Coverage Of Electrode Surface Research Articles

Passivation of the positive electrode during the discharge of Li-O2 and O2-assisted Li-CO2 batteries: A comparative study

The effect of passivation of the positive electrode by solid products under discharge is assessed for the first time as one of the factors determining the discharge characteristics of Li-O2 (LOB) and oxygen-assisted Li-CO2 (LCOB) batteries. In order to estimate the passivation, the electrode surface coverage θ by the reaction product (Li2O2 or Li2CO3) is determined on the basis of a decrease in the double-layer capacitance value in the course of the discharge. It is shown that for a given amount of electricity, the electrode surface coverage by Li2CO3 in LCOB is 1.5–2 times that of the coverage by Li2O2 under discharge in LOB. Furthermore, for each of the batteries, achievement of the maximum discharge capacity does not result in the full electrode surface blocking by the discharge products. LCOB manifests higher discharge characteristics than LOB under the kinetic reaction control (in the 100–500 mA g−1 current density range), owing to the accelerated conversion of intermediates and slower solid reaction product deposition on a larger electrode surface area. As the current density increases from 500 to 2000 mA g−1, the discharge capacity of LOB and LCOB decreases, which is mainly due to the effect of diffusion limitations. Moreover, while in the case of LOB the parameter θ decreases, in the case of LCOB it is practically independent of the current density in the studied range. The latter effect may be due to increased passivating properties of Li2CO3 deposits formed under high current density. The results of the work allow considering θ as a new criterion for estimation of the discharge depth and for predicting the characteristics of LCOB and LOB.

A highly sensitive and selective electrochemical sensor based on polythiourea modified glassy carbon electrode for detecting fenitrothion in vegetables

A sensitive and selective sensor based on a polythiourea-modified glassy carbon electrode (polythiourea/GCE) was fabricated for electrochemical determination of fenitrothion (FT). Cyclic voltammetry and impedance spectroscopy were used to characterize the electrochemical behavior of polythiourea/GCE. The chemical and structural characteristics of the modified electrode were studied with UV-V is and FTIR spectroscopy techniques. The polythiourea (GCE) demonstrated faster electron transfer kinetics, a small charge transfer resistance, and an enhanced electroactive surface area of 0.173 cm2, which was two times greater than that of the bare GCE. The electrochemical behavior of FT at polythiourea/GCE was studied using cyclic voltammetry and square wave voltammetry. The reduction of FT on the surface of the modified electrode followed an adsorption-controlled process, and interestingly, the electrode surface coverage determined from chronocoulometric measurements showed 3.3 times higher accumulation of FT than at the bare GCE. Under optimized experimental parameters, the adsorptive stripping square-wave voltammetric current signal of FT at polythiourea/GCE exhibited an excellent sensitivity of 10.05 μA μM−1, good linearity ranging from 0.05 to 10 µM and 10–50 µM, and low limits of detection and quantification of 2.1 and 7.0 nM, respectively. The selectivity of the sensor was also evaluated in the presence of several common interfering substances, such as nitrophenol, malathion, diazinon, ascorbic acid, K+, Mg2+, and Zn2+ ions, and the percent error was less than ±5 %. The practical application of the suggested electrochemical sensor for FT determination was carried out in tomato, sweet potato, and cabbage samples. The average recoveries of the spiked samples were between 94.3 % and 110 %, indicating that the developed method is accurate for FT determination.

Naproxen electrooxidation using carbon paper electrodes modified with reduced graphene oxide and platinum nanoparticles

This research study investigates the electrooxidation of naproxen (NPX), an anti-inflammatory pharmaceutical, on modified carbon paper (CP) electrodes. Electrochemical modification of CP electrodes was accomplished with Pt or reduced graphene oxide (RGO)-Pt coatings, resulting in the production of electroactive electrodes. RGO coatings synthesized by cyclic voltammetry (CV) for 10 scans provided the optimal coverage for the CP electrode surface. The deposition of Pt nanoparticles (Pt NPs) on the electrodes (CP or CP-RGO) by CV produced a good electrode surface coverage with 20 synthesis scans. The voltammetric analysis of the electrodes in 230 mg/L NPX solution showed oxidation peaks around 1.0 to 1.2 V. Moreover, the inclusion of RGO in the coating led to an increase in the current density of these oxidation peaks and a decrease of the electrode electron transfer resistance as measured by electrochemical impedance spectroscopy.The electrolysis of NPX in different electrolytes (Na2SO4 and Na2SO4/NaCl) was conducted at 1.4 V, and the removal of NPX was analyzed using high-performance liquid chromatography. The CP-RGO-Pt electrode in Na2SO4/NaCl media showed the fastest NPX degradation kinetics, resulting in a 90 % degradation in only 90 min with low charge consumption (0.07 A·h·L-1). The smaller size of Pt NPs deposited on CP-RGO, as observed by field emission scanning electron microscopy and transmission electron microscopy, contributed to the higher electrochemical response in CV and a faster kinetic degradation of NPX.

