Mediated Electron Transfer Mechanism Research Articles

Fabricating high-purity graphite disk electrodes as a cost-effective alternative in fundamental electrochemistry research

Graphite electrodes offer remarkable electrochemical properties, emerging as a viable alternative to glassy carbon (GCE) and other carbon-based electrodes for fundamental electrochemistry research. We report the fabrication and characterization of high-purity graphite disk electrodes (GDEs), made from cost-effective materials and a solvent-free methodology employing readily available laboratory equipment. Analysis of their physical properties via SEM, EDX and XPS reveals no metallic interferences and a notably high porosity, emphasizing their potential. The electrochemical performances of GDEs were found to be comparable to those of GCE. Immobilization of peptides and enzymes, both via covalent coupling and surface adsorption, was used to explore potential applications of GDEs in bioelectrochemistry. Enzyme activity could be addressed both via direct electron transfer and mediated electron transfer mechanism. These results highlight the interesting properties of our GDEs and make them a low-cost alternative to other carbon-based electrodes, with potential for future real-world applications.

Key role of Fe(VI)-activated Bi2WO6 in the photocatalytic oxidation of sulfonamides: Mediated electron transfer mechanism

The widespread use of sulfonamides (SAs) in animals and human infections has raised significant concerns regarding their presence in ambient waterways and potential for inducing antimicrobial resistance. Herein, we report on the capacity of ferrate (VI) (FeVIO42-, Fe(VI)) to facilitate the photocatalytic degradation of sulfamethazine (SMT) via bismuth tungstate (Bi2WO6, BWO) under blue LED light (Vis/BWO/Fe(VI)) exposure, at rates that were 45-fold faster than BWO photocatalysis. Both the stepwise and time-series addition of Fe(VI) contributed to the degradation. Multiple lines of evidence confirmed that the common reactive species (RSs) in BWO-based photocatalytic systems and Fe(VI)-involved systems (e.g., •OH/h+, O2•−, 1O2 and Fe(V)/Fe(IV)) played subtle roles in our study system. Herein, for the first time, it was discovered that the precursor complex (BWO-Fe(V)/Fe(IV)* )) was the main contributor to induce electron transfer of SAs through the "conductive bridge" effect of BWO. The studied system was able to effectively degrade SMT in synthetic hydrolyzed urine (SHU) with low interference from background substances in water. This work not only offers a novel facilitation strategy for BWO, but also holds a great application prospect for contamination remediation in urine.

Activation of periodate by N-doped iron-based porous carbon for degradation of sulfisoxazole: Significance of catalyst-mediated electron transfer mechanism

Periodate (PI) has recently been studied as an excellent oxidant in advanced oxidation processes, and its reported mechanism is mainly the formation of reactive oxygen species (ROS). This work presents an efficient approach using N-doped iron-based porous carbon (Fe@N-C) to activate periodate for the degradation of sulfisoxazole (SIZ). Characterization results indicated the catalyst has high catalytic activity, stable structure, and high electron transfer activity. In terms of degradation mechanism, it is pointed out that the non-radical pathway is the dominant mechanism. In order to prove this mechanism, we have carried out scavenging experiments, electron paramagnetic resonance (EPR) analysis, salt bridge experiments and electrochemical experiments, which demonstrate the occurrence of mediated electron transfer mechanism. Fe@N-C could mediate the electron transfer from organic contaminant molecules to PI, thus improving the efficiency of PI utilization, rather than simply inducing the activation of PI through Fe@N-C. The overall results of this study provided a new understanding into the application of Fe@N-C activated PI in wastewater treatment.

