Open Circuit Potential Conditions Research Articles

Experimental Clarification of the RWGS Reaction Effect in H2O/CO2 SOEC Co-Electrolysis Conditions

In the present investigation, modified X-Ni/GDC electrodes (where X = Au, Mo, and Fe) are studied, in the form of half-electrolyte supported cells, for their performance in the RWGS through catalytic-kinetic measurements. The samples were tested at open circuit potential conditions in order to elucidate their catalytic activity towards the production of CO (rco), which is one of the products of the H2O/CO2 co-electrolysis reaction. Physicochemical characterization is also presented, in which the samples were examined in the form of powders and as half cells with BET, H2-TPR, Air-TPO and TGA re-oxidation measurements in the presence of H2O. In brief, it was found that the rate of the produced CO (rco) increases by increasing the operating temperature and the partial pressure of H2 in the reaction mixture. In addition, the first results revealed that Fe and Mo modification enhances the catalytic production of CO, since the 2wt% Fe-Ni/GDC and 3wt% Mo-Ni/GDC electrodes were proven to perform better compared to the other samples, in the whole studied temperature range (800–900 °C), reaching thermodynamic equilibrium. Furthermore, carbon formation was not detected.

Semiconducting properties assessment of passive oxide films forming on pure tungsten in 1.0 M H3PO4 solution

The current study is mainly to discuss the observed semiconducting characteristics of oxide passive films formed on pure tungsten (W) in H3PO4 solution (1.0 M). Potentiodynamic polarization (PDP) curve reveals that pure tungsten shows passive behavior in the given solution. Also, impedance spectroscopy shows that pure tungsten displays passive behavior at open-circuit potential condition in the solution. Mott–Schottky (M–S) analysis indicates that mentioned films which are formed on pure tungsten in phosphoric acid solution (1.0 M) display the semiconductors behavior of type n. The conduction of these passive films are not affected by anodic passive potential. In addition, according to M–S results, fewer defects are found in the passive film at higher anodic passive potentials. The obtained results show that corrosion resistance of pure tungsten in 1.0 M H3PO4 solution improves at higher passivation potentials due to the formation of passive films that are less defective.

Improved Tribocorrosion Resistance of a CoCrMo Implant Material by Carburising

Tribocorrosion damage is a cause for the premature failure of hip implants made of cobalt-based alloys. Low-temperature carburising can be a plausible solution towards mitigating the tribocorrosion damage of articulating components. This diffusion treatment introduces a supersaturated carbon solid solution, termed S-phase, which hardens the CoCrMo alloy without detriment to the corrosion resistance. This work investigates and compares the tribocorrosion behaviour of untreated and carburised ASTM F1537 CoCrMo alloys tested in Ringer’s solution using a reciprocating sliding configuration against a polycrystalline alumina counterface under different electrochemical conditions. The research shows that whereas the carburised alloy suffered a slightly higher wear loss under a cathodic potential, it was able to reduce the material losses considerably when tested under both open circuit and anodic potential conditions. Under anodic conditions material losses by corrosion due to wear dominated. The better tribocorrosion resistance of the carburised layer was attributed to the better qualities of the passive film for the carburised sample coupled with an increased load support.

EIS Study on Interfacial Properties of Passivated Nitinol Orthodontic Wire in Saliva Modified with Eludril® Mouthwash

This work aimed at first-time use of EIS measurements to study the effect of ready-to-use Eludril® mouthwash containing 0.10% chlorhexidine digluconate as active component on corrosion performance of Nitinol orthodontic wire in artificial saliva at 37°C. In vitro corrosion resistance of the autoclaved Nitinol wire was studied under open circuit potential conditions using EIS combined with cyclic potentiodynamic polarization curves. HREM, SEM, EDS, and microhardness testing were used to study the properties of the Nitinol wire before and after corrosion measurements. EIS study of the interfacial properties of the Nitinol electrode | oxide layer | saliva solution system revealed the capacitive behavior of the material with high corrosion resistance. EIS allowed to determine resistance of charge transfer through the oxide | electrolyte interface. It was found that kinetics of pitting corrosion of the Nitinol electrode in saliva increases with the rising content of Eludril® mouthwash.

