Facilitating two-electron oxygen reduction with pyrrolic nitrogen sites for electrochemical hydrogen peroxide production

Modulation of the electronic structure of nitrogen-carbon sites by sp3-hybridized carbon coupled to chloride ions improves electrochemical carbon dioxide reduction performance

The challenges remain to develop cost-effective carbon-based catalysts with high activity and selectivity. Here, we synergistically modulate carbon-based electrocatalysts through Cl doping with intrinsic defects in sp3-hybridized carbon and apply them to the electrochemical CO2 reduction reaction (CO2RR). The designed electrocatalyst achieved high selectivity over a wide potential range (-0.7 to -1.0 V), with a faraday efficiency of 96.3 % at -0.8 V for CO. In situ Fourier transform infrared spectroscopy, and analytical studies show pyrrole N to be the active site of CO2RR, and doping Cl increases the content of sp3-hybridized carbon in the carbon substrate, which synergistically accelerates the supply of hydrolysis dissociated protons and facilitates the protonation process of the intermediate products from *CO2 to *COOH. Density functional theory calculations show that Cl coupled sp3-hybridized carbon inhibits the adsorption of H* in the pyrrole N site and facilitates the desorption of *CO, thus promoting the whole process of CO2RR.

Co-enhancing volatile organic compound degradation and steam generation in solar interfacial evaporation by integrating with electro-Fenton

Solar interfacial evaporation (SIE) process offers an effective and sustainable approach for alleviating freshwater shortage, but the simultaneous evaporation of volatile organic compound (VOC) limits the application of this technique. Herein, a novel electro-Fenton assisted SIE (EF/SIE) was proposed for the first time to co-enhance steam generation and VOC removal based on an evaporator composed of graphite felt decorated with Fe/N-doped porous carbon (FeNCx/GF). This dual functional evaporator integrating photothermal and electrocatalytic technology achieved a "self-sufficient" degradation process, in which FeNCx acted as the heterogeneous electrocatalyst to in-situ produce H2O2 and reactive oxidizing species (ROS) for VOC degradation at evaporator interface. As a result, the VOC removal efficiency of EF/SIE system achieved 97.8 ± 1.7 % in the condensate, which was 4.8 times that of the sole SIE system. Meanwhile, due to the Joule heating during electro-Fenton process, the conversion rate from water to vapor was accelerated, reaching an evaporation rate to 1.65 kg m-2 h-1 at the cathodic interface, while that of the sole SIE system was only 1.43 kg m-2 h-1. Additionally, an external solar cell enabled complete photo-electro-thermal conversion that ensured an excellent VOC removal efficiency (99 %) of the EF/SIE system in the outdoor experiment. The innovatively designed system also showed versatility in different water substrates. Thus, the dual functional evaporators successfully integrated SIE with EF, providing a sustainable and synergetic strategy for efficient treatment of wastewater containing VOC.

Heterostructure of Fe3O4 Confined in Hierarchical Porous Carbon for Interface-Enhanced Medical-Grade H2O2 Electrosynthesis

The electrocatalytic two-electron oxygen reduction reaction (2e- ORR) presents an environmentally sustainable approach to produce hydrogen peroxide (H2O2). Heterostructures coupling non-noble transition metal oxides (TMOs) with carbon materials hold promise for 2e- ORR, but face challenges in controlling morphology, phase composition, and active centers. In this study, a hierarchically porous tremella-like heterojunction characterized by ultrafine cubic Fe3O4 nanoparticles within the amorphous carbon (UFe3O4@HPAC) is obtained using the integrated platform of green Fe-based deep eutectic solvent via a two-step annealing process. UFe3O4@HPAC exhibits remarkable overall and intrinsic 2e- ORR activity, delivering 96% H2O2 selectivity and a turnover frequency (TOF) of 67.5 s-1. Notably, UFe3O4@HPAC possesses superior H2O2 production capabilities, showing long-term stability of 100 h with a H2O2 production rate of 8.1 g L-1 h-1 in flow-cell, while achieving various medical-grade H2O2 concentrations (3.0-7.8 wt%). Additionally, integrating on-site H2O2 production with electro-Fenton achieved rapid decomposition of contaminants. The unique heterostructure, with the synergistic effect of Fe3O4 and amorphous carbon, enhances electronic conductivity. Moreover, the electronic redistribution at the interface of the heterostructure triggers the thermodynamically favorable multiple active sites of Fe and C centers for the 2e- ORR. This work offers a new perspective on transition metal-based materials for H2O2 production.

Recent Progress in Oxygen Reduction Reaction Toward Hydrogen Peroxide Electrosynthesis and Cooperative Coupling of Anodic Reactions

Electrosynthesis of hydrogen peroxide (H2O2) via two-electron oxygen reduction reaction (2e- ORR) is a promising alternative to the anthraquinone oxidation process. To improve the overall energy efficiency and economic viability of this catalytic process, one pathway is to develop advanced catalysts to decrease the overpotential at the cathode, and the other is to couple 2e- ORR with certain anodic reactions to decrease the full cell voltage while producing valuable chemicals on both electrodes. The catalytic performance of a 2e- ORR catalyst depends not only on the material itself but also on the environmental factors. Developing promising electrocatalysts with high 2e- ORR selectivity and activity is a prerequisite for efficient H2O2 electrosynthesis, while coupling appropriate anodic reactions with 2e- ORR would further enhance the overall reaction efficiency. Considering this, here a comprehensive review is presented on the latest progress of the state-of-the-art catalysts of 2e- ORR in different media, the microenvironmental modulation mechanisms beyond catalyst design, as well as electrocatalytic system coupling 2e- ORR with various anodic oxidation reactions. This review also presents new insights regarding the existing challenges and opportunities within this rapidly advancing field, along with viewpoints on the future development of H2O2 electrosynthesis and the construction of green energy roadmaps.

Regulating the Local Reaction Microenvironment at Chromium Metal-Organic Frameworks for Efficient H2O2 Electrosynthesis in Neutral Electrolytes

The electrochemical synthesis of hydrogen peroxide represents a promising alternative to the traditional anthraquinone process, aiming for zero pollution. However, achieving efficient electrochemical synthesis of hydrogen peroxide in neutral electrolytes is challenging due to the sluggish kinetics of the two-electron oxygen reduction reaction. To address this issue, a unique metal-organic framework (MOF) featuring Cr metal sites coordinated with tetrabromoterephthalic acid (Cr-TBA) is synthesized. This specially designed MOF exhibits a distinctive paper-clip-like structure and remarkably enhanced Lewis acidity. Experimental results demonstrate that the obtained structure can facilitate the attraction of OH- ions in solution, promoting their accumulation on the catalyst surface. This enhancement leads to excellent performances of Cr-TBA in neutral electrolytes, achieving Faradaic efficiencies of 96-98% and a production rate of 13.4 mol gcat -1 h-1 at the current density of 150 mA cm-2. Operando spectroscopy and density functional theory calculations indicate that this modified microenvironment effectively facilitates the conversion of the *OOH intermediates to H2O2 on the catalyst surface.

Internal hydrogen-bond enhanced two-electron oxygen reduction reaction for π-d conjugated metal-organic framework to H2O2 synthesis

Tailoring the electronic structure of electrocatalysts for oxygen reduction reaction (ORR) has been widely adopted to optimize their performance. However, the steric effect originating from the layered or crystal structure of a catalyst is often neglected. Herein, we demonstrate the importance of such steric effect in a one-dimensional π-d conjugated metal-organic framework with Ni-(NH)4 nodes (Ni-BTA) for optimizing its electrocatalytic performance, where the activity and selectivity towards two-electron ORR for H2O2 production are largely enhanced. Theoretical simulation and in-situ characterization demonstrate the formation of inter-layer H-bonds between *OOH intermediates and -N-H groups in the adjacent top layers of the Ni-sites, enhancing the *OOH binding energy to an optimum value. Thus, the as-prepared Ni-BTA catalyst exhibits an outstanding electrocatalytic 2e--ORR performances under neutral and alkaline conditions (e.g., >85% H2O2 selectivity from -0.1-0.4 V vs. RHE and >13.5 mol g-1 h-1 H2O2 yield in neutral electrolytes), also showing great potential on water treatment and disinfection. Here, we highlight the alternative avenues for utilizing the non-coordinated structure to regulate the catalytic performance, thus providing opportunities for the design of catalysts and beyond.

