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Electrocatalytic oxygen reduction reaction (ORR) via two-electron pathway is a promising approach to decentralized and on-site hydrogen peroxide (H2O2) production beyond the traditional anthraquinone process. In recent years, electrochemical H2O2 production in acidic media has attracted increasing attention owing to its stronger oxidizing capacity, superior stability, and higher compatibility with various applications. Here, recent advances of H2O2 electrosynthesis in acidic media are summarized. Specifically, fundamental aspects of two-electron ORR mechanism are firstly presented with an emphasis on the pH effect on catalytic performance. Major categories of promising electrocatalysts are then reviewed, including noble-metal-based materials, non-noble-metal single-atom catalysts, non-noble-metal compounds, and metal-free carbon-based materials. The innovative development of electrochemical devices and in situ/on-site application of electrogenerated H2O2 are also highlighted to bridge the gap between laboratory-scale fundamental research and practically relevant H2O2 electrosynthesis. Finally, critical perspectives on present challenges and promising opportunities for future research are provided.

Summary Achieving high selectivity and production efficiency simultaneously in electrocatalytic H2O2 production to replace the anthraquinone process via two-electron (2e−) oxygen reduction reaction (ORR) and 2e− water oxidation reaction (WOR) is a long-sought-after goal. However, sluggish kinetics and intrinsically unfavored thermodynamics make the electrochemical method still far from practical implementation. Herein, we experimentally demonstrate a high-efficiency two-side H2O2 generation system (WOR//ORR coupling cell) based on an active and stable bifunctional plasma-induced defective TiO2-x nanocatalyst that exhibits dramatically boosted activity/selectivity for both 2e− ORR and 2e− WOR. Such a WOR-ORR coupling strategy enables the H2O2-producing cell to provide an ultrahigh H2O2 yield rate of ∼20 mmol L−1 h−1 and a remarkable cell Faradaic efficiency of up to 134%. In situ Raman spectroscopy results and density functional theory calculations together uncover that oxygen vacancies located at the inner atomic layer and surface distortion are responsible for enhanced 2e− ORR and 2e− WOR performance, respectively.

Hydrogen peroxide (H2O2) is one of the most important industrial oxidants. In principle, photocatalytic H2O2 synthesis from oxygen and H2O using sunlight could provide a cleaner alternative route to the current anthraquinone process. Recently, conjugated organic materials have been studied as photocatalysts for solar fuels synthesis because they offer synthetic tunability over a large chemical space. Here, we used high-throughput experiments to discover a linear conjugated polymer, poly(3-4-ethynylphenyl)ethynyl)pyridine (DE7), which exhibits efficient photocatalytic H2O2 production from H2O and O2 under visible light illumination for periods of up to 10 h or so. The apparent quantum yield was 8.7% at 420 nm. Mechanistic investigations showed that the H2O2 was produced via the photoinduced stepwise reduction of O2. At longer photolysis times, however, this catalyst decomposed, suggesting a need to focus the photostability of organic photocatalysts, as well as the initial catalytic production rates.

The electrochemical two-electron oxygen reduction reaction (2e–1ORR) is a promising route for renewable H2O2 generation as an alternative method to the anthraquinone process. The development of eff...

Ambient electrochemical oxygen reduction into valuable hydrogen peroxide (H2O2) via a selective two-electron (2e-) pathway is regarded as a sustainable alternative to the industrial anthraquinone process, but it requires advanced electrocatalysts with high activity and selectivity. In this study, we report that Mn-doped TiO2 behaves as an efficient electrocatalyst toward highly selective H2O2 synthesis. This catalyst exhibits markedly enhanced 2e- oxygen reduction reaction performance with a low onset potential of 0.78 V and a high H2O2 selectivity of 92.7%, much superior to the pristine TiO2 (0.64 V, 62.2%). Additionally, it demonstrates a much improved H2O2 yield of up to 205 ppm h-1 with good stability during bulk electrolysis in an H-cell device. The significantly boosted catalytic performance is ascribed to the lattice distortion of Mn-doped TiO2 with a large amount of oxygen vacancies and Ti3+. Density functional theory calculations reveal that Mn dopant improves the electrical conductivity and reduces ΔG*OOH of pristine TiO2, thus giving rise to a highly efficient H2O2 production process.

