Platinum Working Electrode Research Articles

Evaluation of Electrochemical Sensor Using Microfluidic System

This paper presents the characterization and testing of electrochemical sensor using microfluidic system. Various geometric patterns were laser cut into the platinum working electrode of a biosensor. In this work, a microfluidic chamber was designed that allows phosphate buffer solution (PBS) to flow across the sensor, using a peristaltic pump, while varying the concentration of hydrogen peroxide. The amperometric characterization of the electrochemical sensor with 25, 50, 75, and 100[Formula: see text][Formula: see text]m perforation and 75[Formula: see text][Formula: see text]m spacing showed the highest sensitivity. This result was to be expected the purpose of patterning the sensors was to provide a 3-dimensional structure to the planar electrode in order for the enzyme, glucose oxidase, to be immobilized. Future work will include selecting one of the patterns for immobilization of glucose oxidase allowing us to realize a fully functional glucose sensor.

A solid state electrolyte based enzymatic acetone sensor

This paper introduces a novel solid-state electrolyte-based enzymatic sensor designed for the detection of acetone, along with an examination of its performance under various surface modifications aimed at optimizing its sensing capabilities. To measure acetone concentrations in both liquid and vapor states, cyclic voltammetry and amperometry techniques were employed, utilizing disposable screen-printed electrodes consisting of a platinum working electrode, a platinum counter electrode, and a silver reference electrode. Four different surface modifications, involving different combinations of Nafion (N) and enzyme (E) layers (N + E; N + E + N; N + N + E; N + N + E + N), were tested to identify the most effective configuration for a sensor that can be used for breath acetone detection. The sensor's essential characteristics, including linearity, sensitivity, reproducibility, and limit of detection, were thoroughly evaluated through a range of experiments spanning concentrations from 1 µM to 25 mM. Changes in acetone concentration were monitored by comparing currents readings at different acetone concentrations. The sensor exhibited high sensitivity, and a linear response to acetone concentration in both liquid and gas phases within the specified concentration range, with correlation coefficients ranging from 0.92 to 0.98. Furthermore, the sensor achieved a rapid response time of 30–50 s and an impressive detection limit as low as 0.03 µM. The results indicated that the sensor exhibited the best linearity, sensitivity, and limit of detection when four layers were employed (N + N + E + N).

QEchemMEMS – A working electrode with high-resolution temperature sensing for studying electrochemical heat management systems

Electrochemical heat pumps are a new and interesting concept for efficient thermal energy management at the micro- and macro-scale. The development of new solutions for electrochemical heat pumps requires reliable and high-resolution measurements of the temperature changes resulting from redox reactions. A device for measuring such temperature variations, manufactured using microelectromechanical system technology, is presented and characterized in this study. The device contains a platinum working electrode suspended on a thin SixNy membrane for the electrochemical cell; this electrode also serves as a resistive thermal device (RTD). The device and temperature readout electronic implementations of the Anderson loop are characterized. The temperature coefficient of resistance is 2736 ppm/K. The theoretical noise performance is predicted and verified in practice. The voltage noise of the RTD is 28 nV, which results in a temperature measurement resolution of 1.3 mK despite a very small RTD bias current of 40 µA.

Photogalvanics of copper and brass working electrodes in the NaOH-Allura Red-d-galactose-DDAC electrolyte for solar power generation.

Solar energy is a limitless energy resource that can be used to produce electricity forever. Photogalvanic cells can convert solar energy into electricity with inherent power storage. The electrolyte(s) and a combination of two electrodes are the main materials required for fabrication of these cells. So far, platinum has been used as the working electrode in photogalvanic cells. Platinum is an extremely rare and expensive metal. Copper and its alloy (brass) have been identified as alternative working electrodes to substitute the platinum working electrode in photogalvanic cells. In addition, copper and brass utilization is identified to be an effective, user-friendly, and safe approach for high-power generation. Therefore, in the present work, cheap and easily obtainable copper and brass (alloy of copper and zinc) working electrodes have been exploited with the twin aim of high-power generation with less input cost. In the present study, the observed power, current, potential, and efficiency for the copper electrode are 552.3 µW, 4030 µA, 713 mV, and 8.54%, respectively, and those for the brass electrode are 546.4 µW, 5320 µA, 739 mV, and 6.12%, respectively. The observed electrical performance is greatly enhanced compared to most of the already reported photogalvanics with platinum electrode. Copper and brass are slightly and slowly corroded by the alkali, but despite this electrode loss, both materials are promising to produce the highest power. In the future, this electrode loss can be checked by using inhibitors.

