Electrochemical H2O2 Production Research Articles

Room temperature oxygenated groups addition in carbon materials via ozone oxidation for boosting electrochemical H2O2 production

The crucial yet delicate 2e− oxygen reduction reaction (ORR) for producing the green chemical H2O2 relies on the uniform coordination environment of the active sites, such as oxygenated groups in metal-free carbon material catalysts. However, conventional harsh carbon material synthesis methods inevitably introduce structural defects and alter morphology, hindering the precise control of active site formation. Herein, we developed the ozone oxidation method under controlled reaction conditions to precisely modify carbon materials at room temperature. Through controlling the ozonation of reaction time, concentration, temperature, and relative humidity, we find the mild method allows us to precisely add active carboxyl group (–COOH) without forming structural defects. Electrochemical tests reveal that the optimal catalyst with the highest –COOH content exhibits the most outstanding mass activity of 164 A/g at 0.65 V and the highest H2O2 selectivity of 91 %. The density functional theory calculations demonstrate that the carbon sites directly connected to –COOH possess the optimized binding strength of *OOH intermediate to favor the two-electron oxygen reduction process. This work offers a novel approach to precisely and gently control carbon surface groups while preserving the structural morphology through ozone gas treatment, which can be readily applied to other material designs.

Potential-Driven Coordinated Oxygen Migration in an Electrocatalyst for Sustainable H2O2 Synthesis.

Local coordination environment (LCE) manipulation has emerged as a significant approach for modulating the electrocatalytic behavior of low-dimensional nanomaterials. However, challenges persist in accurately identifying active sites and understanding dynamic changes during operation. Here, we underscore the influence of LCE on the electrochemical production of H2O2, utilizing the Pd cluster as a model catalyst. Density functional theory (DFT) calculations illustrate the role of first- and second-coordinated sulfur and oxygen in modulating the binding strength of HOO*. Guided by DFT screening, the as-prepared Pd cluster (Pdx/HMCS) catalyst presents exceptional catalytic performance with a high mass activity of 4.06 A mg-1 at 0.45 V and selectivity above 94%. The Pdx/HMCS catalyst also delivers promising potential for industrial practices with a production rate of 16.3 mol gcat-1 h-1 in flow cell evaluation. Elaborated in situ characterizations confirm that under operation, oxygen migrates from the second coordination sphere (CS) to the first CS to achieve oxygen coverage on the catalyst surface. Such an oxygen migration phenomenon and the optimized first and second coordination environment give rise to the outstanding performance.

Modulating Core Polarity in Metal-free Covalent Organic Frameworks for Selective Electrocatalytic Hydrogen Peroxide Production.

Tuning the charge density at the active site to balance the adsorption ability and reactivity of oxygen is extremely significant for driving a two-electron oxygen reduction reaction (ORR) to produce hydrogen peroxide (H2O2). Herein, we have highlighted the influence of intermolecular polarity in covalent organic frameworks (COFs) on the efficiency and selectivity of electrochemical H2O2 production. Different C3 symmetric building blocks have been utilized to regulate the charge density at the active sites. The benzene-cored COF, which exhibits reduced polarity than the triazine-cored COF, displayed enhanced performance in H2O2 production, achieving 93.1% selectivity for H₂O₂ at 0.4 V with almost two-electron transfer and a faradaic efficiency of 90.5%. In-situ electrochemical Raman spectroscopy and scanning electrochemical microscopy (SECM) were employed to confirm H₂O₂ generation and analyze spatial reactivity patterns. These techniques provided detailed insights into localized catalytic behavior, emphasizing the influence of core polarity.

