Rest Potential Research Articles

Biomimetic gels with chemical and physical interpenetrating networks

AbstractThis study aimed to create and to characterize the functional properties of gels with semi‐interpenetrating network (semi‐IPN) with focus on possible use of these composites in biomedical engineering. Polyacrylamide as a synthetic biocompatible polymer was chosen for the chemical network. The physical network comprised the gel‐forming polysaccharides xanthan gum or gellan gum. Gels were synthesized by radical polymerization of acrylamide in aqueous solutions of polysaccharides. Mechanical and electrical properties of gels with 0.2, 0.4, 0.6, 0.8 and 1.0 wt% content of polysaccharide were investigated. It was found that the inclusion of a small amount of xanthan or gellan into the polymeric network of a polyacrylamide gel significantly shifts the gel electrical potential towards the rest potential of living cells and Young's modulus towards the elasticity limits of biological soft tissues like non‐activated muscles. From the viewpoint of biomedical applications, the main advantage of the proposed composites is that the semi‐IPN structure provides a nonlinear dependence of gel tension on gel deformation, which mimics the elasticity of natural tissues. This feature opens the possibility for the promising use of the proposed gels for musculoskeletal minibioimplants or scaffolds for tissue engineering. © 2018 Society of Chemical Industry

The Effects of Galvanic Interactions with Pyrite on the Generation of Acid and Metalliferous Drainage.

Although the acid generating properties of pyrite (FeS2) have been studied extensively, the impact of galvanic interaction on pyrite oxidation, and the implications for acid and metalliferous drainage, remain largely unexplored. The relative galvanic effects on pyrite dissolution were found to be consistent with relative sulfide mineral surface area ratios with sphalerite (ZnS) having greater negative impact in batch leach tests (sulfide minerals only, controlled pH) and galena (PbS) having greater negative impact in kinetic leach column tests (KLCs, uncontrolled pH, >85 wt% silicate minerals). In contrast the presence of pyrite resulted consistently in greater increase in galena than sphalerite leaching suggesting that increased anodic leaching is dependent on the difference in anodic and cathodic sulfide mineral rest potentials. Acidity increases occurred after 44, 20, and 12 weeks in the pyrite-galena, pyrite-sphalerite, and the pyrite containing KLCs. Thereafter acid generation rates were similar with the Eh consistently above the rest potential of pyrite (660 mV, SHE). This suggests that treatment of waste rocks or tailings, to establish and maintain low Eh conditions, may help to sustain protective galvanic interactions and that monitoring of Eh of leachates is potentially a useful indicator for predicting changes in acid generation behavior.

Complex Oxides Based on Silver, Bismuth, and Tungsten: Syntheses, Characterization, and Photoelectrochemical Behavior

Silver-containing complex oxides present interesting light absorption and electronic properties pointing to their applicability for solar fuel generation and environmental remediation. In this vein, the syntheses, characterization, and photoelectrochemical properties of the Aurivillius oxide, AgBiW2O8, and a triphasic material, AgBiW2O8/Bi2WO6/Ag, are described herein. From UV–vis diffuse reflectance analysis, both oxides’ nanoparticles exhibited intense absorption at wavelengths <455 nm, with an additional band centered at ∼500 nm for the triphasic material, attributed to surface plasmon resonance of the metallic Ag phase. The triphasic material was further characterized by a variety of structural and spectroscopic probes, indicating a defect-rich crystalline structure. Voltammetric measurements were performed in the dark and under simulated solar irradiation with polarization at potentials more negative than the rest potential. Thin film electrodes of both materials showed p-type semiconductor behavior,...

Effect of surface oxidation on the flotation response of enargite in a complex ore system

In previous study, the selective separation of enargite from complex ore samples in a batch flotation system under controlled pulp potential was investigated (Tayebi-Khorami et al., 2017b). It has been found that it is possible to make a separation between enargite and the other copper minerals in a real ore system using pulp potential control. In this study, the effect of the surface chemistry on the floatability of enargite and pyrite in complex ore systems were investigated. Based on flotation behaviour, EDTA (Ethylenediaminetetraacetic acid) extraction, pulp potential measurement and pure mineral study, it was found that the galvanic interactions between sulphide minerals, and pulp potential conditions, determined the flotation performances of the ore samples. It was also concluded that enargite had the lowest rest potential compared to the other sulphide minerals, which caused strong galvanic interaction between enargite and pyrite. This study has an important implication in sulphide flotation where enargite is present in the ore samples.

