Change Of Open Circuit Potential Research Articles

Switchable charge-transfer in the photoelectrochemical energy-conversion process of ferroelectric BiFeO₃ photoelectrodes.

Instead of conventional semiconductor photoelectrodes, herein, we focus on BiFeO3 ferroelectric photoelectrodes to break the limits imposed by common semiconductors. As a result of their prominent ferroelectric properties, the photoelectrodes are able to tune the transfer of photo-excited charges generated either in BiFeO3 or the surface modifiers by manipulating the poling conditions of the ferroelectric domains. At 0 V vs Ag/AgCl, the photocurrent could be switched from 0 μA cm(-2) to 10 μA cm(-2) and the open-circuit potential changes from 33 mV to 440 mV, when the poling bias of pretreatment is manipulated from -8 V to +8 V. Additionally, the pronounced photocurrent from charge injection of the excited surface modifiers could be quenched by switching the poling bias from +8 V to -8 V.

Electrochemical Evaluation for Rust Preventive Properties of Rust Preventive Oils Coated on Fe-Cu-C Sintered Steel

Since Fe-Cu-C sintered steels are easily rusted, they are coated with rust preventive oils. High viscosity of those rust preventive oils decrease workability, and low viscosity deteriorates rust preventive performance. Therefore, it is necessary to develop new rust preventive oils with contradictory properties of low viscosity and superior rust prevention. However, precise methodology to evaluate rust prevention ability has not been established. In this study, we developed new technique to quantitatively evaluate rust prevention ability by measuring the open circuit potential through thin corrosive solution on Fe-Cu-C sintered steels coated with a rust preventive oils. As a result, the ability for rust prevention can be measured quantitatively, and it decreases slowly over time, with repeating destruction and restoration. Furthermore, it was found that the deteriorating processes of rust prevention ability for rust prevention oils are composed of three characteristics steps respectively. That is, in the first step the great open circuit potential changes from 0V to-0.3V with repetition were observed where the excellent rust prevention ability was kept, in the second step it decreases slowly from-0.1V to-0.4V with oscillation of the small potential changes where the gradual decrease of rust prevention ability was recognized and in the third step it decreases monotonously in the lower potential than-0.4V where the rust was observed because of the remarkable deteriorating of the rust prevention ability.

Electrochemical Monitoring of Single Nanoparticle Collisions at Mercury-Modified Platinum Ultramicroelectrodes

Here, we report a potentiometric method for detecting single platinum nanoparticles (Pt NPs) by measuring a change in open-circuit potential (OCP) instead of the current during single Pt NP collisions with the mercury-modified Pt ultramicroelectrode (Hg/Pt UME). Similar to the current-time (i-t) response reported previously at Hg/Pt UMEs, the OCP-time (v-t) response consists of repeated potential transient signals that return to the background level. This is because Hg poisons the Pt NP after collision with the Hg/Pt UME due to amalgamation and results in deactivation of the redox reaction. For individual Pt NP collisions the amplitude of the OCP signal reaches a maximum and decays to the background level at a slower rate compared to the comparable i-t response. Due to this, OCP events are broader and more symmetrical in shape compared to i-t "spikes." The collision frequency of Pt NPs derived from v-t plots (0.007 to 0.020 pM(-1) s(-1)) is in good agreement with the value derived from i-t plots recorded at Hg/Pt UMEs (0.016 to 0.024 pM(-1) s(-1)) under similar conditions and was found to scale linearly with Pt NP concentration. Similar to the current response, the amplitude of the OCP response increased with the NP's size. However, unlike the change in current in a i-t response, the change in OCP in a v-t response observed during single Pt NP collisions with Hg/Pt UME is larger than the estimated change in OCP based on the theory. Therefore, the Pt NP sizes derived from the v-t response did not correlate with the TEM-derived Pt NP sizes. In spite of these results the potentiometric method has great value for electroanalysis because of its significant advantages over the amperometric method such as a simpler apparatus and higher sensitivity.

