Electrochemical Production Of Hydrogen Peroxide Research Articles

Innovative carbon materials from lignocellulosic wastes for electrochemical hydrogen peroxide production: Bridging biomass conversion and material properties

This study aims to assess the electrochemical generation of hydrogen peroxide and hydroxyl radicals (*OH) using carbon cathodes synthesized from three different lignocellulosic residues, Phragmites australis (PA), Cladium mariscus (CM) and Typha domingensis (TD). These vegetal species are commonly used in natural wetlands and phytoremediation processes and can accumulate recalcitrant pollutants within these treatment processes, generating a waste that should be properly managed. To convert these residues into valuable carbon materials, they underwent hydrothermal carbonization (HTC) followed by either chemical activation with KOH or pyrolysis at 1000 ºC. The best results were obtained with chemically activated materials, yielding a maximum H2O2 concentration of 313 mg L−1 with the carbon cathode produced from PA. The specific surface area, oxygenated functional groups and presence of structural defects in carbonous structures, were key parameters related to a good performance as catalysts towards the 2e- Oxygen Reduction Reaction (ORR). It was also demonstrated, in comparison with previous studies, that the presence of heavy metals in the structure of the lignocellulosic residue enhanced the decomposition of H2O2 into *OH. However, in the study of the degradation of a model organic contaminant as methylene blue (MB), it was shown that these *OH were not the main contributors to degradation, as direct H2O2 chemical degradation and adsorption on the carbon materials played the most significant role. Therefore, the outstanding capacity of these lignocellulosic residues as catalysts for the electrogeneration of H2O2 was confirmed, suggesting their potential future application in advanced oxidation processes for water decontamination.

Isomerization Engineering of Oxygen-Enriched Carbon Quantum Dots for Efficient Electrochemical Hydrogen Peroxide Production.

Hydrogen peroxide (H2O2) has emerged as a kind of multi-functional green oxidants with extensive industrial utility. Oxidized carbon materials exhibit promises as electrocatalysts in the two-electron (2e-) oxygen reduction reaction (ORR) for H2O2 production. However, the precise identification and fabrication of active sites that selectively yield H2O2 present a serious challenge. Herein, a structural engineering strategy is employed to synthesize oxygen-doped carbon quantum dots (o-CQD) for the 2e- ORR. The surface electronic structure of the o-CQDs is systematically modulated by varying isomerization precursors, thereby demonstrating excellent electrocatalyst performance. Notably, o-CQD-3 emerges as the most promising candidate, showcasing a remarkable H2O2 selectivity of 96.2% (n = 2.07) at 0.68V versus RHE, coupled with a low Tafel diagram of 66.95mV dec-1. In the flow cell configuration, o-CQD-3 achieves a H2O2 productivity of 338.7mmol gcatalyst -1 h-1, maintaining consistent production stability over an impressive 120-hour duration. Utilizing in situ technology and density functional theory calculations, it is unveil that edge sites of o-CQD-3 are facilely functionalized by C-O-C groups under alkaline ORR conditions. This isomerization engineering approach advances the forefront of sustainable catalysis and provides a profound insight into the carbon-based catalyst design for environmental-friendly chemical synthesis processes.

Catalyst-less efficient electrochemical production of hydrogen peroxide

Hydrogen peroxide is produced efficiently in a catalyst-less electrochemical cell manufactured at lab scale (4 cm2 of electrode size) by resin and titanium 3-D printing. The electrolyte inlet and outlet of the cell are designed to promote a very turbulent flow pattern that provides good mixing of the liquid and gas phases and minimizes the mass transport limitations. The mechanization of the titanium contributes to an efficient gas diffusion in the cathode which was successfully adapted to the 3-D printed cell resulting in a very efficient gas–liquid reactive absorbent unit. The effect of the electrolyte, operation mode, gas and liquid flow rates were evaluated on the electrochemical production of hydrogen peroxide and the results obtained were successfully fitted to a simple phenomenological model that helped to obtain a deep understanding of the process. The proposed electrochemical gas–liquid absorber achieved coulombic efficiencies as high as 69.72 % and energy consumptions close to 9 mg H2O2 (Wh)−1 when the system was operated in continuous mode with the most efficient conditions (no cell compartmentation and feeding pure oxygen with electrolytes containing sulphate salts at pH near 3). Those values of efficiencies are in the upper range of the results found in the literature for the electrochemical production of hydrogen peroxide, even though no catalytic coating was used to promote this cathodic reaction. An unexpected effect of the salt contained in the electrolyte was observed indicating the existence of other production mechanisms that require further characterization.