Treatment of Coking Wastewater by α-MnO2/Peroxymonosulfate Process via Direct Electron Transfer Mechanism

Side reactions between free radicals and impurities decelerate the catalytic degradation of organic contaminants from coking wastewater by Advanced Oxidation Processes (AOPs). Herein, we report the disposal of coking wastewater by α-MnO2/PMS process via a direct electron transfer mechanism in this study. By the removal assays of the target compound of phenol, the PMS mediated electron transfer mechanism was identified as the dominated one. Water quality parameters including initial pH, common anions and natural organic matters demonstrated limited influences on phenol degradation. Afterwards, α-MnO2/PMS process was applied on the disposal of coking wastewater. The treatment not only eliminated organic contaminants with COD removal of 73.8% but also enhanced BOD5/COD from 0.172 to 0.419, within 180 min of reaction under conditions of 50 g/L α-MnO2, 50 mM PMS and pH0 7.0. COD removal decreased only 1.1% after five-time cycle application, suggesting a good reuse performance. A quadratic polynomial regression model was further built to optimize the reaction conditions. By the model, the dosage of α-MnO2 was identified as the most important parameters to enhance the performance. The optimal reaction conditions were calculated as 50 g/L α-MnO2, 50 mM PMS and pH0 6.5, under which COD removal of 74.6% was predicted. All aforementioned results suggested that the α-MnO2/PMS process is a promising catalytic oxidation technology for the disposal of coking wastewater with good practical potentials.

Derivatives of two-dimensional MXene-MOFs heterostructure for boosting peroxymonosulfate activation: Enhanced performance and synergistic mechanism

Integrating the merits of the substrate and active sites with the water matrix is of significant importance to design novel catalysts for peroxymonosulfate (PMS)-based advanced oxidation processes. A sandwich-like heterostructure catalyst (MCoO@Co-N-C) were fabricated via anchoring zero-dimensional metal-organic frameworks (MOFs)-derived CoO nanoparticles on two-dimensional Ti3C2Tx MXene nanosheets. Benefiting from the distinctive structure, the resultant catalysts achieved excellent decontamination performance under high salinity conditions (200 mM). Nearly 100% efficiency of bisphenol A (BPA) was degraded within 10 min only using 0.05 g L−1 catalyst and 0.1 g L−1 PMS, with exceptional high turnover frequency (TOF) value (8.64 min−1) which was 22.5 times higher than that of MOFs derived catalysts without MXene. A mediated-electron transfer mechanism is found to be conducive to the oxidation of BPA. This work provides a new approach to novel catalysts designed for removing trace organic contaminants (TrOCs) in saline water.

Efficient and Durable Single-Atom Fe Catalyst for Fenton-like Reaction via Mediated Electron-Transfer Mechanism

Efficient and Durable Single-Atom Fe Catalyst for Fenton-like Reaction via Mediated Electron-Transfer Mechanism

Microbial electrochemical approaches of carbon dioxide utilization for biogas upgrading

Microbial electrochemical approach is an emerging technology for biogas upgrading through carbon dioxide (CO2) reduction and biomethane (or value-added products) production. There is limited literature critically reviewing the latest scientific developments on the bioelectrochemical system (BES) based biogas upgrading technologies, including CO2 reduction efficiency, methane (CH4) yields, reactor operating conditions, and electrode materials tested in the BES reactor. This review analyzes the reported performance and identifies crucial parameters considered for future optimization, which is currently missing. Further, the performances of BES approach of biogas upgrading under various operating settings in particular fed-batch, continuous mode in connection to the microbial dynamics and cathode materials have been thoroughly scrutinized and discussed. Additionally, other versatile application options associated with BES based biogas upgrading, such as resource recovery, are presented. Three-dimensional electrode materials have shown superior performance in supplying the electrons for the reduction of CO2 to CH4. Most of the studies on the biogas upgrading process conclude hydrogen (H2) mediated electron transfer mechanism in BES biogas upgrading.

Activation of peroxymonosulfate via mediated electron transfer mechanism on single-atom Fe catalyst for effective organic pollutants removal

Cheap and abundant Fe based catalysts in advanced oxidation progresses (AOPs) usually exhibit radicals or high-valent Fe species (HV-Fe) dominated activation mechanism. In this contribution, the atomically dispersed Fe on g-C3N4 (SAFe-CN) was fabricated for peroxymonosulfate (PMS) activation to degrade o-phenylphenol (OPP). OPP removal was not impeded by common radical scavengers, indicating the absence of SO4•− and •OH. The involvement of 1O2 and HV–Fe was excluded and the mediated electron transfer was finally identified as the dominated mechanism. Atomically dispersed Fe sites in SAFe-CN were verified as active sites for reacting with OO bond of PMS and ulteriorly electron shuttling in pollutants degradation. A water treatment filter was fabricated using SAFe-CN and it remained 100% of OPP removal after 100 h of operation. These results provide new insights into the mechanism of mediated electron transfer as well as potential application of non-radical dominated process at device level.