Anodic Titanium Oxide Films: Photoelectrochemical and Tribocorrosion Behavior

Titanium oxide films are fabricated by Ti anodization in orthophosphoric acid-ammonium fluoride electrolytes. On the mechanically polished semi-bright Ti substrates the continuous TiO2 films are formed, whereas ordered nanoporosity is formed on the mirror-like surface of Ti substrate at temperatures of 10–20 °C in the H3PO4 electrolyte with NH4F. The photocurrents and photopotentials are affected by the amount of fluorine in the electrolyte and consequently in the deposit. Tribocorrosion tests were performed in a neutral solution, and changes of open-circuit potential (OCP) as well as electrochemical impedance spectra were recorded with/without 0.4 N load. The rapid changes of OCP can be explained by the passive film abrasion, when oxide film becomes damaged and bare Ti surface is exposed. The wear loss depends on the NH4F concentration in the solution used for TiO2 films fabrication. TiO2 films destroyed during sliding tend to restore within 300–400 s after unloading.

A Prognostic Electrochemical Method for Predicting Treatment Outcomes in Transplant Patients

Presently, no known prognostic methods are capable of predicting recovery outcome in postoperative treatment of transplant patients. It is well known that the equilibrium between active oxygen forms and antioxidants in the blood reflects the condition of the organism to a certain extent. It is also known that acute pathological states can cause an imbalance of pro- and antioxidants in the blood [1]. From an electrochemical viewpoint, the ratio of overall oxidant and antioxidant activities can be described by the Nernst equation (Eq. 1): E = E 0 + (RT/nF) ln (Σ[ox]/Σ[red]) (1)Therefore, changes in the open-circuit potential (OCP) of the platinum electrode immersed in blood or blood plasma can be used as an indicator of the redox properties of the above biological media. The interrelation of Pt OCP in biomedia and the presentation of certain pathological conditions in the patient has been established; other data reveal the correlation of the OCP with biochemical parameters of blood, such as the partial pressure of oxygen (pO2) in it or the “middle molecule” toxicity assay.As we have previously shown, changes in Pt OCP in blood plasma must be monitored continuously in the course of measurement, whereas literature OCP were reported as discrete values. Quite importantly, patient condition monitoring revealed significant correlations with Pt OCP changes in blood serum [2].The goal of the present work was to identify diagnostic and prognostic criteria for the monitoring of recovery of kidney and liver transplant patients by means of Pt OCP measurement in blood plasma.Measurement of the time dependence of platinum electrode OCP while immersed in the investigated medium (blood plasma) was recorded with a microcomputer-controlled IPC-Compact potentiostat (NTF Volta, Ltd.) against the silver/silver chloride electrode. Prior to each measurement, the platinum electrode was pre-treated according to the method described in [3]. The duration of each Pt OCP time dependence measurement was 15 min. A control group of 63 apparently healthy subjects aged 19-40 was used, comprising 46 male and 17 female subjects. The experimental group comprised 59 kidney transplant patients (42 male, 17 female) and 64 liver transplant patients (40 male, 24 female). Statistical analysis of the data was performed using the STATISTICA 6.0 software package (StatSoft). A comparison of Pt OCP values in the blood plasma of apparently healthy subjects over against those of kidney and liver patients with unremarkable recoveries (i.e., who did not experience complications) revealed that the OCP range of such transplant patients was more positive, as compared with values for essentially healthy subjects (Table 1).Table 1. Pt OCP values for various subjectsApparently healthyLiver transplantKidney transplantNumber of subjects633235Number of tests63254499Sex: male female 461721112015Mean OCP, mV–33.7-1.50.1Std. deviation, mV22.519.420.9 A comparison of Pt OCP in blood plasma of apparently healthy subjects and patients presenting with postoperative dysfunctions of the transplant showed a significantly greater positive shift of OCP values, as compared with transplant patients whose recovery was unremarkable (Fig. 1).Thus, the analysis of a statistically significant sample of the patient population has shown that the Pt OCP values in blood plasma are more positive in transplant patients, as compared to those in apparently healthy subjects. Since the Pt OCP in blood plasma is much more positive for patients with postoperative transplant dysfunction than for the unremarkable recovery group, it appears possible to predict the likelihood of dysfunction onset based on the measured Pt OCP: OCP values more positive than 0.0 mV indicate an imminent threat of dysfunction onset in a transplant patient.[1] Rao S.K., Palazzo R.S., Metz H.N. et al. // J Pharmacol Toxicol Methods, 1997, 38(3), P.151-156.[2] Khubutiya M.Sh., Goldin M.M., Romasenko M.V. et al. // ECS Transaction, 2010, 25(19), P. 63-71.[3] Khubutiya M.Sh., Evseev A.K., Kolesnikov V.A. et al. // Russ J Electrochem, 2010, 46(5), P. 537-541.==========Figure 1 caption: Fig. 1. Ranges of Pt OCP (mean ± st.dev.) in apparently healthy subjects (1), unremarkable recovery transplant patients (2), and dysfunction transplant patients (3).