A nature-inspired metal-free electrocatalyst towards efficient electron transfer and robust cascade oxygen reduction for wastewater treatment

The pressing demand for removing high-risk emerging contaminants from wastewater calls for tailored treatment strategies, for which heterogeneous electrocatalysis induced by cascade oxygen reduction reaction (ORR) holds considerable potential. This process, however, suffers from poor interfacial electron transfer and discounted performance in non-acidic conditions. Inspired by the electron respiration chain of cells, a metal-free, quinone-based catalyst (PBth-BQ) was innovatively designed and synthesized. With excellent redox reversibility over 50 cycles and no risk of metal leaching, it boosted the direct electron transfer by 110 % compared to the bare graphite substrate and facilitated cascade ORR to generate ·OH for effective contaminant abatement in the pH range of 3-13. Among them, pH 8 demonstrated the best performance, which is suitable for wastewater treatment. In particular, PBth-BQ performed well as both anodic and cathodic electrodes in azithromycin mineralization with different oxygen donors, verified by the in-situ mass spectrum. Considering the abundance of quinone-like structures in oxidized carbon materials, this biomimetic design may inspire the further exploration of cheap and efficient electrocatalysts for wastewater treatment.

Highly Selective Oxygen Electroreduction to Hydrogen Peroxide on Sulfur-Doped Mesoporous Carbon

As a paradigm-shifting material platform in energy catalysis, precisely engineered ordered mesoporous carbon spheres emerge as supreme metal-free electrocatalysts, outperforming conventional carbon-based counterparts through synergistic structural and electronic innovations. Herein, we architecturally design vertically aligned cylindrical mesoporous carbon spheres with atomic-level sulfur doping (S-mC) that establish unprecedented performance benchmarks in the two-electron oxygen reduction reaction (2e--ORR) to hydrogen peroxide. Systematic comparative studies reveal that the S-mC catalysts achieve exceptional H2O2 selectivity (>99%) and activity at current density of -3.5 mA cm-2, surpassing state-of-the-art metal-free catalysts in current density. Impressively, the optimized S-mC electrocatalyst in a flow cell device achieves an exceptional H2O2 yield of 25 mol gcatalyst -1 h-1. The carbon matrix's unique sp2/sp3 hybrid network coupled with S-induced charge redistribution generates electron-deficient hotspots that selectively stabilize *OOH intermediates, as evidenced by in situ spectroscopic characterization and DFT calculations. This structural-electronic synergy endows the carbon framework with metal-like catalytic efficiency while maintaining inherent advantages of chemical robustness and cost-effectiveness. The marriage of S-doping engineering with mesoscopic pore architecture control opens a new way for developing efficient carbon-based electrocatalysts for oxygen selective reduction to H2O2.

Norfloxacin-Derived Carbon Dots with Rich Electron Pyrrolic Nitrogen for Copper Corrosion Inhibition and Antibacterial Functions

The coexisting anticorrosion and antibacterial functions are of great significance for the marine industry. Controllable surface negative charge and wettability of pyrrolic nitrogen-doped carbon dots (NCDs) derived from the single antibiotic norfloxacin precursor with a special nitrogen heterocyclic structure were successfully fabricated through the hydrothermal route. The incorporated functional groups and chemical bonds, surface charge, mechanism of pyrrole nitrogen ring formation at the molecular level, and antibacterial properties of NCDs were revealed by FTIR, XPS, zeta potential, LC-MS, and electrochemical techniques. The present corrosion efficiency (96.1%) in 3.5 wt % NaCl saline solution in the presence of air and N2 or UO22+ is higher than most previously reported values. The proposed electron transfer corrosion mechanism suggests that the negative charge domains of NCDs were strengthened by the saltwater electron sink effect to repel chlorine and simultaneously a large number of electrons of NCDs were injected into copper as the electron reservoir based on energy-level matching, thereby avoiding Cu0 oxidization. Current works provide a guideline for exploring novel eco-friendly and highly efficient NCD corrosion inhibitor materials with antibacterial properties for safeguarding metals in seawater.

Low-temperature construction of high-density Ni single-atom sites on nitrogen-doped carbon to boost dual-channel oxygen reduction

Herein, a low-temperature ligand pre-oxidation strategy is proposed to design high-density Ni single-atom sites on amorphous nitrogen-doped carbon substrates. The obtained Ni-O@NC boosts dual-channel oxygen reduction and exhibits about 92.6% hydrogen peroxide selectivity.

Tuning the Formation Kinetics of *OOH Intermediate with Hollow Bowl-Like Carbon by Pulsed Electroreduction for Enhanced H2O2 Production

The electrochemical synthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e- ORR) is a promising alternative to the conventional anthraquinone method. However, due to local alkalinization near the catalyst surface, the restricted oxygen replenishment and insufficient activated water molecule supply limit the formation of the key *OOH intermediate. Herein, a pulsed electrocatalysis approach based on a structurally optimized S/N/O tridoped hollow carbon bowl catalyst has been proposed to overcome this challenge. In an H-type electrolytic cell, the pulsed method achieves a superior H2O2 yield rate of 55.6 mg h-1 mgcat.-1, approximately 1.6 times higher than the conventional potentiostatic method (34.2 mg h-1 mgcat.-1), while maintaining the Faradaic efficiency above 94.6%. In situ characterizations, finite element simulations, and density functional theory analyses unveil that the application of pulsed potentials mitigates the local OH- concentration, enhances the water activation and proton generation, and facilitates oxygen production within the hollow bowl-like carbon structure. These effects synergistically accelerate the formation kinetics of the *OOH intermediate by the efficient generation of *O2 and *H2O intermediates, leading to superior H2O2 yields. This work develops a strategy to tune catalytic environments for diverse catalytic applications.

Noble-Metal-Free Electrocatalysts for Selective Hydrogen Peroxide Generation via Oxygen Reduction Reaction

Hydrogen peroxide (H2O2) is a versatile chemical widely used in various industries. The traditional anthraquinone method for H2O2 synthesis has environmental and safety concerns due to the use of organic solvents and hazardous by-products. The direct synthesis of H2O2 from H2 and O2 poses risks of flammability and explosion. Recently, the 2-electron oxygen reduction reaction (2e- ORR) method has emerged as a promising alternative, offering safety, environmental friendliness, and cost-effectiveness. This method utilizes gas diffusion electrodes to efficiently generate H2O2 without the need for additional dilution. In this review, we focus on the recent advancements in noble-metal-free materials for 2e- ORR electrocatalysis, which play a crucial role in the efficient production of H2O2. These materials, including transition metal compounds, macrocyclic complexes, carbon-based catalysts, framework materials, and MXenes catalysts, demonstrate significant advantages in enhancing H2O2 yield. The development of these non-precious metal catalysts can reduce costs and improve sustainability and promote the commercialization of related technologies. The review concludes with an outlook on the future trends of 2e- ORR electrocatalysts.

Heteroatom-Substituted Reflashed Graphene

Flash Joule heating is an ultrafast, energy-efficient, and scalable technique used in the production of a variety of organic and inorganic compounds, including flash graphene. This technique has also been used in the production of doped graphene by flash Joule heating of amorphous carbon in the presence of heteroatom-donating compounds. Herein, we report a modified flash Joule heating technique by which graphene is formed with up to 18 atom % of the graphene lattice containing substituted heteroatoms. This is achieved by reflashing graphene in the presence of heteroatom-donating compounds, allowing this substitution to occur at lower temperatures than previously reported for flash Joule heating-synthesized doped graphene and thereby permitting much higher amounts of heteroatom insertion into the graphene lattice. We demonstrate nitrogen, sulfur, phosphorus, and fluorine atom atomic substitution into or upon the graphene lattice, as well as multiheteroatom substitution. Finally, the implementation of the nitrogen-substituted reflashed graphene into battery anodes exhibits improved performance and stability relative to unsubstituted reflashed graphene battery anodes.

