Electrochemical Oxidation Research Articles

Electrochemical Seawater Oxidation by (Ni,Co)3O4-RuO2 Catalysts at Neutral pH in a Forward Osmosis Cell

Electrochemical Seawater Oxidation by (Ni,Co)₃O₄-RuO₂ Catalysts at Neutral pH in a Forward Osmosis Cell

Computational Analysis of Low Overpotential Ammonia Oxidation by Metal-Metal Bonded Ruthenium Catalysts, and Predictions for Related Osmium Catalysts.

The catalyzed electrochemical oxidation of ammonia to nitrogen (AOR) is an important fuel-cell half-reaction that underpins a future nitrogen-based energy economy. Our laboratory has reported spontaneous chemical and electrochemical oxidation of ammonia to dinitrogen via reaction of ammonia with the metal-metal bonded diruthenium complex Ru2(chp)4OTf (chp- = 2-chloro-6-hydroxypyridinate, TfO- = trifluoromethanesulfonate). This complex facilitates electrocatalytic ammonia oxidation at mild applied potentials of -255 mV vs ferrocene, which is the [Ru2(chp)4(NH3)]0/+ redox potential. We now report a comprehensive computational investigation of possible mechanisms for this reaction and electronic structure analysis of key intermediates therein. We extend this analysis to proposed second-generation electrocatalysts bearing structurally similar fhp and hmp (2-fluoro-6-hydroxypyridinate and 2-hydroxy-6-methylpyridinate, respectively) equatorial ligands, and we further expand this study from Ru2 to analogous Os2 cores. Predicted M24+/5+ redox potentials, which we expect to correlate with experimental AOR overpotential, depend strongly on the identity of the metal center, and to a lesser degree on the nature of the equatorial supporting ligand. Os2 complexes are easier to oxidize than analogous Ru2 complexes by ∼640 mV, on average. In contrast to mono-Ru catalysts, which oxidize ammonia via a rate-limiting activation of the strong N-H bond, we find lowest-energy reaction pathways for Ru2 and Os2 complexes that involve direct N-N bond formation onto electrophilic intermediates having terminal amido, imido, or nitrido groups. While transition state energies for Os2 complexes are high, those for Ru2 complexes are moderate and notably lower than those for mono-Ru complexes. We attribute these lower barriers to enhanced electrophilicity of the Ru2 intermediates, which is a consequence of their metal-metal bonded structure. Os2 intermediates are found to be, surprisingly, less electrophilic, and we suggest that Os2 complexes may require access to oxidation states higher than Os25+ in order to perform AOR at reasonable reaction rates.

Efficient electrochemical oxidation of the biomass platform compound furfural on a Ni0.48Co0.36O0.16 electrode

Efficient electrochemical oxidation of the biomass platform compound furfural on a Ni0.48Co0.36O0.16 electrode

Synthesis and characterization of Cu-modified ox-g-C3N4 nanosheets as an electrode for green synthesis of phenyl Benzofuran derivatives via C–H functionalization to C–O and C–C bond formation with an electrochemical oxidation system

Synthesis and characterization of Cu-modified ox-g-C3N4 nanosheets as an electrode for green synthesis of phenyl Benzofuran derivatives via C–H functionalization to C–O and C–C bond formation with an electrochemical oxidation system

Indigo as a Low‐Cost Redox‐Active Sorbent for Electrochemically Mediated Carbon Capture

AbstractClimate change has driven the need for carbon capture to mitigate anthropogenic greenhouse gas emissions, yet current thermochemical methods are hampered by high energy intensities. Electrochemically mediated carbon capture (EMCC) utilizing redox‐active carbon dioxide (CO2) carriers is an attractive alternative for carbon capture. Here, an economical vat dye compound, indigo, is presented, which can reversibly capture and release CO2 upon electrochemical reduction and oxidation, respectively. Electrode and electrolyte engineering strategies are utilized to improve the reversibility and stability of indigo for EMCC. A bench‐scale prototypical fixed‐bed carbon capture device is constructed to demonstrate indigo's EMCC performance under various practically relevant conditions, such as simulated flue gas and extremely dilute sources pertinent to direct air capture. A hybrid sorbent electrode‐gas diffusion layer approach is revealed to alleviate CO2 mass transport limitations, achieving ≈80% CO2 capacity utilization under a 15% CO2 feed stream. Furthermore, a reactive‐diffusive mass transport model is developed to illustrate engineering approaches that can be universally applied to optimize fixed‐bed EMCC systems. This work advances the potential for a class of low‐cost sorbents for EMCC while underscoring the importance of molecular, electrolyte, materials, and device engineering strategies to enable high‐performance carbon capture.

