Heterogeneous Electron Transfer Rate Research Articles

Well-Dispersive Polypyrrole and MoSe2 Embedded in Multiwalled Carbon Nanotube@Reduced Graphene Oxide Nanoribbon Electrocatalysts as the Efficient Counter Electrodes in Rigid and Plastic Dye-Sensitized Solar Cells

In this study, a core–shell structured multiwall carbon nanotube@reduced graphene oxide nanoribbon (MWCNT@rGNR) was prepared by the facile unzipping of MWCNTs with mild conditions to synthesize the composites of the MWCNT@rGNR and polypyrrole (PPy) or MoSe2, which were used as the electrocatalysts for the counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The transmission electron microscopy image of the MWCNT@rGNR showed a graphene sheet structure found on both sides of the MWCNTs, indicating a central core of the MWCNTs and its shell of the rGNR. The obtained MWCNT@rGNR functionalized with PPy or MoSe2 was envisaged to have the advantages of both component, that are the unique electronic structure of the MWCNT@rGNR and the synergistic effects of conductive PPy or electrocatalytically active MoSe2, respectively. The DSSCs with PPy/MWCNT@rGNR0.3 and MoSe2/MWCNT@rGNR0.3 showed comparable efficiency (photoelectric conversion efficiency, PCE = 7.48 and 8.34%, respectively), short-circuit current (Isc = 17.97 and 17.11 mA cm–2, respectively), and open-circuit voltage (Voc = 0.80 and 0.84 V, respectively) without any loss of the fill factor (FF = 0.52 and 0.58, respectively) as compared to the cell fabricated using a standard Pt electrode. The PCE of a standard Pt CE was 7.70% with an Isc of 16.09 mA cm–2, Voc of 0.76 V, and FF of 0.63. According to the results of the electrochemical measurements, composites with PPy or MoSe2 showed better electrocatalytic activity, higher redox-active surface area, and extremely large heterogeneous electron transfer rate constant. The plastic devices assembled with the PPy/MWCNT@rGNR0.3 and MoSe2/MWCNT@rGNR0.3 coated on a flexible plastic substrate (indium tin oxide-coated polyethylene naphthalate; ITO/PEN)exhibited impressive PCEs of 4.61 and 5.25%, respectively, comparable to those coated on the rigid fluorine-doped tin oxide glass substrate. This work presented a facile low-temperature method to fabricate high-performance MWCNT@rGNR composite-based CEs to make them applicable to large-scale plastic DSSCs.

2D MXene-Based Biosensing: A Review.

MXene emerged as decent 2D material and has been exploited for numerous applications in the last decade. The remunerations of the ideal metallic conductivity, optical absorbance, mechanical stability, higher heterogeneous electron transfer rate, and good redox capability have made MXene a potential candidate for biosensing applications. The hydrophilic nature, biocompatibility, antifouling, and anti-toxicity properties have opened avenues for MXene to perform in vitro and in vivo analysis. In this review, the concept, operating principle, detailed mechanism, and characteristic properties are comprehensively assessed and compiled along with breakthroughs in MXene fabrication and conjugation strategies for the development of unique electrochemical and optical biosensors. Further, the current challenges are summarized and suggested future aspects. This review article is believed to shed some light on the development of MXene for biosensing and will open new opportunities for the future advanced translational application of MXene bioassays.

Polypyrrole-MXene supported gold nanoparticles for the trace-level detection of nitrofurantoin

