Electrochemical Reduction Of O2 Research Articles

Synthesis of iron phthalocyanine/CeO2 Z-scheme nanocomposites as efficient photocatalysts for degradation of 2,4-dichlorophenol.

Modulating the photogenerated electrons of CeO2 to activate O2 and efficiently photocatalytic degradation of chlorophenols is a highly desired goal. Herein, we have successfully fabricated an FePc/CeO2 heterojunction through H-bond induced assembly. The photocatalytic degradation of 2,4-DCP by the amount-optimized FePc/CeO2 nanocomposite was improved by 3 times compared with that by pure CeO2. By means of electron paramagnetic resonance (EPR) and single wavelength photocurrent spectroscopy, it is confirmed that the excellent photocatalytic performance is mainly attributed to the formation of the Z-scheme heterojunction, which promotes charge separation and transfer, and the introduction of FePc broadens the visible light absorption range of the heterojunction. Moreover, O2 temperature-programmed-desorbed curves and electrochemical O2 reduction measurement results demonstrate that the single Fe-N4(II) site in FePc is more conducive to promoting O2 activation than that of other metal phthalocyanines. Based on in situ FT-IR and liquid chromatography-tandem mass spectrometry (LC-MS/MS), a possible reaction pathway of 2,4-DCP degradation was proposed. This study provides a novel strategy for preparing CeO2 based Z-scheme heterojunctions with abundant monoatomic sites for pollutant degradation.

Functionalisation of Carbon Catalyst Support By Plasma Treatment for PEMFC Cathode

Proton exchange membrane fuel cell (PEMFC) is one promising electric device to replace the combustion engine using fossil fuel especially for heavy-duty transport. One of the main issue for the widespread of this technology on the European roads is the cost and degradation of their components over time. The sluggish reduction of dioxygen at the cathode require high amount of noble metal (i.e. platinum). Under PEMFC operating conditions, carbon as catalyst support is unstable.This study presents a new approach to improve the stability of the cathode components (catalyst, carbon support and ionomer) thanks to the enhancement of the interaction between the three entities and to reduce carbon corrosion. Plasma treatment were performed on different carbon black sources (different surface area and porosity) to functionalize their surface by nitrogen function using different gas. The modified carbons were characterized by TEM, XPS, Raman spectroscopy, calorimetry, elemental analysis. The plasma treatments were reproducible and allow controlling the degree of functionalisation. The nitrogen doped carbons were catalysed by platinum nanoparticles. A better dispersion of the nanoparticles was observed by TEM showing the interest of the plasma treatment. Cyclic voltammetry were performed and a better catalytic activity toward the electrochemical reduction of O2 was observed.[1] Isothermal titration calorimetry experiments were carried out and show an improved interaction between the nitrogen functionalized carbon and the ionomer.[1] A. Parnière, P.-Y. Blanchard, S. Cavaliere, N. Donzel, B. Prelot, J. Rozière, D.J. Jones, Nitrogen Plasma Modified Carbons for PEMFC with Increased Interaction with Catalyst and Ionomer, J. Electrochem. Soc. 169 (2022) 044502. Figure 1

Efficient oxygen reduction to alkaline peroxide at current densities up to 500 mA cm−2 on a gas diffusion electrode with hydrophobic carbon microporous layer: Influence of fluid dynamics and reactor operation on scale-up

