Anodic Conversion Research Articles

Electrochemical Synthesis of Hollow Nanoparticles via Anodic Transformation of Metastable Core-Shell Precursors.

Recent advances in electrosynthesis of nanomaterials expanded structural and compositional variations accessible by the electrochemical method; however, reliably synthesizable morphological variety fall shy of that available by conventional solvothermal synthesis. In this communication, electrochemical preparation of surfactant-free hollow nanoparticles is demonstrated. By anodic conversion of core-shell precursors with metastable cores, hollowed nickel nanoparticles with uniform dimensions were synthesized and characterized. Implementation of TEM grids as the working electrodes, identical location tracking of the morphological evolution of single particles to anodic stimulus has been demonstrated. The synthesized nanoparticles were employed as catalysts for the alkaline hydrogen evolution reaction and exhibited catalytic rates that compare favorably to the Pt/C benchmark. This marks the first pure electrochemical synthesis of hollow nanoparticles and shall contribute to the structural diversification of electrosynthesized nanomaterials.

Peroxodicarbonate - a renaissance of an electrochemically generated green oxidizer.

The direct anodic conversion of alkali carbonates in aqueous media provides access to peroxodicarbonate, which is a safe to use and green oxidizer. Although first reports date back around 150 years, its low concentrations and limited thermal stability have consigned this reagent to oblivion. Boron-doped diamond anodes, novel electrolyser concepts for heat dissipation, and the mixed cation trick allow record breaking peroxodicarbonate concentrations >900 mM. The electrochemical generation of peroxodicarbonate was already demonstrated on a pilot scale. The inherent safety is ensured by the limited stability of the peroxodicarbonate solution, which decomposes under ambient conditions to oxygen and facilitates subsequent downstream processing. This peroxide has, in particular at higher concentrations, an unusual reactivity and seems to be an ideal reagent when peroxo-equivalents in combination with alkaline base are required. The conversions with peroxodicarbonate include the Dakin reaction, epoxidation, oxidation of amines (aliphatic and aromatic) and sulfur compounds, deborolative hydroxylation reactions, and many more. Since the base equivalents also represent the makeup chemical for pulping plants, peroxodicarbonate is an ideal reagent for the selective degradation of lignin to vanillin. Moreover, peroxodicarbonate can be used as a halogen-free bleaching agent. The emerging electrogeneration and use of this green platform oxidizer are surveyed for the first time.

Selective Anodic Conversion of Technically Relevant Lignin

The electrochemical conversion of less exploited biogenic side streams provides an attractive approach to valuable intermediates. Electrosynthesis represents a future technology, which is characterized by its outstanding sustainability.[1] The translation of electrosynthesis is strong dependent on the subsequent downstream processing and has to be implemented into the electrolytic screening on an early stage.[2] A new strategy is presented to electrochemically convert lignins by ex-cell and in-cell approaches providing selectively access to monomeric species such as vanillin, 5-iodovanillin, vanillic acid and dimethoxybenzoquinone.[3-6] The key is the timely separation of oxidation and liberation event.

Electrochemical Upcycling of Pollutants

The electrochemical conversion of pollutants provides a new and powerful way to upcycle these harmful substances into valuable intermediates. Electrosynthesis represents a future technology, which is characterized by its outstanding sustainability.[1] After carbon dioxide, sulfur dioxide is the most prominent pollutant in flue gas. The direct electrochemical incorporation into more elaborated molecules has started recently.[2] The anodic conversion of arenes and subsequent reaction with sulfur dioxide adducts yield sulfonamides,[3] sulfonates,[4] and sulfamides.[5] Another pollutant from the era of highly chlorinated pesticides is hexachloro-cyclohexane. The non-suitable isomers of Lindane were piled-up in larges deposits ranging >7 Mio. t. By e-shuttle this can be converted to non-fossil benzene source.[6] The talk will discuss in detail the mechanistic details which led to greener processes.