High usage of nitrofurantoin (NFT) has resulted in unacceptable levels in water and foods with negative impacts on animals, humans, and surrounding ecosystems. The accurate and ultra-low sensing of NFT in waterways presents a significant societal challenge. To address this issue, gold nanoparticles (AuNPs) were integrated into polypyrrole (PPy) on Titanium carbide MXene (Ti3C2Tx) using a simple sonochemical route involving the in-situ, oxidant-free polymerization of pyrrole monomer in the presence of HAuCl4. The AuNP-PPy-MXene composite produced was used to modify a glassy carbon electrode (GCE) to construct an ultrasensitive electrochemical sensor for the direct and on-site sensing of NFT in complex samples. Electrochemical impedance spectroscopy (EIS) investigations showed Au-PPy-MXene-GCEs had a heterogeneous electron transfer rate constant (k°) of 1.03 × 10-2 cm s−1 and a lower charge-transfer resistance (Rct = 73 Ω) than Au-MXene, Au-PPy, and PPy-MXene GCEs. In addition, Au-PPy-MXene-GCE exhibited better electrocatalytic reduction performance at a higher cathodic signal intensity and a lower reduction overpotential of −0.38 V (vs Ag/AgCl) for NFT than Au-MXene, Au-PPy, and PPy-MXene GCEs. The fabricated sensor had a wide linear range from 6 to 172 nM (measured at −0.38 V vs Ag/AgCl), an ultra-low detection limit (LOD) of 0.26 nM (at S/N = 3), and an excellent sensitivity of 6.4121 μA nM−1 cm−2 for the electroreduction of NFT. Au-PPy-MXene-GCE also provided specific and accurate amperometric analysis for NFT in the presence of cationic, anionic, and other potentially interfering pesticides. The practicality of the sensor was tested to quantify NFT at trace levels in complex matrices (honey, pond water, and hospital wastewater samples), and achieved recoveries ranging between 97.6 % and 113.2 % and a relative standard deviation of<3.6 %.

Field-Effect Tuning of Electrochemistry at 2D Semiconductor Electrodes: Charge Transfer Kinetics Can be Modulated with a Back Gate Voltage

Semiconductor electrodes are widely used in electrocatalytic reactions. The ability to improve and modulate the heterogeneous charge transfer kinetics on semiconducting electrodes is a major challenge for the electrochemical application of these materials. Instead of changing the electronic occupation of the semiconductor by chemical doping, we adopt an electronic method to modulate band edge alignment and solution electrochemistry at 2D ZnO working electrodes.In our approach, a field-effect transistor with ultrathin ZnO semiconductor (3-5 nm) is fabricated, the heart of which is a metal-insulator-semiconductor (MIS) stack. A high-dielectric-constant material (HfO2) is used as the insulator to realize low-voltage tunability of the device. The ZnO layer of the device functions as the working electrode (WE) for electrochemical reactions. By applying a back gate voltage to this MIS field-effect transistor, charge carriers are electrostatically induced and the ZnO band edges shift at the front face of the ZnO in contact with electrolyte. These effects can be exploited to manipulate the charge transfer kinetics on the ZnO electrode at a given electrode potential. We demonstrate this by focusing on outer-sphere redox chemistry. In order to eliminate mass transfer effects, microfluidic flow cells are coupled to the ZnO devices. Steady state kinetic analysis is carried out to extract the electron transfer rate constant of the redox process as a function of both electrochemical and back gate potentials. The heterogeneous electron transfer rate can be tuned by over an order of magnitude using the back gate voltage. The work demonstrates that a back gate provides another degree of freedom in determining electrochemical reaction kinetics at ultrathin semiconductor working electrodes. The method also opens possibilities for control over a wider range of semiconductor electrochemistry, such as electrocatalytic reactions. Figure 1

A machine learning-based multimodal electrochemical analytical device based on eMoSx-LIG for multiplexed detection of tyrosine and uric acid in sweat and saliva

Multiplexed detection of biomolecules is of great value in various fields, from disease diagnosis to food safety and environmental monitoring. However, accurate and multiplexed analyte detection is challenging to achieve in mixtures using a single device/material. In this paper, we demonstrate a machine learning (ML)-powered multimodal analytical device based on a single sensing material made of electrodeposited molybdenum polysulfide (eMoSx) on laser induced graphene (LIG) for multiplexed detection of tyrosine (TYR) and uric acid (UA) in sweat and saliva. Electrodeposition of MoSx shows an increased electrochemically active surface area (ECSA) and heterogeneous electron transfer rate constant, k0. Features are extracted from the electrochemical data in order to train ML models to predict the analyte concentration in the sample (both singly spiked and mixed samples). Different ML architectures are explored to optimize the sensing performance. The optimized ML-based multimodal analytical system offers a limit of detection (LOD) that is two orders of magnitude better than conventional approaches which rely on single peak analysis. A flexible and wearable sensor patch is also fabricated and validated on-body, achieving detection of UA and TYR in sweat over a wide concentration range. While the performance of the developed approach is demonstrated for detecting TYR and UA using eMoSx-LIG sensors, it is a general analytical methodology and can be extended to a variety of electrochemical sensors to enable accurate, reliable, and multiplexed sensing.

