Electrochemical and Photoelectrochemical Water Oxidation for Hydrogen Peroxide Production

Hydrogen Peroxide Production from Water Oxidation on a CuWO4 Anode in Oxygen-Deficient Conditions for Water Decontamination

Hydrogen peroxide, an environmentally benign oxidant, is an effective chemical agent for water purification. On-site production of H₂O₂ is considered economical because it avoids the cost of storage and transportation. Traditional generation of H₂O₂ from oxygen reduction, as a heterogeneous electrochemical reaction, suffers from mass transfer problems because of the limited solubility and low diffusion rate of oxygen in water. These limitations can be overcome if H₂O₂ is formed by water oxidation. Herein, conversion of water to hydrogen peroxide was achieved efficiently on a CuWO₄ anode. This water oxidation strategy can generate H₂O₂ at a rate of ∼11.8 μmol min^-1 cm^-2 at 3.0 V versus reversible hydrogen electrode. Importantly, this on-site H₂O₂ production shows high efficiency in water purification in O₂-deficient conditions. This water oxidation anode offers a feasible way to provide a green purification agent with only water as the final byproduct, avoiding toxic intermediates and residues during the production and application.

Lignin-Supported Heterogeneous Photocatalyst for the Direct Generation of H2O2 from Seawater

The development of smart and sustainable photocatalysts is in high priority for the synthesis of H₂O₂ because the global demand for H₂O₂ is sharply rising. Currently, the global market share for H₂O₂ is around 4 billion US$ and is expected to grow by about 5.2 billion US$ by 2026. Traditional synthesis of H₂O₂ via the anthraquinone method is associated with the generation of substantial chemical waste as well as the requirement of a high energy input. In this respect, the oxidative transformation of pure water is a sustainable solution to meet the global demand. In fact, several photocatalysts have been developed to achieve this chemistry. However, 97% of the water on our planet is seawater, and it contains 3.0-5.0% of salts. The presence of salts in water deactivates the existing photocatalysts, and therefore, the existing photocatalysts have rarely shown reactivity toward seawater. Considering this, a sustainable heterogeneous photocatalyst, derived from hydrolysis lignin, has been developed, showing an excellent reactivity toward generating H₂O₂ directly from seawater under air. In fact, in the presence of this catalyst, we have been able to achieve 4085 μM of H₂O₂. Expediently, the catalyst has shown longer durability and can be recycled more than five times to generate H₂O₂ from seawater. Finally, full characterizations of this smart photocatalyst and a detailed mechanism have been proposed on the basis of the experimental evidence and multiscale/level calculations.

Sustainable photoanode for water oxidation reactions: from metal-based to metal-free materials

Sunlight affords an inexhaustible and primary energy for Earth. A photoelectrochemical system can efficiently harvest solar energy and convert it into chemicals. However, sophisticated processes and expensive raw materials are...

Enhanced Catalytic Hydrogen Peroxide Production from Hydroxylamine Oxidation on Modified Activated Carbon Fibers: The Role of Surface Chemistry

Herein, direct production of hydrogen peroxide (H2O2) through hydroxylamine (NH2OH) oxidation by molecular oxygen was greatly enhanced over modified activated carbon fiber (ACF) catalysts. We revealed that the higher content of pyrrolic/pyridone nitrogen (N5) and carboxyl-anhydride oxygen could effectively promote the higher selectivity and yield of H2O2. By changing the volume ratio of the concentrated H2SO4 and HNO3, the content of N5 and surface oxygen containing groups on ACF were selectively tuned. The ACF catalyst with the highest N5 content and abundant carboxyl-anhydride oxygen containing groups was demonstrated to have the highest activity toward catalytic H2O2 production, enabling the selectivity of H2O2 over 99.3% and the concentration of H2O2 reaching 123 mmol/L. The crucial effects of nitrogen species were expounded by the correlation of the selectivity of H2O2 with the content of N5 from X-ray photoelectron spectroscopy (XPS). The possible reaction pathway over ACF catalysts promoted by N5 was also shown.

Nanointerface engineering Z-scheme CuBiOS@CuBi2O4 heterojunction with OS interpenetration for enhancing photocatalytic hydrogen peroxide generation and accelerating chromium(VI) reduction

Designing a core-shell nanointerface is beneficial for enhancing the photocatalytic performance of hydrogen peroxide (H₂O₂) production. Hence, a direct Z-scheme one-dimensional (1 D) CuBiOS@CuBi₂O₄ nanorods with a core (oxide)-shell (sulfide) nanostructure and OS interpenetrated nanointerface was controllably synthesized through in-situ anion exchange. The formation of OS interpenetration at the heterogeneous interface with surface oxygen vacancies could effectively boost light absorption, reduce the interface contact resistance, facilitate band bending, and thus enhance charge separation and transfer as a "bridge". The as-prepared catalyst with tunable OS nanointerface greatly improved the photocatalytic performances in the H₂O₂ production with a yield of 201.9 μmol·L^-1 and the in-situ generated H₂O₂ effectively accelerated the reduction of chromium(VI) (Cr(VI), 95.4% within 15 min). The excellent performances were due to the OS interpenetration with rich oxygen vacancies and unique shell-core structure with intimate contact inter-doping nanointerface. Moreover, the photocatalytic mechanism was discussed in detail. This work might provide a guideline in the design and construction of high-performance catalysts with well-defined nanointerface for various applications.