Metal–Organic Framework Fe-BTC as Heterogeneous Catalyst for Electro-Fenton Treatment of Tetracycline

This study explores the use of the iron-containing metal–organic framework (MOF), Basolite®F300, as a heterogeneous catalyst for electrochemically-driven Fenton processes. Electrochemical advanced oxidation processes (EAOPs) have shown promise on the abatement of recalcitrant organic pollutants such as pharmaceuticals. Tetracyclines (TC) are a frequently used class of antibiotics that are now polluting surface water and groundwater sources worldwide. Acknowledging the fast capability of EAOPs to treat persistent pharmaceutical pollutants, we propose an electrochemical Fenton treatment process that is catalyzed by the use of a commercially available MOF material to degrade TC. The efficiency of H2O2 generation in the IrO2/carbon felt setup is highlighted. However, electrochemical oxidation with H2O2 production (ECO-H2O2) alone is not enough to achieve complete TC removal, attributed to the formation of weak oxidant species. Incorporating Basolite®F300 in the heterogeneous electro-Fenton (HEF) process results in complete TC removal within 40 min, showcasing its efficacy. Additionally, this study explores the effect of varying MOF concentrations, indicating optimal removal rates at 100 mg L−1 due to a balance of kinetics and limitation of active sites of the catalysts. Furthermore, the impact of the applied current on TC removal is investigated, revealing a proportional relationship between current and removal rates. The analysis of energy efficiency emphasizes 50 mA as the optimal current, however, balancing removal efficiency with electrical energy consumption. This work highlights the potential of Basolite®F300 as an effective catalyst in the HEF process for pollutant abatement, providing valuable insights into optimizing electrified water treatment applications with MOF nanomaterials to treat organic pollutants.

Electrochemically produced nano-TiO2-coated SiC membranes for photocatalytic water treatment: Preparation, characterization, and hydroxyl radical formation

ABSTRACT Photocatalytically active ceramic flat sheet membranes based on a nanostructured titanium dioxide (TiO2) coating were produced for photocatalytic water treatment. The nano-TiO2 layer was produced by a novel combination of magnetron sputtering of a thin titanium layer on silicon carbide (SiC) membranes, followed by electrochemical oxidation (anodization) and subsequent heat treatment. Characterization by Raman spectra and field emission scanning electron microscopy proved the presence of a nanostructured anatase layer on the membranes. The influence of the titanium layer thickness on the TiO2 formation process and the photocatalytic properties were investigated using anodization curves, by using cyclovoltammetry measurements, and by quantifying the generated hydroxyl radicals (OH•) under UV-A irradiation in water. Promising photocatalytic activity and permeability of the nano-TiO2-coated membranes could be demonstrated. A titanium layer of at least 2 μm was necessary for significant photocatalytic effects. The membrane sample with a 10 μm Ti/TiO2 layer had the highest photocatalytic activity showing a formation rate of 1.26 × 10−6 mmol OH• s−1. Furthermore, the membranes were tested several times, and a decrease in radical formation was observed. Assuming that these can be attributed to adsorption processes of the reactants on the TiO2 surface, initial experiments were carried out to reactivate the photocatalyzer.

