Electrochemical H2O2 Production Research Articles

Revisiting the Oxidizing Capacity of the Periodate-H2O2 Mixture: Identification of the Primary Oxidants and Their Formation Mechanisms.

This study reexamined the mechanisms for oxidative organic degradation by the binary mixture of periodate and H2O2 (PI/H2O2) that was recently identified as a new advanced oxidation process. Our findings conflicted with the previous claims that (i) hydroxyl radical (•OH) and singlet oxygen (1O2) contributed as the primary oxidants, and (ii) •OH production resulted from H2O2 reduction by superoxide radical anion (O2•-). PI/H2O2 exhibited substantial oxidizing capacity at pH < 5, decomposing organics predominantly by •OH. The likelihood of a switch in the major oxidant under varying pH conditions was revealed. IO4- as the major PI form under acidic conditions underwent one-electron reduction by H2O2 to yield radical intermediates, whereas H2I2O104- preferentially occurring at pH > 7 caused 1O2 generation through two-electron oxidation of H2O2. PI reduction by O2•- was suggested to be a key reaction in •OH production, on the basis of the electron paramagnetic resonance detection of methyl radicals in the dimethyl sulfoxide solutions containing PI and KO2, and the absence of deuterated and 18O-labeled hydroxylated intermediates during PI activation using D2O and H218O2. Finally, simple oxyanion mixing subsequent to electrochemical PI and H2O2 production achieved organic oxidation, enabling a potential strategy to minimize the use of chemicals.

Tafel Analysis Guided Optimization of ZnNP-O-C Catalysts for the Selective 2-Electron Oxygen Reduction Reaction in Neutral Media.

The lack of characterizations of the adsorption capability toward intermediates during reactions causes difficulties in determining the structural optimization principle of the catalysts for the 2-electron oxygen reduction reaction (2e- ORR). Here, a Tafel-θ method is proposed to evaluate the surface coverage (θ) of important intermediates (*OOH and *OH) on the material surface and further help optimize the catalyst. With the assistance of Tafel-θ analysis, a Zn nanoparticle incorporated oxygen-doped carbon (ZnNP-O-C) catalyst with high 2e- ORR performance (onset of ∼0.57 V and selectivity of >90.4%) in neutral media was achieved. Both the theoretical calculation and characterization results are consistent with the Tafel-θ deduction, revealing that an appropriate ratio of Zn nanoparticles and bridging O can optimize the *OOH adsorption/desorption strength of the adjacent carbon site. This study not only provides an advanced ZnNP-O-C catalyst for electrochemical H2O2 production but also proposes a fast and precise method for the comprehensive assessment of future catalysts.

Highly efficient and selective electrocatalytic hydrogen peroxide production on Co-O-C active centers on graphene oxide

Electrochemical oxygen reduction provides an eco-friendly synthetic route to hydrogen peroxide (H2O2), a widely used green chemical. However, the kinetically sluggish and low-selectivity oxygen reduction reaction (ORR) is a key challenge to electrochemical production of H2O2 for practical applications. Herein, we demonstrate that single cobalt atoms anchored on oxygen functionalized graphene oxide form Co-O-C@GO active centres (abbreviated as Co1@GO for simplicity) that act as an efficient and durable electrocatalyst for H2O2 production. This Co1@GO electrocatalyst shows excellent electrochemical performance in O2-saturated 0.1 M KOH, exhibiting high reactivity with an onset potential of 0.91 V and H2O2 production of 1.0 mg cm−2 h−1 while affording high selectivity of 81.4% for H2O2. Our combined experimental observations and theoretical calculations indicate that the high reactivity and selectivity of Co1@GO for H2O2 electrogeneration arises from a synergistic effect between the O-bonded single Co atoms and adjacent oxygen functional groups (C-O bonds) of the GO present in the Co-O-C active centres.