As an environmentally friendly oxidant, H2O2 is widely utilized in various fields; however, its production methods remain limited to the chemical anthraquinone process. Alternatively, electrocatalytic oxygen reduction possesses numerous notable advantages (e.g., cost-effectiveness, small-scale, and distributed nature). As electrocatalytic oxygen reduction has been widely investigated in the fields of fuel cells and metal-air batteries, the mechanism of the 2e−-ORR pathway for producing H2O2 is not sufficiently clear. Herein, we explore the effect of the cobalt (Co) coordination environment on the electrochemical production of H2O2. The detailed investigation on N-, P-, and S-coordinated Co catalysts (Co1N1N3, Co1P1N3, and Co1S1N3) demonstrates that changing the coordination environment evidently affects the H2O2 selectivity, and the S-coordinated Co exhibits the best catalytic performance. This finding would lead to the design and selection of catalysts at atomic level for producing H2O2 via electrocatalytic oxygen reduction.

Electrocatalytic oxygen reduction reaction (ORR) provides an attractive alternative to anthraquinone process for H2O2 synthesis. Rational design of earth-abundant electrocatalysts for H2O2 synthesis via a two-electron ORR process in acids is attractive but still very challenging. In this work, we report that nitrogen-doped carbon nanotubes as a multi-functional support for CoSe2 nanoparticles not only keep CoSe2 nanoparticles well dispersed but alter the crystal structure, which in turn improves the overall catalytic behaviors and thereby renders high O2-to-H2O2 conversion efficiency. In 0.1 M HClO4, such CoSe2@NCNTs hybrid delivers a high H2O2 selectivity of 93.2% and a large H2O2 yield rate of 172 ppm·h−1 with excellent durability up to 24 h. Moreover, CoSe2@NCNTs performs effectively for organic dye degradation via electro-Fenton process. Electronic Supplementary Material Supplementary material (SEM images, EDX mapping images, XPS spectrum, XRD patterns, RRDE voltammogram, Tafel plots, cyclic voltammograms, UV-Vis spectra, and Tables S1) is available in the online version of this article at 10.1007/s12274-021-3474-0.

Electrocatalytic two-electron oxygen reduction has emerged as a promising alternative to the energy- and waste-intensive anthraquinone process for distributed H2 O2 production. This process, however, suffers from strong competition from the four-electron pathway leading to low H2 O2 selectivity. Herein, we report using a superhydrophilic O2 -entrapping electrocatalyst to enable superb two-electron oxygen reduction electrocatalysis. The honeycomb carbon nanofibers (HCNFs) are robust and capable of achieving a high H2 O2 selectivity of 97.3 %, much higher than that of its solid carbon nanofiber counterpart. Impressively, this catalyst achieves an ultrahigh mass activity of up to 220 A g-1 , surpassing all other catalysts for two-electron oxygen reduction reaction. The superhydrophilic porous carbon skeleton with rich oxygenated functional groups facilitates efficient electron transfer and better wetting of the catalyst by the electrolyte, and the interconnected cavities allow for more effective entrapping of the gas bubbles. The catalytic mechanism is further revealed by in situ Raman analysis and density functional theory calculations.

Electrochemical reduction of O2 provides a clean and decentralized pathway to produce H2O2 compared to the current energy-intensive anthraquinone process. As the electrochemical reduction of O2 pro...

Electrochemical oxygen reduction to hydrogen peroxide is now being studied as a promising renewable and localized alternative for the traditional complex anthraquinone process. Catalysts for this t...

Hydrogen peroxide (H2 O2 ), as a green fuel and oxidant, has drawn increasing attention in the energy and environmental research. Compared with the traditional anthraquinone process, the electrochemical (EC) and photoelectrochemical (PEC) syntheses of H2 O2 are cost-effective and environmentally friendly. In order to construct membraneless EC/PEC devices for the full H2 O2 synthesis, anodic H2 O2 production by water oxidation, which is less developed than cathodic H2 O2 generation, is highly desirable. Here, we review recent developments for the EC/PEC H2 O2 production by water oxidation, including fundamental aspects, benchmarking activity evaluation, material/catalyst selection, and strategies for increasing selectivity, efficiency, and accumulation. Furthermore, we discuss the challenges and outlook of water oxidation for H2 O2 production, especially device-level development, accumulation and stability, and industrial applications. Our review is intended to stimulate studies further improving EC/PEC H2 O2 production.