Eliminating Warrantless Assumptions Facilitates Consideration of an Electrostatic Model of Ion-Channel Activation

Models of voltage-sensitive ion channels (VSICs) that don’t specify the way reduction in electric field at threshold activation leads to observed outward S4 motions don’t provide satisfactory explanations of voltage sensing [Bezanilla F (2008) Neuron50:456-468]. Current models depend on unrealistic assumptions: screening of charges by a putative water-filled pore, and simple mechanical devices. A gate, screw, paddle or other everyday device cannot physically explain activation of the highly energetic resting channel, a far-from-equilibrium macromolecular system: The α-helix's hydrogen bonds are too weak to support such rigid structures. The energy required to lengthen the H-bonds is provided when the capacitive energy lost in the voltage reduction to threshold does mechanical work on the channel. Similarities exist between excitable membranes and ferroelectrics [Leuchtag HR (1987) J Theor Biol 127:321-340; 127:341-359; (2008) Voltage-Sensitive Ion Channels, Springer]. The ferroelectricity of excitable membranes must originate in the channels, since VSICs are their active components. In ferroelectrics, the dielectric coefficient ε is a function of the electric field. Electrostatic forces are inversely proportional to ε. Evidence from molecules with the sidechains of the branched-chain amino acids isoleucine, leucine and valine shows that their ε becomes remarkably large in a high electric field [Yoshino K, Sakurai T (1991) in: Goodby JW et al. Ferroelectric Liquid Crystals:317-363], comparable to that in a resting channel. According to the Channel Activation by Electrostatic Repulsion (CAbER) model, ε is high at rest potential and drops on depolarization. The consequently increased electrostatic repulsion between positively charged arginine and lysine residues at activation expands the S4 segments. This outward motion reconfigures the VSIC into an “open” structure with pore-domain sites wide enough to accommodate unhydrated permeant ions that hop stochastically across the channel [Leuchtag HR (2016) Biophys. J. 112(3):544a; 112(3):543a-544a].

Communication—The pH Detection of Magnesium Dissolution during Anodic Polarization with Channel Flow Double Electrode

A pH sensing channel flow double electrode was developed for pH detection of magnesium dissolution during anodic polarization. Because the hydroxide ions generated during the anodic polarization of a magnesium working electrode (Mg-WE) flow to a tungsten pH sensor (W-pH) downstream of the Mg-WE, pH changes can be detected by measuring the rest potential of the W-pH. A video recording of the Mg-WE surface was performed during the measurement, indicating that increase of pH was related to the film breakdown on Mg-WE surface. The hydrogen evolution rate of the order of 10−8 mol cm−2 s−1 was estimated from pH values.

Dissolution of Ag/AgCl Reference Electrode and Deposition of Silver Onto the Surface of 5083 H321 Aluminum Alloy, During Corrosion in 3 wt % NaCl Solution at Rest Potential

The dissolution of Ag/AgCl reference electrode and deposition of silver onto 5083-H321 aluminum alloy in 3 wt % NaCl solution have been observed. This result was obtained after one month of AA5083-H321 aluminum alloy corrosion at 25°C and rest potential in a classic cell of three electrodes, the reference electrode is silver/silver chloride bar and the auxiliary electrode is platinum wire. We have observed silver deposition onto three samples prepared from the same sheet. The sample 0 has undergone during the industrial manufacturing process a cold rolling followed by an industrial stabilization (in such industrial process the annealing temperature is maintained between 50 and 200°C), and undergone an annealing at 420°C during 90 minutes in laboratory. The Sample 1 and 2 have undergone a cold rolling of 46% and 92% reduction, respectively.