Tribocorrosion behavior of plasma nitrided Hardox steels in NaCl solution

Abstract In this study, the effect of plasma nitriding treatment on structural, wear, corrosion and tribocorrosion properties of different type Hardox steels (400, 450 and 500 type) was investigated using X-ray diffraction, microhardness tester, scanning electron microscope, 3D profilometer and reciprocating wear tester coupled with electrochemical corrosion cell. The plasma nitriding treatments were performed in 50%N2-50%H2 gas mixture at 500 °C for 1 and 4 h. The tribological tests were carried out in dry and open circuit potential conditions at 10 N normal force in 3.5% wt. NaCl aqueous solution at room temperature. Nitriding changed the electrochemical degradation mechanism of surface to pitting corrosion. Plasma nitriding time of 1 h significantly improved the corrosion and wear resistance of the Hardox steels.

Effect of simulated inflammatory conditions and potential on dissolution and surface oxide of CoCrMo alloy: In situ electrochemical atomic force microscopy study

Inflammation may develop in association with implantation of hip replacements and the inflammatory state of the local body fluids may affect the corrosion of metallic biomaterials like CoCrMo alloy. In this study CoCrMo alloy surfaces were imaged using in situ electrochemical atomic force microscopy (ECAFM) to evaluate oxide film morphology and surface dissolution while immersed in phosphate buffered saline (PBS) solution or simulated inflammatory (SI) solutions across a range of potentials. The SI solution explored here consisted of a 30 mM hydrogen peroxide (H2O2) modified PBS solution. Analysis of ECAFM images, surface roughness and potentiostatic polarization current density data exhibited a correlated relationship between surface oxide morphology, loss of passivity and electrochemical behavior CoCrMo alloy. ECAFM results showed that the presence of H2O2 altered oxide film behavior, leading to positive shifts of open circuit potential (OCP) to 0.32 V (vs Ag/AgCl), higher current density and significantly altered oxide film topography compared to PBS only case. Surface morphology, surface roughness (Ra) and current density exhibited strong potential- and time-dependent behaviors. Significant surface oxide formation on alloy and carbides were observed, followed by dissolution of CoCrMo alloy as potentials were increased above 0.5 V. Carbide boundaries and metal grain boundaries were preferential sites for oxide dissolution at transpassive potential ranges. Formation and evolution of new oxides were directly imaged at 0.65 V in PBS solution. New oxides formed and covered the surface in 10 min at 0.65 V. However, they were less protective compared to the passive oxide films at OCP condition. Simulated inflammatory solutions raise alter corrosion behavior of CoCrMo alloys.

Open-circuit potential of a Pt electrode immersed in different aqueous solutions

The aim of this study is to investigate the multi-day behavior of the electromotive force (EMF) between Pt and reference Ag/AgCl, KClsat. electrodes immersed in various aqueous systems (deionized water, 1 × 10−3 M H2SO4 solution and 0.15 M KCl solution) at 32 °C and also at ambient temperature, without oxygen removal and redox species introduction. The control test of EMF behavior in the presence of redox species was performed with cyanide complexes of Fe2+ and Fe3+ ions at ambient temperature. In experiments with deionized water, systems were protected against the influence of daylight and static electricity. The results have shown diurnal oscillations of EMF in all investigated systems with amplitudes in the range ≈ 1 to 25 mV depending on applied experimental conditions. EMF oscillations in deionized water were independent on the applied temperature and yielded amplitudes of 15–25 mV in daylight regime, and only a few mV when protected from its influence. The effect of electrostatic electricity was not observed. Diurnal EMF oscillations with the amplitudes ≤ 5 mV were observed individually in 0.15 M KCl solution, redox system and after 4 days of investigation in H2SO4 solution. Results presented in this work pointed out that the behavior of Pt–oxygen electrode is specific and very complex, even in the simplest system such as deionized water. To investigate the origin of the observed EMF oscillations and the application of Pt–oxygen electrode in in situ multi-day dynamics studies under open-circuit potential condition, additional theoretical and experimental methods and particularly electrochemical ones, must be applied.

Probing the hydrogen adsorption affinity of Pt and Ir by surface interrogation scanning electrochemical microscopy (SI-SECM)

Scanning electrochemical microscopy in the surface interrogation mode (SI-SECM) has been used to probe the strength of metal-adsorbed H bonds at Pt and Ir. The generally accepted view is that this technique can only give meaningful results for similar probe and substrate electrode dimensions. However, it is shown that SI-SECM can also provide valuable information for H adsorption even when the substrate is much larger than the microelectrode probe (of 500 and 25μm diameter respectively), for properly chosen substrate and mediator combinations that minimize the tip currents under substrate open circuit potential conditions. Linear sweep voltammetry at a microelectrode positioned at a very small probe–substrate distance (2.5μm) showed remarkable positive feedback in the presence of an oxidizable mediator (TMPD) when a full or partial H monolayer was electrochemically pre-formed on the Pt or Ir substrate. The magnitude and shapes of chronoamperometric responses at the tip were interpreted in terms of variation of H coverage with time and changes in the open circuit potential of the substrate. The higher affinity of Ir than Pt for adsorbed H has been used to validate the approach.