Parameter estimations from SARS-CoV-2 electrochemical interactions

Electrochemical pathogen sensing has gathered limelight for its effective and ultrafast detection capabilities. More recently, several electrochemical sensors were developed to counter the increasing testing requirement for the 2019 coronavirus disease (COVID-19) diagnosis. One such sensor developed was the Ultrafast COVID-19 (UFC-19) diagnostic sensor which could detect the SARS-CoV-2 spike protein in saliva samples. Although UFC-19 was established in literature to sense SARS-CoV-2 in saliva samples, the factors causing such an interaction or parameters to model such an interaction are yet to be studied in detail. In this work, an attempt has been made to electrochemically characterize the interactions at the interface by employing cyclic and linear sweep voltammetry on a rotating disk electrode setup. As a result, electrochemical parameters were calculated using chemical and electrochemical principles. The electrochemical surface area, electrode surface coverage, diffusion coefficient, reaction order with respect to SARS-CoV-2 whole virus, electron transfer coefficient have been estimated providing additional insights into the events occurring at the electrical double layer. The reaction order for the interaction was reckoned to be 0.7 confirming a non-elementary, multi-step process occurring at the interface. Theoretical and experimental calculations confirm higher hydroxide ion accumulation at the interface in the presence of SARS-CoV-2 whole virus. Results from this work lay the foundation for developing models for electrochemical SARS-CoV-2 interaction and possible extension toward other pathogenic viruses.

Bioimpedance Measurement under Feature Combination of Time-Frequency Domain and Application for E. coli Detection

Electrochemical impedance sensors are widely used for bacterial detection and interpreted by the equivalent circuit model (ECM) to evaluate the concentration changes on the electrode interface. However, this method is mainly based on prior models and focuses on frequency domain analysis which cannot precisely describe unknown dynamic processes and a fractional surface coverage of electrode. Distribution of Relaxation Times (DRT) method, as an alternative to interpret impedance spectra can be applied to solve the problem. In this research, two electrode schemes with different modification steps were designed to collect impedance data. An Ensemble Tree-SHAP model was then adopted to quantitatively analyze the impedance data processed by ECM-DRT method in time-frequency domain and applied for the detection of Escherichia coli (E. coli). The results showed that using a dataset integrated with time-frequency domain features significantly improved the accuracy of bacterial concentration prediction. As a result, the RMSE of untrained concentration with LightGBM model was 6.4×10−4 log CFU ml−1, with the sensor detection limit about 2.69 log CFU ml−1. The research provided a tool combining time-frequency analysis for accurate prediction of bacterial concentration, which is crucial for evaluation of the antibacterial effect of long-term antibiotics on E. coli in future.

Understanding the Relationship between Electrochemical Fouling Control and Electrode Surface Coverage

Understanding the Relationship between Electrochemical Fouling Control and Electrode Surface Coverage

Osteocalcin active center models: Electrochemical adsorption on platinum and quantum chemical analysis

An attempt was made to simulate the electrochemical behavior of the osteocalcin active site simple models on the platinum component of a bimetallic Ti/Pt implant. Dicarboxylic glutamic acid and dicarboxylic aspartic acid, and ethylmalonic acid as the third model successfully complementing the model range. The surface coverage of the platinum electrode during adsorption of model dicarboxylic acids was estimated using cyclic voltammetry and electrochemical impedance spectroscopy. All three compounds demonstrate similar trends in the surface coverage dependencies on the adsorption potential, acids' adsorption onto platinum surface is weak, and in none of cases studied amino group participates in adsorption on the platinum electrode surface. Using quantum chemical calculations, the most stable conformations of model compounds and the values of voids between adsorbed dicarboxylic acid molecules were obtained. Since all three models have a relatively low surface coverage and are participants in the outer sphere process of nonspecific adsorption on platinum, the residues of γ-carboxyglutamic acid present in osteocalcin will not be specifically adsorbed on the platinum component of the bimetallic implant, and the absence of interactions between it and the platinum electrode should have a positive effect on the dynamics of osteoregeneration.

