Synthesis and characterization of nanostructured electrocatalysts based on nickel and tin for hydrogen peroxide electrogeneration

Decontamination of wastewater containing contaminants of emerging concern by electrooxidation and Fenton-based processes - A review on the relevance of materials and methods

In recent years, there has been an increasingly growing interest regarding the use of electrochemical advanced oxidation processes (EAOPs) which are considered highly promising alternative treatment techniques for addressing environmental issues related to pollutants of emerging concern. In EAOPs, electrogenerated oxidizing agents, such as hydroxyl radical (HO^•), can react non-selectively with a wide range of organic compounds, degrading and mineralizing their structures to unharmful molecules like CO₂, H₂O, and inorganic ions. To this date, a broad spectrum of advanced electrocatalysts have been developed and applied for the treatment of compounds of interest in different matrices, specifically aiming at enhancing the degradation performance. New combined methods have also been employed as alternative treatment techniques targeted at circumventing the major obstacles encountered in Fenton-based processes, such as high costs and energy consumption, which still contribute significantly toward inhibiting the large-scale application of these processes. First, some fundamental aspects of EAOPs will be presented. Further, we will provide an overview of electrode materials which have been recently developed and reported in the literature, highlighting different anode and cathode structures employed in EAOPs, their main advantages and disadvantages, as well as their contribution to the performance of the treatment processes. The influence of operating parameters, such as initial concentrations, pH effect, temperature, supporting electrolyte, and radiation source, on the treatment processes were also studied. Finally, hybrid techniques which have been reported in the literature and critically assess the most recent techniques used for evaluating the degradation efficiency of the treatment processes.

Electrosynthesis of H2O2 through a two-electron oxygen reduction reaction by carbon based catalysts: From mechanism, catalyst design to electrode fabrication

Hydrogen peroxide (H2O2) is an efficient oxidant with multiple uses ranging from chemical synthesis to wastewater treatment. The in-situ H2O2 production via a two-electron oxygen reduction reaction (ORR) will bring H2O2 beyond its current applications. The development of carbon materials offers the hope for obtaining inexpensive and high-performance alternatives to substitute noble-metal catalysts in order to provide a full and comprehensive picture of the current state of the art treatments and inspire new research in this area. Herein, the most up-to-date findings in theoretical predictions, synthetic methodologies, and experimental investigations of carbon-based catalysts are systematically summarized. Various electrode fabrication and modification methods were also introduced and compared, along with our original research on the air-breathing cathode and three-phase interface theory inside a porous electrode. In addition, our current understanding of the challenges, future directions, and suggestions on the carbon-based catalyst designs and electrode fabrication are highlighted.

Recent Progress of Electrochemical Production of Hydrogen Peroxide by Two-Electron Oxygen Reduction Reaction

Shifting electrochemical oxygen reduction reaction (ORR) via two-electron pathway becomes increasingly crucial as an alternative/green method for hydrogen peroxide (H2 O2 ) generation. Here, the development of 2e- ORR catalysts in recent years is reviewed, in aspects of reaction mechanism exploration, types of high-performance catalysts, factors to influence catalytic performance, and potential applications of 2e- ORR. Based on the previous theoretical and experimental studies, the underlying 2e- ORR catalytic mechanism is firstly unveiled, in aspect of reaction pathway, thermodynamic free energy diagram, limiting potential, and volcano plots. Then, various types of efficient catalysts for producing H2 O2 via 2e- ORR pathway are summarized. Additionally, the catalytic active sites and factors to influence catalysts' performance, such as electronic structure, carbon defect, functional groups (O, N, B, S, F etc.), synergistic effect, and others (pH, pore structure, steric hindrance effect, etc.) are discussed. The H2 O2 electrogeneration via 2e- ORR also has various potential applications in wastewater treatment, disinfection, organics degradation, and energy storage. Finally, potential future directions and prospects in 2e- ORR catalysts for electrochemically producing H2 O2 are examined. These insights may help develop highly active/selective 2e- ORR catalysts and shape the potential application of this electrochemical H2 O2 producing method.

Hydrogen peroxide generation from O2 electroreduction for environmental remediation: A state-of-the-art review

The electrochemical production of hydrogen peroxide (H2O2) by 2-electron oxygen reduction reaction (ORR) is an attractive alternative to the present complex anthraquinone process. The objective of this paper is to provide a state-of-the-arts review of the most important aspects of this process. First, recent advances in H2O2 production are reviewed and the advantages of H2O2 electrogeneration via 2-electron ORR are highlighted. Second, the selectivity of the ORR pathway towards H2O2 formation as well as the development process of H2O2 production are presented. The cathode characteristics are the decisive factors of H2O2 production. Thus the focus is shifted to the introduction of commonly used carbon cathodes and their modification methods, including the introduction of other active carbon materials, hetero-atoms doping (i.e., O, N, F, B, and P) and decoration with metal oxides. Cathode stability is evaluated due to its significance for long-term application. Effects of various operational parameters, such as electrode potential/current density, supporting electrolyte, electrolyte pH, temperature, dissolved oxygen, and current mode on H2O2 production are then discussed. Additionally, the environmental application of electrogenerated H2O2 on aqueous and gaseous contaminants removal, including dyes, pesticides, herbicides, phenolic compounds, drugs, VOCs, SO2, NO, and Hg0, are described. Finally, a brief conclusion about the recent progress achieved in H2O2 electrogeneration via 2-electron ORR and an outlook on future research challenges are proposed.