Vacancy-Activated B-Doping for Efficient 2e- Oxygen Reduction through Suppressing H2O2 Decomposition at High Overpotential

The production of hydrogen peroxide (H2O2) through two-electron oxygen reduction reaction (2e- ORR) has emerged as a more environmentally friendly alternative to the traditional anthraquinone method. Although oxidized carbon catalysts have intensive developed due to their high selectivity and activity, the yield and conversion rate of H2O2 under high overpotential still limited. The produced H2O2 was rapidly consumed by the increased intensity of H2O2 reduction, which could ascribe to decomposition of peroxide radicals under high voltage in the carbon catalyst. To overcome this issue, a B doped carbon have been developed to catalyze 2e- ORR with high efficient through suppressing H2O2 decomposition at high potential. Thus, thermal reducing of oxygen containing groups (OCGs) on graphite could construct defects and vacancies, which in situ convert to B-Cx subunits on the edge of graphene sheets. The introduction of B-Cx effectively prevented the decomposition of the *O-O bond and provided suitable adsorption capacity for *OOH, achieving excellent selectivity for the 2e- ORR across a wide voltage range. Finally, a remarkable H2O2 yield of 7.91 mmol cm-2 h-1 was delivered at an industrial current density of 600 mA cm-2, which could provide "green" pathway for scale-upable synthesis H2O2.

Chemical and functional inheritance of carbon quantum dots hydrothermally-derived from chitosan

Owing to their extremely small size, carbon-quantum-dots (CQDs) can cross biological barriers, which makes them attractive for many biomedical and other applications. CQDs can retain key-chemical features and associated functionalities of the molecular sources they are derived from, provided a suitable synthesis method is used at relative mild carbonization temperatures. Here we demonstrate that CQDs hydrothermally-derived from chitosan or 2-hydroxypropyltrimethyl ammonium-chloride (HAC)-chitosan under pressurized conditions at 180 °C have a comparable elemental and molecular composition, as determined using X-ray photoelectron spectroscopy and Fourier-transform-infrared spectroscopy. In addition, both types of CQDs generated reactive-oxygen-species as an added functionality alien to their molecular carbon sources. As a result, CQDs exhibited stronger antibacterial properties against a Gram-positive Staphylococcus aureus and a Gram-negative Escherichia coli strain, while both molecular HAC-chitosan as well as CQDs derived from it had stronger antibacterial properties than molecular chitosan and chitosan CQDs due to the possession of quaternary ammonium groups in HAC-chitosan. Therewith, carbonization of chitosan and HAC-chitosan yields enhanced properties that can be beneficial in a high variety of different applications, including promotion of healing and bacterial infection control, preservation of food and beverages, pesticide control in agriculture and horticulture, water treatment and in many cosmetics and personal care products.

A Chlorine-Resistant Self-Doped Nanocarbon Catalyst for Boosting Hydrogen Peroxide Synthesis in Seawater

Developing seawater-compatible hydrogen peroxide (H2O2) electroproduction technologies is crucial for advancing marine resource utilization in coastal regions. However, designing efficient and highly stable non-noble metal catalysts for two-electron oxygen reduction reaction (2e- ORR) in seawater environment remains a challenging task due to the corrosive and toxic nature of chloride ions (Cl-). Herein, we present, for the first time, a novel nitrogen and oxygen self-doped defect-rich nanocarbon (NO-DC700) catalyst, derived from silk fiber, which addresses these challenges with low toxicity, cost-effectiveness, and high adaptability. The obtained NO-DC700 catalyst demonstrates an impressive H2O2 production rate of up to 4997 mg L-1 h-1, a high Faradaic efficiency of 96.5 %, and produces 4.3 wt % H2O2 after 20 hours of stable operation, placing it among the highest-performing catalysts reported in neutral electrolytes. Theoretical calculations reveal that NO-DC700's superior 2e- ORR performance is due to the synergistic effect of graphitic nitrogen and C-OH, which inhibits Cl- adsorption and promotes *OOH adsorption. Additionally, integrating 2e- ORR with Fenton-like technology enables rapid degradation of organic pollutants and effective inactivation of seawater algae, offering significant potential for mitigating coastal eutrophication and red tide pollution. This work provides valuable insights into H2O2 electrosynthesis in seawater solution and promises advancements in ocean-energy applications.

A facile synthesis of N-doped carbon encapsulated multimetallic carbonitride as a robust electrocatalyst for oxygen evolution reaction

Electrocatalytic water splitting is a promising solution for generating clean hydrogen. Transition metal compounds are among the most extensively investigated catalysts developed to date for water oxidation in alkaline media, a process also known as the oxygen evolution reaction (OER). However, the application of these catalysts was constrained by insufficient stability arising from surface oxidation and metal dissolution under high OER potential. In this work, we developed a facile approach using urea-based gel as the precursor of preparing a series of multimetallic carbonitride particles which were encapsulated by N-doped carbon (NC). In particular, (MoCoFeNiZr)CN@NC core-shell structure delivered a low overpotential of 246 mV at a current density of 10 mA cm-2 in 1 M KOH during OER. Importantly, operando differential electrochemical mass spectrometry (DEMS), together with multiple microscopic and spectroscopic analyses, indicated that the NC shells effectively maintained the crystalline stability of carbonitride via suppressing the surface reconstruction during catalysis. The highly graphitic NC also demonstrates excellent stability against oxidation. This work shows a promising strategy of stabilizing electrocatalyst at high anodic potential, paving the way for the development of robust electrode materials for energy conversion.

Organogel Polymer Electrocatalysts for Two-Electron Oxygen Reduction

Polymer gels, renowned for unparalleled chemical stability and self-sustaining properties, have garnered significant attention in electrocatalysis. Notably, organic polymer gels that exhibit temperature sensitivity and incorporate suitable polar nonvolatile liquids, enhance electronic conductivity, and impart distinct morphological features, but remain largely unexplored as electrocatalysts for oxygen reduction reaction (ORR). To address this issue, an innovative strategy is proposed for synergistic modulation of the rigidity of mainchain molecular skeleton and length of alkyl sidechains, enabling the development of organogel polymers with a sol-gel temperature-sensitive phase transition that promises high selectivity and enhanced activity in electrocatalytic processes. Notably, the shortening of alkyl sidechain length can significantly affect the gelation behavior and internal microstructure of the catalyst, which modifies the electron state, ultimately impacting the catalytic activity of the gel polymer catalysts. In particular, phenyl-containing Ph-FL1 with short alkyl sidechains demonstrates outstanding 2e- ORR activity in alkaline medium, achieving a remarkable hydrogen peroxide (H2O2) selectivity of 98.6% with an impressive yield of 4.08 mol g-1 h-1. This performance surpasses most metal-free carbon-based electrocatalysts. Through theoretical calculation, the carbon atom (site-3) of C═N group is identified as potential active sites, representing a significant advancement toward designing cost-effective and efficient ORR electrocatalysts.

An efficient electrocatalytic in-situ hydrogen peroxide generation for ballast water treatment with oxygen groups

The in-situ electrochemical production of hydrogen peroxide (H2O2) offers a promising approach for ballast water treatment. However, further advancements are required to develop electrocatalysts capable of achieving efficient H2O2 generation in seawater environments. Herein, we synthesized two-dimensional lamellated porous carbon nanosheets enriched with oxygen functional groups, which exhibited exceptional performance in H2O2 electrosynthesis. The carbon nanosheet electrocatalysts demonstrated high selectivity for H2O2 production, reaching 90 % at 0.33 V vs. RHE under neutral conditions. Maximum yields were achieved at 2238 mmol gcat-1 h-1 at -0.5 V in an H-type electrolysis cell and 3681 mmol gcat-1 h-1 at a current density of 150 mA cm-2 in a flow cell, with Faraday efficiencies exceeding 70 %. Notably, a continuous 9-hour electrosynthesis test produced a high cumulative H2O2 concentration of 1.2 wt% at a current density of 100 mA cm-2, highlighting the stability and scalability of carbon nanosheets. The outstanding performance of carbon nanosheets is attributed to the abundant basal plane C-O-C group, which provide optimal *OOH binding energy and minimal overpotential. Additionally, the in-situ generated H2O2 from the electrocatalytic system achieved complete sterilization within 60 min against Escherichia coli and several marine bacterial strains isolated from seawater. Furthermore, treatment of real seawater with H2O2 significantly altered the bacterial population abundance at both the phylum and genus levels, highlighting its effectiveness in microbial control. This study presents a high-performance electrocatalytic system for ballast water treatment, offering both scalability and environmental sustainability.

