Designing Boron Nitride Islands in Carbon Materials for Efficient Electrochemical Synthesis of Hydrogen Peroxide

Ferrihydrite/B, N co-doped biochar composites enhancing tetracycline degradation: The crucial role of boron incorporation in Fe(III) reduction and oxygen activation

Harnessing the redox potential of biochar to activate airborne O2 for contaminant removal is challenging. In this study, ferrihydrite (Fh) modified the boron (B), nitrogen (N) co-doped biochars (BCs) composites (Fh/B(n)NC) were developed for enhancing the degradation of a model pollutant, tetracycline (TC), merely by airborne O2. Fh/B(3)NC showed excellent O2 activation activity for efficient TC degradation with a apparent TC degradation rate of 5.54, 6.88, and 22.15 times that of B(3)NC, Fh, and raw BCs, respectively, where 1O2 and H2O2 were identified as the dominant ROS for TC degradation. The B incorporation into the carbon lattice of Fh/B(3)NC promoted the generation of electron donors, sp2 C and the reductive B species, hence boosting Fe(III) reduction and 1O2 generation. O2 adsorption was enhanced due to the positively charged adsorption sites (C-B+and NC+). And 1O2 was generated via Fe(II) catalyzed low-efficient successive one-electron transfer (O2 → O2·- → 1O2, H2O2), as well as biochar catalyzed high-efficient two-electron transfer (O2 → H2O2 → 1O2) that does not involve .O2- as the intermediate. Moreover, Fh/B, N co-doped biochar showed a wide pH range, remarkable anti-interference capabilities, and effective detoxification. These findings shed new light on the development of environmentally benign BCs materials capable of degradading organic pollutants.

Reverse the Impact of Le Chatelier's Principle in Two-Electron Air Electroreduction

Using high-purity oxygen (O2) for electrofixation would increase the production cost of hydrogen peroxide (H2O2) because of requiring complex pre-treatment procedures. Atmospheric air is an abundant source, but the direct air electrofixation has proved to be very challenging, that in common conception against nitrogen (N2) in the system. According to the Le Chatelier's principle, O2 concentration is diluted by N2 (78%) in atmospheric air, which reduces overall reaction rates/equilibrium. Here we report a catalyst system where the presence of N2 does not impose an adverse effect; rather, it is beneficial for activity. We combine both theoretical and experimental analyses to elucidate the underlying mechanisms, unlocking the critical function of electronic spin, arising from the strong synergy between iron oxide (FeOx) and nickel-metal organic frameworks (Ni-MOF) that optimizes the activation of O2 in air. Consequently, the catalyst for direct air electrofixation has demonstrated an exceptional H2O2 yield rate (262.6 mg h-1 cm-2) and Faradaic efficiency (95.61%), outperforming its high-purity O2 counterpart (184.32 mg h-1 cm-2 and 67.06%). We expect the present findings providing an additional dimension to leverage systems beyond the constraint of traditional rules.

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.

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.

Scalable Electro-Biosynthesis of Ectoine from Greenhouse Gases

Converting greenhouse gases into valuable products has become a promising approach for achieving a carbon-neutral economy and sustainable development. However, the conversion efficiency depends on the energy yield of the substrate. In this study, we developed an electro-biocatalytic system by integrating electrochemical and microbial processes to upcycle CO2 into a valuable product (ectoine) using renewable energy. This system initiates the electrocatalytic reduction of CO2 to methane, an energy-dense molecule, which then serves as an electrofuel to energize the growth of an engineered methanotrophic cell factory for ectoine biosynthesis. The scalability of this system was demonstrated using an array of ten 25 cm2 electrochemical cells equipped with a high-performance carbon-supported isolated copper catalyst. The system consistently generated methane at the cathode under a total partial current of approximately -37 A (~175 mmolCH4 h-1) and O2 at the anode under a total partial current of approximately 62 A (~583 mmolO2 h-1). This output met the requirements of a 3-L bioreactor, even at maximum CH4 and O2 consumption, resulting in the high-yield conversion of CO2 to ectoine (1146.9 mg L-1). This work underscores the potential of electrifying the biosynthesis of valuable products from CO2, providing a sustainable avenue for biomanufacturing and energy storage.

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.

Regulating the Electronic Structure of Cu Single-Atom Catalysts toward Enhanced Electro-Fenton Degradation of Organic Contaminants via 1O2 and •OH

Heterogeneous electro-Fenton degradation with 1O2 and •OH generated from O2 reduction is cost-effective for the removal of refractory organic pollutants from wastewater. As 1O2 is more tolerant to background constituents such as salt ions and a high pH value than •OH, tuning the production of 1O2 and •OH is important for efficient electro-Fenton degradation. However, it remains a great challenge to selectively produce 1O2 and improve the species yield. Herein, the electronic structure of atomically dispersed Cu-N4 sites was regulated by doping electron-deficient B into porous hollow carbon microspheres (CuBN-HCMs), which improved *O2 adsorption and significantly enhanced 1O2 selectivity in electro-Fenton degradation. Its 1O2 yield was 2.3 times higher than that of a Cu single-atom catalyst without B doping. Meanwhile, •OH was simultaneously generated as a minor species. The CuBN-HCMs were efficient for the electro-Fenton degradation of phenol, sulfamethoxazole, and bisphenol A with a high mineralization efficiency. Its kinetic constants showed insignificant changes under various anions and a wide pH range of 1-9. More importantly, it was energy-efficient for treating actual coking wastewater with a low energy consumption of 19.0 kWh kgCOD-1. The superior performance of the CuBN-HCMs was contributed from 1O2 and •OH and its high 1O2 selectivity.

Construction of One-Dimensional Covalent-Organic Framework Coordinated with Main Group Metals for Selective Electrochemical Synthesis of H2O2

Covalent-organic frameworks (COFs) are promising electrocatalysts for the selective synthesis of H2O2 through the two-electron oxygen reduction reaction (2e- ORR). However, the design and synthesis of efficient and stable COF-based electrocatalysts is still challenging. In this work, a predesigned 1,10-phenanthroline-based one-dimensional COF (PYTA-PTDE-COF) was constructed to anchor main group metal (In, Sn, and Sb) as electrocatalysts toward 2e- ORR. The catalysts are featured with fully exposed metalated side chains. Structural characterization revealed that PYTA-PTDE-M's (M = In, Sn, and Sb) are all quite similar, except for the coordinated metal ions with the maintenance of good crystallinity. They all exhibited satisfying activity and selectivity toward 2e- ORR under alkaline conditions. Among them, PYTA-PTDE-Sb exhibited the best performance (Eonset is 0.765 V, the H2O2 selectivity is 96%, and the yield rate is 209.2 mmol gcat-1 h-1). Moreover, it also delivered superior stability with almost no attenuation of current density during the long-time test. Theoretical calculations revealed that the Sb metal site in the COFs has the lowest adsorption strength of *OOH, which could be the main reason for its superior selectivity. The PYTA-PTDE-Sb assembled zinc-air battery realizes not only the supply of clean energy but also the production of green chemicals, showing it is highly promising in practical applications. This work offers an example for designing main group metal-coordinated 1D COFs and reveals fundamental structure-activity relationship toward 2e- ORR.

