Change In Electrode Potential Research Articles

Using Chronopotentiometry to Better Characterize the Charge Injection Mechanisms of Platinum Electrodes Used in Bionic Devices.

The safe charge injection capacity and charge density of neural stimulating electrodes is based on empirical evidence obtained from stimulating feline cortices. Stimulation induced tissue damage may be caused by electrochemical or biological mechanisms. Separating these mechanisms requires greater understanding of charge transfer at the electrode-tissue interface. Clinical devices typically use a biphasic waveform with controlled current. Therefore, the charge injection mechanism and charge injection capacity of platinum was assessed on a commercial potentiostat by chronopotentiometry (controlled current stimulation). Platinum is a non-ideal electrode, charge injection by chronopotentiometry can be passed via capacitive and Faradaic mechanisms. Electrodes were tested under a variety of conditions to assess the impact on charge injection capacity. The change in electrode potential (charge injection capacity) was affected by applied charge density, pulse length, pulse polarity, electrode size, polishing method, electrolyte composition, and oxygen concentration. The safe charge injection capacity and charge density could be increased by changing the electrode-solution composition and stimulation parameters. However, certain conditions (e.g., acid polished electrodes) allowed the electrode to exceed the water electrolysis potential despite the stimulation protocol being deemed safe according to the Shannon plot. Multiple current pulses led to a shift or ratcheting in electrode potential due to changes in the electrode-solution composition. An accurate measure of safe charge injection capacity and charge density of an implantable electrode can only be obtained from suitable conditions (an appropriately degassed electrolyte and clinically relevant electrode structure). Cyclic voltammetric measurement of charge storage capacity can be performed on implantable electrodes, but will not provide information on electrode stability to multiple chronopotentiometric pulses. In contrast, chronopotentiometry will provide details on electrode stability, but the minimum time resolution of typical commercial potentiostats (ms range) is greater than used in a clinical stimulator (μs range) so that extrapolation to short stimulation pulses is required. Finally, an impedance test is typically used to assess clinical electrode performance. The impedance test is also based on a biphasic chronopotentiometic waveform where the measured potential is used to calculate an impedance value. Here it is shown that the measured potential is a function of many parameters (solution composition, electrode area, and surface composition). Subsequently, impedance test results allow electrode comparison and to indicate electrode failure, but use of Ohm’s law to calculate an impedance value is not valid.

Interaction between LDL-mimetic liposomes and acid-treated carbon nanotube electrode during Cu2+-mediated oxidation

Oxidation of low-density lipoproteins (LDL) causes atherosclerosis. Detection of oxidation of LDL-mimetic liposomes using an electrode might serve as a convenient tool in the search of antioxidants for the prevention of atherosclerosis. This report proposes a reaction mechanism between LDL-mimetic liposomes and an acid-treated carbon nanotube (CNT) electrode. Oxidation of the liposomes, mediated by Cu2+, was monitored by the change in electrode potential, and the fluorescence intensity generated by diphenyl-1-pyrenylphosphine (DPPP) as control. The electrode potential and fluorescence intensity increased concomitantly during oxidation, followed by a gradual decrease. Although the electrical potential peaked faster than the fluorescence intensity, addition of CNT to the DPPP reaction accelerated the latter, suggesting the role of CNT as an accelerator of liposome oxidation. Atomic force microscopy showed increased binding of liposomes to CNT along with liposomal deformation. Further, binding of Cu2+ to the liposome-bound CNT surface was observed by quartz crystal microbalance. In conclusion, the interaction of liposomes with Cu2+ and CNT surface explains the rapid response of the electrode in liposome oxidation.