Modulating Core Polarity in Metal‐free Covalent Organic Frameworks for Selective Electrocatalytic Hydrogen Peroxide Production

Tuning the charge density at the active site to balance the adsorption ability and reactivity of oxygen is extremely significant for driving a two‐electron oxygen reduction reaction (ORR) to produce hydrogen peroxide (H2O2). Herein, we have highlighted the influence of intermolecular polarity in covalent organic frameworks (COFs) on the efficiency and selectivity of electrochemical H2O2 production. Different C3 symmetric building blocks have been utilized to regulate the charge density at the active sites. The benzene‐cored COF, which exhibits reduced polarity than the triazine‐cored COF, displayed enhanced performance in H2O2 production, achieving 93.1% selectivity for H₂O₂ at 0.4 V with almost two‐electron transfer and a faradaic efficiency of 90.5%. In‐situ electrochemical Raman spectroscopy and scanning electrochemical microscopy (SECM) were employed to confirm H₂O₂ generation and analyze spatial reactivity patterns. These techniques provided detailed insights into localized catalytic behavior, emphasizing the influence of core polarity.

Simultaneous efficient production of hydrogen peroxide, urea and H2 by bifunctional Cu-doped TiO2 electrocatalyst from CO2, N2 and water

The production of three separated, high-value chemicals (H2O2, urea and H2) from CO2, N2, and H2O represents a significant challenge. It is a prospective and innovative way to simultaneously produce these chemicals in an anion exchange membrane (AEM) electrolyzer, which couples anodic 2e- water oxidation (2e-WOR) and cathodic CO2, N2 and water reduction reaction (CNWRR), but has not yet been realized. Here, we found that bifunctional CuxTi1-xO2-y catalysts can be employed in the electrochemical production of H2O2, urea and H2 from CO2, N2 and water, and the optimized Cu0.12Ti0.88O2-y catalyst exhibits an excellent productivity of 11.8 μmol cm−2 min−1, 0.3 mg cm-2h−1 and 0.82 mmol cm-2h−1 for H2O2, urea and H2 at 4.0 V (50 mA cm−2) in AEM electrolyzer, respectively. Theoretical calculations reveal that the superior performance of the 2e-WOR and CNWRR is attributed to the Cu doping effect, which not only promotes the coupling of *OH but also optimizes the adsorption energy barriers of COOH* and NNH*. It is worth noting that the AEM electrolyzer assembled by bifunctional Cu0.12Ti0.88O2-y reaches a current density of 50 mA cm−2 with a cell voltage of 4.0 V and exhibits excellent stability of 50-hour continuous operation.

Shape-controllable synthesis of lignin-derived boron-doped nanoporous carbons for dye adsorption and electrochemical H2O2 production

Lignin-derived nanocarbon materials (LNCMs) have attracted intense attention due to their excellent properties and promising applications in renewable energy technologies. However, lignins tend to melt and agglomerate during pyrolysis, make it difficult to control the morphology and pore structure of the resulting carbon. In this study, boron-doped porous nanocarbon (BFC) in various shapes (sphere, band, and sheet) were synthesized using ammonium borate as a crosslinking agent to prevent lignin melting, assisted by liquid nitrogen freeze-drying and potassium phosphate (KP) templating. The effects of BFC structure on methylene blue adsorption and electrochemical generation of H2O2 were investigated. The results show that KP-1/1-8BFC exhibits a high specific surface area (912.89 m2/g) and a hierarchical micro-mesoporous structure, achieving a remarkable adsorption capacity of 473.9 mg/g for methylene blue and rapid kinetics. The selectivity of KP-1/20-8BFC for electrochemical production of H2O2 reaches 85 %. This study offers theoretical guidance for the controllable synthesis of LNCMs, contributing to the advancement of sustainable energy solutions.