(Invited) Elucidating the Hydrodynamic Behavior of Multi-Species Gas Bubbles in an Electrochemical Solvent Regenerator for Direct Air Capture

Direct Air Capture (DAC) is very significant to bolstering the global drive towards net negative emissions. DAC technologies/plants have emerged in recent years, with the regeneration of the capture solvent used in the process being the major bottleneck of most aqueous technologies. [1] Leveraging electrochemical principles has offered a potential opportunity to simplify the entire solvent regeneration process and potentially reduce its overall capture cost, compared to traditional approaches. The electrochemical approach also offers the benefit of direct integrating clean energy, and also eliminating the high thermal energy requirements of typical methods.[2] Despite these potentials, the complex three-phase (solid-liquid-gas) interaction on the electrode surface pose a significant impediment to this electrochemical approach for DAC. The evolution of gas bubbles in electrochemical cells are well-known to contribute to energy losses in such reactors, from previous studies. [3],[4],[5] Gas bubbles have been shown to influence ohmic overpotentials in electrochemical reactors and studies have shown that the energy demand for water electrolysis can be reduced by 10-25 percent if the formation of gas bubbles is suppressed. [6],[7] However, the evolution of gas bubbles in electrochemical systems remains a complicated issue requiring further investigation. This study advances previous work by investigating the simultaneous evolution of CO2 gas bubbles along with O2/H2 gas bubbles in an electrochemical reactor for DAC. Gas bubbles are infamous for their ability to cover the active area of electrodes, limiting the transport of reactive species to the electrode surface, thus, increasing cell resistance. In this work, we explore changes in the polarization and hydrodynamics behavior of gas bubbles in the electrolyzer used for DAC solvent regeneration owing to the evolution of CO2 bubbles from pH swing, and the implications of the additional CO2 bubble formation to electrode surface coverage. By using a high-speed camera, we observe that bubbles coverage appears to be larger at the edges of the electrodes, and that the orientation of the electrodes influence bubble coalescence and detachment rate. We also employ different cell designs to mitigate the impact of bubble surface coverage towards reducing cell resistance. References Sabatino, A. Grimm, F. Gallucci, M. Van Sint Annaland, G. J. Kramer, M. Gazzani, Joule, 5(8), 2047-2076 (2021).Gao, A. Omosebi, R. Perrone, K. Liu, Journal of The Electrochemical Society (2022).H. Li, Y. J. Chen, Scientific Reports, 11(1), 1-12 (2021).F. Swiegers, R. N. L.Terrett, G. Tsekouras, T. Tsuzuki, R. J. Pace, R. Stranger, Sustainable Energy & Fuels, 5(11), 3004–3004 (2021).Zhao, H. Ren, L. Luo, Langmuir, 35(16), 5392-5408 (2019).Mazloomi, N. B. Sulaiman, H. Moayedi, International Journal of Electrochemical Science, 7(4), 3314-3326 (2012).C. Wang, C. Y. Chen, Electrochimica Acta, 54(15), 3877-3883 (2009).

Electrode Surface Coverage with Deposit Generated Under Conditions of Electrochemical Nucleation and Growth. A Mathematical Analysis

AbstractThe theory of the diffusion limited electrochemical nucleation and growth of a deposit consisting of isolated 3D hemispherical nuclei has been re-analysed. The analysis focuses on a widely discussed model which assumes formation of “diffusion zones” around the growing nuclei. It has been proposed in the literature that the deposit-free fraction of the surface area of the substrate can be directly calculated from the substrate coverage with the “diffusion zones”. The aim of this work is to analyse whether such an approach can be applied for the growth of isolated 3D hemispherical nuclei. This is accomplished by evaluation of equations which describe nuclei radii at various stages of the deposition process. The formulae allow determining the substrate surface coverage with the growing deposit. This, in turn, allows simulating and analysing faradaic currents due to other than the electrodeposition reactions which take place at the deposit-free fraction of the substrate surface. Both instantaneous and progressive modes of the nucleation are discussed and the influence of the nucleation type on the faradaic currents is outlined. A comparison with other approaches reported in the literature indicates that the deposit-free fraction of the substrate surface may not always be determined by means of recalculation of the substrate coverage with the “diffusion zones”.Graphical abstract

