Performance Study of ACET/PTFE Modified Graphite Felt Electrode for Electrocatalytic H2O2 Reaction

Multiphase electro-Fenton is considered as a promising technology for the degradation of organic pollutants, and in order to ensure its effectiveness and to make it cheaper and easier, this study develops novel cathodes for in situ H2O2 generation. Graphite felt (RGF) modified by acetylene black (ACET)/polytetrafluoroethylene (PTFE) was selected to prepare a superhydrophobic electrode (APGF), and the effects of each factor of ACET:PTFE, oxygen flux, and current density on the production of H2O2 were investigated, and the rate of H2O2 production under the optimized conditions of the experiment was 35.96 mg h−1 cm−2 which can meet the requirements of Electro-Fenton technology. The physicochemical characterization of RGF and APGF electrodes was analyzed, and the electrocatalytic performance was evaluated by using an electrochemical workstation to test APGF (7:1 ∼ 1:3). Probing the mechanism analysis, the APGF electrode surface is hydrophobic and the C/F functional groups synergize to increase the reactive sites and improve the reactivity and selectivity. Dissolved oxygen in the electrolyte diffused to the active center on the cathode surface escaped from the liquid phase, forming a new phase with bubble adsorption for easier activation, and e-conjugated H+ to produce *OOH intermediates, and then e-conjugated H+ to obtain H2O2.

Multiphase electro-Fenton is considered a promising technology for the degradation of organic pollutants based on the ability to activate hydrogen peroxide (H 2 O 2 ) into reactive oxygen species (ROS). [1][2][3][4] To avoid the hazards associated with the acquisition, transportation and storage of H 2 O 2 , and to ensure the effectiveness of electro-Fenton, there is an urgent need to design catalytically stable cathode materials that have the ability to generate sufficient H 2 O 2 in situ. Electro-Fenton is a method based on the generation of strong oxidizing ·OH by H 2 O 2 and divalent iron to degrade pollutants, which usually requires only 0.1%wt concentration of H 2 O 2 . 5 To avoid the hazards associated with the acquisition, transport and storage of H 2 O 2 , continuous in situ generation of H 2 O 2 on the cathode can be chosen, while the ability to generate ·OH depends on the timely replenishment of the consumed H 2 O 2 . 6-8 Therefore, how tto increase the rate of H 2 O 2 generation at the cathode surface is the key to the electro-Fenton technique. In order to increase the reaction rate of H 2 O 2 generation at the cathode electrode, it is necessary to improve the cathode performance and increase the electrocatalytic activity. Carbon-based materials with highcatalytic activity are the most commonly used cathodes for H 2 O 2 electrosynthesis. [9][10][11] And the cathode catalytic materials are usually subjected to hydrothermal activation treatments, 12,13 acid-base treatments, 14,15 and modification treatments such as N, O, F, or metal ion doping, [16][17][18] to modulate the cathode material by increasing its specific surface area, changing its electronic and geometric structure, etc, improved electrocatalytic activity and selectivity for the synthesis of H 2 O 2 . Carbon-based electrodes such as graphite mats, [19][20][21] activated carbon fibers, 22,23 and carbon felts 24,25 have been reported, among which carbon/graphite mats are the most effective in promoting H 2 O 2 production via a two-electron oxygen reduction reaction (2e − -ORR). Hu et al. 26 treated rhodamine B solution using the electro-Fenton technique, and the graphite felt cathode treated with H 2 SO 4 was 110.5 mg l −1 . Yu et al. 27 used tert-butyl anthraquinone (TBAQ) modified carbon material to fabricate gas diffusion electrode (GDE) to improve H 2 O 2 production and enhance the electro-Fenton process, and found that carbon nanotube GDE containing 2% TBAQ had the highest H 2 O 2 production of 150.6 mg l −1 . Yu et al. 28 introduced carbon black/polytetrafluoroethylene into graphite felt and found that the cathode H 2 O 2 concentration reached 472.9 mg l −1 after modification. Acetylene black, a carbon-based catalyst with large specific surface area, high catalytic activity, and good electrical conductivity, was also applied to GDE with significant promotion of H 2 O 2 generation. 29 In addition to the carbon-based catalyst type, heteroatom doping also has a facilitating effect on the selectivity and activity of H 2 O 2 electrosynthesis. For example, Zhou et al. 30 developed fluorine-doped graded porous carbon catalysts with significant H 2 O 2 generation activity using MIL-53 (Aluminum) as a precursor, which exhibited good H 2 O 2 selectivity of 97.5%-83.0% with yields up to 792.6 mmol h −1 g −1 . Fluorine, being the most electronegative nonmetallic element, can induce the polarization of adjacent carbon to create more active sites and enhance the interaction between O 2 and carbon, 31 so it can be used as a dopant atom to improve the activity and selectivity of H 2 O 2 electrosynthesis. However, for now, the rate of H 2 O 2 electrosynthesis is still low, mainly limited by the electrochemical activity of the electrode, 32,33 and thus the development of cathodes with high catalytic activity is a central issue to increase the rate of H 2 O 2 generation.