Summary Hydrogen peroxide (H2O2) is a high-value green chemical oxidant widely used for industrial bleaching, chemical synthesis, and disinfection. Industrially, H2O2 is produced through the energy-intensive anthraquinone process and distributed to the point of use. There is a growing interest in electrochemically producing H2O2 onsite to mitigate transportation cost and safety concerns and leveraging renewable electricity. Most research has been dedicated to the two-electron oxygen reduction to produce H2O2. For the past decade, growing attention has been paid to the two-electron water oxidation reaction (2e-WOR) to produce H2O2. This review focuses on the research progress on 2e-WOR, including basic principles, catalyst development, and H2O2 detection. Computational approaches to study candidate materials for 2e-WOR are detailed, and various experimental reports on catalysts are summarized. Ulterior electrochemical factors that impact H2O2 production are discussed, along with device-level design. Finally, a holistic perspective on water oxidation reaction is offered, and open questions for future work are presented.

Electrochemical production of H2O2 from O2 using simulated seawater provides a promising alternative to the energy-intensive industrial anthraquinone process. In this study, a flow cell system is built for electrocatalytic production of H2O2 under an air atmosphere in simulated seawater using cobalt single-atom catalysts (Co SACs). The Co SACs can achieve a high H2O2 production rate of 3.4 mol gcatalyst−1 h−1 under an air flow at a current density of 50 mA cmgeo−2 and long-term stability over 24 h in 0.5 M NaCl. It is found that Co–N5 rather than the Co–N4 structure in Co SACs is the main active site for H2O2 formation in the two-electron oxygen reduction reaction (ORR) pathway. It also shows high chloride-endurability without inhibition of the ORR process in simulated seawater. The fast production of H2O2 on Co–N5 sites in a flow cell provides a promising path of electrocatalytic oxygen reduction in simulated seawater, eventually converting ubiquitous air and seawater towards energy sustainability.

Electrosynthesis of hydrogen peroxide via oxygen reduction reaction’s two-electron route is the potential alternative to the industrial anthraquinone process for being green and cost-effective. Whereas oxygen-doped graphitic carbons have been reported as efficient catalysts, two issues remained unsettled involving usually abundant carbon-basal-planes and a mixture of oxygen functional groups, which lower the efficiency due to massive inactive planes and functional groups. To achieve carbon-based catalysts with abundant edges and identical functional groups, a ‘bottom-up’ approach to design materials at the molecular level is presented here. Starting from the small molecules of pyrene, a microporous carbon framework is prepared with abundant micropores of 0.5 nm and a large surface area up to 1346 m2 g-1, which facilitates further combination of a high content of C–O–C with the rich carbon edges. The positive correlation between selectivity and oxygen content further confirms the C–O–C as active sites. The catalyst exhibits a comprehensive performance including a considerable selectivity of 87%, a low onsite-potential at 0.77 VRHE, and a high ring current density of 2.79 mA cm−2 at 0.42 VRHE. Such a ‘bottom-up’ structural and functional engineering strategy may extend to the synthesis of more catalysts/electrode materials and energy/environmental related applications.

Hydrogen peroxide (H2O2) is a green oxidant widely used in various fields, from water treatment to rocket propellant. Currently, H2O2 is predominantly manufactured via the anthraquinone process, which requires large infrastructure investments and high energy consumption. In this study, an argon plasma-catalytic bubble process was designed to generate underwater plasma bubbles for efficient delivery of reactive species for H2O2 synthesis, using only water as a reactant and solar radiation as the renewable energy source. The process demonstrates unprecedented energy efficiency by employing a plasma-bubble catalytic reactor capable of operation in two discharge modes, i.e., glow and spark discharges, and using dual reactors within a single AC-circuit to mitigate energy losses around the ground electrode. The results suggest that the principal route of H2O2 generation is from the combination of dissolved ˙OH radicals at the plasma–liquid interface (PLI) of the forming bubbles. The dissolution of H2O2 formed in the gas phase also contributes to aqueous H2O2 generation, especially when employing humid argon. By employing a secondary reactor to utilise the lost energy around the low-voltage electrode and integrating a strongly interfacial-coupled 2D-TiO2/2D-g-C3N4 photocatalyst in the glow discharge area, the achieved H2O2 production rate and energy efficiency of the system are 164.6 mg h−1 and 9.0 g kW h−1, respectively. This study provides new insights for sustainable and decentralised H2O2 production, and the proposed strategy can be further developed as a stand-alone or auxiliary technology in green and sustainable chemistry.