Structure of interfaces on mechanically renewed Sn, Pb, and Sn-Pb electrodes in acetonitrile solutions of surface inactive electrolytes

• Ideal polarizability regions of Sn and Pb electrodes in AN solutions were found. • Zero charge potentials of Sn and Pb in AN solutions were determined. • Time changes of capacitance curves are observed on Sn-Pb electrode after renewal. • It is shown that Pb atoms are squeezed out to the surface layer of Sn-Pb electrode. • Time effects on renewable Sn-Pb/AN solutions interface were analyzed in detail. The electrical double layer (EDL) structure of mechanically renewed electrodes of Sn, Pb, and Sn-Pb alloy (1 at.% Pb) is studied in acetonictrile (AN) solutions of LiClO 4 by the impedance method and cyclic voltammetry. The potential regions are found in which these electrodes can be considered in good approximation as ideal polarizable. In these solutions, the potentials of zero charge ( E σ = 0 ) on Sn and Pb electrodes are found to be –0.37 ± 0.02 and –0.59 ± 0.02 V (vs. aqueous SCE), respectively. The experimental dependences of the capacitance on the potential are shown to be in good agreement with the classical EDL model of Gouy–Chapman–Stern–Grahame. Based on the results of capacitance measurements carried out on renewed Sn-Pb electrodes, it is found that as the time of exposure of the renewed alloy surface to electrolyte increases, the C vs. E curves indicate that the concentration of lead atoms in the surface layer of alloy also increases, i.e., Pb is the surface-active component of these alloys. By analyzing the observed time effects, the surface coverage of Sn-Pb electrode by lead atoms (θ) is calculated in different time ( t ) after the renewal. It is shown that the θ vs. t dependences well agree with the model proposed earlier that describes the process of surface segregation of atoms of the surface-active component of eutectic alloys by the mechanism of surface diffusion. The kinetics of process of surface segregation of lead atoms on the mechanically renewed Sn-Pb electrode is compared for AN and aqueous solutions. The increase in θ is found to proceed slower in AN solutions than in aqueous solutions of the similar composition. The main reason for the differences observed is proposed.

Stability of Interfaces in All-Solid-State Lithium Batteries

High energy density batteries are needed with the rapid growth of electric vehicles market and the increasing demand for energy storage worldwide. Today, conventional lithium-ion batteries have some issues related to the use of flammable liquid electrolytes (safety problems). In addition to thermal stability issues, liquid electrolytes do not presently allow the use of lithium metal as a negative electrode due to the growth of uncontrollable dendrites during cycling. However, increasing the energy density in batteries requires to use metallic lithium which has a great specific capacity (≈ 3800 mAh / g). The substitution of liquid electrolytes by solid electrolytes within electrochemical energy storage devices is one of the most widely promising solutions today. Sulfide-based solid electrolytes are promising candidates for all solid-state batteries’ technology due to their high ionic conductivity, availability of different synthesis routes and low temperature processability, which are critical requirements for scalable fabrication of all-solid-state batteries (ASSB).Many recent studies have demonstrated the reactivity at the interfaces of solid electrolytes with lithium metal during electrochemical cycling, leading to bad electrochemical properties. Indeed, when argyrodite solid electrolyte (Li6PS5Cl) is used in contact with metallic lithium, reduction into Li2S, LiCl and Li3P (5-7) occurs leading to an SEI formation not properly controlled and understood. There is hence a strong need to master the solid electrolyte / lithium metal interface. Moreover, argyrodite is also oxidized by positive active materials during electrochemical cycling, into P2Sx (x ≥ 5), polysulfides, elemental sulfur and phosphates (7-9).The aim of our study is to master the interface between argyrodite and lithium metal, in order to reduce the reactivity, and increase the stability and life cycling. The use of selected protective layers, stable versus lithium and argyrodite will be presented. In our case we decided to work with lithium chloride (LiCl) and lithium sulfide (Li2S), which are relatively stable against lithium metal and argyrodite, as they come from the decomposition products of argyrodite. Dip-coating was used at the beginning, but surface coverage was not good enough, that’s why we developed a new way of coating called slow-evaporation process, which allows to increase the surface coverage of lithium electrode. We also believe that coated directly argyrodite pellet by Li3PO4 and Al2O3 could also decrease the reactivity at the interface. To do that we use atomic layer deposition (ALD), which allow to control the thickness of the coating at nanometer scale, and have a good surface coverage. The impact of temperature on surface coverage, and the coating thickness on reactivity and electrochemistry will be discussed. All these coatings were characterized by SEM, XRD, RAMAN, and XPS to analyzed interfaces chemical reactivity before and after cycling. In addition to interface stability, mechanical stability is also an important issue for ASSBs, leading to dendrites formation during cycling (10)(11). We will also present some strategies to increase the mechanical stability of argyrodite by using selected polymers as PTFE, PEO, or PVdF. Additionally, in order to reduce the oxidation of argyrodite at the positive electrode, a coating of Li4Ti5O12 on NMC111 by solution and spray-dryer will be also discussed. References Kamaya, K. Homma, Y. Yamakawa, et al. Nature Materials. 10 682 (2011).Zhou, L.; Park, K.-H.; Sun, X.; Lalère, F.; Adermann, T.; Hartmann, P.; Nazar, L. F. ACS Energy Lett. 4 (1), 265–270 (2019).Boulineau, S.; Courty, M.; Tarascon, J.-M.; Viallet, V. Solid State Ionics. 221, 1–5 (2012)Yu, C.; van Eijck, L.; Ganapathy, S.; Wagemaker, M. Electrochimica Acta. 215, 93–99 (2016).Tan, D. H. S. et al. ACS Energy Letters. 4, 2418–2427 (2019).Wenzel, S.; Sedlmaier, S. J.; Dietrich, C.; Zeier, W. G.; Janek, J. Solid State Ionics. 318, 102–112 (2018).Auvergniot, J. et al. Solid State Ionics 300, 78–85 (2017)Auvergniot, J. et al. Mater. 29, 3883–3890 (2017)Tan, D. H. S. et al. ACS Energy Lett. 2418–2427 (2019)Doux, J. M. et al. Mater. Chem. A 8, 5049–5055 (2020).Doux, J. M. et al. Energy Mater. 10, 1–6 (2020).

