Heterogeneous Electron Transfer Rate Research Articles

Impact of plasma-induced surface chemistry on electrochemical properties of microfabricated pyrolytic carbon electrodes

Plasma technology is a widely used approach for carbon activation and enhancing the surface energy by generating various functional groups. Gas selection is an important factor determining the type of functional groups to be formed on carbon surfaces. In this study, we investigate the impact of plasma-induced chemical surface alterations on performance of pyrolytic carbon as electrode material. Pyrolytic carbon electrodes were microfabricated by pyrolysis of SU-8 structures defined using UV lithography and treated using Ar, O2, N2 and air plasma gases. The resulting surface chemistry and geometry were characterized by X-ray photoelectron spectroscopy and atomic force microscopy. Close inspection of electrochemical properties was done by using both outer (Ru(NH3)63+/2+) and inner (Fe(CN)63-/4− and dopamine) redox systems. The electrochemical performances of the carbon electrodes treated with various plasma gases were compared based on information on heterogeneous electron transfer rates determined by cyclic voltammetry and electrochemical impedance spectroscopy. This work provides a fundamental insight into electrochemistry of plasma-modified pyrolytic carbon surfaces and strategies on how to enhance surface properties overcoming possible electron transfer limitations for future enhancement in carbon-based electrochemical applications.

Theory for nanoscale curvature induced enhanced inactivation kinetics of SARS-CoV-2

We develop a novel theory for the nanomorphology dependent outer sphere heterogeneous electron transfer (ET) rate constant () based on an energy level alignment approach. is modelled through the activation free energy, which is a product of the water monolayer covered metal work function (WF) and the fractional electronic charge exchanged at the transition state (attained through the alignment of the metal Fermi and HOMO/LUMO energy levels of the electroactive species). The theory shows that is an exponentially increasing and decreasing function of the mean curvature in concave and convex nanomorphologies, respectively, for electroactive species or proteins involving their HOMO energy. For the specific spike protein of SARS-CoV-2, we have estimated the half lifetime (t1/2) and degree of inactivation as a function of the metal WF, nanostructure mean curvature, spike protein HOMO energy, and the environmental temperature (T). By varying the metal from Ag to Au, t1/2 is reduced from 7 h to 4 min, respectively. The reduction in the copper nanoparticle size from 50 to 5 nm increases the degree of inactivation from 60 to 99.6% (with a reduction factor of 10 in t1/2). Similarly, the increase in T from 10 °C to 65 °C causes a 100 times lowering of the t1/2 and t99.9% of SARS-CoV-2 on Cu metal. The theory predicts that involving the HOMO energy level of a protein follows the surface nanostructure shape dependent order as follows: spherical nanoparticle > cylindrical nanorod > cylindrical nanopore > spherical nanocavity, while the opposite trend is observed in the case of the LUMO energy level participation. Finally, the theory shows agreement with the reported experimental data of the degree of inactivation of SARS-CoV-2 on Ag and Cu nanoparticles.

Coulometric and Chronoamperometric Studies on Bisulfite Reduction at a Surfactant/Myoglobin Film on Glassy Carbon Electrode

<i>Background</i>. The redox-active protein, myoglobin (Mb), exchanges electrons very slowly with bare electrodes. Just like on a highly oriented pyrolytic graphite (HOPG) bare electrode, electron transfer between myoglobin (Mb) and a bare glassy carbon (GC) electrode was not observed. The myoglobin (Mb) in di-dodecyl dimethyl ammonium bromide (DDAB) film immobilized on glassy carbon electrode surface had a good charge transport, allowing Mb to be used as a redox catalyst for multi-electron transfer reactions. <i>Objective</i>. We report here the myoglobin on a glassy carbon (GC) electrode as a catalyst for the multi-electron reduction of bisulfite in aqueous buffered solutions. <i>Methods</i>. Coulometry and chronoamperometry are used as tools to probe the Mb/DDAB film on GC electrode as an effective electro-catalyst for the multi-electron reduction of bisulfite. <i>Results</i>. Variation in current with time of bisulfite reduction followed first-order reaction kinetics. The heterogeneous electron transfer rate constant of the film and catalytic rate constant for the reduction of bisulfite were determined. <i>Conclusion</i>. The study confirmed that bisulfite was the reactive species and the catalytic reduction reaction at Mb/DDAB film followed the EC’ catalytic mechanism.

