Core-shell hierarchical tungsten carbide composite microspheres towards methanol electrooxidation
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摘要: 以偏钨酸铵微球为前驱体，在不同反应时间和CO/CO2气氛条件下，通过原位还原碳化反应制备了具有核壳结构碳化钨复合微球。采用X射线粉末衍射（XRD）、X射线光电子能谱（XPS）和扫描电镜（SEM）等对催化剂的形貌和结构进行了表征分析。硼氢化钠还原法将平均粒径为4.6 nm的Pt纳米粒子均匀分布在其表面，得到核壳结构碳化钨复合催化剂。采用循环伏安和计时电流法研究了在酸性溶液中催化剂对甲醇的电催化氧化性能。结果表明，与Pt/WC-15 h和JM Pt/C催化剂的电化学性能相比，Pt/WC-6 h催化剂对甲醇呈现出更高的电催化氧化活性和稳定性。碳化钨复合微球表面少量WO2成分的存在有利于甲醇在其表面的电催化氧化过程的发生。Abstract: Tungsten carbides microspheresare synthesized by in situ reduction of ammonium met tungstate microspheres (AMT) precursors as a function of reaction time under CO/CO2 mixture atmosphere. The morphology, size and composition of the as-prepared tungsten carbide microspheres are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Pt nanoparticles with a diameter of 4.6 nm are loaded onto the surface of WC microspheres using a conventional sodium borohydride reduction method. The electro-catalytic activity and stability toward methanol electrooxidation (MOR) are investigated using cyclic voltammetry (CV) and chronoamperometry(CA). The resultant Pt/WCO-6 h catalyst exhibits low onset potential and excellent catalytic performances in comparison to the commercial JM Pt/C and Pt/WC-15 h catalysts. Further investigation shows that besides the synergistic effect between WC and Pt, the existence of WO2 might also play an important role in improving the electro-catalytic activity, indicating the positive effect of the surface oxide on the activity and stability of Pt/WC catalysts towards MOR.
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Figure 3 XPS spectrum of Pt/WCO-6 h and Pt/WC-15 h, showing the peaks for the (a) C 1s and (b) W 4f elements
Figure 5 (a), (b) Typical TEM images of the as-prepared Pt/WCO-6 h with different magnifications; (c) EDS of Pt/WCO-6 h catalyst
Figure 6 Cyclic voltammetric curves of Pt/WCO-6 h, Pt/WC-15 h and JM Pt/C catalysts in (a) 0.5 mol/L H2SO4 and (b) 0.5 mol/L H2SO4 + 1.0 mol/L CH3OH solution at the scan rate of 50 mV/s
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