Inhibition of Mild Steel Corrosion in Acid Medium

Since inhibition is the simplest mechanism used for mitigating the corrosion of metals and alloys, particularly in acidic environments, the present work aims to investigate the inhibiting effect of N-benzyl-N′-phenyl thiourea (BPTU) and N-cyclohexyl-N′-phenyl thiourea (CPTU) on mild steel corrosion in 0.1M HCl medium using the Tafel extrapolation technique. Tafel experiments were conducted with ±250 mV vs. rest potential (RP) in steps of 20 mV from the cathodic side for recording the corrosion currents, and then, the Tafel plot of potential vs. current was drawn for determining the corrosion current density (icorr). The linear polarization method was also used for validating the Tafel results. It was performed by polarizing the specimen with ±20 mV vs. RP in steps of 5 mV, and the corrosion currents were noted. The plot of potential vs. current was drawn for calculating icorr. The study reveals that both BPTU and CPTU act as anodic inhibitors for mild steel in the HCl medium, and good inhibition efficiency (>97%) was evidenced from both the compounds even at elevated temperatures. The study also reveals that the investigated compounds get adsorbed quickly on the steel surface, following Temkin’s adsorption isotherm. The kinetic parameters obtained from the study indicated that the inhibition was governed by a chemisorption mechanism and the presence of inhibitors substantially reduced the metal dissolution in the studied temperature range. The investigation shows that there was a good correlation between the Tafel extrapolation and linear polarization results

Understanding and controlling the rest potential of carbon nanotube-based supercapacitors for energy density enhancement

Abstract We present a novel method for enhancing the energy density of an electrical double layer capacitor (EDLC). Surface modification of single-walled carbon nanotube (SWNT) electrodes significantly affects the rest potential (E0) of EDLCs; acid treatment and polyethyleneimine (PEI) coating of SWNTs shift E0 toward more positive and more negative values, respectively. Adjusting E0 towards the center of the electrolyte stability window can increase the cell voltage and hence the energy density. PEI coating on SWNTs increases the cell voltage from 0.8 V to 1.7 V in tetrabutylammonium perchlorate (TBAP)/tetrahydrofuran (THF) electrolyte, and from 2.5 V to 3.1 V in tetraethylammonium tetrafluoroborate (TEABF4)/3-cyanopropionic acid methyl ester (CPAME), respectively. Moreover, PEI-SWNT EDLCs exhibit excellent cycling stability (92% of capacitance retention over 10000 cycles). We attribute the shift in E0 to a change in the Fermi level of SWNTs owing to the surface charge modification. Injection of electrical charge into PEI-SWNTs consistently yielded similar trends and thus validated our hypothesis. Our results may help to push various electrolytes that have been overlooked so far to new frontiers for obtaining high energy-density supercapacitors.

Electroplating of Al-Nb Alloys from the Lewis Acidic Chloroaluminate Ionic Liquid

