM results, Pt particles are deposited homogeneously on the surface of CNTs with the average size of 2.2 nm. The Pt/WO3-CNTs catalysts exhibit better catalytic activity with higher current densities and lower overpotential comparing to the Pt/CNTs catalyst. The enhancement of ORR activity on Pt/WO3-CNTs electrocatalyst is probably due to the synergistic effect between Pt and WO3nanoparticles. Specifically, the interaction between Pt and WO3can increase the dispersion of Pt nanoparticles and decrease the adsorption strength of oxygenated species. In addition, a bronze route mechanism is considered to promote ORR. Moreover, the rotating disk electrode measurements suggest that a 4-electron reduction process takes place on the catalyst surface. Nano-WO3-modified CNTs supported Pt electrocatalysts with low cost and unique activity for ORR, are favorable for potential applications in the cathode of fuel cells.