Magnetic field-enhanced oxygen reduction reaction for electrochemical hydrogen peroxide production with different cerium oxide nanostructures

We investigated cerium oxide nanoparticles of various morphologies (nanosheets, nanocubes, and nanoparticles) supported on carbon Vulcan XC-72 for the two-electron oxygen reduction reaction (ORR). A continuous magnetic field (2000 Oe) was used for the first time in the literature. The best results were for 5 % (w/w) CeO2 for all three different morphologies, more than doubling the ring current, enhancing the hydrogen peroxide selectivity from 51 % (Vulcan XC-72) to 84–89 %, and modifying the onset potential to lesser negative values. The presence of the magnetic field led to even higher ring currents with 5 % (w/w) CeO2, H2O2 selectivity from 54 % (Vulcan XC-72) to 88–96 % and changing even more the onset potential. Those results were correlated with the Zeeman effect, the Lorentz force, generating magnetohydrodynamic effects, the Kelvin force, and the formation of Bound Magnetic Polarons. This pioneering research introduces an innovative approach, highlighting the potential of an external continuous magnetic field.

2D Al-MOF with ultrathin nanoflake-assembled hollow microstructures for electrochemical hydrogen peroxide production

Electrochemical transformation from oxygen reduction reaction (ORR) to hydrogen peroxide (H2O2) is one of the promising green techniques to synthesis H2O2. However, due to the competing two processes of 2e− and 4e−ORR with different products, designing and synthesizing highly selective and active 2e− ORR electrocatalysts for H2O2 production is fundamentally and practically important. In this work, we used a simple solvothermal method and self-template strategy to create ultrathin 2D Al-MOF nanosheets for efficient electrocatalytic synthesis of H2O2 by 2e− ORR. The presence of a mixed solvent and sulfate ion is critical to the formation of the specific structure. Naturally, their ultrathin morphology and abundant mesoporous formation leads to the sufficient exposure of electrochemically active sites and high mass/electron transfer capability. Therefore, the Al-MOF NSs show excellent electrocatalytic performance for 2e− ORR. The optimized Al-MOF NSs-1 exhibited the best ORR catalytic performance with almost no overpotential and high selectivity for 2e− ORR to H2O2 (94 %–98 %) in a wide range of low potentials in alkaline electrolyte. Meanwhile, the high reaction rate of 2.56 molgcat−1h−1 for H2O2 production has also been achieved at 0.6 V. Furthermore, the Al-MOF NSs-1 enable to catalyze H2O2 production with excellent durability and selectivity after long-term stability test (10,000 cycles) and 11 h of potentiostatic electrolysis. The present study indicates the promising application of metal organic frameworks (MOFs) materials in H2O2 electrochemical synthesis.

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.

Modulating coal-derived carbon toward electrocatalytic generation of hydroxyl radicals for organic contaminant removal

Coal-derived carbon catalysts are modulated for producing hydroxyl radicals from oxygen gas to remove organic contaminants from water, and the roles of oxygen containing groups are explored, which would contribute to a greener society.

Heteroatom-Coordinated Palladium Molecular Catalysts for Sustainable Electrochemical Production of Hydrogen Peroxide.

Currently, hydrogen peroxide (H2O2) manufacturing involves an energy-intensive anthraquinone technique that demands expensive solvent extraction and a multistep process with substantial energy consumption. In this work, we synthesized Pd-N4-CO, Pd-S4-NCO, and Pd-N2O2-C single-atom catalysts via an in situ synthesis approach involving heteroatom-rich ligands and activated carbon under mild reaction conditions. It reveals that palladium atoms interact strongly with heteroatom-rich ligands, which provide well-defined and uniform active sites for oxygen (O2) electrochemically reduced to hydrogen peroxide. Interestingly, the Pd-N4-CO electrocatalyst shows excellent performance for the electrocatalytic reduction of O2 to H2O2 via a two-electron transfer process in a base electrolyte, exhibiting a negligible amount of onset overpotential and >95% selectivity within a wide range of applied potentials. The electrocatalysts based on the activity and selectivity toward 2e- ORR follow the order Pd-N4-CO > Pd-N2O2-C > Pd-S4-NCO in agreement with the pull-push mechanism, which is the Pd center strongly coordinated with high electronegativity donor atoms (N and O atoms) and weakly coordinated with the intermediate *OOH to excellent selectivity and sustainable production of H2O2. According to density functional theory, Pd-N4 is the active site for selectivity toward H2O2 generation. This work provides an emerging technique for designing high-performance H2O2 electrosynthesis catalysts and the rational integration of several active sites for green and sustainable chemical synthesis via electrochemical processes.