Interaction of C1 Molecules with a Pt Electrode at Open Circuit Potential: A Combined Infrared and Mass Spectroscopic Study

The interaction of CO, HCOOH, HCHO, and CH3OH molecules with a Pt surface initially covered with a layer of oxide under open circuit potential (OCP) is studied by combined infrared and mass spectroscopy. We found that after switching to the fuel containing solution and concomitantly switching off the electrode potential control at 1.2 V, (i) the OCP decays from 1.2 V down to values of 0.58 V (CO), 0.12 V (HCOOH), 0.08 V(HCHO) and 0.24 V(CH3OH); (ii) CO is the only adsorbate formed at the Pt surface from the fuels; (iii) the rates for the decay of OCP and for the buildup of COad adlayer decrease in the order of CO > HCHO > HCOOH > CH3OH; (iv) the rate of CO2 production and the total amount of CO2 produced decreases in the order of CO > HCOOH > HCHO > CH3OH; and (v) a significant amount of HCOOH is formed for the case with HCHO and the main by product from CH3OH is HCHO. Our results indicate that (i) the change in OCP is determined by the change of net charge at the electrode/electrolyte interface due to the production of electrons from fuel oxidation and the consumption of electrons by Oad/OHad reduction; and (ii) even without an externally potential control, the reactions occurring at the interface are controlled by the electrochemical potential of the respective reactants and products. The implication from OCP transient to the local potential distribution and local activity in practical fuel cells are discussed.

Characterization and application of a metallic tungsten electrode for potentiometric pH measurements

This study demonstrated the application of a metallic tungsten electrode for pH measurement. The metallic tungsten electrode exhibited an excellent linear response similar to the tungsten oxide electrode. Both the metallic tungsten electrode and tungsten oxide electrode used in our study exhibited a near-Nernstian response of −51.9mV/pH and −56.8mV/pH, respectively. No obvious interference was observed from the primary cations. The fitted curve for the metallic tungsten electrode showed a smaller slope (−1.87mV/°C) and more linear (R2=0.999) temperature response than those of the tungsten oxide electrode, indicating its suitability in practical pH measurements due to its precise compensation of temperature. Moreover, the metallic tungsten electrode was almost uninfluenced by the hydrodynamic effect, and its open circuit potential change was less than 2mV even at high stirrer rotation speeds (120rev/min) in solution. Long-term stability could be achieved for the metallic tungsten electrode over the pH range 4.5–8.0. Owing to the advantages such as precise temperature compensation, insensitivity to the hydrodynamic effect, long-term stability, good selectivity, and intrinsic properties of the solid-state electrode, the metallic tungsten electrode has shown promise for long-term pH monitoring.