The purpose of this work is to develop new carbon-based electrodes to improve the generation rate of H 2 O 2 generated in situ by oxygen cathodic reduction to meet the requirement of H 2 O 2 concentration for Electro-Fenton treatment of wastewater. To study the prospect of industrialized application in this field, carbon/graphite felt with obvious advantages such as 3D active surface, mechanical integrity, commercial availability, and easy accessibility was selected as the cathode material for the experiment, and attempts were made to modify the modification with ACET and PTFE. PTFE was selected not only for its bonding effect and hydrophobicity, but more importantly, it contains carbon and fluorine doping to increase the catalyst active sites to produce cathode electrodes with different AP modification amounts. The cathode surfaces before and after modification were analyzed by SEM, contact angle test, Raman and XPS characterization, and their electrocatalytic properties were examined by a electrochemical workstation. The electrodes were applied to the preparation of H 2 O 2 with the objective of generating a high concentration of H 2 O 2 . The effects of AP dosing, oxygen flux and current density on the production of H 2 O 2 were investigated under the acidic environment of Electro-Fenton using electrolyte solution with initial pH = 3. The best experimental operating conditions were finally achieved and the mechanism of electrocatalytic reaction on the cathode surface was investigated. z E-mail: xtjltlt@163.com; 2031269242@qq.com; 509652085@qq.com; 1115489104@qq.com; 2583718574@qq.com
Cathode preparation.-The graphite felt was degreased sequentially with acetone and deionized water in an ultrasonic bath and dried at 80°C for 6 h. The appropriate amounts of ACET and PTFE were mixed uniformly in the mass ratio of 7:1, 5:1, 3:1, 1:1 and 1:3 for a total loading of 2 g. Both were mixed with anhydrous ethanol (25%) in an ultrasonic bath for 10 min to form a highly dispersed mixture. The pretreated graphite mats were immersed in the mixture, sonicated for 0.5 h, dried at 80°C for 12 h, and then the samples were calcined in a charcoal furnace under nitrogen atmosphere at 360°C for 1 h. Since the injection ratios of acetylene black to PTFE in the mixture were in five forms, the corresponding modified electrodes were labeled as APGF-5:1 ∼ 1:5, and the unmodified electrodes were labeled as RGF.
Material characterization.-Scanning electron microscopy (SEM, Hitachi Hitachi S-4800, Germany) was used to study the surface structure of the electrodes. A contact angle meter (JY-82B Kruss DSA) was used to analyze the cathodic hydrophobic properties. X-ray photoelectron spectroscopy (XPS, Thermo Kalpha) was used to determine the surface elements and functional groups of the electrodes. Raman spectra of GF samples were obtained using a microconfocal Raman spectrometer (LabRAM HR Evolution, France) at an excitation radiation wavelength of 532 nm.
