Two-electron Oxygen Reduction Research Articles

Enhanced Electrocatalytic Hydrogen Peroxide Production via a CuWO4/WO3 Heterojunction with High Selectivity and Stability.

The electrocatalytic conversion of oxygen to hydrogen peroxide offers a promising pathway for sustainable energy production. However, the development of catalysts that are highly active, stable, and cost-effective for hydrogen peroxide synthesis remains a significant challenge. In this study, a novel polyacid-based metal-organic coordination compound (Cu-PW) was synthesized using a hydrothermal approach. Cu-PW served as a precursor to construct a composite electrocatalyst featuring a heterointerface between CuWO4 and WO3 (CuWO4/WO3) through pyrolysis. The CuWO4/WO3 heterojunction exhibits an impressive H2O2 selectivity of 91.84% at 0.5 V, marking a 19.65% improvement compared to the pristine Cu-PW. Furthermore, the CuWO4/WO3 catalyst demonstrates exceptional stability, maintaining continuous operation for 29 h. At 0.1 V, it delivers a hydrogen peroxide yield of 1537.8 mmol g-1 h-1, with a Faraday efficiency (FE) of 85%. Additionally, this catalyst effectively degrades methyl blue, achieving a 95% removal from an aqueous system within 30 min. Theoretical analysis further corroborates the high electroactivity of CuWO4/WO3 heterojunction structure. The Cu-O-W bridge formed during the reaction facilitates interfacial electron transport and enhances the role of the W-O bond in proton adsorption and transfer kinetics. This strong interfacial coupling in CuWO4/WO3 promotes electron transfer and the formation of *OOH intermediates, thereby favoring hydrogen peroxide generation. Hence, the as-prepared CuWO4/WO3 demonstrates great potential as an efficient electrocatalyst for the green synthesis of hydrogen peroxide, exhibiting high efficiency as a two-electron oxygen reduction reaction catalyst. This work offers a new approach for fabricating CuWO4/WO3 electrocatalyst with high electroactivity and selectivity, paving the way for cost-effective and sustainable hydrogen peroxide production, significantly reducing reliance on the conventional anthraquinone process.

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.

The steric hindrance effect of Co porphyrins promoting two-electron oxygen reduction reaction selectivity.

A new Co 5,10,15,20-tetrakis(2',6'-dipivaloyloxyphenyl)porphyrin (1) with eight ester groups in all ortho and ortho' positions of phenyl groups was designed, which displayed significantly improved 2e oxygen reduction reaction (ORR) selectivity compared with a 5,10,15,20-tetrakis(para-dipivaloyloxyphenyl) porphyrin (2) without large steric groups. This work is significant to reveal the steric hindrance effect of metal porphyrins on electrocatalytic ORR selectivity.

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.

Ambient Synthesis of Cyclohexanone Oxime via In Situ Produced Hydrogen Peroxide over Cobalt-Based Electrocatalyst.

Cyclohexanone oxime, a critical precursor for nylon-6 production, is traditionally synthesized via the hydroxylamine method under industrial harsh conditions. Here is present a one-step electrochemical integrated approach for the efficient production of cyclohexanone oxime under ambient conditions. This approach employed the coupling of in situ electro-synthesized H2O2 over a cobalt (Co)-based electrocatalyst with the titanium silicate-1 (TS-1) heterogeneous catalyst to achieve the cyclohexanone ammoximation process. The cathode electrocatalyst is consisted of atomically dispersed Co sites and small Co nanoparticles co-anchored on carboxylic multi-walled carbon nanotubes (CoSAs/SNPs-OCNTs), which delivered superior electrocatalytic activity toward the two-electron oxygen reduction reaction (2e- ORR) with high-efficient H2O2 production in 0.1m sodium phosphate (NaPi). Theoretical calculations revealed that the introduction of Co nanoparticles effectively optimized the binding strength of *OOH species on Co atomic sites, thus facilitating the 2e- ORR. The subsequent tandem catalytic system achieved a high cyclohexanone conversion of 71.7%±1.1% with a cyclohexanone oxime selectivity of 70.3%±0.6%. In this system, the TS-1 catalyst effectively captured the *OOH intermediate and activated the in situ generated H2O2 to form Ti-OOH species, which promoted the formation of hydroxylamine and thereby enhanced the oxime production performance.

Solar-Driven Hydrogen Peroxide Production via BiVO4-Based Photocatalysts.