Efficient and cost-effective electrocatalytic CO2 to CO reduction over Sn-modified Cu nanowires by pairing with selective HCHO to HCOOH oxidation

Electrocatalytic CO2 reduction reaction (CO2RR) over Cu-based electrocatalysts still suffered from low efficiency but high energy consumption. In this study, atomic-dispersed Sn-modified Cu nanowires (Cu@Sn NWs) were synthesized for selective electrocatalytic CO2RR to CO with an optimized FECO of 96.4 %. Moreover, formaldehyde oxidation half-reaction (FOR) at MnO2/CP anode, replacing water oxidation (WOR), was introduced to build a novel CO2RR/FOR system with CO2RR over Cu@Sn NWs, to further improve CO2RR efficiency and to reduce the energy consumption. Generally, compared with CO2RR/WOR system, CO2RR/FOR system shows a much higher CO2RR performance. Meanwhile, HCHO can be converted to HCOOH at MnO2/CP anode with tunable selectivity (50 ∼ 65 %), depending on the applied cell voltage. Specifically, at a cell voltage of 3.5 V, about 97.9 % of HCHO can be removed with HCHO→HCOOH selectivity of about 50 %. Moreover, the working cell voltage and energy consumption can be significantly reduced over CO2RR/FOR system, versus CO2RR/WOR system. For example, at the current density of − 4 mA/cm2 (FECO = ∼95 %), the cell voltage is lower by about 270 mV, and the energy consumption is lower by about 8.97 %. Compared with the sum of the energy consumption of a single CO2RR and FOR, the energy consumption of the CO2RR/FOR system can be reduced by about 47.3 %. When solar cells were used as the power supply, the CO generation rate in the CO2RR/FOR system is about 1.43 times that in the CO2RR/WOR system, accompanied by the anodic conversion of HCHO to HCOOH with the selectivity of 58.2 %.

Direct Anodic Conversion of 4-Hydroxybenzaldehydes into Benzoquinones

A novel electrosynthetic protocol for the direct conversion of easily accessible 4-hydroxybenzaldehydes into valuable benzoquinones is reported. The transformation is enabled through anodic oxidation and is performed in a reagent-free manner devoid of terminal oxidants and redox mediators to effectively minimize waste. Environmentally benign and inexpensive graphite serves as a metal-free anode material. A broad range of substituents, including halogens, are tolerated in this electrochemical protocol, and the quinones are selectively accessible in yields up to 99%. Furthermore, the compatibility with electrochemical flow synthesis is demonstrated. Moreover, the flow protocol is successfully applied to the biopolymer lignosulfonate and provides quinones in yields up to 7.6 wt%. A mechanistic proposal for this Dakin-type reaction is offered. The sustainability and synthetic utility are evaluated quantitatively and compared to established protocols by application of different green chemistry metrics.

Numerical Study on the Characteristics of Cylindrical Virtual Cathode Reflex Triode Array

The bremsstrahlung cylindrical virtual cathode reflex triode (CVCRT) array is a new type of pulsed warm X-rays load. In this article, we established the CVCRT particle model and simulated and analyzed the working process and the influence of structural parameters on impedance. The results show that the impedance of the CVCRT depends on the structure of electrode and the thickness of anode conversion target. The theoretical impedance calibration relation was given, and the impedance simulation results of particle simulation agree well with the theoretical solution. Based on the Monte Carlo (MC) code, the radiation model of the CVCRT was established, and the influence rule of anode conversion target on X-ray parameters was studied. Results show that the anode thickness is the main factor affecting X-ray intensity. Under the voltage of 300 kV, the optimum thickness of the anode is about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~\mu \text{m}$ </tex-math></inline-formula> . The influence of array arrangement on the spatial distribution of radiation field was calculated. The CVCRT array can superpose the X-rays in the effective radiation region and improve the efficiency of X-ray utilization, and the intensity of X-rays is about 1.9 times higher than that of the cylindrical reflex triode (CRT) under the identical driving conditions.

One-step electrochemical elaboration of SnO2 modified electrode for lead ion trace detection in drinking water using SWASV.

