Increase In Cathodic Current Research Articles

Electrodeposition Behavior of Al-Au Alloys in AlCl3-NaCl-KCl-Aucl Molten Salt

Quartz Crystal Microbalance (QCM) has been used as a highly sensitive mass sensor. This study aims to form porous gold thin films on QCM elements and apply them to highly sensitive gas sensors by attaching selective media. Physical vapor deposition and chemical etching are known methods for forming porous Au thin films. In this study, the electrochemical formation of porous gold films in AlCl3-NaCl-KCl molten salts containing AuCl was investigated. There are few reports about electrodeposition and dissolution potentials of Au in the molten salt electrolyte. As a first step in this study, voltammogram measurements and constant potential electrolysis were performed in the electrolyte, and electrodeposition potentials of Au and Al-Au alloys were discussed.An electrolyte in this study is a mixture of 61 mol% AlCl3- 26 mol% NaCl- 13 mol% KCl molten salt. The mixture salt was melted at 443 K and AuCl was added to the molten salt. A glassy carbon plate (GC) and a pure Al wire were used as the working electrode and reference electrode, respectively. The GC plate and Au mesh were used as the counter electrode for voltammogram measurement and constant potential electrolysis, respectively. Voltammogram measurements were carried out at potential range from -0.1 to 2.4 V vs. Al/Al(Ⅲ). Constant potential electrolysis was performed in the range from -0.2 to 0.3 V with an electric charge density of 40 C cm-2. The electrodeposits were observed by scanning electron microscopy (SEM) and determined the composition of Al and Au by energy dispersive X-ray spectroscopy (EDS).Au ions concentration in the electrolyte was 2.5 mmol dm-3. In voltammogram measurements, a small cathodic current was observed at about 0.8 V, then gradually increased from 0.2 V. In the potential lower than 0 V, a drastical increase of cathodic current was observed, which was attributed to Al electrodeposition. When the potential was reversed, large anodic current flowed from 0 V and a small current peak was also observed at 0.2 V. These were considered to correspond to the dissolution of Al and Al-Au alloys, respectively. Furthermore, a relatively large anodic current peak was observed at about 2 V, which was expected to be due to the dissolution of Au. From the results of constant potential electrolysis, the Au concentration in the electrodeposits at -0.1 V and -0.2 V was less than 1 at%. At 0 V, the Au concentration in the electrodeposit increased sharply to 84 at%, and at 0.3 V it increased moderately to 89 at%. From SEM observation, the morphology of the electrodeposits at -0.1 V and -0.2 V was dense, while that at potentials more than 0 V was sponge-like.AcknowledgementsThis work was supported by JST SICORP and JPMJSC2108.

Evaluating the role of laccase immobilized TiO2 for potential use as biocathode in a microbial electrolysis cell

This research focused on evaluating the role of laccase oxide-reductase enzyme covalently immobilized on TiO2 nanoparticles for potential use as a biocathode. First, nanoparticles were functionalized with alkoxysilane molecules, followed by a reaction with glutaraldehyde, and finally, laccase was covalently immobilized. These materials were characterized by FTIR, ζ-potential, XPS, and SEM. Next, the enzyme-loaded nanoparticles were adsorbed on a glassy carbon (GCE) electrode for electrochemical characterization by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). Findings revealed that the functional groups were attached, and laccase was immobilized in nanoparticles based on the analyses by FTIR, ζ-potential, XPS, and SEM-EDAX. Moreover, it was proven that laccase immobilized on TiO2 enhances the electrocatalytic activity when supported on a GCE; this bioelectrode exhibited a significant increase in oxidation and reduction current peaks compared to bare and TiO2-modified GCE. Also, the electron transfer rate was greatly improved for the laccase-based bioelectrode; the impedance magnitude of this bioelectrode was smaller than the corresponding GCE and GCE/TiO2 electrodes. Finally, polarization curves showed that the overpotential decreases and the cathodic current increases for the laccase-based electrode, indicating that it could perform well as a biocathode in a microbial electrolysis cell.

