Cyclic Voltammetry Profiles Research Articles

Activation of Iridium Electrodes for Neural Stimulation

Introduction: Iridium oxide films have been investigated for multiple uses including electrochromic materials, pH sensors, and neural stimulation electrodes. In neural interfaces, activated iridium oxide film (AIROF) electrodes with planar or 3-dimensional geometries have been used to increase charge storage capacity and charge injection capacity for electrical stimulation of neural tissue. General properties of iridium oxide films have been investigated by several publications, leading to proposed film structures, observations on differences between anhydrous and hydrous iridium oxide films, and reported super-Nernstian changes in potential with pH. [1,2,3] In the present work, we investigated the activation of sharpened iridium microwire electrodes to AIROF using the same approach discussed in prior work. [4,5] We first sought to establish the charge-injection properties of AIROF electrodes in phosphate buffered saline and in an inorganic model of interstitial fluid as a function of the number of activation pulses. As the electrochemical properties of AIROF are known to be highly dependent on the prior oxidation state of the film, [1] we also sought to understand the charge injection Qinj capacity of AIROF when held at 0V compared to +0.6V vs. Ag|AgCl reference. Film cracking and delamination was observed in some electrodes during characterization, and so, we sought to understand the origin of the observed film instability and the role of limiting the maximum current allowed during activation. Methods: Iridium wire probes with 2000µm2 surface area were electrochemically cleaned in phosphate buffered saline (PBS). Cyclic voltammetry (CV) was recorded at 0.05V/s and 50V/s scan rates before and after cleaning. Each probe was activated at 25°C in air equilibrated PBS with 0.05Hz square wave potential pulsing between +0.8V and -0.6V vs. Ag|AgCl. Electrochemical impedance spectroscopy, CV, and voltage transient measurements at 0V and +0.6V bias vs. Ag|AgCl were recorded in both PBS and model interstitial fluid (m-ISF) at 37°C. Changes to the electrode surface were evaluated through cyclic voltammetry at multiple scan rates followed by scanning electron microscope (SEM) images of the film after soaking in DI water and drying. Results: Charge storage capacity (CSC) and maximum charge injection (Qinj) capacity increase significantly within the first 20 activation pulses. While CSC values in m-ISF are similar to values in PBS, Qinj capacity measured in m-ISF is significantly lower. Growth of the iridium oxide film was influenced by limiting the maximum current allowed during potential pulsing for activation. CSC and Qinj capacity of the 2000µm2 AIROF electrodes increased with increasing activation up to 1300 pulses. However, SEM images and CV profiles of probes activated without current limiting showed evidence of cracking in the microstructure of the film, and delamination of the film after 1300 pulses. Conclusions: Kinetics that are more informative for evaluating potential performance of neural stimulation devices in vivo can be observed when AIROF electrodes are measured in m-ISF in addition to PBS. Despite the long history of iridium oxide film characterization, parameters influencing activation are not yet fully understood as the dependence of film growth on current limiting found in this study was not expected. The degree to which activation parameters influence film growth currently appear to be specific to the electrode geometry and the electrochemical cell used and must be further understood to accomplish reliable transition to a stable oxide film covering the metal surface. Further study of the iridium oxide film structure and activation process is needed in order to standardize the activation process for the use of AIROF in neural devices.

Plasma jet printing for preparation of N-doped graphene electrode

Graphene, the 2-D allotrope of carbon, is well known for its remarkable electronic and optical properties. Nitrogen doping can manipulate local electronic structure and thus improve the performance of a graphene powered device. Therefore, developing a method of graphene production that is low in cost, simple in operation and high in controllability is important. It carries a vital value for the industrial applications of graphene materials in the future. For this study, graphene oxide (GO) and GO/AuNPs (gold nanoparticles) films were prepared using plasma jet printing technology. Then, a dielectric barrier discharge at a sub-atmospheric pressure in nitrogen gas was used to obtain N-doped and reduced graphene oxide (N-rGO). The microstructure of the sample was observed using a scanning electron microscope. Then, the materials were analyzed using X-ray diffraction, Raman spectra, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Finally, the cyclic voltammetry profiles and galvanostatic charge/discharge curves of N-rGO and N-rGO/AuNPs capacitors were tested. Results have indicated that the ultimate materials with a porous structure after the nitrogen plasma treatment presented a pretty good capacitor performance.

