Electrocatalytic H2O2 Production Research Articles

Oxidation Evolution and Activity Origin of N-Doped Carbon in the Oxygen Reduction Reaction

N-doped carbon materials, with their applications as electrocatalysts for the oxygen reduction reaction (ORR), have been extensively studied. However, a negletcted fact is that the operating potential of the ORR is higher than the theoretical oxidation potential of carbon, possibly leading to the oxidation of carbon materials. Consequently, the influence of the structural oxidation evolution on ORR performance and the real active sites are not clear. In this study, we discover a two-step oxidation process of N-doped carbon during the ORR. The first oxidation process is caused by the applied potential and bubbling oxygen during the ORR, leading to the oxidative dissolution of N and the formation of abundant oxygen-containing functional groups. This oxidation process also converts the reaction path from the four-electron (4e) ORR to the two-electron (2e) ORR. Subsequently, the enhanced 2e ORR generates oxidative H2O2, which initiates the second stage of oxidation to some newly formed oxygen-containing functional groups, such as quinones to dicarboxyls, further diversifying the oxygen-containing functional groups and making carboxyl groups as the dominant species. We also reveal the synergistic effect of multiple oxygen-containing functional groups by providing additional opportunities to access active sites with optimized adsorption of OOH*, thus leading to high efficiency and durability in electrocatalytic H2O2 production.

Screening of highly efficient electrocatalysts for hydrogen peroxide synthesis using single transition metal atoms embedded in carbon vacancy fullerene C60

The electrocatalytic two-electron oxygen reduction reaction (2e– ORR) synthesis of hydrogen peroxide (H2O2) is an eco-friendly process. In this study, density functional theory (DFT) and machine learning (ML) were utilized to systematically explore various single metal atoms anchored on mono-vacancy fullerene C60 (TM@C60) for H2O2 production. Among 19 single-atom catalysts (SACs), Sc@C60 and Y@C60 were identified for high the thermodynamic feasibility of H2O2 formation, exhibiting overpotentials of 0.01 V and 0.02 V, respectively. Moreover, competitive four-electron oxygen reduction reaction (4e– ORR) and hydrogen evolution reaction (HER) were significantly suppressed on these two catalysts. The formation of peroxide intermediates on the two screened SACs was identified as key to achieving high activity and selectivity for H2O2 formation. Analysis using ML methods also revealed that the balance between bond strengths and adsorption energies for O2 is crucial in regulating the performance of 2e– ORR. These results offer important insights for electrocatalytic H2O2 production.

The introduction of rich active sites on 0D@2D nanocarbon via light illuminating with high-efficient electrocatalytic H2O2 production

Two-dimensional (2D) carbon-based materials are high-quality electrocatalytic materials with high mass transfer interfaces. However, the intrinsic 2D surfaces often lack of abundant active sites and outstanding electron transport channels. Herein, a 0D@2D nanocarbon material with affluent unsaturated oxygen-containing groups (UOCGSs) active sites and excellent electron channels are constructed via a novel sodium ion-capping and light illuminating strategy. With the aid of the light illuminating, the final 0D@2D product exhibits a superior practical H2O2 production rate of up to 1109 mmol·gcatalyst−1 h−1 with a high level of onset potential 0.78V and 94 % H2O2 selectivity in H-cell. This improved performance arises from the introduction of UOCGSs and excellent charge transfer on the 0D@2D interface. Obviously, this work exhibits a new green stagey for the design of 0D@2D carbon-based structure via light illuminating.