A facile method was proposed for the elaboration of an electrochemical sensor for heavy metal's trace detection by using square wave anodic stripping voltammetry (SWASV); this method is based on a simple anodic conversion of tin electrode into Sn/SnO2 modified electrode. Both electrochemical and physico-chemical techniques were used to confirm the modification process and better understand the electrode's behavior. Then, depending on the operating conditions, the response signal was studied and adjusted in order to obtain optimal sensor performance. When optimized, the proposed method reached a lowest detection limit (LOD) of 2.15μg L-1 (0.0104μM), and quantification limit (LOQ) of 5.36μg L-1 (0.0259μM), in linearity range between from 6.2 and 20.7μg L-1. Additionally, after having used the elaborated electrode for ten successive measurements, the repeatability remains very high with an RSD of approximately 5.3%; furthermore, ten other species appear to have very slight effect on Pb(II) detection. Finally, for the method validation, the proposed electrode was able to sense different lead concentration integrated in a local bottled spring water by showing recovery levels ranging from 103.8 to 108.4%.

General Concepts and Recent Advances in the Electrochemical Transformation of Chloro‐ and Hydrosilanes

AbstractOrganosilanes play an important role in organic synthesis as well as in a variety of further areas, ranging from life science to transportation. Especially, the electrochemical access has become increasingly important in the past years and developed into an essential topic due to new conceptual approaches and mediated reaction control. With the commercial availability of high‐quality electrochemical equipment, the technical requirements for electro‐conversion are at hand to a wide audience. This results in the need for a concise survey of electrochemical silane transformation, appropriate for novices as well as experts alike. This review provides an overview of the most relevant work in this field, identifies common obstacles in working with chlorosilanes and hydrosilanes and bridges the gap between known techniques and novel methods with respect to their electrochemical conversion. The historical development is outlined with reference to the various cathodic as well as anodic conversions and should encourage to expand the research field of electrochemical silane transformation.

Reversible Cl/Cl- redox in a spinel Mn3O4 electrode.

A unique prospect of using halides as charge carriers is the possibility of the halides undergoing anodic redox behaviors when serving as charge carriers for the charge-neutrality compensation of electrodes. However, the anodic conversion of halides to neutral halogen species has often been irreversible at room temperature due to the emergence of diatomic halogen gaseous products. Here, we report that chloride ions can be reversibly converted to near-neutral atomic chlorine species in the Mn3O4 electrode at room temperature in a highly concentrated chloride-based aqueous electrolyte. Notably, the Zn2+ cations inserted in the first discharge and trapped in the Mn3O4 structure create an environment to stabilize the converted chlorine atoms within the structure. Characterization results suggest that the Cl/Cl- redox is responsible for the observed large capacity, as the oxidation state of Mn barely changes upon charging. Computation results corroborate that the converted chlorine species exist as polychloride monoanions, e.g., [Cl3]- and [Cl5]-, inside the Zn2+-trapped Mn3O4, and the presence of polychloride species is confirmed experimentally. Our results point to the halogen plating inside electrode lattices as a new charge-storage mechanism.

Reversible Copper Cathode for Nonaqueous Dual‐Ion Batteries

AbstractMost reported cathodes of nonaqueous dual‐ion batteries (DIBs) host anions via insertion reactions. It is necessary to explore new cathode chemistry to increase the battery energy density. To date, transition metals have yet to be investigated for nonaqueous DIBs, albeit they may offer high capacity in anodic conversion reactions. Here, we report that bulk copper powder exhibits a high reversible capacity of 762 mAh g−1at 3.2 V vs. Li+/Li and relatively stable cycling in common organic electrolytes. The operation of the copper electrode is coupled with the transfer of anion charge carriers. An anion exchange membrane separator is employed to prevent Cu2+from crossing from the catholyte to the anode side. We designed an unbalanced electrolyte with a more concentrated anolyte than a catholyte. This addresses the concentration overpotential ensued during charge and facilitates the high specific capacity and enhanced reversibility. This finding provides a promising direction for high‐energy DIBs.

Reversible Copper Cathode for Nonaqueous Dual-Ion Batteries.