Uniform and ultrathin carbon-layer coated layered Na2Ti3O7 and tunnel Na2Ti6O13 hybrid with enhanced electrochemical performance for anodes in sodium ion batteries

Ultrathin and uniform carbon layer-coated layered Na2Ti3O7 and tunnel Na2Ti6O13 hybrids were synthesized via a facile and fast method using supercritical methanol and subsequent carbon coating with liquid carbon dioxide as a coating solvent. The carbon content and relative composition of the layered Na2Ti3O7 and tunnel Na2Ti6O13 phases in the hybrids were controlled by adjusting the calcination temperature. The drawbacks of each material could be overcome in the hybrid by taking advantage of the low volume expansion and high electronic conductivity (Na2Ti6O13), the high capacity (Na2Ti3O7), and a carbon coating. A careful examination of the cyclic voltammetry profiles of the sodium titanate hybrids revealed the existence of two different Na+ ion diffusion pathways in the layered Na2Ti3O7 phase. Under high discharge-charge conditions, some of the Na+ ion uptake in the layered Na2Ti3O7 and the structural integrity of tunnel Na2Ti6O13 resulted in excellent high-rate performance and long-term cyclability in the hybrid.

Layered and Tunnel Hybrid Sodium Titnate Synthetic Process Using Supercritical Fluid and Their Enhanced Electrochemical Performance in Sodium Ion Batteries

Concerned about the environmental pollutant such as greenhouse gas emission caused by extensive use of diesel, gasoline vehicle operation, being increased. Implementation of rechargeable battery in EV application because of EV’s zero emission has become very popular. Lithium ion battery (LIB) is one of the successfully commercialized system due to their high operating potential, high energy density and long cycle life [1]. However, high price and limited resources of lithium still makes hard to produce for reasonable price of EV. In contrast of LIB issue, sodium-ion batteries (SIBs) have drawn a considerable attention as an alternative to LIBs in the EV applications because of its relative abundance in the earth crust, global distribution, and drastically lower cost [2]. However, the fundamental differences between sodium and lithium make it challenging to develop a suitable anode material to host Na+ ions such as well-known graphite intercalation affair in NIB system [3]. Moreover, the higher reduction potential of sodium (–2.71 V vs. S.H.E.) as compared to lithium (–3.04 V vs S.H.E) inherently reduces the energy density of battery system. Therefore, there is still considerable efforts underway to develop a potential anode material that allows to host a large amount of Na+ ions at a low voltage potential. Among the various electrode material, sodium titanates (NTOs) have considered one of promising anode materials for SIBs because of their low starting material cost, environmental friendly, and abundance [4]. Among various type of sodium titanate, layered Na2Ti3O7 is one of the most promising phase. It can uptake two Na+ ions per formula unit into its interlayer space at a low average potential of 0.3 V vs Na/Na+ , which could deliver a high theoretical capacity of 177 mAh g-1 [5]. It makes particularly promising to design an anode material with high energy density. However, the poor electronic conductivity of Na2Ti3O7 associated with its large bandgap (3.7 eV) and structural distortion upon Na+ ion uptake leds to sluggish Na+ ion diffusion and cycling stability [6]. In this study, ultrathin and uniform carbon layer-coated, layered Na2Ti3O7 and tunnel Na2Ti6O13 hybrids anode materials synthetic route was successfully developed using facile and fast supercritical methanol and subsequent carbon coating with low viscosity liquid carbon dioxide as a coating solvent. The deficiency of each material, e.g., poor rate performance and cyclability caused by sluggish Na+ ion diffusion and structural distortion of Na2Ti3O7 and the low capacity of Na2Ti6O13, could be overcome in the hybrid by taking advantages of low volume expansion and high electronic conductivity of Na2Ti6O13 and high capacity of Na2Ti3O7 with enhanced conductivity by carbon coating. Through the HR-TEM technique, conformal, uniform and ultrathin carbon layers on the NTO surface with an average thickness of 15 nm was observed. Moreover, significantly decreased charge transfer resistance was confirmed by way of the EIS measurement. A careful analysis of the cyclic voltammetry profiles of this sodium titanate hybrids revealed that the existence of two different Na+ ion diffusion pathways in the layered structure of Na2Ti3O7 phase. Among two different Na+ diffusion pathways, one is kinetically more favorable but energetically less favorable site and the other is kinetically less favorable but energetically more favorable site. Under the high discharge–charge condition, some of Na+ ion uptake in the layered structure of Na2Ti3O7 and structural integrity of tunnel structure of Na2Ti6O13 resulted in excellent high-rate performance and long-term cyclability in the hybrid. ACKNOWLEDGEMENTS This research was supported by a National Research Foundation of Korea (NRF) grant provided by the Korean Government (MSIP) (No. 2016R1A2B3008800, NRF-2018R1A6A3A01012498). REFERENCES [1] D. Larcher, J.M. Tarascon, Towards greener and more sustainable batteries for electrical energy storage, Nat Chem 7 (2015) 19-29. [2] N. Yabuuchi, K. Kubota, M. Dahbi, S. Komaba, Research Development on Sodium-Ion Batteries, Chem. Rev. 114 (2014) 11636-11682. [3] H. Moriwake, A. Kuwabara, C.A. Fisher, Y. Ikuhara, Why is sodium-intercalated graphite unstable?, RSC Adv. 7 (2017) 36550-36554. [4] F. Xie, L. Zhang, D. Su, M. Jaroniec, S.-Z. Qiao, Na2Ti3O7@N-Doped Carbon Hollow Spheres for Sodium-Ion Batteries with Excellent Rate Performance, Adv. Mater. 29 (2017) 1700989. [5] J. Nava-Avendaño, A. Morales-García, A. Ponrouch, G. Rousse, C. Frontera, P. Senguttuvan, J.-M. Tarascon, M. Arroyo-de Dompablo, M.R. Palacín, Taking steps forward in understanding the electrochemical behavior of Na2Ti3O7, J. Mater. Chem. A 3 (2015) 22280-22286. [6] J. Ni, S. Fu, C. Wu, Y. Zhao, J. Maier, Y. Yu, L. Li, Superior Sodium Storage in Na2Ti3O7 Nanotube Arrays through Surface Engineering, Adv. Energy Mater. 6 (2016) 1502568.

