Two-electron Oxygen Reduction Of Air-breathing Cathode And Application

Hydrogen peroxide（H₂O₂）is a versatile,eco-friendly,strong oxidizing chemical with numerous industrial applications.The traditional methods of H₂O₂ synthesis,such as anthraquinone oxidation process,are complicated with high energy consumption.Besides,the transportation,storage and treatment of H₂O₂ have potential risks and additional costs.Electrochemical synthesis of H₂O₂ is a potential alternative for in-situ synthesis.The core mechanism of electrocatalytic synthesis of H₂O₂ for carbon-based materials is two-electron oxidation reduction reaction（ORR）,therefore,promoting ORR is the key for H₂O₂ production.An ideal balance of hydrophilicity and hydrophobicity can result in a steady three-phase interfaces（TPIs）among the electrolyte solution,O₂ and catalytic sites in the catalyst layer（CL）for the sustainable electro-generation of H₂O₂.In this work,we tuned catalyst mesostructure and hydrophilicity/hydrophobicity by adjusting polytetrafluoroethylene（PTFE）content in graphite-carbon black-PTFE hybrid CL,aimed to improving the two-electron ORR activity for efficient H₂O₂generation.In addition,we investigated the influence mechanisms of calcination on the activity of two-electron ORR,by the means of calcining CL with different time to change the structure.Further,by coupling bioelectrochemical system with advanced oxidation processes,a novel BES/AOPs system for heterotopic formaldehyde（CH₂O）biodegradation through UV/H₂O₂ with in situ H₂O₂ production was established,and the system parameters were optimized to improve the removal performance of CH₂O.It is found that the superhydrophobic air-breathing cathode PTFE_0.57 obtained the highest H₂O₂ yield of 3005±58 mg L^-1 h^-1(at 25 m A cm^-2)and highest current efficiency（CE）of 84%(at 20 m A cm^-2)in the electrochemical system.Higher PTFE content increased the hydrophilicity of CL for excessive H⁺and insufficient O₂ diffusion,which induced H₂O₂ decomposition into H₂O and decreased H₂O₂ yields and CE.In addition,the calcination of CL led to lower content of oxygen-containing functional groups such as C–O and C=O as well as higher F element,which decreased two-electron ORR activity.Besides,longer calcination time,lower H₂O₂ yields and CE.It can be attributed to C–O and C=O were easier to absorb O₂,which were active sites for two-electron ORR.And higher F content created more defects,lower graphitization further decreases of electrode conductivity and reaction kinetics,consequently the two-electron ORR activity for H₂O₂ production decreased.In the coupling BES/AOPs system,H₂O₂ was in situ biosynthesized in the precursory BESs through electron transferred from electrochemically active bacteria and applied in the following UV/H₂O₂ AOPs for efficient·OH generation and CH₂O biodegradation.Compared with in-situ biodegradation technologies,heterotopic CH₂O biodegradation can avoid biotoxicity of CH₂O to microbes efficiently.Furthermore,heterotopic biodegradation of CH₂O was more efficient and faster than in-situ biodegradation,as confirmed by 69%–308%higher removal efficiency and 98% shorter degradation time.