PV Supplied Electrochemical Production of Hydrogen Peroxide: A Green Pathway for Fenton Based Advanced Oxidation Processes

PV Supplied Electrochemical Production of Hydrogen Peroxide: A Green Pathway for Fenton Based Advanced Oxidation Processes

Elucidating Oxygen Reduction Mechanisms on Organic Mixed Ionic-Electronic Conducting Polymers

Atmospheric oxygen is an attractive oxidant for the generation of electricity from chemical fuels and for the electrochemical production of hydrogen peroxide. Although not universal, it is generally assumed that an electrocatalyst is needed to reduce oxygen. Recently, a variety of organic mixed ionic-electronic conducting polymers (OMIECs) have been reported to exhibit catalytic behavior for both the 4-electron/4-proton and the 2-electron/2-proton oxygen reduction reaction (ORR).This work sets out to identify the oxygen reduction mechanism of OMIECs through a multi-faceted experimental and theoretical approach. We primarily focus our efforts on p(NDI-T2 P75)—a random copolymer comprised of naphthalene diimide (NDI) and bithiophene (T2) units with 75% polar sidechains—and then expand the understanding built on this system to a range of other OMIECs. Using rotating ring disk electrochemistry, we find that the investigated OMIECs exhibit a high selectivity towards the 2-electron ORR product. Using operando UV-Vis and Raman spectroscopy measurements, we identify changes in OMIEC performance when in the presence of O2. To gain further insights about the catalytic reaction path, we construct and test a microkinetic model. Through this model, we show that the performance of the tested OMIECs can be rationalized through an EC’D reaction mechanism. Our results suggest that these materials do not operate as electrocatalysts for the initial reduction of oxygen to superoxide but do function as catalysts for the disproportionation of superoxide.

Unlocking the Potential of Sub‐Nanometer Pd Catalysts for Electrochemical Hydrogen Peroxide Production

AbstractThe utilization of nanoscale catalysts represents a valuable and promising strategy for augmenting catalytic performance while mitigating the reliance on expensive noble metals. Nevertheless, a significant knowledge gap persists regarding the intricate interplay between catalyst size, physical properties, and catalytic behavior in the context of the oxygen reduction reaction. In this study, the synthesis of precisely controlled palladium catalysts is presented, spanning a wide range from individual atoms to metal clusters and nanoparticles, followed by a comprehensive evaluation of their performance in acidic conditions. The results show a significant increase in H2O2 selectivity of up to 96% with decreasing catalyst size and strategic approaches are identified to eliminate unselective sites, facilitating the attainment of active and selective catalysts. The enhanced selectivity of the catalysts highlights the potential of single atom catalytic sites and can be adapted to improve the performance of various catalytic processes.

Facilitating two-electron oxygen reduction with pyrrolic nitrogen sites for electrochemical hydrogen peroxide production

Electrocatalytic hydrogen peroxide (H2O2) production via the two-electron oxygen reduction reaction is a promising alternative to the energy-intensive and high-pollution anthraquinone oxidation process. However, developing advanced electrocatalysts with high H2O2 yield, selectivity, and durability is still challenging, because of the limited quantity and easy passivation of active sites on typical metal-containing catalysts, especially for the state-of-the-art single-atom ones. To address this, we report a graphene/mesoporous carbon composite for high-rate and high-efficiency 2e− oxygen reduction catalysis. The coordination of pyrrolic-N sites -modulates the adsorption configuration of the *OOH species to provide a kinetically favorable pathway for H2O2 production. Consequently, the H2O2 yield approaches 30 mol g−1 h−1 with a Faradaic efficiency of 80% and excellent durability, yielding a high H2O2 concentration of 7.2 g L−1. This strategy of manipulating the adsorption configuration of reactants with multiple non-metal active sites provides a strategy to design efficient and durable metal-free electrocatalyst for 2e− oxygen reduction.

O, N Coordination-Mediated Nickel Single-Atom Catalysts for High-Efficiency Generation of H2O2.