Real-Time Observation of Cu Electroless Deposition: Synergetic Suppression Effect of 2,2′-Dipyridyl and 3-N,N-Dimethylaminodithiocarbamoyl-1-propanesulfonic Acid

The effect of 2,2′-dipyridyl and 3-N,N-dimethylaminodithiocarbamoyl-1-propanesulfonic acid (DPS) during Cu electroless deposition was observed in real time by measuring open-circuit potential and mass change of an electrode with a electrochemical quartz crystal microbalance. During Cu electroless deposition, the addition of 2,2′-dipyridyl reduced the deposition rate. DPS switched its role sensitively according to its concentration: deposition was accelerated at low concentrations and strongly suppressed at high concentrations. However, synergetic suppression effect was observed even at low DPS concentrations when 2,2′-dipyridyl was added together. In this system, the rate of suppression depended on DPS concentration: the higher DPS concentration decreased the deposition rate faster, while the minimum deposition rate was independent of the DPS concentration. Using the synergetic suppression effect, electroless Cu filling of 55-nm trenches was also successfully achieved.

Effects of Tritiated Water on Passivation Behavior of SUS304 Stainless Steel

The effects of tritium on the self-passivation behavior of SUS304 stainless steel were studied to elucidate the mechanism of passivation inhibitory effect by tritium. As the experiments, the changes of open circuit potential over time were measured in 1 N H2SO4 solution with changing dissolved oxygen concentration and tritium concentration. It was found that there would be two types of tritium effects in passivation: one is inhibit or prolonging the start passivation, and the other is deceleration of the completion of passivity. From the experimental results, it was supposed that elution of trivalent chromium, one of the principal components of passive film, as hexavalent chromium due to further oxidation by highly oxidative radiolysis products would be the key reaction to inhibit the passivation.

Effects of Conductive Pigments on the Anti-Corrosion Properties of Zinc-Rich Coatings

Effects of replacing partial zinc dust with conductive pigments on the anti-corrosion properties of ethyl silicate zinc-rich coatings with low zinc content were investigated. Salt spray test, salt immersion test and open circuit potential(OCP) measurement were utilized to evaluate anti-corrosion properties. Experimental results revealed that the effects of conductive pigments content on anti-corrosion properties are similar for di-iron phosphide powder, graphite powder and aluminum powder employed in this article. For every kind of conductive pigments, protection life in salt spray test, protection life in salt immersion test, galvanic protection life and initial OCP change with conductive pigments content increase in a similar way. They all reach an extreme point, and all the extreme points correspond to a same replacing ratio named best replacing ratio. The best replacing ratio is 20,15 and 15wt% for di-iron phosphide powder, graphite powder and aluminum powder respectively. Comparing with non-replacing coatings, conductive pigments-containing coatings at best replacing ratio possess both lower zinc content and better anti-corrosion properties.

Open Circuit (Mixed) Potential Changes Upon Contact Between Different Inert Electrodes–Size and Kinetic Effects

We investigate the principle of the open circuit potential (OCP) change upon a particle collision event based on mixed potential theory and confirmed by a mimic experiment in which we studied the changes in the OCP when two different electrodes (Pt and Au) are brought into contact in a solution that contains some irreversible redox couples. A micrometer-sized Au ultramicroelectrode, when connected in parallel to a Pt micro- or nanoelectrode, showed clearly measurable OCP changes whose magnitude matches well with that predicted by a simplified mixed potential theory for a pair of different electrode materials. On the basis of the study, each electrode establishes a different mixed potential involving two or more half reactions that have different heterogeneous electron transfer kinetics at different electrodes and the OCP changes are very sensitive to the relative ratio of the rate constant of the individual half reaction at different materials.