The two-electron electrochemical O2 reduction reaction (2e-ORR) on a gas diffusion electrode (GDE) using clean electricity is an attractive process for generating the green oxidant hydrogen peroxide (H2O2). Electrolyte flooding through the porous catalyst and diffusion layers is one of the major factors inhibiting the operational stability and longevity under industrially relevant current densities (>100 mA cm−2). This study reports for the first time that optimizing the two-phase flow and the mode of reactor operation brings about a remarkable improvement in the high current density operation (up to 500 mA cm−2) on a scalable (20 cm2 geometric area) and commercially available Sigracet 39BB GDE with the microporous carbon layer (MPL) acting as the catalyst layer. The interacting effects of current density, gas and liquid flow rates and the flooding threshold limit for the differential liquid/gas pressure were determined. While high peroxide Faradaic efficiency (FE > 95 %) was attained in a gas flow-by mode during short-term experiments, long-term stability was only established when the gas was switched to the flow-through or quasi-flow-through mode of operation. Under the latter conditions, at 500 mA cm−2 operational stability of more than 20 h was demonstrated with a peak FE of 97 % in 1.0 M KOH, at 293 K, 1 atm. It was found that optimizing the reactor operation has a profound effect during scale-up, and developing novel catalytic materials for 2e-ORR to alkaline peroxide is not warranted since a low-cost microporous carbon-based GDE is sufficient for stable and efficient operation.

Effect of β-fluorinated porphyrin in changing selectivity for electrochemical O2 reduction

The development of catalytic systems that selectively convert O2 to water is required to progress fuel cell technology. As an alternative to platinum catalysts, derivatives of iron and cobalt porphyrin molecular catalysts provide one benchmark for catalyst design. However, the inclusion of these catalysts into homogeneous platforms remains a difficulty. Co-porphyrins have been studied as heterogeneous O2 reduction catalysts; however, they have not been explored much in homogeneous systems. Moreover, they suffer from poor selectivity for the desired four-electron reduction of O2 to H2O. Herein, we present two cobalt-based β-fluorinated porphyrin complexes (CoTPF8(OH)2 and CoTPF8(OH)4) and demonstrate applicability as effective catalysts for the oxygen reduction reaction. Using rotating ring-disk electrochemistry, the catalysts, CoTPF8(OH)2 and CoTPF8(OH)4, showed maximum Faradaic efficiency for H2O of 92 % and 97 %, respectively. DFT calculations suggest that the formation of a phlorin intermediate could occur before O2 reduction and that a stronger H2O2 binding in the cobalt-based β-fluorinated porphyrin species compared to the unsubstituted parent compound, CoTP(OH)2, was responsible for the observed experimental selectivity for H2O. These results reveal that the β-fluorinated porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions.

Enhanced electrochemical O2 reduction to H2O2 through resilient hybrid catalysts modified with DMSO in electro-Fenton

In the face of challenges presented by rapid urbanization and industrialization, the surge in dye wastewater has emerged as a prominent concern. This study introduces a pioneering novel approach aimed at augmenting the electrocatalytic efficiency of O2 reduction to H2O2 through the modification of a hybrid catalyst with dimethyl sulfoxide (DMSO) to construct gas diffusion electrodes (GDEs). The hybrid catalyst, consisting of carbon black and DMSO, was meticulously fabricated, and its electrocatalytic activity was thoroughly investigated using various characterization techniques. Within 180 min, the 3 %DM cathode showcased efficient H2O2 generation, reaching 850 μM, and remarkable oxygen utilization, achieving 60.49 %. Intriguingly, the fabricated 3 %DM hybrid catalyst maintained a three-phase interfacial (TPI) due to its super-hydrophilic property. This study elucidates the pivotal role of DMSO in enhancing the performance of hybrid catalysts for O2 reduction to H2O2. The insights provide valuable perspectives into the development of efficient and resilient electrochemical systems for sustainable energy conversion and environmental applications.

Application of solid electrolytes in electrochemical reduction of CO2 or O2

Electrochemical conversion of abundant CO2/O2 into value-added products and fuels holds great promise to achieve sustainable energy systems. In most cases, aqueous electrolyte containing salts are used, inevitably suffering subsequent purification if pure products needed for further purpose. Instead, the application of solid electrolyte has seen a booming and that thought to be commercially attractive. Nevertheless, there is a scarcity of comprehensive reviews focusing exclusively on the application of solid electrolytes in electrochemical CO2/O2 reduction, in contrast to the more readily available reviews on battery technologies. In this manner, we review recent advance and challenges in the understanding electrochemical reduction of CO2/O2 using solid electrolytes to produce high valuable chemicals like H2O2, formic acid, etc. It begins with a brief introduction of historical development of solid electrolyte and their properties. Then it followed with summarizing of its application used in oxygen reduction reaction (ORR) by power consuming mode (2e--ORR), or by power generating mode in fuel-cell. Afterward, diverse type of solid electrolytes has been systemically reviewed, including the corresponding cells, the production rate along with different roles in electrochemical CO2 reduction. Finally, challenges and prospects of solid electrolytes are discussed, aiming to guide a promising direction for directly producing high-value chemicals in near future.