Solar hydrogen peroxide (H2O2) production has garnered increased research interest owing to its safety, cost-effectiveness, environmental friendliness, and sustainability. The synthesis of H2O2 relies mainly on renewable resources such as water, oxygen, and solar energy, resulting in minimal waste. Bismuth vanadate (BiVO4) stands out among various oxide semiconductors for selective H2O2 production under visible light via direct two-electron oxygen reduction reaction (ORR) and two-electron water oxidation reaction (WOR) pathways. Significant advancements have been achieved using BiVO4-based materials in solar H2O2 production over the last decade. This review explores advancements in BiVO4-based photocatalysts for H2O2 production, focusing on photocatalytic powder suspension (PS) and photoelectrochemical (PEC) systems, representing the main approaches for heterogenous artificial photosynthesis. An overview of fundamental principles, performance assessment methodologies, photocatalyst and photoelectrode development, and optimization of reaction conditions is provided. While diverse strategies, such as heterojunction, doping, crystal facet engineering, cocatalyst loading, and surface passivation, have proven effective in enhancing H2O2 generation, this review offers insights into their similar and distinct implementations within the PS and PEC systems. The challenges and future prospects in this field are also discussed to facilitate the rational design of high-performing BiVO4-based photocatalysts and photoelectrodes for H2O2 generation under visible light.

Balancing Activity and Selectivity in Two-Electron Oxygen Reduction through First Coordination Shell Engineering in Cobalt Single Atom Catalysts.

The electrochemical two-electron oxygen reduction reaction (2e- ORR) offers a potentially cost-effective and eco-friendly route for the production of hydrogen peroxide (H2O2). However, the competing 4e- ORR that converts oxygen to water limits the selectivity towards hydrogen peroxide. Accordingly, achieving highly selective H2O2 production under low voltage conditions remains challenging. Herein, guided by first-principles density functional theory (DFT) calculations, we show that modulation the first coordination sphere in Co single atom catalysts (Co-N-C catalysts with Co-NxO4-x sites), specifically the replacement of Co-N bonds with Co-O bonds, can weaken the *OOH adsorption strength to boost the selectivity towards H2O2 (albeit with a slight decrease in ORR activity). Further, by synthesizing a series of N-doped carbon-supported catalysts with Co-NxO4-x active sites, we were able to validate the DFT findings and explore the trade-off between catalytic activity and selectivity for 2e- ORR. A catalyst with trans-Co-N2O2 sites exhibited excellent catalytic activity and H2O2 selectivity, affording a H2O2 production rate of 12.86 and an half-cell energy-efficiency of 0.07 during a 100-hours H2O2 production test in a flow-cell.

Enhanced H2O2 Production by Two-Electron Oxygen Reduction on Co3O4/MXene Catalyst

The two-electron oxygen reduction reaction (ORR) using an electrochemical method is considered a viable green technology for generating H2O2. Platinum group metals demonstrate excellent H2O2 generation performance due to their superior ORR activity and stability. However, the high cost of these electrocatalysts is a significant barrier to the widespread adoption of this technology, prompting research into non-precious metal catalysts as alternatives. In this work, Co3O4 nanoparticles with sized from 5 to 10 nm were synthesized on MXene sheets. Compared with Co3O4/C and MXene, the results indicated that Co3O4/MXene exhibited the best electrochemical performances, with an electron transfer number of ∼3.1 during oxygen reduction and an H2O2 selectivity of ∼47%. Co3O4/MXene also demonstrated great stability. After 5000 cycles, the H2O2 selectivity and electron transfer number remained at 50% and 3.0, respectively. After 12 h of continuous testing, Co3O4/MXene exhibited a high Faraday efficiency of 50% and H2O2 yield of 0.14 mol h−1 g−1, with H2O2 selectivity increasing to 68.7% and an electron transfer number of 2.6. The excellent electrochemistry is attributed to the synergistic effect between MXene and Co3O4. This study provides valuable insights into non-precious metal electrocatalysts for H2O2 generation.

Hydrogen Radical Enabling Industrial-Level Oxygen Electroreduction to Hydrogen Peroxide.

The electrochemical synthesis of hydrogen peroxide from oxygen and water, powered by renewable electricity, provides a highly attractive alternative to the energy-intensive autoxidation process presently used in industry, but much remains unknown about this two-electron oxygen reduction reaction (2e-ORR), especially the local proton effect. Here, we have investigated the function of hydrogen-associated intermediates in the 2e-ORR using a rationally designed cooperative electrode material with cobalt (II) clusters embedded onto the oxidized carbon nanotube composites (Co-OCNT). We found that the local proton availability can determine both the reaction kinetics and selectivity. A 2e-ORR process involving hydrogen radical transfer is confirmed. Specifically, the carbon sites from the OCNTs promote proton production, and the cobalt sites from the Co cluster facilitate ORR intermediate formation. The high local proton availability and the cooperative dual-active sites both contribute to the superior reaction kinetics and selectivity of the Co-OCNT, reaching an H2O2 production rate of ~40.6 mol gcat -1 h-1 and a faradaic efficiency of 90 % at a current density of 300 mA cm-2. Further cascading the 2e-ORR with the electro-Fenton process shows a high selectivity of oxalic acid up to 97 % for the valorization of ethylene glycol.

