| In recent years, oxygen reduction reaction (ORR) has been widely applied in the fields of energy conversion and storage, sensors and environmetal chemistry, which makes the activation mechanism of the oxygen molecule and its electrochemical behavior become an important research area. To accelerate the reaction rate and current efficiency, various catalysts and modified electrodes have been used in electrocatalytic ORR. Among them, anthraquinones (AQ) and their derivatives have been widely studied because of the electrocatalytic two-electron reduction of ORR on these modified electrodes. Generally, quinonoid compounds which are grafted as spontaneously adsorbed or chemically bound monolayer on the electrode surface, tend to desorb from the surface during the long-term operation, leading to a loss of electrocatalytic ability and stability of the working electrode. By contrast, chemically bound quinonoid compounds possess more stability. On the other hand, graphene, after been found, has been used in various fields, such as energy conversion and storage, high-performance nano-electronic devices, nanocomposite materials, and so on. In elecroctrochemistry, graphene with excellent thermodynamics and electrisity not only can be used as electrocatalysts, but also acts as support material to accelerate electrochemical reaction rate. Hetergeneous electro-Fenton process has been widely applied in treatment of organic wastewater. This novel advanced oxidation process not only overcomes the drawbacks of homogeneous electro-Fenton system, e.g. a limited pH range, production of iron-containing waste sludge and catalysts deactivation, but also makes it possible for catalysts to separate, recover, regenerate and recycle. For the process of ammonia electro-oxidation, it can degrade ammonia with harmless production of N2, simnltaneously, it can produce hydrogen as energy. But the electrocatalysts are commonly precious metals, such as Pt and Ir. Taking above into account, the following three aspects have been investigated to further promote electroactivity and stability of AQs modified electrodes towards ORR, overcome the drawbacks of homogenerous electro-Fenton system and develop the metal-free catalysts with high electroactivity for electro-oxidation of ammonia.Firstly, the functionalized graphene with anthraquinone (AQ) nanocomposite film electrode (AQ/ER-GO) was synthesized via two-step electroreductive method. The nanocomposite film was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra, Fourier transform infrared spectroscopy (FT-IR) and x-ray photoelectron spectroscopy analysis (XPS). The electrocatalytic reduction of oxygen on AQ/ER-GO nanocomposite film was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and rotating disk electrode/rotating ring disk electrode (RDE/RRDE). The results show that electrochemical reduction can effectively reduce graphene oxide to graphene and graft AQ to surface of graphene. AQ/ER-GO/GC electrode presents better electrochemical activity and catalysis ability. It presents the highest electrocatalysis to ORR in pH range of5-7. In the solution of neutral and alkaline, the composite film electrode can show in high efficiency catalysis oxygen reduction reaction of two electrons.Secondly, the heterogeneous electro-Fenton system had been constructed using AQ/ER-GO composite membrane as working electrode, FeOOH/Al2O3as catalyst to degrade dye Rhodamine B (RhB). And the stability of catalyst, effect and mechanism of degradation of RhB had been investigated. The results show that the stability of large-area AQ/ER-GO modified electrode is not good choice in practical application and the degradation effect is not obvious. However, the heterogeneous electro-Fenton system can degrade RhB effectively by adding H2O2. The system operation optimum conditions are:cathode potential is-0.5V/SCE, pH=5, dosage of catalyst is40gram (200g/L), concentration of pollution is5mg/mL, dosage of H2O2is5mL (200mL solution). After5times recycling opration, the FeOOH/Al2O3catalyst still presents high catalysis activity. The AQ/ER-GO nanocomposite modified electrode facilitates Fe3+/Fe2+transformation and produces a beneficial enhancement of the heterogeneous/homogeneous electro-Fenton reaction rates.Finally, the electrocatalytic ability of AQ/ER-GO nanocomposite towards ammonia oxidation was also investigated. It was found that the modified electrode has a positive effect on ammonia oxidation at1.1V. But the stability of the modified electrode should be improved to solve the overoxidation caused by too positive potential during reaction. |
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