Electron Transfer Rate Constant Research Articles

Nickel-Cobalt Salen Organometallic Complexes Encapsulated in Mesoporous NaA Nanozeolite for Electrocatalytic Quantification of Ascorbic Acid and Paracetamol.

Goal of current study was fabrication of novel voltammetric nanosensor for the synchronize quantification of ascorbic acid (AA) and paracetamol (PAR) by nickel-cobalt salen complexes encapsulated in the supercages of NaA nanozeolite modified carbon paste electrode (NiCoSalenA/CPE). For this purpose, NiCoSalenA nanocomposite was firstly prepared and characterized by various methods. Also, cyclic voltammetry (CV), choronoamperometry (CHA) and differential pulse voltammetry (DPV) were utilized to evaluate performance of the modified electrodes. The effects of pH and modifier amount were considered on the electrochemical oxidation of AA and PAR on the surface of NiCoSalenA/CPE. Results from this method indicated that pH of 3.0 in phosphate buffer solution (0.1M) and 15 wt% of NiCoSalenA nanocomposite in the modified CPE results in the maximum current density. The oxidation signals of AA and PAR was amplified affectively at NiCoSalenA/CPE versus unmodified CPE. The limit of detection (LOD) and linear dynamic range (LDR) for the simultaneous measurement of them were founds to be 0.82 and 2.73-80.70 for AA and 0.51 µM, 1.71-32.50 and 32.50-137.60 µM for PAR, respectively. The catalytic rate constants (kcat) were attained to be 3.73 × 107 and 1.27 × 107 cm3 mol-1s-1 for AA and PAR via CHA method, respectively. Also, the amounts of diffusion coefficient (D) were found to be 1.12 × 10-7 and 1.92 × 10-7 cm2 s-1 for AA and PAR, respectively. The average value of electron transfer rate constant between NiCoSalenA/CPE and PAR was obtained to be 0.016s-1. The NiCoSalen-A/CPE displayed worthy stability, repeatability and extraordinary recovery for simultaneous measurements of AA and PAR. Application of offered sensor was confirmed by quantifying concentrations of AA and PAR in human serum solution as a real sample.

Evaluating Analytical Expressions for Scanning Electrochemical Cell Microscopy (SECCM).

Scanning electrochemical cell microscopy (SECCM) maps the electrochemical activity of a surface with nanoscale resolution using an electrolyte-filled nanopipette. The meniscus at the end of the pipet is sequentially placed at an array of locations across the surface, forming a series of nanometric electrochemical cells where the current-voltage response is measured. Quantitative interpretation of these responses typically employs numerical modeling to solve the coupled equations of transport and electron transfer, which require costly software or self-written code. Expertise and time are required to build and solve numerical models, which must be rerun for each new experiment. In contrast, algebraic expressions directly relate the current response to physical parameters. They are simpler to use, faster to calculate, and can provide greater insight but frequently require simplifying assumptions. In this work, we provide algebraic expressions for current and concentration distributions in SECCM experiments, which are formulated by approximating the pipet and meniscus using 1-D spherical coordinates. Expressions for the current and concentration distributions as a function of experimental parameters and in various conditions (steady state and time dependent, diffusion limited, and including migration) all show excellent agreement with numerical simulations employing a full geometry. Uses of the analytical expressions include determination of expected currents in experiments and quantifying electron-transfer rate constants in SECCM experiments.

Disposable Pencil Lead as an Electrochemical Transducer for Monitoring Catechol in River and Tap Water