Nature-Inspired N, O Co-Coordinated Manganese Single-Atom Catalyst for Efficient Hydrogen Peroxide Electrosynthesis

The two-electron oxygen reduction reaction (2e- ORR) is a pivotal pathway for the distributed production of hydrogen peroxide (H2O2). In nature, enzymes containing manganese (Mn) centers can convert reactive oxygen species into H2O2. However, Mn-based heterogeneous catalysts for 2e- ORR are scarcely reported. Herein, we developed a nature-inspired single-atom electrocatalyst comprising N, O co-coordinated Mn sites, utilizing carbon dots as the modulation platform (Mn CD/C). As-synthesized Mn CD/C exhibited exceptional 2e- ORR activity with an onset potential of 0.786 V and a maximum H2O2 selectivity of 95.8 %. Impressively, Mn CD/C continuously produced 0.1 M H2O2 solution at 200 mA/cm2 for 50 h in the flow cell, with negligible loss in activity and H2O2 faradaic efficiency, demonstrating practical application potential. The enhanced activity was attributed to the incorporation of Mn atomic sites into the carbon dots. Theoretical calculations revealed that the N, O co-coordinated structure, combined with abundant oxygen-containing functional groups on the carbon dots, optimized the binding strength of intermediate *OOH at the Mn sites to the apex of the catalytic activity volcano. This work illustrates that carbon dots can serve as a versatile platform for modulating the microenvironment of single-atom catalysts and for the rational design of nature-inspired catalysts.

Fragmented Polymetric Carbon Nitride with Rich Defects for Boosting Electrochemical Synthesis of Hydrogen Peroxide in Alkaline and Neutral Media

Electrocatalytic oxygen reduction reaction via 2e- pathway is a safe and friendly route for hydrogen peroxide (H2O2) synthesis. In order to achieve efficient synthesis of H2O2, it is essential to accurately control the active sites. Here, fragmented polymetric carbon nitride with rich defects (DCN) is designed for H2O2 electrosynthesis. The multi-type defects, including the sodium atom doping in six-fold cavities, the boron atom doping at N-B-N sites and the cyano groups, are successfully created. Owing to the synergistic effect of these defects, the fragmented DCN achieves a high H2O2 production rate of 2.28 mol gcat. -1 h-1 and a high Faradic efficiency of nearly 90 % in alkaline media at 0.4 V vs. RHE in H-type cell. In neutral media, the H2O2 concentration produced by DCN can reach 1815 μM within 6 h at a potential of 0.2 V vs. RHE, and the H2O2 production rate of DCN is 0.23 mol gcat. -1 h-1. In addition, DCN shows excellent long-term durability in alkaline and neutral media. This study provides a new approach for the development of the boron, nitrogen doped carbon-based electrocatalysts for H2O2 electrochemical synthesis.

Structural Modulation of Nanographenes Enabled by Defects, Size and Doping for Oxygen Reduction Reaction

Nanographenes are among the fastest-growing materials used for the oxygen reduction reaction (ORR) thanks to their low cost, environmental friendliness, excellent electrical conductivity, and scalable synthesis. The perspective of replacing precious metal-based electrocatalysts with functionalized graphene is highly desirable for reducing costs in energy conversion and storage systems. Generally, the enhanced ORR activity of the nanographenes is typically deemed to originate from the heteroatom doping effect, size effect, defects effect, and/or their synergistic effect. All these factors can efficiently modify the charge distribution on the sp2-conjugated carbon framework, bringing about optimized intermediate adsorption and accelerated electron transfer steps during ORR. In this review, the fundamental chemical and physical properties of nanographenes are first discussed about ORR applications. Afterward, the role of doping, size, defects, and their combined influence in boosting nanographenes' ORR performance is introduced. Finally, significant challenges and essential perspectives of nanographenes as advanced ORR electrocatalysts are highlighted.

Metal-organic frameworks as thermocatalysts for hydrogen peroxide generation and environmental antibacterial applications

Reactive oxygen species (ROS) are highly reactive, making them useful for environmental and health applications. Traditionally, photocatalysts and piezocatalysts have been used to generate ROS, but their utilization is limited by various environmental and physical constraints. This study introduces metal-organic frameworks (MOFs) as modern thermocatalysts efficiently producing hydrogen peroxide (H2O2) from small temperature differences. Temperature fluctuations, abundant in daily life, offer tremendous potential for practical thermocatalytic applications. As proof of concept, MOF materials coated onto carbon fiber fabric (MOF@CFF) created a thermocatalytic antibacterial filter. The study compared three different MOFs (CuBDC, MOF-303, and ZIF-8) with bismuth telluride (Bi2Te3), a known thermocatalytic material. ZIF-8 demonstrated superior H2O2 generation under low-temperature differences, achieving 96% antibacterial activity through temperature variation cycles. This work advances potential in thermoelectric applications of MOFs, enabling real-time purification and disinfection through H2O2 generation. The findings open interdisciplinary avenues for leveraging thermoelectric effects in catalysis and various technologies.

Species mass transfer governs the selectivity of gas diffusion electrodes toward H2O2 electrosynthesis

The meticulous design of advanced electrocatalysts and their integration into gas diffusion electrode (GDE) architectures is emerging as a prominent research paradigm in the H2O2 electrosynthesis community. However, it remains perplexing that electrocatalysts and assembled GDE frequently exhibit substantial discrepancies in H2O2 selectivity during bulk electrolysis. Here, we elucidate the pivotal role of mass transfer behavior of key species (including reactants and products) beyond the intrinsic properties of the electrocatalyst in dictating electrode-scale H2O2 selectivity. This tendency becomes more pronounced in high reaction rate (current density) regimes where transport limitations are intensified. By utilizing diffusion-related parameters (DRP) of GDEs (i.e., wettability and catalyst layer thickness) as probe factors, we employ both short- and long-term electrolysis in conjunction with in-situ electrochemical reflection-absorption imaging and theoretical calculations to thoroughly investigate the impact of DRP and DRP-controlled local microenvironments on O2 and H2O2 mass transfer. The mechanistic origins of diffusion-dependent conversion selectivity at the electrode scale are unveiled accordingly. The fundamental insights gained from this study underscore the necessity of architectural innovations for mainstream hydrophobic GDEs that can synchronously optimize mass transfer of reactants and products, paving the way for next-generation GDEs in gas-consuming electroreduction scenarios.

In-depth understanding the synergisms of Cu atomic clusters on Cu single atoms for highly effective electrocatalytic oxygen reduction reaction and Zn-Air battery

In this paper, a novel, simple and mild soft template assisted strategy and further carbonization approach has been constructed to the size-tunable preparation of porous Cu-N-C/Surfactant catalysts successfully. Note that the pluronic F127 has a significant influence on the synthesis of porous Cu-N-C/F127 with the atomically dispersed Cu-N4 and adjacent Cu atomic clusters (ACs) than other surfactants owing to their particular non-ionic structure. By combining a series of experimental analysis and density functional theory (DFT) calculations, the synergistic effects between the adjacent Cu ACs and atomically dispersed Cu-N4 are favorable for manipulating the binding energy of O2 adsorption and intermediates desorption at the atomic interface of catalysts, resulting in an excellent electrocatalytic ORR performance with a faster kinetics for Cu-N-C/F127 than those of the Cu-N-C, Cu-N-C/CTAB, Cu-N-C/SDS, and comparable with the commercial Pt/C catalyst. This method not only provides a novel approach for synthesizing highly effective copper based single atom catalysts toward ORR, but also offers an in-depth understanding of the synergisms of adjacent ACs on the Cu single atoms (SAs) for highly effective electrocatalytic ORR and Zn-air Battery.