Electrochemistry of Praseodymium in Aqueous Solution Using a Liquid Gallium Cathode

The electrochemistry of liquid Ga electrodes in aqueous media was examined in the presence of praseodymium acetate (PrOAc) as an alternate path for low temperature reduction of rare earth elements (REE). This study investigated the aqueous electrochemistry of Ga with and without REEs (Pr). Cyclic voltammetry experiments showed that in the presence of PrOAc, an order of magnitude increase in cathodic current was observed for the Ga electrode, compared to that in the absence of Pr. Decrease in the reduction current with the increase of scan rate, with and without Pr, suggests catalytic reactions following electron transfer, which was attributed to the Ga2O disproportionation reaction. Chronoamperometric experiments performed in Pr containing solutions formed a precipitate. Over 50% of the Pr ions from the aqueous electrolyte were immobilized in the precipitate; a solid Ga-rich phase. Formation of this precipitate was only possible when Ga oxidation was induced. This condition was achieved by circulation of liquid Ga from the pool via external pump and returned dropwise to the liquid Ga pool. When the collected precipitate was leached in dilute HCl, Pr was released with H2 evolved as a byproduct, and Ga returned to its initial liquid metallic state. These preliminary results show encouraging new routes that could be applied for the recovery of diluted REE leachates, such as those obtained from magnets, coal fly ash, and ores.

Real-Time Cortisol Detection Using Electrocatalytic Polymer-Based Sensor

Cortisol is a steroid hormone produced by the adrenal gland in response to stress or agitate states. Deficiency or excess cortisol level can be triggered by physical or psychological stress, which is considered a biomarker for many diseases, such as Cushing syndrome [1]. In the human body, cortisol concentrations fluctuate in a circadian rhythm, being the highest in the early morning and the lowest in the night. A reliable cortisol test cannot depend on a single or one-day average measurement. Instead, screening a patient's dynamic cortisol levels over the circadian cycle is expected. The existing clinical cortisol measurements require blood, urine, or saliva samples sent to a lab to await results. The detection methods are mainly based on immunoassay that requires labeled antigens for a competitive assay and time-consuming incubation time (15–30 min), which hinders continuous detection needed for real-time stress management. To enable accurate time course measurements, a new detection approach is required to allow real-time determination of cortisol without costly reagents, labeling processes, additional redox reagents, and cumbersome laboratory equipment.Nanomaterials that mimic the catalytic behaviors of enzymes have great potential for continuous monitoring of cortisol levels through the direct electrochemical reading from cortisol redox reaction. There are very few reports on artificial cortisol catalytic sensors which require complicated fabrication or extremely non-neutral pH conditions for sensing [2]. Copper phthalocyanine (CuPc), a macrocycle with transitional copper (Cu) ion, holds electrocatalytic behavior and can be utilized for electrochemical redox reactions of various biomolecules, including H2O2, phenol, dopamine and serotonin. However, the detection of steroid hormones using CuPc has not been demonstrated yet. Compared to similar compounds based on porphyrin, phthalocyanine has N atoms in the meso positions and rich π-electrons that permit the formation of stable metallic phthalocyanine complexes. In this work, we develop copper phthalocyanine tetrasulfonate doped polypyrrole (PPy:CuPcTS) nanocomposite onto disposable screen-printed electrodes (SPEs) and demonstrate its electrocatalytic activity for real-time cortisol sensing. The incorporation of water-soluble CuPcTS into the PPy film forms an electrochemically conducting polymer in the negative potential window and catalyzes the reduction reaction of cortisol. The PPy:CuPcTS/SPE sensor can directly determine cortisol concentrations in real-time.The PPy:CuPcTS film was formed through one-step anodic electropolymerization on SPEs. The morphology and elemental composition of the film were characterized by scanning electron microscopy (SEM) and energy dispersive X-Ray analysis (EDX), respectively. Electrochemical responses were obtained with cyclic voltammetry (CV) and chronoamperometry. Cortisol detection was performed with 1x PBS solution.During the electropolymerization of PPy with CuPcTS, parts of the pyrrole rings hold a positive charge and form a complex with the sulfonated group in the CuPcTS. The CuPcTS and the PPy rings can also bond through π-π stacking. The stacked arrangement creates more conduction pathways due to highly delocalized electrons. The chelated Cu in CuPcTS catalyzes the reduction of ketone group in cortisol to an alcohol group [3], as schematically shown in Fig. 1(a). The SEM images in Fig.1 (b) show that the polymerization of PPy in the presence of CuPcTS results in a rough surface, very different from the smooth surface morphology on an undoped PPy film. The successful doping of CuPcTS in the PPy film is further confirmed by the presence of Cu peaks in the EDX (Fig.1 (b)). The CV curves in Fig. 1(c) indicate that cortisol reduction can be achieved using PPy:CuPcTS/SPE, evidenced by the increase in cathodic current at -1 V vs. Ag/AgCl upon adding cortisol. The phenomenon was not observed with PPy/SPE. The cathodic current increases with cortisol concentrations. The proposed sensor provides a dynamic detection range from 1 nM to 500 nM (Fig. (d)). Fig. 1(e) shows that the cortisol sensor also exhibits a selective detection against common interfering molecules, including glucose, ascorbic acid, and dopamine.PPy:CuPcTS nanocomposite was successfully demonstrated for electrocatalytic cortisol sensing. The sensor was achieved by a facile fabrication method and can operate at neutral pH without redox probes and labeling steps. The new sensor possesses great potential for low-cost, real-time monitoring of stress levels.