Electrochemical impedance analysis of the Li/Au-Li7La3Zr2O12 interface during Li dissolution/deposition cycles: Effect of pre-coating Li7La3Zr2O12 with Au

The influence of pre-coating Li7La3Zr2O12 (LLZ) with Au on the charge transfer resistance (Rint) at the interface of LLZ and lithium (Li) is examined by AC impedance spectroscopy using a three-electrode system. The Au diffuses into Li after physical contact with Li, and the open-circuit potential reaches approximately 0mV (vs. Li/Li+) accompanied by a decrease in Rint. During the Li dissolution/deposition cycles, the electrode potential changes with 0mV as the central potential, indicating that Li metal dissolution/deposition on Li metal proceeds predominantly at the interface. Rint increases and decreases during Li dissolution and deposition, respectively, regardless of the presence or absence of the Au coating; however, the increase in Rint during Li dissolution is suppressed at the Li/Au-coated LLZ (Au-LLZ) interface. The decreased Rint is considered to be due to an increase in the effective contact area at the electrode/LLZ interface, which is achieved by pre-coating Au onto the LLZ surface.

Adjoint approach to beam optics sensitivity based on Hamiltonian particle dynamics

We develop a sensitivity function for the design of electron optics using an adjoint approach based on a form of reciprocity implicit in Hamilton's equations of motion. The sensitivity function, which is computed with a small number of time-reversed runs of a beam optics code, allows for the determination of the effects on specific beam quality figures of merit of small, but arbitrary changes in electrode potentials, positions, and shapes and in magnet strengths and locations. The sensitivity function can thus be used in an optimization cycle of a focusing system's design and/or to predict the sensitivity of a particular design to manufacturing, assembly, and alignment errors.

Visualization of Potential Distribution inside Crevice of Type 430 and 304 Stainless Steels

Stainless steels are widely used in industries because of their high anti-corrosive performance due to their passivation ability. However, crevice corrosion sometimes occurs in chloride environments. It is known that crevice corrosion is initiated when electrode potential inside crevice changes from the passive to active state. Therefore, the potential is the important factor to understand the mechanism of crevice corrosion. In this research, visualization of the potential inside the crevice for type 430 and 304 stainless steels was performed in 0.01 M NaCl at pH 3.0. An indium-tin oxide (ITO) glass with a sensing layer was applied for visualizing the potential. In the sensing layer, a redox indicator was entrapped. Figure 1 shows the schematic illustration of apparatus for the calibration procedure for color change of the plate. The ITO glass with the sensing layer (sensing plate) was used as a working electrode. In an electrolyte, a mirror polished Pt plate was put below the sensing plate to reflect the image of the sensing plate, and the optical microscope images were taken through the sensing plate by a CCD camera system. Electrode potential of the sensing plate was changed from -0.52 to 1.08 V in 0.01 M NaCl (pH 3.0 adjusted with HCl). All potentials reported in this work refer to Ag/AgCl (3.33 M KCl). Figure 2 shows the optical micrographs of the sensing plate placed above the Pt. It is clear that the color was changed from light green to dark blue with increasing electrode potential. The sensing plate was applied to crevice corrosion tests in 0.01 M NaCl (pH 3.0 adjusted with HCl). In the crevice corrosion tests, the sensing plate was used as a crevice former. The distributions of electrode potentials inside the crevice of the stainless steels were monitored from the color of the sensing plate. Figure 1

Study on Li Metal Deposition, SEI Formation on Anodes and Cathode Potential Change during the Pre-Lithiation Process in a Cell Prepared with Laminated Porous Anodes and Cathodes

The pre-doping of Li+ ions (pre-lithiation) in graphite anodes, which is needed to improve the initial charging/discharging efficiency of lithium ion batteries, was examined from the viewpoints of lithium metal deposition, surface electrolyte interface (SEI) formation and electrode potential changes in the cathode during the pre-lithiation. Using a cell composed of pre-laminated, through-holed anodes and cathodes, the anodes were pre-lithiated with the perpendicular pre-doping method, as explained in this work, which can effectively enhance the pre-lithiation process in laminated cells. In the pre-lithiation system, Li deposition was not observed on the anode surfaces during pre-lithiation, and the thickness of the SEI layers formed on the anodes did not increase. Moreover, the SEI layer has the same composition as that formed by the electrochemical lithiation (charging) process, even when the pre-lithiation of the anodes is accelerated by through-holes formed on the anode and cathode electrodes. In addition, the electrode potential of cathodes inserted between pre-lithiated anodes does not change during the pre-lithiation process, and the capacity of the cathodes does not degrade upon pre-lithiation. The perpendicular pre-doping method examined in this study is found to be applicable to the production process of lithium ion batteries with high charging/discharging efficiency.

