Electrochemical H2O2 Production Research Articles

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

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

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

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

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

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

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

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

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

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

Recent advances in electrosynthesis of H2O2via two-electron oxygen reduction reaction.

The electrosynthesis of hydrogen peroxide (H2O2) via a selective two-electron oxygen reduction reaction (2e- ORR) presents a green and low-energy-consumption alternative to the traditional, energy-intensive anthraquinone process. This review encapsulates the principles of designing relational electrocatalysts for 2e- ORR and explores remaining setups for large-scale H2O2 production. Initially, the review delineates the fundamental reaction mechanisms of H2O2 production via 2e- ORR and assesses performance. Subsequently, it methodically explores the pivotal influence of microstructures, heteroatom doping, and metal hybridization along with setup configurations in achieving a high-performance catalyst and efficient reactor for H2O2 production. Thereafter, the review introduces a forward-looking methodology that leverages the synergistic integration of catalysts and reactors, aiming to harmonize the complementary characteristics of both components. Finally, it outlines the extant challenges and the promising avenues for the efficient electrochemical production of H2O2, setting the stage for future research endeavors.

Low-Cost and Scalable Electrodes for Anodic Production of Hydrogen Peroxide Via 2e- Water Oxidation

Hydrogen peroxide (H2O2) is a crucial chemical that is widely utilized in various industrial processes. The conventional anthraquinone process for H2O2 production has limitations in terms of energy consumption, high costs, and waste generation [1]. An alternative, greener and more sustainable approach is the electrochemical production of H2O2 from oxygen and water using renewable energy. Our research group has been extensively investigating the two electron (2e-) water oxidation reaction (WOR) for production of H2O2 using various electrode materials, including metal oxides, commercial carbon materials, and boron-doped diamond (BDD) [2, 3]. We also investigated the role of carbonate ions (HCO3 - and CO3 2-) in the process of water oxidation to H2O2. The enhancing effect e of CO3 2- ions on anodic H2O2 production was studied in a continuous flow reactor, where the optimal flow rate, process configuration and cell design, and chemical stabilizer were determined. Among other parameters, chemical composition and pH regime of the electrolyte were found to be crucial.Recently, we explored the use of graphite bipolar plates (BPP) as a low-cost alternative to BDD electrodes for anodic H2O2 generation [4]. Three different commercial BPPs with varying fluoropolymer content were examined, and a correlation was found between fluoropolymer content and H2O2 generation. In that study we found that a BPP sample with high fluoropolymer content resulted in a stable H2O2 production for up to 100 hours at a current density of 200 mA cm–2, with a constant faradaic efficiency of 40%. The results demonstrate that low-cost commercial carbon electrode materials can selectively oxidize water to H2O2, enabling economically viable technical applications of anodic H2O2 production.

Microwave-Assisted Synthesis of Nitrogen-Doped Carbon Catalysts for Oxygen Reduction Reaction with Tunable Selectivity