Fatal Impurity for Electrochemical Mg Deposition/Dissolution

Rechargeable magnesium batteries (RMBs) are promising large-scale stationary energy storage devices. A manufacturing system similar to that used for lithium-ion batteries should be adoptable to the fabrication of RMBs. However, the compatibility of RMB components with atmospheric components other than moisture has not been studied yet. This might be due to the uncertain preconception and misunderstanding of the passivation characteristics of magnesium. In this study, we investigated the effects of atmospheric conditions on the electrochemical dissolution–deposition behavior of magnesium in non-aqueous electrolytes.1 The compatibility of magnesium metal and electrolytes incorporating air-stable weakly-coordinated anions [B(HFIP)4]− or [Al(HFIP)4]− (HFIP: hexafluoro-iso-propoxyl) with dry air was investigated. The results of a simple cyclic voltammetry (CV) clearly demonstrate the far excessive care of magnesium metals against atmospheric O2, because reversible magnesium deposition/dissolution is possible using magnesium metals polished under dry air. However, cells assembled under a dry-air atmosphere show no features of electrochemical magnesium deposition/dissolution. To identify which component of a dry air has a significant detrimental effect on the electrochemical characteristics, systematic CV and open-circuit potential (OCP) measurements were conducted under certain atmospheric conditions with Ar, N2, and O2 and an air-tight voltammetry cell equipped with gas-inlet lines. The platinum and magnesium working electrodes show characteristic responses dependent on the inlet gases, and O2 gas is found to be detrimental for the electrochemical activities of magnesium (Figure 1). The time-profile of OCP and that of O2 content in the electrolyte under steady flow of O2 gas are correlated well, suggesting passivation of magnesium metal upon uptake of O2 in the electrolyte. The electrochemical impedance spectra of symmetric magnesium metal cells using oxygenated and deoxygenated electrolytes and X-ray photoelectron spectra further corroborate inactivation of magnesium by even miniscule amount, ca., 10 ppm, of O2 impurity. Acknowledgement This work was financially supported by the Advanced Low-Carbon Technology-Specially Promoted Research for Innovative Next Generation Batteries Program (ALCA-SPRING, Grant Number JPMJAL1301), NEXT Center of Innovation Program (COI-NEXT, Grant Number JPMJPF2016) of the Japan Science and Technology Agency, and KAKENHI (Grant No. 21K05263) of the Japan Society for the Promotion of Science. Reference T. Mandai and M. Watanabe, under revision. Figure 1

Replacement of conventional reference electrode with platinum electrode for electronic tongue based analysis of dairy products

This work demonstrates the utility of platinum metal electrode as replacement for conventional Ag/AgCl reference electrode for voltammetric electronic tongue based analysis of edible dairy products. It overcomes the limitations of conventional silver-based reference electrode that presents a potential health hazard when employed for analysis of edible dairy products. Various dairy products like toned milk, Lassi and skimmed milk powder were tested using a cluster of platinum, gold and rhodium working electrodes. Responses of electrode cluster were captured using cyclic voltammetry. Comparative investigations were carried out between responses with platinum reference electrode and Ag/AgCl reference electrode. Repeatability and reproducibility of results have been examined. Our results suggest that platinum metal reference electrode can be reliably used for voltammetric electronic tongue based analysis of dairy products. Further this shall pave way for commercial development of electronic tongue technology in food sector adhering to hygienic and food safety regulations.

An In Situ, multi-electrode electrochemical method to assess the open circuit potential corrosion of Cr in unpurified molten FLiNaK

An in situ electrochemical method to investigate the time-dependent spontaneous corrosion of pure Cr in an unpurified LiF-NaF-KF eutectic salt at 600 °C was developed. A multi-electrode electrochemical cell and a dual-electrode method were utilized to detect Cr(II) and Cr(III) ions on a platinum working electrode using cyclic voltammetry as a function of exposure time and compensating for the distance from the Cr electrode. XRD was performed to characterize the crystalline composition of the exposed FLiNaK and the salt films formed on the working electrodes. The fate of all electro-oxidized Cr must be accounted for to quantify corrosion rates. The concentrations of Cr(II) and Cr(III) species obtained were compared with the gravimetric mass change and ICP-OES analysis of the residual salt. Outcomes, difficulties, and limitations are discussed.