Electrochemical enzymatic biosensor for tyramine based on polymeric matrix derived from 4-mercaptophenylacetic acid

In this paper, we investigated a novel functionalized polymeric film derived from 4-mercaptophenylacetic acid (MPAA). The polymerization was carried out through cyclic voltammetry (CV). Electrochemical, spectroscopic, and morphological analyses were used for characterization. Only acidic medium provided an efficient electrode modification as the electrochemical and morphological profiles obtained from treatment in alkaline solution resembles the unmodified electrode. The electrostatic repulsion between the carboxylate anions in the polymer and ferricyanide probe was verified by the current decrease in CV profiles and by the resistance of charge transfer increase through electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) images showed a complete and homogeneous coverage with a splinter-like morphology. The polymer presents stability under storage conditions until 35 days with no lixiviation during washing steps or loss of activity. The FT-IR measurements confirm the presence of the carboxyl group in the polymer suggesting a polymerization through the sulfur atom, which led to a mechanism proposal. The immobilization of enzyme tyrosinase over this platform and the detection of tyramine were performed successfully. 50 U of the enzyme for 18 h at pH 7.2 was the optimum parameters leading to a limit of detection and limit of quantification of 3.16 μmol L and 10.52 μmol L, respectively. With Kmapp of 62.11 μmol L and a recovery rate of 110.84% in a wine sample, the novel, stable, functionalized material formed over a low-cost electrode is suitable for further electrochemical applications exploiting the chemical reaction of carboxyl groups for biosensor purposing.