Pourbaix Diagrams for H2O Oxidation to Adsorbed OH on Pt(111) and Why They Differ from Those for Bulk Solids

Density functional calculations show that Pourbaix diagrams for reactions involving surface species are not the same as for bulk solids. This finding is based on calculations for the onset potentials over the pH range 0–14 for 15 water oxidation reactions forming OH(ads) + H+(aq) + e– on Pt(111). The deviations are results of the dependencies of Gibbs energies of adsorbed reactants on the electrode potential, causing their activities to change with potential instead of being fixed at unity, which is the case for Pourbaix diagrams of solids. In a sense, the redox couple changes as the electrode potential changes because at each potential the adsorbed reactants and products have new structures.

(Keynote) Modification of the Electrocatalyst Surface Composition By the Electrode Potential and the Substantial Resulting Effects on the Cell Characteristic

This talk addresses a fundamental aspect of electrocatalysis: the dependence of the rate of the electrocatalytic process on electrode potential. Discussions with Ratko Adzic related to this subject, starting back in the early 1990’s, are appreciatively recognized. In a complete description of the dependence of the rate of an electrocatalytic process on electrode potential, the effect of the potential has to include two components: acceleration of the electrode reaction by lowering the activation energy of any step involving electronic charge transfer and, modification of the composition of the catalyst/electrolyte interface by the change in electrode potential. The latter effect has only rarely been included rigorously in quantitative descriptions of the rate dependence on electrode potential, thereby missing in the description an important factor determining the dependence of the rate on overpotential and , consequently, determining the power output and conversion efficiency observed in a fuel cell or electrolyzer given some combination of electrocatalyst and electrolyte. This talk will cover examples of ORR , OER and HOR processes taking place at electrocatalysts which undergo significant changes in surface composition with change of the potential within the window of relevance to fuel cells or water electrolyzers. The examples cover several types of effects on the rate of the faradaic process as result of the dependence of the interfacial composition on overpotential, including: * rate acceleration by potential-induced generation of active surface sites * rate decay by potential-induced deactivation of surface sites * rate effects by potential-induced electrolyte layer formation Complete quantitative description of these effects in mathematical form, is, in many cases, not straightforward. Nevertheless, recognition of such effects in the general expression for the rate of the electrocatalytic process can and should be reflected by a pre-exponential factor which is potential dependent [1,2]. Assuming a potential independent pre-exponential factor, as typically done, results in misinterpretation of fundamental aspects of the kinetics of electrocatalytic process, for example the reason for commonly observed increase in "Tafel slope" with the increase in overpotential. Finally, the argument made frequently that electrocatalytic processes can be fully understood using a single “descriptor”, e.g., a M-O or M-H bond strength (where M stands for an active metal surface site) , does not recognize the change of the number of active M sites with overpotential as result of a potential-induced surface modification process. This dependence of the number of active sites on potential has to be covered by , at least, a second “descriptor” , for a full description of the electrocatalytic process.

Simulated response to process abnormalities during spent nuclear fuel electrorefining

During normal operations, the only deposition on a spent nuclear fuel electrorefiner cathode consists of uranium. A computer model, ERAD, was used to simulate conditions under which the electrorefiner salt was progressively contaminated from spent nuclear fuel processing without operator intervention. The model was adjusted to reflect three scenarios: one in which salt removed with every cathode deposit was returned but the UCl3 concentration was never adjusted, one in which the salt was not removed and UCl3 concentration was never adjusted, and one in which the Pu/U ratio in the salt was allowed to reach a value of one before starting the first scenario. Under the base conditions simulated, uranium initially deposits alone but eventually plutonium begins to co-deposit along with uranium. Up to 350g of plutonium was calculated to deposit along with 8.3–9.5kg of uranium. While precise tracking of changes in the salt composition may not be possible, the model was able to identify markers for plutonium deposition by tracking changes in electrode potential. This type of marker should ultimately provide inspectors with more options for situations when they have limited access to electrorefiner data.