A cheap and disposable pencil graphite electrode (PGE) was developed by the incorporation of amine groups (Am-PGE-1). A further improvement in the performance was observed when the aminated electrode (Am-PGE-1) was activated by applying a negative potential scan (Am-PGE-2). The electrochemical transport properties were evaluated through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The Nyquist plot showed a reduced charge transfer resistance value of 24.3 Ω for Am-PGE-2, while it was 95.1 Ω for bare PGE. Thus, Am-PGE-2 was used as a sensing platform for the detection of catechol. It was found that the electrochemical response of catechol oxidation at Am-PGE-2 was twice than the current obtained for bare PGE. Additionally, the effect of pH of the supporting electrolyte and reaction kinetic were studied. The heterogeneous electron transfer rate constant was calculated to be 0.01 s−1. Moreover, CV study revealed that the redox reaction of catechol was a quasi-reversible and diffusion-controlled process. The square wave voltammetry (SWV) technique was applied for the quantitative determination of catechol. The peak current showed a linear dependency on the concentration of catechol from 3 to 150 µM. Furthermore, the analyte could be detected as low as 3.86 µM. Likewise, the sensor demonstrates a good selectivity towards the target analyte than the other possible interfering molecules or ions. Aiming to examine practical applicability, real samples, such as river and household tap water, were tested by using the proposed transducer, and the satisfactory recoveries demonstrate the effectiveness of Am-PGE-2 in real life applications.

Photoinduced electron transfer across the polymer-capped CsPbBr3 interface in a polar medium.

In-situ polymer capping of cesium lead bromide (CsPbBr3) nanocrystals with polymethyl acrylate is an effective approach to improve the colloidal stability in the polar medium and thus extends their use in photocatalysis. The photoinduced electron transfer properties of polymethyl acrylate (PMA)-capped CsPbBr3 nanocrystals have been probed using surface-bound viologen molecules with different alkyl chains as electron acceptors. The apparent association constant (Kapp) obtained for the binding of viologen molecules with PMA-capped CsPbBr3 was 2.3 × 107 M-1, which is an order of magnitude greater than that obtained with oleic acid/oleylamine-capped CsPbBr3. Although the length of the alkyl chain of the viologen molecule did not show any impact on the electron transfer rate constant, it influenced the charge separation efficiency and net electron transfer quantum yield. Viologen moieties with a shorter alkyl chain length exhibited a charge separation efficiency of 72% compared with 50% for the longer chain alkyl chain length viologens. Implications of polymer-capped CsPbBr3 perovskite nanocrystals for carrying out photocatalytic reduction in the polar medium are discussed.

Characterization of the solid/electrolyte interphase at hard carbon anodes via scanning (electrochemical) probe microscopy

Nanostructural properties impacting ion and electron transfer processes at the electrolyte-electrode interface are of pivotal importance for the overall performance of rechargeable batteries such as sodium-ion batteries (SIBs). Compared to lithium-ion batteries (LIBs), less is known about the solid electrolyte interphase (SEI) formation at the negative electrode of SIBs. In this contribution, we present conductive atomic force microscopy (AFM), AFM-based nanomechanical mappings and AFM-scanning electrochemical microscopy (AFM-SECM) measurements addressing the interphase formation on hard carbon (HC) providing insight on the effect of additives like 4-fluoro-1,3-dioxolan-2-one (FEC) and the potential cumulative impact of the electrochemical and nanomechanical properties. The additive strongly influences the adhesion forces, whereas in contrast the Young's modulus appears significantly increased after cycling independent of an added additive to the electrolyte solution. AFM-SECM images before and after cycling clearly indicate the formation of an electrically insulating interphase layer. In addition, the effective heterogeneous rate constant of electron transfer was determined at single HC particles.

Room-Temperature Ionic Liquid Cation Effects on the Structure and Stability of Anionic Lanthanide Complexes.

Room-temperature ionic liquids (RTILs) are a subset of molten salts that are liquids at room temperature and may offer an elegant, low-temperature route to predicting the properties of solvated metal complexes in their high-temperature analogues. This work studied the chemistry of chloride anion-containing RTILs to determine their similarity to inorganic molten chloride salts. The behaviors of complexes of Mn, Nd, and Eu were evaluated in a variety of chloride RTILs by absorption spectrophotometry and electrochemistry to elucidate trends in cation effects on the coordination geometry and redox properties of the solvated species. Spectrophotometric data indicated the metals are present as anionic complex (e.g., MnCl42- and NdCl63-) analogous to those observed in molten chloride salts. Strongly polarizing, charge-dense RTIL cations induced distortions to the symmetry of these complexes, resulting in lower oscillator strengths and red-shifted energies for the observed transitions. Cyclic voltammetry experiments were used to characterize the Eu(III/II) redox couple producing diffusion coefficients on the order of 10-8 cm2 s-1 and heterogeneous electron transfer rate constants ranging between 6 × 10-5 and 2 × 10-4 cm s-1. The E1/2 potentials for Eu(III/II) were also found to shift positively with increasing cation polarization power, stabilizing the Eu(II) oxidation state by removing electron density from the metal center over chloride bond networks. Both the optical spectrophotometry and electrochemistry results suggest that the polarization strength of an RTIL cation plays a major role in the geometry and stability of a metal complex.