Influence of Electric Fields on Biofouling of Carbonaceous Electrodes.

Biofouling commonly occurs on carbonaceous capacitive deionization electrodes in the process of treating natural waters. Although previous work reported the effect of electric fields on bacterial mortality for a variety of medical and engineered applications, the effect of electrode surface properties and the magnitude and polarity of applied electric fields on biofilm development has not been comprehensively investigated. This paper studies the formation of a Pseudomonas aeruginosa biofilm on a Papyex graphite (PA) and a carbon aerogel (CA) in the presence and the absence of an electric field. The experiments were conducted using a two-electrode flow cell with a voltage window of ±0.9 V. The CA was less susceptible to biofilm formation compared to the PA due to its lower surface roughness, lower hydrophobicity, and significant antimicrobial properties. For both positive and negative applied potentials, we observed an inverse relationship between biofilm formation and the magnitude of the applied potential. The effect is particularly strong for the CA electrodes and may be a result of cumulative effects between material toxicity and the stress experienced by cells at high applied potentials. Under the applied potentials for both electrodes, high production of endogenous reactive oxygen species (ROS) was indicative of bacterial stress. For both electrodes, the elevated specific ROS activity was lowest for the open circuit potential condition, elevated when cathodically and anodically polarized, and highest for the ±0.9 V cases. These high applied potentials are believed to affect the redox potential across the cell membrane and disrupt redox homeostasis, thereby inhibiting bacterial growth.

Impedance and Raman Spectroscopy Study of Effect of H2S on Ni‐YSZ SOFC Anodes

AbstractThe electrical behavior of a Ni‐YSZ anode of a solid oxid fuel cell (SOFC) cell under H2S has been monitored by impedance spectroscopy combined with in situ Raman spectroscopy and post mortem scanning electron microscopy (SEM) at 500 °C in open circuit potential (OCP) and at 500 mV polarization. In OCP condition, the electrode impedance spectra evolved slowly corresponding quite well to the evolution of Raman signals' intensities. Meanwhile, at 500 mV polarization, the impedance spectra transformed much faster, indicating a quick and severe H2S‐induced poisoning, which is then confirmed by post mortem examinations by SEM with the densification of the bulk anode porous structure with (Ni, S) phase. Based on the experimental data, the elementary steps and location of H2 oxidation are discussed.

Corrosion resistance improvement of nitinol by anodisation in the presence of molybdate ions

The corrosion behaviour of Nitinol (NiTi) alloy was studied in Ringer solution. In order to improve its corrosion resistance, protective films were formed on the NiTi surface by means of anodisation under potentiostatic or galvanostatic control in the presence of the corrosion inhibitor molybdate in alkaline and acidic solutions.The anodisation process reduces considerably the Ni content and increases the Ti content in the oxide film, indicating that the Ti/Ni stoichiometry in the outermost surface is much higher than in pure NiTi. The titanium enrichment on the outermost surface as TiO2 enhanced its anticorrosion performance, as was suggested by the decrease in the amount of Ni and Ti released in Ringer solution under open circuit potential (OCP) condition and under potentials where the bare substrate suffers pitting attack.The best anodised film in terms of corrosion protection was obtained under potentiostatic condition in alkaline solution. The presence of oxidised molybdenum species in the oxide potentiostatically grown in alkaline solution, generates a corrosion protective film with a smoother and denser surface than other oxides formed in acidic solutions, without any defects like micro-cracks or pores.

Immobilization and release of copper species from a microstructured polypyrrole matrix.

Copper species immobilization in hollow rectangular-sectioned microtubes of polypyrrole (PPy) electrosynthesized on 316L stainless steel was carried out using two different methods. One of them involved the immobilization after the PPy electropolymerization and the other one during the electrosynthesis process. The electrodes modified with copper species were rotated at different speeds in well water under open-circuit potential conditions. The release of copper species from the PPy matrix and the antibacterial activity against Escherichia coli were analyzed. The obtained results demonstrate that the amount of copper species released as well as the bactericidal effects against E. coli increases with rotation speed. The PPy coating modified with copper species after the electropolymerization reaction exhibited the best performance in terms of antibacterial activity and corrosion protection. These electrodes were tested in a lab-scale continuous flow system for well water disinfection.