Exploration of the mechanism of levofloxacin removal by N-doped-induced interfacial micro-electric field-activated persulfate

The defects formed by N doping always coexist with pyrrole nitrogen (Po) and pyridine nitrogen (Pd), and the synergistic mechanisms of H2O2 production and PMS activation between the different Po: Pd are unknown. This paper synthesized MOF-derived carbon materials with different nitrogen-type ratios as cathode materials in an electro-Fenton system using precursors with different nitrogen-containing functional groups. Several catalysts with different Po: Pd ratios (0:4, 1:3, 2:2, 3:1, 4:0) were prepared, and the best catalyst for LEV degradation was FC-CN (Po: Pd=3:1). X-ray Photoelectron Spectroscopy (XPS) and density-functional theory (DFT) calculations show that the introduction of nitrogen creates an interfacial micro-electric field (IMEF) in the carbon layer and the metal, accelerates the electron transfer from the carbon layer to the Co atoms, and promotes cycling between the Fe3+/Co2+ redox pairs, with the electron transfer reaching a maximum at Po: Pd = 3:1. FC-CN (Po: Pd=3:1) achieved more than 95 % LEV degradation in 90 min at pH = 3-9, with a lower energy consumption of 0.11 kWh m-3 order-1. and the energy consumption of the catalyst for LEV degradation is lower than that of those catalysts reported. In addition, the degradation pathway of LEV was proposed based on UPLC-MS and Fukui function. This study offers some valuable information for the application of MOF derivatives.

Double coordination shell modulation of nitrogen-free atomic manganese sites for enhancing oxygen reduction performance

The rational design and fabrication of the active sites of single-atom catalysts (SACs) remains the main breakthrough for efficient electrocatalytic oxygen reduction reaction (ORR). Although metal-nitrogen-carbon (M-N-C) materials have been reported to exhibit good ORR performance, the M-N bond is prone to oxidation and subsequent destruction in Fenton-like reactions. Here, we report a nitrogen-free Mn-based SAC (Mn-S1O4G-600) anchored on a nitrogen-free graphene substrate, where manganese is bound to four oxygen atoms and one sulfur atom across two different coordination shells. In 0.1 M KOH, the Mn-S1O4G-600 demonstrates a half-wave potential of 0.86 V and a high kinetic current density of 10.3 mA cm-2 at 0.6 V. Due to the lack of nitrogen coordination, the Mn-S1O4G-600 has good anti-Fenton reaction properties. Notably, the Mn-S1O4G-600-based zinc-air battery displays an open circuit voltage of 1.46 V and outstanding cycle stability, which is superior to Pt/C. Theoretical calculations reveal that the introduction of the second S-coordination layer increases the charge density of the manganese center and decreases the energy barrier. This work identifies a novel active coordination configuration model for the ORR, paving the way for innovative design and synthesis of efficient SACs.

The Still Elusive Role of Lightweight Doping in Carbon-Based Electrocatalysts for the Selective Oxygen Reduction Reaction to Hydrogen Peroxide

The two-electron electrocatalytic oxygen reduction reaction (ORR) to hydrogen peroxide (H2O2) is a valuable alternative to the more conventional and energy-intensive anthraquinone process. From a circularity viewpoint, metal-free catalysts constitute a sustainable alternative for the process. In particular, lightweight hetero-doped C-materials are cost-effective and easily scalable samples that replace - more and more frequently - the use of critical raw elements in the preparation of highly performing (electro)catalysts. Anyhow, their large-scale exploitation in industrial processes still suffers from technical limits of samples upscale and reproducibility other than a still moderate comprehension of their action mechanism in the process. This concept article offers a comprehensive and exhaustive "journey" through the most representative lightweight hetero-doped C-based electrocatalysts and their performance in the 2e- ORR process. It provides an interpretation of phenomena at the triple-phase interface of solid catalyst, liquid electrolyte and gaseous oxygen based on the doping-driven generation of ideal electronic microenvironments at the catalyst surface.

Consolidating the Oxygen Reduction with Sub-Polarized Graphitic Fe-N4 Atomic Sites for an Efficient Flexible Zinc-Air Battery

The effectuation of the Zn-air battery (ZAB) is appealing for active and durable catalysts to kinetically drive the sluggish cathodic oxygen reduction reaction (ORR). Atomic metal-Nx-C sites are widely witnessed with Pt-like activity, but their demetalations still severely restrict the durability in ORR. Here we have profiled an ordered hierarchical porous carbon supported Fe-N4 single-atom (FeNC) catalyst by a template derivation method for efficient ORR and flexible ZAB studies. The FeNC structure is observed with a sub-polarized graphitic Fe-N4 coordination with a shortened Fe-N bond for potentially consolidating the ORR, together with the hierarchical porous matrix for kinetical mass transfer. Resultantly, the optimized FeNC catalyst showcases Pt-beyond alkaline ORR activity (E1/2 = 0.95 V) with long-term durability for 100 h, delivering the flexible ZAB device with high power density (251 mW cm-2) and durable cycle life (80 h). This research underscores the criterion in rationalizing active and robust ORR catalysts through metal-nitrogen bond modulation.

A Computation-Guided Design of Highly Defined and Dense Bimetallic Active Sites on a Two-Dimensional Conductive Metal-Organic Framework for Efficient H2O2 Electrosynthesis

Electrochemical synthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e--ORR) provides an alternative method to the energy-intensive anthraquinone method. Metal macrocycles with precise coordination are widely used for 2e--ORR electrocatalysis, but they have to be commonly loaded on conductive substrates, thus exposing a large number of 2e--ORR-inactive sites that result in poor H2O2 production rate and efficiency. Herein, guided by first-principle predictions, a substrate-free and two-dimensional conductive metal-organic framework (Ni-TCPP(Co)), composed of CoN4 sites in porphine(Co) centers and Ni2O8 nodes, is designed as a multi-site catalyst for H2O2 electrosynthesis. The approperiate distance between the CoN4 and Ni2O8 sites in Ni-TCPP(Co) weakens the electron transfer between them, thus ensuring their inherent activities and creating high-density active sites. Meanwhile, the intrinsic electronic conductivity and porosity of Ni-TCPP(Co) further facilitate rapid reaction kinetics. Therefore, outstanding 2e--ORR electrocatalytic performance has been achieved in both alkaline and neutral electrolytes (>90 %/85 % H2O2 selectivity within 0-0.8 V vs. RHE and >18.2/18.0 mol g-1 h-1 H2O2 yield under alkaline/neutral conditions), with confirmed feasibility for water purification and disinfection applications. This strategy thus provides a new avenue for designing catalysts with precise coordination and high-density active sites, promoting high-efficiency electrosynthesis of H2O2 and beyond.

Sludge-derived hydrochar modulates complete nonradical electron transfer in peroxydisulfate activation via pyrrolic-N and carbon defect: Implication for degrading electron-rich ionizable anilines compounds

Nonradical electron transfer process (ETP) is a promising pathway for pollutant degradation in peroxydisulfate-based advanced oxidation processes (PDS-AOPs). However, there is a critical bottleneck to trigger ETP by sludge-derived hydrochar due to its negatively charged surface, inferior porosity and electrical conductivity. Herein, pyrrolic-N doped and carbon defected sludge-derived hydrochar (SDHC-N) was constructed for PDS activation to degrade anilines ionizable organic compounds (IOC) through complete nonradical ETP oxidation. Degradation of anilines IOC was not only affected by the electron-donating capacity but also proton concentration in solution because of the ionizable amino group (-NH2). Diverse effects including proton favor, insusceptible and inhibition were observed. Impressively, addition of HCO3 with strong proton binding capacity boosted aniline degradation nearly 10 times. Moreover, characterizations and theoretical calculations demonstrated that pyrrolic-N increased electron density and created positively charged surface, profoundly promoting generation of SDHC-N-S2O82-* complexes. More delocalized electrons around carbon defect could enhance electron mobility. This work guides a rational design of sludge-derived hydrochar to mediate nonradical ETP oxidation, and provides insights into the impacts of proton on anilines IOC degradation.