Reactive argon-plasma activation of screen-printed carbon electrodes for highly selective dopamine determination.

Dopamine (DA) deficiency has been linked to several psychiatric disorders. Electrochemical determination of the level of DA suffers from abundant ascorbic acid (AA) and uric acid (UA) in body fluids. In this work, a facile argon (Ar) plasma treatment was utilized to enhance the electrocatalytic reactivity of screen-printed carbon electrodes (SPCEs) for selective DA detection. Surface characterization of the Ar-treated SCPEs verified that the carbon paste binders were successfully removed and single-bonded oxygenated moieties (-OH and C-O-C) were generated. Interestingly, the sharper D* and D'' Raman interbands were new key evidence of a higher exposure of carbon defect sites. Electrochemical studies further revealed that the Ar-treated SPCEs possessed faster heterogeneous electron-transfer rates, larger electroactive surface areas, and much higher conductivity when compared with untreated electrodes. As a result, the oxidation potentials of AA, DA, and UA in the mixture could be well-resolved and the current responses were significantly increased. The selective determination of DA in the presence of AA and UA by differential pulse voltammetry gave two linear responses with the limit of detection of 0.27 μM (0.15-10 μM range). Moreover, this Ar-treated SPCE had high reproducibility and good storage stability. These results suggest that Ar-plasma treatment could be a promising method to enhance the electrocatalytic properties of SPCEs for the detection of biomolecules.

Spectroscopic and electrochemical studies of the pH-Induced transition in the CuA centre from Thermus thermophilus

A detailed study of the pH induced conformational changes at the Cu2S2 coordination site of the CuA centre of cytochrome oxidase from Thermus thermophilus has been carried out to unravel the role of the pH-induced changes in the coordination geometry on the redox potential and electron transfer kinetics of the metal centre. The pH dependence of the UV–visible absorption bands as well as of the visible circular dichroism spectra corresponding to the metal centre of the protein could be analyzed by the model involving two protonation/deprotonation steps associated with the pKa values of 3.5 and 9.6. The redox potential of the protein determined by direct electrochemistry also showed analogous pH dependence. The results suggested that the metal centre undergoes equilibrium conformational transition involving three forms, viz., ‘low pH’ form, ‘neutral pH’ form and ‘high-pH’ form characterized by different redox potentials of the metal centre. The rates of heterogeneous electron transfer were found to decrease drastically at low pH as well as at high pH. The electron transfer from cytochrome c to the CuA site of the cytochrome oxidase is proposed to be gated by conformation changes at the CuA site through a protonation-induced conformation change, which may act as a sensor for optimum proton transfer across the enzyme. The results also have been discussed in the light of understanding fast electron transfer from the CuA to the heme a in the intact enzyme.

Enzyme-immobilized 3D silver nanoparticle/graphene aerogel composites towards biosensors

The detection of allergen sulfite is essential for food quality control and public health supervision. Here, a high-performance sulfite biosensor was developed from a sulfite oxidase enzyme (SOx) immobilized on silver nanoparticles (AgNPs) decorated on 3D reduced graphene oxide (3D-rGO). 3D-rGO with high specific pore volume and high electroactive surface area is ideal as a supporting material. AgNPs further provide high electrical conductivity or fast charge transfer and serve as an enzyme anchoring site via a stable thiol bonding. The composite material was initially functionalized with the folic acid and cysteine namely rGO@Ag-Cys-FA before immobilized with the SOx. The resultant rGO@Ag-Cys-FA-SOx exhibits high sensitivity and selectivity towards sulfite detection, high bio-electrocatalytic activity, and fast heterogeneous electron transfer rate constant. The biosensor is also tested in a continuous flow injection system to demonstrate the practical use. Besides, the as-produced sensor in this work can be used in the real sample, which is the canned fruit product indicating its potential practical application.

