Preparation Of Carbon-based Materials And Their Electrocatalytic Oxygen Reduction To Produce Hydrogen Peroxide Application

Hydrogen peroxide(H₂O₂)is an environmentally friendly oxidant,which has been widely used in bleaching,chemical synthesis,water disinfection and other fields.At present,the method of large-scale production of hydrogen peroxide in industry is anthraquinone process.However,the anthraquinone method is tedious,requires large-scale equipment,high energy consumption,and will produce a lot of waste in the production process.In addition,the instability of hydrogen peroxide brings safety problems to storage and long-distance transportation.Moreover,the H₂O₂ can be directly synthesized from the hydrogen and oxygen in the presence of catalysts.However,the production selectivity and production rate of H₂O₂are low,and the safety problems related to the explosion of H₂ and O₂ further hinder their practical application.Therefore,a green,efficient and low-cost hydrogen peroxide production method needs to be developed urgently.The electrosynthesis strategy provides an attractive way for on-site production of hydrogen peroxide and can effectively solve the problems existing in anthraquinone method and direct synthesis method.The production of H₂O₂ by oxygen reduction,as a strategy of electrosynthesis of hydrogen peroxide,has been widely concerned by people,and a large number of catalysts have been developed and reported.At present,most of the catalysts for efficient oxygen reduction to produce hydrogen peroxide are precious metal catalysts,and the earth's reserves are low and expensive.Compared to noble metal-based catalysts,carbon-based materials are inexpensive and earth abundant,and have unique surface and structural properties that can be finely tuned.Thus,carbon-based materials are thought to be interesting alternative to precious metals for H₂O₂ electrochemical synthesis.In this thesis,we studied the surface treated carbon-based materials toward electrosynthesis of H₂O₂ through oxygen reduction reaction.The main contents are as follows:1.Carbon nanotubes were treated by the mixture of concentrated nitric acid and sodium chlorate at room temperature.The obtained functionalized carbon nanotubes(O-CNTs-X)were characterized by transmission electron microscopy(TEM),X-ray diffractometer(XRD),X-ray photoelectron spectroscopy(XPS)and Raman spectroscopy,and their electrochemical properties were tested.The structural characterizations show that O-CNTS-X maintained the original tubular structure and contained abundant oxygen-containing functional groups on their surface.The electrochemical tests show that O-CNTS-X have good electrocatalytic activity for oxygen reduction.The H₂O₂ selectivity of the optimal catalyst O-CNTs-7 in alkaline electrolyte is up to 90%and has excellent electrochemical stability.In addition,the H₂O₂ yield of 191 m M g^-1 h^-1 was obtained under 0.4 V RHE,showing excellent activity,selectivity and stability.However,concentrated nitric acid will produce nitrogen dioxide in the oxidation process to pollute the environment,so it is necessary to explore other green oxidation methods.2.In view of the shortcomings of concentrated nitric acid-sodium chlorate oxidation,we use the sulfate radical(SO₄^-·)produced by thermally activated sodium persulfate to oxidize carbon nanotubes to prepare functionalized carbon nanotubes(O-CNTs-x,x represents oxidation time).Among them,O-CNTs-6 has the best electrocatalytic performance,in alkaline electrolyte(0.1 M KOH),the initial potential(E_onset potential)is 0.79 V RHE,and the selectivity for H₂O₂ is as high as 92%in a wide potential window(0.2-0.7 V RHE).In addition,high H₂O₂yield of 296.84 m M g^-1 h^-1 was obtained under 0.4 V RHE.Compared with the original carbon nanotubes,the improvement of catalytic activity is mainly due to the newly formed defects and oxygen-containing functional groups on the surface of O-CNTs-x.In addition,the oxidation process is also effective to improve the ORR activity and H₂O₂ selectivity of carbon black(CB).Therefore,the above two methods provide an effective reference for the synthesis of 2e^-ORR carbon catalyst.