Rapid screening of electrochemically active bacteria based on a biocathode-functional bipolar electrode-electrochemiluminescence platform.

A functional bipolar electrode-electrochemiluminescence (BPE-ECL) platform based on biocathode reducing oxygen was constructed for detecting electrochemically active bacteria (EAB) in this paper. Firstly, thiolated trimethylated chitosan quaternary ammonium salt (TMC-SH) layer was assembled on the gold-plated cathode of BPE. TMC-SH contains quaternary ammonium salt branch chain, which can inhibit the growth of microorganisms on the surface or in the surrounding environment while absorbing bacteria. Then, the peristaltic pump was used to flow all of the samples through the cathode, and the EAB was electrostatically adsorbed on the electrode surface. Finally, applying a constant potential to the BPE, bacteria can catalyze electrochemical reduction of O2, and decrease the overpotential of O2 reduction at the cathode, which in turn generates an ECL reporting intensity change at the anode. In this way, live and dead bacteria can be distinguished, and the influence of complex food substrates on detection can be greatly reduced.

Phosphorus‐Doped Porous Carbon Coated Graphite Felt as An Efficient and Reusable Cathode for Electro‐Fenton Degradation of Parabens

AbstractPharmaceuticals and personal care products (PPCPs) are currently drawing significant attention due to their environmental impact. Electro‐Fenton, one of the advanced oxidation processes (AOPs), is an efficient and comprehensive technology to degrade all kinds of organic pollutants, but the degradation efficiency relies on cathode material. In this work, phosphorus‐doped porous carbon material coated graphite felt (P‐GF) was prepared by adopting phytic acid as a phosphorus source through high temperature solid‐state method. The microstructure and the elements composition of this fabricated material were investigated by SEM, BET and XPS. With phosphorus doping and plenty of carbon porous structures, the hydrophilicity and infiltrating property of the P‐GF had been greatly improved. The prepared P‐GF material enhanced the electrochemical reduction of O2 and could significantly enhance the yield of H2O2. It was used as a cathode to degrade pollutants under a constant potential, and methylparaben (MePa) was chosen as a research model for optimizing the experimental conditions and analyzing the possible degradation pathway. The P‐GF cathode achieved an excellent ability of degrading nearly 100 % of methylparaben within 3 h. The simultaneous removal ability of the P‐GF to four parabens was impressed. Additionally, the P‐GF material exhibited outstanding reusability.

Electronic States Regulation Induced by the Synergistic Effect of Cu Clusters and Cu‐S1N3 Sites Boosting Electrocatalytic Performance

AbstractThe precise coordination environment manipulation and interfacial electron redistribution are significant strategies for the modulation of electronic configuration and intermediates adsorption behaviors, while the complex synergistic effect is yet to materialize due to the lack of catalyst platform. Herein, an atomic‐scale catalyst platform containing single Cu site with tunable coordination environment (Cu‐N4 or Cu‐S1N3) and easy decoration of Cu cluster (Cux) for electrochemical O2 reduction reaction (ORR) is reported. Theoretical analysis shows that the charge redistribution and up‐shifting d‐band center of single Cu site induced by the asymmetrical coordination environment and Cux effectively strength *OOH adsorption. The modulation in intermediates adsorption enables Cu‐S1N3/Cux a superior ORR performance compared with the samples without S atom and/or Cux. Moreover, the adsorption behavior of *OOH and d‐band center of single Cu site tuned by coordination environment and interfacial interactions are correlated linearly with catalytic potential, e.g., half‐wave potential and reaction kinetic, e.g., Tafel slope for ORR, indicating the high applicability of the intermediate adsorption strength and d‐band center as the indicators for catalytic performance. This study provides a comprehensive modulation strategy for electron configuration and intermediates adsorption behaviors, and can be extended to facilitate other proton‐coupled electron transfer reactions.