Electrochemical selective two-electron oxygen reduction shows great potential for on-site electrochemical production of hydrogen peroxide (H2O2). Herein, we demonstrated the synthesis of Ni single-atom sites coordinated by three oxygen atoms and one nitrogen atom (i.e., Ni-N1O3) supported by oxidized carbon black (OCB) by pyrolyzing nickel-(pyridine-2,5-dicarboxylate) coordination complexes. Aberration-corrected scanning transmission electron microscopy (AC-STEM) combined with X-ray absorption spectroscopy (XAS) proves the presence of atomically dispersed Ni atoms attached on OCB (labeled as Ni-SACs@OCB), in which Ni single atoms are stabilized by a N, O-mediated coordination configuration. This Ni-SACs@OCB catalyst shows high H2O2 selectivity (95%) in a range of 0.2-0.7 V undergoing a two-electron oxygen reduction process, with a kinetic current density of 2.8 mA cm-2 and a mass activity of 24 A gcat.-1 at 0.65 V (vs RHE). In practice, H-cells with Ni-SACs@OCB as catalysts displayed a high H2O2 production rate of 98.5 mmol gcat.-1 h-1 with negligible current loss during testing, suggesting the high H2O2 generation efficiency and robust stability. DFT theoretical calculations revealed that Ni single-atom sites coordinated by O, N coordination exhibit advantages in oxygen adsorption and increased reactivity toward the intermediate species, *OOH, which is beneficial to high selectivity for H2O2 production. This work provides a novel N, O-mediated four-coordinate nickel single-atom catalyst as a promising candidate for practical decentralized production of H2O2.

Optimizing the binding of the *OOH intermediate via axially coordinated Co-N5 motif for efficient electrocatalytic H2O2 production

Electrochemical production of hydrogen peroxide (H2O2) is a sustainable and environmentally benign process. The electrochemical oxygen reduction process (ORR) via a two electron pathway (2e- ORR) offers a practical method for on-site H2O2 generation. As an earth-abundant catalyst, the cobalt-nitrogen coordinated systems integrated into the carbon matrix (Co-NC) has caused wide attention for its high activity in 2e- ORR. Even though most of the reported Co-NC catalysts have classical planar Co-N4 coordination, axial coordination engineering has recently emerged as an effective way to control the active sites in the axial direction by using different coordination ligands. The structure-function link between the Co-N configuration of non-planar coordination and 2e- ORR activity is, however, not fully understood. An axial-N coordinated Co-N5 motif embedded in hierarchically porous graphite-3R carbon (Co-N5C) was effectively synthesized using a template-sacrificing method. The Co-N5C has a high selectivity for 2e- ORR and a high H2O2 molar production rate of up to 6.78 mol peroxide/gcatalyst/h in acidic media, both of which are better than its Co-N4 counterpart. DFT analyses demonstrate that axial-N ligands regulated the d-band center of the Co atom in the Co-N5C catalyst, inducing a shift in ΔG*OOH near the Sabatier volcano plot's peak (ΔG*OOH = 4.22 eV). This optimized the binding of the *OOH intermediate and then enhanced the protonation of *OOH to produce H2O2 more efficiently.

The atomic interface effect of single atom catalysts for electrochemical hydrogen peroxide production

The atomic interface effect of single atom catalysts for electrochemical hydrogen peroxide production

Cu/C Composite Electrocatalysts for Electrochemical Production of Hydrogen Peroxide

Hydrogen peroxide (H2O[Formula: see text] is an important chemical with wide fields of applications in the chemical industry, medicine and environmental protection. The preparation of H2O2 by the oxygen reduction reaction (ORR) via the two-electron pathway has the advantages of simple operation and environmental friendliness. Nevertheless, the kinetics of ORR is relatively slow, and the energy efficiency of electrochemical synthesis of H2O2 is seriously limited by the competitive four-electron pathway. Therefore, the electrosynthesis of H2O2 requires an electrocatalyst with both high catalytic activity and selectivity. In this study, Cu nanoparticles supported on carbon composites (Cu/C) were proposed and had been applied as the catalysts for the electrochemical synthesis of H2O2. Taking advantage of the cross-linking reaction between sodium alginate (SA) and metal ions, Cu nanoparticles were directly supported on carbon materials. The porous structure of carbon materials and the introduction of Cu improved the H2O2 selectivity of the catalysts. In O2-saturated 0.1[Formula: see text]M KOH, the optimized catalyst exhibited good activity with a selectivity of 88–90% in the potential range of 0.2–0.6[Formula: see text]V for the electrosynthesis of H2O2, and the selectivity remained 70% after 6[Formula: see text]h of operation.

Metal-free boron catalyst with oriented crystal phase interfacial interaction for efficient electrochemical production of hydrogen peroxide

The in-depth research on the interfacial interaction of crystal phases in metal-free catalysts during the 4 e− oxygen reduction reaction (ORR) are scarce. Herein, the modified amorphous boron (A-boron) with high electrochemical performance was fabricated with a simple high-temperature annealing process. The self-regulation of the crystal phases interface in modified A-boron (A-B-600N2) was realized through the designed synthesis process, which result in the formation of strong electronic interaction between the amorphous phase and crystalline phase. The increased oxygen adsorption and reduced internal resistance contribute to the improvement of electrochemical activity. In an alkaline solution, the A-B-600N2 exhibited as high as 85 mmol·gcatalyst−1·h−1 H2O2 production rate and 65% Faradaic efficiency (FE) value. Besides, A-B-600N2 also presented excellent activity for degrading a series of organic pollutants in the electro-Fenton (EF) system. This discovery provides a new idea for the modification of a boron-based electrocatalyst that is practicable for a high H2O2 production rate in the alkaline medium and excellent pollutant degradation efficiency in the EF system.