Epitaxial Self-Assembly of Interfaces of 2D Metal-Organic Frameworks for Electroanalytical Detection of Neurotransmitters.

This paper identifies the electrochemical properties of individual facets of anisotropic layered conductive metal–organic frameworks (MOFs) based on M3(2,3,6,7,10,11-hexahydroxytriphenylene)2 (M3(HHTP)2) (M = Co, Ni). The electroanalytical advantages of each facet are then applied toward the electrochemical detection of neurochemicals. By employing epitaxially controlled deposition of M3(HHTP)2 MOFs on electrodes, the contribution of the basal plane ({001} facets) and edge sites ({100} facets) of these MOFs can be individually determined using electrochemical characterization techniques. Despite having a lower observed heterogeneous electron transfer rate constant, the {001} facets of the M3(HHTP)2 systems prove more selective and sensitive for the detection of dopamine than the {100} facets of the same MOF, with the limit of detection (LOD) of 9.9 ± 2 nM in phosphate-buffered saline and 214 ± 48 nM in a simulated cerebrospinal fluid. Langmuir isotherm studies accompanied by all-atom MD simulations suggested that the observed improvement in performance and selectivity is related to the adsorption characteristics of analytes on the basal plane versus edge sites of the MOF interfaces. This work establishes that the distinct crystallographic facets of 2D MOFs can be used to control the fundamental interactions between analyte and electrode, leading to tunable electrochemical properties by controlling their preferential orientation through self-assembly.

Electron Transfer in Binary Hemin-Modified Alkanethiol Self-Assembled Monolayers on Gold: Hemin's Lateral and Interfacial Interactions.

Orientated coupling of redox enzymes to electrodes by their reconstitution onto redox cofactors, such as hemin conjugated to self-assembled monolayers (SAMs) formed on the electrodes, poses the requirements for a SAM design enabling reconstitution. We show that the kinetics of electron transfer (ET) in binary SAMs of alkanethiols on gold composed of in situ hemin-conjugated 11-amino-1-undecanethiol (AUT) and diluting OH-terminated alkanethiols with 11, 6, and 2 methylene groups (MC11OH, MC6OH, and MC2OH) depends on both the SAM composition and surface density of hemin, Γheme. In AUT/MC11OH SAMs composed of equal linker/diluent lengths, the heterogeneous ET rate constant ks decreased with the Γheme and varied between 70 and 500 s-1. For shorter diluents, the ks of 245-330 s-1 (C6) and 300-340 s-1 (C2) showed a little (if any) Γheme dependence. In AUT/MC11OH SAMs, the increasing Γheme resulted in the steric crowding of hemin species and their neighboring lateral interactions in the plane of hemin localization, affecting the potential distribution at the SAM/electrode interface and inducing local electrostatic effects interfering with hemin oxidation. In AUT/MC6OH and AUT/MC2OH SAMs, hemin discharged at the plane of the closest approach to the gold surface, equal to the diluent length and permeable to electrolyte ions, which lessened those effects. All studied binary SAMs provided steric hindrance for protein reconstitution on the hemin cofactor conjugated to the extended AUT linker. Further use of SAM-modified electrodes with the covalently attached hemin as interfaces for heme proteins' reconstitution should consider SAMs with loosely dispersed redox centers terminating more rigid molecular wires. Such wires place hemin at fixed distances from the electrode surface and thus ensure the interfacial properties required for the effective on-surface reconstitution of proteins and enzymes.