Defective PTFE with Dense Active Sites Enabling Rapid H2O2 Production for Efficient Water Purification

AbstractThe electrosynthesis of hydrogen peroxide (H2O2) via two‐electron oxygen reduction reaction (2e−‐ORR) enables high energy utilization and distributed H2O2 production. Rational catalyst design is essential for achieving efficient H2O2 production, in which fluorine‐modified carbon materials hold great potential. However, conventional methods can only induce limited loading of fluorine atoms in carbon‐based catalysts, leading to unsatisfying electrochemical performance. Herein, the design of fluorine‐containing active sites with high density and high 2e−‐ORR selectivity is achieved by loading fluorine‐containing chained polytetrafluoroethylene precursors onto conductive carbon substrates by plasma‐assisted ball milling technique. Consequently, the defect‐rich PTFE@CNTs show a high selectivity of over 95% and a high H2O2 yield of more than 35 mol g−1 h−1. Furthermore, the electrochemical production of H2O2 can be readily integrated with water purification units to decompose contaminants, showing over 80% degradation of multiple dyes within 1 h and over 95% removal ratio of antibiotics within 4 h. In addition, 100% sterilization of staphylococcus aureus is achieved by on‐site accumulating H2O2 in commercial saline for only 30 min. This defect engineering strategy through plasma ball milling provides a promising and universal avenue toward designing highly active and efficient electrocatalysts for 2e−‐ORR as well as other electrochemical processes.

First-principles study of electrochemical H2O2 production on Pd-B40 single-atom catalyst

Hydrogen peroxide (H2O2), a versatile green compound, is increasingly in demand. The electrochemical two-electron oxygen reduction reaction (2e− ORR) is a simple and environmentally friendly substitute method to the traditional anthraquinone oxidation method for H2O2 production. This study systematically investigates the 2e− ORR process on single transition metal atom-loaded boron fullerene (M − B40) using density functional theory calculations. In evaluating the stability of the catalysts, we found that Au, Pd, Pt, Rh, and Ir atoms adsorbed on hexagonal or heptagonal sites of B40 exhibit good stability. Among these, Pd-modified B40 heptagonal cavity (Pd-B40-heptagonal) demonstrates an ideal Gibbs free energy change for OOH* (4.49 eV) and efficiently catalyzes H2O2 production at a low overpotential (0.27 V). Electronic structure analysis reveals that electron transfer between Pd-B40-heptagonal and adsorbed O2 facilitates O2 activation. Additionally, the high 2e− ORR activity of Pd-B40-heptagonal is attributed to electron transfer from the Pd-d orbitals to the π* anti-bonding of p orbitals of OOH*, moderately activating the O-O bond. This study offers valuable understanding designing high-performance electrocatalysts for 2e− ORR.

Modelling Anodic H2O2 Accumulation in Alkaline Water Electrolysis with Experimental Validation

Hydrogen peroxide (H2O2) is a high value commodity chemical used as a green oxidant in industries such as paper milling and textile bleaching, and is currently produced by the anthraquinone oxidation process. The anodic co-production of H2O2 during alkaline water electrolysis has gained interest as a sustainable alternative for anthraquinone oxidation. However, electrochemical H2O2 production is often studied with idealized laboratory setups to determine the H2O2 formation kinetics. In this work, we perform the reaction using a flow cell with separately recirculating anolyte and catholyte. We then fit the H2O2 accumulation data to an analytical model that we derive based on mole balances that accounts for anodic generation, anodic oxidation, and bulk disproportionation of H2O2, as well as anolyte reservoir volume and anode chamber volume. We performed experiments to derive values for maximum H2O2 production at 300 mA cm-2, with values of 0.540 mmol s-1 for anodic generation of H2O2 (FEH2O2 = 58%) and 0.416 min-1 for anodic oxidation of H2O2, with a bulk disproportionation rate constant of 1.85 × 10−3 min-1. We successfully applied our model to two sources in literature to derive values for their systems as well. In all cases, the contribution of anodic oxidation of H2O2 was found to be the larger loss mechanism in comparison to bulk disproportionation. Figure 1

Selective electrochemical H2O2 production by a molecular copper catalyst: A crucial relation between reaction rate and mass transport

Selective electrochemical H2O2 production by a molecular copper catalyst: A crucial relation between reaction rate and mass transport

Bioinspired Tetranuclear Manganese Cubane Complex as an Efficient Molecular Electrocatalyst for Two‐Electron Water Oxidation Towards Hydrogen Peroxide