Currently ionic liquid (IL) is a common technical term. A great number of scientists and engineers in various fields are using it to create new technologies because of IL’s interesting features, e.g., relatively high ionic conductivity, high electrochemical stability, low-flammability, negligible vapor pressure, and antistatic property.1 Although the chloroaluminate IL system consisting of organic halide and aluminum halide seems to be outdated one, only this IL system gives a high quality Al electroplating.2 To date, many chloroaluminate ILs have been reported for obtaining pure Al and Al alloy electroplating with a high coulomb efficiency. Usually Lewis acidic AlCl3–1-ethyl-3-methylimidazolium chloride ([C2mim]Cl) IL containing more than 50 mol% AlCl3 is employed. However, there is no report on Al-Nb alloy electroplating in the chloroaluminate IL while in inorganic AlCl3–NaCl molten salt it can be obtained.3 In this study, we examined to clarify the electrochemical behavior of Nb(V) in the Lewis acidic AlCl3–[C2mim]Cl IL. Based on the results, Al-Nb alloy electroplating was carried out under various experimental conditions. The procedures used for the preparation and purification of the AlCl3−[C2mim]Cl IL were identical to those described in previous articles.2 All the electrochemical experiments were conducted using a three-electrode cell. A Teflon® sheathed platinum rotating disk electrode was employed for the working electrode. A coil of 1.00 mm diameter aluminum wire was used for the counter electrode. The reference electrode was an aluminum wire immersed in a neat 66.7-33.3 mol % AlCl3–[C2mim]Cl. These two electrodes were separated from the bulk IL by porosity E glass frits. All experiments were carried out in an Ar gas-filled glove box with O2 and H2O < 1 ppm. The Nb ion was electrochemically supplied by anodic dissolution of pure Nb metal to the chloroaluminate IL. Alloy samples were electroplated from the 66.7-33.3 m/o AlCl3−[C2mim]Cl with different Nb(V) concentrations onto Teflon®-sheathed 2.0 mm diameter copper cylinder electrodes. Figure 1 shows cyclic voltammograms recorded at a Pt stationary disk electrode in the 66.7 mol % AlCl3–[C2mim]Cl with and without 19.6 mmol L-1 Nb(V). In the neat melt, Al deposition/stripping waves appeared at 0 V vs. Al(III)/Al by the known electrode reactions.2 After addition of Nb(V) to the neat IL, in a negative sweep initiated from the rest potential, four reduction waves appeared except the reduction wave for Al electroplating. Electrochemical analytical techniques revealed that the first two reduction waves correspond to electrode reactions for Nb(V)/Nb(IV) and Nb(IV)/Nb(III), respectively. Diffusion coefficient for the Nb(V) estimated from Levich equation and Cottrell equation was ca. 1.9 × 10-6 cm2 s-1 at 353 K. However, it was difficult for us to conduct further investigation on the other two reduction waves due to probably the precipitation of NbCl3 derived from the subsequent chemical reaction of the Nb(IV)/Nb(III) electrode reaction onto the electrode. In fact, electrochemistry of vanadium, which is the homologous elements of niobium, also shows a similar behavior.4 In this case, the alloying mechanism is likely different from that obtained by direct reduction from the transition metal ions dissolved in the chloroaluminate ILs, but nevertheless Al alloy can be obtained the same.2 Therefore, the Al-Nb alloy was prepared on Cu substrates rotated at a fixed rate of 2,000 rpm in the 66.7 mol % AlCl3–[C2mim]Cl with 5 ~ 48 mmol L-1 Nb(V) by a dc galvanostatic method at 353 K. As shown in Figure 2, Nb content in the Al-Nb alloys decreased with increasing the applied current density in all Nb(V) concentrations and with decreasing the Nb(V) concentration in all applied current density. The highest Nb content reached 65 at% when the Nb(V) concentration in the solution was 48 mmol L-1 and the applied current density was -5 mA cm-2. XRD patterns for the resulting Al-Nb alloys revealed that the alloys have a solid solution phase with an fcc structure because those for Al slightly shifted to lower angle with increasing the Nb content. When the content is 9.3 at%, XRD patterns for Al completely disappeared. It suggests that Al-Nb alloy forms microcrystalline or amorphous phase. T. Torimoto, T. Tsuda, K. Okazaki, and S. Kuwabata, Adv. Mater., 22, 1196 (2010).T. Tsuda, G. R. Stafford, and C. L. Hussey, J. Electrochem. Soc., 164, H5007 (2017) and references therein.G. R. Stafford and G. M. Haarberg, Plasmas & Ions, 1, 35 (1999).T. Tsuda and C. L. Hussey, J. Min. Metall. B, 39, 3 (2003). Figure 1

Development of pH Sensing CFDE to Investigate Anodic Dissolution of Magnesium

Magnesium (Mg) is widely used as a large transportation and structural materials for their weight savings. However, Mg has large corrosion rate, and the hydrogen evolution occurs during the anodic dissolution of Mg. It was reported that the hydrogen evolution rate on Mg increases with noble potential from corrosion potential, which is called the Negative Difference Effect (NDE) 1-8). In order to analysis of the NDE phenomenon, Rossrucker et al.4) applied an electrochemical flow cell coupled to downstream analysis for investigation of the influence of pH alteration in the near surface region of dissolving Mg. In this method, the polarization measurement and simultaneous determination of the amount of dissolved Mg ions via inductively coupled plasma - mass spectroscopy. In the present study, we developed the pH sensing channel flow double electrode (CFDE) to monitor the pH changes on the Mg electrode due to the anodic dissolution. Schematic of the pH sensing CFDE is shown in Fig. 1. In the CFDE cell, the working electrode (WE) and detecting electrode (DE) were placed upstream and downstream in the channel. An Mg (1×4 mm2) and a W (0.1×4 mm2) were used for the WE and DE. The counter electrode (CE) was a Pt wire, which was set at channel outlet. The reference electrode was KCl-saturated silver/silver chloride electrode (SSE). The rest potential of W (DE) was measured for estimation of pH during the anodic dissolution of Mg (WE). The 0.1 mol dm-3 sodium sulfate solution (pH = 5.9) was used for the measurement. The degassing of the electrolyte solution was carried out for 1 h under an N2stream. A laminar flow condition was established in this measurement. Furthermore, the surface of WE was recorded by a USB digital microscope. The anodic polarization curve measurement of Mg and pH measurement was carried out by developed system. It was confirmed that the increase of pH is corresponded to the increase of anodic current of Mg with hydrogen generation. Reference [1] G. Song, A. Atrens, D. Stjohn, J. Nairn, and Y. Li, Corros. Sci., 39, 855 (1997). [2] R. L. Petty, A.W. Davidson, J. Am. Chem. Soc., 76, 363-366 (1954). [3] G. Song, A. Atrens, D. Stjohn, X. Wu, and J. Nairn, Corros. Sci., 39, 1981 (1997). [4] L. Rossrucker, A. Samaniego, J.-P. Grote, A. M. Mingers, C. A. Laska, N. Birbilis, G. S. Frankel, K. J. J. Mayrhofer, J. Electrochem. Soc., 162, C333-C339 (2015). [5] G. S. Frankel, A. Samaniego, and N. Birbilis, Corros. Sci., 70, 104 (2013). [6] G. Williams, N. Birblis, and H. N. McMurray, Electrochem. Commum., 36, 1 (2013). [7] G. L. Song and A. Atrens, Ave. Eng. Mater., 1, 11 (1999). [8] G. L. Song and A. Atrens, Ave. Eng. Mater., 5, 837 (2003). Figure 1