Amine Groups in the Second Sphere of Iron Porphyrins Allow for Higher and Selective 4e-/4H+ Oxygen Reduction Rates at Lower Overpotentials.

Iron porphyrins with one or four tertiary amine groups in their second sphere are used to investigate the electrochemical O2 reduction reaction (ORR) in organic (homogeneous) and aqueous (heterogeneous) conditions. Both of these complexes show selective 4e-/4H+ reduction of oxygen to water at rates that are 2-3 orders of magnitude higher than those of iron tetraphenylporphyrin lacking these amines in the second sphere. In organic solvents, these amines get protonated, which leads to the lowering of overpotentials, and the rate of the ORR is enhanced almost 75,000 times relative to rates expected from the established scaling relationship for the ORR by iron porphyrins. In the aqueous medium, the same trend of higher ORR rates at a lower overpotential is observed. In situ resonance Raman data under heterogeneous aqueous conditions show that the presence of one amine group in the second sphere leads to a cleavage of the O-O bond in a FeIII-OOH intermediate as the rate-determining step (rds). The presence of four such amine groups enhances the rate of O-O bond cleavage such that this intermediate is no longer observed during the ORR; rather, the proton-coupled reduction of the FeIII-O2- intermediate with a H/D isotope effect of 10.6 is the rds. These data clearly demonstrate changes in the rds of the electrochemical ORR depending on the nature of second-sphere residues and explain their deviation from linear scaling relationships.

A portable electrochemical microsensor for in-site measurement of dissolved oxygen and hydrogen sulfide in natural water

Dissolved oxygen (O2) and hydrogen sulfide (H2S) are two important indicators of water quality, their levels are of intimate dependence and varying over time. It is of great significance to monitoring of dissolved O2 and H2S simultaneously in natural water, yet has not been reported because of lack of effective approaches. In this work, a portable electrochemical microsensor was developed for simultaneously quantifying dissolved O2 and H2S. Here, Pd@Ni nanoparticles (NPs) were self-assembled onto the microelectrode by MXene titanium carbide (Ti3C2Tx), which were of responsibility towards O2 and H2S detection within single electrochemical reduction process. On this regard, Pd NPs facilitated catalyzing the electrochemical reduction of O2, while Ni NPs were employed as recognition element for H2S detection. With the electrochemical reduction sweep, the initial application of a positive voltage rendered the Ni to be oxidized to be Ni ions, contributing to their following capture of surrounding S2− to form nickel sulfide. Nickel sulfide with highly electrochemical activity were capable of generating detecting reduction current. In consequence, the as-designed microsensor can simultaneously determine O2 concentrations ranging from 36 to 318 μM and H2S levels ranging from 0.1 to 2.5 μM with high selectivity. Finally, the portable microsensor was successfully applied to simultaneous detection dissolved O2 and H2S in natural water in-site, the results of which were comparable to the classical methods.

Synergistic Effect of Sn and Fe in Fe-Nx Site Formation and Activity in Fe-N-C Catalyst for ORR.