AbstractStable homogeneous two‐electron water oxidation electrocatalysts are highly demanded to understand the precise mechanism and reaction intermediates of electrochemical H2O2 production. Here we report a tetranuclear manganese complex with a cubane structure which can electrocatalyze water oxidation to hydrogen peroxide under alkaline and neutral conditions. Such a complex demonstrates an optimal Faradaic efficiency (FE) of 87 %, which is amongst (if not) the highest FE(H2O2) of reported homogeneous and heterogeneous electrocatalysts. In addition, active species were identified and co‐catalysts were excluded through ESI‐MS characterization. Furthermore, we identified water binding sites and isolated one‐electron oxidation intermediate by chemical oxidation of the catalyst in the presence of water substrates. It is evident that efficient proton‐accepting electrolytes avoid rapid proton building‐up at electrode and substantially improve reaction rate and selectivity. Accordingly, we propose a two‐electron catalytic cycle model for water oxidation to hydrogen peroxide with the bioinspired molecular electrocatalyst. The present work is expected to provide an ideal platform to elucidate the two‐electron WOR mechanism at the atomic level.

Bioinspired Tetranuclear Manganese Cubane Complex as an Efficient Molecular Electrocatalyst for Two-Electron Water Oxidation Towards Hydrogen Peroxide.

Stable homogeneous two-electron water oxidation electrocatalysts are highly demanded to understand the precise mechanism and reaction intermediates of electrochemical H2O2 production. Here we report a tetranuclear manganese complex with a cubane structure which can electrocatalyze water oxidation to hydrogen peroxide under alkaline and neutral conditions. Such a complex demonstrates an optimal Faradaic efficiency (FE) of 87 %, which is amongst (if not) the highest FE(H2O2) of reported homogeneous and heterogeneous electrocatalysts. In addition, active species were identified and co-catalysts were excluded through ESI-MS characterization. Furthermore, we identified water binding sites and isolated one-electron oxidation intermediate by chemical oxidation of the catalyst in the presence of water substrates. It is evident that efficient proton-accepting electrolytes avoid rapid proton building-up at electrode and substantially improve reaction rate and selectivity. Accordingly, we propose a two-electron catalytic cycle model for water oxidation to hydrogen peroxide with the bioinspired molecular electrocatalyst. The present work is expected to provide an ideal platform to elucidate the two-electron WOR mechanism at the atomic level.

Enhanced electroproduction of hydrogen peroxide with oxidized boron-doped carbon catalysts synthesized from gaseous CO2

As an eco-friendly alternative to the conventional anthraquinone process, electrochemical production of hydrogen peroxide (H2O2) through the oxygen reduction reaction has been attracting attention. The goal of this work is to derive a carbon-based material from carbon dioxide (CO2) to achieve high performance in electrochemical H2O2 production. Doping heterogeneous element such as oxygen on a carbon catalyst has been mainly explored to increase the selectivity and activity, but little research has been conducted on enhancing catalytic activity with oxidized boron insertion. This study proposes porous carbon materials synthesized from CO2 as electrocatalysts. Polyethylene oxide (PEO) was thermally treated together to increase the boron-oxygen bonding sites. As a result, the synthesized carbon materials having oxidized boron functional groups of BC2O and BCO2 showed high activity (1.25 mA cm−2) and selectivity (∼90 %) over a wide voltage range in two-electron ORR (Oxygen Reduction Reaction) at alkaline media. Furthermore, in an H-cell where 0.4 V vs. RHE was applied, the average H2O2 production rate was maintained at 452.96 mmol g−1 h−1 for four hours with a high faraday efficiency of 90 %.