The oxygen reduction reaction (ORR) is the core reaction in electrocatalysis systems such as fuel cells, metal-air batteries and hydrogen peroxide (H2O2) electro-generation. The ORR reaction mechanism has two possible pathways, namely, two-electron (2e−) or four-electron (4e−) processes that enable a reduction of oxygen into H2O2 or water (H2O), respectively. Both paths are useful where the former can provide on-site direct production of H2O2 and the latter is desired in fuel cells and batteries since it enables higher energy efficiency. Optimal ORR electrocatalyst should exhibit high activity, selectivity, stability, and low cost. Carbon materials modified with heteroatoms (e.g. nitrogen (N)) are considered potential alternatives for costly noble metal catalysts including Pt for ORR in fuel cells, and Au for the ORR to H2O2 (1,2). The typical synthesis procedure for the porous nitrogen-doped carbons (N–C) is based on the single or multiple pyrolysis steps of nitrogen-rich carbon precursor. The reactions required a pyrolysis step at the temperature range of 500-1200 °C and timing of one to tens of hours. Such processes showed a highly negative environmental impact due to high energy consumption. The production of 1 ton of activated carbon from lignocellulosic biomass feedstock requires 669.83 kWh (equivalent to an emission of 62.78 tons of CO2) (3). The synthesis of the N–C by microwave (MW) irradiation can reduce energy usage and ensure a more environmentally sustainable and economically viable approach. This procedure necessitates non-transparent materials to electromagnetic waves that can convert MW energy into heat and simultaneously enable the carbonization of the starting material.This work investigated the electrocatalytic activity towards ORR for N–C–MW catalysts derived from polyaniline (PANI) prepared in a one-step MW carbonization approach. PANI was selected due to two reasons: (i) N–C made by thermal pyrolysis of PANI showed improved electrocatalytic activity toward ORR where both the 4e− and the 2e− electron transfer pathways are feasible depending on the nature of active sides (4), (ii) PANI displayed good MW adsorption properties (5). The work aimed to identify the influence of the MW reaction condition on the resulting structure of the N–C–MW and the direction of the ORR. The N–C–MW samples were prepared under MW power of 450 and 800 W and time of 70, 140 and 210 s. The ORR activity of N–C–MW samples was investigated by cyclic voltammetry in the alkaline media (O2-saturated 0.1 M KOH). The experiment was performed in a three-electrode configuration composed of a rotating ring (Pt)–disk (glassy carbon) electrode (RRDE), a graphite rod as the counter electrode and a reversible hydrogen electrode (RHE) as the reference electrode. An influence of catalyst loading on disk electrode (0.05, 0.1 and 0.2 mg/cm2) was analyzed. All investigated MW reaction conditions resulted in the formation of porous disordered carbon structures with nitrogen and oxygen functionalities confirmed by X-ray photon-electron spectroscopy. The shorter time (70 s) and lower power (450 W) of MW treatment resulted in the formation of structures with a low carbonization rate and simultaneously a relatively poor catalytic activity for ORR (an onset potential of ∼0.65 V vs RHE). The samples carbonized under moderate (power of 450 W and 800 W, time of 140 s) and severe (power of 450 W, time of 210 s) reaction conditions showed higher selectivity to H2O2 or water H2O, respectively. The selectivity of 80 % to H2O2 was achieved for the N–C–MW-800W-140s sample at the potential of 0.6 V vs RHE at the catalyst loading of 0.05 mg/cm2. The results showcase the potential of MW carbonization in producing ORR electrocatalysts with diverse functionalization, leading to modified reaction selectivity that can be utilized in various electrocatalytic applications. Acknowledgments The research leading to these results was supported by the Johannes Amos Comenius Programme, European Structural and Investment Funds, project 'CHEMFELLS V‘ (No. CZ.02.01.01/00/22_010/0003004). References Yang, S. et al., Toward the decentralized electrochemical production of H2O2: A focus on the catalysis. ACS Catalysis, 2018.Bouleau, L. et al., Best practices for ORR performance evaluation of metal-free porous carbon electrocatalysts. Carbon, 2022.Wang, YX. et al., Quantifying environmental and economic impacts of highly porous activated carbon from lignocellulosic biomass for high-performance supercapacitors. Energies, 2022.Silva, R. et al., Efficient metal-free electrocatalysts for oxygen reduction: Polyaniline-derived N- and O-doped mesoporous carbons. Journal of the American Chemical Society, 2013.Oyharçabal, M. et al., Influence of the morphology of polyaniline on the microwave absorption properties of epoxy polyaniline composites. Composites Science and Technology, 2013. Figure 1

Crossover Understanding of a Hydrogen Peroxide Electrosynthesis Device By Combining Oxygen Reduction and Organics Oxidation Reaction

Hydrogen peroxide (H2O2) is a highly useful and green liquid chemical for daily life and industry. It is traditionally employed in wood industry, food packaging, fine chemicals synthesis and environmental depollution. Moreover, it is recently considered in the context of energy storage and conversion such as metal–hydrogen peroxide batteries since the world is trying to find high energy density batteries to replace lithium-ion batteries for electric vehicles and electrified aircraft [1].Electrochemical production of H2O2 driven by cheap renewable electricity has emerged recently as an alternative to non-sustainable anthraquinone oxidation (AO) process. The recent surge of H2O2 electrosynthesis studies is mainly focused on advanced H2O2 production catalyst design aiming at achieving high activity and selectivity during the last couple of years [2]. As an essential part of H2O2 electrochemical reactors, anode reaction/process is given very little attention among investigators until recently. Water oxidation is the most used anodic reaction, but it suffers from high energy input, the use of expensive catalyst, and low-priced oxygen gas generation. This problem might be mitigated by using alternative organics oxidation processes with the possible generation of value-added products [3]. In order to be economically viable for these systems above, the organics in anode reservoir should not transport to the cathode part through the membrane. However, organic molecules crossover has already been identified in direct alcohol fuel cells and CO2 electrolyzers. Such organics crossover, to the best of our knowledge, has never been considered in previous reports on hydrogen peroxide electrosynthesis devices.We use conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) for ORR via a two-electron pathway to H2O2. 4,5-Dihydroxy-1,3-benzenedisulfonic acid disodium salt monohydrate (BQDS) was used as a model organic molecule since its oxidation process does not require catalysts as a typical electrolyte used in redox flow batteries. We investigated electrolyte and electric field effects on crossover and H2O2 production.[1] Chem Catal. 2023, 3, 100568[2] Nat. Rev. Chem.2019, 3, 442[3] Nat. Energy 2021, 6, 904

Langmuir-Blodgett Monolayer of Cobalt Phthalocyanine as Ultralow Loading Single-Atom Catalyst for Highly Efficient H2O2 Production.