Iron-nitrogen-carbon (Fe-N-C) materials emerged as one of the best non-platinum group material (non-PGM) alternatives to Pt/C catalysts for the electrochemical reduction of O2 in fuel cells. Co-doping with a secondary metal center is a possible choice to further enhance the activity toward oxygen reduction reaction (ORR). Here, classical Fe-N-C materials were co-doped with Sn as a secondary metal center. Sn-N-C according to the literature shows excellent activity, in particular in the fuel cell setup; here, the same catalyst shows a non-negligible activity in 0.5 M H2SO4 electrolyte but not as high as expected, meaning the different and uncertain nature of active sites. On the other hand, in mixed Fe, Sn-N-C catalysts, the presence of Sn improves the catalytic activity that is linked to a higher Fe-N4 site density, whereas the possible synergistic interaction of Fe-N4 and Sn-Nx found no confirmation. The presence of Fe-N4 and Sn-Nx was thoroughly determined by extended X-ray absorption fine structure and NO stripping technique; furthermore, besides the typical voltammetric technique, the catalytic activity of Fe-N-C catalyst was determined and also compared with that of the gas diffusion electrode (GDE), which allows a fast and reliable screening for possible implementation in a full cell. This paper therefore explores the effect of Sn on the formation, activity, and selectivity of Fe-N-C catalysts in both acid and alkaline media by tuning the Sn/Fe ratio in the synthetic procedure, with the ratio 1/2 showing the best activity, even higher than that of the iron-only containing sample (jk = 2.11 vs 1.83 A g-1). Pt-free materials are also tested for ORR in GDE setup in both performance and durability tests.

Biocathodes reducing oxygen in BPE-ECL system for rapid screening of E. coli O157:H7

After discovery of electron transfer from bacteria, most bacteria known to be electrochemically active are utilized as a self-regenerable catalyst at the anode of microbial fuel cells (MFCs). However, the reverse phenomenon, cathodic catalysts is not so widely researched. This present study demonstrated that E. coli O157:H7 was electrochemically active, and it was able to catalyze oxygen reduction at the cathode of bipolar electrode (BPE). Applying a constant potential to the BPE, E. coli O157:H7 can catalyze electrochemical reduction of O2, decrease the overpotential of O2 reduction at the cathode, which in turn generates an electrochemiluminescence (ECL) reporting intensity change at the anode. Significantly, a majority of food matrix does not exhibit catalytic activity for electrochemical reduction of O2. Meanwhile, due to the physically separation of two poles of closed BPE, complex food matrix at the cathode does not interfere with the ECL reaction at the anode. Therefore, the effect of food matrix is negligible when measuring E. coli O157:H7 levels in food. A low detection limit of 10 CFU mL−1 E. coli O157:H7 could be identified within 1 h. Thus, biocathodes reducing oxygen in BPE-ECL system has shown excellent characteristics in the field of rapid detection of electroactive bacteria in food.

Intrinsic Carbon Defects for the Electrosynthesis of H2O2.

Carbon materials have manifested promising potential in electrochemical reduction of O2 to H2O2. The oxygen functional groups have been identified as the catalytic sites. However, the intrinsic carbon defects abundant in carbon materials have often been neglected. Herein, a three-dimensional carbon framework with abundant intrinsic defects and oxygen functional groups (the oxygen content and chemical states of oxygen are comparable to those of commercial carbon black) was introduced and exhibited outstanding catalytic activity and selectivity toward H2O2 electrosynthesis. Through a combination of in situ Raman spectroscopy and density functional theory calculations, the intrinsic carbon defects, such as zigzag edge and zigzag pentagon sites with optimal binding energy for OOH, were also determined to be active sites. It was further revealed that intrinsic carbon defects with large negative charge density and asymmetric spin density may have high activity toward H2O2 production.

A Sandwich-Type Electrochemical Immunosensor for Insulin Detection Based on Au-Adhered Cu5 Zn8 Hollow Porous Carbon Nanocubes and AuNP Deposited Nitrogen-Doped Holey Graphene.