Electrochemical performance testing.-Cyclic voltammetry (CV), linear scanning voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) tests were performed on the cathode material using an electrochemical workstation (Shanghai, CHI660E) to analyze the electrochemical properties of the cathode. All electrochemical tests were performed in a three-electrode system with RGF or APCF 7:1 ∼ 1:3 as the working electrode (WE), platinum sheet as the counter electrode (CE) and saturated glycerol as the reference electrode (RE). The electrolyte required for the electrochemical tests was Na 2 SO 4 (0.2 M), and the initial pH of the solution was 3. The pH selected in the reaction system was adjusted with 1 M H 2 SO 4 , and oxygen saturation was reached by passing O 2 for 30 min before the experiment. CV curves were performed at potentials from 2.0 to −1.2 V, and LSV was scanned in the potential range from 0 to −1.6 V. The scan rates of both CV and LSV were 25 mV s −1 . The frequency range of EIS measurements was 0.1 ∼ 10 kHz with a voltage amplitude of 5 mV. The whole process was carried out at room temperature of 25°C.
Electro-synthetic H 2 O 2 and its concentration detection.-Scaled-up experiments were carried out at room temperature (25°C), atmospheric pressure and initial pH = 3 of the electrolyte solution. An electrolytic cell of size (9 cm × 9 cm × 12 cm), graphite felt (5 cm × 9 cm, thickness 1 cm) as the cathode and carbon plate (5 cm × 9 cm) as the anode were selected. The oxygen flux at a certain flow rate was controlled by a rotameter, and H 2 O 2 electrosynthesis was investigated under different AP dosing ratio, oxygen flux and current density conditions in a solution with a concentration of 0.2 M Na 2 SO 4 , and samples were taken every 10 min during the experiment to analyze the concentration of H 2 O 2 . The H 2 O 2 concentration was detected using the titanium sulfate spectrophotometric method.
The UV spectrophotometer (UV1901PC) measured the light wavelength of 407 nm, measured the spectrophotometric value, and calculated the H 2 O 2 concentration through the standard curve of the H 2 O 2 concentration value corresponding to the pre-determined spectrophotometric value.

Results and Discussion
Surface properties of electrodes.-SEM electron microscope analysis.-The SEM electron microscopy analysis of the cathodic graphite felt is shown in Fig. 1, where (a) and (b) are unmodified cathodic RGF, and (c) and (d) are modified cathodic APGF. From (a) and (b), it can be seen that the graphite felt shows a clear interlaced three-dimensional fiber structure with a smooth surface, there are more crossed gaps. In contrast, the internal fiber structure of the modified graphite felt obviously shows a rough surface. Indicating that the modification is in the form of a flaky structure adhering to the fiber surface and wrapping it, ACET and PTFE loaded to fill the voids where the graphite mat fibers cross, which indicates the modification is successful.
Contact angle measurement analysis.-As shown in Figs. 2a and 2b the contact angles of RGF and APGF are not much different, 138.2°and 134.3°, respectively, indicating that they are similar in hydrophobicity. The added AP is also a hydrophobic material, so the cathode modified by AP remains hydrophobic. However, the slightly smaller contact angle of the modified graphite felt may be due to the presence of lamellar structured attachments on the surface of the modified cathode, which makes the internal surface of the graphite felt unsmooth resulting in the angle change.
XPS analysis.-XPS was used to analyze the surface elements of RGF and APGF. As shown in Figs. 3a, 3a wide range of XPS-full spectra from −500 to −1500 eV, C and O elements were detected in both RGF and APGF, while F elements were-added in APGF with 8.256% F content. As shown in Fig. 3b, the C1s spectra of RGF have three separate peaks corresponding to C-C, C-O and C=O bonds, respectively, as shown in Fig. 3c, and the C1s spectra of APGF have six separated peaks, with additional C-CF, CF 2 and CF 3 chemical bonds compared to RGF. As shown in Figs. 3d, 3e, the O1s fine spectra of both RGF and APGF are shown with. three peaks of C-O, C=O· and H-O-H. 34 The OF chemical bond is also present in APGF compared to RGF. At the same time, the original functional groups of RGF were not destroyed, and the fluorine element of APGF electrode was effectively doped, which was mainly manifested as C-CF, CF 2 , and CF 3 , as well as OF chemical bonding.