Most reported cathodes of nonaqueous dual-ion batteries (DIBs) host anions via insertion reactions. It is necessary to explore new cathode chemistry to increase the battery energy density. To date, transition metals have yet to be investigated for nonaqueous DIBs, albeit they may offer high capacity in anodic conversion reactions. Here, we report that bulk copper powder exhibits a high reversible capacity of 762 mAh g-1 at 3.2 V vs. Li+ /Li and relatively stable cycling in common organic electrolytes. The operation of the copper electrode is coupled with the transfer of anion charge carriers. An anion exchange membrane separator is employed to prevent Cu2+ from crossing from the catholyte to the anode side. We designed an unbalanced electrolyte with a more concentrated anolyte than a catholyte. This addresses the concentration overpotential ensued during charge and facilitates the high specific capacity and enhanced reversibility. This finding provides a promising direction for high-energy DIBs.

Electrochemical Alkoxyhalogenation of Alkenes with Organohalides as the Halide Sources via Dehalogenation.

A general, ideal atom utilization electrochemical technology to enable alkene alkoxyhalogenation and organohalide dehalogenation in one pot is presented. This technology is highlighted by convergent strategy integrating several reactions, such as alkene alkoxyhalogenation, organohalide dehalogenation, and dehalogenation deuteration. Experimental data suggest that alkenes have the lowest oxidation potential, which lead to anodic conversion of the C═C bond to the radical cation intermediates, and cathodic transformations of organohalides, including alkyl and aryl halides, as the nucleophilic halogen sources.

An Electrochemical Approach toward the Metastable Type II Clathrate Germanium Allotrope.

By using an anodic conversion process at 280 °C, the type II clathrates Na1.7(6)Ge136 and Na23.0(5)Ge136 were obtained from Na12Ge17 as the starting material. An alkali-metal iodide molten-salt electrolyte complied with the reaction conditions, allowing for the formation of microcrystalline products. Characterization by powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy also revealed Na4Ge13 as an intermediate and α-Ge and Cs8–xGe136 as byproducts, with the latter likely resulting from cation exchange between the starting material and electrolyte. Taking such minor side reactions and a small contribution of material without suitable electrical contact into account, anodic conversion of Na12Ge17 to Na1.7Ge136 proved to proceed without parasitic processes and to comprise the material bulk. The hitherto existing preparation method for Nax→0Ge136 by gas–solid oxidation of Na12Ge17 has thus been translated into a scalable high-temperature electrochemical approach with enhanced tools for reaction control, promising access to pure Ge(cF136) and Na24Ge136 after process optimization.

Diferulate: A highly effective electron donor

The screening of new molecules with high electron-donor properties is important for the design of new bioactive and technologically applicable substances. Here we propose diferulate (1), (Z)-2-(5-((E)-2-carboxyvinyl)-2-hydroxy-3-methoxyphenyl)-3-(4-hydroxy-3-methoxyphenyl)acrylic acid, to be an efficient electron donor which undergoes anodic conversion in aqueous media (pH 7) at around +0.15 V, vs. Ag|AgCl|3 M KCl. The low potential of oxidation of 1 indicates its high electron-donor capacity, which was documented by DPPH and ABTS radical scavenging and anti-lipoperoxidation activity analyses and also supported by in silico approaches. The results showed that compound 1, unlike ferulic acid 2 and the P1 benzofuranone synthetic precursor of 1, exhibits unique antiradical and antioxidant properties compared to trolox 3, which served as the positive control. No cytotoxic effects were observed for 1 in the 1–50 μM range. We conclude that the proposed structure 1 can be used for the further design of molecules whose biological (chemoprotective) activity is associated with high electron-donor properties.

Outstandingly robust anodic dehydrogenative aniline coupling reaction

Oxidative treatment of anilines usually leads to the formation of black polymers, often referred to as “aniline black”. This over-oxidation is hardly controllable and also a challenging task in the anodic conversion of anilines. Here, a quick and efficient access to valuable building blocks by anodic cross- and homo-coupling of aniline and benzidine derivatives is reported. This electrosynthesis is easily performed in a simple undivided cell using constant current conditions. The key to the observed outstanding performance and robustness of this system is attributed to the used solvent 1,1,1,3,3,3-hexafluoroisopropanol. The extraordinary performance over a broad range of current density is unprecedented for reactions involving extremely oxidation labile substrates such as anilines and their derivatives.