Short-range order in amorphous nickel oxide nanosheets enables selective and efficient electrochemical hydrogen peroxide production

Achieving high selectivity and activity with the oxygen reduction reaction (ORR) is significant for developing efficient energy conversion techniques and chemical production. Here, we report that selective ORRs can be achieved by tuning short-range order in amorphous and crystalline NiO nanosheets (a-NiO NSs and c-NiO NSs, respectively). X-ray absorption spectroscopy analysis reveals that the short-range order of a-NiO NSs and c-NiO NSs mainly adopt the NiO5 pyramidal and NiO6 octahedral structures, respectively. The a-NiO NSs for electrochemical H2O2 production in 0.1 M KOH exhibits both high selectivity over 90% and high activity (1 mA cm−2 at 0.66 V versus RHE), while c-NiO NSs tends to catalyze ORRs through 4-electron pathways to generate H2O. Theoretical calculations indicate that the changed short-range order of a-NiO NSs leads to alteration of Ni d-orbital states, which can regulate the adsorption orientation and strength of ∗OOH intermediates to achieve high selectivity and activity of 2-electron ORRs.

Mechanism investigation of enhanced electrochemical H2O2 production performance on oxygen-rich hollow porous carbon spheres

Mechanism investigation of enhanced electrochemical H2O2 production performance on oxygen-rich hollow porous carbon spheres

N, O-coupling towards the selectively electrochemical production of H2O2

Hydrogen peroxide (H2O2) synthesis generally involves the energy-intensive anthraquinone process. Alternatively, electrochemical synthesis provides a green, economical, and environmentally friendly route to prepare H2O2 via the two-electron oxygen reduction reaction, but this process requires efficient catalysts with high activity and selectivity simultaneously. Here, we report an N, O co-doped carbon xerogel-based electrocatalyst (NO-CX) prepared by a simple and economical method. The NO-CX catalyst exhibits a high H2O2 selectivity over 90% in a potential range of 0.2–0.6 V and a high H2O2 production rate of 1410 mmol gcat−1 h−1. The density functional theory calculations demonstrate that the coupling effect between N and O can effectively induce the redistribution of surface charge and the edge carbon atom adjacent to an ether group and a graphite nitrogen atom is the active site. This work provides a straightforward and low-cost process to produce highly selective H2O2 catalysts, which is in place for the expansion of electrocatalytic synthesis of useful chemicals.

Synergistic Effects of Bi2o3 and Ta2o5 for Efficient Electrochemical Production of H2o2

Synergistic Effects of Bi2o3 and Ta2o5 for Efficient Electrochemical Production of H2o2

Epoxidation of olefins enabled by an electro-organic system

An integrated organic electrosynthesis system was developed with a phase-separated membrane-electrode assembly strategy, couplingin situelectrochemical H2O2production and olefin epoxidation, with only H2O and O2consumption under ambient conditions.

High‐Efficiency Electrosynthesis of Hydrogen Peroxide from Oxygen Reduction Enabled by a Tungsten Single Atom Catalyst with Unique Terdentate N1O2 Coordination

AbstractSingle‐atom catalysts (SACs) have shown great potential in the electrochemical oxygen reduction reaction (ORR) toward hydrogen peroxide (H2O2) production. However, current studies are mainly focused on 3d transition‐metal SACs, and very little attention has been paid to 5d SACs. Here, a new kind of W SAC anchored on a porous O, N‐doped carbon nanosheet (W1/NO‐C) is designed and prepared via a simple coordination polymer‐pyrolysis method. A unique local structure of W SAC, terdentate W1N1O2 with the coordination of two O atoms and one N atom, is identified by the combination of aberration‐corrected scanning transmission electron microscopy, X‐ray photoelectron spectroscopy and X‐ray absorption fine structure spectroscopy. Remarkably, the as‐prepared W1/NO‐C catalyzes the ORR via a 2e– pathway with high onset potential, high H2O2 selectivity in the wide potential range, and excellent operation durability in 0.1 m KOH solution, superior to most of state‐of‐the‐art H2O2 electrocatalysts ever reported. Theoretical calculations reveal that the C atoms adjacent to O in the W1N1O2‐C moiety are the most active sites for the 2e– ORR to H2O2 with the optimal binding energy of the HOO* intermediate. This work opens up a new opportunity for the development of high‐performance W‐based catalysts for electrochemical H2O2 production.