Novel magneto-electrochemical determination of Mn(II)

This study describes the robust modification of a screen-printed carbon electrode (SPE) for the magneto-electrochemical determination of Mn2+, in real soil samples, by square wave cathodic stripping voltammetry (SW-CSV). The carbon surface of a SPE was modified with electrodeposited Au, then dropcast with Fe3O4 NPs functionalised with l-cysteine within a graphene oxide matrix. The magnetic Fe3O4 NPs within the modification significantly increased the diffusion coefficient of the paramagnetic Mn2+ ion during deposition. Likewise, it also increased the number of hydroxyls available for the formation of the MnO2 layer, attributed to chiral induced spin selectivity. The reduced graphene oxide (RGO) served to increase the surface area and heterogenous electron transfer rate of the intermediate reactions. The Au/l-cys/Fe3O4/RGO modification displayed two significant improvements: enhancement of the Mn2+ response signal (212-fold increase) and improved flexibility for the analytical method (linear ranges from 0.5 to 300 µg L-1 to 62 – 1500 µg L-1 using deposition times of 300 or 30 s, respectively). Ten soil sample extracts were tested for Mn2+, by SW-CSV using the Au/l-cys/Fe3O4/RGO modified SPE, and showed good agreement with FAAS, average error of 6.8%.

Electrochemical impedimetric analysis of different dimensional (0D–2D) carbon nanomaterials for effective biosensing of L-tyrosine

Electrochemical biosensors employing nano-transduction surfaces are considered highly sensitive to the morphology of nanomaterials. Various interfacial parameters namely charge transfer resistance, double layer capacitance, heterogeneous electron transfer rate and diffusion limited processes, depend strongly on the nanostructure geometry which eventually affects the biosensor performance. The present work deals with a comparative study of electrochemical impedance-based detection of L-tyrosine (or simply tyrosine) by employing carbon nanostructures (graphene quantum dots, single walled carbon nanotubes (CNTs) and graphene) along with tyrosinase as the bio-receptor. Specifically, the role of carbon nanostructures (i.e. 0D, 1D and 2D) on charge transfer resistance is investigated by applying time-varying electric field at the nano-bioelectrode followed by calculating the heterogeneous electron transfer rate, double layer capacitor current and their effects on limits of detection and sensitivities towards tyrosine recognition. A theoretical model based on Randel’s equivalent circuit is proposed to account for the redox kinetics at various carbon nanostructure/enzyme hybrid surfaces. It was observed that, the 1D morphology (single walled CNTs) exhibited lowest charge transfer resistance ∼2.62 kΩ (lowest detection limit of 0.61 nM) and highest electron transfer rate ∼0.35 μm s−1 (highest sensitivity 0.37 kΩ nM−1 mm−2). Our results suggest that a suitable morphology of carbon nanostructure would be essential for efficient and sensitive detection of tyrosine.

(Sensor Division Outstanding Achievement Award) Controlling Carbon Shape and Microstructure for Suspended Wires, Mats, Interdigitated Arrays and Origami