The electrochemical production of H2O2 via the two-electron oxygen-reduction reaction (2e- ORR) has been actively studied using systems with atomically dispersed metal-nitrogen-carbon (M-N-C) structures. However, the development of well-defined M-N-C structures that restrict the migration and agglomeration of single-metal sites remains elusive. Herein, we demonstrate a Langmuir-Blodgett (LB) monolayer of cobalt phthalocyanine (CoPc) on monolayer graphene (LB CoPc/G) as a single-metal catalyst for the 2e- ORR. The as-prepared CoPc LB monolayer has a β-form crystalline structure with a lattice space for the facile adsorption of oxygen molecules on the cobalt active sites. The CoPc LB monolayer system provides highly exposed Co atoms in a well-defined structure without agglomeration, resulting in significantly improved catalytic activity, which is manifested by a very high H2O2 production rate per catalyst (31.04 mol gcat-1 h-1) and TOF (36.5 s-1) with constant production stability for 24 hours. To the best of our knowledge, the CoPc LB monolayer system exhibits the highest H2O2 production rate per active site. This fundamental study suggests that an LB monolayer of molecules with single-metal atoms as a well-defined structure works for single-atom catalysts.

Electrochemical In Situ Hydrogen Peroxide Production Can Reduce Microbial Load in Bioponic Nutrient Solutions Derived from Organic Waste

Technological advancement in recent decades has allowed for crop cultivation in soilless controlled environments, known as hydroponics, and this is being employed in an increasing number of factories worldwide. With continued local and regional disruptions in the supply chain to provide mineral fertilizers, new pathways to generate nutrient solutions are being developed. One potential approach is the recovery of nutrients from organic waste and wastewater using bioponics. Bioponics refers to the biological mineralization of organic residues through processes such as anaerobic and aerobic digestion and the use of such organically produced nutrient solutions in hydroponic systems. However, without disinfection of the nutrient solution, the high microbial loads increase the risk of pathogens affecting plant and consumer health. In this work, electrochemical hydrogen peroxide (H2O2) demonstrated success in reducing microbial loads. Different scenarios of application were considered: (1) variation in the H2O2 concentration in the nutrient solution by dosing H2O2 from ex situ electrochemical production, (2) variation in the dosing time-dependent reaction between the nutrient solution and H2O2 produced ex situ, and (3) the in situ production of H2O2 of the organic nutrient solution. The highest tested H2O2 concentration of 200 mg L−1 showed a microbial load reduction of bacteria at 93.3% and of fungi at 81.2%. However, the in situ production showed the highest reduction rate for bacteria and fungi in bioponic nutrient solutions, where longer reaction times also impact microbial concentrations in situ. Final microbial reductions of 97.8% for bacteria and of 99.1% for fungi were determined after a H2O2 production time of 60 min. Overall, our results show that electrochemical H2O2 production can be used to disinfect bioponic nutrient solutions, and the production cell can be implemented in bioponic systems in situ.

Waste tire upcycling for the efficient electrogeneration of H2O2 in advanced degradation of the antibiotic tinidazole by electro-Fenton process

The electrochemical production of H2O2 using small- and medium-size modular devices has emerged as an interesting approach for water treatment. In this work, waste tire-derived carbon (WTC) has been innovatively employed as a cheap and recycled electroactive material to manufacture a gas-diffusion cathode. It was found that acidification with HNO3 significantly enhanced the H2O2 production, attaining a concentration of up to 1161 mg/L with a current efficiency around 40 %–60 %. These results were superior to those obtained by treating the WTC with H2SO4 or KOH, being also better than the values reached with reported carbons. Liner and cyclic voltammetries informed about the oxygen reduction reaction profiles; transmission electron microscopy revealed the morphological features of the synthesized carbons, whereas other properties were obtained by Brunauer−Emmett−Teller analysis, Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy. The cathode was further employed to degrade tinidazole (TNZ), a typical nitroimidazole antibiotic, in water by electro-Fenton at pH 3.0, producing more than 10 mM H2O2. The effect of solution pH, Fe2+ dosage and initial TNZ concentration was investigated. Under optimal conditions (0.5 mM Fe2+ and 20 mA/cm2), the treatment of solutions containing 20 mg/L TNZ at pH 3.0 yielded a pseudo-first-order constant (k1) of 0.449 min−1. Besides, the degradation pathways were proposed according to the 7 identified transformation products. This study demonstrates that waste tires can become a source of inexpensive carbon able to catalyze the in-situ H2O2 synthesis for water decontamination, in excellent agreement with new policies on circular economy.