Limited role of sessile acidophiles in pyrite oxidation below redox potential of 650\u2009mV

Pyrite oxidation by mixed mesophilic acidophiles was conducted under conditions of controlled and non-controlled redox potential to investigate the role of sessile microbes in pyrite oxidation. Microbes attached on pyrite surfaces by extracellular polymeric substances (EPS), and their high coverage rate was characterized by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). The dissolution of pyrite was negligible if the redox potential was controlled below 650 mV (near the rest potential of pyrite), even though the bacteria were highly active and a high coverage rate was observed on pyrite surfaces. However, with un-controlled redox potential the rate of pyrite oxidation increased greatly with an increasing redox potential. This study demonstrates that sessile microbes play a limited role in pyrite oxidation at a redox potential below 650 mV, and highlight the importance of solution redox potential for pyrite oxidation. This has implications for acid mine drainage control and pyrite oxidation control in biometallurgy practice.

Effect of Applied Potential on Fatigue Life of Electropolished Nitinol Wires.

Nitinol is used as a metallic biomaterial in medical devices due to its shape memory and pseudoelastic properties. The clinical performance of nitinol depends on factors which include the surface finish, the local environment, and the mechanical loads to which the device is subjected. Preclinical evaluations of device durability are performed with fatigue tests while electrochemical characterization methods such as ASTM F2129 are employed to evaluate corrosion susceptibility by determining the rest potential and breakdown potential. However, it is well established that the rest potential of a metal surface can vary with the local environment. Very little is known regarding the influence of voltage on fatigue life of nitinol. In this study, we developed a fatigue testing method in which an electrochemical system was integrated with a rotary bend wire fatigue tester. Samples were fatigued at various strain levels at electropotentials anodic and cathodic to the rest potential to determine if it could influence fatigue life. Wires at potentials negative to the rest potential had a significantly higher number of cycles to fracture than wires held at potentials above the breakdown potential. For wires for which no potential was applied, they had fatigue life similar to wires at negative potentials.

Chalcopyrite dissolution: Scanning photoelectron microscopy examination of the evolution of sulfur species with and without added iron or pyrite

Dissolution and oxidation of sulfide minerals play key roles in both acid and metalliferous rock drainage and supergene enrichment. Surface speciation heterogeneity, critical to understanding mechanisms of mineral sulfide dissolution, has to date largely not been considered. To this end synchrotron scanning photoelectron microscopy (SPEM) was employed to examine freshly fractured and partially dissolved chalcopyrite (CuFeS2) surfaces (pH 1.0 HClO4 solution, redox potential 650mV relative to a standard hydrogen electrode, 75°C). S2− (bulk), S22− and Sn2− were found to be present on all samples at varying concentrations. Oxidation was observed to take place heterogeneously at the sub-micron scale. As compared to chalcopyrite partially dissolved for 5days, extended dissolution to 10days did not show appreciably enhanced oxidation of surface species; however surface roughness increased markedly due to the growth/overlap of oxidised sulfur species. On addition of 4mM iron both S0 and SO42− were observed but not SO32−, indicating that the greater Fe3+ activity/concentration promotes heterogeneous sulfur oxidation. On contact of pyrite (FeS2) with chalcopyrite, significantly greater chalcopyrite surface oxidation was observed than for the other systems examined, with S0, SO32− and SO42− being identified heterogeneously across the surface. It is proposed that chalcopyrite oxidative dissolution is enhanced by increasing its cathodic area, e.g. contacting with pyrite, while increased Fe3+ activity/concentration also contributes to increased dissolution rates. The high degree of surface heterogeneity of these surface products indicates that these surfaces are not passivated by their formation. These results suggest that chalcopyrite dissolution will be accelerated when in contact with pyrite at solution redox potential intermediate between the rest potentials of chalcopyrite and pyrite (560mV and 660mV, respectively) and/or iron rich acidic waters with resulting enhanced formation of secondary sulfur containing species and release of copper and iron. This in turn suggests accelerated supergene formation and enhanced metalliferous drainage under these conditions.

