Preparation And Electro-Generation Of H₂O₂ Based On The Modified Graphite/PTFE Composite Electrode With Exterior Hydrophobic Film

Hydrogen peroxide?H₂O₂?is known as a versatile environmentally friendly oxidizing agent and often used either alone or combined with other agents(Fe²⁺and O₃)or UV light for the organic/inorganic bearing wastewater purification.Currently,electrochemical 2-electrons oxygen reduction process?ORR?at the cathode has been regarded as the effective strategy for in situ H₂O₂ generation in wastewater treatment.Normally,carbon black is utilized as the catalyst for electro-generation of H₂O₂.However,its large-scale application is still limited by the relatively high cost of the carbon materials and short-term stability.In comparison with carbon black,graphite owns many advantages,such as high conductivity,commercially available and lower price,which makes it a promising and cost-effective catalyst in the large-scale preparation of gas diffusion cathode for H₂O₂ production.However,the activity of graphite toward H₂O₂ generation was not so appreciable for industrial application.Thus,in order to obtain enough concentration of H₂O₂ for wastewater treatment in short bursts,the electrocatalytic activity of graphite toward H₂O₂ generation should be improved.In view of this,this study fabricated a nitric acid modified graphite/polytetrafluoroethylene?PTFE?composite cathode with exterior hydrophobic film.To clarify the underlying modification mechanism for the graphite/PTFE composite cathode,its surface physicochemical properties and the electrocatalytic activity toward ORR were characterized by contact angle,X-ray photoelectron spectroscopy?XPS?,Raman spectra,and cyclic voltammetry,respectively.As a result,2 mol L^-11 HNO₃ modification rendered the introduction of much more defect sites and oxygen/nitrogen-containing groups on graphite,which caused that H₂O₂electrogeneration was 3.0 times as much as that of virgin graphite counterpart at 3 mA cm^-2.Moreover,the additional introduction of exterior hydrophobic film on the as-prepared graphite/PTFE cathode did not only further promote H₂O₂ electrogeneration,but also endowed the cathode with strong hydrophobic stability.As for the modified cathode with exterior hydrophobic film,the influence of mass graphite/PTFE binder ratio?1:1-4:1?and pH?3.0-9.0?on H₂O₂ generation was slight,but the current density(3.0-15 mA cm^-2)had evident effect on H₂O₂ generation.Besides,we prepared a graphite/PTFE composite cathode with exterior hydrophobic film using H₂ modified graphite as electrocatalyst.To clarify the underlying modification mechanism for the graphite/PTFE composite cathode,its surface physicochemical properties and the electrocatalytic activity toward ORR were characterized by Raman spectra,Scanning electron microscope?SEM?and cyclic voltammetry,respectively.Experimental results show that the surface of graphite was introduced more defect sites,and the peak electric potential and current response of graphite modified by H₂ heat treatment were higher than those of virgin graphite.The optimal operating conditions are as follows:the heat treatment temperature of 750^oC,the solution pH of 3 and the mass graphite/PTFE binder ratio of 2:1.Under the optimal conditions,approximately 410 mg L^-1 of H₂O₂ was produced with a current efficiency of 66%for H₂ heat-treated graphite/PTFE composite cathode with an exterior hydrophobic film at current density of 15 mA cm^-2 after 120 min electrolysis.Especially,the production of H₂ only decreased to 330 mg L^-1 after 20 cycles at current density of15 mA cm^-2,which indicated that the composite cathode with exterior hydrophobic film had high stability during a long-term process.Generally,this study developed simple and feasible modification methods to convert low-cost graphite to high-efficiency electrocatalysts for H₂O₂ production.More importantly,the introduction of an exterior hydrophobic film on as-prepared cathode can elevate the hydrophobic stability of the composite cathode and further improve its stability for H₂O₂ electrogeneration.Therefore,this study provided theoretical guidance for improving the electrogeneration of H₂O₂,and provided technical guidance for preparing the gas diffusion cathode for the large-scale electrogeneration of H₂O₂ in industry.