Single-Atom Zinc Sites with Synergetic Multiple Coordination Shells for Electrochemical H2 O2 Production.

Precise manipulation of the coordination environment of single-atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two-step strategy to fabricate a series of hollow carbon-based SACs featuring asymmetric Zn-N2 O2 moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn-N2 O2 -S). Systematic analyses demonstrate that the synergetic effects between the N2 O2 species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O2 reduction to H2 O2 . Remarkably, the Zn-N2 O2 moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H2 O2 generation. Consequently, the Zn-N2 O2 -S SAC exhibits impressive electrochemical H2 O2 production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm-2 in the flow cell, it shows a high H2 O2 production rate of 6.924 mol gcat -1 h-1 with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h.

Single‐Atom Zinc Sites with Synergetic Multiple Coordination Shells for Electrochemical H2O2 Production

AbstractPrecise manipulation of the coordination environment of single‐atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two‐step strategy to fabricate a series of hollow carbon‐based SACs featuring asymmetric Zn−N2O2 moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn−N2O2−S). Systematic analyses demonstrate that the synergetic effects between the N2O2 species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O2 reduction to H2O2. Remarkably, the Zn−N2O2 moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H2O2 generation. Consequently, the Zn−N2O2−S SAC exhibits impressive electrochemical H2O2 production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm−2 in the flow cell, it shows a high H2O2 production rate of 6.924 mol gcat−1 h−1 with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h.

Tuning the electronic configuration of Co-Nx for highly efficient H2O2 production in acidic solution

The production of hydrogen peroxide (H2O2) through electrochemically reducing O2 in a two-electron pathway is a potential substitute for the traditional process based on anthraquinone. In this paper, F doping is carried out to prepare N and F co-doped porous carbon embedded Co nanoparticles. The electro-catalytic activity for the electrochemical production of H2O2 is systematically investigated. The composite material demonstrates exceptional electro-catalytic selectivity, reaching approximately 92.5%, and shows an ultra-high rate of producing H2O2 in 4021.4 mmol g−1 h−1 at 0.1 V versus RHE in a 0.5 M H2SO4 electrolyte. It is found that the synergetic effect of Co-Nx and F in the composite material result in its exceptional performance. Adding F atom modulates the Zeta potential of the catalyst and alters the electronic configuration around Co-Nx, creating favorable conditions for the uptake of O2 and consequently forming OOH*. Additionally, the highly electronegative F atom facilitate desorbing OOH* through electrostatic repulsion, preventing any further degradation. In a homemade electrolyzer containing 80 mg L−1 of Rh B, the H2O2 produced in situ in a 0.5 M H2SO4 electrolyte degrades up to 97.76% of Rh B in just 22.5 minutes, showcasing its potential for practical wastewater treatment applications.

Recent Progress on the Catalysts and Device Designs for (Photo)Electrochemical On‐Site H2O2 Production

AbstractLow‐cost and on‐site H2O2 production is desirable for industrial and civilian usage. (Photo)electrochemical H2O2 production is proposed to be a safer, greener, and cheaper strategy for on‐site H2O2 production as compared to the conventional anthraquinone process and the direct thermal synthesis. However, the efficiency, selectivity, and durability of the (photo)electrochemical H2O2 production devices are still not satisfactory. Therefore, there is an urgent need to revisit the (photo)electrocatalyst and device designs for (photo)electrochemical on‐site H2O2 production, thus to rationalize the research thoughts and provide valuable guidance. This review comprehensively summarizes and discusses the mechanism of two‐electron oxygen reduction reaction (2e− ORR) and two‐electron water oxidation reaction (2e− WOR) for H2O2 production, and the current research status on the (photo)electrocatalysts and (photo)electrochemical devices. In particular, the pros and cons of the four types of (photo)electrochemical device designs, which are Type I (2e− ORR + oxygen evolution reaction), Type II (2e− ORR + hydrogen oxidation reaction), Type III (2e− WOR + hydrogen evolution reaction) and Type IV (2e− WOR + 2e− ORR), are discussed in detail. Finally, a practical perspective on the future research directions for the on‐site (photo)electrochemical H2O2 production based on the technical challenges of this technique is provided.