Transient Study of Adsorbed Oxygen Species Arising from Exposure to Dissolved Oxygen

The oxygen reduction reaction (ORR) was studied using Pt based microelectrodes under different mass transfer regimes. Current transients at different potentials were recorded by first applying a cleaning waveform and a rest potential 1–3 transformed to sampled current voltammograms and finally normalised using the equation proposed by Mahon and Oldham 4. In the steady state, the normalised current is akin to an apparent number of electrons n app, while for shorter times, the presence of an extra current that is attributed to the reduction of oxygen adsorbed species (adspecies) can be seen 2,3. These adspecies are only observed after exposure of the surface to dissolved oxygen during the rest potential and their reduction was tested with different types of Pt electrodes. First, Pt nanoparticles were deposited on carbon fibre microdisc electrodes (7 μm Ø). The normalisation gave n app = 3 at steady state conditions; this value is large for an electrode of this size 5 and it is believed that this is due to the effectiveness of the nanoparticles to reduce peroxide towards water due to their close proximity with each other. At shorter times, the normalisation showed an extra current attributed to the reduction of oxygen adspecies 2,3 but also to the reduction of carbon functionalities. To solve this, carbon nanoelectrodes were electroplated with Pt until sub-micron spheres were obtained and covered the carbon surface completely. At the steady state, n app = 2. Since no carbon was exposed to the solution, this n appis attributed to the high rate of mass transfer that can be achieved with these electrodes. At short timescales, the extra current due to the reduction of oxygen adspecies was also visible. Different sizes of Pt microdiscs were also used (5, 10, 25 and 50 μm Ø). The value of n app for each electrode agrees with those reported under steady state conditions 5. Using the equation proposed by Mahon and Oldham 4, a subtraction between the experimental and theoretical current densities was obtained and integrated to calculate the charge density associated to the reduction of the oxygen adspecies. The results from the millisecond to the second scale showed a value of 55 μC cm-2 in agreement with previous works 2,3. This value corresponds to 0.1 monolayers and seems to indicate that the coverage does not depend on the electrode size. Further analysis of the current transients assuming a first order process for the rate of reduction of the oxygen adspecies suggests that the maximum coverage that can be obtained corresponds to approximately 0.3 monolayers. This is currently being studied by recording current transients at the microsecond scale. The dependency of the rate of reduction of the oxygen adspecies on the applied potential is also under study. It is expected that this work will help elucidate the lifetime of the processes involved, namely the reduction of oxygen adsorbed species and the reduction of diffusion controlled oxygen that comes from the bulk. Overall these transient experiments shed new light on the interaction between dissolved oxygen and Pt electrodes and provide new insight on the oxygen reduction reaction. (1) Perry, S. C.; Al Shandoudi, L. M.; Denuault, G. Sampled-Current Voltammetry at Microdisk Electrodes: Kinetic Information from Pseudo Steady State Voltammograms. Anal. Chem. 2014, 86(19), 9917–9923. (2) Perry, S. C.; Denuault, G. Transient Study of the Oxygen Reduction Reaction on Reduced Pt and Pt Alloys Microelectrodes: Evidence for the Reduction of Pre-Adsorbed Oxygen Species Linked to Dissolved Oxygen. Phys. Chem. Chem. Phys. 2015, 17(44), 30005–30012. (3) Perry, S. C.; Denuault, G. The Oxygen Reduction Reaction ( ORR ) on Reduced Metals : Evidence for a Unique Relationship between the Coverage of Adsorbed Oxygen Species and Adsorption Energy. Phys. Chem. Chem. Phys. 2016, 18, 10218–10223. (4) Mahon, P. J.; Oldham, K. B. Diffusion-Controlled Chronoamperometry at a Disk Electrode. Anal. Chem. 2005, 77(18), 6100–6101. (5) Sosna, M.; Denuault, G.; Pascal, R. W.; Prien, R. D.; Mowlem, M. Development of a Reliable Microelectrode Dissolved Oxygen Sensor. Sensors Actuators, B Chem. 2007, 123 (1), 344–351.