Effect of magnesium sulfate on the electrochemical behavior of lead electrodes for lead acid batteries

AbstractThe lead acid battery technology has undergone several modifications in the recent past, in particular, the electrode grid composition, oxide paste recipe with incorporation of foreign additives into the electrodes and similarly additives added in the electrolytes to improve electrical performance of the lead acid battery. In this paper, the electrochemical behavior of the lead electrodes with different weight/volume percentages (wt./v%) of MgSO4(0.0., 0.5., 1.0., 2.0., and 5.0) added into the electrolyte have been investigated with cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). The CV profile showed better redox behavior of the lead electrodes which was attributed to the increased active surface area of the electrode. Further studies of the gas evolution found a mixed trend and a considerable drop in the impedance as observed by LSV and EIS analysis as compared to the blank electrolyte solution. The influence of a modified electrolyte on the electrochemical activity of the lead electrodes is correlated and discussed.

Towards better quality criteria of European honeydew honey: Phenolic profile and antioxidant capacity

Concerning the particular nutritive value of honeydew honey compared to blossom honey, and small number of studies defining botanical origin of honeydew honey, comprehensive analysis of phenolic profile of 64 honeydew honey samples of specific botanical origin was performed. Two advanced techniques of liquid chromatography hyphenated with mass spectrometry were used for identification of a total of 52 compounds and quantification of 25 of them. Pattern recognition analysis applied on data on phenolic compounds content confirmed that quercetin, naringenin, caffeoylquinic acid, hydroxyphenylacetic acid, apigenin and genistein, could be considered as potential markers of botanical origin of honeydew honey. Spectroscopic and electrochemical approaches were applied for the evaluation of the antioxidant capacity. Quercus sps. samples, Quercus frainetto and Quercus ilex, showed high biological activity and specific chemical composition. Additionally, cyclic voltammetry profiles were used for characterization and natural clustering of honeydew honey for the first time.

Novel spherical cobalt/nickel mixed-vanadates as high-capacity anodes in lithium ion batteries

In the past four years, transition metal vanadates have received booming attention as anode materials for lithium ion batteries (LIBs) due to their outstanding specific capacities, decent cycling performance and superior rate properties. Among them, Co3V2O8 is the most reported species. However the cobalt is expensive, thus the replacement of cobalt would be a favorable route. So far, mixed vanadates have been rarely reported because of the remarkable difficulty in fabrication, among which cobalt/nickel mixed vanadates are the most attractive. In this work, a facile and green hydrothermal method with organic linker has been developed, to achieve modulated cobalt/nickel mixtures. It was corroborated by the X-ray diffraction (XRD) patterns and cyclic voltammetry (CV) profiles that single phase of cubic Co3V2O8 crystal structures were formed. The mixed vanadates demonstrated ultrahigh reversible capacity of over ∼1800 mAh/g at the current density of 0.2 A/g after ∼200 cycles and superb rate capability of ∼600 mAh/g at 4 A/g. The enhanced electrochemical performances of the higher-nickel-ratio indicated their considerable potential as high-capacity anode materials in LIBs.

Structural Transformation of Monocrystalline Platinum Electrodes upon Electro-oxidation and Electro-dissolution

Atomic-level understanding of the degradation of Pt materials is important for the rational design of nanoscopic Pt electrocatalysts for fuel cells. We report on the dissolution and structural transformation of spherical, monocrystalline, polyoriented Pt (Pt(spherical)) in 0.50 M aqueous H2SO4 upon potential cycling in the surface oxide formation–reduction region. The potential cycling is performed in the EL–EU range (EL = 0.07 V and 0.90 ≤ EU ≤ 1.50 V) to correlate dissolution and morphology data to EU. The amount of dissolved Pt is monitored using flow injection coupled to inductively coupled plasma mass spectrometry (ICPMS), and structural changes, which modify cyclic voltammetry profiles, are examined using scanning electron microscopy (SEM). In the case of EU ≤ 1.20 V, there is minor dissolution of the (100) and (110) facets, while the (111) facet remains stable. In the case of EU ≥ 1.30 V, all facets undergo significant dissolution. Changes in the surface morphology of Pt(spherical) upon repetitive ...