Fluorescence and Electrochemistry to Study the Electronic Transfer from an Organic Dye to Battery Active Materials: Towards Developing an Operating Photobattery

Intensive efforts are currently dedicated towards developing devices that can convert and store renewable energy derived from renewable sources. These are to address the current global energy consumption needs and reduce the carbon footprint that is associated with the use of primary non-renewable energy resources. Indeed, many of these approaches are promising for reducing energy inequalities. They can also mitigate greenhouse emissions. Within this context, solar energy is among one of the best suited candidates to address the global energy needs in a sustainable manner. It is also an attractive energy source because of its widespread availability. A major challenge of using solar energy is that it must be stored for use during periods when there is no sun. Devices are therefore required that can convert, store, and deliver the stored energy during dark periods.To address the energy storage needs, lithium-ion batteries have been successfully coupled to solar cells such as silica based photovoltaic panels. Indeed, lithium-ion batteries are suitable candidates because they are a proven technology that offers high energy density and a long cycle life. Furthermore, they are ideal for portable applications such as photobatteries. These are energy capturing and storage devices that combine a light harvesting solar cell with an energy storing battery. The collective efforts of our research groups have been focused on developing a single device that can collectively harvest the energy derived from sun light and store its energy courtesy of redox reactions that are specific to a battery. Our approach involves merging dye-sensitized solar cell technology (DSSC) with a proven lithium ion battery to ultimately make an all-in-one device. Towards this end, we investigated an organic dye as the light harvesting component. The given dye was selected because it satisfies many of the physical and electrochemical requirements for its use in the combined photobattery. Of importance, is the dye’s photophysical properties. It broadly absorbs in the visible spectrum, it is capable of being reduced by the battery’s electroactive component upon light absorption, it exhibits a high degree of colorfast, and it is photostable.While the organic dye in principle possesses the required properties that are suited for its use as the light harvesting component of the photobattery, these have not been experimentally validated under. Both the photophysical and electrochemical properties of the dye under device-like conditions must therefore be evaluated. To confirm the concept, the capacity of the organic dye to undergo required electron transfer from the lithium active compound of the battery upon photoexcitation was therefore evaluated. Studies done by both steady-state and time-resolved emission quenching measurements in a systematic way will be presented. These will be complemented with transient absorption spectroscopy measurements. These were done to confirm that the desired dye radical anion was indeed formed by electron transfer from the lithium active component. Step-wise electrochemical studies such as galvanostatic cycling and chroroamperometry under illumination, with the various photoactive and battery components, will also be presented as evidence for the required light mediated electron transfer mechanism. It will be presented that collectively the individual photo- and electrochemical studies provide sound evidence for electron transfer between the constitutional “solar” and “battery” components, laying the experimental groundwork for an all-in-one photobattery. It will further be presented that conventional solvents in batteries can be replaced with environmentally benign water. The combined aqueous photobattery will therefore have a positive ecological impact both in terms of using sustainable means for energy harvesting/storage and the constitution components of the device.

B-doped graphitic porous biochar with enhanced surface affinity and electron transfer for efficient peroxydisulfate activation

In this study, B-doped graphitic porous biochar (B-KBC) was prepared and used to activate peroxydisulfate (PDS) for the removal of sulfamethoxazole (SMX). Experimental and theoretical results revealed that the introduction of boron species not only act as Lewis acid sites enhanced the surface affinity towards PDS but also modulate the electronic structure of carbon matrix evidently increase the electron transfer rate, and thus result in an excellent catalytic capacity. More importantly, owing to the high stability boron sites, B-KBC endows a superior long-term durability in comparison with popular N-doped carbon catalysts. Given the uncertainty of quenching experiments, the electron paramagnetic resonance, materials balance calculation combined with electrochemical measures confirmed the biochar mediated electron transfer mechanism, rather than 1O2, was primarily responsible for the nonradical route. This study is expected to pave a new avenue to develop cost-effective and eco-friendliness metal-free carbon catalyst with adequate activity and reuse stability.