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.

Isomerization Engineering of Oxygen-Enriched Carbon Quantum Dots for Efficient Electrochemical Hydrogen Peroxide Production

Hydrogen peroxide (H2O2) has emerged as a kind of multi-functional green oxidants with extensive industrial utility. Oxidized carbon materials exhibit promises as electrocatalysts in the two-electron (2e-) oxygen reduction reaction (ORR) for H2O2 production. However, the precise identification and fabrication of active sites that selectively yield H2O2 present a serious challenge. Herein, a structural engineering strategy is employed to synthesize oxygen-doped carbon quantum dots (o-CQD) for the 2e- ORR. The surface electronic structure of the o-CQDs is systematically modulated by varying isomerization precursors, thereby demonstrating excellent electrocatalyst performance. Notably, o-CQD-3 emerges as the most promising candidate, showcasing a remarkable H2O2 selectivity of 96.2% (n = 2.07) at 0.68 V versus RHE, coupled with a low Tafel diagram of 66.95 mV dec-1. In the flow cell configuration, o-CQD-3 achieves a H2O2 productivity of 338.7 mmol gcatalyst -1 h-1, maintaining consistent production stability over an impressive 120-hour duration. Utilizing in situ technology and density functional theory calculations, it is unveil that edge sites of o-CQD-3 are facilely functionalized by C-O-C groups under alkaline ORR conditions. This isomerization engineering approach advances the forefront of sustainable catalysis and provides a profound insight into the carbon-based catalyst design for environmental-friendly chemical synthesis processes.

Understanding the preparative chemistry of atomically dispersed nickel catalysts for achieving high-efficiency H2O2 electrosynthesis

Electrochemical hydrogen peroxide (H2O2) production via two-electron oxygen reduction reaction (2e- ORR) has received increasing attention as it enables clean, sustainable, and on-site H2O2 production. Mimicking the active site structure of H2O2 production enzymes, such as nickel superoxide dismutase, is the most intuitive way to design efficient 2e- ORR electrocatalysts. However, Ni-based catalysts have thus far shown relatively low 2e- ORR activity. In this work, we present the design of high-performing, atomically dispersed Ni-based catalysts (Ni ADCs) for H2O2 production through understanding the formation chemistry of the Ni-based active sites. The use of a precoordinated precursor and pyrolysis within a confined nanospace were found to be essential for generating active Ni-N x sites in high density and increasing carbon yields, respectively. A series of model catalysts prepared from coordinating solvents having different vapor pressures gave rise to Ni ADCs with controlled ratios of Ni-N x sites and Ni nanoparticles, which revealed that the Ni-N x sites have greater 2e- ORR activity. Another set of Ni ADCs identified the important role of the degree of distortion from the square planar structure in H2O2 electrosynthesis activity. The optimized catalyst exhibited a record H2O2 electrosynthesis mass activity with excellent H2O2 selectivity.

Metal Atom-Support Interaction in Single Atom Catalysts toward Hydrogen Peroxide Electrosynthesis

Single metal atom catalysts (SACs) have garnered considerable attention as promising agents for catalyzing important industrial reactions, particularly the electrochemical synthesis of hydrogen peroxide (H2O2) through the two-electron oxygen reduction reaction (ORR). Within this field, the metal atom-support interaction (MASI) assumes a decisive role, profoundly influencing the catalytic activity and selectivity exhibited by SACs, and triggers a decade-long surge dedicated to unraveling the modulation of MASI as a means to enhance the catalytic performance of SACs. In this comprehensive review, we present a systematic summary and categorization of recent advancements pertaining to MASI modulation for achieving efficient electrochemical H2O2 synthesis. We start by introducing the fundamental concept of the MASI, followed by a detailed and comprehensive analysis of the correlation between the MASI and catalytic performance. We describe how this knowledge can be harnessed to design SACs with optimized MASI to increase the efficiency of H2O2 electrosynthesis. Finally, we distill the challenges that lay ahead in this field and provide a forward-looking perspective on the future research directions that can be pursued.

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.

Sustainable H2O2 production in a floating dual-cathode electro-Fenton system for efficient decontamination of organic pollutants

Electrochemical advanced oxidation processes (EAOPs) based on natural air diffusion electrode (NADE) promise efficient and affordable advanced oxidation water purification, but the sustainable operation of such reaction systems remains challenging due to severe cathode electrowetting. Herein, a novel floating cathode (FC) composed of a stable hydrophobic three-phase interface was established by designing a flexible catalytic layer of FC. This innovative electrode configuration could effectively prolong the service life of the cathode by mitigating the interference of H2 bubbles from the hydrogen evolution reaction (HER), and the H2O2 production rate reached 37.59 mg h-1·cm-2 and realize a long-term stable operation for 10 h. Additionally, an FC/carbon felt (CF) dual-cathode electro-Fenton system was constructed for in situ sulfamethoxazole (SMX) degradation. Efficient H2O2 production on FC and Fe(III) reduction on CF were synchronously achieved, attaining excellent degradation efficiency for both SMX (ca. 100%) with 2.5 mg L-1 of Fe(Ⅱ) injection. For real wastewater, the COD removal of the FC/CF dual-cathode electro-Fenton system was stabilized at exceeding 75%. The practical application potential of the FC/CF dual-cathode electro-Fenton system was also demonstrated for the treatment of actual landfill leachate in continuous flow mode. This work provides a valuable path for constructing a sustainable dual-cathode electro-Fenton system for actual wastewater treatment.

Chemical and engineering bases for green H2O2 production and related oxidation and ammoximation of olefins and analogues

Plastics, fibers and rubber are three mainstream synthetic materials that are essential to our daily lives and contribute significantly to the quality of our lives. The production of the monomers of these synthetic polymers usually involves oxidation or ammoximation reactions of olefins and analogues. However, the utilization of C, O and N atoms in current industrial processes is <80%, which represents the most environmentally polluting processes for the production of basic chemicals. Through innovation and integration of catalytic materials, new reaction pathways, and reaction engineering, the Research Institute of Petroleum Processing, Sinopec Co., Ltd. (RIPP) and its collaborators have developed unique H2O2-centered oxidation/ammoximation technologies for olefins and analogues, which has resulted in a ¥500 billion emerging industry and driven trillions of ¥s' worth of downstream industries. The chemical and engineering bases of the production technologies mainly involve the integration of slurry-bed reactors and microsphere catalysts to enhance H2O2 production, H2O2 propylene/chloropropylene epoxidation for the production of propylene oxide/epichlorohydrin, and integration of H2O2 cyclohexanone ammoximation and membrane separation to innovate the caprolactam production process. This review briefly summarizes the whole process from the acquisition of scientific knowledge to the formation of an industrial production technology by RIPP. Moreover, the scientific frontiers of H2O2 production and related oxidation/ammoximation processes of olefins and analogues are reviewed, and new technological growth points are envisaged, with the aim of maintaining China's standing as a leader in the development of the science and technologies of H2O2 production and utilization.