Comparative electrochemical and spectroscopic analysis of the inhibition effect of molybdates and boiled red onion extract on the corrosion of tin in acidic solution

The corrosion inhibition efficiency (η%) and its passivation mechanisms of tin in 0.2 M malic acid by two different types of potential inhibitors, boiled red onion skin extracts (BROE) and molybdate (MoO4 2−), were examined and compared. The influence of the two inhibitors was evaluated by using the electrochemical polarization and the electrochemical impedance spectroscopy (EIS) methods. The electrode surface coverage was analyzed employing scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The electrochemical polarization curves revealed that increasing inhibitor concentration led to a significant reduction of the tin corrosion rate. The presence of BROE and molybdates produced inhibition efficiency (η%) values of 93 and 87%, respectively. Electrochemical measurements and surface analysis have shown satisfactory agreement, that both inhibitor compounds effectively inhibited tin corrosion in 0.2 M maleic acid by forming protective inhibiting deposits that hindered the active electrochemical corrosion sites on the tin surface. Comprehensive insights into the corrosion inhibition mechanism of these compounds in a 0.2-M maleic acid environment, through the suggested equivalent circuits, are also provided.

Unraveling optimal interfacial conditions for highly efficient and reproducible organic photovoltaics under low light levels

The insertion of interfacial layers between the photoactive layer and electrodes is effective for improving the power conversion efficiency (PCE) of organic photovoltaics (OPVs). Further understanding on effects of the interlayers is needed to optimize OPV performance in low light applications, as the operating mechanism of OPVs varies depending on the light intensity. Here, the critical roles of the electron transport layer (ETL) on the performance of OPVs are demonstrated in different irradiation environments involving low-intensity lighting. ZnO ETL was found to deliver better performance and reproducibility compared with a conjugated polyelectrolyte ETL regardless of the irradiation conditions, showing high PCEs exceeding 18% under low light conditions such as a 500 lx light-emitting diode. In addition to the great charge selectivity and electronic properties, the uniform surface coverage of the bottom indium tin oxide electrode was a key factor in preventing shunt path formation and consequently reducing recombination and leakage current, which mainly determine the low light performance of OPVs. This study provides important design considerations for interfacial contact materials to achieve high-performance and reproducible OPVs that operate unconditionally over a wide range of light intensities for various applications.

