Electrochemical Synthesis Of H2O2 Research Articles

Identifying the two-electron oxygen reduction mechanism on BC3 site in Cl−-containing electrolytes

The electrochemical synthesis of H2O2 has great potential for applications in the treatment of environmental pollution and energy, but the toxic effect of Cl− on the active sites of catalysts has severely limited the application of this technology in these fields. Developing efficient non-metal-doped catalysts represents an effective strategy to address this issue. Although B-doped carbon materials have demonstrated excellent ORR activity, the understanding of the ORR mechanism on B surface sites remains highly controversial, particularly in seawater electrolytes. The influence of Cl− adsorption behavior on the catalytic reaction center mechanism is still unknown. In this paper, catalysts containing the BC3 structure were successfully prepared with an H2O2 yield of 3.55 mol/ (gcat h) in simulated seawater. The DFT results demonstrated that BC3 functions as a 2e− ORR active site, and the presence of Cl− does not poison it. Instead, it promotes the hydrogenation process of *OOH on its surface, further enhancing its ORR performance. The results provide clarity on how the Cl− of the catalytic environment affects the ORR performance and pathway selectivity of non-metallic B-sites. Additionally, the results offer valuable insights for designing electrocatalysts in complex environments.

Recent advances in the electrochemical production of hydrogen peroxide

Hydrogen peroxide (H2O2) is an innovative and environmentally friendly oxidant that finds wide-ranging applications across multiple industries. In the past, H2O2 production predominantly relied on the anthraquinone method, which had drawbacks such as the generation of organic waste and the requirement for energy-intensive reactions. A cheap, efficient, and sustainable way of producing H2O2 may be achieved through the redox reaction between oxygen and water. On both small and large scales, the electrosynthesis of H2O2 is practical and affordable. In recent years, it has been thought that the energy-intensive anthraquinone process may be replaced by the electrochemical synthesis of H2O2 via the two-electron oxygen reduction reaction (ORR) route. To eliminate the organic pollutants found in drinking water and industrial effluent, highly effective hydrogen peroxide (H2O2) must be produced electrochemically using gas diffusion electrodes (GDEs). Compared to other carbonaceous cathodes, the GDEs as cathodic electrocatalysts demonstrate greater cost-effectiveness, lower energy consumption, and higher oxygen utilization efficiency for the formation of H2O2. A promising alternative for enabling the growth of sustainable economics in the W&W sector is microbial electrochemical systems (MESs) that create H2O2. To enhance the efficiency and predictability of H2O2 production in MESs, a machine-learning approach was adopted, incorporating a meta-learning methodology to forecast the generation rate of H2O2 in MES based on the seven input variables, comprising several design and operational parameters.

Regulating N Species in N-Doped Carbon Electro-Catalysts for High-Efficiency Synthesis of Hydrogen Peroxide in Simulated Seawater.

Electrochemical oxygen reduction reaction (ORR) is an attractive and alternative route for the on-site production of hydrogen peroxide (H2 O2 ). The electrochemical synthesis of H2 O2 in neutral electrolyte is in early studying stage and promising in ocean-energy application. Herein, N-doped carbon materials (N-Cx ) with different N types are prepared through the pyrolysis of zeolitic imidazolate frameworks. The N-Cx catalysts, especially N-C800 , exhibit an attracting 2e- ORR catalytic activity, corresponding to a high H2 O2 selectivity (≈95%) and preferable stability in 0.5m NaCl solution. Additionally, the N-C800 possesses an attractive H2 O2 production amount up to 631.2mmolg-1 h-1 and high Faraday efficiency (79.8%) in H-type cell. The remarkable 2e- ORR electrocatalytic performance of N-Cx catalysts is associated with the N species and N content in the materials. Density functional theory calculations suggest carbon atoms adjacent to graphitic N are the main catalytic sites and exhibit a smaller activation energy, which are more responsible than those in pyridinic N and pyrrolic N doped carbon materials. Furthermore, the N-C800 catalyst demonstrates an effective antibacterial performance for marine bacteria in simulated seawater. This work provides a new insight for electro-generation of H2 O2 in neutral electrolyte and triggers a great promise in ocean-energy application.