Pyrolyzed polydopamine-modified carbon black for selective and durable electrocatalytic oxygen reduction to hydrogen peroxide in acidic medium

Electrochemical production of H2O2 from O2 via the two-electron reaction pathway (2e-ORR) is a promising alternative to the energy- and organic pollutant-intensive industrial anthraquinone process. However, irrespective of numerous research efforts on catalyst design and remarkable advances made in this area, the catalysts displaying high H2O2 production rate so far unexceptionally required expensive/hazardous catalyst precursors and involved tedious steps and/or harsh treating conditions. Herein, we report a slightly nitrogen-doped carbon 2e-ORR catalyst that was synthesized simply by pyrolyzing a polydopamine (PDA) coating on Vulcan XC72 carbon black (p-PDA/XC). In H2O2 production via ORR in an acidic electrolyte, the catalyst showed 185 mV less overpotential than XC and remarkably high selectivity up to 96%. Highly efficient and durable H2O2 production was demonstrated by the stable accumulation of H2O2 to 1368 mmol gcat−1 within 8 h, translating to a H2O2 production rate of 171 mmol gcat−1 h−1. A good linear relationship was identified between the H2O2 partial current and the surface content of the C–O/C–N and CO species for the XC and p-PDA/XC catalysts, inferring that the C atoms in or adjacent to these species serve as the active sites for 2e-ORR to H2O2. The inexpensive starting materials, facile synthetic strategy, and excellent catalytic performance of the p-PDA/XC catalyst may accelerate the establishment of an affordable, safe, and direct O2-to-H2O2 electrochemical process.

Non-precious metal electrocatalysts for two-electron oxygen electrochemistry: Mechanisms, progress, and outlooks

Hydrogen peroxide (H2O2) is a valuable chemical for a wide variety of applications. The environmentally friendly production route of the electrochemical reduction of O2 to H2O2 has become an attractive alternative to the traditional anthraquinone process. The efficiency of electrosynthesis process depends considerably on the availability of cost-effective catalysts with high selectivity, activity, and stability. Currently, there are many outstanding issues in the preparation of highly selective catalysts, the exploration of the interface electrolysis environment, and the construction of electrolysis devices, which have led to extensive research efforts. Distinct from the existing few comprehensive review articles on H2O2 production by two-electron oxygen reduction, the present review first explains the principle of the oxygen reduction reaction and then highlights recent advances in the regulation and control strategies of different types of catalysts. Key factors of electrode structure and device design are discussed. In addition, we highlight the promising co-production combination of this system with renewable energy or energy storage systems. This review can help introduce the potential of oxygen reduction electrochemical production of high-flux H2O2 to the commercial market.

Recent advances in electrocatalytic oxygen reduction for on-site hydrogen peroxide synthesis in acidic media

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.

ZnO nanoparticles embedded in hollow carbon fiber membrane for electrochemical H2O2 production by two-electron water oxidation reaction

Electrochemical two-electron water oxidation reaction (2e-WOR) provides a promising alternative route for hydrogen peroxide (H2O2) production, where the design of earth abundant and environmentally friendly electrocatalysts with both high selectivity and production rate is crucial. Here we report the synthesis of ZnO nanoparticles embedded in hollow carbon fiber membrane as efficient 2e-WOR electrocatalyst by a metal-organic framework engaged electrospinning-pyrolysis method. The resultant ZnO@carbon composite fiber exhibits a foam-like hierarchical structure composed of interconnected hollow carbon nanocubes encapsulated with oxygen vacancy rich ZnO nanocrystals. Owing to the improved selectivity of ZnO, excellent conductivity of carbon fiber, promoted active site exposure and mass transfer of hollow structure, the free-standing membrane electrode shows superior 2e-WOR performances with high selectivity (83.8% at 2.8 V vs. RHE), H2O2 generation rate (19.7 μmol cm−2 min−1) and robust stability.