TEM, FTIR and Electrochemistry Study: Desorption of PVP from Pt Nanocubes

Abstract Polyvinylpyrrolidone (PVP) polymer is among one of the widely used surfactants to prepare nano-materials with desired particle shape and particle size. The critical challenge is to remove PVP polymer from the metal surface without loss of the surface arrangement and particle agglomeration. Here, we developed a strategy to remove the surfactant PVP which prefers to form a multi-layer shell and thus blocks the catalytically active surface of the Pt nanocubes (6–7 nm). Since PVP is partially soluble in polar solvents, we studied four different solvent mixtures (volume ratio), (i) methanol/ethanol (3:1), (ii) acetone/water (3:1), (iii) ethanol/chloroform (3:1), and (iv) aqueous 0.1 M acetic acid by using transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR) and cyclic voltammetry (CV). Only, the washing process with methanol/ethanol and acetone/water generates Pt nanocubes with almost clean particle surface. Based on our FTIR results, a shift of the carbonyl band in IR spectrum was observed for methanol/ethanol-washed Pt nanocubes, indicating the coordination of the carbonyl oxygen of the PVP to platinum. The electrochemical experiments showed that the surface area of the methanol/ethanol-washed Pt nanocubes was increased by a factor of 14 compared to the unwashed, while an improvement of 11 times was achieved by washing in acetone/water. However, the CV profile still signifies the presence of strongly adsorbed PVP on the Pt surface. To remove the chemisorbed PVP, an electrochemical cleaning including 200 potential cycles between 0.06 and 1.00 V vs. RHE at 200 mV s−1 was applied. The potential cycling reveals the potential-controlled ad/desorption behavior of the PVP at the Pt surface. Altogether, we designed a cleaning procedure for surfactant-capped metal nanoparticles and provide insights into the interactions between the PVP and Pt surface.

Effect of chelating agent on the sol-gel thermolysis synthesis of LiNiPO4 and its electrochemical properties for hybrid capacitors

The present work reports the preparation of olivine structured LiNiPO4 nanoparticles through sol-gel thermolysis method using three different chelating agents of citric acid (LiNi-C), l-ascorbic acid (LiNi-A) and D-sorbitol (LiNi-S). The flame temperature and enthalpy change of each reaction using the chelating agent is calculated. Further, the sharp X-ray diffraction peak reveals the phase pure and high crystalline nature of the prepared LiNiPO4 nanoparticles with the space group of Pnma (62) irrespective of the chelating agents. The four possible fundamental vibrations of phosphate anion PO43− are revealed through Fourier Transform Infrared Spectroscopy (FTIR) studies. The presence of elements such as Ni, P and O and its valence state is identified through X-Ray Photoelectron Spectroscopy analysis. The spherical shape particles with the uniform size distribution of LiNi –S is observed than the LiNi-C, LiNi-A particles through FESEM analysis. The redox peaks and plateau regions in the cyclic voltammetry (CV) and Galvanostatic charge-discharge (GCD) profiles infer the dominance of battery-type charge process rather than a capacitive mechanism. As a result, LiNiPO4 exhibits a maximum specific capacitance of 417 F g−1 at 2 mV s−1 and 357 F g−1 at 1 mA cm−2 in 1 M LiOH, which enables as a suitable cathode material for hybrid supercapacitor. Also, the assembled hybrid supercapacitor delivered a high energy density of 12.5 Wh kg−1 at 200 W kg−1 as well as a longer cycle life of 89% at a current density of 1 mA cm−2 over 2000 cycles is noticed. These results infer that LiNiPO4 could be used as a novel electrode material for hybrid supercapacitor application.