Electroreduction of O2 into H2O2 holds great promise to replace the energy-intensive anthraquinone process that is currently used as an industry standard, but its practical feasibility still requires materials with high catalytic efficiencies. It is now shown that Co-tetramethoxyphenylporphyrin-carbon nanotube (CoTMPP/CNT) nanohybrid acts as a high-performance catalyst with fast electron delivery to active sites toward electrochemically generating H2O2 under acidic aqueous conditions, attaining a H2O2 selectivity of over 95% and achieving strong stability. More impressively, it reduces O2 to H2O2 with an unprecedented mass activity of 9694 A g−1 and a high turnover frequency of up to 6.95 s−1 (0.6 VRHE), representing the most active molecule-based two-electron O2 reduction reaction (ORR) electrocatalyst under an acidic environment so far. It also performs efficiently in neutral media. Taking advantage of the well-defined structure of TMPP unit, we systematically study the trends in catalytic activity as well as selectivity toward ORR at the M-N4 site (M = Mn, Fe, Co, Ni, Cu) with identical chemical environment of TMPP. In situ attenuated total reflection infrared spectroscopy and density functional theory calculations were used to reveal further the catalytic mechanism.

Development of efficient and affordable catalytic systems for direct H2O2 production from abundant resources is necessary to replace the current anthraquinone process and also to enable broader use...

Electrochemical H2O2 production via two-electron (2e–) oxygen reduction is a green onsite alternative to the current anthraquinone process. However, searching for cost-effective, metal-free electro...

Hydrogen peroxide (H2O2) is a kind of basic inorganic chemical product, which has been extensively developed in biology, chemistry, pharmacy, and environmental protection. H2O2 is mainly produced by the energy-wasting and environmentally-harmful anthraquinone process in industry. Photocatalyic synthesis of H2O2 by utilizing solar energy, water and O2 can reduce the production cost and the environment pollution, therefore has brought a hot-spot of research. In this review, we summarize the recent research advances in synthesizing and modificating polymer carbon nitride-based photocatalysts, and their applications in the photosynthesis of H2O2. The current challenges and opportunities of the polymer carbon nitride-based photocatalysts for the photosynthesis of H2O2 are also discussed.

Hydrogen peroxide produced by electrochemical oxygen reduction reaction provides a potentially cost effective and energy efficient alternative to the industrial anthraquinone process. In this study, we demonstrate that by modulating the oxygen functional groups near the atomically dispersed cobalt sites with proper electrochemical/chemical treatments, a highly active and selective oxygen reduction process for hydrogen peroxide production can be obtained in acidic electrolyte, showing a negligible amount of onset overpotential and nearly 100% selectivity within a wide range of applied potentials. Combined spectroscopic results reveal that the exceptionally enhanced performance of hydrogen peroxide generation originates from the presence of epoxy groups near the Co–N4 centers, which has resulted in the modification of the electronic structure of the cobalt atoms. Computational modeling demonstrates these electronically modified cobalt atoms will enhance the hydrogen peroxide productivity during oxygen reduction reaction in acid, providing insights into the design of electroactive materials for effective peroxide production. The production of hydrogen peroxide by electrochemical oxygen reduction is an attractive alternative to the industrial process, but catalysts should be optimized. Here, the authors enhance hydrogen peroxide production in acidic media with epoxy groups near cobalt centers on carbon nanotubes.

Selective two-electron (2 e−) pathway oxygen reduction reaction (ORR) has gained prominence for enabling small-scale, on-site electrochemical H2O2 production and has emerged as a promising alternative to the conventional anthraquinone process. The rational design of catalysts that can suppress the competing four-electron pathway ORR is critical. This review highlights catalyst design strategies for promoting the selective 2 e− pathway ORR, including alloying with inert metals, partial surface poisoning, and generating atomically dispersed sites. The major results and advances, as well as unresolved challenges are summarized.

Electrochemical production of H2O2 from O2 is a promising alternative to the energy-intensive anthraquinone process that is currently used as an industry standard. Although most research on the oxy...

Hydrogen peroxide (H2O2) synthesis by electrochemical oxygen reduction reaction has attracted great attention as a green substitute for anthraquinone process. However, low oxygen utilization efficiency (, H2O2 electrosynthesis has garnered great attention as a green alternative to the anthraquinone process. Here the authors propose a cost-effective cathode to greatly improve the O2 diffusion coefficient, resulting in a high H2O2 production without the need for aeration.