Application of the all-in-one electrode for in situ H2O2 generation in hydroxylation catalyzed by unspecific peroxygenase from Agrocybe aegerita

The versatile unspecific peroxygenase from the fungus Agrocybe aegerita (AaeUPO) is capable to perform hydroxylation of various substrates, even unactivated CH bonds. The technical application of AaeUPO is still limited due to an instability towards its co-substrate hydrogen peroxide (H2O2). Electrochemical synthesis of H2O2 is an attractive approach that provides controllable in situ generation of H2O2. The aims of this study are to promote catalyst efficiency and develop an individually tailored system for H2O2-dependent reactions. Herein, an All-in-One electrode (AiO) system with a carbon felt cathode is used to generate H2O2in situ and combined for the first time with an enzymatic hydroxylation. The AiO electrode combines the counter and working electrode in a single rod structure. This shape provides convenient integration into conventional bioreactors, thus, converting them into bioelectrochemical systems (BES). Hydroxylation of 4-ethylbenzoic acid (EBA) catalyzed by the recombinant AaeUPO (rAaeUPO) was chosen as the model reaction. Total turnover number (TTN) up to 450,000 mol mol−1 and turnover frequency (TOF) up to 7.7 s − 1 were achieved using the AiO electrode system. The H2O2 productivity was identified as the limiting factor in the hydroxylation of EBA. However, with numbering-up or surface enlargement, this process could have great potential as an optimizable platform for H2O2-dependent enzymatic reactions.

Superstructures of Zeolitic Imidazolate Frameworks to Single- and Multiatom Sites for Electrochemical Energy Conversion.

The exploration of electrocatalysts with high catalytic activity and long-term stability for electrochemical energy conversion is significant yet remains challenging. Zeolitic imidazolate framework (ZIF)-derived superstructures are a source of atomic-site-containing electrocatalysts. These atomic sites anchor the guest encapsulation and self-assembly of aspheric polyhedral particles produced using microreactor fabrication. This review provides an overview of ZIF-derived superstructures by highlighting some of the key structural types, such as open carbon cages, 1D superstructures, hollow structures, and the interconversion of superstructures. The fundamentals and representative structures are outlined to demonstrate the role of superstructures in the construction of materials with atomic sites, such as single- and dual-atom materials. Then, the roles of ZIF-derived single-atom sites for the electroreduction of CO2 and electrochemical synthesis of H2 O2 are discussed, and their electrochemical performance for energy conversion is outlined. Finally, the perspective on advancing single- and dual-atom electrode-based electrochemical processes with enhanced redox activity and a low-impedance charge-transfer pathway for cathodes is provided. The challenges associated with ZIF-derived superstructures for electrochemical energy conversion are discussed.

Rational design of Ruddlesden–Popper perovskite electrocatalyst for oxygen reduction to hydrogen peroxide

AbstractAlthough the oxygen reduction process to hydrogen peroxide (H2O2) is a green option for H2O2 generation, the low activity and selectivity hindered the industry's process. In recent years, the electrochemical synthesis of H2O2 through a 2e– transfer method of oxygen reduction reaction (ORR) has piqued the interest of both academics and industry. Metal oxide catalysts have emerged as a novel family of electrochemical catalysts due to their unusual physical, chemical, and electrical characteristics. In this work, we first developed a Ruddlesden–Popper perovskite oxide (Pr2NiO4+δ) as a highly selective and active catalyst for 2e– ORR to produce H2O2. Molybdenum was introduced here to adjust the oxidation states of these transition metals with successful substitution into Ni‐site to prepare Pr2Ni1‐xMoxO4+δ, and the molybdenum substitution improves the H2O2 selectivity during the ORR process, in 0.1 M KOH, from 60% of Pr2NiO4+δ to 79% of Pr2Ni0.8Mo0.2O4+δ at 0.55 V versus RHE. A limiting H2O2 concentration of 0.24 mM for Pr2NiO4+δ and 0.42 mM for Pr2Ni0.8Mo0.2O4+δ was obtained at a constant current of 10 mA/cm2 using a flow‐cell reactor using a gas‐diffusion electrode.

Electricity + Air + Water = Hydrogen Peroxide

Hydrogen peroxide (H2O2) is one of the most important chemicals in the world, and is currently produced exclusively by the energy- and waste-intensive anthraquinone cycling process. Electrochemical synthesis of H2O2, including both oxygen reduction reaction (ORR) and water oxidation reaction (WOR) to H2O2, provides a promising alternative route to realize green and delocalized H2O2 production. In this talk I will introduce both catalytic materials design and solid electrolyte reactor engineering for highly active and selective generation of pure H2O2 solutions.

Precise Design of Covalent Organic Frameworks for Electrocatalytic Hydrogen Peroxide Production.

Electrochemical synthesis of H2 O2 with high productivity is a significant challenge in electrocatalysis. Herein, we develop Mg-ion contained covalent organic frameworks (MgP-DHTA-COF), comprising stacked 2D layers, well-defined skeletons, and well-ordered monodispersed active sites, for the electrocatalytic production of H2 O2 directly from O2 and H2 O. The precise-designed MgP-DHTA-COF achieves H2 O2 selectivity up to 96%, high Faradaic efficiency of 91% and reliable stability for H2 O2 synthesis in 0.10 mol L-1 KOH aqueous solution. Both experiments and simulations demonstrate that the pyrrolic-N fixed Mg ions in the knots promote the reactivity of COF and enhance the adsorption ability of OOH*. This work provides a valuable example for the design of an efficient electrocatalyst based on COFs for H2 O2 production.