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.

Hydrogen Peroxide Electrosynthesis via Selective Oxygen Reduction Reactions Through Interfacial Reaction Microenvironment Engineering.

The electrochemical two-electron oxygen reduction reaction (2e- ORR) offers a compelling alternative for decentralized and on-site H2O2 production compared to the conventional anthraquinone process. To advance this electrosynthesis system, there is growing interest in optimizing the interfacial reaction microenvironment to boost electrocatalytic performance. This review consolidates recent advancements in reaction microenvironment engineering for the selective electrocatalytic conversion of O2 to H2O2. Starting with fundamental insights into interfacial electrocatalytic mechanisms, an overview of various strategies for constructing the favorable local reaction environment, including adjusting electrode wettability, enhancing mesoscale mass transfer, elevating local pH, incorporating electrolyte additives, and employing pulsed electrocatalysis techniques is provided. Alongside these regulation strategies, the corresponding analyses and technical remarks are also presented. Finally, a summary and outlook on critical challenges, suggesting future research directions to inspire microenvironment engineering and accelerate the practical application of H2O2 electrosynthesis is delivered.

Facet-dependent spatial separation of dual cocatalysts on MOF photocatalysts for H2O2 production coupling biomass oxidation with enhanced performance

Cooperative coupling of photocatalytic two-electron oxygen reduction reaction (2e-ORR) with oxidative organic synthesis holds great promise for sustainable production of valuable chemicals. To achieve high performance, the rational design of photocatalysts with effective electron-hole separation and redox capability is crucial. Herein, a MOF-based photocatalyst with crystal facet-dependent spatial separation of dual cocatalysts is constructed for photocatalytic 2e-ORR coupled with vanillyl alcohol oxidation reaction (VAOR). The facet-dependent growth of reductive Pd and oxidative CoOx cocatalysts respectively on the {100} and {001} facets of MIL-125-NH2 enables the directional migration of photogenerated carries, facilitating the charge separation for redox reactions. Additionally, the interaction between Pd and MIL-125-NH2 modulates the Pd sites into electron-sufficient state with upshifted d-band center, promoting the O2 activation and *OOH intermediate formation. The rationally designed composite photocatalyst delivers an excellent H2O2 yield of 74.8 mM g−1 h−1 and a high vanillic acid production rate of 80.9 mM h−1 g−1 with the conversion and selectivity of 96.8 % and 91.1 %, respectively.

Generative Pretrained Transformer for Heterogeneous Catalysts.

Discovery of novel and promising materials is a critical challenge in the field of chemistry and material science, traditionally approached through methodologies ranging from trial-and-error to machine-learning-driven inverse design. Recent studies suggest that transformer-based language models can be utilized as material generative models to expand the chemical space and explore materials with desired properties. In this work, we introduce the catalyst generative pretrained transformer (CatGPT), trained to generate string representations of inorganic catalyst structures from a vast chemical space. CatGPT not only demonstrates high performance in generating valid and accurate catalyst structures but also serves as a foundation model for generating the desired types of catalysts by text-conditioning and fine-tuning. As an example, we fine-tuned the pretrained CatGPT using a binary alloy catalyst data set designed for screening two-electron oxygen reduction reaction (2e-ORR) catalyst and generated catalyst structures specialized for 2e-ORR. Our work demonstrates the potential of generative language models as generative tools for catalyst discovery.

Nitrogen-Doped Mesoporous Carbons Fabricated from Self-Assembled Block Copolymers for Electrochemical Production of H2O2