A H2O2 PEM Electrolyser with Continuous Online Spectrophotometric Product Detection: Load Flexibility Studies

Hydrogen peroxide (H2O2) is a commodity chemical with an increasing annual worldwide demand. The green oxidant is widely used in various fields, including pulp and paper bleaching industry, chemical synthesis, and wastewater treatment. H2O2 is commonly produced by the industrial anthraquinone process, which suffers from high energy consumption and the generation of a variety of undesirable by-products [1]. The electrochemical production of H2O2 via the two-electron oxygen reduction reaction is a promising approach for the replacement of the industrial anthraquinone process, yet it is not able to compete economically. However, the electrochemical H2O2 production opens the possibility to produce hydrogen peroxide using renewable energies. Naturally, green energy sources underlie fluctuations regarding the accessible power, resulting in a fluctuating energy market. Being able to respond to the energy market with increasing or decreasing the load of an electrochemical unit can offer a significant economic value. This economic advantage can help to bridge the gap between the production costs for hydrogen peroxide produced by renewable energies and by the state-of-the-art industrial anthraquinone process. Due to a limited time resolution, classical off-line characterisation techniques for the detection of H2O2 are not suitable to investigate the influence of dynamic conditions upon the H2O2 production rates.Here we present a novel on-line analysis setup based on the spectrophotometric analysis with titanium oxalate [2], which allows the determination of hydrogen peroxide continuously at the moment it is formed. For this purpose, we combined two mass flow controller, one continuously delivering the H2O2 containing electrolyte and the other delivering the titanium oxalate solution. Both solutions were mixed in a subsequent micromixer and pumped though a spectrophotometric flow cell, where the absorbance of the resulting pertitanic acid is recorded and the corresponding H2O2 concentration is calculated. Therefore, with our setup, the concentration of H2O2 can be continuously measured and the influence of varying process parameter can be directly monitored. We validated the setup with load flexibility experiments, where current load steps above and below a reference load were performed and the resulting Faraday efficiencies and production rates within an electrolyser were monitored.

Polymer electrolyte membrane (PEM) electrolysis of H2O2 from O2 and H2O with continuous on-line spectrophotometric product detection: Load flexibility studies

Hydrogen peroxide (H2O2) is a green oxidant, widely used in industry. The electrochemical production of H2O2 via the two-electron oxygen reduction reaction (2eORR) is a promising approach for the replacement of the industrial anthraquinone process because it opens the possibility to produce hydrogen peroxide using renewable energies. Classical off-line characterize techniques for the detection of hydrogen peroxide are not suitable for dynamic conditions. To quantify the efficiency of the peroxide formation we developed a novel on-line analysis setup based on the spectrophotometric analysis with titanium oxysulfate, which allows the determination of hydrogen peroxide continuously at the moment it is formed. With our setup, the concentration is continuously measured and the influence of varying process parameter can be directly monitored. We validated the setup with load flexibility experiments, were rectangular current load steps by 33.3% above and below a reference load were performed within an electrolyzer. The evolution of the hydrogen peroxide concentration was directly measurable within 35 s and 95% of the main H2O2 concentration was detectable after 2 min. The applied load steps led to no visible performance decrease of the electrolyzer and faraday efficiencies of > 98% with a maximum production rate of 122.4 mg cm−2h−1 were reached in 0.1 M H2SO4 + 0.05 M K2SO4 for current densities up to −200 mA cm−2.