Energy-Saving Ambient Electrosynthesis of Nylon-6 Precursor Coupled with Electrocatalytic Upcycling of Polyethylene Terephthalate

Cyclohexanone oxime is an important intermediate in the chemical industry, especially for the manufacture of nylon-6. The traditional cyclohexanone oxime production strongly relies on cyclohexanone-hydroxylamine and cyclohexanone ammoxidation processes, which require harsh reaction conditions and consume considerable amounts of energy. Herein, direct electrosynthesis of cyclohexanone oxime is reported from environmental pollutants nitrite and cyclohexanone with almost 100% yield by using low-cost Cu2Se nanosheets as electrocatalysts. Combination of in situ Fourier transform infrared spectroscopy and theoretical calculations verifies that the p-d orbital hybridization between Cu and Se elements could synergistically optimize the surface electronic structure and enable improved adsorption and formation of the key active N intermediate NH2OH*, thereby enhancing cyclohexanone/nitrite-to-cyclohexanone oxime conversion over the Cu2Se nanosheets. Based on these, an efficient asymmetric co-electrolysis system is further demonstrated by coupling cyclohexanone/nitrite-to-cyclohexanone oxime conversion with the upcycling of polyethylene terephthalate plastics, achieveing energy-saving simultaneously production of value-added products (cyclohexanone oxime and glycolic acid).

Photovoltaic-driven stable electrosynthesis of H2O2 in simulated seawater and its disinfection application

Electrosynthesis of H2O2 through O2 reduction in seawater provides bright sight on the H2O2 industry, which is a prospective alternative to the intensively constructed anthraquinone process. In this work, a photovoltaic-driven flow cell system is built for the electrosynthesis of H2O2 in simulated seawater using N-doped carbon catalysts. The N-doped carbon catalysts with multiple N-doped carbon defects can achieve a record-high H2O2 production rate of 34.7 mol gcatalyst -1 h-1 under an industrially relevant current density of 500 mA cm-2 and a long-term stability over 200 h in simulated seawater (0.5 M NaCl). When driven by the photovoltaic system, a H2O2 solution of ∼1.0 wt% in 0.5 M NaCl is also obtained at about 700 mA cm-2. The obtained solution is applied for disinfection of mouse wounds, with a removal rate of 100% for Escherichia coli and negligible toxicity to living organisms. It provides bright prospects for large-scale on-site H2O2 production and on-demand disinfection.

Progress and Opportunities in Photocatalytic, Electrocatalytic, and Photoelectrocatalytic Production of Hydrogen Peroxide Coupled with Biomass Valorization

Hydrogen peroxide (H2O2) has been considered an energy carrier (fuel) and oxidizer for various chemical synthesis and environmental remediation processes. Biomass valorization can generate high-value-added products in a green and pollution-free way to solve the energy and environmental crisis. The biomass valorization coupled with H2O2 generation via photo-, electro-, and photoelectrocatalysis plays a positive role in sustainable targets, which can maximize energy utilization and realize the production of value-added products and fuel synthesis. Recently, catalyst design and mechanism studies in H2O2 generation coupled with biomass valorization are in the infancy stage. Herein, this review begins with a background on photo-, electro-, and photoelectrocatalytic techniques for H2O2 generation, biomass valorization, and the H2O2 generation couples with biomass valorization. Meanwhile, the progress and reaction mechanism are reviewed. Finally, the prospects and challenges of a synergistic coupled system of H2O2 synthesis and value-added biomass in achieving high conversion, selectivity, and reaction efficiency are envisioned.

Advanced Nanocarbons Toward two-Electron Oxygen Electrode Reactions for H2O2 Production and Integrated Energy Conversion

Hydrogen peroxide (H2O2) plays a pivotal role in advancing sustainable technologies due to its eco-friendly oxidizing capability. The electrochemical two-electron (2e-) oxygen reduction reaction and water oxidation reaction present an environmentally green method for H2O2 production. Over the past three years, significant progress is made in the field of carbon-based metal-free electrochemical catalysts (C-MFECs) for low-cost and efficient production of H2O2 (H2O2EP). This article offers a focused and comprehensive review of designing C-MFECs for H2O2EP, exploring the construction of dual-doping configurations, heteroatom-defect coupling sites, and strategic dopant positioning to enhance H2O2EP efficiency; innovative structural tuning that improves interfacial reactant concentration and promote the timely release of H2O2; modulation of electrolyte and electrode interfaces to support the 2e- pathways; and the application of C-MFECs in reactors and integrated energy systems. Finally, the current challenges and future directions in this burgeoning field are discussed.

Enhanced Electron Delocalization Induced by Ferromagnetic Sulfur doped C3N4 Triggers Selective H2O2 Production

For the 2D metal-free carbon catalysts, the atomic coplanar architecture enables a large number of pz orbitals to overlap laterally, thus forming π-electron delocalization, and the delocalization degree of the central atom dominates the catalytic activity. Herein, designing sulfur-doped defect-rich graphitic carbon nitride (S-Nv-C3N4) materials as a model, we propose a strategy to promote localized electron polarization by enhancing the ferromagnetism of ultra-thin 2D carbon nitride nanosheets. The introduction of sulfur (S) further promotes localized ferromagnetic coupling, thereby inducing long-range ferromagnetic ordering and accelerating the electron interface transport. Meanwhile, the hybridization of sulfur atoms breaks the symmetry and integrity of the unit structure, promotes electron enrichment and stimulating electron delocalization at the active site. This optimization enhances the *OOH desorption, providing a favorable kinetic pathway for the production of hydrogen peroxide (H2O2). Consequently, S-Nv-C3N4 exhibits high selectivity (>95 %) and achieves a superb H2O2 production rate, approaching 4374.8 ppm during continuous electrolysis over 300 hour. According to theoretical calculation and in situ spectroscopy, the ortho-S configuration can provide ferromagnetic perturbation in carbon active centers, leading to the electron delocalization, which optimizes the OOH* adsorption during the catalytic process.

Active nitrogen sites on nitrogen doped carbon for highly efficient associative ammonia decomposition

Nitrogen doped carbon materials have been studied as catalyst support for ammonia decomposition. There are 4 different types of nitrogen environments (graphitic, pyrrolic, pyridinic and nitrogen oxide) on the amorphous support identified. In this paper, we report a 5%Ru on MgCO3 pre-treated nitrogen doped carbon catalyst with high content of edge nitrogen-containing sites which displays an ammonia conversion rate of over 90% at 500°C and WHSV = 30,000 mL gcat -1 h-1. It also gives an impressive hydrogen production rate of 31.3 mmol/(min gcat) with low apparent activation energy of 43 kJ mol-1. Fundamental studies indicate that the distinct average Ru-N4 coordination site on edge regions is responsible for such high catalytic activity. Ammonia is stepwise decomposed via a Ru-N(H)-N(H)-Ru intermediate. This associative mechanism circumvents the direct cleavage of energetic surface nitrogen from metal to form N2 hence lowering the activation barrier for the decomposition over this catalyst.

Advancing H2O2 electrosynthesis: enhancing electrochemical systems, unveiling emerging applications, and seizing opportunities

Hydrogen peroxide (H2O2) is a highly desired chemical with a wide range of applications. Recent advancements in H2O2 synthesis center on the electrochemical reduction of oxygen, an environmentally friendly approach that facilitates on-site production. To successfully implement practical-scale, highly efficient electrosynthesis of H2O2, it is critical to meticulously explore both the design of catalytic materials and the engineering of other components of the electrochemical system, as they hold equal importance in this process. Development of promising electrocatalysts with outstanding selectivity and activity is a prerequisite for efficient H2O2 electrosynthesis, while well-configured electrolyzers determine the practical implementation of large-scale H2O2 production. In this review, we systematically summarize fundamental mechanisms and recent achievements in H2O2 electrosynthesis, including electrocatalyst design, electrode optimization, electrolyte engineering, reactor exploration, potential applications, and integrated systems, with an emphasis on active site identification and microenvironment regulation. This review also proposes new insights into the existing challenges and opportunities within this rapidly evolving field, together with perspectives on future development of H2O2 electrosynthesis and its industrial-scale applications.