Plasticizer-free Hydrazonic Dibenzo-18-crown-6 derived lead ion sensing electrodes

The redox behaviours of three dibenzo-18-crown-6 hydrazones were investigated via cyclic and square wave voltammetries, prior to their electropolymerization onto a platinum working electrode to yield three novel Ion Selective Electrodes (ISEs) whose lead sensing behaviours were investigated via Differential Pulse Anodic Stripping Voltammetry (DPASV) and Electrochemical Impedance Spectroscopy (EIS), subsequent to their characterization via Scanning Electron Microscopy (SEM). For all three ISEs, the electrosynthesized polymeric Ion Selective Membranes (ISM) are multi-layered with pores of diverse dimensions; a feature which allows wide linear ranges (4–107 ppm) in all cases, relative to Flame Atomic Absorption Spectroscopy (FAAS); one of the traditional “go-to” methods for metal ion quantification. Additionally, these ISEs allow selective detection of Pb2+ at concentrations below 20 ppm even in the presence of high concentrations of competing metal ions, except when excess Al3+ is present. Overall, given the relative ease of modification and low cost of these hydrazonic dibenzo-18-crown-6 ISEs, coupled with their performance, they represent a viable starting point for the development of high quality, low cost lead ISEs.

Differentiating between Ion Transport and Plating–Stripping Phenomena in Magnesium Battery Electrolytes Using Operando Raman Spectroscopy

Understanding metal plating–stripping and mass transport processes is necessary for the development of new electrolytes for post-lithium energy storage applications. Operando vibrational spectroscopy is a valuable analytical tool for this purpose, enabling structural and chemical changes at electrode–electrolyte interfaces to be probed dynamically, under battery cycling conditions. In this work we apply operando Raman spectroscopy to characterize the behavior of the Mg based “all phenyl complex” [Mg2Cl3]+[AlPh4]− in tetrahydrofuran (THF), an exemplar electrolyte for emerging Mg battery technologies. We demonstrate that the observed electrolyte Raman band intensities vary reversibly with electrochemical cycling due to anion migration in response to the applied electric field, while Mg plating and stripping can be monitored independently through the broad background scattering intensity. Spectral measurements across different sites of the platinum working electrode indicate that the ion transport response is spatially heterogeneous, while the plating and stripping response is ubiquitous.

A novel method for Ion Exchange Capacity characterization applied to Anion Exchange Membranes for Water Electrolysers

Hydrogen production from water electrolysis, hydrogen fuel cells and redox flow batteries are the right approach for the renewable energy sector because the electricity generated by solar, wind, photovoltaic, hydroelectric can be managed with a carbon-free approach. These technologies all have in common one fundamental component: the membrane. Different types of membranes have been developed for both cationic and anionic exchange, and recently, research activity focalized on improving their performances is very fervent. One fundamental characteristic of a membrane is its Ion Exchange Capacity (IEC), i.e. the density of charged functionalizing groups. Within our research project NEMESI, funded by EU-PNRR (ID: RSH2B_000002), and dedicated to Anion Exchange Membrane Water Electrolysis, we studied and validated a novel alternative method to measure IEC. The present titration methods have limitations for the need of dedicated hardware or qualitative inspection of their color-turning endpoint. The proposed method, based on the redox titration of potassium ferricyanide with ascorbic acid, allows a quantitative and independent assessment based on both potentiometric and spectrophotometric measurements, along with the usually adopted visual observation, as the yellow-colored ferricyanide is reduced to colorless ferrocyanide. Moreover, if compared to the classical Mohr titration with silver nitrate, the new method can be carried out at variable ferricyanide concentrations during the addition of the ascorbic acid, so a complete curve of the redox reaction can be constructed: the initial ferricyanide ion load of the membrane (IEC) can thus be derived in a more precise way than with a single-point evaluation. Only one Ag/AgCl reference electrode and a platinum working electrode are required without any power supply/potentiostat. The proposed method was validated using Anion Exchange Membranes with known IEC.