Over the last two decades, scientists acquired more and more insights on the conversion of patterned polymer precursors into predictable 3D carbon shapes using pyrolysis (also carbonization). Our team, using photo lithography, electrospinning or a combination of both techniques, patterned polymer precursor structures so that after pyrolysis they yielded, for example, suspended carbon nanowires (see Figure 1a), carbon mats (see Figure 1b), carbon interdigitated arrays (C-IDEAS) (see Figure 1c) and even carbon origami (see Figure 1 d).More recently, gaining better control over the carbon microstructure in some of those carbon shapes also became possible. The key to the latter is a precise control of the polymer precursor chains and the exact atomic composition of the polymer before and during pyrolysis.Using simultaneous control of the linear speed of the spinneret and the rotational speed of a drum collector in near field electrospinning (NFE) enables one to organize polymer precursor chains, that after pyrolysis, lead to aligned ultra-thin (as low as 5 nm) highly crystalline carbon fibers freely suspended and in good ohmic contact with carbon scaffolds on a silicon substrate (Figure 1a) 1.The application of far field electrospinning (FFE) techniques allows one to utilize electrohydrodynamic forces to align polymer molecular chains within the spun fiber mats. This polymer chain alignment was then preserved by mechanical compression of the polymer fabrics during the formative stabilization step. Perhaps the most surprising outcome of this second C-MEMS approach illustrated in Figure 1 b was the demonstration of the conversion of these PAN fiber mats through pyrolysis into a uniformly graphitized carbon. The resulting carbon exhibits an oriented but fragmented lattice structure, as visualized by HRTEM imaging. Further characterization with XPS indicated that this type of stress activated pyrolytic carbon is innately rich in nitrogen heteroatoms. The electrochemical kinetics of these carbon mats reveal a heterogenous electron transfer rate 5 to 14 times higher than that of standard pyrolytic PAN carbons and 2 to 10 times higher than polished commercial glassy carbon in both the surface insensitive and sensitive redox probes 2.Using conventional UV photolithography to pattern SU8, followed by pyrolysis, we fabricated 3D carbon interdigitated electrode arrays (C-IDEAS) with redox amplification factors as high as 37 (Figure 1c)3. In ongoing follow-on work, we are now investigating means to further increase the amplification factor by reducing the electrode gap and increasing the electrode height. In this case the mechanical alignment of polymer chains (see FFE and NFE) is not applicable and we are converting the top carbon electrode material to graphene through the deposition of Ni and annealing instead.Two years ago (2019), we demonstrated for the first time an origami-based carbon microfabrication method for permanently folded three-dimensional structures by combining lithography, controlled thermal softening and hardening, and elastocapillarity4. Selective lithography for cross-linking of photopolymers was used to obtain localized control over the material properties (for folds and faces) to enable selective and programmed folding of the origami. In addition to achieving tailorable inhomogeneous material properties, selective exposure was also used to bond the origami shapes onto a substrate surface. The three-dimensional polymer structures were then converted through pyrolysis into carbon shapes thus enhancing the achievable structural, electrical, and electrochemical properties and to broaden the applications of this elastocapillary-based fabrication method (see Figure 1 d). Finally in 2020, we were able to create the same carbon origami by heat-assisted self-folding, doing away with the need for droplet induced folding 5. Pyrolysis leads to a glassy carbon microstructure in the carbon origami shapes obtained. As for C-IDEAS, Ni deposition and annealing can be employed to convert the microstructure from glassy carbon to graphene.References Jufeng Deng, Chong Liu, Marc Madou, "Ultra-thin carbon nanofibers based on graphitization of near-field electrospun polyacrylonitrile," Nanoscale, Royal Society of Chemistry, Issue 19, 2020.Holmberg, Sunshine, et al. "Stress-activated pyrolytic carbon nanofibers for electrochemical platforms." Electrochemical Acta290 (2018): 639-648.Kamath and M. J. Madou, "Three-Dimensional Carbon Interdigitated Electrode Arrays for Redox-Amplification," Anal. Chem., vol. 86, no. 6, pp. 2963-2971, Mar. 2014.Fabrication of polymer and carbon polyhedra through controlled cross-linking and capillary deformations, Derosh George, Edwin A. Peraza Hernandez, a Roger C. Lo and Marc Madou, Soft Matter, Volume 15 Issue 45 (2019): Pages 9171-9177.George, Derosh, Marc Madou, and Edwin A. Peraza Hernandez. "Programmable single-layer polymer films for millimeter and sub-millimeter self-folding origami." Active and Passive Smart Structures and Integrated Systems IX. Vol. 11376. International Society for Optics and Photonics, 2020. Figure 1

Cyclic voltammetry to study kinetics of blast furnace slag and cerium dioxide modified electrode

Abstract The use of a voltammetric sensor to measure hazardous elements has gotten a lot of coverage. The electrochemical sensor in this study was modified with cerium dioxide (CeO2) and blast furnace slag (BFS), which opens up new possibilities for improving the electrocatalytic properties of the fabricated sensor. In general chemical kinetics or mass transport can restrict the reactions involved in electrochemical detection. The prepared electrodes were tested against potassium ferricyanide, K3Fe(CN)6 solution by cyclic voltammetry. Cyclic voltammetry was used to investigate the chemical reactions involve during redox process. The electron transfer kinetics, chemical rate constant, and diffusion characteristics of reactions can all be extracted using this method. Further this sensor was applied in the detection of lead and copper ions in aqueous solution. The results show that the redox reaction is a one-electron transfer mechanism with high selectivity and sensitivity. The value of transfer coefficient (α) for the electrode reaction was calculated as 0.61. Also the calculated heterogeneous electron transfer rate constant (Ks) of the modified electrode was 2.41.