Cation-dependent restructure of the electric double layer on CO-covered Pt electrodes: Difference between hydrophilic and hydrophobic cations

Structural changes in water layers on a CO-covered Pt electrode triggered by rapid pulsed laser heating of the interface are studied using potential transient measurements. When the laser energy density is below 20mJcm−2, the water layers undergo a change in orientation, which causes a negative shift in the rest potential that recovers within 20μs with the cooling of the interface. In contrast, when the laser intensity exceeds 20mJcm−2, the CO is desorbed and the rest potential first experiences a positive shift, which is followed by a negative shift. This positive shift is caused by replacement of the CO by water and subsequent restructuring of the water layer. The restructuring rate depends strongly on the electrolyte cation: the rest potential reaches a maximum value within ~100μs for hydrophilic cations such as H+ and Li+, whereas it takes >10ms for hydrophobic cations such as Et4N+ and Bu4N+. Surface-enhanced IR absorption measurements suggest that the water molecules around the hydrophobic cations are more strongly hydrogen-bonded than those around the hydrophilic cations. Because the restructuring involves a reforming of the hydrogen-bonding network at the electric double layer, Et4N+ and Bu4N+, which have more strongly hydrogen-bonded hydration shells, require more time than H+ and Li+.

Effect of wire fretting on the corrosion resistance of common medical alloys.

Metallic medical devices such as intravascular stents can undergo fretting damage in vivo that might increase their susceptibility to pitting corrosion. As a result, the US Food and Drug Administration has recommended that such devices be evaluated for corrosion resistance after the devices have been fatigue tested in situations where significant micromotion can lead to fretting damage. Three common alloys that cardiovascular implants are made from [MP35N cobalt chromium (MP35N), electropolished nitinol (EP NiTi), and 316LVM stainless steel (316LVM)] were selected for this study. In order to evaluate the effect of wire fretting on the pitting corrosion susceptibility of these medical alloys, small and large fretting scar conditions of each alloy fretting against itself, and the other alloys in phosphate buffered saline (PBS) at 37°C were tested per ASTM F2129 and compared against as received or PBS immersed control specimens. Although the general trend observed was that fretting damage significantly lowered the rest potential (Er ) of these specimens (p < 0.01), fretting damage had no significant effect on the breakdown potential (Eb , p > 0.05) and hence did not affect the susceptibility to pitting corrosion. In summary, our results demonstrate that fretting damage in PBS alone is not sufficient to cause increased susceptibility to pitting corrosion in the three common alloys investigated. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2487-2494, 2017.

Rest Potentials of Binary Mixtures of Ionic Liquids and Threshold Voltages of Electric-Double-Layer Transistors

There is a growing attention to the electric-double-layer (EDL) transistors, in which electrolytes are adopted as gate dielectrics, because a strong electric field produced by EDLs improves transistor performance. In our previous study, we investigated the relation between the rest potentials and the threshold voltages of EDL transistors, using two kinds ambipolar phthalocyanines and various ionic liquids. It was found that the rest potential is a unique property of ionic liquid, and the threshold voltages of the EDL transistors are proportional to the rest potentials of the ionic liquids. This means that the threshold voltages of the EDL transistors can be tuned by controlling the rest potentials, though what determines the rest potentials of the ionic liquids is still unclear. In the present study, we tried to understand the rest potentials of the ionic liquids and to control the threshold voltages of the EDL transistors, by making the binary mixtures of ionic liquids, because their mixing ratios can be continuously changed. We prepared the binary mixtures of the ionic liquids, combining DEME-TFSI and five kinds of ionic liquids, shown in the inset of Figs. 1 and 2. These combinations were selected, because these ionic liquids are miscible each other and the rest potential of DEME-TFSI is higher than those of the others. The rest potentials of the binary ionic liquids were examined with an Ag/AgCl reference electrode and a Pt working electrode. The rest potentials of the binary ionic liquids were found to change non-linearly with respect to the mixing ratio of the ionic liquids (Fig. 1). This dependence can be well fit to the equation of y = a + b*log(x), where x is the mixing ratio and, a and b are the fitting parameters. This strongly suggests that the rest potential of ionic liquid is governed by its chemical potential μ, because this equation has the same form as that of the chemical potential, μ = μ 0 + RTln(x), where R is the gas constant. Then, we tested the EDL transistors of platinum phthalocyanine (PtPc) which showed a high stability even in various ionic liquids. It was found that there was a linear relation between the rest potentials and the threshold voltages of the EDL transistors (Fig. 2), and the threshold voltages can be continuously controlled by changing the mixing ratio of the ionic liquids. Figure 1