Characterizing Recast Nafion® Film Electrode Interface Diffusion and Kinetics in a Non-Aqueous System

The effect of recast Nafion® films on platinum working electrodes in acetonitrile will be characterized by cyclic voltammetry and rotating disk voltammetry. Until now, the behavior of recast Nafion® in a non-aqueous system has not been reported in this way. The behavior of recast Nafion® films in acetonitrile has been anecdotally observed to be different from the behavior in aqueous solutions, which have also been comprehensively studied1,2. The reversible redox couple of Tris(2,2′-bipyridine)ruthenium(II) hexafluorophosphate, Ru(bpy)3 2 ++, in an acetonitrile electrolyte solution will be compared between a bare platinum working electrode and a recast Nafion® film coated platinum working electrode by cyclic voltammetry. In cyclic voltammetry the convective mass transport of the species is limited only to the diffusion at the stationary electrode interface. In rotating the working electrode (RDE) the limitation on mass transport is extended beyond the stationary diffusion behavior. The current is dependent on and limited by the mass transport of the species to the electrode interface where it can undergo redox, the limiting current of both a bare platinum working electrode system and of a recast Nafion® film coated platinum working electrode will be observed by changing the rotation rate of the RDE. The diffusion interface of the electrode inside an acetonitrile solution of Ru(bpy)3 2 + and an electrolyte will be determined by rotating disk voltammetry at a bare platinum working electrode and at a recast Nafion® film coated platinum working electrode. The film solution interface thickness will be reported along with the effect on the diffusion of the interface between bare and recast Nafion® coated platinum working electrodes.1. S. K. Zecevic et al 1997 J. Electrochem. Soc. 144 29732. T. A. Zowodzinski, S. Gottesfeld et al 1997 Advances in Electrochemical Sciences and Engineering

Acetone sensing in liquid and gas phases using cyclic voltammetry

This paper presents the use of cyclic voltammetry to measure acetone concentration in liquid and vapor forms at disposable screen-printed electrodes of platinum working electrode, platinum counter electrode, and silver/silver chloride reference electrode. The main characteristics of the acetone sensor including its linearity, sensitivity, reproducibility, and limit of detection (LOD) were studied by doing different experiments to test both liquid and vapor samples in the physiological range of 1 µM to 10 mM. The change in acetone concentration was monitored by comparing the lineshape of butterfly region before and after injecting the acetone sample in the baseline solution that contains 0.5 M H2SO4. The sensor was shown to have a good sensitivity, reproducibility, and a linear response with respect to the acetone concentration in both liquid and gas phases over a range of 1 µM to 10 mM with R2 > 0.97 and LOD of 0.1 µM. The system stability was improved by building a closed glass system to reduce the exchange of acetone with the surrounding air in an open environment. The closed system was tested using vapor samples and the error bars in the calibration curve were reduced to more than half of their values before using the closed system. The new system will be used extensively in future for an enzyme-based acetone sensor that will be used for diabetes monitoring.