Photo-assisted electrochemical detection of bisphenol A in water samples by renewable {001}-exposed TiO2 single crystals

Bisphenol A (BPA) is a semi-persistent environmental endocrine disrupter and widely present in aqueous environments. Electrochemical detection is an effective method to monitor pollutants like BPA in aqueous environments. However, the electrode fouling from anodic polymeric products is one main barrier of electrochemical sensors for their practical applications. In this work, a renewable electrochemical sensor was rationally designed, constructed and tested for efficient BPA detection. The TiO2 anodic material was surface-engineered by inorganic-framework molecular imprinting sites with tailored morphological shape, exposed facet and crystal structure. This electrode could be activated mainly as an electrochemical catalyst and partially as a photochemical catalyst. The developed TiO2-based sensor exhibited a good detection reliability and cyclic stability for determining BPA in water samples, with an electrochemical signal decrease of less than 5.0% in 10-run cyclic tests. By virtue of the bi-functional properties of the tailored TiO2 anodic material, a unique photo-assisted electrochemical sensor was further developed, in which analyte digestion and analytical signal originated mainly from anodic conversion. Such a synergistic digesting mechanism distinguishes it from the reported electro-assisted photochemical TiO2 sensors. Our work provides a robust sensor for monitoring pollutants in aqueous environments and a new opportunity to develop renewable electrode materials with good reusability.

Microbial electrolysis using aqueous fractions derived from Tail-Gas Recycle Pyrolysis of willow and guayule

This study investigated microbial electrolysis of two aqueous phase waste products derived from guayule and willow generated from Tail Gas Recycle Pyrolysis (TGRP). The highest average current density achieved was 5.0 ± 0.7 A/m2 and 1.8 ± 0.2 A/m2 for willow and guayule respectively. Average hydrogen productivity was 5.0 ± 1.0 L/L-day from willow and 1.5 ± 0.2 L/L-day for guayule. Willow also generated higher coulombic efficiency, anode conversion efficiency, and hydrogen recovery than guayule at most organic loading conditions. Compounds investigated exceeded 80% degradation, which included organic acids, sugar derivatives, and phenolics. Mass spectrometric analysis demonstrated the accumulation of a long chain amine not present in either substrate before treatment, and the persistence of several peptide residues resulting from the TGRP process. New biorefineries may one day capitalize on this otherwise discarded byproduct of TGRP, further improving the potential applications and value of microbial electrolysis towards energy production.

Electrochemical Arylation Reaction.

Arylated products are found in various fields of chemistry and represent essential entities for many applications. Therefore, the formation of this structural feature represents a central issue of contemporary organic synthesis. By the action of electricity the necessity of leaving groups, metal catalysts, stoichiometric oxidizers, or reducing agents can be omitted in part or even completely. The replacement of conventional reagents by sustainable electricity not only will be environmentally benign but also allows significant short cuts in electrochemical synthesis. In addition, this methodology can be considered as inherently safe. The current survey is organized in cathodic and anodic conversions as well as by the number of leaving groups being involved. In some electroconversions the reagents used are regenerated at the electrode, whereas in other electrotransformations free radical sequences are exploited to afford a highly sustainable process. The electrochemical formation of the aryl-substrate bond is discussed for aromatic substrates, heterocycles, other multiple bond systems, and even at saturated carbon substrates. This survey covers most of the seminal work and the advances of the past two decades in this area.

Electrochemical behavior of CoSb3 in sulfuric and oxalic acids over the potential range 0 to 40 V

The electrochemical behavior of pure Co, pure Sb, and CoSb3 has been investigated over a large anodic potential range (0 to 40 V) in two acids, i.e., oxalic acid or sulfuric acid at different concentrations (0.01 to 1 M). Potentiodynamic polarizations performed on CoSb3 plates reveal the possible formation of a passive layer between 1 and 3 V (vs SCE), on a passivation plateau. The oxidation of CoSb3 at 2 V in sulfuric and oxalic acids results in the growth of an anodic conversion layer. This coating is mainly made of a porous layer of amorphous antimony oxides due to dealloying of CoSb3. In the specific case of oxalic acid, rods of crystallized oxalates are tangled between the oxide sheets.