Tuning Vertical Electron Transfer on Graphene Bilayer Electrochemical Devices

AbstractPristine graphene electrodes exhibit slow vertical (off‐plane) heterogeneous electron transfer (HET) rate that limits their application in electrochemical devices. This can be minimized by generating defects in the graphene structure. However, these defects adversely affect the horizontal (in‐plane) electrical conductivity characteristic to graphene. Here, the fabrication of graphene bilayer devices with modulated vertical HET is reported. Strategically, the upper sheet is used as a sacrificial layer for the introduction of extrinsic defects via electrochemical oxidation while preserving the structure of the graphene underlying layer. For [Fe(CN)6]4−/[Fe(CN)6]3− vertical HET in solution‐phase, oxidized electrodes present a very low charge transfer resistance. For vertical HET in surface adsorbed ferrocene on oxidized electrodes, the vertical HET rate constant is about five times higher than on pristine electrodes. Based on data from scattering‐type scanning near‐field optical microscopy (s‐SNOM) and Raman spectroscopy, the improvement on the electrochemical properties is attributed to the defects that are incorporated in the upper layer graphene lattice. This fundamental study on the atomic behavior of defects and stacking layers of graphene provides a new strategic design of graphene‐based devices with superior electrochemical performance.

Effect of Supporting Background Electrolytes on the Nanostructure Morphologies and Electrochemical Behaviors of Electrodeposited Gold Nanoparticles on Glassy Carbon Electrode Surfaces.

Electrodeposition is an electrochemical method employed to deposit stable and robust gold nanoparticles (AuNPs) on electrode surfaces for creating chemically modified electrodes (CMEs). The use of several electrodeposition techniques with different experimental parameters allow in obtaining various surface morphologies of AuNPs deposited on the electrode surface. By considering the electrodeposition of AuNPs in various background electrolytes could play an important strategy in finding the most suitable formation of the electrodeposited AuNP films on the electrode surface. This is because different electrode roughnesses can have different effects on the electrochemical activities of the modified electrodes. Thus, in this study, the electrodeposition of AuNPs onto the glassy carbon (GC) electrode surfaces in various aqueous neutral and acidic electrolytes was achieved by using the cyclic voltammetry (CV) technique with no adjustable CV parameters. Then, surface morphologies and electrochemical activities of the electrodeposited AuNPs were investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), CV, and electrochemical impedance spectroscopy (EIS). The obtained SEM and 3D-AFM images show that AuNPs deposited at the GC electrode prepared in NaNO3 solution form a significantly better, uniform, and homogeneous electrodeposited AuNP film on the GC electrode surface with nanoparticle sizes ranging from ∼36 to 60 nm. Meanwhile, from the electrochemical performances of the AuNP-modified GC electrodes, characterized by using a mixture of ferricyanide and ferrocyanide ions [Fe(CN6)3–/4–], there is no significant difference observed in the case of charge-transfer resistances (Rct) and heterogeneous electron-transfer rate constants (ko), although there are differences in the surface morphologies of the electrodeposited AuNP films. Remarkably, the Rct values of the AuNP-modified GC electrodes are lower than those of the bare GC electrode by 18-fold, as the Rct values were found to be ∼6 Ω (p < 0.001, n = 3). This has resulted in obtaining ko values of AuNP-modified GC electrodes between the magnitude of 10–2 and 10–3 cm s–1, giving a faster electron-transfer rate than that of the bare GC electrode (10–4 cm s–1). This study confirms that using an appropriate supporting background electrolyte plays a critical role in preparing electrodeposited AuNP films. This approach could lead to nanostructures with a more densely, uniformly, and homogeneously electrodeposited AuNP film on the electrode surfaces, albeit utilizing an easy and simple preparation method.

Disposable stencil-printed carbon electrodes for electrochemical analysis of sildenafil citrate in commercial and adulterated tablets

Forensic studies are extremally important to investigate suspected adulterations of consumable products, such as Viagra®. This report describes the determination of sildenafil citrate (SC) in commercial and adulterated tablets based on square-wave voltammetry (SWV) measurements using disposable stencil-printed carbon electrodes. The conductive ink used for the manufacture of integrated electrodes was produced by combining graphite powder and glass varnish. To promote a reusable strategy for limiting the geometric area of the electrodes, a 3D-printed holder was constructed. Detailed morphological and electrochemical characterization studies revealed well-defined graphite flakes incorporated on the polymeric substrate and a faster heterogeneous electron-transfer rate constant (Ks = 1.3 × 10–3 cm s–1). Based on the analytical performance, a linear behavior was observed in a SC concentration range from 1 to 20 µmol L–1 with limit of detection equal to 0.2 µmol L–1. The selectivity of the proposed method was evaluated and the presence of potentially interfering compounds like phosphate, lactose, paracetamol and tadalafil and no difference higher than 15% was observed. The analysis of SC was performed in commercial and seized tablets and the achieved values were 50 ± 1 mg for Viagra® tablet, 54 ± 1 mg for generic formulations 38 ± 1 mg for seized tablet. In addition, the proposed method offered satisfactory accuracy (98.2 – 102.0%) no noticeable matrix effect. Lastly, considering the achieved results, the use of stencil-printed carbon electrodes and SWV has demonstrated to be a powerful and robust analytical tool for forensic investigations.