Synergistic effects of Bi2O3 and Ta2O5 for efficient electrochemical production of H2O2

Electrochemical oxygen reduction reaction (ORR) through a two-electron pathway has been provided a green route for on-site hydrogen peroxide (H2O2) production. Developing high-selective electrocatalysts for H2O2 production are urgently sought. Herein, a m-Bi2O3/Ta2O5 electrocatalyst (m: “Bi” mass contents) has been successfully synthesized by simple physical mixing associated with an outstanding selectivity towards H2O2 (94.7%), over 10% higher than Ta2O5 (80.9%) and Bi2O3 (81.7%). 10-Bi2O3/Ta2O5 also exhibits 471 mmol/(gcat·h) H2O2 yield with 91.8% Faraday Efficiency. The in-situ generated H2O2 can function as disinfection agent for efficiently deactivating model bacteria (e.g., Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli) within 30 min. In-situ Raman and DFT proposed the synergistic effects of Bi2O3 and Ta2O5 in boosting 2e- ORR performance. In this work, it not only presents a high-selective electrocatalyst for 2e- ORR, but also provides a new idea for electrocatalyst design from the perspective of reaction process.

Generation of Pd–O for Promoting Electrochemical H2O2 Production

Electrochemical production of H2O2 via 2 electron (2e–) oxygen reduction reaction (ORR) represents a promising route due to its safe, efficient, and decentralized process. Herein, using the extended surface of Pd with Cu electrodeposition as the model material, we identify that the introduction of Cu can promote the production of H2O2. With spectroscopic tools, we found that Cu stabilizes Pd–O and Pd–O improves 2e– ORR activity of Pd site according to computation. As a demonstration of a practical electrocatalyst, PdCu nanowire is synthesized and shows nearly 100% selectivity and 1.866 mol g–1cat h–1 production rate toward H2O2.

Penta nitrogen coordinated cobalt single atom catalysts with oxygenated carbon black for electrochemical H2O2 production

The two-electrons (2e–) oxygen reduction reaction (ORR) offers a sustainable and decentralized alternative to the traditional synthetics for hydrogen peroxide (H2O2) production. Although various Co single atom catalysts (SACs) have been proposed as highly effective 2e– ORR catalysts, there is still room for improvement through fine-tuned coordination environment. Here, a Co-N5-O-C with the combination of highly coordinated Co-N5 moieties and nearby electro-withdrawing epoxides is first time developed to reach the optimal binding energy of *OOH intermediate, resulting in the ultrahigh mass activity of 87.5 A g−1 at 0.75 V vs. RHE. Moreover, a high H2O2 production rate of 11.3 mol g−1 h−1 at 200 mA cm−2 is also obtained by a flow cell device. Such an efficient in-situ generation of H2O2 further enables 100% degradation of the organic methylene blue pollutant within 15 min through the electro-Fenton process. These findings will provide a new direction for on-site H2O2 synthesis and wastewater treatment.

Machine Learning Assisted Analysis of Electrochemical H2O2 Production

The two-electron water oxidation reaction (2e– WOR) provides an option for on-site production of the valuable chemical hydrogen peroxide (H2O2). A major challenge for the 2e– WOR is the need to improve its selectivity toward H2O2 over O2 production through the oxygen evolution reaction. Electrolyte engineering has shown great promise in improving the selectivity and production rates toward H2O2. However, experimental efforts in optimizing the electrolyte only yield results at discrete conditions, which does not provide a complete picture of performance over the entire parameter range. Here, we apply a machine learning assisted prediction to map out the performance of electrochemical H2O2 production over the continuous parameter space of electrolyte composition and applied potential. We collected experimental data of faradaic efficiencies (FEH2O2) and current densities toward H2O2 (JH2O2) as functions of the applied potential and carbonate ion mole fractions (HCO3– and CO32–) in the electrolyte. The data were then used to train a support vector regression model with 5-fold cross-validation. The accuracy of the model was verified against additional experimental results. The model identified that a maximum H2O2 current density of 2.16 mA/cm2 can be achieved from an optimized bicarbonate ion mole fraction of 0.225 at an applied potential of 3.25 V vs RHE. Lastly, the continuous model enables us to evaluate the thermal efficiency, H2O2 electricity cost, and time needed to produce a set amount of H2O2 over a broad range of electrolytes and applied potential conditions. This work demonstrates how machine learning enables the use of discrete experimental points to construct a continuous picture of electrochemical H2O2 production with high accuracy.