Real-Time Observation of Cu Electroless Deposition: Adsorption Behavior of PEG during Cu Electroless Deposition

The adsorption kinetics of polyethylene glycol (PEG) during Cu electroless deposition was investigated in real-time by measuring the open-circuit potential (OCP) and mass change of a Cu electrode. The addition of PEG during the deposition caused an OCP decrease with a reduction in the deposition rate. It was found that the adsorption of PEG blocked active sites for the adsorption of formaldehyde, a reducing agent, resulting in the suppression effect. The adsorption kinetics of PEG was strongly dependent on the concentration and diffusion coefficient which is directly related to the molecular weight of PEG. The diffusion-controlled adsorption was observed when PEG concentration was low. At high PEG concentrations, the adsorption kinetics was adsorption-controlled when the PEG molecular weight was low and diffusion-controlled when the PEG had a high molecular weight. The strength of the suppression effect was also affected by the molecular weight of PEG: increasing the molecular weight enhanced the suppression effect.

The electrochemical synthesis of poly(o-phenylenediamine) on stainless steel and its corrosion protection ability in 3.5 % NaCl solution

In this study, electrochemical synthesis of poly(o-phenylenediamine) (PoPDA) on 316L stainless steel and its corrosion inhibition effect were studied. Electropolymerization of o-phenylenediamine (oPDA) was carried out by a potentiodynamic method using 0.5 M H2SO4 solution containing 0.05 M oPDA monomer. The corrosion protection ability of the PoPDA in 3.5 % NaCl was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, and change of open circuit potential with immersion time (EOCP − t). The results showed that PoPDA acted as a protective layer on stainless steel against corrosion in 3.5 % NaCl solution.

Formation process and properties of phytic acid conversion coatings on magnesium

PurposeThe purpose of this paper is to investigate a chromium‐free conversion coating treatment for magnesium with phytic acid solution.Design/methodology/approachPure magnesium was selected for the tests. Phytic acid solution was used as the conversion solution of surface treatment. The samples of magnesium were immersed in the solution under certain conditions to form a conversion coating on the surface of magnesium. The formation process of phytic acid conversion coating was studied by detecting the open circuit potential (OCP) and weight change of the pure magnesium for different conversion treatment times. Scanning electron microscopy (SEM) and electron energy spectrum (EDS) were used to examine the morphologies and compositions of the coatings, respectively.FindingsThe experimental results showed that the conversion coating had a multideck structure with netlike morphology, which is similar in nature to chromate conversion coatings, and was composed mainly of Mg, P, O and C. The contents of C and P and the size of the cracks in different conversion layers decreased from the external layer to the inner layer. The thickness of the conversion coating varied from 1.0μm to 15μm according to the processing parameters. The hydroxyl groups and phosphate carboxyl groups in the coating, which have similar properties to an organic paint coat, are beneficial to the combination of substrate and organic paint coating. The formation mechanism and thickness variation of the conversion coatings also are discussed.Originality/valueThe paper shows that phytic acid conversion coating could improve the electrochemical properties of magnesium and provide effective protection, which can improve the corrosion resistance of magnesium.

Observation of Single Metal Nanoparticle Collisions by Open Circuit (Mixed) Potential Changes at an Ultramicroelectrode

Single nanoparticle (NP) collisions were successfully observed by a potentiometric measurement. The open circuit potential (OCP) of a measuring Au ultramicroelectrode (UME) changes when Pt NPs collide with the UME in a hydrazine solution. The OCP change is related to the redox processes, the concentration of particles, particle size, and electrode size. Compared with the amperometric technique, this approach has several advantages: higher sensitivity, simpler apparatus, fewer problems with NP decomposition, and contamination.

Corrosion of organosilane coated Mg4Y alloy in sodium chloride solution evaluated by impedance spectroscopy and pH changes

Electrochemical impedance spectroscopy (EIS), open circuit potential and pH changes were used to examine the corrosion of magnesium 4% yttrium alloy (Mg4Y) with and without a silane-epoxy-coating (SEC) in a stirred 0.154 M NaCl solution at 37 °C. For a good quality SEC we find a relatively low non-Faradaic resistance of 266 Ω cm2. The quality of the SEC was affected by the curing temperature. In this article we compare the electrochemical measurements taken during corrosion of bare Mg4Y, Mg4Y with a SEC that remained intact, and a SEC that did not protect the Mg from corrosion.