Laser Scribing Fabrication of Graphitic Carbon Biosensors for Label-Free Detection of Interleukin-6.

Interleukin-6 (IL-6) is an important immuno-modulating cytokine playing a pivotal role in inflammatory processes in disease induction and progression. As IL-6 serves as an important indicator of disease state, it is of paramount importance to develop low cost, fast and sensitive improved methods of detection. Here we present an electrochemical immunosensor platform based on the use of highly porous graphitic carbon electrodes fabricated by direct laser writing of commercial polyimide tapes and chemically modified with capture IL-6 antibodies. The unique porous and 3D morphology, as well as the high density of edge planes of the graphitic carbon electrodes, resulted in a fast heterogeneous electron transfer (HET) rate, k0 = 0.13 cm/s. The resulting immunosensor showed a linear response to log of concentration in the working range of 10 to 500 pg/mL, and low limit of detection (LOD) of 5.1 pg/mL IL-6 in phosphate buffer saline. The total test time was approximately 90 min, faster than the time required for ELISA testing. Moreover, the assay did not require additional sample pre-concentration or labelling steps. The immunosensor shelf-life was long, with stable results obtained after 6 weeks of storage at 4 °C, and the selectivity was high, as no response was obtained in the presence of another inflammatory cytokine, Interlukin-4. These results show that laser-fabricated graphitic carbon electrodes can be used as selective and sensitive electrochemical immunosensors and offer a viable option for rapid and low-cost biomarker detection for point-of-care analysis.

Template-free synthesis of ZnO/Fe3O4/Carbon magnetic nanocomposite: Nanotubes with hexagonal cross sections and their electrocatalytic property for simultaneous determination of oxymorphone and heroin

A new method is introduced to synthesize ZnO/Fe3O4/Carbon magnetic hexagonal nanotubes arrays named ZnO/Fe3O4/C MHNTA using a one-pot synthesis. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), BET surface area analysis, and energy dispersive X-ray spectroscopy (EDX) are used for the characterization of composition and morphology of Fe3O4/ZnO/C MHNTA, demonstrating its high specific surface area of the synthesized material. The synthesized nanotube possesses hexagonal cross-sections and wall thicknesses of about 25 nm, long lengths of around 1.2 µm and side lengths of about 100 nm. The mentioned properties provided rapid electron transfer and large electrochemically active surface area and assisted in the discrimination of analytes that reduce or oxidize under the same potentials. The enhanced electrode demonstrated appropriate sensing ability to oxymorphone and heroin after performing fixation of ZnO/Fe3O4/C MHNTA. Kinetic factors charge transfer coefficient, standard heterogeneous electron transfer rate constant and other different electrochemical factors are predicted using voltammetry methods. Low limits of detection (LODs), 3.5 nM and 4.7 nM, and broad liner ranges, 0.01–500.0 μM are obtained in the case of oxymorphone and heroin, respectively. In addition, the mentioned suggested a suitable potential for profiling of oxymorphone and heroin with appropriate long-term stability, repeatability and reproducibility. The excellent efficiency for the measurement of real samples demonstrated the most significant future perspectives of this sensor. In the last step, the feasible sensing approach is suggested.

Surface Roughness and Electrochemical Performance Properties of Biosynthesized α-MnO2/NiO-Based Polyaniline Ternary Composites as Efficient Catalysts in Microbial Fuel Cells