Aldehyde-catalyzed epoxidation of unactivated alkenes with aqueous hydrogen peroxide

The organocatalytic epoxidation of unactivated alkenes using aqueous hydrogen peroxide provides various indispensable products and intermediates in a sustainable manner. While formyl functionalities typically undergo irreversible oxidations when activating an oxidant, an atropisomeric two-axis aldehyde capable of catalytic turnover was identified for high-yielding epoxidations of cyclic and acyclic alkenes. The relative configuration of the stereogenic axes of the catalyst and the resulting proximity of the aldehyde and backbone residues resulted in high catalytic efficiencies. Mechanistic studies support a non-radical alkene oxidation by an aldehyde-derived dioxirane intermediate generated from hydrogen peroxide through the Payne and Criegee intermediates.

Enhanced Electrochemical H2O2 Production via Two-Electron Oxygen Reduction Enabled by Surface-Derived Amorphous Oxygen-Deficient TiO2-x

The electrochemical oxygen reduction reaction (ORR) is regarded as an attractive alternative to the anthraquinone process for sustainable and on-site hydrogen peroxide (H₂O₂) production. It is however hindered by low selectivity due to strong competition from the four-electron ORR and needs efficient catalysts to drive the 2e^- ORR. Here, an acid oxidation strategy is proposed as an effective strategy to boost the 2e^- ORR activity of metallic TiC via in-site generation of a surface amorphous oxygen-deficient TiO_2-x layer. The resulting a-TiO_2-x/TiC exhibits a low overpotential and high H₂O₂ selectivity (94.1% at 0.5 V vs reversible hydrogen electrode (RHE)), and it also demonstrates robust stability with a remarkable productivity of 7.19 mol g_cat.^-1 h^-1 at 0.30 V vs RHE. The electrocatalytic mechanism of a-TiO_2-x/TiC is further revealed by density functional theory calculations.

H2O2 production on a carbon cathode loaded with a nickel carbonate catalyst and on an oxide photoanode without an external bias

Efficient H₂O₂ production both on a carbon cathode modified with various metal salts and on an oxide photoanode was investigated. The cathodic current density and faradaic efficiency for H₂O₂ production (FE(H₂O₂)) on a carbon cathode in KHCO₃ aqueous solution were significantly improved by the loading of an insoluble nickel carbonate basic hydrate catalyst. This electrode was prepared by a precipitation method of nickel nitrate and KHCO₃ aqueous solution at ambient temperature. The nickel carbonate basic hydrate electrode was very stable, and the accumulated concentration of H₂O₂ was reached at 1.0 wt% at a passed charge of 2500C (the average FE(H₂O₂) was 80%). A simple photoelectrochemical system for H₂O₂ production from both the cathode and a BiVO₄/WO₃ photoanode was demonstrated without an external bias or an ion-exchange membrane in a one-compartment reactor under simulated solar light. The apparent FE(H₂O₂) from both electrodes was calculated to be 168% in total, and the production rate of H₂O₂ was approximately 0.92 μmol min^-1 cm^-2. The solar-to-chemical energy conversion efficiency for H₂O₂ production (STC_H2O2 ) without an external bias was approximately 1.75%.

Efficient capturing of hydrogen peroxide in dilute aqueous solution by co-crystallization with amino acids

X-ray structure analyses of co-crystals of H2O2 and l-Phe, dl-Phe, or dl-Asp prepared in a dilute aqueous solution (30 wt%) indicated that multi-layer motifs including water molecule is important for highly efficient H2O2 capture in dilute solutions.

Synthesis and characterization of Sb2O3: a stable electrocatalyst for efficient H2O2 production and accumulation and effective degradation of dyes

Sb₂O₃ films are synthesized and characterized as electrocatalysts showing efficient H₂O₂ production and accumulation properties.

KNO3-Assisted incorporation of K dopants and N defects into g-C3N4 with enhanced visible light driven photocatalytic H2O2 production

Facile KNO3-assisted synthesis of g-C3N4 incorporated with K dopants and N defects for efficient visible light driven photocatalytic H2O2 production.