Passive behaviour of alloy corrosion-resistant steel Cr10Mo1 in simulating concrete pore solutions with different pH

The passive behaviour of new alloy corrosion-resistant steel Cr10Mo1 and plain carbon steel (as a comparison) in simulating concrete pore solutions of different pH (ranging from 13.5 to 9.0) under open circuit potential conditions, was evaluated by various electrochemical techniques: potentiodynamic polarization, capacitance measurements and electrochemical impedance spectroscopy. The chemical composition and structure of passive films were investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The electrochemical responses of passive films show that Cr10Mo1 steel has an increasing passivity with pH decreasing while carbon steel dose conversely, revealing carbonation does no negative effect on passivation of the corrosion-resistant steel. SIMS reveals that the passive film on the corrosion-resistant steel presents a bilayer structure: an outer layer mainly consisting of Fe oxides and hydroxides, and an inner layer enriched in Cr species, while only a Fe-concentrated layer for carbon steel. According to the XPS analysis results, as the pH decreases, more stable and protective Cr oxides are enriched in the film on Cr10Mo1 steel while Fe oxides gradually decompose. Higher content of Cr oxides in the film layer provides Cr10Mo1 corrosion-resistant steel more excellent passivity at lower pH.

Silver release from polypyrrole matrix in well water

Polypyrrole (PPy) films constituted by hollow rectangular microtubes were electrosynthesised from a salicylate (Sa) solution on 316L stainless steel (316L SS) electrodes. The covered electrodes were dipped in AgNO3 solution achieving the immobilisation of silver species. After this, they were rotated at different speeds and silver transport from the PPy matrix to well water under open circuit potential (OCP) condition was studied. The results indicate that the diffusion process of silver from the polymeric matrix is accelerated when the electrode speed is increased. The disinfection process of well water contaminated with Escherichia coli was also analysed for the electrode covered with PPy/Ag films. A faster release of Ag species was obtained when a potential step was applied. The microtubular morphology of the polymer does not suffer any alteration during the experiments.

Effect of immersion time on the electrochemical behaviour of AZ31B alloy

Effect of immersion time on the electrochemical behaviour of AZ31B alloy in 0.01 M KOH solution under open circuit potential (OCP) conditions was studied by various electrochemical methods. Polarization results revealed that increasing immersion time leads to decrease the corrosion rate of this alloy. Also, electrochemical impedance spectroscopy (EIS) results showed that the reciprocal capacitance of the passive film is proportional to its thickness which increases with increasing immersion time. In Mott–Schottky analysis, no evidence of p-type semiconducting behaviour was found, indicating that the oxygen vacancies preponderated over the cation vacancies. Moreover, the Mott–Schottky results showed that the donor density increases by increasing the immersion time from 1 to 6 h, while it decreases when the immersion time reaches 9 and 24 h. Therefore, it is clear that higher immersion time offers better conditions for forming the passive films with higher protection behaviour, due to the growth of a much thicker and less defective films.

Tribocorrosion Behavior of Overlay Welded Super Duplex Stainless Steel in Chloride Medium

The tribocorrosion behavior of super duplex stainless steel overlay weldment, sliding against alumina counterpart in a pin-on-disk tribometer in 1 M NaCl solution, was investigated under open circuit potential and potentiostatic conditions. The results demonstrated the significant effect of applied potential on the tribocorrosion behavior; by shifting the potentiostatic potential from cathodic to anodic range, the material degradation increased due to the introduction of synergistic wear-accelerated corrosion. Moreover, by shifting from cathodic to anodic potentiostatic polarization, the wear track became smoother and the coefficient of friction decreased. Although some evidences of corrosion-accelerated wear, such as occasional corrosion pits as well as reduction of work hardening inside the wear track, were observed, based on the synergistic approach followed, it was inferred that the dominant degradation components of the overlay welded specimen were sequentially wear and wear-accelerated corrosion.