Electrosynthesis of H2O2 Promoted by π-π Interaction on a Metal-Free Carbon Catalyst

The synthesis of hydrogen peroxide (H2O2) through electrocatalytic oxygen reduction reaction is an ideal alternative to the current energy-intensive anthraquinone process, but developing cost-effective and high-efficiency electrocatalysts is still challenging. Herein, a metal-free graphitic carbon nitride/carbon nanotube (g-C3N4/CNT) hybrid catalyst can enhance H2O2 production via π-π interaction is reported, achieving almost unity (97%) H2O2 production at 0.57 V with high selectivity of over 92% across the wide potential range from 0.6 to 0 V. Other carbon materials with weak interaction with g-C3N4, such as acetylene black and super P, show markedly weakened H2O2 production, indicating the importance of π-π interaction. Electron transfer kinetic analysis combined with density functional theory calculations indicates that the synergistic effect between g-C3N4 and CNT enhances electron transfer and O2 activation between g-C3N4 and CNT, leading to enhanced H2O2 production performance. This work provides a complementary approach for H2O2 production from oxygen reduction besides introducing oxygenated groups or heteroatom doping into carbon materials.

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.

Boosting electrochemical oxygen reduction to hydrogen peroxide coupled with organic oxidation

The electrochemical oxygen reduction reaction (ORR) to produce hydrogen peroxide (H2O2) is appealing due to its sustainability. However, its efficiency is compromised by the competing 4e- ORR pathway. In this work, we report a hierarchical carbon nanosheet array electrode with a single-atom Ni catalyst synthesized using organic molecule-intercalated layered double hydroxides as precursors. The electrode exhibits excellent 2e- ORR performance under alkaline conditions and achieves H2O2 yield rates of 0.73 mol gcat-1 h-1 in the H-cell and 5.48 mol gcat-1 h-1 in the flow cell, outperforming most reported catalysts. The experimental results show that the Ni atoms selectively adsorb O2, while carbon nanosheets generate reactive hydrogen species, synergistically enhancing H2O2 production. Furthermore, a coupling reaction system integrating the 2e- ORR with ethylene glycol oxidation significantly enhances H2O2 yield rate to 7.30 mol gcat-1 h-1 while producing valuable glycolic acid. Moreover, we convert alkaline electrolyte containing H2O2 directly into the downstream product sodium perborate to reduce the separation cost further. Techno-economic analysis validates the economic viability of this system.

Unveiling the potential of a BCN-biphenylene monolayer as a high-performance anode material for alkali metal ion batteries: a first-principles study

Inspired by a freshly synthesized two-dimensional biphenylene carbon network, which features a captivating combination of hexagonal, square, and octagonal rings, we explored a similar biphenylene network composed of boron, carbon, and nitrogen (bpn-BCN) using first-principles calculations. There are six possible phases of borocarbonitrides, which are isoelectronic to biphenylene carbon networks with a stoichiometric ratio of 1 : 1 : 1 for boron (B), carbon (C), and nitrogen (N) atoms. All possible isoelectronic structures of the BCN combination of biphenylene networks are found to be stable, according to first-principles calculations. However, the geometry has a relatively large number of robust C-C and B-N bonds and strong partially ionic-covalent B-C and C-N bonds inside these bpn-BCN monolayers are effectively more stable. Furthermore, we employed first-principles calculations to investigate the electrochemical properties of the most stable geometry of BCN biphenylene as a potential anode material for alkali metal (AM) ion batteries. A global search has been made to find the most favourable alkali metal ion adsorption sites. The biphenylene monolayer has octagonal, square, and hexagonal motifs with different adsorption strengths. Furthermore, the partially ionic bond of B-N (due to the electronegativity difference) also supports the alkali metal ions for adsorption. The electronic properties of the stable phase of bpn-BCN reveal its narrow bandgap semiconductor nature. The ion diffusion calculations show a low activation barrier for Li, Na, and K of 0.65 eV, 0.26 eV, and 0.23 eV, respectively, indicating a fast charge/discharge rate. Furthermore, the theoretical capacities of the BCN biphenylene monolayer for Li (1057.33 mA h g-1), Na (647.27 mA h g-1), and K (465.98 mA h g-1) are found to be greater than those of commercial graphite. The average open-circuit voltage for AM decreases with increasing metal ion concentrations. It falls within a reasonable range of 0.34-1.89 V. Our results show that the BCN biphenylene monolayer could be a promising anode material in alkali metal ion rechargeable batteries.

Electrochemical Generation of Hydroxide and Hydrogen Peroxide for Hydrolysis of Sulfuryl Fluoride Fumigant

The post-harvest fumigant, sulfuryl fluoride (SO2F2), is a >1000-fold more potent greenhouse gas than carbon dioxide and methane. Pilot studies have shown that SO2F2 fumes vented from fumigation chambers can be captured and hydrolyzed by hydroxide (OH-) and hydrogen peroxide (H2O2) at pH ∼ 12 in a scrubber, producing SO42- and F- as waste salts. To reduce the costs and challenges associated with purchasing and mixing these reagents onsite, this study evaluates the electrochemical generation of OH- and H2O2 within spent scrubbing solution, taking advantage of the waste SO42- and F- as free sources of electrolyte. The study used a gas diffusion electrode constructed from carbon paper coated with carbon black as a catalyst selective for the reduction of O2 to H2O2. Under galvanostatic conditions, the study evaluated the effect of electrochemical conditions, including applied cathodic current density and electrolyte strength. Within an electrolyte containing 200 mM SO42- and 400 mM F-, comparable to the waste salts generated by a SO2F2 scrubbing event, the system produced 250 mM H2O2 at pH 12.6 within 4 h with a Faradaic efficiency of 98.8% for O2 reduction to H2O2. In a scrubbing-water sample from lab-scale fumigation, the system generated ∼200 mM H2O2 at pH 13.5 within 4 h with a Faradaic efficiency of 75.6%. A comparison of the costs to purchase NaOH and H2O2 against the electricity costs for electrochemical treatment indicated that the electrochemical approach could be 38-71% lower, depending on the local cost of electricity.