Efficient Neutral H2O2 Electrosynthesis from Favorable Reaction Microenvironments via Porous Carbon Carrier Engineering

The efficient electrosynthesis of hydrogen peroxide (H2O2) via two-electron oxygen reduction reaction (2e- ORR) in neutral media is undoubtedly a practical route, but the limited comprehension of electrocatalysts has hindered the system advancement. Herein, we present the design of model catalysts comprising mesoporous carbon spheres-supported Pd nanoparticles for H2O2 electrosynthesis at near-zero overpotential with approximately 95 % selectivity in a neutral electrolyte. Impressively, the optimized Pd/MCS-8 electrocatalyst in a flow cell device achieves an exceptional H2O2 yield of 15.77 mol gcatalyst -1 h-1, generating a neutral H2O2 solution with an accumulated concentration of 6.43 wt %, a level sufficiently high for medical disinfection. Finite element simulation and experimental results suggest that mesoporous carbon carriers promote O2 enrichment and localized pH elevation, establishing a favorable microenvironment for 2e- ORR in neutral media. Density functional theory calculations reveal that the robust interaction between Pd nanoparticles and the carbon carriers optimized the adsorption of OOH* at the carbon edge, ensuring high active 2e- process. These findings offer new insights into carbon-loaded electrocatalysts for efficient 2e- ORR in neutral media, emphasizing the role of carrier engineering in constructing favorable microenvironments and synergizing active sites.

Atomic-Level Engineered Cobalt Catalysts for Fenton-Like Reactions: Synergy of Single Atom Metal Sites and Nonmetal-Bonded Functionalities

Single atom catalysts (SACs) are atomic-level-engineered materials with high intrinsic activity. Catalytic centers of SACs are typically the transition metal (TM)-nonmetal coordination sites, while the functions of coexisting non-TM-bonded functionalities are usually overlooked in catalysis. Herein, the scalable preparation of carbon-supported cobalt-anchored SACs (CoCN) with controlled Co─N sites and free functional N species is reported. The role of metal- and nonmetal-bonded functionalities in the SACs for peroxymonosulfate (PMS)-driven Fenton-like reactions is first systematically studied, revealing their contribution to performance improvement and pathway steering. Experiments and computations demonstrate that the Co─N3C coordination plays a vital role in the formation of a surface-confined PMS* complex to trigger the electron transfer pathway and promote kinetics because of the optimized electronic state of Co centers, while the nonmetal-coordinated graphitic N sites act as preferable pollutant adsorption sites and additional PMS activation sites to accelerate electron transfer. Synergistically, CoCN exhibits ultrahigh activity in PMS activation for p-hydroxybenzoic acid oxidation, achieving complete degradation within 10 min with an ultrahigh turnover frequency of 0.38 min-1, surpassing most reported materials. These findings offer new insights into the versatile functions of N species in SACs and inspire rational design of high-performance catalysts in complicated heterogeneous systems.

Sustainable electro-Fenton simultaneous reduction of Cr (VI) and degradation of organic pollutants via dual-site porous carbon cathode driving uncoordinated molybdenum sites conversion

Simultaneous removal of heavy metals and organic contaminants remains a substantial challenge in the electro-Fenton (EF) system. Herein, we propose a facile and sustainable "iron-free" EF system capable of simultaneously removing hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP). The system comprises a nitrogen-doped and carbon-deficient porous carbon (dual-site NPC-D) cathode coupled with a MoS2 nanoarray promoter (MoS2 NA). The NPC-D/MoS2 NA system exhibits exceptional synergistic electrocatalytic activity, with removal rates for Cr (VI) and 4-CP that are 20.3 and 4.4 times faster, respectively, compared to the NPC-D system. Mechanistic studies show that the dual-site structure of NPC-D cathode favors the two-electron oxygen reduction pathway with a selectivity of 81 %. Furthermore, an electric field-driven uncoordinated Mo valence state conversion of MoS2 NA enchances the generation of dynamic singlet oxygen and hydroxyl radicals. Notably, this system shows outstanding recyclability, resilience in real wastewater, and sustainability during a 3 L scale-up operation, while effectively mitigating toxicity. Overall, this study presents an effective approach for treating multiple-component wastewater and highlights the importance of structure-activity correlation in synergistic electrocatalysis.

Polyphenol-Derived Carbonaceous Frameworks with Multiscale Porosity for High-Power Electrochemical Applications

With the escalating global demand for electric vehicles and sustainable energy solutions, increasing focus is placed on developing electrochemical systems that offer fast charging and high-power output, primarily governed by mass transport. Accordingly, porous carbons have emerged as highly promising electrochemically active or supporting materials due to expansive surface areas, tunable pore structures, and superior electrical conductivity, accelerating surface reaction. Yet, while substantial research has been devoted to crafting various porous carbons to increase specific surface areas, the optimal utilization of the surfaces remains underexplored. This review emphasizes the critical role of the fluid dynamics within multiscale porous carbonaceous electrodes, leading to substantially enhanced pore utilization in electrochemical systems. It elaborates on strategies of using sacrificial templates for incorporating meso/macropores into microporous carbon matrix, while exploiting the unique properties of polyphenol moieties such as sustainable carbons derived from biomass, inherent adhesive/cohesive interactions with template materials, and facile complexation capabilities with diverse materials, thereby enabling adaptive structural modulations. Furthermore, it explores how multiscale pore configurations influence pore-utilization efficiency, demonstrating advantages of incorporating multiscale pores. Finally, synergistic impact on the high-power electrochemical systems is examined, attributed to improved fluid-dynamic behavior within the carbonaceous frameworks, providing insights for advancing next-generation high-power electrochemical applications.

Selective oxygen reduction reaction: mechanism understanding, catalyst design and practical application

The oxygen reduction reaction (ORR) is a key component for many clean energy technologies and other industrial processes. However, the low selectivity and the sluggish reaction kinetics of ORR catalysts have hampered the energy conversion efficiency and real application of these new technologies mentioned before. Recently, tremendous efforts have been made in mechanism understanding, electrocatalyst development and system design. Here, a comprehensive and critical review is provided to present the recent advances in the field of the electrocatalytic ORR. The two-electron and four-electron transfer catalytic mechanisms and key evaluation parameters of the ORR are discussed first. Then, the up-to-date synthetic strategies and in situ characterization techniques for ORR electrocatalysts are systematically summarized. Lastly, a brief overview of various renewable energy conversion devices and systems involving the ORR, including fuel cells, metal-air batteries, production of hydrogen peroxide and other chemical synthesis processes, along with some challenges and opportunities, is presented.

Catalase-like Fe Nanoparticles and Single Atoms Catalysts with Boosted Activity and Stability of Oxygen Reduction for Pesticide Detection

Although oxygen reduction reaction (ORR) as an effective signal amplification strategy has been extensively investigated for the improvement of sensitivity of electrochemical sensors, their activity and stability are still a great challenge. Herein, single-atom Fe (FeSA) and Fe nanoparticles (FeNP) on nitrogen-doped carbon (FeSA/FeNP) catalysts demonstrate a highly active and stable ORR performance, thus achieving the sensitive and stable electrochemical sensing of organophosphorus pesticides (OPs). Experimental investigations indicate that FeNP in FeSA/FeNP can improve the ORR activity by adjusting the electronic structure of FeSA active sites. Besides, owing to the excellent catalase-like activity, FeSA/FeNP can rapidly consume in situ generated H2O2 in the ORR process and avoid the leakage of active sites, thereby improving the stability of ORR. Utilizing the excellent ORR performance of FeSA/FeNP, an electrochemical sensor for OPs is established based on the thiocholine-induced poison of the active sites, demonstrating satisfactory sensitivity and stability. This work provides new insight into the design of high performance ORR catalysts for sensitive and stable electrochemical sensing.