Short-Term Strong Cathodic Polarization of Ni/YSZ and Pt/YSZ

The initial stages of YSZ reduction and formation of intermetallic phases at Ni∣YSZ interfaces on strongly cathodically polarized electrodes were studied by a number of potential sweep and impedance techniques. The measurements were carried out in the potential range −1.0 V to −3.0 V vs E°(O2) in H2/H2O at 650 and 750 °C. Below −1.7 V the cathodic current increases almost exponentially, mainly due to electronic conductivity in the YSZ. Reduction and oxidation peaks develop below and above −1.9 V, respectively. The peaks reveal a simultaneous reduction of YSZ at the Ni∣YSZ interface and reoxidation of a Ni-Zr phase. Charges calculated from the reoxidation peaks indicate a thickness of 200 nm for the layer formed by conditioning the electrode for 300 s at −2.6 V vs E°(O2). Impedance measurements show a suppressed arc decreasing with increasing polarization. Below −2.3 V vs E°(O2) a capacitive high frequency arc segment and an inductive low frequency loop develop. Both are ascribed to electronic conductivity. SEM/EDS microscopy on cross sections of samples cooled with and without polarization showed the formation of uniform and homogeneous intermetallic reaction layers which after reoxidation resulted in a two-phased nanostructures.

Electrochemical Formation of RE–Ni Alloys (RE=Nd, Dy) in Molten CaCl2–RECl3

１． Introduction Rare earth elements (REs) were used in many industrial materials in the past few decades. Especially, the demand for Nd–Fe–B magnets has rapidly increased due to the popularization of electric vehicles (EVs) and hybrid electric vehicles (HEVs) in recent years. Since the magnets in motors need to work under high temperature environment, the addition of Dy to magnets is necessary to maintain their strong magnetic properties. However, the supply risk of Dy is high due to its insufficient reserves and uneven distribution. Based on this background, an efficient recycling process of Dy from Nd magnet scraps is a social demand.We proposed a separation / recovery method using the differences of the formation potential and formation rate of RE–Ni (RE=Nd, Dy) alloys [1]. In our previous reports, we have already studied on the formation of RE–Ni alloys and separation ratio of Dy/Nd in molten LiCl–KCl at 723 K [2], NaCl–KCl at 973 K [3] and LiF–CaF2 at 1123 K [4]. Although the higher separation ratio was achieved in the chloride systems at 723–923 K, alloy formation rate was higher in the fluoride system at 1123 K.In the present study, we focused on a low vapor pressure chloride salt CaCl2, to achieve both high separation ratio of Dy/Nd and high alloy formation rate. Electrochemical formation of RE–Ni alloys was investigated in CaCl2–RECl3 at 1123 K. ２． Experimental The experiments were conducted in a dry Ar atmosphere at 1123 K. Reagent-grade CaCl2 with 1 mol% NdCl3 or DyCl3 was loaded in a graphite crucible. The crucible was placed at the bottom of a stainless-steel vessel in an air-tight Kanthal container and dried under vacuum at 773 K for 24 h. Mo and Ni wires were used as the working electrodes. A carbon rod and a Ni2+/Ni electrode were used as the counter and reference electrodes, respectively. The potential was calibrated by the deposition potential of Ca metal on a Mo wire. Electrochemical formation behaviors of RE–Ni alloys were investigated by cyclic voltammetry. Samples prepared by