Hydroxyl-Bonded Co Single Atom Site on Boroncarbonitride Surface Realizes Nonsacrificial H2O2 Synthesis in the Near-Infrared Region

Photocatalytic synthesis of hydrogen peroxide (H2O2) from O2 and H2O under near-infrared light is a sustainable renewable energy production strategy, but challenging reaction. The bottleneck of this reaction lies in the regulation of O2 reduction path by photocatalyst. Herein, the center of the one-step two-electron reduction (OSR) pathway of O2 for H2O2 evolution via the formation of the hydroxyl-bonded Co single-atom sites on boroncarbonitride surface (BCN-OH2/Co1) is constructed. The experimental and theoretical prediction results confirm that the hydroxyl group on the surface and the electronic band structure of BCN-OH2/Co1 are the key factor in regulating the O2 reduction pathway. In addition, the hydroxyl-bonded Co single-atom sites can further enrich O2 molecules with more electrons, which can avoid the one-electron reduction of O2 to •O2 -, thus promoting the direct two-electron activation hydrogenation of O2. Consequently, BCN-OH2/Co1 exhibits a high H2O2 evolution apparent quantum efficiency of 0.8% at 850 nm, better than most of the previously reported photocatalysts. This study reveals an important reaction pathway for the generation of H2O2, emphasizing that precise control of the active site structure of the photocatalyst is essential for achieving efficient conversion of solar-to-chemical.

Integrative Active Sites of Cathode for Electron-Oxygen-Proton Coupling To Favor H2O2 Production in a Photoelectrochemical System

The oxygen reduction process generating H2O2 in the photoelectrochemical (PEC) system is milder and environmentally friendly compared with the traditional anthraquinone process but still lacks the efficient electron-oxygen-proton coupling interfaces to improve H2O2 production efficiency. Here, we propose an integrated active site strategy, that is, designing a hydrophobic C-B-N interface to refine the dearth of electron, oxygen, and proton balance. Computational calculation results show a lower energy barrier for H2O2 production due to synergistic and coupling effects of boron sites for O2 adsorption, nitrogen sites for H+ binding, and the carbon structure for electron transfer, demonstrating theoretically the feasibility of the strategy. Furthermore, we construct a hydrophobic boron- and nitrogen-doped carbon black gas diffusion cathode (BN-CB-PTFE) with graphite carbon dots decorated on a BiVO4 photoanode (BVO/g-CDs) for H2O2 production. Remarkably, this approach achieves a record H2O2 production rate (9.24 μmol min-1 cm-2) at the PEC cathode. The BN-CB-PTFE cathode exhibits an outstanding Faraday efficiency for H2O2 production of ∼100%. The newly formed h-BN integrative active site can not only adsorb more O2 but also significantly improve the electron and proton transfer. Unexpectedly, coupling BVO/g-CDs with the BN-CB-PTFE gas diffusion cathode also achieves a record H2O2 production rate (6.60 μmol min-1 cm-2) at the PEC photoanode. This study opens new insight into integrative active sites for electron-O2-proton coupling in a PEC H2O2 production system that may be meaningful for environment and energy applications.

General Design Concept of High-Performance Single-Atom-Site Catalysts for H2O2 Electrosynthesis

Hydrogen peroxide (H2O2) as a green oxidizing agent is widely used in various fields. Electrosynthesis of H2O2 has gradually become a hotspot due to its convenient and environment-friendly features. Single-atom-site catalysts (SASCs) with uniform active sites are the ideal catalysts for the in-depth study of the reaction mechanism and structure-performance relationship. In this review, the outstanding achievements of SASCs in the electrosynthesis of H2O2 through 2e- oxygen reduction reaction (ORR) and 2e- water oxygen reaction (WOR) in recent years, are summarized. First, the elementary steps of the two pathways and the roles of key intermediates (*OOH and *OH) in the reactions are systematically discussed. Next, the influence of the size effect, electronic structure regulation, the support/interfacial effect, the optimization of coordination microenvironments, and the SASCs-derived catalysts applied in 2e- ORR are systematically analyzed. Besides, the developments of SASCs in 2e- WOR are also overviewed. Finally, the research progress of H2O2 electrosynthesis on SASCs is concluded, and an outlook on the rational design of SASCs is presented in conjunction with the design strategies and characterization techniques.

BiVO4-Based Heterojunction Photocathode for High-Performance Photoelectrochemical Hydrogen Peroxide Production

Photoelectrochemical (PEC) cells provide a promising solution for the synthesis of hydrogen peroxide (H2O2). Herein, an integrated photocathode of p-type BiVO4 (p-BVO) array with tetragonal zircon structure coupled with different metal oxide (MOx, M = Sn, Ti, Ni, and Zn) heterostructure and NiNC cocatalyst (p-BVO/MOx/NiNC) was synthesized for the PEC oxygen reduction reaction (ORR) in production of H2O2. The p-BVO/SnO2/NiNC array achieves the production rate 65.46 μmol L-1 h-1 of H2O2 with a Faraday efficiency (FE) of 76.12%. Combined with the H2O2 generation of water oxidation from the n-type Mo-doped BiVO4 (n-Mo:BVO) photoanode, the unbiased photoelectrochemical cell composed of a p-BVO/SnO2/NiNC photocathode and n-Mo:BVO photoanode achieves a total FE of 97.67% for H2O2 generation. The large area BiVO4-based tandem cell of 3 × 3 cm2 can reach a total H2O2 production yield of 338.84 μmol L-1. This work paves the way for the rational design and fabrication of artificial photosynthetic cells for the production of liquid solar fuel.

All-in-one continuous electrochemical monitoring of 2-phenylphenol removal from water by electro-Fenton treatment

The biggest allure of heterogeneous electro-Fenton (HEF) processes largely fails on its high efficiency for the degradation of a plethora of hazardous compounds present in water, but still challenging to search for good and cost-effective electrocatalyst. In this work, carbon black (CB) and oxidised carbon black (CBox) materials were investigated as cathodes in the electrochemical production of hydrogen peroxide involved in HEF reaction for the degradation of 2-phenylphenol (2PP) as a target pollutant. The electrodes were fabricated by employing carbon cloth as support, and the highest H2O2 production yields were obtained for the CBox, pointing out the beneficial effect of the hydrophilic character of the electrode and oxygen-type functionalization of the carbonaceous surface. HEF degradation of 2PP was explored at -0.7 V vs. Ag/AgCl exhibiting the best conversion rates and degradation grade (total organic carbon) for the CBox-based cathode. In addition, the incorporation of an electrochemical sensor of 2PP in line with the HEF reactor was accomplished by the use of screen-printed electrodes (SPE) in order to monitor the pollutant degradation. The electrochemical sensor performance was evaluated from the oxidation of 2PP in the presence of Fe2+ ions by using square wave voltammetry (SWV) technique. The best electrochemical sensor performance was based on SPE modified with Meldola Blue showing a high sensitivity, low detection limit (0.12 ppm) and wide linear range (0.5-21 ppm) with good reproducibility (RSD 2.3 %). The all-in-one electrochemical station has been successfully tested for the degradation and quantification of 2PP, obtaining good recoveries analysing spiked waters from different water matrices origins.