Voltammetric Evidence of Proton Transport through the Sidewalls of Single-Walled Carbon Nanotubes.

Understanding ion transport in solid materials is crucial in the design of electrochemical devices. Of particular interest in recent years is the study of ion transport across 2-dimensional, atomically thin crystals. In this contribution, we describe the use of a host-guest hybrid redox material based on polyoxometalates (POMs) encapsulated within the internal cavities of single-walled carbon nanotubes (SWNTs) as a model system for exploring ion transport across atomically thin structures. The nanotube sidewall creates a barrier between the redox-active molecules and bulk electrolytes, which can be probed by addressing the redox states of the POMs electrochemically. The electrochemical properties of the {POM}@SWNT system are strongly linked to the nature of the cation in the supporting electrolyte. While acidic electrolytes facilitate rapid, exhaustive, reversible electron transfer and stability during redox cycling, alkaline-salt electrolytes significantly limit redox switching of the encapsulated species. By "plugging" the {POM}@SWNT material with C60-fullerenes, we demonstrate that the primary mode of charge balancing is proton transport through the graphenic lattice of the SWNT sidewalls. Kinetic analysis reveals little kinetic isotope effect on the standard heterogeneous electron transfer rate constant, suggesting that ion transport through the sidewalls is not rate-limiting in our system. The unique capacity of protons and deuterons to travel through graphenic layers unlocks the redox chemistry of nanoconfined redox materials, with significant implications for the use of carbon-coated materials in applications ranging from electrocatalysis to energy storage and beyond.

How Clustered DNA Damage Can Change the Electronic Properties of ds-DNA-Differences between GAG, GAOXOG, and OXOGAOXOG.

Every 24 h, roughly 3 × 1017 incidences of DNA damage are generated in the human body as a result of intra- or extra-cellular factors. The structure of the formed lesions is identical to that formed during radio- or chemotherapy. Increases in the clustered DNA damage (CDL) level during anticancer treatment have been observed compared to those found in untreated normal tissues. 7,8-dihydro-8-oxo-2'-deoxyguanosine (OXOG) has been recognized as the most common lesion. In these studies, the influence of OXOG, as an isolated (oligo-OG) or clustered DNA lesion (oligo-OGOG), on charge transfer has been analyzed in comparison to native oligo-G. DNA lesion repair depends on the damage recognition step, probably via charge transfer. Here the electronic properties of short ds-oligonucleotides were calculated and analyzed at the M062x/6-31++G** level of theory in a non-equilibrated and equilibrated solvent state. The rate constant of hole and electron transfer according to Marcus' theory was also discussed. These studies elucidated that OXOG constitutes the sink for migrated radical cations. However, in the case of oligo-OGOG containing a 5'-OXOGAXOXG-3' sequence, the 3'-End OXOG becomes predisposed to electron-hole accumulation contrary to the undamaged GAG fragment. Moreover, it was found that the 5'-End OXOG present in an OXOGAOXOG fragment adopts a higher adiabatic ionization potential than the 2'-deoxyguanosine of an undamaged analog if both ds-oligos are present in a cationic form. Because increases in CDL formation have been observed during radio- or chemotherapy, understanding their role in the above processes can be crucial for the efficiency and safety of medical cancer treatment.