A Benign Synthesis Route to Terephthalic Acid via Two-Step Electrochemical Oxidation of P-xylene

Abstract Terephthalic acid is conventionally synthesized through the AMOCO process under harsh conditions, making milder electrosynthesis routes desirable. Electrooxidation of p-xylene has been demonstrated but the degree of oxidation is limited, resulting in low terephthalic acid yields. Here, we demonstrate a process with two electrochemical steps enabling the complete oxidation of p-xylene into terephthalic acid. The first electrochemical step achieves C-H activation of p-xylene using electrochemically generated bromine as a mediator, while the second electrochemical step does alcohol oxidation of 1,4-benzenedimethanol into terephthalate on NiOOH. The divided cell in the first step simultaneously generates acid and base that are utilized subsequently, negating the need of external acid and base addition and thus offering a cost competitive synthesis route. The competing bromide oxidation in the second step is suppressed by using constant voltage electrolysis at 0.50 V, where an optimal yield of terephthalic acid of 81% is achieved.

Improved Electrocatalytic Degradation of Alizarin Yellow R by Ti/Zr-SnO2/PbO2 Electrodes Doped with Ytterbium

Introduction: Electrochemical oxidation of Alizarin Yellow R (AYR) was investigated on Ytterbium (Yb) doped Ti/PbO2 electrodes prepared by an electrodeposition method. Method: The etching of the Ti sheet by using a mixed acid of H2SO4 and TA (volume ratio= 2: 1) for 50 min at 100 °C could produce a suitable interface for further modification. The morphologies, composition, and electrochemical properties of Yb doping on the electrode were characterized by SEM (Scanning Electron Microscopy), EDS (Energy-Dispersive Spectroscopy), Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The introduction of an appropriate intermediate layer, Zr-SnO2, was performed. We also tried to fabricate Ytterbium (Yb) doped Ti/Zr-SnO2/PbO2 electrodes by an electrodeposition method on the intermediate layer of Zr-SnO2. The surface morphology of the Ti/Zr-SnO2/PbO2 electrode was changed due to the Yb doping, which affected the electrocatalytic activity of the modified electrode. Result: The developed Yb-doped Ti/Zr-SnO2/PbO2 electrode showed improved removal efficiencies toward AYR. Conclusion: The effects of current density and initial AYR concentration on the electrochemical oxidation of AYR by Yb-doped Ti/Zr-SnO2/PbO2 were investigated. The removal rate of AYR was 97.3% in 180 min under the conditions of the current density of 60 mA/cm2 , initial AYR concentration of 50.0 mg L-1 , and Na2SO4 concentration of 0.10 mol L-1 .

Sustainable Electrochemical Mechanical Polishing (ECMP) for 4H-SiC wafer using chemical-free polishing slurry with hydrocarbon-based solid polymer electrolyte

Large-diameter single-crystal silicon carbide (SiC) wafers with good surface quality are desirable to dramatically improve the performance of SiC-based power electronic devices. However, the preparation of such wafers using a strong oxidative polishing slurry has the limitations of low material removal rate (MRR) and high environmental impact. Electrochemical–mechanical polishing (ECMP) initiates surface removal by electrochemical oxidation without using harsh chemicals, making it an alternative with low environmental impact to conventional polishing. Herein, we propose the use of polystyrene sulfonic acid (PSS), a hydrocarbon-based polymer electrolyte without perfluoro compounds, for ECMP. The SiC surface was effectively oxidized by ECMP using PSS. The effects of the polyelectrolyte crosslinking treatment on the lifetime of polyelectrolyte-incorporated nonwoven cloths were investigated. The optimum electrolytic and mechanical conditions yielded high MRRs of 37 and 14 µm/h for 2- and 4-inch SiC wafers. Moreover, the surface morphologies of the growth face and nonfacet areas was discussed. The wafer-scale evaluation demonstrated the roughness reduction to 0.85 nm Sa (average) after 15-min ECMP of the 4-inch wafer. The polishing-induced residual stress was investigated using microscale and wafer-scale Raman mapping. Overall, the proposed ECMP process offers significant advantages in terms of speed, cost-effectiveness, and environmental impact.