Cyclic voltammetric studies of electron transfer reactions associated with bioactive iron–KA complexation at different biological pH

This study explores electrochemical interactions of a pharmaceutical drug, kojic acid (5-hydroxy-2-hydroxymethyl-4 H-pyran-4-one, KA), with bioactive iron Fe(III) at different pH systems by using cyclic voltammetric technique. For this study, buffers relevant to physiological pH of blood and digestive system have been selected. Bioactive iron was found to form an electroactive complex [Fe(III)L3] in the presence of KA at all studied pH, whereas electrochemical behavior of KA was also changed by complex formation. This electrochemical investigation reveals that under the experimental conditions, [Fe(III)L3] complex undergoes a diffusion controlled, one electron redox process that is quasi-reversible in nature. It was also found that [Fe(III)L3] complex undergoes coupled chemical reaction according to EC (an electron transfer reaction followed by a chemical reaction) mechanism, and this interaction is pH dependent. Modified Nicholson and Shain, Gileadi, and Kochi methods were used to determine standard heterogeneous electron transfer rate constant ( k0) of [Fe(III)L3] complex. It was found to be in the range of 10−3 to 10−5 cm/s.

Fabrication of an Organofunctionalized Talc-like Magnesium Phyllosilicate for the Electrochemical Sensing of Lead Ions in Water Samples.

A talc-like magnesium phyllosilicate functionalized with amine groups (TalcNH2), useful as sensor material in voltammetry stripping analysis, was synthesized by a sol–gel-based processing method. The characterizations of the resulting synthetic organoclay by scanning electron microscopy (SEM), X-ray diffraction, N2 sorption isotherms (BET method), Fourier transform infrared spectroscopy (FTIR), CHN elemental analysis and UV–Vis diffuse reflectance spectroscopy (UV–Vis-DRS) demonstrated the effectiveness of the process used for grafting of amine functionality in the interlamellar clay. The results indicate the presence of organic moieties covalently bonded to the inorganic lattice of talc-like magnesium phyllosilicate silicon sheet, with interlayer distances of 1568.4 pm. In an effort to use a talc-like material as an electrode material without the addition of a dispersing agent and/or molecular glue, the TalcNH2 material was successfully dispersed in distilled water in contrast to natural talc. Then, it was used to modify a glassy carbon electrode (GCE) by drop coating. The characterization of the resulting modified electrode by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) revealed its charge selectivity ability. In addition, EIS results showed low charge transfer resistance (0.32 Ω) during the electro-oxidation of [Fe(CN)6]3−. Kinetics studies were also performed by EIS, which revealed that the standard heterogeneous electron transfer rate constant was (0.019 ± 0.001) cm.s−1, indicating a fast direct electron transfer rate of [Fe(CN)6]3− to the electrode. Using anodic adsorptive stripping differential pulse voltammetry (DPV), fast and highly sensitive determination of Pb(II) ions was achieved. The peak current of Pb2+ ions on TalcNH2/GCE was about three-fold more important than that obtained on bare GCE. The calculated detection and quantification limits were respectively 7.45 × 10−8 M (S/N = 3) and 24.84 × 10−8 M (S/N 10), for the determination of Pb2+ under optimized conditions. The method was successfully used to tap water with satisfactory results. The results highlight the efficient chelation of Pb2+ ions by the grafted NH2 groups and the potential of talc-like amino-functionalized magnesium phyllosilicate for application in electrochemical sensors.

Synthesis and Application of Heteroatom-Doped Graphite as the Electrode Material: Influences of Defect Density and Heteroatom on Heterogeneous Electron Transfer Rate

Thermal method was applied for the synthesis of O-doped and N-doped graphite materials using melamine and glucose as the sources of O and N, respectively. Graphite paste electrodes were prepared with the synthesized O-doped and N-doped graphite materials. The route of synthesis was explored by cyclic voltammetry using the fabricated paste electrodes and [Fe(CN)6]3–/4– as a simple outer-sphere redox probe. The results of structural and electrochemical investigations clearly showed that doping of O and N as heteroatom in the synthesized materials not only increased the defect density, the ratio of edge to basal plane sites, of graphite materials but also enhanced the rate of heterogeneous electron transfer at their corresponding paste electrodes. The heterogeneous electron transfer rate constant (k0) for [Fe(CN)6]3–/4– at the fabricated O-doped and N-doped graphite paste electrodes were about 51 and 46 times that observed for graphite paste electrode, respectively. The values of electroactive surface area calculated for both O-doped and N-doped graphite materials were about 5 times that obtained for graphite paste electrode. Thereafter, electrochemical behaviors of isoniazid, ascorbic acid, dopamine, and uric acid as the models of biologically relevant molecules were investigated at the prepared heteroatom-doped graphite paste electrodes, and the obtained results were compared with those obtained using paste electrodes prepared by pristine graphite, pristine multiwalled carbon nanotubes, and oxidized multiwalled carbon nanotubes and also by glassy carbon electrode.

