MnO2@graphene复合材料的制备及其对微生物燃料电池阴极氧还原反应的催化活性

摘要

MnO2@graphene composites were prepared by a chemical co-precipitation method using KMnO4, MnC2O4·2H2O and graphene as raw materials.The microstructure, morphology of the prepared composites were analyzed using X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrum, Raman spectroscopy, X-ray photoelectron spectroscopy(XPS), scanning electron microscopy (SEM) and specific area measurements. The electrochemical performances of MnO2@graphene composites as catalysts for cathodic oxygen reduction reaction in microbial fuel cell were analyzed using cyclic voltammetry, electrochemical impedance spectrometry (EIS). The results show that spherical MnO2 with uniform particle size of 400 nm is tightly formed on the surface of paper-like graphene by electrostatic interaction. Moreover, the peak potential of MnO2@graphene electrode (−0.440 V) is very close to that for Pt/C electrode (−0.434 V), though the initial peak potential of MnO2@graphene electrode is 0.048 V negative than that for Pt/C electrode. With the increase of cycling times, the initial peak potential of MnO2@graphene electrode decreases, while there is only a small decline for the peak current density of MnO2@graphene electrode, indicating that the MnO2@graphene composites have better catalytic activity and cycling stability for cathodic oxygen reduction reaction in microbial fuel cell than that for Pt/C catalysts. EIS results show that the electron-transfer resistance of MnO2@graphene is only 12.6 Ω, which is smaller than that for Pt/C catalysts and MnO2 catalysts, suggesting MnO2@graphene catalysts promote the cathodic oxygen reduction reaction by decareasing the electron-transfer resistance and accelerating the charge transfer due the introduction of the excellent conductive graphene.%以高锰酸钾、草酸锰、石墨烯为原料，采用化学共沉淀法制备MnO2@graphene 复合材料，用X射线衍射、红外光谱、拉曼光谱、扫描电镜、比表面测定等对其进行表征。以MnO2@graphene为MFC阴极氧还原反应催化剂，采用循环伏安法和电化学阻抗法研究MnO2@graphene催化电极对氧还原反应的催化活性。结果表明：粒度为400 nm 左右的 MnO2颗粒通过静电相互作用均匀而牢固地分散在纸片状 graphene 表面，形成MnO2@graphene复合材料。循环伏安测试结果表明：当扫描速率为5 mV/s时，虽然MnO2@graphene催化电极在pH为7.0的磷酸盐缓冲体系(PBS)的氧还原反应起峰电位比Pt/C催化电极负0.048V，但其峰电位(−0.440 V)与Pt/C催化电极的起峰电位(−0.434 V)接近。随着循环次数的增加，MnO2@graphene催化电极的起峰电位稍有下降，但峰电流密度下降很小，表明MnO2@graphene催化剂具有更好的氧还原催化活性和更优秀的循环稳定性。电化学阻抗实验发现：MnO2@graphene催化电极的电荷转移阻抗为12.6Ω，比同条件下Pt/C催化电极和MnO2催化电极的低，表明由于graphene增加MnO2的导电性，降低催化电极电荷转移阻抗，加快电子的转移速率，促进阴极氧还原反应。