Studies on DNA Interaction with 2(3),9(10), 16(17), 23(24)‐Tetrakis 2((4‐Phenoxyphenyl) Diazeylbenzoic acid)phthalocyaninato Zinc (II) Compound

AbstractIn this study, 2(3), 9(10), 16(17), 23(24)‐tetrakis 2((4‐phenoxyphenyl) diazeylbenzoic acid)phthalocyaninato zinc (II) compound was chosen to study DNA binding activities. The binding activities of zinc (II) phthalocyanine compound bearing 2(3),9(10), 16(17), 23(24)‐tetrakis 2((4‐Phenoxyphenyl) diazeylbenzoic acid) ligand with Calf Thymus (CT)‐DNA was investigated using absorption titration, fluorescence spectroscopy, cyclic voltammetry and thermal melting profile in a Tris‐HCl buffer system at pH 7.0. In addition to these methods, gel electrophoresis and viscosity measurements were also carried out to determine DNA binding activities with compound 6 in a buffer solution. The results indicated that compound 6 interacts with CT‐DNA through partial intercalation binding mode.

Electrodeposited molybdenum selenide sheets on nickel foam as a binder-free electrode for supercapacitor application

Two-dimensional nanostructured metal chalcogenides have significant consideration as electrode materials for energy storage application owing to their fascinating properties. In this work, we have grown two-dimensional MoSe2 sheets directly on the surface of nickel foam via facile one-step electrochemical deposition method and examined their use as a binder-free electrode for supercapacitor. The physicochemical characterizations such as X-ray diffraction, field emission scanning electron microscope, X-ray photoelectron spectrum, and Raman analysis confirmed the formation of MoSe2 sheets on Ni foam. The effect of deposition time (5 and 10 min) on the electrochemical properties of the MoSe2 sheets are examined in detail using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopic analyses, respectively. The cyclic voltammetry profiles confirmed that the charge-storage mechanism in MoSe2 sheets is due to the ion intercalation/de-intercalation kinetics. A high specific capacity of 548 mAh g−1 was obtained for the MoSe2/Ni electrode from CV profile measured using a scan rate of 5 mV s−1. The MoSe2/Ni electrode delivered a specific capacity of 325.92 mAh g−1 from charge-discharge analysis obtained at constant discharge current density of 4 mA cm−2 with good cyclic stability. The capacitive properties and the mechanism of charge-storage in the MoSe2/Ni electrode deposited at different time intervals were examined by the electrochemical impedance spectroscopy using Nyquist and Bode phase angle plot. The experimental results ensure that the MoSe2/Ni electrode might be used as the high-performance electrode for the next-generation energy storage devices.

Re-Examination of CuO Reduction Steps and Understanding of the Factors Influencing the Cyclic Voltammetry Profile of CuO

Whether CuO reduction is one step or two steps reaction has been argued for several decades, and one step reaction mechanism is mainly supported by CuO CV (cyclic voltammetry) profile, where only one cathodic peak represents the direct reduction from CuO to Cu. However, some researchers support two steps reaction mechanism, because they observed Cu2O as intermediate with spectroscopy technique or two cathodic peaks in the CV profile. In this study, two colloid electrodes containing crystal CuO particles are electrolyzed in KCl electrolyte at −1.7 V and −1.65 V respectively, and both of the products are composed of Cu2O and Cu. The electrolysis voltage can change the weight ratio of Cu2O and Cu, and the electrolysis results firmly prove that CuO reduction is two steps reaction: CuO is reduced to Cu2O, then to Cu. Therefore, the rationality of the criterion for determining one step reaction is re-considered in this study. The experimental conditions and parameters, including CV scan rate, atom arrangement of CuO, particle size of CuO, and anions and pH value of electrolyte, are discussed in the present study, and all these factors can affect CuO reduction process, thus influencing the cathotic peaks, such as the number, shape and potential of the peaks in CuO CV profile. It could lead to incorrect conclusion,when CuO reduction steps is determined by the cathode peak without comprehensive consideration of the effect from all these factors. In another word, cathodic peak number in the CV profile sometimes is not a straightforward and appropriate criterion to determine the number of steps of CuO reduction. In addition, S2− ions is found to be an effective addtive to enhance the cyclic ability and discharge plateau of Cu alkaline battery in this study.