Determination of rSpike Protein by Specific Antibodies with Screen-Printed Carbon Electrode Modified by Electrodeposited Gold Nanostructures.

In this research, we assessed the applicability of electrochemical sensing techniques for detecting specific antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike proteins in the blood serum of patient samples following coronavirus disease 2019 (COVID-19). Herein, screen-printed carbon electrodes (SPCE) with electrodeposited gold nanostructures (AuNS) were modified with L-Cysteine for further covalent immobilization of recombinant SARS-CoV-2 spike proteins (rSpike). The affinity interactions of the rSpike protein with specific antibodies against this protein (anti-rSpike) were assessed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods. It was revealed that the SPCE electroactive surface area increased from 1.49 ± 0.02 cm2 to 1.82 ± 0.01 cm2 when AuNS were electrodeposited, and the value of the heterogeneous electron transfer rate constant (k0) changed from 6.30 × 10−5 to 14.56 × 10−5. The performance of the developed electrochemical immunosensor was evaluated by calculating the limit of detection and limit of quantification, giving values of 0.27 nM and 0.81 nM for CV and 0.14 nM and 0.42 nM for DPV. Furthermore, a specificity test was performed with a solution of antibodies against bovine serum albumin as the control aliquot, which was used to assess nonspecific binding, and this evaluation revealed that the developed rSpike-based sensor exhibits low nonspecific binding towards anti-rSpike antibodies.

Graphene electrochemistry: ‘Adiabaticity’ of electron transfer

Graphene materials currently open new perspectives to electrochemical systems, providing high electron transfer rates, electrochemical stability in a wide potential range, and ability to control these properties, for instance, by introducing impurity atoms. One of the most important electrochemical characteristics of the graphene is the heterogeneous electron transfer rate (or electrochemical activity). However, contradictory results have been presented on the electrochemical activity of graphene, and how structural defects, the number of graphene layers, and the graphene substrate alter its activity. We found here that the question of an electron transfer regime on graphene, which is disputable and rarely considered, is critically important in understanding its electrochemical activity. We provide an evidence of different electron transfer regimes for O2/O2− and ferrocenium/ferrocene redox on the graphene electrode, that result in different structure-activity relationships. Our results contribute to further understanding of the graphene electrochemistry.

Inconsistency of BDD reactivity assessed by ferri/ferro-cyanide redox system and electrocatalytic degradation capability

Ferri/ferro-cyanide ([Fe(CN)6]3−/4−) redox couple has been extensively used as a benchmark to assess electrocatalytic degradation capability of boron-doped diamond (BDD) electrodes. However, the [Fe(CN)6]3−/4− is far more sensitive to the surface terminal groups of BDD surface than the other factors (e.g. surface morphology and electrode configuration) that are closely related to electrocatalytic degradation properties. Thus, inconsistency exists while correlating the degradation properties of BDD with electrochemical properties determined from ferri/ferro-cyanide redox couple. Herein, an exemplar pollutant, reactive blue 19 (RB-19), was electrochemically degraded using various terminated BDD electrodes, including hydrogen-terminated (H-BDD), oxygen-terminated (O-BDD) and porous oxygen-terminated BDDs (OE-BDD), obtained via cathodic and anodic polarization as well as oxygen plasma etching, respectively. Surprisingly, OE-BDD with the lower heterogeneous electron transfer rate constant for [Fe(CN)6]3−/4− showed a better electrocatalytic degradation capability toward RB-19, indicating the inconsistency for qualitatively evaluating degradation properties according to the kinetic parameters extracted from [Fe(CN)6]3−/4− redox system.