Electrochemical hydrogen peroxide production from two-electron oxygen reduction reaction, a cost-effective, sustainable and reliable method compared with the traditional anthraquinone process, is attracting growing attention. However, it is challenged by the selectivity of electrocatalysts. In this context, nitrogen and oxygen co-doped ordered mesoporous carbon materials have been successfully fabricated. Benefiting from the ordered pore structure, better dispersion behavior and valid doping effect, a high selectivity (~95.00%), good activity and stability toward H2O2 production were achieved. Systematic characterizations like physical adsorption, zeta potential, X-ray photoelectron spectroscopy and density functional theory (DFT) calculation revealed that interactive effects between pyridinic N and functional groups of COOH/COC largely facilitated the desorption of intermediates (*OOH, * represents an unoccupied active site) in turn enhance the selectivity of electrocatalysts toward H2O2 production. Interestingly, H2O2 produced in situ was applied to Electro-Fenton, the formaldehyde mineralization rate was high to about 88.06%. These findings offer a rational chemical design of electrocatalysts toward H2O2 production and pollutant purification.

Hydrogen peroxide is a commodity chemical with immense applications as an environmentally benign disinfectant for water remediation, a green oxidant for synthetic chemistry and pulp bleaching, an energy carrier molecule and a rocket propellant. It is typically synthesized by indirect batch anthraquinone process, where sequential hydrogenation and oxidation of anthraquinone molecules generates H2O2. This highly energy demanding catalytic sequence necessitates the advent of new reaction pathways with lower energy expenditure. Here we demonstrate a Zn-quinone battery for paired H2O2 electrosynthesis at the three phase boundary of its cathodic half-cell during electric power generation. The catalytic quinone half-cell of the Zn-quinone battery, mediates proton coupled electron transfer with molecular oxygen during its chemical regeneration thereby pairing peroxide electrosynthesis with electricity generation. Hydrogen peroxide synthesizing Zn-quinone battery (HPSB) demonstrated a peak power density of ~90 mW/cm2 at a peak current density of ~145 mA/cm2 while synthesizing ~230 mM of H2O2. HPSB offers immense opportunities as it distinctly couples electric power generation with peroxide electrosynthesis which in-turn transforms energy conversion in batteries truly multifunctional.

The continuous on-site production of H2O2 using an inexpensive metal catalyst based electrochemical approach as the alternative of the widely used complex anthraquinone process is particularly promising. Although tremendous progress has been made in recent years towards developing oxygen reduction reaction (ORR) catalyst for H2O2 production, fabricating highly active, selective, and stable H2O2 catalyst that works at high pH is always the challenge. Here, we describe a rationally designed non-precious metal-based nitrogen-doped Fe2O3-carbon nanotubes (NC@Fe2O3-CNTs) catalyst, which not only exhibits high ORR activity and low overpotential but also shows a unique selectivity towards H2O2 generation (97.3%) in alkaline media. Moreover, the NC@Fe2O3-CNTs catalyst retains a much higher relative current after continuous operation for 10 h, as compared to commercial Pt/C catalyst. The optimized NC@Fe2O3-CNTs shows the superior overall performance of H2O2 generation as compared to the present catalysts under high pH. The catalytic mechanism analysis indicates that the nitrogen species, Fe chemical states, oxygen vacancies and CNTs skeleton play important roles in improving the selectivity and current density of H2O2 generation.

Despite the growing demand for hydrogen peroxide it is almost exclusively manufactured by the energy-intensive anthraquinone process. Alternatively, H2O2 can be produced electrochemically via the two-electron oxygen reduction reaction, although the performance of the state-of-the-art electrocatalysts is insufficient to meet the demands for industrialization. Interestingly, guided by first-principles calculations, we found that the catalytic properties of the Co–N4 moiety can be tailored by fine-tuning its surrounding atomic configuration to resemble the structure-dependent catalytic properties of metalloenzymes. Using this principle, we designed and synthesized a single-atom electrocatalyst that comprises an optimized Co–N4 moiety incorporated in nitrogen-doped graphene for H2O2 production and exhibits a kinetic current density of 2.8 mA cm−2 (at 0.65 V versus the reversible hydrogen electrode) and a mass activity of 155 A g−1 (at 0.65 V versus the reversible hydrogen electrode) with negligible activity loss over 110 hours. Producing H2O2 electrochemically currently use electrocatalysts that are insufficient to meet the demands for industrialization. A single-atom electrocatalyst with an optimized Co–N4 moiety incorporated in nitrogen-doped graphene is shown to exhibit enhanced performance for H2O2 production.