O2 Reduction in Enzymatic Biofuel Cells.

Catalytic four-electron reduction of O2 to water is one of the most extensively studied electrochemical reactions due to O2 exceptional availability and high O2/H2O redox potential, which may in particular allow highly energetic reactions in fuel cells. To circumvent the use of expensive and inefficient Pt catalysts, multicopper oxidases (MCOs) have been envisioned because they provide efficient O2 reduction with almost no overpotential. MCOs have been used to elaborate enzymatic biofuel cells (EBFCs), a subclass of fuel cells in which enzymes replace the conventional catalysts. A glucose/O2 EBFC, with a glucose oxidizing anode and a O2 reducing MCO cathode, could become the in vivo source of electricity that would power sometimes in the future integrated medical devices. This review covers the challenges and advances in the electrochemistry of MCOs and their use in EBFCs with a particular emphasis on the last 6 years. First basic features of MCOs and EBFCs are presented. Clues provided by electrochemistry to understand these enzymes and how they behave once connected at electrodes are described. Progresses realized in the development of efficient biocathodes for O2 reduction relying both on direct and mediated electron transfer mechanism are then discussed. Some implementations in EBFCs are finally presented.

Membraneless enzymatic ethanol/O2 fuel cell: Transitioning from an air-breathing Pt-based cathode to a bilirubin oxidase-based biocathode

The bioelectrooxidation of ethanol was investigated in a fully enzymatic membraneless ethanol/O2 biofuel cell assembly using hybrid bioanodes containing multi-walled carbon nanotube (MWCNT)-decorated gold metallic nanoparticles with either a pyrroloquinoline quinone (PQQ)-dependent alcohol dehydrogenase (ADH) enzyme or a nicotinamide adenine dinucleotide (NAD+)-dependent ADH enzyme. The biofuel cell anode was prepared with the PQQ-dependent enzyme and designed using either a direct electron transfer (DET) architecture or via a mediated electron transfer (MET) configuration through a redox polymer, 1,1′-dimethylferrocene-modified linear polyethyleneimine (FcMe2-C3-LPEI). In the case of the bioanode containing the NAD+-dependent enzyme, only the mediated electron transfer mechanism was employed using an electropolymerized methylene green film to regenerate the NAD+ cofactor. Regardless of the enzyme being employed at the anode, a bilirubin oxidase-based biocathode prepared within a DET architecture afforded efficient electrocatalytic oxygen reduction in an ethanol/O2 biofuel cell. The power curves showed that DET-based bioanodes via the PQQ-dependent ADH still lack high current densities, whereas the MET architecture furnished maximum power density values as high as 226 ± 21 μW cm−2. Considering the complete membraneless enzymatic biofuel cell with the NAD+-dependent ADH-based bioanode, power densities as high as 111 ± 14 μW cm−2 were obtained. This shows the advantage of PQQ-dependent ADH for membraneless ethanol/O2 biofuel cell applications.

Integration of β-cyclodextrin into graphene quantum dot nano-structure and its application towards detection of Vitamin C at physiological pH: A new electrochemical approach