Design and Development of Instrumentations for the Preparation of Platinum Single Crystals for Electrochemistry and Electrocatalysis Research Part 3: Final Treatment, Electrochemical Measurements, and Recommended Laboratory Practices

In this contribution, which is the final paper in a topic-focused series of three papers, we report on the development of experimental methodology that is applied to acquire cyclic voltammetry (CV) profiles for hemispherical Pt(111), Pt(110), and Pt(100) as well as polyoriented monocrystalline Pt electrodes. The paper describes an effective, multi-step procedure for cleaning of electrochemical and annealing glassware. The procedure comprises a four-step process for cleaning glassware and a three-step process for cleaning Viton and Teflon parts to minimize any contamination that can originate from these setup components. The contribution also outlines general laboratory practices that need to be followed in order to maintain clean conditions for conducting electrochemical experiments. The paper discusses a thermal treatment methodology that consists of two steps, namely flame-based annealing and induction-based annealing. The application of this approach produces reproducible, clean, defect-free, and atomically-ordered Pt surfaces. The complete procedure of Pt electrode annealing, cooling in a controlled atmosphere, protecting with a droplet of water, and transferring to an electrochemical cell allows one to conserve a metallic character of the electrode surface (it does not form any oxide during the transfer) while maintaining an atomic order. In addition, the paper describes the design and operation of a multi-component electrochemical workstation, which is employed in measurements on platinum electrochemistry and electrocatalysis. The paper presents and discusses the hanging meniscus configuration that is used to maintain an electrolytic contact between a monocrystalline Pt electrode and an aqueous electrolyte solution. Finally, the contribution presents CV profiles for hemispherical Pt(111), Pt(110), and Pt(100) as well as polyoriented, monocrystalline Pt electrodes, which are characteristics of high-quality electrodes and clean experimental conditions. These results validate the instrumentation described in the series of papers and the laboratory practices developed in the course of our research.

Electrochemical performance of MnFe2O4 nano-ferrites synthesized using thermal decomposition method

Manganese nanoferrites (MnFe2O4) were synthesized via thermal decomposition method using metal organic precursors in organic solvent. The structural and optical properties of the nanoparticles were investigated using X-ray diffraction (XRD), Field emission gun scanning electron microscopy (FEG-SEM), Fourier transform infrared (FTIR) spectroscopy and Ultraviolet visible spectrophotometer (UV–Vis). Electrochemical performance of MnFe2O4 was evaluated using cyclic voltammetry (CV). The voltammograms were obtained using Pt as the working electrode within a potential range of −0.5 to +0.5 V at a scan rate of 50 mVs−1. The electrochemical behavior of the nanoferrites were studied in different electrolytes such as acidic, basic and phosphate buffer (PBS). The CV profile clearly indicates that the capacitive behavior of nanoferrites changes with change in electrolyte media. The results obtained from this study will be useful for the further applications such as magnetic materials, semiconductors, sensors and energy storage devices.

Influence of the Surface Roughness of Platinum Electrodes on the Calibration of the Electrochemical Quartz-Crystal Nanobalance.

The electrochemical quartz-crystal nanobalance (EQCN) is an in situ technique that measures mass changes (Δm) associated with interfacial phenomena. Analysis of Δm sheds light on the mass balance (in addition to the charge and energy balances) and provides new insight into the nature of electrochemical processes. The EQCN measures changes in frequency (Δf) of a quartz-crystal resonator, which are converted into Δm using the Sauerbrey equation containing the characteristic constant (Cf). The value of Cf is determined by physical parameters of the crystal and refers to an atomically smooth surface. However, real resonators are not smooth and electrodes have their intrinsic roughness. Thus, the conversion of Δf to Δm should be done using an experimentally determined characteristic constant (Cf,exp) for a given value of the surface roughness factor (R). Here, we calibrate the system using Ag electrodeposition on Pt electrodes of gradually increasing R; the latter is adjusted through Pt electrodeposition. The surface morphology of the Pt substrates prior to and after Ag electrodeposition is examined using atomic force microscopy. The values of Cf,exp are determined by analyzing the slopes of charge density versus Δf plots for the Ag electrodeposition. They are different than Cf and increase logarithmically with R. The Cf and Cf,exp values are used in a comparative analysis of the mass changes (δΔm) for complete cyclic voltammetry profiles covering the 0.05-1.40 V range. This reveals that the employment of Cf instead of Cf,exp provides inaccurate values of δΔm, and the magnitude of the discrepancy increases with R.