Objective Observations of the Electrochemical Production of H2O2 in KHCO3 Aqueous Electrolyte and Related Application Inspirations

Objective Observations of the Electrochemical Production of H₂O₂ in KHCO₃ Aqueous Electrolyte and Related Application Inspirations

Integrating H2O2 generation from electrochemical oxygen reduction with the selective oxidation of organics in a dual-membrane reactor

The electrochemical reduction of oxygen to H2O2 is a sustainable substitution for the current anthraquinone process. However, the concentration, transportation, and storage of H2O2 increases not only the cost but also the risks in safety. Herein, we report a method of coupling electrochemical production of H2O2 with its in situ application in the selective oxidation of organics in a dual-membrane microflow electrolyzer, where the OOH− generated from 2e− reduction of O2 at cathode subsequently oxidizes organic substrates into value-added products under the catalysis of TS-1. When applied to phenol oxidation, the selectivity to target catechol and hydroquinone is as high as 94.68% with an overall Faradic efficiency (FE) up to 30.25% at a conversion of 10.61% under the optimized condition. Further study revealed that this method is also feasible for the coupling of various other organic oxidation reactions such as alcohol oxidation, styrene epoxidation and ammoximation with high selectivity and FE. Additionally, an overall FE of 132.79% was achieved in the paired oxidation of furfural to furoic acid, where furfural was oxidized both indirectly via H2O2 generated on cathode and directly on the anode.

The Role of Bicarbonate-Based Electrolytes in H2O2 Production through Two-Electron Water Oxidation

Two-electron water oxidation (2e–WOR) is a promising route toward efficient production of a valuable product in H2O2. Recent attention has focused on developing new electrocatalysts for 2e–WOR, but the role of the electrolyte species in determining water oxidation selectivity and promoting 2e–WOR has not been established. Here, we use electroanalytical experiments to confirm the role of HCO3– as a selective 2e–WOR redox catalyst. We find minimal differences in H2O2 consumption pathways among common electrolytes, indicating that the role of HCO3– is to promote H2O2 production. Mechanistically, our rotating ring disk experiments show that H2O2 is not generated directly at the disk electrode in KHCO3 but formed after a time delay, suggesting electrolyte oxidation and subsequent hydrolysis as the promotional mechanism. Further electrochemical and spectroscopic experiments confirm this hypothesis, demonstrating anodic oxidation of carbonaceous electrolyte species occurs at Faradaic potentials relevant for water oxidation and that these species (likely HCO4– or C2O62–) subsequently oxidize water to H2O2 (t1/2 ≈ 5 min). The H2O2 production rate at 2.5 V vs RHE scales linearly with the concentration of HCO3–, confirming the catalytic role of HCO3– in 2e–WOR and suggesting the electrolyte can be leveraged to enhance electrochemical H2O2 production.

Enhancing Electrocatalytic Production of H2O2 by Modulating Coordination Environment of Cobalt Center

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.

Promoting the Two-Electron Oxygen Reduction Reaction Performance of Carbon Nanospheres by Pore Engineering

Electrochemical production of hydrogen peroxide from the two-electron oxygen reduction reaction (ORR) is emerging as a promising method for in situ production of H2O2. However, carbon materials, one of the most prospective catalysts for the two-electron ORR, remain not active enough for mass production of H2O2 in acidic or neutral media. Pore channel engineering is an effective strategy to enhance the ORR activity of carbon materials by enlarging the electrochemically accessible surface and facilitating oxygen diffusion. Here, carbon nanospheres with different pore sizes (diameter and depth) were controllably prepared by a soft-template method. The optimized catalyst exhibited an excellent two-electron ORR activity in alkaline and neutral media. Furthermore, electrochemical production of H2O2 in neutral solution with a production rate as high as 1.27 mol g–1 h–1 and a Faraday’s efficiency (FE) > 98% were obtained. By combining electrochemical tests with physical characterizations and numerical simulations, the origin of the enhanced ORR performances was elucidated.