Preparation of electrocatalytic KC-GR/GF membrane cathode and its application in electro-Fenton

ABSTRACT Tetracycline is a common antibiotic that threatens the water environment and requires more stable and efficient ways to degrade it. In this paper, a novel filtered cathode material was prepared by proportionally loading Ketjen Black Carbon (KC) and Graphene (GR) onto Graphite Felt(GF) by coating method, and applied to remove tetracycline from water by electro-Fenton system. The results showed that the highest hydrogen peroxide yield of up to 28.86 mg/L was achieved at the electrodes prepared with a carbon loading of 0.228 g, m (KC):m(polytetrafluoroethylene) = 1:9, and m (KC):m (GR) = 2:2. By characterisation, the contact angle of the loaded graphite felt electrode increased from 71.5° to 126.3°, with faster current responsiveness and larger electrochemically active area than the unloaded electrode. Furthermore, in the application of electro-Fenton: when I = 100 mA, Air = 0.45 L/min, pH = 3 and Fe2+ = 0.3 mol/L, the optimal removal rate of 50 mg/L tetracycline was 99.1%, and the energy consumption was only 8.49 kWh/kg. This electrode has a great advantage in treating the low concentration of tetracycline, and 99.4% of tetracycline can be removed within 30 min. After 8 cycles of tests, the removal rate of tetracycline by this electrode was above 95%. The article demonstrated that the reactor coupled with electrochemical advanced oxidation technology and membrane filtration technology has the effect of enhanced mass transfer, and the Ketjen Black Carbon-Graphene/Graphite Felt (KC-GR/GF) electrocatalytic membrane cathode has the potential and practical significance to be applied for the removal of tetracycline under the electro-Fenton system.

Insights in Pt-based electrocatalysts on carbon supports for electro-oxidation of carbohydrates: an EIS-DEMS analysis

In this work, the electrochemical oxidation of carbohydrates (glucose, fructose, and sucrose) was induced at the interface of Pt-nanoparticles supported on different carbon-based materials as carbon vulcan (C) and carbon black (CB). It was found that the support plays an important role during carbohydrates electro-oxidation as demonstrated by electrochemical techniques. In this context, current-concentration profiles of the redox peaks show the behavior of the pathways at carbohydrates-based solutions. Herein, the trend of current measured was glucose > sucrose > fructose, attributed to differences in the organic functional groups and chain-structure. Raman, XRD, SEM-EDS and XPS put in clear important structural, morphological, and electronic differences linked with the intrinsic nature of the obtained material. Differential Electrochemical Mass Spectroscopy (DEMS) indicated that the selectivity and the conversion of the formed reaction products during oxidation is linked with the catalyst nature (distribution, particle size) and the interaction with the carbon-based support.

Electrochemical Oxidation of Ethylene Glycol in Aqueous Media Using Lead Dioxide Titanium Anode

Experiments on the electrochemical oxidation of ethylene glycol (EG) have been carried out in laboratory conditions using lead dioxide titanium anode (LDOTA) in electrochemical cell. It has been found that the chemical oxygen consumption in the solution on LDOTA at a current density of 5.5 A/dm2 and processing time of 120 min is reduced to the values that allow its further bio-purification. It has been concluded that the efficiency of the electrochemical oxidation process, leading to further destruction of the EG molecule, is explained by both direct oxidation, in which the hydroxyl radicals arise that oxidize EG on the anode surface, and indirect oxidation, accompanied by the formation of strong oxidizing agents, for example, peroxodisulfuric acid anions capable of oxidizing the organic matter in the solution volume.

Electrocatalytic Glycerol Conversion: A Low-Voltage Pathway to Efficient Carbon-Negative Green Hydrogen and Value-Added Chemical Production.

Electrochemical glycerol oxidation reaction (GLYOR) could be a promising way to use the abundantly available glycerol for production of value-added chemicals and fuels. Completely avoiding the oxygen evolution reaction (OER) with GLYOR is an evolving strategy to reduce the overall cell potential and generate value-added chemicals and fuels on both the anode and cathode. We demonstrate the morphology-controlled palladium nanocrystals, afforded by colloidal chemistry, and their established morphology-dependent GLYOR performance. Although it is known that controlling the morphology of an electrocatalyst can modulate the activity and selectivity of the products, still it is a relatively underexplored area for many reactions, including GLYOR. Among nanocube (Pd-NC), truncated octahedron (Pd-TO), spherical and polycrystalline (Pd-PC) morphologies, the Pd-NC electrocatalyst deposited on a Ni foam exhibits the highest glycerol conversion (85%) along with 42% glyceric acid selectivity at a low applied potential of 0.6 V (vs reversible hydrogen electrode (RHE)) in 0.1 M glycerol and 1 M KOH at ambient temperature. Owing to the much favorable thermodynamics of GLYOR on the Pd-NC surface, the assembled electrolyzer requires an electricity input of only ∼3.7 kWh/m3 of H2 at a current density of 100 mA/cm2, in contrast to the requirement of ≥5 kWh/m3 of H2 with an alkaline/PEM electrolyzer. Sustainability has been successfully demonstrated at 10 and 50 mA/cm2 and up to 120 h with GLYOR in water and simulated seawater.

