Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, st...Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy-dispersive spectrometer （EDS）, respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃ is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm^2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V （vs SCE）.展开更多
Fuel cell using borohydride as the fuel has received much attention. AB5-type hydrogen storage alloy used as the anodic material instead of noble metals has been investigated. In order to restrain the generation of hy...Fuel cell using borohydride as the fuel has received much attention. AB5-type hydrogen storage alloy used as the anodic material instead of noble metals has been investigated. In order to restrain the generation of hydrogen and enhance the utilization of borohydride, Ti/Zr metal powders has been added into the parent LmNi4.78Mn0.22 （where Lm is La-richened mischmetal） alloy （LNM） by ball milling and heat treatment methods. It is found that the addition of Ti/Zr metal powders lowers the electrochemical catalytic activity of the electrodes, at the same time, restrains the generation of hydrogen and enhances the utilization of the fuel. All the results show that the hydrogen generation rate or the utilization of the fuel is directly relative to the electrochemical catalytic activity or the discharge capability of the electrodes. The utilization of the fuel increases with discharge current density. It is very important to find a balance between the discharge capability and the utilization of the fuel.展开更多
We reported a novel protocol to efficiently synthesize tungsten carbide （WC） nanomaterials with pure crystal structure and certain specific morphology. The key step in this protocol is the preparation of the catalys...We reported a novel protocol to efficiently synthesize tungsten carbide （WC） nanomaterials with pure crystal structure and certain specific morphology. The key step in this protocol is the preparation of the catalyst precursor W18049 with surface oxygen vacancies. The existence of large quantities of oxygen vacancies gives plenty channels for diffusion and keeps the specific morphology of WC in the carbonization process. Efforts to build WC blocks with well-defined geometrical shapes （e.g., rods, wires, spheres and flakes） have further expanded its possibility to be the support for methanol electrooxidation catalyst. The platinum supported on pure phase WC materials served as an effective CO tolerant electrocatalyst for methanol oxidation. Electrochemical experiments indicated that the improved catalytic activity was related to the special morphologies of WC supports. Its sea urchin like feature leads to substantial interfaces between WC and Pt by preparing more anchor points for Pt loading and also the barriers for the subsequent crystal growth, which enhances the synergistic effect between WC and Pt.展开更多
基金This work was supported by the National Natural Scmnce Foundation of China(Grant Nos.20276069,20476097)
文摘Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy-dispersive spectrometer （EDS）, respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃ is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm^2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V （vs SCE）.
文摘Fuel cell using borohydride as the fuel has received much attention. AB5-type hydrogen storage alloy used as the anodic material instead of noble metals has been investigated. In order to restrain the generation of hydrogen and enhance the utilization of borohydride, Ti/Zr metal powders has been added into the parent LmNi4.78Mn0.22 （where Lm is La-richened mischmetal） alloy （LNM） by ball milling and heat treatment methods. It is found that the addition of Ti/Zr metal powders lowers the electrochemical catalytic activity of the electrodes, at the same time, restrains the generation of hydrogen and enhances the utilization of the fuel. All the results show that the hydrogen generation rate or the utilization of the fuel is directly relative to the electrochemical catalytic activity or the discharge capability of the electrodes. The utilization of the fuel increases with discharge current density. It is very important to find a balance between the discharge capability and the utilization of the fuel.
文摘We reported a novel protocol to efficiently synthesize tungsten carbide （WC） nanomaterials with pure crystal structure and certain specific morphology. The key step in this protocol is the preparation of the catalyst precursor W18049 with surface oxygen vacancies. The existence of large quantities of oxygen vacancies gives plenty channels for diffusion and keeps the specific morphology of WC in the carbonization process. Efforts to build WC blocks with well-defined geometrical shapes （e.g., rods, wires, spheres and flakes） have further expanded its possibility to be the support for methanol electrooxidation catalyst. The platinum supported on pure phase WC materials served as an effective CO tolerant electrocatalyst for methanol oxidation. Electrochemical experiments indicated that the improved catalytic activity was related to the special morphologies of WC supports. Its sea urchin like feature leads to substantial interfaces between WC and Pt by preparing more anchor points for Pt loading and also the barriers for the subsequent crystal growth, which enhances the synergistic effect between WC and Pt.