potentiostatic electrolysis were analyzed by XRD and SEM/EDX. ３． Result and discussion Fig. 1 shows cyclic voltammograms at a Ni electrode measured before and after the addition of 1.0 mol% RECl3. The cathodic currents increase from around 1.0 V (vs. Ca2+/Ca) in both the NdCl3-added system and the DyCl3-added system, suggesting the formation of RE–Ni alloys. For the NdCl3 system, the cathodic current largely increases from 0.48 V, which is likely attributed to the formation of Nd–Ni intermetallic compound with a high Nd concentration. Several anodic current peaks probably correspond to the dissolutions of Nd from different Nd–Ni alloy phases. For the DyCl3 system, a steep increase of cathodic current is observed from 0.51 V, indicating the formation of Dy–Ni intermetallic compound with a high Dy concentration.To confirm the formation of RE–Ni alloys, potentiostaic electrolysis was conducted at a Ni plate at 0.50 V for 1 h in both the NdCl3 and DyCl3 systems. Fig. 2-a shows a cross-sectional SEM image of the sample obtained in NdCl3 system. An alloy layer with the thickness of approximately 10 μm was observed. From XRD and EDX results, the alloy layer was confirmed to be NdNi5. Fig. 2-b shows a cross-sectional SEM image of the sample obtained in DyCl3 system. Ni plate was completely alloyed with Dy and the thickness of plate increased from 100 μm to 200 μm due to the alloying. The formation of DyNi2 was confirmed by XRD and EDX. Based on these results, selective formation of Dy–Ni alloy can be expected at 0.50 V in molten CaCl2–NdCl3–DyCl3. Acknowledgement This work was supported by Grant-in-Aid for JSPS Fellows 19J20301.The present address of Kouji Yasuda is Graduate School of Engineering, Kyoto University. R eferences [1] T. Oishi, H. Konishi, T. Nohira, M. Tanaka and T. Usui, Kagaku Kogaku Ronbunshu, 36, 299 (2010).[2] H. Konishi, H. Ono, T. Nohira and T. Oishi, ECS Trans., 50, 463 (2012).[3] K. Yasuda, K. Kondo, S. Kobayashi, T. Nohira and R. Hagiwara, J. Electrochem. Soc., 163, D140 (2016).[4] T. Nohira, S. Kobayashi, K. Kondo, K. Yasuda, R. Hagiwara, T. Oishi and H. Konishi, ECS Trans., 50, 473 (2012). Figure 1

Electrochemical activation of CO2 by a di-Schiff base of N, N′-bis(2-hydroxy-1-naphthaldehyde)-m-phenylenediimine

Electrochemical behavior of a di-Schiff base, N, N′-bis(2-hydroxy-1-naphthaldehyde)-m-phenylenediimine, NMPD, was investigated using cyclic voltammetry, chronoamperometry and controlled-potential coulometry in acetonitrile solution containing tetrabutylammonium perchlorate, as supporting electrolyte. The effect of different parameters such as potential scan rates, and time window of the chosen electrochemical method was examined in studying the electrochemical behavior of NMPD. According to the results of experiments, an EC2CE mechanism was proposed to electrochemical reduction of NMPD on the glassy carbon electrode surface. Furthermore, NMPD is an efficient electrocatalyst in reduction of CO2. This electrocatalytic activity is confirmed by 700 mV decreases in overpotential of CO2 reduction, significant increase in cathodic current of NMPD and also the spectrum characterization of the main product of the electrolysis process which is oxalic acid.

Combined Effect of Alternating Current Interference and Cathodic Protection on Pitting Corrosion and Stress Corrosion Cracking Behavior of X70 Pipeline Steel in Near-Neutral pH Environment.