The exploration of high-efficiency, robust and low-cost electrocatalysts for hydrogen peroxide (H2O2) production receives increasing attention due to its key role in developing a new alternative to replace the traditional anthraquinone process. In recent years, significant achievements of non-noble metal electrocatalysts for H2O2 production have been made. Herein, this review presents recent advances of noble-metal-free electrocatalysts toward H2O2 production. Specifically, we first introduce the fundamental principle of on-site electrochemical synthesis of H2O2. Then, the classification and corresponding recent advances of noble-metal-free electrocatalysts are reviewed, including carbon-based materials (modified by pore structure adjustment, topology defects, heteroatom-doping and surface oxygen functionalization), metal compounds (e.g., NiO, MnO, FeO, Bi2Te3, and CoS2), metal single atom catalysts (e.g., Fe, Co, Ni, Mn, and Mo) and metal complexes. In parallel, the synthesis strategy, component, structure, electrochemical properties and reaction mechanism are highlighted. Finally, an outlook on current advances, challenges, and potential of noble-metal-free electrocatalysts towards H2O2 production is also discussed.

Hydrogen peroxide (H2O2) is a versatile and environmentally friendly oxidant with a wide range of industrial and household applications. In recent years, the decentralization of H2O2 production through the two-electron oxygen reduction reaction (ORR) has emerged as an attractive alternative to the well-established anthraquinone process. And of the many electrocatalysts developed for the two-electron ORR to produce H2O2, metal-free carbon catalysts (MFCCs) have received extensive attention due to their cost-effectiveness and natural abundance. Based on this, this review will provide an in-depth overview into MFCC design and fabrication with an emphasis on porosity control, heteroatom doping, oxygen functionalization, defect engineering and organic–inorganic interface engineering. This review will also discuss and analyze the interplays between these factors in terms of MFCC catalytic activity and selectivity towards H2O2 production. Furthermore, major technical challenges are presented, and future research directions are proposed to guide further development towards practical application.

The electroproduction of H2O2 through 2e oxygen reduction reaction (ORR) as an alternative strategy for the conventional anthraquinone process is highly energy-efficient and environment-friendly. Different kinds of electrocatalysts with high selectivity, activity, and stability have been recently reported, and are an essential part of the whole electroproduction process of H2O2. In this review, we expound the ORR mechanism and introduce some methods to screen out potential electrocatalysts through theoretical calculations and experimental verifications. In addition, recent advances in reactor design for large-scale on-site production of H2O2 and integrated systems for electricity-H2O2 co-generation are mentioned. With ideal electrocatalysts and rational reactor design, different concentrations of H2O2 can be obtained depending on the practical applications. Utilizing the solar or chemical energy, it can promote energy efficiency and sustainability of the process. Finally, we make a brief conclusion about recent developments in electrocatalysts, device design, as well as integrated systems, and give an outlook for future research challenges, which are meaningful for advancing the electrochemical on-site production of H2O2via 2e ORR to the marketplace.

Electro-reduction of O2 to generate H2O2 is an attractive alternative to the current anthraquinone process and quite necessary for chemical industries and environmental remediation. In general, suf...

The electrochemical production of hydrogen peroxide is enjoying increasing attention by endowing a promising alternative to the traditional complex and energy-intensive anthraquinone process. Engin...

The electrochemical production of hydrogen peroxide (H(2)O(2)) by 2-electron oxygen reduction reaction (ORR) is an attractive alternative to the present complex anthraquinone process. The objective of this paper is to provide a state-of-the-arts review of the most important aspects of this process. First, recent advances in H(2)O(2) production are reviewed and the advantages of H(2)O(2) electrogeneration via 2-electron ORR are highlighted. Second, the selectivity of the ORR pathway towards H(2)O(2) formation as well as the development process of H(2)O(2) production are presented. The cathode characteristics are the decisive factors of H(2)O(2) production. Thus the focus is shifted to the introduction of commonly used carbon cathodes and their modification methods, including the introduction of other active carbon materials, hetero-atoms doping (i.e., O, N, F, B, and P) and decoration with metal oxides. Cathode stability is evaluated due to its significance for long-term application. Effects of various operational parameters, such as electrode potential/current density, supporting electrolyte, electrolyte pH, temperature, dissolved oxygen, and current mode on H(2)O(2) production are then discussed. Additionally, the environmental application of electrogenerated H(2)O(2) on aqueous and gaseous contaminants removal, including dyes, pesticides, herbicides, phenolic compounds, drugs, VOCs, SO(2), NO, and Hg(0), are described. Finally, a brief conclusion about the recent progress achieved in H(2)O(2) electrogeneration via 2-electron ORR and an outlook on future research challenges are proposed.