Nitrogen-doped mesoporous carbons are attracting significant attention as next-generation electrocatalytic materials due to their high specific surface area, high electrical conductivity, and exceptional chemical stability. Especially, due to the facilitated mass transport of products, high selectivity for the two-electron oxygen reduction reaction is expected, making it applicable to the synthesis of hydrogen peroxide (H2O2).¹ In this study, we focused on the soft template method by utilizing the self-assembly of a block copolymer (BCP) through microphase separation.² In our laboratory, we have been working on the synthesis of poly(4-vinylpyridine)-b-poly(2,2,2-trifluoroethyl methacrylate) (P4VP-b-PTFEMA). The significant repulsive interaction between these two components allows extensive control of the domain size. Furthermore, poly(4-vinylpyridine) serves as both the nitrogen and carbon sources and is selectively crosslinked by resol, thus enabling a high carbonization yield to be obtained. We employed this BCP as a soft template and introduce resol as a cross-linker for fabricating nitrogen-doped mesoporous carbons. Here, we investigated in detail the effects of the composition of the block copolymer and the amount of the crosslinker on the morphology and nitrogen content of the mesoporous carbon.P4VP-b-PTFEMA was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. A mixture of P4VP-b-PTFEMA and resol was dissolved in DMF at 5 wt%, and the solution was evaporated and dried under vacuum at 100 °C for 24 hours to prepare a composite film. Subsequently, the film was heated to 900 °C to fabricate nitrogen-doped mesoporous carbons.Small-angle X-ray scattering (SAXS) analysis of the composite film revealed various microphase-separated structures depending on the BCP-to-resol ratio (Fig. 1 (a)). Furthermore, nitrogen-doped mesoporous carbons with pore diameters ranging from 6.2 nm to 24 nm were fabricated using various molecular weights of PTFEMA (Fig. 1 (b)). Additionally, in our presentation, we will discuss how the pore size affects the selectivity of the two-electron reaction and the catalytic efficiency in the oxygen reduction reaction.[Reference](1) Park et al., ACS Catal. 2014, 4, 3749.(2) Liu et al., Polym. Chem. 2014, 5, 6452.[Acknowledgement]This study was financially supported by JSPS-KAKENHI(21K04828). Figure 1

Ionic liquid modifying conductivity and hydrophobicity of B4C for enhanced electrosynthesis of H2O2

Electrosynthesis of hydrogen peroxide (H2O2) via two-electron oxygen reduction reaction (2e− ORR) is an attractive energy-efficient and decentralized alternative to the conventional anthraquinone process. However, designing non-precious metal catalysts with high activity, selectivity and stability is a great challenge. Here, we report a facile and effective approach to improve the catalytic performance of commercial boron carbide (B4C) by loading ionic liquid (IL), which exploits the complementary properties of high electrical conductivity and hydrophobicity of IL. The B4C catalyst with optimal IL loading possesses the highest conductivity and O2 adsorption, exhibiting high H2O2 selectivity in both neutral (∼96 %) and alkaline (∼93 %) electrolyte, which are nearly ∼34 % and ∼19 % higher than pristine B4C, respectively. Moreover, its production rate is ∼1.5 times that of pristine B4C at 130 mA cm−2 current density, resulting in a high concentration of H2O2 (5.93 wt%) produced in flow-cell reactor. The long-term cycle test demonstrates the desirable stability of IL@B4C/GDE, which is attributed to the high hydrophobicity and tight bonding between IL@B4C and the substrate, giving a strong flood-proof capability at the three-phase interface and avoiding rapid flooding by the electrolyte. This work provides new insights into designing non-precious metal electrocatalysts for efficient electrosynthesis of H2O2, emphasizing the role of IL in interface engineering.

Homoleptic and Heteroleptic Coordination Environment of Palladium Molecular Catalysts for Oxygen Reduction to Hydrogen Peroxide

Hydrogen peroxide (H2O2) serves a wide range of purposes in industries such as chemical manufacturing, energy production, and wastewater treatment, either alone or in combination with other oxidizers. The demand for H2O2 has seen a notable increase due to its heightened use in disinfection amid the COVID-19 pandemic. Currently, industrial synthesis of H2O2 relies on anthraquinone technology, a complex process involving multiple steps including the use of H2 gas, transfer of H2O2 between solvents, distillation of concentrated H2O2, and potentially hazardous transportation. Thus, advancements in developing efficient and selective electrocatalysts for the two-electron oxygen reduction reaction (2e- ORR) are crucial for promoting the adoption of electrochemical synthesis of H2O2 production. In our study, we synthesized single-atom electrocatalysts—Pd-N4-CO, Pd-S4-NCO, and Pd-N2O2-C through an in-situ synthesis approach involving heteroatom-rich ligands and activated carbon under mild reaction conditions. These catalysts feature both homoleptic (Pd-N, Pd-S) and heteroleptic (Pd-NO) coordination spheres, which are expected to demonstrate selectivity in the two-electron/four-electron pathway of the oxygen reduction rection (ORR). Moreover, the coordination of the Schiff base and poly pyridyl ligands to the palladium atom could be observed via the thiol ligand (Pd-S4-NCO), azomethine nitrogen and hydroxyl oxygen atoms (Pd-N2O2-C), and the pyridinic nitrogen atom of 1,10-phenathroline-5,6-dione (Pd-N4-CO). Notably, Pd-N4-CO shows promise as an electrocatalyst for two-electron ORR, facilitating green H2O2 production with high activity and selectivity in a basic electrolyte, exhibiting minimal onset overpotential and over 95% selectivity across various potentials. The electrocatalysts performance in ORR follows Pd-N4-CO > Pd-N2O2-C > Pd-S4-NCO, aligning with the Pull-Push mechanism. This mechanism underscores the significance of strong coordination of Pd with electronegative donor atoms like N and O, and weak coordination with intermediate *OOH, enhancing selectivity and green H2O2 production. Our findings, both experimental and DFT calculations, offer new insights into engineering heteroatom-rich ligands to tune the electronic structure of catalytic active sites. This understanding informs the atomic-level structure-activity and selectivity relationship, facilitating the development of more effective and efficient catalysts for the electrochemical synthesis of hydrogen peroxide.