(Keynote, Digital Presentation) An Electrochemical Potential Perspective on Exchange Current Density and Work Function for Hydrogen Evolution Reaction (HER)

In 1972, Trasatti compiled the exchange current densities j0 and work functions \U0001d6bd for the hydrogen evolution reaction (HER) on 31 polycrystalline metals at pH 0. Exchange current density measures the HER rate and the work function measures the energy required to remove an electron from the surface of the metal to a point outside the metal. Trasatti showed a plot of log j0 vs \U0001d6bd linear for the so called d metals and for the sp metals. The slopes are statistically the same for the d and sp metals (6.44 and 6.6 excludes Hg) but the intercepts differ (-35.4 and -38).Here, a thermodynamic specification for the slope of log j0 versus \U0001d6bd is suggested as \U0001d6c2F/RT, where \U0001d6c2 is the transfer coefficient for heterogeneous electron transfer.Electrochemical potentials for species i in phase j have been used to derive the rates of heterogeneous electron transfer within a transition state context for Butler Volmer kinetics (Bard and Faulkner).The standard chemical potential, activity, and ion charge for species i are \U0001d741i 0,j, ai j, and zi is the electrical potential is \U0001d753j.Extrapolation of the electrochemical potential to include \U0001d6bd and derive a rate expression for j0 yield: The electrode potential and the work function group into a common term. The slope of log j0 versus \U0001d6bd as \U0001d6c2F/RT. An explanation of how Pt with the highest energetic cost to remove an electron \U0001d6bd yields the highest log j0 is presented. At 25 oC, F/RT = (0.05916 V)-1. Within the electrochemical potential model for log j0 versus \U0001d6bd, the slopes of 6.44 and 6.6 for the d and sp metals at room temperature yield \U0001d6c2 of 0.381 and 0.39. Across 30 metals, \U0001d6c2 is estimated the same. The value of 0.4 is common in measurements of \U0001d6c2 found for the potential dependent term in Butler Volmer kinetics. References Trasatti, S. Work Function, Electronegativity, and Electrochemical Behavior of Metals. III. Electrolytic Hydrogen Evolution in Acid Solution. Electroanalytical Chemistry and Interfacial Electrochemistry 39, 163-184 (1972).A.J. Bard and L. R. Faulkner, Electrochemical Methods, 1980, wiley and Sons, Chapter 2. Acknowledgments This work was supported by the National Science Foundation and the Army Research Office. The University of Iowa Obermann Center for Advanced Studies is acknowledged.

Electrochemical Characterization and Application of Graphene Oxide Materials Obtained By Electrochemical Exfoliation of Graphite

Graphene oxide (GO) materials possess oxygen functional groups located at the edges and at the surface of the graphitic layers, confering them dispersibility in water, biocompatibility, and high affinity for specific molecules. These properties are highly appealing for their use in electrochemical sensors. However, the density and type of functional groups and defects in these materials also influence the heterogeneous electron transfer rate of redox processes occurring at the GO-based electrodes 1,2. In this respect, it is necessary to investigate the physicochemical and electrochemical properties of GO materials to choose the most suitable one for a target application.Here, we report a simple and facile platform for the electrochemical characterization of GO materials 3. The GO sheets are self-assembled on a glassy carbon electrode (GCE) through an aminophenyl-film linker (AP) through electrostatic interaction and pi-pi stacking, Figure 1a. Then, the modified electrodes are characterized by cyclic voltammetry with 1 mM [Fe(CN)6]3-/4- redox couple to determine the electrochemical surface area (ESA) through the Randles-Sevcik equation and to calculate the standard rate constant of electron transfer (k0) by the Nicolson method.In this work, series of GO materials were obtained by electrochemical exfoliation of graphite in 0.1 M H2SO4. The electrochemical exfoliation of graphite in aqueous solution is an easy and “green” method that allows the synthesis of large amounts (in the order of grams) of materials (EGO: electrochemically exfoliated graphene oxide) with tunable composition in a short time (few hours). The applied voltage and the distance between the graphite and the counter electrodes were varied, Figure 1b, to obtain EGOs with different physicochemical properties such as the number of layers, structural defects, type and content of oxygenated groups. Transmission electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy analysis were used to investigate the physicochemical properties of the EGOs. As shown in Figure 1c, the measured ESA and k0 scale with each other and are sensitive to the physicochemical properties of EGOs. This confirms the suitability of the proposed platform to characterize the EGO materials 3.Finally, selected EGO materials were used to fabricate electrochemical aptasensors for the detection of cocaine. The influence of the EGO physicochemical properties on the performance of the aptasensors will be presented and discussed.References(1) Kampouris, D. K.; Banks, C. E. Chemical Communications 2010, 46, 8986-8988.(2) Ambrosi, A.; Bonanni, A.; Sofer, Z.; Cross, J. S.; Pumera, M. Chemistry – A European Journal 2011, 17, 10763-10770.(3) Lei, Y.; Ossonon, B. D.; Chen, J.; Perreault, J.; Tavares, A. C. Journal of Electroanalytical Chemistry 2021, 887, 115084. Figure 1