Identification of the highly active Zn-N4 sites with pyrrole/pyridine-N synergistic coordination by dz2+s-band center for electrocatalytic H2O2 production

Single metal atoms anchored on nitrogen-doped carbon materials (M-N4) have been identified as effective active sites for catalyzing the two-electron oxygen reduction reaction (2e-ORR). However, the relationship between the local atomic/electronic environments of the M-N4 sites (metal atoms coordinated with different types of N species) and their catalytic activity for 2e-ORR has rarely been elaborated clearly, which imposes significant ambiguity for the rational design of catalysts. Herein, guided by the comprehensive density-functional theory calculations and predictions, a series of Zn-N4 single-atom catalysts (SACs) are designed with pyrrole/pyridine-N (NPo/NPd) synergistic coordination and prepared by controlling the pyrolysis temperature (600, 700, and 800 °C). Among them, the dominated Zn-N4 configurations with rationally combined NPo/NPd coordination show *OOH adsorption strength close to the optimal value, much superior to those with mono N species. Thus, the as-prepared catalyst exhibits a high H2O2 selectivity of over 90% both in neutral and alkaline environments, with a superb H2O2 yield of up to 33.63 mol g−1 h−1 in an alkaline with flow cell. More importantly, a new descriptor, dz2+s band center, has been proposed, which is especially feasible for predicting the activity for metal types with fully occupied s and d orbitals. This work thus presents clear guidance for the rational design of highly active SACs toward ORR and provides a complement to the d-band theory for more accurately predicting the catalytic activity of the materials.

Hydrophilic phthalocyanine covalent organic frameworks for enhanced electrocatalytic H2O2 production

The electrocatalytic 2e− oxygen reduction reaction (ORR) is considered as a promising pathway to replace conditional anthraquinone process for hydrogen peroxide (H2O2) manufacture. However, the efficient electrocatalysts towards 2e− ORR remain urgently desired. Herein, hydrophilic two-dimensional cobalt phthalocyanine (CoPc) covalent organic frameworks (COFs), denoted as CoPc-2SO3H-COF and CoPc-SO3H-COF, were afforded via the imidization reaction of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato cobalt(II) with hydrophilic building blocks 2,5-diaminobenzenesulfonic acid and 1,4-benzenedisulfonic acid, respectively. Powder X-ray diffraction, transmission electron microscope, and N2 sorption experiment results reveal the crystalline and porous structure of these two COFs. Moreover, the water contact angle and proton conduction measurements demonstrate the hydrophilic properties of these two COFs owing to the introduction of −SO3H into their skeleton. This, in combination with the high-efficiency active Co-N4 sites towards 2e− ORR, endows these two COFs with enhanced 2e− ORR activity in the aqueous electrolyte. In particular, CoPc-2SO3H-COF exhibits outstanding electrocatalytic H2O2 production performance with a stable H2O2 selectivity of 88.3 % under a high current density of 125 mA cm−2 for 20 h in a flow cell.

Mechanism insights into H2O2in situ generation and activation for ciprofloxacin degradation by electro-peroxidation using the ACF@RuO2/Ti cathode

Electrocatalytic H2O2 production via the two-electron oxygen reduction reaction on the cathode surface plays a crucial role in the electro-peroxidation (EO-H2O2). In this work, the H2O2 generation potential of the EO-H2O2 process using an activated carbon fiber attached RuO2/Ti cathode (ACF@RuO2/Ti) was evaluated by simulation experiments with a high-precision syringe pump. Results shown that the actual average H2O2 accumulation rate reached up to 4.92 mg h−1 cm−2, while more than 95 % of the electrogenerated H2O2 was decomposed quickly. Electron paramagnetic resonance and quenching tests confirmed that the primary oxidant •OH was produced from H2O2 activation by ACF, RuO2 catalyst and their synergistic effect, while RuO2 played dominant role. The production of •OH in the EO-H2O2 process was also confirmed by the degradation and mineralization of antibiotic ciprofloxacin. The characterization results indicated that heterogeneous catalysis of cathode was due to both the pyridinic nitrogen and oxygen-containing groups of ACF, along with RuO2 catalyst on the RuO2/Ti surface. This study provides new insights into the mechanisms of the in situ H2O2 generation and activation in the EO-H2O2 process.

