H₂O₂ Electrocatalytic Synthesis And The Enhancement Of Generation And Utilization Efficiency Of ·OH

Pollutants control technologies and high-efficiency utilization technologies for heavy carbon call for green and efficient oxidation technology.Hydrogen peroxide?H₂O₂?,an environmentally-friendly oxidant,could decompose into highly oxidative hydroxyl radicals?·OH?and thus be an important choice for these two technologies.H₂O₂ is conventionally produced by the anthraquinone process which is energy-intensive and polluted.Moreover,the concentrated H₂O₂ is also difficult to transport.Electrochemical methods for H₂O₂ production,has characteristics such as green and on-site,have received wide attention recently.However,the low efficiency makes the scaling-up still a challenge.The efficient catalytic decomposition of H₂O₂ to highly oxidative·OH and the enhancement methods of the reaction between·OH and target chemicals is another important question in H₂O₂-based oxidation systems.H₂O₂ generation via O₂ electroreduction is the most promising technology for H₂O₂ electrochemical production,where the low efficiency hinders its real application.This work explores the efficiency improvement methods from multi-scale of“reaction-transportation-flow”.?1?To enhance the O₂ electroreduction and H₂O₂ generation from the scale of reaction,this work investigated H₂O₂ electrogeneration by activated carbon-based cathode,H₂O₂electrogeneration and enhancement by graphitic carbon;?2?To enhance the diffusion of O₂ and H₂O₂ from the scale of species transportation,this work studied H₂O₂ electrogeneration enhanced by the control of diffusion process of O₂ and H₂O₂;?3?To achieve the continuous H₂O₂ production from the scale of flow conditions regulation,this work developed the flow-through reactor for continuous H₂O₂production.Moreover,aimed at improving the efficiency of·OH,this work studied the enhanced regeneration of Fe²⁺ to improve the ·OH production,and the control of ·OH by adjusting the addition methods of reactants.Conventional cathode materials are expensive and the fabrication are relatively complex.To solve this obstacle,this work proposed an activated carbon/stainless steel mesh?ACSS?hybrid electrode,which achieved simultaneous H₂O₂ generation,H₂O₂ activation,and organic pollutants adsorption.Results of characterization,H₂O₂generation and activation show that both electrolyte pH and current influence the H₂O₂ production.The initial concentration of H₂O₂,the mass of AC,electrolyte pH,and stirring could impact the activation of H₂O₂.Coupled with adsorption process,the ACSS-enabled electro-Fenton process is more effective.Moreover,this work found that although AC adsorbed organics,the“self-cleaning”mechanism can regenerate the ACSS electrode over several operational cycles.Conventional graphitic carbon has a low activity towards H₂O₂ production.This work presented the oxidative modification of graphitic carbon cathodes by electrode polarity reversal?PR? technique,and verify its applicability on graphite felt?GF? and reticulated vitreous carbon foam?RVC foam?.Different with previous reports,this work achieved the in situ O doping in acid-free,low-conductivity electrolyte.Results show that the PR technique can significantly increase the O/C ratio and improve the hydrophilicity of electrodes.After modification,the catalytic activity of electrodes towards O₂ reduction increased and thus the H₂O₂ production increased ca.2 times.Neutral pH and low current could support effective H₂O₂production.Moreover,the electro-Fenton?EF? process enabled by the modified electrode could generate more·OH,and thus resulted in higher removal efficiency compared with the original electrode.To enhance the diffusion of O₂ to porous cathode,this work presented the“floating cathode”structure,and studied the effects of key parameters on H₂O₂ production.Results show that compared with submerged cathode,the“floating cathode”can improve the H₂O₂ production by 4.3 times.Solution pH,current,and stirring can have significant effect on H₂O₂ production.Additionally,to study the disproportion pathway,anodic oxidation,and cathodic reduction of H₂O₂,this work studied the contribution of these pathways in a decoupling way,and proposed that pulsed current could enhance the H₂O₂ production.Results show that H₂O₂ disproportion pathway is significantly affected by the initial concentration of H₂O₂,and the concentration of electrolyte,the H₂O₂ anodic oxidation pathway is affected by current,and the H₂O₂ cathodic reduction has relation with both current and the porosity of cathode.This work found“2sON+2sOFF”was the best parameters and increased the H₂O₂ yield 61.3%.To solve the problem that O₂ and acidic conditions are required in conventional process,this work fabricated a 3-electrode flow-through reactor where reactants O₂ and H⁺ can be self-supported.Compared with 3-electrode static batch reactor,the following conclusions were drawn:in static batch reactor,Ti/mixed metal oxides?Ti/MMO? anode could supply O₂ to cathode via oxygen evolution reaction.The mass transfer of dissolved O₂ to cathode vicinity and the acidic conditions determine the H₂O₂ production.In flow-through reactor,a localized pH of 2.5-3.5 could be generated after the Ti/MMO anode.The current and flow rate significantly impact the concentration of H₂O₂ and accumulative production of H₂O₂ in column reactor.Experiments also show that the accumulation of O₂ bubbles underneath the cathode could potentially deteriorate the O₂ mass transfer.How to effectively transform the electrogenerated H₂O₂ into·OH and increase its utilization efficiency is another key focus of this work.This work proposed that the enhancement of·OH production can be facilitated by the accelerated Fe³⁺ reduction,and the control of·OH competitive reactions can be regulated by the addition approaches of reactants.Hydroxylamine,hydroquinone?HQ?,1,4-benzoquinone?BQ?,and sodium sulfate were selected as model additives to reveal the different regeneration mechanism of Fe²⁺.Results show that hydroxylamine facilitate Fe²⁺ regeneration by transforming itself into other products,HQ and BQ could build quinone cycle which could continuously regenerate Fe²⁺.The higher the molar ratio of initial concentration of HQ and BQ to Fe²⁺,the longer time that Fe²⁺concentration could retain.However,the stability of quinone cycles decreased due to the consumption of HQ and BQ by highly oxidative ·OH.Results of different addition approaches of Fe²⁺ and H₂O₂ show that the micro-scale ·OH competitive reactions could be effectively regulated by the macro-scale addition approaches and the diffusion processes of reactants.The essence of the regulation of OH competitive reactions are that the useless consumption of ·OH was regulated by Fe²⁺ and H₂O₂.