The selective electrocatalytic reduction of dioxygen (O2) to hydrogen peroxide (H2O2) could be an alternative to the anthraquinone process used industrially, as well as enable the on-demand production of a useful chemical oxidant, obviating the need for long-term storage. There are challenges associated with this, since the two-proton/two-electron reduction of H2O2 to two equivalents of water (H2O) or disproportionation to O2 and H2O can be competing reactions. Recently, we reported a Mn(III) Schiff base-type complex, Mn(tbudhbpy)Cl, where 6,6′-di(3,5-di-tert-butyl-2-phenolate)-2,2′-bipyridine = [tbudhbpy]2–, which is active for the electrocatalytic reduction of O2 to H2O2 (ca. 80% selectivity). The less-than-quantitative selectivity could be attributed in part to a thermal disproportionation reaction of H2O2 to O2 and H2O. To understand the mechanism in greater detail, spectrochemical stopped-flow and electrochemical techniques were employed to examine the catalytic rate law and kinetic reaction paramete...

Hydrogen peroxide (H2O2), first synthesized in 1818 through the acidification of barium peroxide (BaO2) with nitric acid, is a clear and colorless liquid which is entirely miscible with water and variety of organic solvents such as carboxylic esters. Anthraquinone process (an old production process of H2O2), a batch process carried out in large facilities is an energy demanding process that requires large facilities, and involves oxidation of anthraquinone molecules and sequential hydrogenation. Moreover, the direct synthesis method enables production in a continuous mode as well as it permits small scale, decentralized production. Many drawbacks associated with these processes such as, energetic inefficiency and inherent disadvantages have motivated researchers, industry and academia to find out alternative for synthesis of H2O2. Electrochemical route based on catalyst selectively reduce oxygen to hydrogen peroxide. O2 is cathodically reduced to produce H2O2 via 2-electron pathway or 4-electron pathway to get H2O. Electrolysis of water has an important place in storage and electrochemical energy conversion process where problem is to choose a sufficiently stable and active electrode for anodic oxygen evolution reaction. Most commonly used catalysts on the cathode are carbon based materials such as carbon black, carbon nanotubes, graphite, carbon sponge, and carbon fiber. In perspective of expanding demand of production and usage of hydrogen peroxide we review the past literature to summarize different production processes of H2O2. In this review paper, we mainly focus on electrochemical production of hydrogen peroxide along with other alternatives such as, anthraquinone method for industrial H2O2 production and direct synthesis process. We also review the catalytic activity, selectivity and stability for enhanced yield of H2O2. From revision of experimental and theoretical data from the past literature; we argue that successful implementation of electrochemical H2O2 production can be realized on the basis of stable, active and selective catalyst.

Electrochemical synthesis of hydrogen peroxide (H2O2) through O2 electroreduction is an attractive alternative to the currently used anthraquinone process, and highly desirable for green chemical industries and environmental remediation. However, it remains a great challenge to develop cost-effective and durable electrocatalysts. Hence, rational strategy for developing electrocatalyst materials to achieve highly efficient 2e− pathway oxygen reduction reaction (ORR) electrocatalysis is extremely important for in situ electrochemical synthesis of H2O2. In the present work, an economical activated graphite felt (AGF) material, following a simple and low-cost gaseous acetic acid activation method, is developed. With this activation process, the electrochemical performance of the AGF shows a great promotion for H2O2 production rate. Compared with raw graphite felt (RGF) material, the yield of H2O2 achieved on AGF is enhanced by several folds. The enhanced performance might be attributed to its specific pore structure, high content of defects and transformation of surface chemical bonds, which derives from the activation with gaseous acetic acid at high temperature. It is found that the factors responsible for the remarkable electrocatalytic performance of AGF1100 are: 1) the special pore structure, which offers large area for reaction, obtained through gaseous acetic acid activation process at high temperature; 2) high content of sp3 C bonds, defects, and oxygen-containing functional groups, which can act as active sites for oxygen adsorption or reduction during the electrocatalytic process.