Rapid, accurate, and sensitive insulin detection is crucial for managing and treating diabetes. A simple sandwich-type electrochemical immunosensor is engineered using gold nanoparticle (AuNP)-adhered metal-organic framework-derived copper-zinc hollow porous carbon nanocubes (Au@Cu5 Zn8 /HPCNC) and AuNP-deposited nitrogen-doped holey graphene (NHG) are used as a dual functional label and sensing platform. The results show that identical morphology and size of Au@Cu5 Zn8 /HPCNC enhance the electrocatalytic active sites, conductivity, and surface area to immobilize the detection antibodies (Ab2 ). In addition, AuNP/NHG has the requisite biocompatibility and electrical conductivity, which facilitates electron transport and increases the surface area of the capture antibody (Ab1 ). Significantly, Cu5 Zn8 /HPCNC exhibits necessary catalytic activity and sensitivity for the electrochemical reduction of H2 O2 using (i-t) amperometry and improves the electrochemical response in differential pulse voltammetry. Under optimal conditions, the immunosensor for insulin demonstrates a wide linear range with a low detection limit and viable specificity, stability, and reproducibility. The platform's practicality is evaluated by detecting insulin in human serum samples. All these characteristics indicate that the Cu5 Zn8 /HPCNC-based biosensing strategy may be used for the point-of-care assay of diverse biomarkers.

Second-Sphere Hydrogen-Bond Donors and Acceptors Affect the Rate and Selectivity of Electrochemical Oxygen Reduction by Iron Porphyrins Differently.

The factors that control the rate and selectivity of 4e-/4H+ O2 reduction are important for efficient energy transformation as well as for understanding the terminal step of respiration in aerobic organisms. Inspired by the design of naturally occurring enzymes which are efficient catalysts for O2 and H2O2 reduction, several artificial systems have been generated where different second-sphere residues have been installed to enhance the rate and efficiency of the 4e-/4H+ O2 reduction. These include hydrogen-bonding residues like amines, carboxylates, ethers, amides, phenols, etc. In some cases, improvements in the catalysis were recorded, whereas in some cases improvements were marginal or nonexistent. In this work, we use an iron porphyrin complex with pendant 1,10-phenanthroline residues which show a pH-dependent variation of the rate of the electrochemical O2 reduction reaction (ORR) over 2 orders of magnitude. In-situ surface-enhanced resonance Raman spectroscopy reveals the presence of different intermediates at different pH's reflecting different rate-determining steps at different pH's. These data in conjunction with density functional theory calculations reveal that when the distal 1,10-phenanthroline is neutral it acts as a hydrogen-bond acceptor which stabilizes H2O (product) binding to the active FeII state and retards the reaction. However, when the 1,10-phenanthroline is protonated, it acts as a hydrogen-bond donor which enhances O2 reduction by stabilizing FeIII-O2.- and FeIII-OOH intermediates and activating the O-O bond for cleavage. On the basis of these data, general guidelines for controlling the different possible rate-determining steps in the complex multistep 4e-/4H+ ORR are developed and a bioinspired principle-based design of an efficient electrochemical ORR is presented.

1T′-MoTe2 monolayer: A promising two-dimensional catalyst for the electrochemical production of hydrogen peroxide

The direct synthesis of hydrogen peroxide (H2O2) via a two-electron oxygen reduction reaction (2e-ORR) in acidic media has emerged as a green process for the production of this valuable chemical. However, such an approach employs expensive noble-metal-based electrocatalysts, which severely undermines its feasibility when implemented on an industrial scale. Herein, based on density functional theory computations and microkinetic modeling, we demonstrate that a novel two-dimensional (2D) material, namely a 1T′-MoTe2 monolayer, can serve as an efficient non-precious electrocatalyst to facilitate the 2e-ORR. The 1T′-MoTe2 monolayer is a stable 2D crystal that can be easily produced through exfoliation techniques. The surface-exposed Te sites of the 1T′-MoTe2 monolayer exhibit a favorable OOH* binding energy of 4.24 eV, resulting in a rather high basal plane activity toward the 2e-ORR. Importantly, kinetic computations indicate that the 1T'-MoTe2 monolayer preferentially promotes the formation of H2O2 over the competing four-electron ORR step. These desirable characteristics render 1T′-MoTe2 a promising candidate for catalyzing the electrochemical reduction of O2 to H2O2.