LaSn3 as a novel anode material for Na-ion battery

As a novel Na-ion battery anode, we studied electrochemical reactions of a LaSn3 electrode, and evaluated its cycling performance by comparison with that of a SmSn3 electrode. The LaSn3 electrode showed a reversible capacity of 580mAhcm−3 at the first cycle, and a gradual increase in the capacity with cycling number. The LaSn3 electrode exhibited a high capacity of 1470mAhcm−3 even at the 400th cycle, which is three times higher than that of a hard carbon electrode. The electrode reactions of elemental Sn were observed in a cyclic voltammetry profile of the LaSn3 electrode, indicating that a phase separation of LaSn3 gradually occurs to form Sn. We suggested that the phase separation provides a Na-inactive La3Sn5 matrix, which can suppress the aggregation of Sn particles and can improve the cyclability. On the other hand, the SmSn3 electrode showed a higher initial capacity of 970mAhcm−3 and an earlier capacity decay by the 200th cycle. It is suggested that the phase separation of SmSn3 progresses more rapidly while that of LaSn3 slowly occurs because of a higher thermodynamic stability for LaSn3 than SmSn3.

Catalytic Duality of Platinum Surface Oxides in the Oxygen Reduction and Hydrogen Oxidation Reactions

In polymer electrolyte membrane fuel cells (PEMFCs), the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) take place on the surface of platinum nanoparticles (Pt-NPs) residing on carbon support. Polycrystalline platinum (Pt(poly)) serves as a model polyoriented system due to its randomly oriented grains separated by grain boundaries, and research using Pt(poly) creates important background knowledge that is used to identify and understand electrochemical phenomena occurring in fuel cells. In this study, we report new results on the electrochemical behavior of Pt(poly) in 0.50 M H2SO4 aqueous solution saturated with reactive gases, namely O2(g) and H2(g). We analyze the influence of the potential scan rate over a broad range of values (1.00–50.0 mV s−1) on the cyclic voltammetry (CV) behavior of Pt(poly). A comparative analysis of the impact of dissolved O2 and H2 on the electrochemical behavior of Pt(poly) is performed using CV profiles and capacitance transients. Their analysis reveals the existence of new features that are observed in the potential range corresponding to the Pt surface oxide formation and reduction. The results indicate that the Pt surface oxide reveals catalytic duality because it acts both as an inhibitor and a catalyst in both the ORR and HOR. In the case of the ORR, the anodic-going transients reveal that the process becomes inhibited as the Pt surface oxide develops, while in the cathodic-going transients, the reduction of Pt surface oxide significantly (ca. 65%) increases the reaction rate. In the case of the HOR, the anodic-going transients also reveal that the process becomes inhibited as the Pt surface oxide develops, while in the cathodic-going transients, the reduction of Pt surface oxide increases (ca. 15%) the reaction rate. The catalytic effect can be attributed either to changes in the surface electronic structure that accompanies the surface oxide reduction or to short-lived increase in the electrochemically active surface area.

Kinetic Study of High Voltage Spinel Cathode Material in a Wide Temperature Range for Lithium Ion Battery

This study represents the electrochemical performance and lithium transportation behaviors of spinel LiNi0.5Mn1.5O4 cathode operated in a wide range of temperatures from −20 to 60°C. The correlative lithium diffusion coefficients are derived via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques, respectively. Based on the modeling of EIS, the lithium diffusivity of LiNi0.5Mn1.5O4 is estimated in the range of 10−11 around 25°C. The specific capacity of LiNi0.5Mn1.5O4 cathode is highly associated with the change of Li-ion mobility, which reveals a distinctive trend with applied temperatures. A strong correlation is also found between the apparent activation energy and lithium diffusivity. The change of activation energy is a key factor in dominating the kinetic reaction of Li/LiNi0.5Mn1.5O4 cells. Furthermore, the voltage polarization recorded from CV profile also perfectly follows the lithium transportation scenario. This study elaborates a profound discussion for temperature effects on electrochemical properties of LiNi0.5Mn1.5O4 cathode material.