3D printed electrodes design and voltammetric response

The limiting aspects in the voltammetric response of 3D printed electrodes is thoroughly investigated with numerical simulations and new 3D printed electrode designs. Severe diffusion limitations, resulting from a recessed electrode geometry, is found in a commonly used 3D printed electrode and electrochemical cell design, impeding the investigation of electron transfer kinetics at these electrodes by classical methods, such as Nicholson's, widely used on this and similarly mass transport-limited designs. A new 3D printed electrode design, an inlaid disk (non-recessed) geometry, is used to investigate the voltammetric response of printed electrodes in bulk solution, i.e., without mass transport limitations. At this condition, it is clear that the voltammetric response is limited by contact resistance, arising from the printed material low electrical conductivity. Gold modified electrodes, deliberately designed with different contact resistances, highlight the resistive behavior, with quasi-reversible voltammetric profiles. This contrasts with the common assumption of a voltammetric response limited by finite electron kinetics. Electron transfer rate constants (k0) and transfer coefficients (α) for electrodes with and without surface modifications are calculated from experimental data using a modified Butler-Volmer equation, incorporating ohmic losses. The reported k0 and α values are independent of electrode geometry or printing parameters, unlike the observable rate constant usually reported for 3D printed electrodes. By accounting for contact resistance and finite electron transfer kinetics, cathodic and anodic peak potentials and currents of voltammograms recorded with 3D printed electrodes are predicted before printing, allowing electrode designs to be optimized in the virtual space.

Programmed Control of Fluorescence Blinking Patterns based on Electron Transfer in DNA.

Fluorescence imaging uses changes in the fluorescence intensity and emission wavelength to analyze multiple targets simultaneously. To increase the number of targets that can be identified simultaneously, fluorescence blinking can be used as an additional parameter. To understand and eventually control blinking, we used DNA as a platform to elucidate the processes of electron transfer (ET) leading to blinking, down to the rate constants. With a fixed ET distance, various blinking patterns were observed depending on the DNA sequence between the donor and acceptor units of the DNA platform. The blinking pattern was successfully described with a combination of ET rate constants. Therefore, molecules with various blinking patterns can be developed by tuning ET. It is expected that the number of targets that can be analyzed simultaneously will increase by the power of the number of blinking patterns.

Electrochemistry at Back-Gated, Ultrathin ZnO Electrodes: Field-Effect Modulation of Heterogeneous Electron Transfer Rate Constants by 30× with Enhanced Gate Capacitance.

We report steady-state voltammetry of outer-sphere redox species at back-gated ultrathin ZnO working electrodes in order to determine electron transfer rate constants kET as a function of independently controlled gate bias, VG. We demonstrate that kET can be modulated as much as 30-fold by application of VG ≤ 8 V. The key to this demonstration was integrating the ultrathin (5 nm) ZnO on a high dielectric constant (k) insulator, HfO2 (30 nm), which was grown on a Pd metal gate. The high-k HfO2 dramatically decreased the required VG values and increased the gate-induced charge in ZnO compared to previous studies. Importantly, the enhanced gating power of the Pd/HfO2/ZnO stack meant it was possible to observe a nonmonotonic dependence of kET on VG, which reflects the inherent density of redox acceptor states in solution. This work adds to the growing body of literature demonstrating that electrochemical kinetics (i.e., rate constants and overpotentials) at ultrathin working electrodes can be tuned by VG, independent of the conventional electrochemical working electrode potential.

Effect of adsorption of pyocyanin on the electron transfer rate at the interface of a glassy carbon electrode