Influence of fluoride content and pH on corrosion and tribocorrosion behaviour of Ti13Nb13Zr alloy in oral environment

CpTi and Ti6Al4V alloy are the most widely used materials for implant application, but the release of toxic elements (e.g. Al and V) and the so-called stress-shielding effect are still a concern. In recent years, β and near-β titanium alloys have been developed, which overcome these issues with reduced modulus of elasticity and biocompatible alloying elements. However, literature is scarce studying the tribocorrosion behaviour of these alloys for dental implantology. The present work studies the tribocorrosion behaviour of the near-β Ti13Nb13Zr alloy in oral environment, using CpTi4 for comparison purposes. To that end, the influence of the pH and fluoride concentration in artificial saliva was analysed. Reciprocating sliding corrosion tests were carried out under open circuit potential and potentiostatic conditions. Results reveal a negative influence of the increase of fluoride concentration and the acidified artificial saliva on the material degradation. Moreover, some light has been shed on the different tribocorrosion mechanisms of Ti13Nb13Zr and CpTi4 in simulated oral environment.

Ion exchange ability of N-octylpyridinium hexafluorophosphate in carbon ionic liquid electrode for efficient adsorptive preconcentration and selective determination of ultratrace gold chlorocomplexes

A new application of a carbon ionic liquid electrode (CILE) has been explored for preconcentration and quantification of trace amount of Au(III) chlorocomplexes. The procedure is based on the accumulation of tetrachloroaurate complexes at the electrode surface under an open circuit potential condition followed by cyclic voltammetry (CV) and differential pulse cathodic stripping voltammetry (DPCSV). An ion exchange mechanism has been proposed for efficient and fast accumulation of Au(III) chlorocomplexes. Effects of different experimental parameters such as electrolyte concentration, pH, and preconcentration time on the voltammetric signals were investigated. It was found that under the optimized experimental conditions, the linear range of measurement and the detection limit were 5.00 × 10−9–2.25 × 10−6 and 0.80 × 10−9 mol L−1, respectively. Possible interference from coexisting ions was also studied. The procedure was applied for determination of gold in water and human blood serum samples, and acceptable accuracy was achieved.

Cathodic voltage-controlled electrical stimulation of titanium implants as treatment for methicillin-resistant Staphylococcus aureus periprosthetic infections

Effective treatment options are often limited for implant-associated orthopedic infections. In this study we evaluated the antimicrobial effects of applying cathodic voltage-controlled electrical stimulation (CVCES) of -1.8 V (vs. Ag/AgCl) to commercially pure titanium (cpTi) substrates with preformed biofilm-like structures of methicillin-resistant Staphylococcus aureus (MRSA). The in vitro studies showed that as compared to the open circuit potential (OCP) conditions, CVCES of -1.8 V for 1 h significantly reduced the colony-forming units (CFU) of MRSA enumerated from the cpTi by 97% (1.89 × 106 vs 6.45 × 104 CFU/ml) and from the surrounding solution by 92% (6.63 × 105 vs. 5.15 × 104 CFU/ml). The in vivo studies, utilizing a rodent periprosthetic infection model, showed that as compared to the OCP conditions, CVCES at -1.8 V for 1 h significantly reduced MRSA CFUs in the bone tissue by 87% (1.15 × 105 vs. 1.48 × 104 CFU/ml) and reduced CFU on the cpTi implant by 98% (5.48 × 104 vs 1.16 × 103 CFU/ml). The stimulation was not associated with histological changes in the host tissue surrounding the implant. As compared to the OCP conditions, the −1.8 V stimulation significantly increased the interfacial capacitance (18.93 vs. 98.25 μF/cm2) and decreased polarization resistance (868,250 vs. 108 Ω-cm2) of the cpTi. The antimicrobial effects are thought to be associated with these voltage-dependent electrochemical surface properties of the cpTi.

Modified Point Defect Model for the Electrochemical Behavior of the Passive Films Formed on Alloy C (UNS N10002) in Borax Solutions

Utilizing potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS), the passive films properties of alloy C in borax solutions under open circuit potential condition were evaluated. The potentiodynamic polarization curves suggested that alloy C showed excellent passive behavior in borax solutions. The capacitance versus potential curves revealed that the passive films displayed p-type semiconductive characteristics, where the Ni(II) vacancies preponderated over the oxygen vacancies and interstitials. The EIS data showed that the equivalent circuit \({{R}_{{\rm s}}[({R}_{{\rm fs}}{Q}_{{\rm fs}})({R}_{{\rm f}}{Q}_{{\rm f}}) ({R}_{{\rm mf}}{Q}_{{\rm mf}})]}\) by three time constants is applicable. These results also revealed that the measured value of polarization resistance increases with decreasing concentration of borax solutions.