Electrocatalysts for the Formation of Hydrogen Peroxide by Oxygen Reduction Reaction.

Hydrogen peroxide (H2O2) is a widely used strong oxidant, and its traditional preparation methods, anthraquinone method, and direct synthesis method, have many drawbacks. The method of producing H2O2 by two-electron oxygen reduction reaction (2e- ORR) is considered an alternative strategy for the traditional anthraquinone method due to its high efficiency, energy saving, and environmental friendliness, but it remains a big challenge. In this review, we have described the mechanism of ORR and the principle of electrocatalytic performance testing, and have summarized the standard performance evaluation techniques for electrocatalysts to produce H2O2. Secondly, according to the theoretical calculation and experimental results, several kinds of efficient electrocatalysts are introduced. It is concluded that noble metal-based materials, carbon-based materials, non-noble metal composites, and single-atom catalysts are the preferred catalyst materials for the preparation of H2O2 by 2e- ORR. Finally, the advantages and novelty of 2e- ORR compared with traditional methods for H2O2 production, as well as the advantages and disadvantages of the above-mentioned high-efficiency catalysts, are summarized. The application prospect and development direction of high-efficiency catalysts for H2O2 production by 2e- ORR has been prospected, which is of great significance for promoting the electrochemical yield of H2O2 and developing green chemical production.

Membrane-free Electrolysis Production of Hydrogen Peroxide on Low-cost Metal-free Electrocatalysts for Dye Degradation.

The efficient production of hydrogen peroxide (H2O2) solution was achieved by combining cathodic two-electron oxygen reduction (2e- ORR) and anodic two-electron water oxidation (2e- WOR) in two half-reaction cells. h-BN loaded on carbon fibers (h-BN@C) is prepared and employed as an anode material to catalyze 2e- WOR, while sulfonated commercial BP-2000 carbons (BP-2000-SO3H) were prepared as the cathode materials for 2e- ORR. In a 2 M KHCO3 solution, an overall Faradaic efficiency of 97 % and a total H2O2 production rate of 1872 mmol g-1 h-1 over metal-free electrodes were accomplished in a membrane-free flow cell. The dilute H2O2 solution could be directly used to degrade Rhodamine B, methyl blue and methylene orange dyes in water. This work proved low-cost production of dilute H2O2 solution in simple membrane-free flow cells with single electrolyte and on-site utilization for efficient dye degradation.

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.

Defect engineering induced high metal loading Co-single-atom catalyst on carbon dots for efficient H2O2 electrosynthesis

Co-single atom catalysts (Co-SACs) exhibit high selectivity and efficiency for H2O2 electrosynthesis via the two-electron oxygen reduction reaction (2e−ORR), with the catalytic activity as significantly influenced by the loading content of Co atoms. However, the loading of Co atoms is typically confined to a low level (<1.0 wt%), which restricts their overall catalytic performance. Herein, we proposed a defect engineering strategy that utilized the carbon dots (CDs) as a platform to capture Co atoms, and constructed a series of Co-SACs with high Co atoms loading (with a maximum of 6.16 wt%), representing a substantial improvement compared to existing benchmarks in the literature. Experimental and characterization results revealed that the defect sites on CDs allowed adequate spacing between the Co atoms, effectively preventing their aggregation and promoting the generation of highly loaded metal atoms. It is worth noting that ECDs-CoSA demonstrated remarkable efficacy and catalytic activity with 93.70 % H2O2 selectivity and an impressive H2O2 yield of 9.71 mol L−1 h−1 gcat.−1 in neutral condition. This study presents an effective route for the controlled prepared of Co-SACs with high metal loading, aiming at sustainable and the efficient H2O2 electrosynthesis.