A sustainable electrochemical strategy utilizing pulsed alternating current and dual carbon felt electrodes for enhanced degradation of organic pollutants: Oxidation performance and mechanisms

In this work, a novel electrochemical (EC) oxidation system utilizing pulsed alternating current (PAC) and dual carbon felt (CF) electrodes has been established for sustainable degradation of sulfamethoxazole (SMX) with no addition of extra oxidant. The EC/PAC system showed high degradation efficiency and energy efficiency compared to the pulsed direct current (PDC) and direct current (DC) systems. The EC/PAC process was effective across a wide pH range of 3–11 for SMX removal. The results showed that the 1O2 confined to the CF electrode surface was the dominant oxidative specie that was generated from dissolved oxygen in the system. Under PAC conditions, the cathode and anode were rapidly switched on the same CF electrode, increasing the generation of 1O2 for enhanced SMX oxidation. Furthermore, the EC/PAC system demonstrated resistance to interference from various anions of different concentration levels found in natural environment. In contrast to the EC/PDC system, the EC/PAC system emerged as a promising option for more efficient H2O2 production. High-resolution mass spectrometry results revealed the SMX degradation pathways and byproducts, which were then evaluated for toxicity removal. Overall, the EC/PAC system offers a green and sustainable solution to future wastewater treatment, with high degradation rates, energy efficiency, and sustainability.

Utilizing Activated Carbon Nanopores for Electrochemical Oxidation of Perylene to Redox-Active 3,10-Perylenedione: Application in Electrochemical Capacitor Electrodes.

We demonstrate that nanopores of activated carbon (AC) function as nanoreactors that oxidize perylene (PER) to a redox-active organic compound, 3,10-perylenedione (PERD), without any metal catalysts or organic solvents. PER is first adsorbed on AC in the gas phase, and the PER-adsorbed AC is subjected to electrochemical oxidation in aqueous H2SO4 as the electrolyte. Because gas-phase adsorption is solvent-free, PER is completely adsorbed on AC as long as the amount of PER does not exceed the saturated adsorption capacity of the AC, which enables accurate control of the amount adsorbed. PER is electrochemically oxidized to PERD in the nanopores of AC at above 0.7 V vs Ag/AgCl. The hybridized PERD undergoes a rapid reversible two-electron redox reaction in the nanopores owing to the large contact interface between the conductive carbon pore surfaces and PERD. The resulting AC/PERD hybrids serve as electrodes for electrochemical capacitors, utilizing the rapid redox reaction of PERD. The hybridization method is advantageous for quantitatively optimizing electrochemical capacitor performance by adjusting the amount of adsorbed PER. Moreover, because PERD hybridization in the AC nanopores does not expand the electrode volume, the volumetric capacitance increases with increasing hybridized PERD content. In three-electrode cell measurements, the volumetric capacitance at 0.05 A g-1 reaches 299 F cm-3, and 61% of this capacitance is retained at 10 A g-1 when 5 mmol of PER is used per gram of AC. Meanwhile, pristine AC delivers 117 F cm-3 at 0.05 A g-1 with a capacitance retention of 46% at 10 A g-1. Two-electrode cell measurements reveal that self-discharge is significantly suppressed by the hybridized PERD when AC/PERD hybrids and AC are used as cathodes and anodes, respectively, compared to that of a symmetrical AC cell. Moreover, PERD does not undergo cross-diffusion in the asymmetrical cells during self-discharge tests for 24 h.