Raman spectrometer.-In Fig. 4, the degree of sp 3 bonding and carbon defects of RGF and APGF can be investigated by Raman measurements, and the spectra show peaks of 1360 cm −1 and Figure 1. The SEM of RGF (a), (b) and APGF (c), (d). band, respectively. The intensity ratio (I D /I G ) between the D and G bands gives an idea of the extent of carbon defects in the material. 35 The D band is associated with sp 3 bonds and carbon defect structures, and the G band is associated with graphitic carbon on the edge or base. As shown in the figure, APGF has a higher I D /I G value of 1.23 than RGF, which has an I D /I G value of 1.11, suggesting that APGF has an increased degree of carbon defects over RGF. This is due to the fact that the acetylene black dependents are filled on the fiber surface and in the cross-fiber voids, so that the cathode-conducting fiber surface provides more active sites due to the loading of ACET and PTFE. Contributes to the adsorption of oxygen and desorption of reactive intermediate ions, thus improving the electrochemical performance. 36 Electrochemical performance testing.-As shown in Fig. 5a, the cathodic oxygen reduction reaction (ORR) electrocatalytic activity of RGF and APGF-7:1 ∼ 1:3 was characterized by CV, LSV and EIS methods. The CV curves obtained for APGF have no symmetric peaks, with only oxidation peaks and no reduction peaks, indicating that the redox reaction is irreversible. The crossover point between the oxidation and reduction curves indicates the presence of catalytically active substances in the reaction system here. Because the standard potential of the cathodic oxygen reduction system H 2 O 2 half-reaction is −0.69 (V vs RHE), when the saturated calomel electrode was chosen as the reference electrode in the experimental test, the electrode potential was −0.2714 (V vs SCE) at Ph = 3, and the potential range of the intersection point −0.323 V ∼ −0.443 V was more negative than −0.2714 V, and the overpotential −0.0516 V ∼ −0.1716V, assuming that the difference in potential is used to overcome the solution resistance, interfacial layer charge transfer resistance and other resistances, then the oxygen reduction occurs to generate H 2 O 2 according to the theoretical potential. The values of potential and current at the intersection of oxidation and reduction curves in Fig. 5a and impedance in Fig. 5c are listed in Table I below, and the total resistance corresponding to the converted potential/current at the crossing point, the resistance Rη calculated over the potential/current and the Rη-Rs-Rct values are listed in Table I, it can be seen that the APGF-3:1 electrode has the most negative Rη-Rs-Rct and the strongest reduction performance, which is most favorable for the generation of H 2 O 2 .
As shown in Fig. 5b, APGF has a lower starting potential and higher electrocatalytic activity compared to RGF. And among the modified cathodes with different addition ratios, ACET:PTFE addition ratio of 3:1 can show stronger current response at the same overpotential compared to other ratio conditions. The EIS impedance diagram is shown in Fig. 5c and fitted by the equivalent circuit, 37 where Rs, Rct, W and C denote the solution resistance, interfacial layer charge transfer resistance, Warburg impedance and bilayer capacitance, respectively. 38 The fitting results showed that the Rct of APGF was significantly smaller than that of RGF (Table I), indicating that the modified graphite felt cathode impedance was small and had better electrical conductivity, while the cathode resistance with a addition ratio of 3:1 was the smallest and the most conductive among all APGFs.
As can be seen from Fig. 5d, the Tafel slope can clearly show the ease of electron transfer under different conditions, and the Tafel slope of APGF is smaller compared to that of RGF, indicating that the modified cathode material is easier and stronger in electron transfer, while the Tafel slope of the addition ratio of 3:1 is the smallest among all modified materials, 283 mA dec −1 , indicating that the cathode material under this condition has the best ORR catalytic performance. In summary, the electrocatalytic activity of the cathode material was obviously improved after the GF cathode was treated with AP modification, which further increased the generation rate of H 2 O 2 .