Adsorption and inhibition effect of 2-thiohydantoin on mild steel corrosion in 0.1 M HCl

2-Thiohydantoin (2-THD) was investigated as a corrosion inhibitor of mild steel (MS) in 0.1M HCl solution using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and linear polarization resistance (LPR) measurements. The effects of temperature, hydrogen gas evolution and change of open circuit potential with immersion time were also studied. The MS surfaces with, and without inhibitor has been characterized by SEM. The results showed that 2-THD acts as a mixed type inhibitor in 0.1M HCl by suppressing simultaneously the cathodic and anodic processes via physical adsorption on the MS surface followed by the Langmuir adsorption isotherm.

Preparation and Anti-corrosion Property of Polyaniline Waterborne Coatings

Polyaniline doped with an organic phosphate(PANI-OP) was blended with water-borne epoxy resin and used as an anti-corrosion material.The long-term anti-corrosion behavior of the material was investigated.Transmission electron microscopy showed that the PANI-OP powder was uniformly dispersed in the waterborne epoxy resin when the PANI content was below 1%.The diameter of the particle decreased to ca.50~100 nm when the PANI content was 0.1%.Electrochemical impedance spectroscopy and the changes in open circuit potential indicated that the presence of polyaniline coating significantly improved the anti-corrosion effect.X-rays photoelectron spectra showed that a dense passive film of iron oxide(FeO and Fe2O3) on the surface was accounted for the anti-corrosion;in the meanwhile,the presence of P indicated that the dopant ion was also involved in the corrosion protection process.

Investigation of inhibition effect of rhodanine-N-acetic acid on mild steel corrosion in HCl solution

Corrosion inhibition effect of rhodanine-N-acetic acid (R-NA) on mild steel (MS) corrosion in 0.1 M HCl solution was investigated. For this purpose, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) as well as hydrogen gas evolution ( V H 2 − t ) and the change of open circuit potential as a function of immersion time ( E ocp − t) were used. The MS surfaces exposed to 0.1 M HCl solution in the absence and presence of inhibitor were examined by scanning electron microscopy (SEM). The thermodynamic parameters of adsorption were calculated and discussed. In order to gain more information about the adsorption mechanism, the EIS technique was used to evaluate the potential of zero charge (PZC) and a mechanism of adsorption process was proposed. It was found that, R-NA is a good corrosion inhibitor for the MS corrosion in 0.1 M HCl solution. The inhibition efficiency increased with increasing inhibitor concentration and reached 98% at 1.0 × 10 −2 M R-NA. The high inhibition efficiency was related to adsorption of R-NA on steel surface. Surface SEM images showed a good surface coverage of inhibitor on the metal surface.

Inhibition efficiency of benzidine for mild steel in acidic media

In this study, the inhibition effect of different concentrations of benzidine possessing amine groups in its structure on the corrosion behavior of mild steel (MS) in 1.0 M HCl solution at 293 K temperature was practiced in both short and long immersion times by measuring electrochemical impedance spectroscopy (EIS), hydrogen evolution (V H2 − t) and change of open circuit potential (E ocp − t). For short-term tests, potentiodynamic polarization and linear polarization resistance (R lp ) were also studied. Polarization data indicate that this compound act as mixed-type inhibitor for mild steel in 1.0 M HCl. With regard to the results cited, it was identified that the increase in the inhibitor efficiencies with concentration was emanated from the adsorption of benzidine molecules on the electrode surface. Pertinent to this adsorption, it followed Langmuir isotherm. Adsorption equilibrium constant and adsorption free energy were determined. The effect of temperature on the corrosion behaviour in the absence of any inhibitor and in the presence of 75 mM benzidine was studied in the range of 293–323 K. Activation energies (E a * ) were calculated from the obtained corrosion rates at different temperatures. Furthermore, in order to identify the adsorption mechanism of the inhibitor on the metal surface, the zero-charge potential (PZC) was determined by EIS measurement technique. Surface morphology of mild steel electrodes were emerged by means of the scanning electron microscope.