Surface Redox Chemistry Regulates the Reaction Microenvironment for Efficient Hydrogen Peroxide Generation

Electrosynthesis has emerged as an enticing solution for hydrogen peroxide (H2O2) production. However, efficient H2O2 generation encounters challenges related to the robust gas-liquid-solid interface within electrochemical reactors. In this work, we introduce an effective hydrophobic coating modified by iron (Fe) sites to optimize the reaction microenvironment. This modification aims to mitigate radical corrosion through Fe(II)/Fe(III) redox chemistry, reinforcing the reaction microenvironment at the three-phase interface. Consequently, we achieved a remarkable yield of up to 336.1 mmol h-1 with sustained catalyst operation for an extensive duration of 230 h at 200 mA cm-2 without causing damage to the reaction interface. Additionally, the Faradaic efficiency of H2O2 exceeded 90% across a broad range of test current densities. This surface redox chemistry approach for manipulating the reaction microenvironment not only advances long-term H2O2 electrosynthesis but also holds promise for other gas-starvation electrochemical reactions.

Dipole-Dipole Tuned Electronic Reconfiguration of Defective Carbon Sites for Efficient Oxygen Reduction into H2O2

Metal-free carbon-based materials are one of the most promising electrocatalysts toward 2-electron oxygen reduction reaction (2e-ORR) for on-site production of hydrogen peroxide (H2O2), which however suffer from uncontrollable carbonizations and inferior 2e-ORR selectivity. To this end, a polydopamine (PDA)-modified carbon catalyst with a dipole-dipole enhancement is developed via a calcination-free method. The H2O2 yield rate outstandingly reaches 1.8 mol gcat -1 h-1 with high faradaic efficiency of above 95% under a wide potential range of 0.4-0.7 VRHE, overwhelming most of carbon electrocatalysts. Meanwhile, within a lab-made flow cell, the synthesized ORR electrode features an exceptional stability for over 250 h, achieved a pure H2O2 production efficacy of 306 g kWh-1. By virtue of its industrial-level capabilities, the established flow cell manages to perform a rapid pulp bleaching within 30 min. The superior performance and enhanced selectivity of 2e-ORR is experimentally revealed and attributed to the electronic reconfiguration on defective carbon sites induced by non-covalent dipole-dipole influence between PDA and carbon, thereby prohibiting the cleavage of O-O in OOH intermediates. This proposed strategy of dipole-dipole effects is universally applicable over 1D carbon nanotubes and 2D graphene, providing a practical route to design 2e-ORR catalysts.

Pyrrolic Nitrogen Boosted H2 Generation from an Aqueous Solution of HCHO at Room Temperature by Metal-Free Carbon Catalysts

Hydrogen production from organic hydrides represents a promising strategy for the development of safe and sustainable technologies for H2 storage and transportation. Nonetheless, the majority of existing procedures rely on noble metal catalysts and emit greenhouse gases such as CO2/CO. Herein, we demonstrated an alternative N-doped carbon (CN) catalyst for highly efficient and robust H2 production from an aqueous solution of formaldehyde (HCHO). Importantly, this process generated formic acid as a valuable byproduct instead of CO2/CO, enabling a clean H2 generation process with 100% atom economy. Mechanism investigations revealed that the pyrrolic N in the CN catalysts played a critical role in promoting H2 generation via enhancing the transformation of O2 to generate •OO- free radicals. Consequently, the optimized CN catalysts achieved a remarkable H2 generation rate of 13.6 mmol g-1 h-1 at 30 °C. This finding is anticipated to facilitate the development of liquid H2 storage and its large-scale utilization.

Metal-Free Nitrogen-Doped Mesoporous Carbons for the Mild and Selective Synthesis of Pyrroles from Nitroarenes via Cascade Reaction

The cascade synthesis of pyrroles from nitroarenes is an attractive alternative strategy. However, metal catalysts and relatively high temperatures cover the existing reported catalytic systems for this strategy. The development of nonmetallic heterogeneous catalytic systems for the one-pot synthesis of pyrrole from nitroarenes under mild conditions is both worthwhile and challenging. Herein, we describe an exceptionally efficient method for the synthesis of N-substituted pyrroles by the reductive coupling of nitroarenes and diketones over heterogeneous metal-free catalysts under mild conditions. Nonmetallic NC-X catalysts with high activity were prepared from the pyrolysis of well-defined ligands via simple sacrificing hard template methods. Hydrazine hydrate, formic acid, and molecular hydrogen can all be used as reducing agents in the hydrogenation/Paal-Knorr reaction sequence to efficiently synthesize various N-substituted pyrroles, including drugs and bioactive molecules. The catalytic system was featured with good tolerance to sensitive functional groups and no side reactions such as dehalogenation and aromatics hydrogenation. Hammett correlation studies have shown that the electron-donating substituents are beneficial for the one-pot synthesis of N-substituted pyrroles. The results established that the outstanding performance of the catalyst is mainly attributed to the contribution of graphitic N in the catalyst as well as the promotion effect of the mesoporous structure on the reaction.

Hydrogen peroxide electrogeneration from O2 electroreduction: A review focusing on carbon electrocatalysts and environmental applications

Hydrogen peroxide (H2O2) stands as one of the foremost utilized oxidizing agents in modern times. The established method for its production involves the intricate and costly anthraquinone process. However, a promising alternative pathway is the electrochemical hydrogen peroxide production, accomplished through the oxygen reduction reaction via a 2-electron pathway. This method not only simplifies the production process but also upholds environmental sustainability, especially when compared to the conventional anthraquinone method. In this review paper, recent works from the literature focusing on the 2-electron oxygen reduction reaction promoted by carbon electrocatalysts are summarized. The practical applications of these materials in the treatment of effluents contaminated with different pollutants (drugs, dyes, pesticides, and herbicides) are presented. Water treatment aiming to address these issues can be achieved through advanced oxidation electrochemical processes such as electro-Fenton, solar-electro-Fenton, and photo-electro-Fenton. These processes are discussed in detail in this work and the possible radicals that degrade the pollutants in each case are highlighted. The review broadens its scope to encompass contemporary computational simulations focused on the 2-electron oxygen reduction reaction, employing different models to describe carbon-based electrocatalysts. Finally, perspectives and future challenges in the area of carbon-based electrocatalysts for H2O2 electrogeneration are discussed. This review paper presents a forward-oriented viewpoint of present innovations and pragmatic implementations, delineating forthcoming challenges and prospects of this ever-evolving field.

Carboxylated Hexagonal Boron Nitride/Graphene Configuration for Electrosynthesis of High-Concentration Neutral Hydrogen Peroxide

The electrosynthesis of hydrogen peroxide (H2 O2 ) via two-electron (2e- ) oxygen (O2 ) reduction reaction (ORR) has great potential to replace the traditional energy-intensive anthraquinone process, but the design of low-cost and highly active and selective catalysts is greatly challenging for the long-term H2 O2 production under industrial relevant current density, especially under neutral electrolytes. To address this issue, this work constructed a carboxylated hexagonal boron nitride/graphene (h-BN/G) heterojunction on the commercial activated carbon through the coupling of B, N co-doping with surface oxygen groups functionalization. The champion catalyst exhibited a high 2e- ORR selectivity (>95 %), production rate (up to 13.4 mol g-1  h-1 ), and Faradaic efficiency (FE, >95 %). The long-term H2 O2 production under the high current density of 100 mA cm-2 caused the cumulative concentration as high as 2.1 wt %. The combination of in situ Raman spectra and theoretical calculation indicated that the carboxylated h-BN/G configuration promotes the adsorption of O2 and the stabilization of the key intermediates, allowing a low energy barrier for the rate-determining step of HOOH* release from the active site and thus improving the 2e- ORR performance. The fast dye degradation by using this electrochemical synthesized H2 O2 further illustrated the promising practical application.