(Invited, Digital Presentation) Tafel Analysis Algorithm: Objective Identification of the Linear Region

Electrocatalysts for hydrogen evolution and oxidation (HER and HOR) reactions, oxygen reduction and evolution (ORR and OER) reactions, and carbon dioxide reduction reactions (CO2RR) are evaluated by Tafel analysis. The Tafel equation specifies the log-linear relationship between current and overpotential \U0001d6c8. Heterogenous electron transfer parameters of exchange current density j o and transfer coefficient \U0001d6c2 are found. Standard heterogenous electron transfer rate k 0 can be found from j o.Conventionally, Tafel analysis is an extension of the Butler-Volmer equation applied at high overpotentials but where mass transport is not significant and the reverse reaction rate is negligible. Applicable at high \U0001d6c8 when electron transfer rates are slow, kinetic parameters are extracted by linear regression. The conventional method is, however, subject to inaccuracies because the linear region is often determined subjectively, without attention to the constraints on overpotential range, no mass transport limitations, and low j o.An algorithm is developed to automate Tafel analysis with the objective to increase measurement accuracy and decrease subjective identification of the linear region. From linear sweep voltammograms (LSVs), j o and α are determined from Tafel slopes in the best fit, linear range.Comparisons of kinetic parameters between conventional and algorithmic Tafel analyses are made for the hydrogen evolution reaction (HER, 2H+ + 2e- ⇌ H2) on various unmodified electrodes and electrodes modified with Nafion® composites. The algorithmic Tafel analysis parameters correlate well with conventional Tafel analyses that respect constraints on mass transport, \U0001d6c8, and j o. Similar agreement is observed between literature and algorithmically fitted kinetic parameters for different electrochemical systems. The algorithm allows for straightforward, rapid Tafel analysis for improved measurement of rate parameters that is independent of user bias in selection of the linear region. Acknowledgments This work was supported by the Army Research Office.

Conductive printable electrodes tuned by boron-doped nanodiamond foil additives for nitroexplosive detection

An efficient additive manufacturing-based composite material fabrication for electrochemical applications is reported. The composite is composed of commercially available graphene-doped polylactide acid (G-PLA) 3D printouts and surface-functionalized with nanocrystalline boron-doped diamond foil (NDF) additives. The NDFs were synthesized on a tantalum substrate and transferred to the 3D-printout surface at 200 °C. No other electrode activation treatment was necessary. Different configurations of low- and heavy-boron doping NDFs were evaluated. The electrode kinetics was analyzed using electrochemical procedures: cyclic voltammetry and electrochemical impedance spectroscopy. The quasi-reversible electrochemical process was reported in each studied case. The studies allowed confirmation of the CV peak-to-peak separation of 63 mV and remarkably high heterogeneous electron transfer rate constant reaching 6.1 × 10−2 cm s−1 for 10 k ppm [B]/[C] thin NDF fitted topside at the G-PLA electrode. Differential pulse voltammetry was used for effective 2,4,6-trinitrotoluene (TNT) detection at the studied electrodes with a 87 ppb limit of detection, and wide linearity range between peak current density and the analyte concentration (0.064 to 64 ppm of TNT). The reported electrode kinetic differences originate primarily from the boron-dopant concentration in the diamond and the various contents of the non-diamond carbon phase.Graphical abstract

Siloxene-Functionalized Laser-Induced Graphene via COSi Bonding for High-Performance Heavy Metal Sensing Patch Applications.