Influence of alternating current (AC) on pitting corrosion and stress corrosion cracking (SCC) behavior of X70 pipeline steel in the near-neutral pH environment under cathodic protection (CP) was investigated. Both corrosion and SCC are inhibited by −0.775 VSCE CP without AC interference. With the superimposition of AC current (1–10 mA/cm2), the direct current (DC) potential shifts negatively under the CP of −0.775 VSCE and the cathodic DC current decreases and shifts to the anodic direction. Under the CP potential of −0.95 VSCE and −1.2 VSCE, the applied AC current promotes the cathodic reaction and leads to the positive shift of DC potential and increase of cathodic current. Local anodic dissolution occurs attributing to the generated anodic current transients in the positive half-cycle of the AC current, resulting in the initiation of corrosion pits (0.6–2 μm in diameter). AC enhances the SCC susceptibility of X70 steel under −0.775 VSCE CP, attributing to the promotion of anodic dissolution and hydrogen evolution. Even an AC current as low as 1 mA/cm2 can enhance the SCC susceptibility.

Highly Efficient Electrochemical Detection of Phenolic Compounds Utilizing Superior Catalytic Activity of Nanohybrids Consisting of Magnetic Nanoparticles and Gold Nanoclusters.

Although Fe3O4 magnetic nanoparticles (MNPs) have gathered particular interest as potent peroxidase mimetics, their practical utility has been critically limited by their low catalytic activity. Here, we have developed a nanohybrid material to significantly enhance the catalytic activity of MNPs by incorporating other enzyme mimetics, gold nanoclusters (AuNCs), through electrostatic attraction. Owing to the synergistic effect of MNPs and AuNCs, the constructed nanohybrid yielded highly enhanced peroxidase-like activity and higher resolution in electrochemical detection of H2O2 than bare MNPs. The nanohybrids were also successfully applied to detecting phenolic compounds including phenol and cresol, producing a concentration-dependent increase of cathodic current. Based on this result, we expect that the nanohybrids consisting of AuNCs and MNPs can serve as potent peroxidase mimetics for environmental monitoring.

Direct electrochemistry of nitrate reductase from the fungus Neurospora crassa

We report the first direct (unmediated) catalytic electrochemistry of a eukaryotic nitrate reductase (NR). NR from the filamentous fungus Neurospora crassa, is a member of the mononuclear molybdenum enzyme family and contains a Mo, heme and FAD cofactor which are involved in electron transfer from NAD(P)H to the (Mo) active site where reduction of nitrate to nitrite takes place. NR was adsorbed on an edge plane pyrolytic graphite (EPG) working electrode. Non-turnover redox responses were observed in the absence of nitrate from holo NR and three variants lacking the FAD, heme or Mo cofactor. The FAD response is due to dissociated cofactor in all cases. In the presence of nitrate, NR shows a pronounced cathodic catalytic wave with an apparent Michaelis constant (KM) of 39μM (pH7). The catalytic cathodic current increases with temperature from 5 to 35°C and an activation enthalpy of 26kJmol−1 was determined. In spite of dissociation of the FAD cofactor, catalytically activity is maintained.

Mechanistic studies of pyridinium electrochemistry: alternative chemical pathways in the presence of CO2.

Protonated heterocyclic amines, such as pyridinium, have been utilized as catalysts in the electrocatalytic reduction of carbon dioxide. While these represent a new and exciting class of electrocatalysts, the details of the mechanism and faradaic processes occurring in solution are unclear. We report a series of cyclic voltammetry experiments involving Pt, Ag, Au, and Cu electrodes, under both aqueous and nonaqueous conditions, directed towards gaining an improved mechanistic understanding of pyridinium electrochemistry. Surface-enhanced Raman (SER) spectroelectrochemistry was also performed on Cu film-over-nanosphere electrodes in order to identify adsorbed species. It was found that the reduction potential of pyridinium (-0.58 V vs. SCE) and its electrochemical reversibility are unique features of platinum electrodes. In contrast, the reduction potentials on Ag, Au, and Cu electrodes are ∼400 mV more negative than Pt in both the presence and the absence of CO2. SER spectroelectrochemistry of pyridinium solutions shows no evidence for a pyridinium radical or a pyridinium ion. Increased cathodic current in the presence of CO2 is only detected at scan rates less than 10 mV s(-1) in aqueous solutions. The addition of CO2 resulted in a shift in the potential for the hydrogen evolution reaction. Pyridinium electrochemistry was observed under nonaqueous conditions; however no increase in cathodic current was observed when CO2 was added to the solution. Based on this set of results it is concluded that the reduction potential of pyridinium is surface dependent, CO2 acts as a pseudo-reserve of H(+), and pyridinium and CO2 create an alternative mechanism for hydrogen evolution.