For the first time, β-Cyclodextrin (β-CD) attachment to graphene quantum dot (GQD) structure was performed using simultaneous electrodeposition of GQD and β-CD on the surface of glassy carbon electrode (GCE). Cyclic voltammetry at potential range −1.0 to 1.0V from mixture of GQD and β-CD produced a well-defined β-CD-GQD deposited on the surface of glassy carbon electrode. β-CD-GQD modified GCE was used as a new electrocatalytical nanocomposite towards electrooxidation of Vitamin C (as sample analyte). The synergistic effects and the catalytic activity of the β-CD-GQD modified GCE were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) chronoamperometry (CA) and square wave voltammetry (SWV). The process of oxidation involved and its kinetics were established by using cyclic voltammetry, chronoamperometry techniques. It has been found that in the course of an anodic potential sweep the electro-oxidation of Vitamin C is catalyzed by synergetic effect of β-CD and GQD through a mediated electron transfer mechanism. Therefore, β-CD-GQDs promote the rate of oxidation by increasing the peak current. The cyclic voltammetric results indicate that β-CD-GQDs-GCE can remarkably enhance electroactivity towards the oxidation of Vitamin C in buffer solution. We have illustrated that the as-obtained β-CD-GQDs-GCE exhibited a much higher electrocatalytical behavior than GQDs for the electrooxidation and detection of Vitamin C which was about two fold higher than for GQDs. The electrochemical behavior was further exploited as detection scheme for the Vitamin C electrooxidation by square wave voltammetry.

A Re-evaluation of Electron-Transfer Mechanisms in Microbial Electrochemistry: Shewanella Releases Iron that Mediates Extracellular Electron Transfer.

Exoelectrogenic bacteria can couple their metabolism to extracellular electron acceptors, including macroscopic electrodes, and this has applications in energy production, bioremediation and biosensing. Optimisation of these technologies relies on a detailed molecular understanding of extracellular electron‐transfer (EET) mechanisms, and Shewanella oneidensis MR‐1 (MR‐1) has become a model organism for such fundamental studies. Here, cyclic voltammetry was used to determine the relationship between the surface chemistry of electrodes (modified gold, ITO and carbon electrodes) and the EET mechanism. On ultra‐smooth gold electrodes modified with self‐assembled monolayers containing carboxylic‐acid‐terminated thiols, an EET pathway dominates with an oxidative catalytic onset at 0.1 V versus SHE. Addition of iron(II)chloride enhances the catalytic current, whereas the siderophore deferoxamine abolishes this signal, leading us to conclude that this pathway proceeds via an iron mediated electron transfer mechanism. The same EET pathway is observed at other electrodes, but the onset potential is dependent on the electrolyte composition and electrode surface chemistry. EET pathways with onset potentials above −0.1 V versus SHE have previously been ascribed to direct electron‐transfer (DET) mechanisms through the surface exposed decaheme cytochromes (MtrC/OmcA) of MR‐1. In light of the results reported here, we propose that the previously identified DET mechanism of MR‐1 needs to be re‐evaluated.

Investigation of the mediated electron transfer mechanism of cellobiose dehydrogenase at cytochrome c-modified gold electrodes

The present study reports on the comparison of direct and mediated electron transfer pathways in the interaction of the fungal enzyme cellobiose dehydrogenase (CDH) with the redox protein cytochrome c (cyt c) immobilised at a modified gold electrode surface. Two types of CDHs were chosen for this investigation: a basidiomycete (white rot) CDH from Trametes villosa and a recently discovered ascomycete from the thermophilic fungus Corynascus thermophilus. The choice was based on the pH-dependent interaction of these enzymes with cyt c in solution containing the substrate cellobiose (CB). Both enzymes show rather similar catalytic behaviour at lower pH, dominated by a direct electron exchange with the electrode. With increasing pH, however, also cyt c-mediated electron transfer becomes possible. The pH-dependent behaviour in the presence and in the absence of cyt c is analysed and the potential reaction mechanism for the two enzymes with a different pH-behaviour is discussed.