Redox mediators (RM) are an alternative to improve the performance of microbial electrochemical systems (MES) as they help significantly to develop the indirect electron transfer. However, their use is limited when the redox processes between the RM and the electrode surface are not thoroughly understood. The adsorption, the intermolecular interactions with the electrode, and the effects on charge transfer kinetics are important issues in MES such as microbial sensors, microbial electrosynthesis or microbial fuel cells, but are rarely analyzed. Pyocyanin, considered an RM, may present these features due to its chemical structure. Today, the electrochemical studies indicate that pyocyanin can presents adsorption processes on glassy carbon electrodes. However, the effects of adsorption on electron transfer rate and changes as a function of pyocyanin concentration have not yet been studied. Therefore, this work presents an electrochemical study of pyocyanin to determine the effect of concentration and adsorption on the electron transfer rate at a glassy carbon electrode. Analysis of the electrochemical profiles obtained by cyclic voltamperometry (CV) indicates that there is an effect of concentration (C*) on the heterogeneous electron transfer rate constant (k0) since the criterion ΔEp varies as a function of C*. In addition, the peak proportionality parameter Ipa/Ipc and the voltamperometric function Ip/v½ help deduct the adsorption to the electrode. Experimental data obtained by chronocoulometry (CC) and CV, indicate that k0 = 5.7 × 1011 m/s and Rct = 3.40 × 10−16 Ω under the C* = 0.14 mM condition, while k0 = 1.10 × 103 m/s and Rct = 1.60 × 10−7 Ω under the C* = 0.49 mM condition. The differences in k0 and Rct values at different values of C* are due to an accumulation of pyocyanin on the electrode surface in the inner Helmholtz plane (IHP), preventing the electron transfer of bulk-dissolved pyocyanin molecules present in the outer Helmholtz plane (OHP) region. The varying values of α, indicate that a part of the energy of the redox reaction could be employed for the adsorption processes. As for the interactions at the electrode, the values of the Laviron parameter (ν'gθT) indicate that attraction interactions between the pyocyanin molecules and the electrode dominate, since the values of ν'gθT are higher than 0. The results of this study will provide a comprehensive understanding of the redox cycle of pyocyanin. The information will be useful for the future development of electrochemical-microbial systems since that the interactions mediator-electrode may be an operational variable to facilitate their practical applications in environmental, sensing and electrosynthesis areas.

Direct electrochemical detection of extracellular nitric oxide in Arabidopsis protoplast based on cytochrome P450 55B1 biosensor

Cytochrome P450 55B1(CYP55B1) from Chlamydomonas reinhardtii reduces nitric oxide (NO) to dinitrogen oxide (N2O) with the electron supply from NAD(P)H in vivo. Here a novel nitric oxide biosensor was developed by immobilized CYP55B1 on the surface of pyrolytic graphite electrode (PGE) by cross-linking with glutaraldehyde (GA) and bovine serum albumin (BSA). The direct electrochemistry of CYP55B1 was realized with the redox peak potential of −0.355 V and −0.385 V and the catalytic reduction peak of NO by CYP55B1 is at −0.85 V at the scan rate of 0.5 V S−1 in pH 7.0 phosphate buffer. The apparent coverage (Γ = 1.43 × 10−11 mol cm−2), the electron transfer rate constant (ks = 17.39 s−1) and apparent affinity to NO (Kmapp = 11.64 nM) of CYP55B1 in GA/BSA film were obtained. The catalytic mechanism of CYP55B1 towards NO with NADH was examined by the biosensor. The linear range of NO detection was investigated by differential pulse voltammetry with the results of 5–50 nM and the detection limit of 0.5 nM (S/N = 3). The selectivity and stability of the electrochemical biosensor were investigated. Furthermore, the CYP55B1electrochemical biosensor was applied to monitor NO release from Arabidopsis protoplasts with the average content of 0.848 fmol per cell under anaerobic condition.

Shungite (Mineralized Carbon) as a Promising Electrode Material for Electroanalysis.

In this study, two different types of amorphous carbonaceous Precambrian rock, classified as noble elite shungite and black raw shungite, were tested as possible electrode materials of natural origin. Both types were machined into cylindrical shapes to form the corresponding solid electrodes and their physicochemical and electrochemical properties were compared with the standard glassy carbon electrode (GCE). The raw stones were first subjected to microscopic imaging by using scanning electron microscopy and energy-dispersive X-ray spectroscopy, both of which indicated significant differences in their morphology and in the content of impurities. An electrode prototype manufactured from noble elite shungite (EShE) with a carbon content of about 94% (w/w) has offered a very satisfactory electrochemical performance with a nearly identical heterogeneous electron-transfer rate constant of 7.8 × 10-3 cm s-1 for ferro/ferricyanide redox couple, a slightly narrower potential range (~2.1 V) and a relatively low double-layer capacitance (of ca. 50 μF), resulting in low background currents comparable to those at the GCE. In contrast, the second electrode based on black raw shungite (BShE) with a carbon content of ca. 63% (w/w) exhibited markedly worse electrochemical properties and more than four times higher double-layer capacitance, both of which were probably due to the presence of poorly conductive impurities. The whole study has been completed with three different examples of electroanalytical applications, revealing that the first type, EShE, is a more suitable material for the preparation of electrodes and may represent a cheap alternative to commercially marketed products.