A novel naturally aspirated cathode for efficient electrosynthesis of hydrogen peroxide and wastewater purification in electro-Fenton systems

Electrochemical synthesis of hydrogen peroxide (H2O2) has developed rapidly in recent years as an alternative process to the anthraquinone method. However, the low H2O2 production and high energy consumption limit its further application. In this study, we propose a simple method to fabricate a naturally aspirated cathode (NAC), which significantly reduces the mass transfer resistance of oxygen and achieves a high oxygen diffusion coefficient (7.11 × 10-6 m2 s−1) and oxygen utilization efficiency (39.6 %). Additionally, the NAC provides a high density of reaction sites to achieve efficient production of H2O2 (0–84.33 mg h−1 cm−2) at near industrial current densities (0–240 mA cm−2) without external aeration. Meanwhile, the prepared NAC can degrade over 97.5 % of dyes within 10 min during the electro-Fenton process. The NAC exhibits excellent H2O2 production performance and great stability during long-term operation, which offers huge potential for industrial-scale electrochemical H2O2 production and the advanced oxidation processes (AOP) derived from it.

TCE degradation of modified graphite felt cathode in a flow-through electro-Fenton system and its H2O2 production ability in a real contaminated field

A modified graphite felt (MGF) was prepared with carbon black (CB) and polytetrafluoron (PTFE) for cathodic electrochemical H2O2 production, which was used in a flow-through cathodic electro-Fenton reactor to degrade chlorinated hydrocarbons. Cathode electrode was floating on aqueous surface and 369.1 mg/L H2O2 could be produced after 1 h 150 mA power applied without O2 aeration. The main O2 source for H2O2 production was confirmed from air with this floating position. In a 2.0 L flow-through cathodic electro-Fenton system, 95.97 % degradation efficiency for 5.0 mg/L trichloroethylene (TCE) was achieved in 90 min with 13.4 mL/min influent rate. Reducing the reactor volume to 0.14 L, 5.0 mg/L TCE could be degraded completely in 10 min with continuous 4 L influent. The mixed chlorinated hydrocarbons (TCE, cis-1,1-dichloroethylene, 1,2-dichloroethane, and dichloromethane) were also rapidly degraded in 20 min. The flow-through cathodic electro-Fenton reactor presented excellent degradation ability for chlorinated hydrocarbons with a smaller volume. In the simulated sand tank system, after continuously operated 27 days, H2O2 concentration in electrode well was still remained at 80 mg/L. In the contaminated field in Tianjin, China, H2O2 yield of MGF in groundwater could keep at about 60 mg/L after 220 min operating.

Effect of the pressure on the cathodic production of H2O2 and on electro-Fenton in undivided and divided cells

The key step for both the electrochemical H2O2 production and the electro-Fenton (EF) process is the cathodic reduction of O2 which is adversely affected by the low oxygen solubility in water contacted at atmospheric pressure of air. In this work, we studied the effect of current density and air pressure on the H2O2 production and on the EF process using both a divided and an undivided cell. It was shown that the use of pressures between 5 and 15 bar allows to enhance drastically the H2O2 production in both undivided and divided cells and that the best results were achieved in the presence of the separator. Moreover, the coupled use of pressurized air and divided cells made it possible to accelerate the organics removal achieved by the EF process. Eventually, the advantages given by the utilization of divided and undivided cells and of pressurized air were analyzed from both technical and economic points of view.

An experimentally validated model for anodic H2O2 production in alkaline water electrolysis and its implications for scaled-up operation

The anodic co-production of hydrogen peroxide (H2O2) during alkaline water electrolysis has gained interest as a sustainable alternative for anthraquinone oxidation. However, electrochemical H2O2 production is often studied with idealized laboratory setups to determine the H2O2 formation kinetics. In this work, we perform the reaction with industrially relevant operating principles using a flow cell with separately recirculating anolyte and catholyte. We then fit the data to an analytical model that we derive based on mole balances that accounts for anodic generation, anodic oxidation, and bulk disproportionation of H2O2, as well as electrolyte volumes and electrode surface area. We performed experiments at 100, 200, and 300 mA cm-2 to derive values for the reaction system. At 200 mA cm-2, we found a generation rate of 0.037 mmol min-1 cm-2 (FEH2O2 = 59%) and an anodic decomposition rate constant of 0.304 cm min-1, with a bulk disproportionation rate constant of 1.85 × 10-3 min-1. We successfully applied our model to two sources in literature to derive values for their systems as well. In all cases, the contribution of anodic oxidation of H2O2 was found to be the larger loss mechanism in comparison to bulk disproportionation. Using the analytical model, we show that decreasing the reservoir volume is a simple way to increase the H2O2 concentration over time. Further refinement of the model can be achieved through the use of mass transfer relationships based on electrolyzer geometries to describe the anodic oxidation of H2O2 in the mole balance equations.