Oxygen vacancy based WO3/SnO2-x promote electrochemical H2O2 accumulation by two-electron water oxidation reaction and toxic uniform dimethylhydrazine degradation

The key to constructing an anodic electro-Fenton system hinges on two pivotal criteria: enhancing the catalyst activity and selectivity in water oxidation reaction (WOR), while simultaneously inhibiting the decomposition of hydrogen peroxide (H2O2) which is on-site electrosynthesized at the anode. To address the issues, we synthesized novel WO3/SnO2-x electrocatalysts, enriched with oxygen vacancies, capitalize on the combined activity and selectivity advantages of both WO3 and SnO2-x for the two-electron pathway electrocatalytic production of H2O2. Moreover, the introduction of oxygen vacancies plays a critical role in impeding the decomposition of H2O2. This innovative design ensures that the Faraday efficiency and yield of H2O2 are maintained at over 80 %, with a noteworthy production rate of 0.2 mmol h−1 cm−2. We constructed a novel electro-Fenton system that operates using only H2O as its feedstock and applied it to treat highly toxic uniform dimethylhydrazine (UDMH) from rocket launch effluent. Our experiments revealed a substantial total organic carbon (TOC) removal, achieving approximately 90 % after 120 mins of treatment. Additionally, the toxicity of N-nitrosodimethylamine (NDMA), a byproduct of great concern, was shown to be effectively mitigated, as evidenced by acute toxicity evaluations using zebrafish embryos. The degradation mechanism of UDMH is predominantly characterized by the advanced oxidative action of H2O2 and hydroxyl radicals, as well as by complex electron transfer processes that warrant further investigation.

Selective Cobalt-Mediated Formation of Hydrogen Peroxide from Water under Mild Conditions via Ligand Redox Non-Innocence.

Despite the broad importance of hydrogen peroxide (H2O2) in oxidative transformations, there are comparatively few viable routes for its production. The majority of commercial H2O2 is currently produced by the stepwise reduction of dioxygen (O2) via the anthraquinone process, but direct electrochemical formation from water (H2O) would have several advantages─namely, avoiding flammable gases or stepwise separations. However, the selective oxidation of H2O to form H2O2 over the thermodynamically favored product of O2 is a difficult synthetic challenge. Here, we present a molecular H2O oxidation system with excellent selectivity for H2O2 that functions both stoichiometrically and catalytically. We observe high efficiency for electrocatalytic H2O2 production at low overpotential with no O2 observed under any conditions. Mechanistic studies with both calculations and kinetic analyses from isolated intermediates suggest that H2O2 formation occurs in a bimolecular fashion via a dinuclear H2O2-bridged intermediate with an important role for a redox non-innocent ligand. This system showcases the ability of metal-ligand cooperativity and strategic design of the secondary coordination sphere to promote kinetically and thermodynamically challenging selectivity in oxidative catalysis.

Dithiine-linked metalphthalocyanine framework with undulated layers for highly efficient and stable H2O2 electroproduction

Realization of stable and industrial-level H2O2 electroproduction still faces great challenge due large partly to the easy decomposition of H2O2. Herein, a two-dimensional dithiine-linked phthalocyaninato cobalt (CoPc)-based covalent organic framework (COF), CoPc-S-COF, was afforded from the reaction of hexadecafluorophthalocyaninato cobalt (II) with 1,2,4,5-benzenetetrathiol. Introduction of the sulfur atoms with large atomic radius and two lone-pairs of electrons in the C-S-C linking unit leads to an undulated layered structure and an increased electron density of the Co center for CoPc-S-COF according to a series of experiments in combination with theoretical calculations. The former structural effect allows the exposition of more Co sites to enhance the COF catalytic performance, while the latter electronic effect activates the 2e− oxygen reduction reaction (2e− ORR) but deactivates the H2O2 decomposition capability of the same Co center, as a total result enabling CoPc-S-COF to display good electrocatalytic H2O2 production performance with a remarkable H2O2 selectivity of >95% and a stable H2O2 production with a concentration of 0.48 wt% under a high current density of 125 mA cm−2 at an applied potential of ca. 0.67 V versus RHE for 20 h in a flow cell, representing the thus far reported best H2O2 synthesis COFs electrocatalysts.