Here, 2D Siloxene nanosheets are newly applied to functionalize porous laser-induced graphene (LIG) on polydimethylsiloxane, modify the surface chemical properties of LIG, and improve the heterogeneous electron transfer rate. Meanwhile, the newly generated COSi crosslink boosts the binding of LIG and Siloxene. Thus, the Siloxene/LIG composite is used as the basic electrode material for the multifunctional detection of copper (Cu) ions, pH, and temperature in human perspiration. Moreover, to enhance the sensing performance of Cu ions, Siloxene/LIG is further modified by carbon nanotubes (CNTs). The fabricated Siloxene-CNT/LIG-based Cu-ion sensor shows linear response within a wide range of 10-500 ppb and a low detection limit of 1.55 ppb. In addition, a pH sensor is integrated to calibrate for determining the accurate concentration of Cu ions due to pH dependency of the Cu-ion sensor. The polyaniline-deposited pH sensor demonstrates a good sensitivity of -64.81 mV pH-1 over the pH range of 3-10. Furthermore, a temperature sensor for accurate skin temperature monitoring is also integrated and exhibits a stable linear resistance response with an excellent sensitivity of 9.147 Ω°C-1 (correlation coefficient of 0.139%°C-1 ). The flexible hybrid sensor is promising in applications of noninvasive heavy-metal ion detection and prediction of related diseases.

Expression, purification, characterization and direct electrochemistry of two HiPIPs from Acidithiobacillus caldus SM-1

High-potential iron-sulfur proteins (HiPIPs) from extremely acidophilic chemolithotrophic non-photosynthetic Acidithiobacillus commonly play a crucial role in ferrous or sulfurous biooxidation. Acidithiobacillus exhibit important industrial applications for bioleaching valuable metals from sulfide ores. In this study, two HiPIP genes from thermophilic Acidithiobacillus caldus SM-1 were cloned and successfully expressed, and their proteins were purified. The proteins displayed a brownish color with an optical absorbance peak at approximately 385 nm and an electronic paramagnetic resonance (EPR) g value of approximately 2.01, which confirmed that the iron-sulfur cluster was correctly inserted into the active site when the proteins were generated in E. coli. The proteins were more thermostable than HiPIPs from mesophilic Acidithiobacillus. The direct electron transfer (DET) between HiPIPs and electrode was achieved by the 2-mercaptopyrimidine (MP) surface-modified gold electrodes; the redox potentials of the HiPIP1 and HiPIP2 measured by cyclic voltammetry were approximately 304.5 mV and 400.5 mV, respectively. The electron transfer rate constant was estimated to be 0.75 s−1 and 0.66 s−1, respectively. The MP/Au electrode and Au electrode showed consistent differences in heterogeneous electron transfer rates and electron transfer resistances. Bioinformatics and molecular simulations further explained the direct electron transfer between the proteins and surface-modified electrode.

Enhanced stability of electrochemical performance of few-layer black phosphorus electrodes by noncovalent adsorption of 1,4-diamine-9,10-anthraquinone

In this paper, the novel noncovalent functionalisation strategy of few-layer black phosphorus by 1,4-diamine-9,10-anthraquinone electrode was proposed and studied. The degradation of few-layer black phosphorus under exposure to oxygen and water is a significant obstacle to its use as an electroanalytical electrode. The anthraquinone compound adsorbed at black phosphorus flakes results in improved prevention of the phosphorus surface against degradation and electrode decomposition. Furthermore, a large concentration of amino group present in 1,4-diamine-9,10-anthraquinone enhances the electrochemical performance of electrode revealed by a faster rate of heterogeneous electron transfer observed in cyclic voltammetry studies. The designed electrode exhibits stable redox peaks over 100 cycles with separation between the peaks of 79 ± 2 mV and the formal redox potential reaching 257 ± 3 mV. The differential pulse voltammetry was utilised for the detection of ascorbic acid, revealing a limit of detection equal to 3.29 ppm (18.68 µM) and a limit of quantification of 9.98 ppm (56.66 µM). The linear range of 1–20 ppm was achieved, allowing for the detection of ascorbic acid in real conditions. Thus, anthraquinone-modified few-layer black phosphorus may be an attractive novel electrode material for sensitive electroanalytical applications.