In this study, biosynthesized α-MnO2/NiO NPs and chemically oxidative polyaniline (PANI) were synthesized to form ternary composite anode material for MFC. The synthesized materials were characterized with different materials (UV-Vis, FTIR, XRD, TGA-DTA-DSC, SEM-EDX-Gwyddion, CV, and EIS) to deeply examine their optical, structural, morphological, thermal, roughness, and electrocatalytic properties. The degree of surface roughness for α-MnO2/NiO/PANI was23.65±5.652 nm. This value was higher than the pure α-MnO2, pure PANI, and even α-MnO2/PANI nanocomposite due to surface modification. The total charge storing performance for bare PGE, α-MnO2/PGE, PANI/PGE, α-MnO2/PANI/PGE, and α-MnO2/NiO/PANI/PGE were 5.291, 17.267, 20.659, 23.258, and 24.456 mC. From this, the charge storing performance formed by α-MnO2/NiO/PANI-modified PGE was highest, indicating that this electrode is best in cycle stability and increases its life cycle during energy conversion time in MFC. This is also supported by its effective surface area, having a value of 0.00984 cm2. From this, it is evidenced that the ternary composite catalyst-modified anode facilitates the fast electrocatalytic activity as observed from its high peak current and lower peak-to-peak potential separation (ΔEp=0.216 V) than other electrodes. Such surface modification helps to store more electrical charge by increasing electrical conductivity during its charge/discharge processing time. In addition, the lower charge transfer resistance property with a value of 788.9 Ω and the fast heterogeneous electron transfer rate of ~2.92 s-1 enable to facilitate glucose oxidation, and this enhances to produce high power output and increase wastewater treatment efficiency. As a result, the bioelectrical activity of α-MnO2/NiO/PANI composite-modified PGE was very effective in producing a maximum power density of 506.96 mW m-2 with COD of 81.92%. The above observations justified that α-MnO2/NiO/PANI/PGE serves as an effective anode material in double-chambered MFC application.

Characteristics of the voltammetric behavior of the hydroxide ion oxidation at disordered mesoporous titanium dioxide electrocatalyst

The alkaline water electrochemical splitting reactions need economical, very energetic, and durable catalysts. Here, a disordered mesoporous and highly defected titanium dioxide (dom-TiO2) electrocatalyst for the oxidation of hydroxide ion was prepared via ligand-assisted evaporation-induced self-assembly. The (dom-TiO2) electrocatalyst showed significant electrocatalytic performance for the oxidation of hydroxide ion compared to that of non-porous TiO2 (bare-TiO2) and highly-ordered hexagonal mesoporous (hm-TiO2) electrodes. The chemical and electrochemical parameters of the diffusion (D), concentration in the bulk (Cb), the number of transferred electrons (n), rate constant of heterogeneous electron transfer (ks), redox potential (E°), and homogeneous chemical rate constant (kc) for the oxidation of hydroxide ion reaction at the porous TiO2 electrodes were determined via the convolution–deconvolution voltammetry and competed against that of non-porous (bare-TiO2) and hm-TiO2 and catalysts. In addition to the effect of dom-TiO2 film thickness and the type of supporting electrolytes on the electrochemical parameters of the electrocatalytic oxidation of OH– ions have been estimated. The convolutive–deconvoluted results show that the dom-TiO2 electrode catalyst exhibits a superior reaction rate constant among the studied electrodes that depend on the film thickness and type of supporting electrolyte.

(General Student Poster Session Winner - 3rd Place) Designing and Implementing a Tailored Alternative Data Analysis Algorithm (TADAA) to Evaluate Quasireversible Heterogeneous Electron Transfer Measurements By Square Wave Voltammetry

Square wave voltammetry (SWV) is used to investigate fast electron transfer kinetics across a wide range of redox active species. SWV is an inherently faster, frequency dependent method as compared to most potential sweep methods. Sweep methods commonly implement an applied potential as a staircase of small potential steps. The frequencies of SWV can be related to sweep methods as the product of SWV frequency and the potential increment at each staircase step.Recent work in our group has shown that k0 measurements for tris-bipyridine transition metal complexes can be made using SWV as the wave morphology changes with k0. Heterogeneous electron transfer rates are not reliably measured at the slower voltage perturbations (scan rates) available with cyclic voltammetry (CV). The heterogeneous electron transfer rates k0 for M(bpy)3 z+ complexes, where M = Ru2+, Os2+, Cr3+, Co2+, Co3+, and Fe2+ are sufficiently rapid that k0 is not reliably measured by CV for most of these complexes. Analysis of the SWV data is possible but not as facile as analysis of CV data. To better evaluate k0 measurements, an alternative data analysis algorithm for quasireversible heterogeneous electron transfer is developed based on classical finite difference simulations. The algorithm can be envisioned as converting voltammograms between CV and SWV. Because CV and SWV both contain a potential parameter and a time parameter (mV/s in CV; frequency and step height in SWV), the algorithm uses a “universal scan rate” to convert between all of the other potential and time-dependent parameters. The purpose of the algorithm is to simplify quantitative SWV data analysis and present information in context of the more commonly used CV.