Electrochemical Monitoring of Manganese in Drinking Water

Low levels of Mn are essential for many metabolic processes in the human body, yet excessive exposure to this heavy metal has been correlated to neurodegenerative diseases with Parkinson’s like symptoms in adults and neurological deficits in children. Erosion of Mn rich soil and rocks and human activities directly pollute groundwater which supplies drinking water for 51% of the total US population and 99% of the rural population. Hence contaminated drinking water represents one of the major sources of Mn intake. The non-enforceable updated guideline set by the EPA is 50ppb Mn. Trace metal analytical methods such as ICP-MS and AAS are limited to centralized laboratory testing and not feasible for point-of-care. Our work is aimed at the development of an electrochemical platform for efficient and rapid Mn detection in drinking water. The core technique is Square Wave Cathodic Stripping Voltammetry (SWCSV), carried out on disposable three-electrode sensors with a platinum working electrode, platinum counter electrode and an electroplated Ag/AgCl reference electrode. A 3D printed interface integrates a small vibration motor for effective agitation of the 12µL droplet sample during the deposition phase and allows connection to a commercial potentiostat. Figure 1(a) depicts the hardware components of the platform, with an onset on the sensor configuration. First, the system performances are characterized in standard solutions. Compared to peak amplitude, peak area is found to be a more suitable indicator of Mn concentration, with a linearity of R^2=0.998 in the range 5ppb-200ppb. The introduction of an embedded agitation mechanism allows for a reduction in the limit of quantitation (LOQ) from 5ppb to 3ppb and an approximate 2.3X increase in sensitivity from 9.09nC/ppb to 20.75nC/ppb. Analysis of tap water is then performed to confirm the capabilities of the electrochemical platform in more complex matrices. With optimal SWCSV parameters a limit of quantitation of 6ppb, a sensitivity of 26.45 nC/ppb and a linearity with R^2=0.995 are achieved. The developed protocol requires minimal sample preparation of the water samples, with a 2X dilution in 0.2M Acetate Buffer to provide enough ionic strength to sustain the faradaic reactions and buffer the pH at 4.7. 3-point standard addition is executed to determine the Mn concentration in unknown specimens and performances are compared to ICP-MS on the analysis of 78 tap water and well water samples from Holliston, MA with concentrations in the range 0.03ppb-5.3ppm. 100% agreement, 70% accuracy and 91% precision were obtained. Figure 1(b) shows typical voltammograms from the measurement of the unknown sample and the 3 spikes at known Mn concentrations to implement the 3-point standard addition. To enhance monitoring of water quality in local communities and rural areas, parallelization of the measurements can further reduce the analytical time and improvements in the interface can ultimately make the devised portable and easy-to-use electrochemical station soon deployable for practical on-the-field testing. Figure 1

Study of the histidine complex of uranium(IV): synthesis, spectrophotometric, magnetic and electrochemical properties

We synthesized the novel histidine complex of uranium(IV). A 1:3 mole ratio was found between metal and ligand by the mole ratio method, while –NH2 and –COO– groups of histidine behave as coordinating sites. The IR spectra confirmed the lone pair donating or coordinating sites. The elemental analysis confirmed the stoichiometry. The bathochromic shift with an increase in the optical density in the UV-Visible range indicated that the compound and its central metal ion hold uniform electronic charge distribution. The electrochemical results indicated a quasi-reversible (neither completely reversible nor completely irreversible) oxidation of the complex to its uranium(V) product at the platinum working electrode. The quasi-reversible process shows a comparatively slow electron transfer (ET) rate with the heterogeneous electron transfer rate constant ‘ks’ (3.4 × 10–4 cm s-1) at 50 mV s-1 and 305 ± 0.5 K. The kinetics such as diffusion and charge transfer lead the reaction with an ECE (electrochemical–chemical–electrochemical) mechanism. The thermodynamic parameters of activation such as ΔH*; 4.257 kJ mol–1, ΔS*; -2.519 × 10–3 J mol–1 K–1 and ΔG* 4.26 kJ mol–1 helped to propose an associative mechanism of the electron transfer at the platinum working electrode.
 
 KEY WORDS: Uranium, Histidine, Spectroscopy, Electrochemistry, Kinetics
 
 Bull. Chem. Soc. Ethiop. 2020, 34(3), 557-569. 
 DOI: https://dx.doi.org/10.4314/bcse.v34i3.11

Development of voltammetric methods for antioxidant activity determination based on Fe(III) reduction

Numerous methods have been developed for determination of antioxidant (AO) activity in vitro, but only several spectrophotometrical assays are frequently applied. Among them, probably the most simple is FRAP assay, based on the reduction of Fe(III) to Fe(II) by antioxidants. In this work the applicability of that reaction for the development of electrochemical method for AO activity determination was examined. The two common electrochemical techniques: direct current polarography and cyclic voltammetry on platinum working electrode were used. The developed fast, simple and without a need for the calibration against standard (such as Trolox or gallic acid) electrochemical methods were applied to determination of the AO activity of ten natural antioxidants. The AO activities determined by two developed methods and three frequently applied spectrophotometric assays (ABTS, DPPH and FRAP) correlated well. All the obtained correlation coefficients (R) were above 0.9. The cyclic voltammetric method fulfills green chemistry principles.