Incorporation of Cu into Goethite Stimulates Oxygen Activation by Surface-Bound Fe(II) for Enhanced As(III) Oxidative Transformation.

The dark production of reactive oxygen species (ROS) coupled to biogeochemical cycling of iron (Fe) plays a pivotal role in controlling arsenic transformation and detoxification. However, the effect of secondary atom incorporation into Fe(III) oxyhydroxides on this process is poorly understood. Here, we show that the presence of oxygen vacancy (OV) as a result of Cu incorporation in goethite substantially enhances the As(III) oxidation by Fe(II) under oxic conditions. Electrochemical and density functional theory (DFT) evidence reveals that the electron transfer (ET) rate constant is enhanced from 0.023 to 0.197 s-1, improving the electron efficiency of the surface-bound Fe(II) on OV defective surfaces. The cascade charge transfer from the surface-bound Fe(II) to O2 mediated by Fe(III) oxyhydroxides leads to the O-O bond of O2 stretching to 1.46-1.48 Å equivalent to that of superoxide (•O2-), and •O2- is the predominant ROS responsible for As(III) oxidation. Our findings highlight the significant role of atom incorporation in changing the ET process on Fe(III) oxyhydroxides for ROS production. Thus, such an effect must be considered when evaluating Fe mineral reactivity toward changing their surface chemistry, such as those noted here for Cu incorporation, which likely determines the fates of arsenic and other redox sensitive pollutants in the environments with oscillating redox conditions.

Spontaneous Intercluster Electron Transfer X2– + X0 → 2 X– (X = PtAu24(SCnH2n+1)18) in Solution: Promotion by Long Alkyl Chains

In this work, we systematically investigated the ligand effects on spontaneous electron transfer (ET) between alkanethiolate-protected metal clusters in solution. The donor and acceptor clusters used were [PtAu24(SCnH2n+1)18]2- (8e(Cn)) and [PtAu24(SCmH2m+1)18]0 (6e(Cm)) (n, m = 2-16), which have icosahedral Pt@Au12 cores with eight and six valence electrons, respectively. The ET rate constant (kET) from 8e(Cn) to 6e(Cm) in benzene exhibited a novel turnover behavior as a function of the total chain length n + m: the kET decreased with n + m in the range of 4-12, whereas it monotonically increased with n + m in the range of 12-32. Electrospray ionization mass spectrometry of the mixture of 8e(Cn) and 6e(Cm) detected the dimer complex 8e(Cn)·6e(Cm), the relative population of which increased with n + m. The activation energy (Ea), determined based on the Arrhenius plots for n = m, monotonically decreased with n (≥ 6). Based on these results, we proposed that the promotion of ET by longer alkanethiolates was ascribed to two effects on the key intermediate 8e(Cn)·6e(Cm): (1) elongation of the lifetime and (2) the contraction of the distance between 8e(Cn) and 6e(Cm) due to the stronger van der Waals interaction between the longer alkyl chains. Such alkyl-chain-promoted ET is specific to ultrasmall clusters in solution because a nonuniform ligand layer could be formed due to the large curvature of the cluster core.

Elucidating Electrocatalytic Oxygen Reduction Kinetics via Intermediates by Time-Dependent Electrochemiluminescence.