A CV Study of Copper Complexation with Guanine Using Glassy Carbon Electrode in Aqueous Medium

Voltammetric behaviors of Copper (II) nitrogen bearing nucleobases, such as Guanine (C5H4N5O2) was studied in electro analyzer using cyclic voltammetry (CV) on a Glassy Carbon Electrode. Assessment of the chemical and physical conditions that may favor optimum current enhancement was done by studying the effect of variation of concentration of metal and ligand ions, variation of scan rate, variation of step height, variation of pH values, and variation of supporting electrolyte as (NH4)2SO4, KCl, and NaCl. It was observed that Copper and Guanine forms a 1 : 2 ratio complex. The work reflects that increasing the concentration of either metal ion or ligand ion increases the corresponding current. Increasing the scan rate increases the corresponding current linearly with the square root of the scan rate. As the step height decreases the peaks become sharp. Anodic and cathodic current increases linearly with decreasing step height. For the complex mixture the complexation occurs maximum at a pH of 2.3–7.0 and is badly restricted in the slightly alkaline medium and the complexing order of the supporting electrolyte showed a trend as (NH4)2SO4>NaCl>KCl.

Hemin-adsorbed carbon felt for sensitive and rapid flow-amperometric detection of dissolved oxygen

Hemin was physically adsorbed onto porous carbon felt (CF), a microelectrode ensemble of micro-carbon fiber (ca. 7 μm in diameter) and possessing a three-dimensional random structure. The hemin-CF exhibited a well-defined redox wave that is due to Fe(III)/Fe(II) redox process in hemin, with a formal potential of −0.32 V (vs. Ag/AgCl) in deoxygenated buffer solution of pH 7.0. The surface coverage of the electroactive hemin molecules on the surface of the CF was calculated to be 5.0 × 10−11 mol cm−2, and the apparent heterogeneous electron transfer rate constant is 3.35 s−1. The hemin-CF electrode displays excellent electrocatalytic activity for the reduction of dissolved oxygen (DO), and the magnitude of the cathodic current increases with increasing concentrations of DO in the sample solution. The electrode was used as a flow-through detector for sensitive and rapid consecutive determination of DO. Deoxygenated pH 7.0 solutions were analyzed at a flow rate of 8.0 mL min−1 at an applied potential of −0.2 V, and highly reproducible cathodic peak current responses to DO were observed in the 0.72 to 13.3 mg L−1 concentration range. The maximum throughput is 170 samples h−1. The hemin-CF-based amperometric flow-sensor was applied to determine the concentration of DO in environmental water samples.

Surface characterization of BiSbTe thermoelectric films electrodeposited from chlorides aqueous solutions and choline chloride based ionic liquids

Investigations of obtaining BiSb, BiTe, SbTe and BiSbTe films in concentrated chloride aqueous solution (5 M NaCl + 1 M HCl) or in ionic liquid based on choline chloride + malonic acid mixture were reported. The concentrations of Bi, Sb, Te, existing as complex anions due to high Cl − concentration, were within 10–90 mM. The measurements were carried out at room temperature for aqueous medium and 85 °C for ionic liquid. Cyclic voltammetry and electrochemical impedance spectroscopy using Pt electrode were used for investigating the interface process in both electrolytes. The morphology and chemical composition of films deposited on Cu in chloride aqueous solution using current pulses or potential pulses were determined by AFM and SEM microscopy. For BiSb, the effects of change from unipolar to reverse pulses and increase in cathodic current were shown as favorable. SEM images for BiSbTe confirmed the morphology modification by increasing the current pulses, while energy dispersive spectroscopy analyses indicate a dramatic change of composition.