Electrical and spectroelectrochemical investigation of thiophene-based donor-acceptor copolymers with 3,4-ethylenedioxythiophene

Abstract This work reports the spectroelectrochemical and electrical behavior of electropolymerized donor-acceptor like (D-A) copolymer films, based on 3,4-ethylenedioxythiophene (EDOT) and beta-substituted electron-acceptor thiophenes. Initially, the copolymer films were deposited on indium tin oxide substrates, which spectroelectrochemistry measurements were carried out with an UV-Vis spectrophotometer. Hence, it was possible to observe the electrochromic properties of these materials, visualizing the color changing towards different potentials applied. The experiments have shown that these D-A like copolymers presented good electrochromic properties, such as optical contrast, coloration efficiency, and switching times. Additionally, films prepared on a platinum working electrode were investigated by electrochemical impedance spectroscopy, which has shown the electrical behavior of those copolymers and their potential as candidates to capacitive devices building. Therefore, the combination of electron-donor EDOT with those electron-acceptor monomers is indeed a useful strategy to tailoring and fine-tuning the physicochemical properties of polythiophenes with innovative applications.

Electrochemical investigation of novel reference electrode Ni/Ni(OH)₂ in comparison with silver and platinum inert quasi-reference electrodes for electrolysis in eutectic molten hydroxide

An efficient and green energy carrier hydrogen (H2) generation via water splitting reaction has become a major area of focus to meet the demand of clean and sustainable energy sources. In this research, the splitting steam via eutectic molten hydroxide (NaOH–KOH; 49–51 mol%) electrolysis for hydrogen gas production has been electrochemically investigated at 250–300 °C. Three types of reference electrodes such as a high-temperature mullite membrane Ni/Ni(OH)2, quasi-silver and quasi-platinum types were used. The primary purpose of this electrode investigation was to find a suitable, stable, reproducible and reusable reference electrode in a molten hydroxide electrolyte. Cyclic voltammetry was performed to examine the effect on reaction kinetics and stability to control the working electrode at different scan rate and molten salt temperature. The effect of introducing water to the eutectic molten hydroxide via the Ar gas stream was also investigated. When the potential scan rate was changed from 50 to 150 mV s−1, the reduction current for the platinum wire working electrode was not changed with newly prepared nickel reference electrode that designates its stability and reproducibility. Furthermore, increasing the operating temperature of molten hydroxides from 250 to 300 °C the reduction potential of the prepared nickel reference electrode is slightly positive shifted about 0.02 V. This suggests that it has good stability with temperature variations. The prepared nickel and Pt reference electrode exhibited stable and reliable cyclic voltammetry results with and without the presence of steam in the eutectic molten hydroxide while Ag reference electrode exposed positive shifts of up to 0.1 V in the reduction potential. The designed reference electrode had a more stable and effective performance towards controlling the platinum working electrode as compared to the other quasi-reference electrodes. Consequently, splitting steam via molten hydroxides for hydrogen has shown a promising alternative to current technology for hydrogen production that can be used for thermal and electricity generation.

High-Rate Dissolution of Corrosion Resistant Alloys in Nonaqueous Solutions at Room Temperature