Destructive impact of molecular noise on nanoscale electrochemical oscillators

We study the loss of coherence of electrochemical oscillations on meso- and nanosized electrodes with numeric simulations of the electrochemical master equation for a prototypical electrochemical oscillator, the hydrogen peroxide reduction on Pt electrodes in the presence of halides. On nanoelectrodes, the electrode potential changes whenever a stochastic electron-transfer event takes place. Electrochemical reaction rate coefficients depend exponentially on the electrode potential and become thus fluctuating quantities as well. Therefore, also the transition rates between system states become time-dependent which constitutes a fundamental difference to purely chemical nanoscale oscillators. Three implications are demonstrated: (a) oscillations and steady states shift in phase space with decreasing system size, thereby also decreasing considerably the oscillating parameter regions; (b) the minimal number of molecules necessary to support correlated oscillations is more than 10 times as large as for nanoscale chemical oscillators; (c) the relation between correlation time and variance of the period of the oscillations predicted for chemical oscillators in the weak noise limit is only fulfilled in a very restricted parameter range for the electrochemical nano-oscillator.

Changes in SOFC Cathode Crystallographic Structure Induced by Oxygen Deficiency in Cathode Room

Porous and monolithic La0.6Sr0.4CoO3 −δ, Gd0.15Sr0.85CoO3 −δ and La0.6Sr0.4MnO3 −δ cathodes for intermediate temperature solid oxide fuel cell applications have been studied at different cathode potentials and at different oxygen partial pressures using high-temperature in situ XRD (HT-XRD) method. The kinetic response of the crystallographic structure and lattice parameters on the changes of electrode potential has been correlated with the electrochemical measurement data and discussed. Reversible changes in the lattice parameters were observed depending on the temperature (T), electrode potential (E) and oxygen partial pressure (pO2) applied. At fixed T and electrode potential the oxygen partial pressure remarkably influences the unit cell volume, which is very sensible with the electrode microstructure and porosity as well as electrode chemical composition.

Short-term influence of interfering ion activity change on ion-selective micropipette electrode potential; another factor that can affect the time needed for imaging in potentiometric SECM

The applicability of ion-selective microelectrodes (ISME) in scanning electrochemical microscopy (SECM) in the presence of potentially interfering ions is investigated. Decreasing the time needed for potentiometric SECM imaging is a key aim. It is generally accepted that the long response time of potentiometric cells with high impedance microelectrodes limits the imaging speed that can be obtained without distortion. In this study we show that a change in the activity of interfering ions can result in a short-term electrode potential transient that should be taken into consideration in parameter setting for SECM measurements. The activity step method was employed, using NH4+-ion-measuring micropipettes. Solutions containing equal concentrations of NH4+ ions with or without K+ ions were rapidly introduced and the short-term change in electrode potential was recorded. Rapid transient potential signals appeared following the K+ activity step in the range where the interfering K+ did not affect the long-term electrode potential. The possible influence of this on SECM applications is discussed.

Borate 완충용액에서 알루미늄의 산화피막의 생성과정과 전기적 성질에 대한 대기의 영향

In a borate buffer solution, the growth kinetics and the electronic properties of passive film on aluminum were investigated, using the potentiodynamic method, chronoamperometry, and multi-frequency electrochemical impedance spec- troscopy. The corrosion of aluminum was heavily influenced by the degree of oxygen concentration because of the increasing reduction current. The oxide film formed during the passivation process of aluminum has showed the electronic properties of n-type semiconductor, which follow from the Mott-Schottky equation. It was found out that the passive film (Al(OH)3) of Al formed in the low electrode potential changes to Al2O3 while the electrode potential increases. The growth kinetics data as measured by chronoamperometry suggests a mechanism in which the growth of the film of Al2O3 is determined by field-assisted trans- port of ions through the film.