Electroactive Molecularly Imprinted Polymer for Selective Detection of 4-Nitrophenol

We propose to develop a reusable electro-chemical sensor for selective detection of 4-nitrophenol (4-NP), based on molecularly imprinted polymer (MIP) technology. MIP technology is the design of an artificial receptor with high selectivity for a specific analyte. Our approach combines N-isopropylacrylamide (NIPAM) backbone polymer with different functional monomers to improve the selectivity and sensitivity of 4-nitrophenol (4-NP) detection.The key points of our sensor polymer are:1) reduced amount of covalent crosslinker methylene bis-acrylamide (MBA) to increase rebinding kinetics and affinity and 2) modified polymer backbone with an electroactive block deposited on a gold surface. To get rapid high affinity template rebinding, we used a reduced amount of covalent crosslinker and used noncovalent crosslinking based on acid-base and hydrophobic interactions. To form acid-base crosslinking, we used 4-vinylpyridine (4-VP) as the basic monomer and methacrylic acid (MAA) as acidic monomer.In MIPs synthesis part, our strategy takes the advantage of reversible addition fragmentation-chain transfer (RAFT) polymerization to control the polymer chain length and modify the terminus as poly-ferrocene methyl methacrylate (FMMA), an electroactive block. The RAFT agent contains R group and Z group which are at different ends of polymer. The Z side is reduced to a thiol and deposited on gold. The PolyFMMA block is on the R side. RAFT agent, FMMA monomers and initiator were added to a batch system to synthesis the first electroactive block. Then, all chemicals including backbone monomers, functional monomers, crosslinkers and templates (4-NP) were added to form the major polymer block. After synthesis, templated-MIPs were dialyzed to remove the template for further target selective detection.One of the major challenges of our sensor is polymer tangling which affect measurement stability. To reduce polymer tangling effects, we dissolved the template-removed MIPs into tetrahydrofuran (THF) and controlled the gold electrode surface coverage. We deposited MIPs on an additional flat gold chip and used atomic force microscope (AFM) to characterize the surface coverage distribution.The modified gold electrode can be used in electrical impedance spectroscopy (EIS) or cyclic voltammetry (CV) to measure charge transfer distance before and after template rebinding to detect unknown concentration target analytes.

Removable Composite Electrode Made of Silver Nanoparticles on Pyrolyzed Photoresist Film for the Electroreduction of 4-Nitrophenol

Access to removable nanocomposite electrodes for electrosensing of pollutants is of great importance. However, the preparation of reproducible and reliable carbon electrodes decorated with metallic nanoparticles, a prerequisite for trustworthy devices, remains a challenge. Here we describe an innovative and easy method to prepare such electrodes. These latter are silicon-coated with a thin carbon film on which controlled silver nanostructures are grafted. Different silver nanostructures and surface coverage of the carbon electrode (16, 36, 51, and 67%) can be obtained through a careful control of the time of the hydrogenolysis of the N-N' isopropyl butylamidinate silver organometallic precursor (t = 1, 5, 15, and 60 min, respectively). Importantly, all nanocomposite surfaces are efficient for the electrodetection of 4-nitrophenol with a remarkable decrease of the overpotential of the reduction of such molecule up to 330 mV. The surfaces are characterized by atomic force microscopy, grazing incidence X-ray diffraction, scanning electronic microscopy, and Raman spectroscopy. Furthermore, surface-enhanced Raman scattering effect is also observed. The exaltation of the Raman intensity is proportional to the surface coverage of the electrode; the number of hot spots increases with the surface coverage.

Highly Sensitive Method to Isolate Photocurrent Signals from Large Background Redox Currents on Protein‐Modified Electrodes

AbstractThe high quantum efficiency in converting light energy into a charge‐separated state is a major advantage in using photosynthetic proteins in biophotovoltaic applications. Photocurrents are typically measured at open circuit potential (OCP), where the electrochemical redox or faradaic currents are minimized. However, at potentials far from the OCP, the photocurrents produced by the proteins may be impossible to measure against the large background current, owing to electrochemical redox reactions of charge‐transfer mediators and/or sacrificial electron donors. Demonstrated here is a highly sensitive method using a sinusoidal‐modulated intensity of an LED excitation light source to isolate the protein‐based photocurrent component from the total current irrespective of electrode surface coverage. Using a genetically modified photochemical reaction center from Rhodobacter sphaeroides as a proof‐of‐concept, photocurrents up to 104–105 orders of magnitude smaller than the background electrochemical redox current (due to redox reactions directly on the electrode surface) were measured at applied voltages >0.4 V from the OCP. The phase relationship between the optical excitation and photocurrent response was also measured and shown to be analytically useful.