Recent advances in electrosynthesis of H2O2via two-electron oxygen reduction reaction

The electrosynthesis of hydrogen peroxide (H2O2) via a selective two-electron oxygen reduction reaction (2e- ORR) presents a green and low-energy-consumption alternative to the traditional, energy-intensive anthraquinone process. This review encapsulates the principles of designing relational electrocatalysts for 2e- ORR and explores remaining setups for large-scale H2O2 production. Initially, the review delineates the fundamental reaction mechanisms of H2O2 production via 2e- ORR and assesses performance. Subsequently, it methodically explores the pivotal influence of microstructures, heteroatom doping, and metal hybridization along with setup configurations in achieving a high-performance catalyst and efficient reactor for H2O2 production. Thereafter, the review introduces a forward-looking methodology that leverages the synergistic integration of catalysts and reactors, aiming to harmonize the complementary characteristics of both components. Finally, it outlines the extant challenges and the promising avenues for the efficient electrochemical production of H2O2, setting the stage for future research endeavors.

Recent Progress of Transition Metal Selenides for Electrochemical Oxygen Reduction to Hydrogen Peroxide: From Catalyst Design to Electrolyzers Application

Hydrogen peroxide (H2O2) is a highly value-added and environmental-friendly chemical with various applications. The production of H2O2 by electrocatalytic 2e- oxygen reduction reaction (ORR) has emerged as a promising alternative to the energy-intensive anthraquinone process. High selectivity Catalysts combining with superior activity are critical for the efficient electrosynthesis of H2O2. Earth-abundant transition metal selenides (TMSs) being discovered as a classic of stable, low-cost, highly active and selective catalysts for electrochemical 2e- ORR. These features come from the relatively large atomic radius of selenium element, the metal-like properties and the abundant reserves. Moreover, compared with the advanced noble metal or single-atom catalysts, the kinetic current density of TMSs for H2O2 generation is higher in acidic solution, which enable them to become suitable catalyst candidates. Herein, the recent progress of TMSs for ORR to H2O2 is systematically reviewed. The effects of TMSs electrocatalysts on the activity, selectivity and stability of ORR to H2O2 are summarized. It is intended to provide an insight from catalyst design and corresponding reaction mechanisms to the device setup, and to discuss the relationship between structure and activity.

Enhanced electrocatalytic performance for H2O2 generation by boron-doped porous carbon hollow spheres

Electrocatalytic generation of H2O2 via the 2-electron pathway of oxygen reduction reaction (2e-ORR) is an attractive technology compared to the anthraquinone process due to convenience and environmental friendliness. However, catalysts with excellent selectivity and high activity for 2e-ORR are necessary for practical applications. Reported here is a catalyst comprising boron-doped porous carbon hollow spheres (B-PCHSs) prepared using the hard template method coupled with borate transesterification. In an alkali electrolyte, the selectivity of B-PCHS for 2e-ORR above 90% in range of 0.4-0.7 VRHE and an onset potential of 0.833 V was obtained. Meanwhile, the generation rate of H2O2 reached 902.48 mmol h-1 gcat-1 at 0.4 VRHE under 59.13 mA cm-2 in batch electrolysis. The excellent catalytic selectivity of B-PCHS for 2e-ORR originates from the boron element, and the catalytic activity of B-PCHS for H2O2 generation is contributed to the morphology of porous hollow spheres, which facilitates mass transfer processes.

Emerging Two-Dimensional Carbonaceous Materials for Electrocatalytic Energy Conversions: Rational Design of Active Structures through High-Temperature Chemistry

Electrochemical energy conversion and storage technologies involving controlled catalysis provide a sustainable way to handle the intermittency of renewable energy sources, as well as to produce green chemicals/fuels in an ecofriendly manner. Core to such technology is the development of efficient electrocatalysts with high activity, selectivity, long-term stability, and low costs. Here, two-dimensional (2D) carbonaceous materials have emerged as promising contenders for advancing the chemistry in electrocatalysis. We review the emerging 2D carbonaceous materials for electrocatalysis, focusing primarily on the fine engineering of active structures through thermal condensation, where the design, fabrication, and mechanism investigations over different types of active moieties are summarized. Interestingly, all the recipes creating two-dimensionality on the carbon products also give specific electrocatalytic functionality, where the special mechanisms favoring 2D growth and their consequences on materials functionality are analyzed. Particularly, the structure-activity relationship between specific heteroatoms/defects and catalytic performance within 2D metal-free electrocatalysts is highlighted. Further, major challenges and opportunities for the practical implementation of 2D carbonaceous materials in electrocatalysis are summarized with the purpose to give future material design guidelines for attaining desirable catalytic structures.

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.

Carbon Catalysts Empowering Sustainable Chemical Synthesis via Electrochemical CO2 Conversion and Two-Electron Oxygen Reduction Reaction

Carbon materials hold significant promise in electrocatalysis, particularly in electrochemical CO2 reduction reaction (eCO2 RR) and two-electron oxygen reduction reaction (2e- ORR). The pivotal factor in achieving exceptional overall catalytic performance in carbon catalysts is the strategic design of specific active sites and nanostructures. This work presents a comprehensive overview of recent developments in carbon electrocatalysts for eCO2 RR and 2e- ORR. The creation of active sites through single/dual heteroatom doping, functional group decoration, topological defect, and micro-nano structuring, along with their synergistic effects, is thoroughly examined. Elaboration on the catalytic mechanisms and structure-activity relationships of these active sites is provided. In addition to directly serving as electrocatalysts, this review explores the role of carbon matrix as a support in finely adjusting the reactivity of single-atom molecular catalysts. Finally, the work addresses the challenges and prospects associated with designing and fabricating carbon electrocatalysts, providing valuable insights into the future trajectory of this dynamic field.

Ru nanoclusters anchored on boron- and nitrogen-doped carbon for a highly efficient hydrogen evolution reaction in alkaline seawater

Electrochemical seawater splitting is an intriguing strategy for green hydrogen production. Constructing advanced electrocatalysts for the hydrogen evolution reaction (HER) in seawater is extremely demanded for accelerating the sluggish kinetic process. Herein, a Ru nanocluster anchored on boron- and nitrogen-doped carbon (Ru/NBC) catalyst was successfully synthesized for the HER in alkaline/seawater electrolytes. Remarkably, Ru/NBC exhibits outstanding activity and durability, delivering low overpotentials@10 mA cm-2 in 1.0 M KOH (30 mV) and 1.0 M KOH + seawater electrolyte (35 mV), outperforming Pt/C, Ru/NC, Ru/BC and Ru/C. Additionally, Ru/NBC also provides a high specific activity of 0.093 mA cm-2ECSA at an overpotential of 150 mV, which is higher than those of Ru/NC, Ru/BC and Ru/C, respectively. Density functional theory calculation results demonstrate that the Ru-B formed interfacial chemical bond can regulate the electronic structure of Ru active sites of Ru/NBC, which can facilitate the adsorption of water and hydrogen in alkaline media. This work provides a feasible strategy to fabricate outstanding electrocatalysts for the HER in alkaline/alkaline seawater electrolytes.

