Electrochemical advanced oxidation processes (EAOPs) have emerged as novel water treatment technologies for the elimination of a broad-range of organic contaminants. Considerable validation of this technology has been performed at both the bench-scale and pilot-scale, which has been facilitated by the development of stable electrode materials that efficiently generate high yields of hydroxyl radicals (OH˙) (e.g., boron-doped diamond (BDD), doped-SnO2, PbO2, and substoichiometic- and doped-TiO2). Although a promising new technology, the mechanisms involved in the oxidation of organic compounds during EAOPs and the corresponding environmental impacts of their use have not been fully addressed. In order to unify the state of knowledge, identify research gaps, and stimulate new research in these areas, this review critically analyses published research pertaining to EAOPs. Specific topics covered in this review include (1) EAOP electrode types, (2) oxidation pathways of select classes of contaminants, (3) rate limitations in applied settings, and (4) long-term sustainability. Key challenges facing EAOP technologies are related to toxic byproduct formation (e.g., ClO4− and halogenated organic compounds) and low electro-active surface areas. These challenges must be addressed in future research in order for EAOPs to realize their full potential for water treatment.

Critical review of electrochemical advanced oxidation processes for water treatment applications

The ever-increasing demand for high-performing, economical, and safe power storage for portable electronics and electric vehicles stimulates RD in Li-ion cells, the objective of current research is to develop a 5-volt cell, and at the same time to maintain high specific charge capacity, excellent cycling, and safety. Since current anode materials possess working potentials fairly close to the potential of a lithium metal, the focus is on the development of cathode materials. This work reviews and analyzes the current state of the art, achievements, and challenges in the field of high-voltage cathode materials for Li-ion cells. Some suggestions regarding possible approaches for future development in the field are also presented.

Higher, Stronger, Better…︁ A Review of 5 Volt Cathode Materials for Advanced Lithium-Ion Batteries

Substantial developments have been achieved in the synthesis of chemical vapour deposition (CVD) diamond in recent years, providing engineers and designers with access to a large range of new diamond materials. CVD diamond has a number of outstanding material properties that can enable exceptional performance in applications as diverse as medical diagnostics, water treatment, radiation detection, high power electronics, consumer audio, magnetometry and novel lasers. Often the material is synthesized in planar form; however, non-planar geometries are also possible and enable a number of key applications. This paper reviews the material properties and characteristics of single crystal and polycrystalline CVD diamond, and how these can be utilized, focusing particularly on optics, electronics and electrochemistry. It also summarizes how CVD diamond can be tailored for specific applications, on the basis of the ability to synthesize a consistent and engineered high performance product.

https://iopscience.iop.org/article/10.1088/0953-8984/21/36/364221/pdf

Chemical vapour deposition synthetic diamond: materials, technology and applications.

Conducting, boron doped diamond (BDD), in addition to its superior material properties, offers several notable attributes to the electrochemist making it an intriguing material for electrochemical research. These include the widest solvent window of all electrode materials; low background and capacitive currents; reduced fouling compared to other electrodes and; the ability to withstand extreme potentials, corrosive and high temperature/pressure environments. However, BDD is not your typical electrode material, it is a semi-conductor doped degenerately with boron to present semi-metallic characteristics. Input from materials scientists, chemists and physicists has been required to aid understanding of how to work with this material from an electrochemical viewpoint and improve electrode quality. Importantly, depending on how the BDD has been grown and then subsequently treated, prior to electrochemical measurement, the resulting material properties can vary quite significantly from one electrode to the next. This likely explains the variability seen by different researchers working on the same experimental systems. The aim of this "protocols" article is not to provide a state-of-the-art review of diamond electrochemistry, suitable references are provided to the interested reader, but instead serves as a reference point for any researcher wishing to commence work with diamond electrodes and interpret electrochemical data. It provides information on how best to characterise the material properties of the electrode before use and outlines the interplay between boron dopant density, non-diamond-carbon content, grain morphology, surface chemistry and redox couple identity. All should ideally be considered when interpretating electrochemical data arising from the diamond electrode. This will aid the reader in making meaningful comparisons between data obtained by different researchers using different diamond electrodes. The guide also aims to help educate the researcher in choosing which form of BDD is best suited to their research application.

A practical guide to using boron doped diamond in electrochemical research.