Electrocatalytic Oxygen Reduction to Hydrogen Peroxide: From Homogeneous to Heterogeneous Electrocatalysis

AbstractHydrogen peroxide (H2O2) is an environmentally friendly oxidant, finding widespread use across the chemical industry, in sanitation and environmental remediation. Currently, H2O2 is manufactured via the anthraquinone process which has a number of disadvantages including nondistributed production, high‐energy consumption, substantial organic by‐product waste, and the need to transport the obtained H2O2 to the point‐of‐use. Accordingly, the electrochemical synthesis of H2O2 is now attracting a lot of interest as an alternative, cost‐effective, small‐scale, and distributed technology for H2O2 manufacture. This review summarizes recent advancements in the development of Homogeneous and Heterogeneous catalysts for electrocatalytic O2 reduction reaction (ORR) to H2O2. The basic principles of the ORR, and methodologies for investigating the ORR to H2O2 are first introduced. Next, H2O2 production over Homogeneous catalysts is discussed, with a focus on the reaction mechanisms and the factors that influence activity, selectivity, and reaction kinetics. Subsequently, recent breakthroughs in H2O2 synthesis over Heterogeneous catalysts, including nonnoble metal‐based nanomaterials, carbon materials, and single‐atom catalysts are described. The latter are given special attention, since they serve as a bridge between Homogeneous catalysis and Heterogeneous catalysis, while also offering excellent performance. Finally, the challenges and opportunities for electrochemical ORR to H2O2 are critically discussed.

On-Demand Synthesis of H2 O2 by Water Oxidation for Sustainable Resource Production and Organic Pollutant Degradation.

H2 O2 is a versatile and environmentally friendly chemical involved in water treatment, such as advanced oxidation processes. Anthraquinone oxidation is widely used for large-scale production of H2 O2 , which requires significant energy input and periodic replacement of the carrier molecule. H2 O2 production should be customized considering the specific usage scenario. Electrochemical synthesis of H2 O2 can be adopted as alternatives to traditional method, which avoids concentration, transportation, and storage processes. Herein, we identified Bi2 WO6 :Mo as a low-cost and high-selectivity choice from a series of Bi-based oxides for H2 O2 generation via two-electron water oxidation reaction. It can continuously provide H2 O2 for in situ degradation of persistent pollutants in aqueous solution. Clean energy from H2 can also be produced at the cathode. This kind of water splitting producing sustainable resources of H2 O2 and H2 is an advance in environmental treatment and energy science.

Partially Pyrolyzed Binary Metal-Organic Framework Nanosheets for Efficient Electrochemical Hydrogen Peroxide Synthesis.

Herein, we developed a partially controlled pyrolysis strategy to create evenly distributed NiO nanoparticles within NiFe-MOF nanosheets (MOF NSs) for electrochemical synthesis of H2 O2 by a two-electron oxygen reduction reaction (ORR). The elemental Ni can be partially transformed to NiO and uniformly distributed on the surface of the MOF NSs, which is crucial for the formation of the particular structure. The optimized MOF NSs-300 exhibits the highest activity for ORR with near-zero overpotential and excellent H2 O2 selectivity (ca. 99 %) in 0.1 m KOH solution. A high-yield H2 O2 production rate of 6.5 mol gcat -1 h-1 has also been achieved by MOF NSs-300 in 0.1 m KOH and at 0.6 V (vs. RHE). In contrast to completely pyrolyzed products, the enhanced catalytic activities of partially pyrolyzed MOF NSs-300 originates mainly from the retained MOF structure and the newly generated NiO nanoparticles, forming the coordinatively unsaturated Ni atoms and tuning the performance towards electrochemical H2 O2 synthesis.

Promoting H2O2 production via 2-electron oxygen reduction by coordinating partially oxidized Pd with defect carbon

Electrochemical synthesis of H2O2 through a selective two-electron (2e−) oxygen reduction reaction (ORR) is an attractive alternative to the industrial anthraquinone oxidation method, as it allows decentralized H2O2 production. Herein, we report that the synergistic interaction between partially oxidized palladium (Pdδ+) and oxygen-functionalized carbon can promote 2e− ORR in acidic electrolytes. An electrocatalyst synthesized by solution deposition of amorphous Pdδ+ clusters (Pd3δ+ and Pd4δ+) onto mildly oxidized carbon nanotubes (Pdδ+-OCNT) shows nearly 100% selectivity toward H2O2 and a positive shift of ORR onset potential by ~320 mV compared with the OCNT substrate. A high mass activity (1.946 A mg−1 at 0.45 V) of Pdδ+-OCNT is achieved. Extended X-ray absorption fine structure characterization and density functional theory calculations suggest that the interaction between Pd clusters and the nearby oxygen-containing functional groups is key for the high selectivity and activity for 2e− ORR.