Effect of pH on Aqueous Se(IV) Reduction by Pyrite

Interaction of aqueous Se(IV) with pyrite was investigated using persistently stirred batch reactors under O2-free (<1 ppm) conditions at pH ranging from 4.5 to 6.6. Thermodynamic calculations, an increase in pH during the experiments, and spectroscopic observation indicate that the reduction of aqueous Se(IV) by pyrite is dominated by the following reaction: FeS2+3.5HSeO3−+1.5H+=2SO4(2−)+Fe2++3.5Se(0)+2.5H2O. The released Fe(II) was partitioned between the bulk solution and pyrite surface at pH≈4.5 and 4.8, with the Fe2+ density at pyrite-solution interface about 4 orders of magnitude higher than that in the bulk solution, while iron oxyhydroxide precipitated at pH≈6.6, resulting in the decrease of dissolved iron. In the Se(IV) concentration range of the experiments, aqueous Se(IV) reduction rate follows the pseudofirst order which is in the form of ln mSe(IV)=−k′t+ln mSe(IV)0, where k′ is apparent rate constant combining the rate constant k and pyrite surface area to mass of solution ratio (A/M). And the aqueous Se(IV) reduction rate constant for a standard system (k) with 1 m2 pyrite surface area per 1 kg solution was obtained to be 1.65×10(−4) h(−1), 3.28×10(−4) h(−1), and 4.76×10(−4) h(−1) at pH around 4.5, 4.8, and 5.1, respectively. The positive correlation between reaction rate and pH disagrees with the theories that protons are consumed when HSeO3− is reduced to Se0, and negative charge density on pyrite surface increases as pH increases. Thus, a ferrous iron mediated electron transfer mechanism is proposed to operate during the reduction of aqueous Se(IV) by pyrite. pH and iron concentration affect significantly on Se(IV) reaction rate and reaction product.

Copper-poly(2-aminodiphenylamine) as a novel and low cost electrocatalyst for electrocatalytic oxidation of methanol in alkaline solution

In the present work we demonstrate the carbon paste as a new electrode substrate for the electropolymerization of 2-aminodiphenylamine and fabrication of polymer film modified electrode. Then transition metal of copper is incorporated into the polymer by electrodepositing of Cu(II) from CuCl 2 acidic solution using potentiostatic technique. The electrocatalytic oxidation of methanol was studies by cyclic voltammetry and chronoamperometry methods at the surface of obtained Cu/P(2ADPA)/MCPE. It has been found that in the course of an anodic potential sweep, the electro-oxidation of methanol follows the formation of Cu(III) and is catalyzed by this species through a mediated electron transfer mechanism. The obtained current density for this catalytic oxidation is very high which could be come from high surface area of caused by the P(2ADPA) modification. The effects of various parameters such as the copper loading, scan rate and methanol concentration on the electrocatalytic oxidation of methanol were also investigated at the surface of Cu/P(2ADPA)/MCPE. Finally, using a chronoamperometric method, the catalytic rate constant ( k) for methanol was found to be 0.2 × 10 5 cm 3 mol −1 s −1 that the high k can be ascribed for the fast electron transfer process due to electrode modification.

Kinetic Study of the Electro‐Catalytic Oxidation of Acetaldehyde on Copper Electrode

AbstractElectrocatalytic oxidation of acetaldehyde was investigated on a copper electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry and chronoamperometry techniques as well as steady state polarization measurements. It has been found that in the course of an anodic potential sweep the electro‐oxidation of acetaldehyde follows the formation of Cu(III) and is catalysed by this species through a mediated electron transfer mechanism. A mechanism based on the electrochemical generation of Cu(III) active sites and their subsequent consumption by the acetaldehyde in question was also investigated.

A study of the electrocatalytic oxidation of cyclohexanol on copper electrode

Electrocatalytic oxidation of cyclohexanol was investigated on copper electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry, chronoamperometry techniques as well as steady state polarization measurements. It has been found that in the course of an anodic potential sweep the electro-oxidation of cyclohexanol follows the formation of Cu (III) and is catalysed by this species through a mediated electron transfer mechanism. A mechanism based on the electrochemical generation of Cu (III) active sites and their subsequent consumption by the cyclohexanol in question was also investigated.

Electro-oxidation of methanol on copper in alkaline solution

The electro-oxidation of methanol on copper in alkaline solutions has been studied by the methods of cyclic voltammetry, quasi-steady state polarization and chronoamperometry. It has been found that in the course of an anodic potential sweep the electro-oxidation of methanol follows the formation of Cu III and is catalysed by this species through a mediated electron transfer mechanism. The reaction also continues in the early stages of the reversed cycle until it is stopped by the prohibitively negative potentials. The process is diffusion controlled and the current–time responses follow Cottrellian behavior. The rate constants, turnover frequency, anodic transfer coefficient and the apparent activation energy of the electro-oxidation reaction are reported.