Facile evaluation of oxygen reduction reaction (ORR) kinetics for electrocatalysts is critical for sustainable fuel-cell development and industrial H2 O2 production. Despite great success in ORR studies using mainstream strategies, such as the membrane electrode assembly, rotation electrodes, and advanced surface-sensitive spectroscopy, the time and spatial distribution of reactive oxygen species (ROS) intermediates in the diffusion layer remain unknown. Using time-dependent electrochemiluminescence (Td-ECL), we report an intermediate-oriented method for ORR kinetics analysis. Owing to multiple ultrasensitive stoichiometric reactions between ROS and the ECL emitter, except for electron transfer numbers and rate constants, the potential-dependent time and spatial distribution of ROS were successfully obtained for the first time. Such exclusively uncovered information would guide the development of electrocatalysts for fuel cells and H2 O2 production with maximized activity and durability.

Elucidating Electrocatalytic Oxygen Reduction Kinetics via Intermediates by Time‐Dependent Electrochemiluminescence

AbstractFacile evaluation of oxygen reduction reaction (ORR) kinetics for electrocatalysts is critical for sustainable fuel‐cell development and industrial H2O2 production. Despite great success in ORR studies using mainstream strategies, such as the membrane electrode assembly, rotation electrodes, and advanced surface‐sensitive spectroscopy, the time and spatial distribution of reactive oxygen species (ROS) intermediates in the diffusion layer remain unknown. Using time‐dependent electrochemiluminescence (Td‐ECL), we report an intermediate‐oriented method for ORR kinetics analysis. Owing to multiple ultrasensitive stoichiometric reactions between ROS and the ECL emitter, except for electron transfer numbers and rate constants, the potential‐dependent time and spatial distribution of ROS were successfully obtained for the first time. Such exclusively uncovered information would guide the development of electrocatalysts for fuel cells and H2O2 production with maximized activity and durability.

Homogeneous Carbon Dot-Anchored Fe(III) Catalysts with Self-Regulated Proton Transfer for Recyclable Fenton Chemistry.

Fenton chemistry has been widely studied in a broad range from geochemistry, chemical oxidation to tumor chemodynamic therapy. It was well established that Fe3+/H2O2 resulted in a sluggish initial rate or even inactivity. Herein, we report the homogeneous carbon dot-anchored Fe(III) catalysts (CD-COOFeIII) wherein CD-COOFeIII active center activates H2O2 to produce hydroxyl radicals (•OH) reaching 105 times larger than that of the Fe3+/H2O2 system. The key is the •OH flux produced from the O-O bond reductive cleavage boosting by the high electron-transfer rate constants of CD defects and its self-regulated proton-transfer behavior probed by operando ATR-FTIR spectroscopy in D2O and kinetic isotope effects, respectively. Organic molecules interact with CD-COOFeIII via hydrogen bonds, promoting the electron-transfer rate constants during the redox reaction of CD defects. The antibiotics removal efficiency in the CD-COOFeIII/H2O2 system is at least 51 times large than the Fe3+/H2O2 system under equivalent conditions. Our findings provide a new pathway for traditional Fenton chemistry.

A vertically paired electrode for redox cycling and its application to immunoassays.

An electrochemical immunoassay based on the redox cycling method was presented using vertically paired electrodes (VPEs), which were fabricated using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as an electrode material and parylene-C as a dielectric layer. For the application to immunoassays, different electrochemical properties of PEDOT:PSS were analyzed for the redox reaction of 3,3',5,5'-tetramethylbenzidine (TMB, the chromogenic substrate for enzyme-immunoassays) at different pH conditions, including the conductivity (σ), electron transfer rate constant (kapp), and double-layer capacitance (Cdl). The influencing factors on the sensitivity of redox cycling based on VPE based on PEDOT:PSS were analyzed for the redox reaction of TMB, such as the electrode gap and number of electrode pairs. Computer simulation was also performed for the redox cycling results based on VPEs, which had limitations in fabrication, such as VPEs with an electrode gap of less than 100 nm and more than five electrode pairs. Finally, the redox cycling based on VPE was applied to the medical diagnosis of human hepatitis-C virus (hHCV) using a commercial ELISA kit. The sensitivity of the redox cycling method for the medical diagnosis of hHCV was compared with conventional assay methods, such as TMB-based chromogenic detection, luminol-based chemiluminescence assay, and a rapid test kit (lateral flow immunoassay).