Density functional theory studies on graphene/h-boron nitride hybrid nanosheets for supercapacitor electrode applications

Pristine graphene (C32), hexagonal boron nitride (h-BN), and graphene/h-BN hybrid nanosheets were examined using density functional theory calculations in order to find their suitability as an electrode material for supercapacitor applications. The stability of the structure, charge density, electronic properties, and quantum capacitance of pristine graphene and graphene/h-BN hybrid nanosheets were studied. The structural optimization results reveal that all the nanosheets are stable with zero transverse displacement of atoms along the z-direction. Further, replacing the C-C pair with B-N altered the average bond length and angle, thereby maintaining structural stability. The interaction between graphene and h-BN is higher for C16B8N8 compared to other hybrid nanosheets because of the delocalized distribution of the electron density cloud. The doping of the B-N pair into the graphene nanosheet shifts the Fermi level into either the valence band or the conduction band based on the concentration of the B-N pair. Meanwhile, the effective mass is increased and is relatively high for the hybrid nanosheets with a localized state. The pristine B16N16 nanosheet exhibits a quantum capacitance of 31.539 μF cm-2, while among the hybrid nanosheets, the C4B14N14 nanosheet exhibits a maximum quantum capacitance of 22.518 μF cm-2, and from the outcomes, they are suitable as an electrode for asymmetric supercapacitors.

Tailoring the Atomic-Local Environment of Carbon Nanotube Tips for Selective H2 O2 Electrosynthesis at High Current Densities

The atomic-local environment of catalytically active sites plays an important role in tuning the activity of carbon-based metal-free electrocatalysts (C-MFECs). However, the rational regulation of the environment is always impeded by synthetic limitations and insufficient understanding of the formation mechanism of the catalytic sites. Herein, the possible cleavage mechanism of carbon nanotubes (CNTs) through the crossing points during ball-milling is proposed, resulting in abundant CNT tips that are more susceptible to be modified by heteroatoms, achieving precise modulation of the atomic environment at the tips. The obtained CNTs with N,S-rich tips (N,S-TCNTs) exhibit a wide potential window of 0.59 V along with H2 O2 selectivity for over 90.0%. Even using air as the O2 source, the flow cell system with N,S-TCNTs catalyst attains high H2 O2 productivity up to 30.37 mol gcat. -1  h-1 @350 mA cm-2 , superior to most reported C-MFECs. From a practical point of view, a solid electrolyzer based on N,S-TCNTs is further employed to realize the in-situ continuous generation of pure H2 O2 solution with high productivity (up to 4.35 mmol cm-2  h-1 @300 mA cm-2 ; over 300 h). The CNTs with functionalized tips hold great promise for practical applications, even beyond H2 O2 generation.

Interfacial engineering of a vertically stacked graphene/h-BN heterostructure as an efficient electrocatalyst for hydrogen peroxide synthesis

Recently, it was reported that an in-plane graphene (G)/hexagonal boron nitride (h-BN) (G/h-BN) heterostructure provided the catalytic activity for H2O2 synthesis by the 2 e- oxygen reduction reaction (ORR). However, there are few reports on the vertically stacked G/h-BN heterostructure, which refers to the stacking of graphene domains on the surface of h-BN. Herein, a simulated chemical vapor deposition method is proposed for fabricating a heterostructure of abundant vertically stacked G/h-BN by in situ growing graphene quantum dots (GQDs) on porous h-BN sheets. The performance of our vertically stacked heterostructure catalyst is superior to that of reported carbon-based electrocatalysts under an alkaline environment, with an H2O2 selectivity of 90-99% in a wide potential range (0.35 V-0.7 V vs. RHE), over 90% faradaic efficiency, and high mass activity of 1167 mmol gcatalyst-1 h-1. The experimental results and density functional theory (DFT) simulation verified that the vertically stacked heterostructure exhibits an excellent catalytic performance for the 2 e- ORR, and the edge B atoms in the B-centered AB stacking model are the most active catalytic sites. This research adequately demonstrates the promising catalytic activity of the vertically stacked G/h-BN heterostructure and provides a facile route for fabricating other vertically stacked heterostructures.

Electrosynthesis of Hydrogen Peroxide through Selective Oxygen Reduction: A Carbon Innovation from Active Site Engineering to Device Design

Electrochemical synthesis of hydrogen peroxide (H2 O2 ) through the selective oxygen reduction reaction (ORR) offers a promising alternative to the energy-intensive anthraquinone method, while its success relies largely on the development of efficient electrocatalyst. Currently, carbon-based materials (CMs) are the most widely studied electrocatalysts for electrosynthesis of H2 O2 via ORR due to their low cost, earth abundance, and tunable catalytic properties. To achieve a high 2e- ORR selectivity, great progress is made in promoting the performance of carbon-based electrocatalysts and unveiling their underlying catalytic mechanisms. Here, a comprehensive review in the field is presented by summarizing the recent advances in CMs for H2 O2 production, focusing on the design, fabrication, and mechanism investigations over the catalytic active moieties, where an enhancement effect of defect engineering or heteroatom doping on H2 O2 selectivity is discussed thoroughly. Particularly, the influence of functional groups on CMs for a 2e- -pathway is highlighted. Further, for commercial perspectives, the significance of reactor design for decentralized H2 O2 production is emphasized, bridging the gap between intrinsic catalytic properties and apparent productivity in electrochemical devices. Finally, major challenges and opportunities for the practical electrosynthesis of H2 O2 and future research directions are proposed.

Engineering of Local Coordination Microenvironment in Single-Atom Catalysts Enabling Sustainable Conversion of Biomass into a Broad Range of Amines

Utilizing renewable biomass as a substitute for fossil resources to produce high-value chemicals with a low carbon footprint is an effective strategy for achieving a carbon-neutral society. Production of chemicals via single-atom catalysis is an attractive proposition due to its remarkable selectivity and high atomic efficiency. In this work, a supramolecular-controlled pyrolysis strategy is employed to fabricate a palladium single-atom (Pd1 /BNC) catalyst with B-doped Pd-Nx atomic configuration. Owing to the meticulously tailored local coordination microenvironment, the as-synthesized Pd1 /BNC catalyst exhibits remarkable conversion capability for a wide range of biomass-derived aldehydes/ketones. Thorough characterizations and density functional theory calculations reveal that the highly polar metal-N-B site, formed between the central Pd single atom and its adjacent N and B atoms, promotes hydrogen activation from the donor (reductants) and hydrogen transfer to the acceptor (C═O group), consequently leading to exceptional selectivity. This system can be further extended to directly synthesize various aromatic and furonic amines from renewable lignocellulosic biomass, with their greenhouse gas emission potentials being negative in comparison to those of fossil-fuel resource-based amines. This research presents a highly effective and sustainable methodology for constructing C─N bonds, enabling the production of a diverse array of amines from carbon-neutral biomass resources.