Removal of 6-methylquinoline from shale gas wastewater using electrochemical carbon nanotubes filter

6-Methylquinoline (6-MQ) is identified as a high-concentration organic compound pervasive in shale gas wastewater (SGW) and poses a significant risk of environmental pollution. In response, this study aimed to address these challenges by introducing an innovative electrochemical membrane constructed with multi-walled carbon nanotubes (CNTs) for the removal of 6-MQ. The investigation systematically explored the impact of voltage, initial pollutant concentration, and salinity on the performance of the electrochemical CNTs filter. It was found a positive correlation between removal efficiency and increasing voltage and salinity levels. Conversely, as the initial concentration of pollutants increased, the efficiency showed a diminishing trend. The electrochemical CNTs filter exhibited remarkable efficacy in both adsorption removal and electrochemical oxidation of 6-MQ. Notably, the CNTs membrane exhibited robust adsorption capabilities, evidenced by the sustained adsorption of 6-MQ for over 33 h. Furthermore, applying an electrochemical oxidation voltage of 3 V consistently maintained a removal rate exceeding 34.0% due to both direct and indirect oxidation, underscoring the sustained efficacy of the electrochemical membranes. Besides, real wastewater experiments, while displaying a reduction in removal efficiency compared to synthetic wastewater experiments, emphasized the substantial potential of the electrochemical CNTs filter for practical applications. This study underscores the significant promise of electrochemical membranes in addressing low molecular weight contaminants in SGW, contributing valuable insights for advancing SGW treatment strategies.

Two interesting reports in electrochemical oxidation of o-tolidine: presentation ECDispE mechanism and electrosynthesis of a diazine compound

Two interesting reports in electrochemical oxidation of o-tolidine: presentation ECDispE mechanism and electrosynthesis of a diazine compound

Selective electrocatalytic oxidation of ammonia to nitrogen by using titanium dioxide nanorod array decorated with ultrasmall Ir nanoparticles and non-noble metal Fe nanoparticles

Electrochemical ammonia oxidation process through active chlorine has been proposed as a potentially effective method for ammonia removal. Currently, most of the anodes require to use high-stable TiO2 loaded with large particles of noble metal Ru or Ir, which have low activity and high cost. Herein, we prepare ultrasmall and uniform metal nanoparticles of Ir on TiO2 to remove ammonia. Moreover, we use non-noble metal Fe to replace noble metals. The ammonia removal efficiency of Fe/TiO2 under 2 VVS Ag / AgCl during 2 h is 100 % and 94 % of ammonia is converted to N2. The Fe/TiO2 anodes not only have higher catalytic activity but also show excellent stability and reusability. Fe/TiO2 anodes still exhibit excellence activity and selectivity after 1 year. As a common metal, Fe will have more application space than iridium in ammonia removal for its low cost and selectively high efficiency.

A Density Functional Theory Analysis of Electrochemical Oxidation of Methane to Alcohol over High-Entropy Oxide (CoCrFeMnNi)3O4 Catalysts.

The direct conversion of methane into alcohol is a promising approach for achieving a low-carbon future, yet it remains a major challenge. In this study, we utilize density functional theory to explore the potential of the (CoCrFeMnNi)3O4 (CCFMNO) high entropy oxide (HEO) for electrochemical oxidation of methane to methanol and ethanol, alongside their competition with CO2 production. Our primary focus in this study is on thermodynamics, enabling a prompt analysis of the catalyst's potential, with the calculation of electrochemical barriers falling beyond our scope. Among all potential active sites within CCFMNO HEO, we identify Co as the most active site for methane activation when using carbonate ions as oxidants. This results in methanol production with a limiting potential of 1.4 VCHE, and ethanol and CO2 productions with a limiting potential of 1.2 VCHE. Additionally, our findings suggest that the occupied p-band center of O* on CCFMNO HEO is a potential descriptor for identifying the most active site within CCFMNO HEO. Overall, our results indicate that CCFMNO HEO holds promise as catalysts for methane oxidation to alcohols, employing carbonate ions as oxidants.