Effect of experimental conditions.-Effect of modifier addition ratio.-As shown in Fig. 6a, RGF and APGF 7:1 ∼ 1:3 as cathode obtained H 2 O 2 yield with time: H 2 O 2 yield increased with time, APGF at different addition ratios H 2 O 2 yield are larger than RGF, but at different times H 2 O 2 concentration tends to level off, in particular, cathodes with higher concentrations of ACET tends to level off earlier; which Fig. (b), when the addition ratio is 5:1, in the reaction the maximum H 2 O 2 concentration of 1208.4 mg l −1 was obtained at 40 min, and the production rate of H 2 O 2 was 40.68 mg h −1 cm −2 , followed by H 2 O 2 concentration of 1195.2 mg l −1 at 60 min of the reaction when the addition ratio was 3:1, and the production rate of H 2 O 2 at 40 min of reaction was 35.96 mg h −1 cm −2 . However, during the experiment, it was discovered that APGF-7:1 had obvious shedding phenomenon and APGF-5:1 electrolyte became turbid at the late stage of the reaction, therefore, APGF-3:1 was chosen as the best modified cathode.
Effect of oxygen flow.- Figure 7a shows the effect of oxygen flow rate on APGF cathode H 2 O 2 generation with time: H 2 O 2 generation of APGF at oxygen flux 0 ∼ 80 ml min −1 increased with time. As shown in Fig. 7b, the oxygen flux increased from 0 to 60 ml min −1 during the first 40 min of the reaction, and the rate of H 2 O 2 production also increased, and the maximum rate of H 2 O 2 production was 35.96 mg h −1 cm −2 at 60 ml min −1 . When the oxygen flow rate was 0, the production of H 2 O 2 was low compared with that under the aerobic condition, and the growth rate was slow, which was because the oxygen obtained from the anode reaction was not enough to supply the oxygen required for the cathode reaction. However, when the oxygen flow rate was increased to 80 ml min −1 , the amount of H 2 O 2 generated decreased to 1136.12 mg l −1 . The results of the analysis showed that the supply of oxygen to provide raw material for the cathodic reaction was beneficial to the generation of H 2 O 2 ; however, blowing in too much oxygen would not promote the generation of H 2 O 2 , but would hinder its effective catalytic reaction at the gas-liquid-solid interface, 39 and also indirectly cause oxygen waste. Therefore, the optimal oxygen flux of APGF cathode was determined to be 60 ml min −1 .
Effect of current density.-The pattern of the magnitude of the externally applied current density on the H 2 O 2 generated by the APGF cathode is shown in Fig. 8a: The current densities ranged from 30 to 60 mA cm −2 and the concentrations of H 2 O 2 prepared using the APGF electrode all increased with time during the first 60 min. Figure 8b shows that the rate of H 2 O 2 production increased when the current density is increased from 30 mA cm −2 to 50 mA cm −2 , the concentration and rate of H 2 O 2 production decreased when the current density is increased from 50 mA cm −2 to 60 mA cm −2 . The maximum amount of H 2 O 2 generated by APGF at a current density of 50 mA cm −2 was 1195.2 mg l −1 , at 40 min of reaction the H 2 O 2 generation rate was 35.96 mg h −1 cm −2 . A suitable current density will promote the electron transfer between the electrolyte and the cathode, 40 and thus the reaction will occur at the active sites of the cathode. However, when the current density reaches too high, the amount of H 2 O 2 production decreases, since high current density will promote the cathode 4e − transfer to generate the side reaction product H 2 O and the hydrogen precipitation side reaction, 41 and accelerate the oxidation decomposition of the generated H 2 O 2 at the anode. Therefore, too high a current is not conducive to the generation of H 2 O 2 , and the optimal current density was chosen to be 50 mA cm −2 under experimental conditions.  developed in this study was modified with cheap and easily available GF carbon material loaded with ACET and PTFE, which takes advantage of the good electrical conductivity and large specific surface area of ACET. And PTFE not only serves as a bonding agent, but also functions as a fluorine-doped carbon-based catalyst. The cathode graphite felt electrode was produced by controlling the surface of the cathode to make it hydrophobic and the synergistic effect of C/F effective doping. By optimizing the experimental conditions, the H 2 O 2 production rate of the new APGF-3:1 electrode was 35.96 mg h −1 cm −2 , which was slightly higher than the H 2 O 2 production rate of other graphite felt modified cathode materials, showing the superiority of this cathode material, but the performance of the electrode is inferior compared to that of the O/F polyatomic doped modified graphite felt electrode, which can meet the requirements for eletro-Fenton. APGF is easy to synthesize, avoids expensive modified materials and complicated reaction environment, and is expected to be a promising cathode for the in situ generation of H 2 O 2 by Electro-Fenton.