Deuterium-Grown Highly-Oriented Boron-Doped Diamond Electrodes

Boron-doped diamond (BDD) have attracted increasing attention as a material for electrochemical sensors and biosensors due to its remarkable properties such as its chemical inertness, wide electrochemical potential window, low background current and biocompatibility. Diamond layers are synthesized mainly from a gas phase consisting of carbon, hydrogen, and a dopant source by microwave plasma-assisted chemical vapour deposition (MPACVD). The gas composition during the growth of diamond film has a significant influence on its surface morphology, crystallographic structure, dopant concentration, and superficial non-diamond carbon phases. Thus, the growth conditions of the diamond layer affect the electrochemical properties of the material.Herein we demonstrate the electrochemical and physicochemical studies of as-grown boron-doped diamond thin-film electrodes, synthesized in a deuterium-rich plasma (BDDD). It is the first report concerning the study of the effect of replacing hydrogen by deuterium during BDD growth. The substitution of hydrogen to deuterium in the gas phase is primarily responsible for the enhanced boron doping and significantly decrease of nondiamond sp2 phase in diamond films. Moreover, the crystallographic structure of BDDD layer is dominated by the (111) configuration while the texture of the BDDH electrode film is oriented along the (220) direction [1].The proposed boron-doped diamonds synthesized in the deuterium-rich plasma electrodes were revealed to have a higher activity towards [Fe(CN)6]3-/4- and [Ru(NH3)6]2+/3+ redox mediators than BDD electrode grown in hydrogen-rich plasma (BDDH). The peak-to-peak separation recorded on BDDD electrode reaches 60.6 mV, and 59.8 mV in [Fe(CN)6]3-/4- and [Ru(NH3)6]2+/3+ redox couples, respectively. Moreover, in Ru(NH3)6 2+/3+ solution, the apparent heterogeneous electron transfer rate constant k° app for the BDDD was equal to 5.84·10-3 cm s-1. The BDDD and BDDH electrodes were also used as an electrochemical sensor for the paracetamol detection. BDDD electrode exhibits better sensing performance towards PCM comparing to BDDH electrode. The value of limit of detectionfor the BDDD electrode was 765 nM, whereas for the BDDH was 2510 nM. The better electrocatalytic behavior of the BDDD electrodes may result from the higher amount of electroactive zones on deuterium-terminated diamond strictly related to (111) crystal facets.AcknowledgementThis work was supported by the Polish National Science Centre [2020/01/0/ST7/00104]. The DS funds of the Faculty of Electronics, Telecommunications, and Informatics of the Gdansk University of Technology are also acknowledged.Reference:[1] A. Dettlaff et al., Carbon [In press]. Doi: doi.org/10.1016/j.carbon.2020.11.096.

Electrochemiluminescence at 3D Printed Titanium Electrodes.

The fabrication and electrochemical properties of a 3D printed titanium electrode array are described. The array comprises 25 round cylinders (0.015 cm radius, 0.3 cm high) that are evenly separated on a 0.48 × 0.48 cm square porous base (total geometric area of 1.32 cm2). The electrochemically active surface area consists of fused titanium particles and exhibits a large roughness factor ≈17. In acidic, oxygenated solution, the available potential window is from ~-0.3 to +1.2 V. The voltammetric response of ferrocyanide is quasi-reversible arising from slow heterogeneous electron transfer due to the presence of a native/oxidatively formed oxide. Unlike other metal electrodes, both [Ru(bpy)3]1+ and [Ru(bpy)3]3+ can be created in aqueous solutions which enables electrochemiluminescence to be generated by an annihilation mechanism. Depositing a thin gold layer significantly increases the standard heterogeneous electron transfer rate constant, ko, by a factor of ~80 to a value of 8.0 ± 0.4 × 10−3 cm s−1 and the voltammetry of ferrocyanide becomes reversible. The titanium and gold coated arrays generate electrochemiluminescence using tri-propyl amine as a co-reactant. However, the intensity of the gold-coated array is between 30 (high scan rate) and 100-fold (slow scan rates) higher at the gold coated arrays. Moreover, while the voltammetry of the luminophore is dominated by semi-infinite linear diffusion, the ECL response is significantly influenced by radial diffusion to the individual microcylinders of the array.