Temporal sensing platform based on anodic dissolution of Ag and cathodic biocatalysis of oxygen reduction for Staphylococcus aureus detection

An Ag@C hybrid bipolar electrode (BPE) sensing platform has been established for the temporal detection of Staphylococcus aureus (S. aureus) in food. Combining the advantages of anodic dissolution of Ag and cathodic biocatalysis of oxygen (O2) reduction, this strategy showed an ultralow detection limit down to 10 CFU mL−1. As the formation of Ag@C completely quenched the electrochemiluminescence (ECL) emission of luminol, the ECL emission recovery reflected the extent of anodic dissolution. Meanwhile, S. aureus catalyzed the electrochemical reduction of O2 at the cathode, reducing the overpotential for cathodic O2 reduction and thus increasing the rate of anodic electron loss, facilitating Ag dissolution and restoring the ECL emission of luminol. When a constant potential was applied, through monitoring the ECL recovery time before and after the incubation of S. aureus on the cathode, S. aureus could be quantified due to the slight difference of the conductivity.

Coupling electrode aeration and hydroxylamine for the enhanced Electro-Fenton degradation of organic contaminant: Improving H2O2 generation, Fe3+/Fe2+ cycle and N2 selectivity

To improve H2O2 generation and Fe3+/Fe2+ cycle simultaneously for enhancing Electro-Fenton performance, the electrode aeration (EA) and hydroxylamine sulfate (HA) were coupled. With dimethyl phthalate (DMP) as main target contaminant, combination of HA and EA greatly accelerated the degradation of DMP and exhibited a synergy in the pH of 2.0–6.9 through promoting the key reactions, including electrochemical two-electron reduction of O2 into H2O2 and redox cycles of Fe3+/Fe2+, which then improved the generation of hydroxyl radicals (·OH). The coupling EA and HA reduced the use of HA and converted most of HA into environment-friendly N2 (60.1–62.1% of HA products), while HA/solution aeration(SA) system consumed HA rapidly and the generated N2 only accounted for 5.8–6.7% of HA products. Furthermore, compared with HA/SA and EA Electro-Fenton systems, enhancement degree of DMP degradation in HA/EA Electro-Fenton process was higher in actual waterbody than in ultrapure water. The coupling EA and HA in the Electro-Fenton process could solve the low Fe3+/Fe2+ cycle efficiency and low H2O2 production simultaneously, and improve the N2 selectivity of HA transformation, which advanced its application in practical environmental remediation.

Improved visible-light activities of ultrathin CoPc/g-C3N4 heterojunctions by N-doped graphene modulation for selective benzyl alcohol oxidation

The interface modulation is the key factor affecting the photoactivity of metal phthalocyanine (MPc)/g-C3N4 heterojunctions for aerobic selective alcohol oxidation. Here, we have successfully fabricated the N-doped graphene-modulated CoPc/g-C3N4 nanosheets (CoPc/NG/CN) heterojunctions. Optimal CoPc/NG/CN photocatalyst demonstrates approximately fourfold photoactivity improvement for benzyl alcohol oxidation with ∼99% selectivity toward benzyl aldehyde and of approximately ninefold 2,4-dichlorophenol degradation rate compared with bare CN, using O2 as oxidant. By means of steady-state surface photovoltage responses in N2 atmosphere, time-resolved photoluminescence spectra, single-wavelength photocurrent action spectra, and electrochemical O2 reduction measurements, it is confirmed that the exceptional photoactivities of resulting CoPc/NG/CN heterojunction are attributed to the facilitated interfacial charge transfer between CoPc and CN by the modulation of NG with favorable electron-induced capacity. In addition, more enriched hydroxyl groups of NG by N doping could induce high dispersion of CoPc molecules via H-bonding effect, resulting in the increase of exposed number of CoPc as visible-light absorption units and single Co2+ sites as catalytic centers for O2 activation so as to further benefit the photocatalytic oxidation processes. This work provides a feasible interfacial modulation strategy to fabricate efficient supported MPc-based heterojunction photocatalyst nanomaterials.