Hydrogen peroxide (H2 O2 ) is a highly value-added and environmentally friendly chemical with various applications. The production of H2 O2 by electrocatalytic 2e- oxygen reduction reaction (ORR) has drawn considerable research attention, with a view to replacing the currently established anthraquinone process. Electrocatalysts with low cost, high activity, high selectivity, and superior stability are in high demand to realize precise control over electrochemical H2 O2 synthesis by 2e- ORR and the feasible commercialization of this system. This Review introduces a comprehensive overview of non-noble metal-based catalysts for electrochemical oxygen reduction to afford H2 O2 , providing an insight into catalyst design and corresponding reaction mechanisms. It starts with an in-depth discussion on the origins of 2e- /4e- selectivity towards ORR for catalysts. Recent advances in design strategies for non-noble metal-based catalysts, including carbon nanomaterials and transition metal-based materials, for electrochemical oxygen reduction to H2 O2 are then discussed, with an emphasis on the effects of electronic structure, nanostructure, and surface properties on catalytic performance. Finally, future challenges and opportunities are proposed for the further development of H2 O2 electrogeneration through 2e- ORR, from the standpoints of mechanistic studies and practical application.

Hydrogen peroxide (H2O2) electrosynthesis from 2-electron O2 reduction reaction (2eORR) is widely regarded as a promising alternative to the current industry-dominant anthraquinone process. Design and fabrication of effective, low-cost carbon-based electrodes is one of the priorities. Many previous work well confirmed that hydrophilic carbon-based electrodes are preferable for 2eORR. Here, we proposed a strategy of hydrophilicity-hydrophobicity regulation. By using commercially available graphite felt (GF) as electrodes, we showed that both hydrophilic GF, hydrophobic GF, and Janus GF yielded significantly higher H2O2 production, which is 7.3 times, 7.6 times, and 7.7 times higher than the original GF, respectively. Results showed that currents and stirring rates affect the H2O2 yields. The enhancement of hydrophilic GF is due to the incorporation of oxygen-containing functional groups, while the hydrophobic and Janus GF comes from the locally confined O2 bubbles, which built a gas-liquid-solid interface inside GF and thus enhance the H2O2 formation kinetics. Finally, the effectiveness of the hydrophilicity-hydrophobicity regulation concept was tested in Electro-Fenton process by removing typical dyes and antibiotics. This work supply an effective but facile strategy to enhance the performance of carbon-based electrodes towards 2eORR by regulating the micro-environment of electrodes.

Hydrogen peroxide is an environmentally friendly oxidizing agent that is important in several industries. It is currently produced industrially via the anthrahydroquinone (AHQ) process where O2 reacts with a functionalised version of anthrahydroquinone to produce H2O2 and anthraquinone. In the previously published DFT pathway for this process the transition of the OOH? radical across the partially dehydrogenated AHQ catalyst was not explored. In this paper, we will use DFT to explore this step and show that there is a deep potential energy minimum that inhibits the OOH. from being fully reduced. We then examine other similar sized polycyclic molecules with two OH-groups on the same side that could serve as alternative catalysts without this issue. In this analysis, we identify Phenanthraquinone as a possible alternative and present the pathway for this candidate to produce H2O2 as well as its regeneration with H2.

Electrochemical reduction of O2 provides a clean and decentralized pathway to produce H2O2 compared to the current energy-intensive anthraquinone process. As the electrochemical reduction of O2 proceeds via either two-electron or four-electron path- way, it is thus essential to control the selectivity as well as to maximize the catalytic activity. Siahrostami et al. demonstrated a novel approach to control the reaction pathway by optimizing an adsorption ensemble to tune adsorption sites of reaction intermediates, and identified Pt-Hg catalysts from density functional theory (DFT) calculations and experimentally validated this catalyst (Nat. Mater. 2013, 12, 1137). Inspired by this concept, in this work, we apply a state-of-the-art high-throughput screening to develop O2 reduction catalyst for selective H2O2 production. Starting from Materials Project database, we evaluate activity, selectivity and electrochemical stability. To efficiently perform the screening, we introduce an active motif based approach which pre-screens unpromising materials and only performs DFT calculations for promising materials, which significantly reduce the number of the required calculations. We not only provide a list of promising candidates identified by DFT calculations, but also suggest element species to achieve high catalytic activity or H2O2 selectivity for future experimental attempts. Finally, we discuss a strategy for efficient future high-throughput screening using a machine learning pipeline consisting of a non-linear dimension reduction and a density-based clustering.