In recent years, conductive diamond electrodes for electrochemical applications have been a major focus of research and development. The impetus behind such endeavors could be attributed to their wide potential window, low background current, chemical inertness, and mechanical durability. Several analytes can be oxidized by conducting diamond compared to other carbon-based materials before the breakdown of water in aqueous electrolytes. This is important for detecting and/or identifying species in solution since oxygen and hydrogen evolution do not interfere with the analysis. Thus, conductive diamond electrodes take electrochemical detection into new areas and extend their usefulness to analytes which are not feasible with conventional electrode materials. Different types of diamond electrodes, polycrystalline, microcrystalline, nanocrystalline and ultrananocrystalline, have been synthesized and characterized. Of particular interest is the synthesis of boron-doped diamond (BDD) films by chemical vapor deposition on various substrates. In the tetrahedral diamond lattice, each carbon atom is covalently bonded to its neighbors forming an extremely robust crystalline structure. Some carbon atoms in the lattice are substituted with boron to provide electrical conductivity. Modification strategies of doped diamond electrodes with metallic nanoparticles and/or electropolymerized films are of importance to impart novel characteristics or to improve the performance of diamond electrodes. Biofunctionalization of diamond films is also feasible to foster several useful bioanalytical applications. A plethora of opportunities for nanoscale analytical devices based on conducting diamond is anticipated in the very near future

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Boron-doped diamond electrode: synthesis, characterization, functionalization and analytical applications.

Electrochemical selectivity for redox systems at oxygen-terminated diamond electrodes ☆

AC impedance studies of anodically treated polycrystalline and homoepitaxial boron-doped diamond electrodes

To develop the capability to create diamond electrodes with greater functionality, covalent modification was carried out on homoepitaxial single-crystal diamond electrode surfaces. (100) and (111) single-crystal boron-doped diamond electrodes were first prepared homoepitaxially, then subjected to oxidative treatments, and the functional groups on the oxidized surfaces were analyzed by employing X-ray photoelectron spectroscopy (XPS). Based on the results, we conclude that both singly and doubly bonded oxygen groups (C-O and C=O) were generated on the anodically treated (100) diamond electrode surfaces, whereas only singly bonded oxygen groups (C-O) were generated on the (111) surfaces. Second, selective surface modifications of anodically treated (100) and (111) diamond surfaces with 2,4-dinitrophenylhydrazine and 3-aminopropyltriethoxysilane moieties were carried out. Based on the tendencies of these surface modifications, together with the XPS results, we propose that carbonyl and hydroxyl groups are generated on anodically treated (100) diamond surfaces, and hydroxyl groups are mainly generated on anodically treated (111) diamond surfaces. The study of chemical modification of single-crystal diamond electrode surfaces should be useful, not only for creating new types of functional electrodes, but also for better understanding the properties of polycrystalline diamond electrodes and their possible applications.

Covalent Modification of Single-Crystal Diamond Electrode Surfaces

In order to study the properties of single-crystal boron-doped diamond electrodes for electroanalysis, (100) and (111) boron-doped homoepitaxial single-crystal and polycrystalline diamond thin films were deposited by means of microwave plasma-assisted chemical vapor deposition. Features in the cyclic voltammograms (CVs) for aqueous H 2 SO 4 supporting electrolyte and Fe(CN) 3-/4- 6 in aqueous Na 2 SO 4 for polycrystalline electrodes were dominated by behavior typical of (111) single-crystal facets, rather than (100) facets. Apparent heterogeneous electron-transfer rate constants (k 0 ) for various redox systems were estimated with CV simulation at polycrystalline, (111) and (100, off-axis. 4°). Based on comparison with the Marcus model, the behavior of the k° values, except for that of Fe(CN) 3-/4- 6 , indicates apparent outer-sphere electron-transfer, but with a lower density of states compared to glassy carbon or typical metal electrodes. The (111) homoepitaxial film performed better than a polycrystalline film in the cyclic voltammetric detection of serotonin, with signal-to-background ratios of 5 and 2, respectively. Single-crystal diamond may thus be an even more optimal electrode material for electroanalysis than polycrystalline diamond, which has been shown to have superior characteristics as an electrode material.

Takeshi Kondo

Papers

Electrochemical selectivity for redox systems at oxygen-terminated diamond electrodes ☆

AC impedance studies of anodically treated polycrystalline and homoepitaxial boron-doped diamond electrodes

Covalent Modification of Single-Crystal Diamond Electrode Surfaces

Homoepitaxial Single-Crystal Boron-Doped Diamond Electrodes for Electroanalysis

Factors controlling the electrochemical potential window for diamond electrodes in non-aqueous electrolytes