Polarity reversal for enhanced in-situ electrochemical synthesis of H2O2 over banana-peel derived biochar cathode for water remediation

The fabrication of a cost-efficient cathode is critical for in-situ electrochemical generation of hydrogen peroxide (H2O2) to remove persistent organic pollutants from groundwater. Herein, we tested a stainless-steel (SS) mesh wrapped banana-peel derived biochar (BB) cathode for in-situ H2O2 electrogeneration to degrade bromophenol blue (BPB) and Congo red (CR) dyes. Furthermore, polarity reversal is evaluated for the activation of BB surface via introduction of various oxygen containing functionalities that serve as active sites for the oxygen reduction reaction (ORR) to generate H2O2. Various parameters including the BB mass, current, as well as the solution pH have been optimized to evaluate the cathode performance for efficient H2O2 generation. The results reveal formation of up to 9.4 mg/L H2O2 using 2.0 g BB and 100 mA current in neutral pH with no external oxygen supply with a manganese doped tin oxide deposited nickel foam (Mn-SnO2@NF) anode to facilitate the oxygen evolution reaction (OER). This iron-free electrofenton (EF) like process enabled by the SSBB cathode facilitates efficient degradation of BPB and CR dyes with 87.44 and 83.63% removal efficiency, respectively after 60 min. A prolonged stability test over 10 cycles demonstrates the effectiveness of polarity reversal toward continued removal efficiency as an added advantage. Moreover, Mn-SnO2@NF anode used for the OER was also replaced with stainless steel (SS) mesh anode to investigate the effect of oxygen evolution on H2O2 generation. Although Mn-SnO2@NF anode exhibits better oxygen evolution potential with reduced Tafel slope, SS mesh anode is discussed to be more cost-efficient for further studies.

Manipulating local coordination of copper single atom catalyst enables efficient CO2-to-CH4 conversion

Electrochemical CO2 conversion to methane, powered by intermittent renewable electricity, provides an entrancing opportunity to both store renewable electric energy and utilize emitted CO2. Copper-based single atom catalysts are promising candidates to restrain C-C coupling, suggesting feasibility in further protonation of CO* to CHO* for methane production. In theoretical studies herein, we find that introducing boron atoms into the first coordination layer of Cu-N4 motif facilitates the binding of CO* and CHO* intermediates, which favors the generation of methane. Accordingly, we employ a co-doping strategy to fabricate B-doped Cu-Nx atomic configuration (Cu-NxBy), where Cu-N2B2 is resolved to be the dominant site. Compared with Cu-N4 motifs, as-synthesized B-doped Cu-Nx structure exhibits a superior performance towards methane production, showing a peak methane Faradaic efficiency of 73% at -1.46 V vs. RHE and a maximum methane partial current density of -462 mA cm-2 at -1.94 V vs. RHE. Extensional calculations utilizing two-dimensional reaction phase diagram analysis together with barrier calculation help to gain more insights into the reaction mechanism of Cu-N2B2 coordination structure.

Fabrication of superhydrophilic porous carbon materials through a porogen-free method: Surface and structure modification promoting the two-electron oxygen reduction activity

HYPOTHESIS

Electrochemical manufacture of H₂O₂ through the two-electron oxygen reduction reaction (2e^- ORR), providing prospects of the distributed production of H₂O₂ in remote regions, is considered a promising alternative to the energy-intensive anthraquinone oxidation process.

EXPERIMENTS

In this study, one glucose-derived oxygen-enriched porous carbon material (labeled as HGC₅₀₀) is developed through a porogen-free strategy integrating structural and active site modification.

FINDINGS

The superhydrophilic surface and porous structure together promote the mass transfer of reactants and accessibility of active sites in the aqueous reaction, while the abundant CO species (e.g., aldehyde groups) are taken for the main active site to facilitate the 2e^- ORR catalytic process. Benefiting from the above merits, the obtained HGC₅₀₀ possesses superior performance with a selectivity of 92 % and mass activity of 43.6 A g_cat^-1 at 0.65 V (vs. RHE). Besides, the HGC₅₀₀ can operate steadily for 12 h with the accumulation of H₂O₂ reaching up to 4090±71 ppm and a Faradic efficiency of 95 %. The H₂O₂ generated from the electrocatalytic process in 3 h can degrade a variety of organic pollutants (10 ppm) in 4-20 min, displaying the potential in practical applications.

Preparation of oxidized acetylene black by high-temperature calcination for luminol efficient cathodic electrochemiluminescence

The improvement of electrochemiluminescence (ECL) intensity in luminol, a classic electrochemiluminescent material, remains a controversial topic. In this study, synthesis of acetylene black oxide (ACETO) through simple air annealing was successful in introducing oxygen-containing groups and defects, which can act as active sites for the oxygen reduction reaction (ORR) and exhibit excellent catalytic activity. By introducing the two-electron (2e^-) ORR into the cathode ECL system of luminol, integration of ACETO and luminol allows for in situ generation of dissolved oxygen into reactive oxygen species (ROS), thereby enhancing the ECL intensity of luminol. It is worth noting that iron-nitrogen-carbon (FeNC), as a secondary antibody (Ab₂) label, can catalyze the decomposition of H₂O₂, the product of 2e^- ORR, into ROS to achieve ECL amplification. Alpha-fetoprotein (AFP), an important tumor marker, was successfully detected with a detection limit of 0.01 pg/mL, indicating that this ECL signal amplification strategy has broad application prospects in biological analysis.

Strategies for Sustainable Production of Hydrogen Peroxide via Oxygen Reduction Reaction: From Catalyst Design to Device Setup

An environmentally benign, sustainable, and cost-effective supply of H2O2 as a rapidly expanding consumption raw material is highly desired for chemical industries, medical treatment, and household disinfection. The electrocatalytic production route via electrochemical oxygen reduction reaction (ORR) offers a sustainable avenue for the on-site production of H2O2 from O2 and H2O. The most crucial and innovative part of such technology lies in the availability of suitable electrocatalysts that promote two-electron (2e-) ORR. In recent years, tremendous progress has been achieved in designing efficient, robust, and cost-effective catalyst materials, including noble metals and their alloys, metal-free carbon-based materials, single-atom catalysts, and molecular catalysts. Meanwhile, innovative cell designs have significantly advanced electrochemical applications at the industrial level. This review summarizes fundamental basics and recent advances in H2O2 production via 2e--ORR, including catalyst design, mechanistic explorations, theoretical computations, experimental evaluations, and electrochemical cell designs. Perspectives on addressing remaining challenges are also presented with an emphasis on the large-scale synthesis of H2O2 via the electrochemical route.

NBOH Site-Activated Graphene Quantum Dots for Boosting Electrochemical Hydrogen Peroxide Production

Carbon materials are considered promising 2/4 e^- oxygen reduction reaction (ORR) electrocatalysts for synthesizing H₂ O₂ /H₂ O via regulating heteroatom dopants and functionalization. Here, various doped and functionalized graphene quantum dots (GQDs) are designed to reveal the crucial active sites of carbon materials for ORR to produce H₂ O₂ . Density functional theory (DFT) calculations predict that the edge structure involving edge N, B dopant pairs and further OH functionalization to the B (NBOH) is an active center for 2e^- ORR. To verify the above predication, GQDs with an enriched density of NBOH (NBO-GQDs) are designed and synthesized by the hydrothermal reaction of NH₂ edge-functionalized GQDs with H₃ BO₃ forming six-member heterocycle containing the NBOH structure. When dispersed on conductive carbon substrates, the NBO-GQDs show H₂ O₂ selectivity of over 90% at 0.7 -0.8 V versus reversible hydrogen electrode in the alkaline solution in a rotating ring-disk electrode setup. The selectivity retains 90% of the initial value after 12 h stability test. In a flow cell setup, the H₂ O₂ production rate is up to 709 mmol g_catalyst ^-1  h^-1 , superior to most reported carbon- and metal-based electrocatalysts. This work provides molecular insight into the design and formulation of highly efficient carbon-based catalysts for sustainable H₂ O₂ production.