Electrosynthesis of peracetic acid using in-situ generated H2O2 enabled by carbon-based bifunctional electrodes

Electrosynthesis of peracetic acid (PAA) using in-situ generated H2O2 is a sustainable route to bypass the complexity and hazards of current industrial production routes of PAA. However, efficient electrochemical operation requires advancements in both electrocatalytic H2O2 production and the subsequent oxidation of acetic acid. Herein, we report a bifunctional carbon electrode for PAA electrosynthesis, which features metal-free carbon catalysts structured on a hierarchical array-like graphene substrate. With such a three-dimensional architecture to maximise active site utilisation and enhance mass transfer, this carbon electrode exhibits acidic H2O2 production performance comparable to metal-based counterparts. Moreover, the same electrode activates OH· from H2O2 by virtue of its surface functional group, facilitating strong oxidation of acetic acid to PAA. In a flow electrolyser that couples H2O2 production and acetic acid oxidation, the bifunctional electrode achieved continuous production of industrially relevant concentrations of PAA at high rates and low energy consumption. Our work highlights the critical role of electrode design for the decentralised synthesis of PAA, providing new insights for the electrification of the chemical industry towards a sustainable future.

Catalyst durability in electrocatalytic H2O2 production: key factors and challenges.

On-demand electrocatalytic hydrogen peroxide (H2O2) production is a significant technological advancement that offers a promising alternative to the traditional anthraquinone process. This approach leverages electrocatalysts for the selective reduction of oxygen through a two-electron transfer mechanism (ORR-2e-), holding great promise for delivering a sustainable and economically efficient means of H2O2 production. However, the harsh operating conditions during the electrochemical H2O2 production lead to the degradation of both structural integrity and catalytic efficacy in these materials. Here, we systematically examine the design strategies and materials typically utilized in the electroproduction of H2O2 in acidic environments. We delve into the prevalent reactor conditions and scrutinize the factors contributing to catalyst deactivation. Additionally, we propose standardised benchmarking protocols aimed at evaluating catalyst stability under such rigorous conditions. To this end, we advocate for the adoption of three distinct accelerated stress tests to comprehensively assess catalyst performance and durability.

A wheel-like polyoxometalate for haloperoxidase-inspired antibiofouling with H2O2in situ provided by electrocatalysis

An “additional H2O2 free” antibiofouling method is developed using Ni16Mo16P24, which possesses haloperoxidase mimic and electrocatalytic H2O2 production properties.

Indium oxide with oxygen vacancies boosts O2 adsorption and activation for electrocatalytic H2O2 production.

Oxygen reduction reaction via the two-electron pathway (2e- ORR) offers a sustainable opportunity for hydrogen peroxide (H2O2) production, but suffers from low selectivity. In this work, indium oxide with oxygen vacancies (In2O3-x) exhibits a H2O2 selectivity close to 98% at 0.6 V vs. RHE. Further, a Faradaic efficiency (FE) of around 95% at 0.4-0.6 V vs. RHE and a H2O2 productivity of 3.7 mol gcatalyst-1 h-1 are reached in a flow cell. In situ Raman spectra indicate that In2O3-x promotes the adsorption and activation of O2 and stabilizes oxygen intermediates. This work provides an insight into improving H2O2 selectivity for 2e- ORR catalysts.

Catalyst Stability in Electrolytic Production of Hydrogen Peroxide: Importance, Challenges, and Standardized Degradation Protocols