Study on self-assembled monolayer of functionalized thiol on gold electrode forming capacitive sensor for chromium(VI) determination

A capacitive sensor based on S-{12-[1-(pyridin-4-ylmethyl)-1H-1,2,3-triazol-4-yl]dodecyl} ethanethioate (FT), a compound with a functional group exhibiting selective affinity towards Cr(VI) ions, was developed. FT was mixed with shorter-chain thiol-decanethiol (DT), to obtain an Au electrode surface well covered by a thiol monolayer. The composition and high quality of self-assembled monolayers (SAMs) were crucial factors influencing the performance of the capacitive sensor. In this work, SAMs formed from FT and DT mixtures with different compositions were studied. For physicochemical characterization of SAMs X-ray photoelectron spectroscopy (XPS), contact angle measurements as well as atomic force microscopy (AFM) were used. Cyclic voltammetry was employed to estimate an electrode surface coverage. Based on the obtained results, the composition of thiol layer providing the best parameters for capacitive sensing of chromium(VI) was chosen. Moreover, the analytical performance of sensor was verified.

Highly Sensitive Electrocatalytic Determination of Formaldehyde Using a Ni/Ionic Liquid Modified Carbon Nanotube Paste Electrode

In this study, ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate was applied as additives to fabricate a novel ionic liquid/carbon nanotube paste electrode (IL/CNPE). This electrode was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. Results showed that the electron transfer rate and reversibility of the electrode were increased by the ionic liquid. The morpho-logy of prepared IL/CNPE was studied by scanning electron microscopy. Nickel/ionic liquid modified carbon nanotube paste electrode (Ni/IL/CNPE) was also constructed by immersion of the IL/CNPE in nickel sulfate solution. Ionic liquid showed significant effect on the accumulation of nickel species on the surface of the electrode. Also, the values of electron transfer coefficient, charge-transfer rate constant and electrode surface coverage for Ni(II)/Ni(III) redox couple of the Ni/IL/CNPE were found to be 0.32 and 2.37×10-1 s-1 and 2.74×10-8 mol.cm-2, respectively. The Ni/IL/CNPE was applied successfully to highly efficient electrocatalytic oxidation of formaldehyde in alkaline medium. The effects of various factors on the efficiency of electrocatalytic oxidation of formaldehyde were optimized. Under the optimized condition, cyclic voltammetry of formaldehyde at the modified electrode exhibited two linear dynamic ranges in the concentration ranges of 7.00×10-6 to 9.60×10-5 mol.L-1 and 9.60×10-5 to 32.00×10-3 mol.L-1 with excellent detection limit of 9.50×10-7 mol.L-1 (3σ/slope), respectively. Also, the method was successfully applied for formaldehyde measurement in real sample.

Synthesis and characterisation of cobalt oxide nanoparticles decorated graphene oxide and its electrocatalytic behaviour

Electrocatalytic behaviour of graphene oxide nanosheets (GONS) and cobalt oxide nanoparticles (Co3O4NPs) composite modified glassy carbon based sensor for 2,4 dichlorophenol (2,4 DCP) is investigated in this work. The GONS and Co3O4NPs were successfully synthesised and characterised by Fourier Transform Infrared Red (FTIR) spectroscopy, UV–Vis spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX) spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. The electrode surface area and surface coverage were 0.13 cm2 and 1.31 × 10−12 mol cm−2 respectively after modification with GONS/Co3O4NPs composite. The modified electrode had an electro-oxidation catalytic rate constant, k, of 3.6 × 106 M−1 s−1 and limit of detection of 3.5 × 10−7 M for the same test analyte. The electrode showed good reproducibility and an appreciably low oxidation potential (0.8 V) for 2,4-DCP.

Kinetics of island growth in the framework of “planar diffusion zones” and “3D nucleation and growth” models for electrodeposition

In the electrochemical deposition of thin films the measurement of the current-time curve does not allow for a direct determination of the nucleus growth law, electrode surface coverage and mean film thickness. In this work we present a theoretical approach suitable to gain insight into these quantities from the knowledge of nucleation density, solution parameters and current-time behavior. The model applies to both isotropic and anisotropic growth rates of nuclei and a study on the effect of nucleus shape and aspect ratio on the kinetics is presented. Experimental results from literature are also discussed in the framework of the present approach.