Influence of Heat Treatment and Scandium Addition on the Electrochemical Polarization Behavior of Al-Zn-Mg-Cu-Zr Alloy

In this study, the electrochemical polarization behaviors of Al-Zn-Mg-Cu-Zr (7010) alloy in three different heat treatments, namely, underaged, peak-aged, and overaged, were examined in 3.5 wt pct NaCl solution. Experimental results show that the cathodic current increases marginally in the order of underaged < peak-aged < overaged alloys, which has been attributed to an increase in copper content of the precipitates in general and the grain boundary precipitates (GBPs) in particular. The change in the precipitate chemical composition has been found to affect the anodic polarization behavior even in a more significant way. Thus, both the anodic polarization curves of underaged and peak-aged alloys exhibit two distinct breakdown potentials and current reversal immediately below the second breakdown potential, whereas such a phenomenon is found to be absent in the overaged alloy. The overaged alloy exhibits only one breakdown potential without any current reversal. Detailed study of the polarization data and corroded surfaces of the alloy shows that the anodic current reversal is due to H2 evolution on the alloy surface just after the occurrence of passive film breakdown along the grain boundary. Notably, it is only those heat treatments that are prone to intergranular corrosion (IGC) seems to exhibit the tendency to reduce H+ ions, when they are anodically polarized. The chemical composition of the precipitates that can be altered by heat treatments is responsible for this behavior. The addition of 0.25 wt pct scandium to type 7010 Al alloy did not show any improvement in the corrosion resistance of the alloy. The Ecorr of scandium containing alloy shifted toward the active direction as compared to the base alloy. Noticeably, the peak-aged scandium containing alloy also exhibited two distinct breakdown potentials in the anodic polarization curve similar to the peak-aged base alloy, thus revealing its susceptibility to IGC and pitting corrosion.

Electrocatalytic Reduction of Hydrogen Peroxide on Polymethylpyrrole–Peroxidase Composite Film Plated on Gold Electrode

Horse radish peroxidase (POD), which is codeposited with polymethylpyrrole on a gold electrode, catalyzes hydrogen peroxide electroreduction. In the case of thin films deposition (Q 4 mC cm–2), the cathodic current increases only at low polarizations. In this case, probably, the POD molecules located on the surface and in the bulk film are involved in the reaction. From these results we conclude that, in the composite system studied, polymethylpyrrole provides the electron transfer to enzyme molecules, and the reaction's mechanism is likely to be the same in the cases of both carbon and gold substrates.

Enzyme immunosenser: Ill. Amperometric determination of human cherienic gonadotropin by membrane-bound antibody

An enzyme immunosensor was constructed for the determination of human chorionic gonadotropin (HCG), which is a hormone and an important diagnostic measure of pregnancy. An antibody to HCG was immobilized to a membrane. The antibody-bound membrane was placed onto an oxygen probe so as to react with HCG either specifically or selectively. Catalase, which catalyzes the decomposition of H 2O 2 into H 2O and O 2, was used to label HCG. Nonlabeled HCG to be assayed and catalase-labeled HCG were competitively reacted with the membrane-bound antibody of the sensor to form an antigen-antibody complex on the membrane surface. After the removal of nonspecifically adsorbed HCG, the sensor was contacted with a H 2O 2 solution. The membrane-adsorbed catalase enzymatically generated oxygen with a resulting increase in cathodic current of the sensor. The HCG concentration was determined from the initial rate of the current increase. The enzyme immunosensor was applied to the determination of HCG in the concentration range of 2 × 10 −2 to 10 2 IU/ml.

金属の陰極防蝕の研究（第1報）

The mechanism of cathodic protection was studied with aluminium alloys, containing copper, in 3% NaCl aqueous solution. For this purpose, a model experiment was made using an aluminium-NaCl2 couple as a model of corrosion cell in aluminium alloy. When external electric potential for cathodic protection is applied to an Al-CuAl2 couple, the corrosion current decreases in the rate of inverse proportion to the external potential. On the other hand, the current flowing from the liquid into the cathode (CuAl2) remains the same, until the corrosion current becomes zero. Therefore, the actual cathodic polarization curve is invariable and independent of the external current, till the cathodic current increases to such a heighr as to suppress the corrosion of anode. In order to assure complete protection, the cathodic current must be applied proportionally to the cathode area, but the polarized potential of the couple remains constant. To compare these model experiment with actual results with various alloys, the other experiment was made with an Sn-Zn couple as a model of their alloy, and with ordinary Sn-Zn (8.1%) alloy. The correlation was found satisfactory between these two cases of the model and of the alloy.