On-demand electrolytic hydrogen peroxide (H2O2) production is a significant technological advancement that offers a promising alternative to the traditional anthraquinone process.1,2 This method, which employs electrocatalysts to selectively reduce oxygen via two electrons transfers (ORR-2e–), has the potential to provide a sustainable and cost-effective method of producing H2O2. However, several challenges must be overcome in order to enable on-demand H2O2 electrosynthesis, including designing affordable and selective catalytic materials and preventing oxidative damage or degradation of catalytic materials.1,2 While catalyst development has traditionally focused on maximizing activity and selectivity, it is equally important to ensure that the catalysts maintain their performance over time in real-world applications. The stability of electrocatalysts is critical due to the harsh conditions they are subjected to during electrochemical reactions, such as high applied potential or currents, high temperatures, high pressures, and highly acidic or basic environments, as well as the oxidative power of H2O2 and reactive oxygen species that it can generate.3,4 If an electrocatalyst degrades or undergoes chemical changes during the reaction, it can result in reduced activity or selectivity, or even complete reaction failure. This not only leads to decreased yields and increased costs, but also poses potential safety hazards. The performance and degradation processes of catalysts can vary substantially depending on the reaction environment and the lineage of the catalyst used.3,4 In the last years, numerous classes of catalysts have emerged as highly active and selective for the electrocatalytic production of H2O2, especially transition metal-based materials and metal-free carbon-based materials.5 However, while numerous studies have focused on the activity and selectivity of catalysts for the ORR-2e–, research on their stability is still lacking. To effectively address the issue of catalyst material degradation under stress conditions and understand the underlying factors driving the degradation pathways, a unified and standardized approach is crucial. In this study, we focus on the deactivation processes in electrolytic H2O2 production and propose the use of specifically designed degradation protocols, employing a rotating ring-disk electrode setup. Our approach takes into account the most active and selective classes of catalyst for H2O2 production in acidic media, with the aim of enabling more researchers to tackle this crucial aspect and provide a comprehensive understanding and evaluation of the stability of electrocatalysts.

Flower-like WO2@C prepared from the pyrolyzation of ionic liquid for effective elctrocatalytic two-electron water oxidation

Flower-like tungsten dioxide@carbon (WO2@C) is prepared through the pyrolysis of 1-octyl-3-methylimidazolium tungstate ionic liquids. The resultant WO2 particles are surrounded by a few of carbon fibers, displaying the unique flower-like morphology. The WO2@C testified efficient electrocatalytic activity for two-electron water oxidation reaction (2e- WOR) to H2O2. The electrocatalytic H2O2 production rate reaches about 6.55 μmol min−1 cm−2, over 2 times higher than WO2. This may be ascribed to the enhanced electron transferring capacities and abundant defects of WO2@C. This work introduces a special ionic liquid-derived metal oxide@C with the improved electrocatalytic activity for 2e- WOR.

Atomically Dispersed Iron Regulating Electronic Structure of Iron Atom Clusters for Electrocatalytic H2 O2 Production and Biomass Upgrading.

The integration of highly active single atoms (SAs) and atom clusters (ACs) into an electrocatalyst is critically important for high-efficiency two-electron oxygen reduction reaction (2e- ORR) to hydrogen peroxide (H2 O2 ). Here we report a tandem impregnation-pyrolysis-etching strategy to fabricate the oxygen-coordinated Fe SAs and ACs anchored on bacterial cellulose-derived carbon (BCC) (FeSAs/ACs-BCC). As the electrocatalyst, FeSAs/ACs-BCC exhibits superior electrocatalytic activity and selectivity toward 2e- ORR, affording an onset potential of 0.78 V (vs. RHE) and a high H2 O2 selectivity of 96.5 % in 0.1 M KOH. In a flow cell reactor, the FeSAs/ACs-BCC also achieves high-efficiency H2 O2 production with a yield rate of 12.51±0.18 mol gcat -1 h-1 and a faradaic efficiency of 89.4 %±1.3 % at 150 mA cm-2 . Additionally, the feasibility of coupling the produced H2 O2 and electro-Fenton process for the valorization of ethylene glycol was explored in detail. The theoretical calculations uncover that the oxygen-coordinated Fe SAs effectively regulate the electronic structure of Fe ACs which are the 2e- ORR active sites, resulting in the optimal binding strength of *OOH intermediate for high-efficiency H2 O2 production.