Syntheses of pharmaceuticals often require a series of intermediate steps involving reactions in organic solvents. Some of these solutions can be aggressive towards the metallic materials that constitute the reaction vessels used, so often corrosion resistant alloys (CRA) such as the Ni-Cr-Mo UNS N06022, N06035 and N10362 are employed. Such materials are expensive, but their use is required to prevent contamination of the product by metal ions. Among the reagents commonly present in pharmaceutical processes is 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), a strong oxidant that is widely used in the dehydrogenation of organic compounds. Understanding the interaction of DDQ with the alloys that constitute the reaction vessels is essential. Ni-Cr-Mo alloys are known to exhibit outstanding corrosion resistance in reducing and oxidizing aqueous solutions as a result of their passive oxide film. However, the application of passive alloys in nonaqueous solvents raises additional concerns due to: i) limited availability of water and/or oxygen for passivation; ii) different behavior of aggressive anions and acids as a result of the solvent’s physical properties. Nevertheless, the literature on corrosion of CRAs is focused on behavior in aqueous solutions and little is known about the influence of quinones in corrosion in general. The aim of this work is to investigate the corrosion of Ni-Cr-Mo alloys in organic solutions containing DDQ. Preliminary work was carried out with anhydrous solutions containing acetonitrile, ethanol, DDQ and HCl (or EtAlCl2) at room temperature. Mass loss tests have shown that alloy N06022 exhibits high-rate dissolution and crystallographic pits in such conditions. The corrosion rates observed after 24 h of immersion are greater than 10 mm/year, which is remarkably high when compared with the existing literature on corrosion of Ni-Cr-Mo alloys. The dissolution process appears to be caused by a synergistic effect between DDQ and HCl, in which corrosion rate, total mass loss, and corrosion morphology are strongly dependent on acidity and Cl- anion concentration. In order to understand the electrochemical reactions that govern the dissolution observed, potentiodynamic polarizations and electrochemical impedance spectroscopy were performed, followed by surface characterization. Various solution compositions were tested in order to characterize the dependence of the corrosion of N06022, N06035 and N10362 on the variables of importance, namely time, water content, chloride concentration, acidity, and acid type. The highest corrosion current density is observed in the presence of both HCl and DDQ, where DDQ acts as oxidant and HCl enables active dissolution at anodic potentials. The influence of acidity and Cl- on the electrochemistry of DDQ were studied by performing cyclic voltammetries with a platinum working electrode in different solutions. With support of results from exposure and electrochemical tests for different alloys, the relation between corrosion behavior and alloy composition was assessed. Ultimately, this investigation will provide understanding of the passivity of different Ni-based alloys in organic solvents, assisting the selection of CRAs for nonaqueous applications.

Stable Electrochemical Measurements of Platinum Screen-Printed Electrodes Modified with Vertical ZnO Nanorods for Bacterial Detection

The study is aimed at investigating the stability of electrochemical and biosensing properties of ZnO nanorod-based platinum screen-printed electrodes (SPEs) applied for detection of bacterial pathogens. The platinum SPEs were designed and patterned according to standard photolithography and lift-off process on a silicon wafer. ZnO nanorods (NRs) were grown on the platinum working electrode by the hydrothermal method, whereas Salmonella polyclonal antibodies were selected and immobilized onto ZnO NR surface via a crosslinking process. Morphological and structural characteristics of ZnO NRs were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results showed that the ZnO NRs were grown vertically on platinum electrodes with a diameter around 20-200 nm and a length of 5-7 μm. These modified electrodes were applied for detection of Salmonella enteritidis at a concentration of 103 cfu/mL by electrochemical measurements including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The ZnO NR-modified platinum electrodes could detect Salmonella bacteria well with stable measurements, and the signal to noise ratio was much higher than that of 3 : 1. This study indicated that ZnO NR-modified platinum SPEs could be potential for the development of biochips for electrochemical detection of bacterial pathogens.

Differential Pulse Voltammetric (DPV) Determination of the Local Anesthetic Bupivacaine using Polyimide Membrane-Based Electrodes

Aromatic selective polyimide (PI) membrane based voltammetric electrodes were prepared for bupivacaine measurements. Polyimide membranes were synthesized from 4,4′-diaminobenzanilide (DABA) and different aromatic dianhydrides (pyromellitic dianhydride (PMDA), benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA)) through two-step polycondenzation reactions. The structural properties of the obtained benzanilide based PIs were characterized by various analytical techniques. For the preparation of voltammetric electrodes, these polyimide films were coated with polyimide solution by drop-casting on the surface of a platinum working electrode. Due to the excellent film properties and suitable porosity, the prepared benzanilide based polyimide films were used as the membrane for selective determination of bupivacaine in the presence of interferents that included lactose, glucose and sucrose. For this reason, the selectivity of the modified electrode to bupivacaine obtained from the prepared PI film toward the potential interferences was investigated by differential pulse voltammetry (DPV). The results of voltammetric study showed that polyimide films responded to only bupivacaine at a potential of approximately +0.92 V. The polyimide membrane modified electrode showed a rapid response time, a high R-value of 0.9941, high reproducibility and good selectivity for bupivacaine. The limit of detection (LOD) and the limit of quantitation (LOQ) were determined to be 16.82 µM and 50.46 µM, respectively. Thus, benzanilide based polyimides may be successfully used as selective membranes for preparation of bupivacaine sensors. This structure may be a precursor for the preparation of simultaneous or needle-shaped sensors in the future.