Evaluating key properties of carbon materials as cathodes for the electrogeneration of hydrogen peroxide

Twenty two carbon materials of different origins (e.g., graphite, graphene, carbon black, hydrochars, activated carbons, carbon nanotubes and nanofibers) and with varied physicochemical characteristics (e.g., electrical conductivity, structural order, surface functionalization, porosity) were investigated as cathodes in the electrochemical production of hydrogen peroxide. A screening of the electrocatalytic performance was carried out in 0.2 cm2 (inks casted on a glassy carbon) and 4 cm2 electrodes (Toray paper). The highest H2O2 production yields were obtained for carbon nanotubes and carbon nanofibers, outperforming common carbon benchmarks for this application -i.e., carbon black, carbon felt-. Furthermore, a good catalytic activity was obtained with low-cost and disordered carbon cathodes with moderate electrical conductivity and density of structural defects (e.g., nanoporous carbons), both in terms of overall production rate, selectivity and energy consumption. Data also revealed that the H2O2 production yield and the faradaic efficiency are closely related to the structural parameters of the carbon materials (i.e., density of structural defects), rather than to the electrical conductivity, composition or porous features. An AD/AG threshold value of 1.5 can be used to discriminate the electrocatalytic activity of carbon cathodes for the production of H2O2 through a 2e-ORR, in terms of high production rates and good faradaic efficiencies.

Valorization of polluted biomass waste for manufacturing sustainable cathode materials for the production of hydrogen peroxide

A circular economy approach was followed to convert biomass wastes polluted with metals (obtained from phytoremediation processes) to generate electroactive carbon materials to be used in the electrochemical production of hydrogen peroxide. Carbon materials were pretreated using hydrothermal carbonization at 200ºC and 130 g soil mL−1 water and post treated through pyrolysis at different temperatures (300ºC, 500ºC and 1000ºC) and using different chemical precursors as KOH or H3PO4. These materials would modify the carbon paper (CP) cathodes to substitute the commonly used carbon black (CB), that comes from fossil fuels. Porosity, thermochemical behavior, electrical conductivity, electrocatalytic response and H2O2 accumulation tests were evaluated to determine the potential performance of these materials in the electrochemical production of hydrogen peroxide. Delays in mass losses observed in thermogravimetric studies indicate the improvement of the thermal stability of materials which are related with the highest electrical conductivity (that correspond to hydrochar pyrolyzed at 1000 ºC). High specific surface areas (1097 and 704 m2/g) were also found with hydrochars treated with chemical precursors with values even superior to commercial CB. Results show that all activated hydrochars present electrocatalytic activity towards the production of hydrogen peroxide and that the materials chemically activated with KOH can achieve a 70% of the H2O2 production obtained with commercial CB. Moreover, it was found that the presence of metals in the synthesized materials may promote a Fenton-like reaction, increasing by 40% the generation of hydroxyl radicals with respect to commercial CB. This paramount finding opens the window for the use of this phytoremediation waste to produce sustainable electrode materials for upgraded electrochemical advanced oxidation processes.

Insights into the Electrochemical Production of Hydrogen Peroxide over Single-Atom Co–N–C Catalysts with the Introduction of Carbon Vacancy Defect near the Co–N4 Site

With the introduction of carbon divacancy, trivacancy, and tetravacancy defects near the Co-N4 site, we have explored the 2e- ORR activity at the Co-N4 site from the perspective of spatial structure and the atomic orbital by DFT calculations. We demonstrate the hybridization strength between Co 3dyz (3dxz) and O 2py (2px) orbitals is the origin of 2e- ORR activity at the Co-N4 site and the hybridization strength relates to the height of the Co 3d projected orbital in the Z direction. The bond length (LCo-O, LO-O), the charge transfer from the Co site to the *OOH adsorbate (ΔQCo-O), the d-band center of the Co site (εd), and the ICOHP value between Co 3d and O 2p orbitals as descriptors can well predict the 2e- ORR activity at the Co-N4 site. This work provides original insights into the 2e- ORR activity over the single-atom Co-N-C catalysts.