Electrochemical disinfection using a modified reticulated vitreous carbon cathode for drinking water treatment

A reticulated vitreous carbon (RVC) cathode modified by anodic polarization in 20 wt% H₂SO₄ solution was used for drinking water disinfection under a neutral low electrolyte concentration (0.25 g/L Na₂SO₄) condition. The contribution of the modified RVC anode and the Ti/RuO₂ cathode to disinfection was investigated. The influences of current, initial Escherichia coli load, temperature and water volume were studied. The results show that H₂O₂ generation increased to approximately three times using the modification of the RVC. E. coli was mainly deactivated by the H₂O₂ generated at the cathode. For water with about 10⁶ CFU/mL E. coli, the detection limit (<4 CFU/mL) was reached under different conditions. Increasing current could simultaneously shorten the treatment time and increase the energy consumption (EC) simultaneously. Although decreasing the initial load reduced the treatment time, the EC for per log E. coli removal increased. The time required for disinfection shortened from 3.5 to 2.5 h and the EC for per log removal decreased from 218.5 to 123.2 Wh/m³ when the temperature increased from 20 to 40 °C. Although more time was required for disinfection, the EC decreased from 218.5 to 141.4 Wh/m³ when the volume was doubled.

Detailed Characterization of the Surface and Growth Mechanism of Monodisperse Ni3Sn4 Nanoparticles

Synthesis of most tin-based bimetallic nanoparticles is a challenging task because of the differences in the redox potential and the melting point between both components. This article presents a co-reduction synthesis of monoclinic Ni₃Sn₄ nanoparticles. Varying time and temperature gives the possibility to control the size of the nanoparticles in the range of 4-12 nm. The products were characterized by X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy measurements. Although the synthesis was conducted entirely oxygen free, the postsynthetic treatment undertaken under air leads to the formation of an amorphous oxide shell. The oxide shell consists of an outer tin-rich region and a nickel-rich region at the interface to the metallic Ni₃Sn₄ core. On the basis of the investigation of the particles at different stages of the synthesis, we propose a growth mechanism for the Ni₃Sn₄ nanocrystals. These results can be a guidepost for the synthesis of other tin-based bimetallic nanoparticles.

Cost-effective electrogeneration of H2O2 utilizing HNO3 modified graphite/polytetrafluoroethylene cathode with exterior hydrophobic film

Electrochemical 2-electrons oxygen reduction process has been regarded as the effective strategy for H₂O₂ generation in wastewater treatment. However, its large-scale application is still limited by the relatively high cost of the carbon materials and short-term stability. In this study, a nitric acid modified graphite/polytetrafluoroethylene (PTFE) composite cathode with exterior hydrophobic film was fabricated for cost-effective electrogeneration of hydrogen peroxide (H₂O₂). Experimental results show that 2 M HNO₃ modification rendered the introduction of much more defect sites and oxygen/nitrogen-containing groups on graphite. As a result, H₂O₂ electrogeneration was 3.0 times as much as that of virgin graphite counterpart at 3 mA cm^-2. Moreover, the additional introduction of exterior hydrophobic film on the as-prepared graphite/PTFE cathode did not only further promote H₂O₂ electrogeneration, but also endowed the cathode with strong hydrophobic stability. As for the modified cathode with exterior hydrophobic film, the influence of mass graphite/PTFE binder ratio (1:1-4:1) and pH (3.0-9.0) on H₂O₂ electrogeneration was slight, but the current density (3.0-15 mA cm^-2) had evident effect on H₂O₂ electrogeneration. Generally, owing to its low price and being easily available, the modified graphite would be cost-effectively utilized to prepare the gas diffusion cathode for the large-scale electrogeneration of H₂O₂ in industry.

Metal Foam-Based Fenton-Like Process by Aeration

A novel metal foam-based Fenton-like process for wastewater treatment is illustrated in this study. In the system, H₂O₂ was generated in situ by taking advantage of O₂ in air, as metal could activate dissolved O₂ to produce ^•O₂^- and then generate H₂O₂. Furthermore, metal foam can enhance the Fe³⁺/Fe²⁺ cycling, which eventually improved the efficiency of the Fenton process. The performance of the novel Fenton-like process was assessed by methyl blue (MB), and 94% MB removal could be achieved within 5 min in nickel (Ni) foam system. The degradation of MB in this study was based on both ^•OH and ^•O₂^- radicals, where ^•O₂^- radical served as the precursor to generate ^•OH for MB degradation through a Fenton process. The pH value of 3 with the initial Fe²⁺ concentration of 0.25 mM was found to be the optimum condition for the Fenton-like process. This study provides a general and new strategy for efficient wastewater treatment just using aeration and metal foams (such as Ni, Al, and Cu foams), which also offers a good alternative for rational design and application of traditional Fenton process.

Influences of M–Sn intermetallics (M = Ni, Cu) prepared by mechanical alloying on phenol hydroxylation

This work discusses the effect of the crystal structure of Ni–Sn and Cu–Sn intermetallic catalysts on phenol hydroxylation.

Nanocomposites by the use of simultaneous twin polymerization: tin alloys in a carbon/silica matrix

Twin polymerization is used as a novel nonaqueous route to synthesize composites composed of nanoparticular tin alloys in a porous carbon/silica matrix.

In situ electrosynthesis of hydrogen peroxide with an improved gas diffusion cathode by rolling carbon black and PTFE

A simply structured gas diffusion electrode (GDE) was constructed by rolling carbon black and PTFE as a conductive catalyst layer to enhance the producibility of hydrogen peroxide.