Efficient and stable heterogeneous electro-Fenton system using iron oxides embedded in Cu, N co-doped hollow porous carbon as functional electrocatalyst

Heterogeneous electro-Fenton reaction, constituted by Fenton chemistry and electrochemical synthesis of H2O2, exhibits the powerful ability for wastewater treatment by virtue of the continuous production of strong oxidizing ·OH radical. However, the slow reduction of Fe(III) to Fe(II) of Fenton phase hinders the continuous and effective ·OH generation. Strengthening the interfacial electron transfer from conductive carbon support to Fenton phase is a feasible strategy to promote Fe(II) regeneration, which can be achieved by chemical modifications of the carbon support with N and Cu doping. In this study, we constructed a functional electrocatalyst constituted by Cu, N co-doped hollow porous carbon with embedded iron oxide nanoparticles (FeOx/CuNxHPC) by carbonizing Cu doped iron metal-organic frameworks NH2-MIL-88B(Fe). The electro-Fenton system of FeOx/CuNxHPC exhibited almost 100% removal efficiency of phenol (50 ppm) within 90 min at the pH of 4, 6, 8 and 10 at a potential of −0.6 V vs SCE. Particularly, at pH 6, the phenol mineralization efficiency reached 81.6% within 180 min. Moreover, FeOx/CuNxHPC exhibited outstanding stability and reusability after consecutive ten tests of electron-Fenton reactions. Such enhanced electro-Fenton performance of FeOx/CuNxHPC could be ascribed to the facilitated surface Fe(II) regeneration, which greatly promoted in-situ decomposition of H2O2 into ·OH. By virtue of the excellent electro-Fenton performance and the facile preparation, this kind of iron-based metal-organic frameworks derived functional catalysts was proposed as the suitable cathodic material for the efficient and stable heterogeneous electro-Fenton catalysis.

Selective Electrochemical H2O2 Production through Two‐Electron Oxygen Electrochemistry

AbstractDirect electrochemical production of hydrogen peroxide (H2O2) through two‐electron oxygen electrochemistry, for example, the oxygen reduction in fuel cells or water oxidation in water electrolyzers, could provide an attractive alternative to locally produce this chemical on demand. The efficiency of these processes depends greatly on the availability of cost‐effective catalysts with high selectivity, activity, and stability. In recent years, various novel nanostructured materials have been reported to selectively produce H2O2. Through combined experimental and theoretical approaches, underlying mechanisms in the electrochemical synthesis of H2O2 via oxygen electrochemistry have been unveiled. Considering the remarkable progress in this area, the authors summarize recent developments regarding the direct production of H2O2 through two‐electron electrochemical oxygen reactions. The fundamental aspects of electrochemical oxygen reactions are first introduced. Various types of catalysts that can effectively produce H2O2 via two‐electron oxygen electrochemistry are then presented. In parallel, the unique structure‐, component‐, and composition‐dependent electrochemical performance together with the underlying catalytic mechanisms are discussed. Finally, a brief conclusion about the recent progress achieved in electrochemical generation of H2O2 and an outlook on future research challenges are given.

High-efficiency oxygen reduction to hydrogen peroxide catalysed by oxidized carbon materials

Hydrogen peroxide (H2O2) is a valuable chemical with a wide range of applications, but the current industrial synthesis of H2O2 involves an energy-intensive anthraquinone process. The electrochemical synthesis of H2O2 from oxygen reduction offers an alternative route for on-site applications; the efficiency of this process depends greatly on identifying cost-effective catalysts with high activity and selectivity. Here, we demonstrate a facile and general approach to catalyst development via the surface oxidation of abundant carbon materials to significantly enhance both the activity and selectivity (~90%) for H2O2 production by electrochemical oxygen reduction. We find that both the activity and selectivity are positively correlated with the oxygen content of the catalysts. The density functional theory calculations demonstrate that the carbon atoms adjacent to several oxygen functional groups (–COOH and C–O–C) are the active sites for oxygen reduction reaction via the two-electron pathway, which are further supported by a series of control experiments. The direct synthesis of hydrogen peroxide via oxygen reduction is an attractive alternative to the anthraquinone process. Here, a general trend linking oxygenation of carbon surfaces with electrocatalytic performance in peroxide synthesis is demonstrated, and computational studies provide further insight into the nature of the active sites.