Reaction Mechanism
In electrochemical reactors, the reaction process is composed of cathodic process at the electrode/solution interface, anodic process, and liquid-phase mass transfer process. The special characteristics of the electrode reaction are mainly manifested in the existence of a double electric layer and surface electric field on the electrode surface. The electrode surface is the reaction site, and the electrode plays a role equivalent to that of a catalyst in a heterogeneous catalytic reaction, which is a non-homogeneous solid-gas-liquid  reaction. As shown in Fig. 9, the solid phase is GF electrode surface loaded with fluorine doped porous carbon material ACET/ PTFE electrode, the liquid phase aqueous solution contains electrolyte Na 2 SO 4 , H 2 SO 4 to adjust the pH value, and the gas phase is O 2 and dissolved oxygen (DO) to provide the reaction material. Under the action of electric field force, the aqueous solution of cations H + , Na + and dissolved oxygen DO moves directionally toward the cathode to reach the cathode interface, and the aqueous solution of anions SO 4 2− moves directionally toward the anode to reach the anode interface. Oxidation reaction occurs on the anode surface. At the three-phase interface where the cathodes meet, there is mainly competition between the primary reaction of O 2 2e − reduction to generate H 2 O 2 and two side reactions of O 2 4e − reduction to H 2 O and H + 2e − reduction to H 2 , regardless of the 2e − /4 e − -ORR occurring in O 2 , the reaction firstly all get an electron with H + to generate *OOH intermediate(Ⅱ), whose H 2 O 2 selectivity is related to the adsorption energy of *OOH intermediates on the electrocatalyst surface. 45 Usually, the binding nature of *OOH intermediates on the catalyst can be controlled by changing their electronic structure. Here, a threepoint analysis of the reaction mechanism is performed to control the electronic structure of the APGF electrode.   (1) Figure 5 of the CV curve clearly indicates an irreversible reaction, with oxidation peaks appearing and no reduction peaks for the oxidized material, but the experimental detection of H 2 O 2 proves that the cathodic oxygen reduction reaction occurs. The electrode process is continuous, depletion occurs on the electrode surface, the reactant mass transfer rate does not keep up with the electrochemical reaction rate, and the redox curves cross. The presence of catalytically active substances in the reaction system can also be considered as the emergence of new phases, the crossover point is caused by the overpotential. Due to the hydrophobicity of the electrode, the cathode surface and the electrolyte non-flat surface is regarded as droplet-like, and the oxygen dissolved therein moves out to be adsorbed in bubbles at the active site, which is confirmed to be a solid-gasliquid reaction. (2) Solid gas liquid three different forms of material are all present at the interface, and there are several different forces at the same time. The interrelationship between several forces, in simple terms, solid electrodes want the molecules on the surface of the solid to leave the body by interacting with gas or liquid molecules requires a lot of energy, the so-called high surface energy solids. When the ability of solid molecules to attract liquid molecules is stronger than the ability of liquid molecules to attract each other, the liquid molecules tend to be "pulled" to the solid surface and the liquid spreads more easily on a macroscopic scale. On the contrary, on low surface energy solids. For example, PTFE, GF, the mutual force between liquid molecules prevails. Figure 2 shows that the contact angle of the electrode surface in contact with water is greater than 130°, the hydrophobicity is so good that spherical droplets are easily formed, and the