Additive manufacturing-derived free-standing 3D pyrolytic carbon electrodes for sustainable microbial electrochemical production of H2O2

Producing H2O2 via microbial electrosynthesis is a cost-effective and environmentally favorable alternative to the costly and environmentally hazardous anthraquinone method. However, most studies have relied on carbon electrodes with two-dimensional (2D) surfaces (e.g., graphite), which have limited surface area and active sites, resulting in suboptimal H2O2 production. In this study, we demonstrate the enhanced efficiency of microbial H2O2 synthesis using three-dimensional (3D) electrodes produced through additive manufacturing technology due to their larger surface area than conventional carbon electrodes with 2D surfaces. This work innovatively combines 3D printed pyrolytic carbon (3D PyrC) electrodes with highly defined outer geometry and internal mesh structures derived from additive manufacturing with high-temperature resin precursors followed by pyrolysis with microbial electrochemical platform technology to achieve efficient H2O2 synthesis. The 3D PyrC electrode produced a maximum of 129.2 mg L−1 of H2O2 in 12 h, which was 2.3–6.9 times greater than conventional electrodes (e.g., graphite and carbon felt). Furthermore, the scalability, reusability and mechanical properties of the 3D PyrC electrode were exemplary, showcasing its practical viability for large-scale applications. Beyond H2O2 synthesis, the study explored the application of the 3D PyrC electrode in the bio-electro-Fenton process, demonstrating its efficacy as a tertiary treatment technology for the removal of micropollutants. This dual functionality underscores the versatility of the 3D PyrC electrode in addressing both the synthesis of valuable chemicals and environmental remediation. This study shows a novel electrode design for efficient, sustainable synthesis of H2O2 and subsequent environmental remediation.

Recent advances in Fe‐N‐C single‐atom site coupled synergistic catalysts for boosting oxygen reduction reaction

AbstractMetal–air batteries, fuel cells, and electrochemical H2O2 production currently attract substantial consideration in the energy sector owing to their efficiency and eco‐consciousness. However, their broader use is hindered by the complex oxygen reduction reaction (ORR) that occurs at cathodes and involves intricate electron transfers. Despite the significant ORR performance of platinum‐based catalysts, their high cost, operational limitations, and susceptibility to methanol poisoning hinder broader implementation. This emphasizes the need for efficient non‐precious metal‐based ORR electrocatalysts. A promising approach involves utilizing single‐atom catalysts (SACs) featuring metal–nitrogen–carbon (M‐N‐C) coordination sites. SACs offer advantages such as optimal utilization of metal atoms, uniform active centers, precisely defined catalytic sites, and robust metal–support interactions. However, the symmetrical electron distribution around the central metal atom of a single‐atom site (M‐N4) often results in suboptimal ORR performance. This challenge can be addressed by carefully tailoring the surrounding environment of the active center. This review specifically focuses on recent advancements in the Fe‐N4 environment within Fe‐N‐C SACs. It highlights the promising strategy of coupling Fe‐N4 sites with metal clusters and/or nanoparticles, which enhances intrinsic activity. By capitalizing on the interplay between Fe‐N4 sites and associated species, overall ORR performance improved. The review combines findings from experimental studies and density functional theory simulations, covering synthesis strategies for Fe‐N‐C coupled synergistic catalysts, characterization techniques, and the influence of associated particles on ORR activity. By offering a comprehensive outlook, the review aims to encourage research into high‐efficiency Fe single‐atom sites coupled synergistic catalysts for real‐world applications in the coming years.

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.