Surface oxidation of commercial activated carbon with enriching carboxyl groups for high-yield electrocatalytic H2O2 production

Two-electron oxygen reduction reaction (2e− ORR) for H2O2 production is regarded as a more ecologically friendly substitute to the anthraquinone method. However, the search of selective and cheap catalysts is still challenging. Herein, we developed a neutral-selective and efficient nonprecious electrocatalyst that was prepared from a commercial activated carbon (AC) by simply microwave-assisted ash impurity elimination and hydrogen peroxide oxidation for surface functional sites optimization. The oxygen configuration can be tuned with enriching carboxyl group up to 6.65 at.% by the dosage of hydrogen peroxide (mass ratio of H2O2/C = ∼0–8.3). Chemical titration experiments identified the carbonyl groups as the most potential active sites, with selectivity boosted by the additional carboxyl groups. The microwave-assisted moderate-oxidized activated carbon (MW-AC5.0) demonstrated optimal 2e− ORR activity and selectivity in neutral electrolyte (0.1 M K2SO4), with H2O2 selectivity reaching ∼75%–97%, a maximum H2O2 production rate (1.90 mol·gcatal −1·h−1@0.1 V) and satisfying faradaic efficiency (∼85%) in gas-diffusion-electrode. When coupled with Fenton reaction, it can degrade a model organic pollutant (methylene blue [MB], 50 ppm) to colorless in a short time of 20 min, indicating the potential applications in the environmental remediation.

Conjugated Nickel Phthalocyanine Derivatives for Heterogeneous Electrocatalytic H2 O2 Synthesis.

Electrocatalytic hydrogen peroxide (H2 O2 ) production has emerged as a promising alternative to the chemical method currently used in industry, due to its environmentally friendly conditions and potential for higher activity and selectivity. Heterogeneous molecular catalysts are promising in this regard, as their active site configurations can be judiciously designed, modified, and tailored with diverse functional groups, thereby tuning the activity and selectivity of the active sites. In this work, nickel phthalocyanine derivatives with various conjugation degrees are synthesized and identified as effective pH-universal electrocatalysts for H2 O2 production after heterogenized on nitrogen-decorated carbon, with increased conjugation degrees leading to boosted selectivity. This is explained by the regulated d-band center, which optimized the binding energy of the reaction intermediate, reducing the energy barrier for oxygen reduction and leading to optimized H2 O2 selectivity. The best catalyst, NiPyCN/CN, exhibits a high H2 O2 electrosynthesis activity with ≈95% of H2 O2 faradic efficiency in an alkaline medium, demonstrating its potential for H2 O2 production.

Research progress of electrocatalysts for the preparation of H2O2 by electrocatalytic oxygen reduction reaction

AbstractAs an eco‐friendly oxidant and energy carrier, H2O2 is used in various fields. The industrial production of H2O2 mostly depends on the large‐scale anthraquinone oxidation processes with high costs. Electrocatalytic production of H2O2 has attracted attention as a renewable and cost‐effective approach to replace traditional ones. With the recent development of oxygen reduction reaction (ORR) catalysts, remarkable progress in electrocatalysts for electrocatalytic H2O2 production by 2e− ORR has been reported. This review summarizes a detailed overview of the recent progress in 2e− ORR for H2O2 production with the mechanism and various efficient catalysts. The catalysts were divided into three parts: noble metal‐based catalyst, non‐noble metal‐based catalyst, and non‐metal‐based catalyst. The influences of the catalytic activity and selectivity were also discussed. Finally, this review explores the prospects of electrocatalytic 2e− ORR for H2O2 synthesis and potential research directions for electrocatalysts. It aims to offer guidance in designing efficient 2e− ORR electrocatalysts and inspire further innovation in electrocatalytic H2O2 synthesis.

Efficient electrocatalytic two-electron oxygen reduction over aminophenol formaldehyde resin-derived carbon microspheres

The electrocatalytic 2-electron oxygen reduction reaction (2e-ORR) to hydrogen peroxide (H2O2) required cheap and efficient electrocatalytic materials. Herein cheap 3-aminophenol formaldehyde resin microspheres were synthesized at a large scale of about 15 g in one run. By annealing it, nitrogen-doped carbon spheres could be conveniently obtained, which was found to be efficient electrocatalyst for 2e-ORR with the highest H2O2 selectivity of about 94% at 0.4 V vs RHE. The electrolysis H2O2 production rate over N-doped carbon in 0.1 M KOH solution reached 48 mmol gcat-1h−1. Aminophenol formaldehyde resin-derived carbon provided a cheap and effective catalyst for electrocatalytic H2O2 production.