Detection Method of Corrosion Site of Reinforcing Steel in Concrete By Two Electrode System

A reinforced concrete has been used for the building structures and bridge in the world. However, the degradation of reinforced concrete related to the corrosion of the reinforcing steel in concrete is now serious problem. It is important to establish the method to evaluate the durability of reinforced steel in concrete. Dawson et al. [1] applied the electrochemical impedance spectroscopy to investigation of the corrosion resistance of reinforced steel in concrete. Koleva et al. [2] investigated the durability of the steel rebar casted mortal cylinder by the rest potential, polarization curve and electrochemical impedance measurements. The present study developed the method to determine the corroded reinforcing steel in concreate by two electrode system. Figure 1 shows the schematic of developed system in the present study. Two copper electrodes are placed on the surface of the concrete in which the steel bar was embedded. The cover thickness of concrete was 10 mm. The half side of the steel bar corroded to simulate the degradation of the steel bar. Schematic of the impedance spectrum of reinforcing steel in concrete measured by two electrode system is shown in Fig. 2. Two loops were observed in the impedance spectrum when the copper electrodes are placed on the concrete in which corroded steel was embedded. It indicated that the current flowing though the copper electrodes was flowed into the corroded region of the steel bar. The loop in the high frequency range was related to concrete and the loop in the low frequency range was related to interface of concrete between steel rebar. Reference:[1] J. L. Dawson, L. M. Callow, K. Hladky and J. A. Richardson, Corrossion/78, 125 (1978).[2] D. A. Koleva, K. van Breugel, J. H. W. de Wit, E. van Westing, N. Boshkov and A. L. A. Fraaij, J. Electrochem. Soc., 154, E45 (2007). Figure 1

Effect of Temperature on Behavior of Oxygen Transport through Solution Layer Formed on Metals

It is very important for investigate environmental corrosion behavior of steels to maintain and safely use of the steels structures. To understand environmental corrosion behavior of steels, environmental factors such as temperature, relative humidity, amounts of airborne salinity, SOx, and transport behavior of oxygen in thin water layer formed on the steels are also important. Therefore, exposure tests and measurement of some of the environmental factors were carried out in three counties, Japan, Vietnam and Thailand, under "Corrosion Mapping of Structural Materials in Asian Area with Understanding Effects of Environmental Factors, e-Asia Project". The corrosion results showed that the corrosion rate in heavy snow and cold region such as Hokkaido is higher than that expected from temperature. To clarify the unexpected corrosion rate in Hokkaido, transport behavior of oxygen in thin water layer formed on the metals at low temperature was examined. The zinc and iron sheets were used for specimens, and specimens temperature was controlled by Peltier device form 298 K to 273 K. Three different solutions, 0.1 kmol/m3 NaCl, 1 kmol/m3 NaCl, and 1 kmol/m3 NaCl + 0.5 kmol m-3 H3BO3 / 0.05 kmol m-3 Na2B4O7 were used to form thin solution layers. The thickness of the solution layers were controlled by plastic tape from 200 µm to 1 mm. A Pt and AgCl coated Ag wires were used as counter electrode and reference electrode. The cathodic polarization curves were measured to obtain limiting current of oxygen with scanning rate of 20 mV/min. Before the polarization measurements, immersion potential was measured. In order to ensure the reproducibility, more than three times of electrochemical tests were carried out as same conditions. The measured rest potential of both zinc and iron were strongly depends on concentration of used solution, while slightly change of the rest potential was observe by the thickness of the solution layers. A clear limiting current of oxygen was observed in every solution and it increased with increasing invers of the solution thickness. The clear increase was observed with thin solution layer at low specimen temperatures.