Photocatalytic and Electrocatalytic Generation of Hydrogen Peroxide: Principles, Catalyst Design and Performance

Hydrogen peroxide (H2O2) is a high-demand organic chemical reagent and has been widely used in various modern industrial applications. Currently, the prominent method for the preparation of H2O2 is the anthraquinone oxidation. Unfortunately, it is not conducive to economic and sustainable development since it is a complex process and involves unfriendly environment and potential hazards. In this context, numerous approaches have been developed to synthesize H2O2. Among them, photo/electro-catalytic ones are considered as two of the most promising manners for on-site synthesis of H2O2. These alternatives are sustainable in that only water or O2 is required. Namely, water oxidation (WOR) or oxygen reduction (ORR) reactions can be further coupled with clean and sustainable energy. For photo/electro-catalytic reactions for H2O2 generation, the design of the catalysts is extremely important and has been extensively conducted with an aim to obtain ultimate catalytic performance. This article overviews the basic principles of WOR and ORR, followed by the summary of recent progresses and achievements on the design and performance of various photo/electro-catalysts for H2O2 generation. The related mechanisms for these approaches are highlighted from theoretical and experimental aspects. Scientific challenges and opportunities of engineering photo/electro-catalysts for H2O2 generation are also outlined and discussed.

Promotion of the Efficient Electrocatalytic Production of H2O2 by N,O- Co-Doped Porous Carbon

H₂O₂ generation via an electrochemical two-electron oxygen reduction (2e^- ORR) is a potential candidate to replace the industrial anthraquinone process. In this study, porous carbon catalysts co-doped by nitrogen and oxygen are successfully synthesized by the pyrolysis and oxidation of a ZIF-67 precursor. The catalyst exhibits a selectivity of ~83.1% for 2e^- ORR, with the electron-transferring number approaching 2.33, and generation rate of 2909.79 mmol g^-1 h^-1 at 0.36 V (vs. RHE) in KOH solution (0.1 M). The results prove that graphitic N and -COOH functional groups act as the catalytic centers for this reaction, and the two functional groups work together to greatly enhance the performance of 2e^- ORR. In addition, the introduction of the -COOH functional group increases the hydrophilicity and the zeta potential of the carbon materials, which also promotes the 2e^- ORR. The study provides a new understanding of the production of H₂O₂ by electrocatalytic oxygen reduction with MOF-derived carbon catalysts.

Charge-Polarized Selenium Vacancy in Nickel Diselenide Enabling Efficient and Stable Electrocatalytic Conversion of Oxygen to Hydrogen Peroxide

Vacancy engineering is deemed as one of the powerful protocols to tune the catalytic activity of electrocatalysts. Herein, Se-vacancy with charge polarization is created in the NiSe2 structure (NiSe2 -VSe ) via a sequential phase conversion strategy. By a combined analysis of the Rietveld method, transient photovoltage spectra (TPV), in situ Raman and density functional theory (DFT) calculation, it is unequivocally discovered that the presence of charge-polarized Se-vacancy is beneficial for stabilizing the structure, decreasing the electron transfer kinetics, as well as optimizing the free adsorption energy of reaction intermediate during two-electron oxygen reduction reaction (2e- ORR). Benefiting from these merits, the as-prepared NiSe2 -VSe delivered the highest selectivity of 96% toward H2 O2 in alkaline media, together with a selectivity higher than 90% over the wide potential range from 0.25 to 0.55 V, ranking it in the top level among the previously reported transition metal-based electrocatalysts. Most notably, it also displayed admirable stability with only a slight selectivity decay after 5000 cycles of accelerated degradation test (ADT).

Regulating the Electronic Structure of Cu-Nx Active Sites for Efficient and Durable Oxygen Reduction Catalysis to Improve Microbial Fuel Cell Performance

The efficient and durable oxygen reduction reaction (ORR) catalyst is of great significance to boost power generation and pollutant degradation in microbial fuel cells (MFCs). Although transition metal-nitrogen-codoped carbon materials are an important class of ORR catalysts, copper-nitrogen-codoped carbon is not considered a suitable MFC cathode catalyst due to the insufficient performance and especially instability. Herein, we report a three-dimensional (3D) hierarchical porous copper, nitrogen, and boron codoped carbon (3DHP Cu-N/B-C) catalyst synthesized by the dual template method. The introduced B atom as an electron donor increases the electron density around the Cu-N_x active site, which significantly promotes the efficiency of the ORR process and stabilizes the active site by preventing demetallization. Thus, the 3DHP Cu-N/B-C catalyst exhibited excellent ORR performance with the half-wave potential of 0.83 V (vs reversible hydrogen electrode (RHE)) in a 0.1 M KOH electrolyte and 0.68 V (vs RHE) in a 50 mM PBS electrolyte. Meanwhile, 3DHP Cu-N/B-C had satisfactory stability with 94.16% current retention after 24 h of chronoamperometry test, which is better than that of 20% Pt/C. The MFCs using 3DHP Cu-N/B-C not only showed a maximum power density of up to 760.14 ± 19.03 mW m^-2 but also operating durability of more than 50 days. Moreover, the 16S rDNA sequencing results presented that the 3DHP Cu-N/B-C catalyst had a positive effect on the microbial community of the MFC with more anaerobic electroactive bacteria in the anode biofilm and fewer aerobic bacteria in the cathode biofilm. This study provides a new approach for the development of Cu-based ORR electrocatalysts as well as guidance for the rational design of high-performance MFCs.

Adsorption Energy in Oxygen Electrocatalysis

Adsorption energy (AE) of reactive intermediate is currently the most important descriptor for electrochemical reactions (e.g., water electrolysis, hydrogen fuel cell, electrochemical nitrogen fixation, electrochemical carbon dioxide reduction, etc.), which can bridge the gap between catalyst's structure and activity. Tracing the history and evolution of AE can help to understand electrocatalysis and design optimal electrocatalysts. Focusing on oxygen electrocatalysis, this review aims to provide a comprehensive introduction on how AE is selected as the activity descriptor, the intrinsic and empirical relationships related to AE, how AE links the structure and electrocatalytic performance, the approaches to obtain AE, the strategies to improve catalytic activity by modulating AE, the extrinsic influences on AE from the environment, and the methods in circumventing linear scaling relations of AE. An outlook is provided at the end with emphasis on possible future investigation related to the obstacles existing between adsorption energy and electrocatalytic performance.