wetting performance decreases. The O 2 dissolved in the electrolyte will be wrapped around the droplet and will be uniformly distributed in the droplet, but with the diffusion of the electric field effect toward the cathode, the H + will tend to the outer surface of the droplet, and when it is close to the surface of the cathode, it will be more concentrated on the outer surface of the droplet leaning toward the direction of the cathode surface. Due to the hydrophobicity of the electrode, the droplet does not infiltrate the cathode, reducing the opportunity for H + to gain electrons from the cathode to generate H 2 , so that the advantage of the reduction reaction of H + in preference to O 2 disappears. And O 2 with higher electronegativity preferentially adsorbs on ACET to get electrons on a low surface energy solid cathode containing PTFE and ACET, the positive reaction selectivity is improved and the generation of H 2 O 2 is promoted.
(3) Raman spectroscopy of the surface of the negative electrode ( Fig. 4) analyzes the modified electrode material with carbon defect fraction and XPS analysis of the F-doped APGF negative electrode containing mainly C/F (C-CF, CF 2 and CF 3 ) chemical bonds. Figure 6a illustrates that APGF is more favorable than RGF for H 2

Conclusions
In this study, GF was used as the base carbon material carrier and ACET/PTFE mixture was tested as cathode modification material to successfully prepare superhydrophobic electrode for the effective synthesis of H 2 O 2 . As shown by SEM and Raman spectroscopy characterization analysis, AP hybrid catalyst was successfully loaded onto graphite felt carrier. XPS analysis showed that APGF added new Fluorine elements compared to RGF and carbon fluorine bond appeared on the surface of the structure. RGF and APGF-7:1 ∼ 1:3 were tested for ORR electrocatalytic performance by CV, LSV and EIS methods, and the results showed that APGF-7:1 ∼ 1:3 showed larger current response, larger reduction performance, lower solution impedance and enhanced electrochemical oxygen reduction performance compared to RGF, where APGF-3:1 showed the best electrocatalytic performance.  APGF-3:1 was used to produce H 2 O 2 in O 2 saturated pH = 3, 0.2 M Na 2 SO 4 electrolysis environment, selected oxygen flux 60 ml min −1 , current density 50 mA cm −2 reaction conditions to obtain the highest concentration of H 2 O 2 1195.2 mg l −1 , and with a generation rate of 35.96 mg h −1 cm −2 , which can meet the H 2 O 2 concentration requirement for Electro-Fenton treatment of wastewater. APGF fabrication method is expected to be a promising negative electrode with industrial application for the in situ generation of H 2 O 2 by Electro-Fenton because of its simplicity and avoidance of expensive modified materials and complicated reaction environment.
Mechanistic analysis shows that the proposed new APGF porous carbon material for ORR electrocatalytic reaction is an irreversible non-homogeneous gas-liquid-solid reaction. In order to improve the selectivity of O 2 to generate H 2 O 2 reaction, it is to be controlled by changing the electronic structure of *OOH intermediates on the electrocatalyst surface. Experimental development of APGF with hydrophobicity on the surface and effective C/F doping synergism increases the electrocatalytic active sites and improves ORR activity and selectivity. During the reaction process saturated O 2 diffuses to the electrode surface in the form of droplets of dissolved oxygen encapsulated in electrolyte, the dissolved oxygen breaks away from the droplets and the formed bubbles form a new phase on the solid cathode, which is adsorbed on the electrocatalytic active site and is activated to yield one electron and H + to generate *OOH; the resulting *OOH intermediate then combines one electron and H + to generate H 2 O 2 .