Understanding Electron Transport in a Durable Mixed Community Microbial Biocathode Enriched from Seawater

Biocathode MCL (Marinobacter, Chromatiaceae, Labrenzia) is a cathode associated microbial consortium enriched from seawater.(1-4) It is extremely durable, having been maintained in the laboratory for at least 6 years with minimal care, and acquires energy by coupling electron uptake from graphite or gold electrodes with reduction of O2, directing a portion of the acquired electrons and energy to reduce CO2 for cell growth. Here we report electrochemical gating measurements performed on Biocathode MCL grown on interdigitated microelectrode arrays (IDAs) to characterize its extracellular electron transport (EET) properties in the same manner recently utilized for Geobacter sulfurreducens.(5-9) These measurements revealed a peak-shaped dependency of electrical conductivity on gate potential, consistent with redox conduction (i.e., electron hopping). The maximum biofilm conductivity at 30°C is 60 µS/cm, more than 10-fold greater than that of G. sulfurreducens biofilms.(5) In addition, conductivity of Biocathode MCL decreases with decreasing temperature in an Arrhenius manner also consistent with redox conduction. The apparent reorganization energy (λ = 0.58 ± 0.015 eV) is similar to that of G. sulfurreducens, suggesting hemes act as the EET cofactors. Voltammetric peaks attributable to EET cofactors are not observed under non-turnover condition (oxygen removed) however, indicating relatively low cofactor abundance. The apparent cofactor formal potential, indicated by the conductivity vs. gate potential dependency, is 0.14 V positive of the O2 reduction catalytic midpoint potential, indicating that the consortium utilizes electrons for oxygen reduction at potentials for which the majority of EET cofactors are reduced and the biofilm possesses only a fraction of its maximum conductivity. Confocal microscopy and fluorescent in situ hybridization indicate that Biocathode MCL biofilms are spatially organized such that the putative electroautotrophic organism is localized at the electrode surface. 16S rRNA gene sequencing analysis indicates that the community composition is stable on different electrode materials (gold or graphite electrodes). Finally, an unidentified iron-sulfur protein was detected by confocal resonance Raman microscopy (CRRM). We study biocathode MCL with the long-term goal of gaining mechanistic insights for engineering rugged and efficient electrode catalysts for electrosynthesis of liquid fuel precursors from CO2 accumulating in seawater. The results reported her expand upon our fundamental understanding of its EET properties. 1. Wang Z, et al. (2015) A Previously Uncharacterized, Nonphotosynthetic Member of the Chromatiaceae Is the Primary CO2-Fixing Constituent in a Self-Regenerating Biocathode. Applied and Environmental Microbiology 81(2):699-712. 2. Leary DH, et al. (2015) Metaproteomic evidence of changes in protein expression following a change in electrode potential in a robust biocathode microbiome. Proteomics 15(20):3486-3496. 3. Strycharz-Glaven SM, et al. (2013) Electrochemical Investigation of a Microbial Solar Cell Reveals a Nonphotosynthetic Biocathode Catalyst. Applied and Environmental Microbiology 79(13):3933-3942. 4. Malik S, et al. (2009) A self-assembling self-repairing microbial photoelectrochemical solar cell. Energy & Environmental Science 2(3):292-298. 5. Yates MD, et al. (2015) Thermally activated long range electron transport in living biofilms. Physical Chemistry Chemical Physics 17(48):32564-32570. 6. Boyd DA, et al. (2015) Measuring Electron Transport Rates through Electrochemically Active Biofilms Electrochemically-Active Biofilms in Bioelectrochemical Systems: From Laboratory Practice to Date Interpretation, ed Beyenal H (John Wiley and Sons, Inc., New York). 7. Strycharz-Glaven SM, et al. (2014) Electron Transport through Early Exponential-Phase Anode-Grown Geobacter sulfurreducens Biofilms. ChemElectroChem 1(11):1957-1965. 8. Snider RM, Strycharz-Glaven SM, Tsoi SD, Erickson JS, & Tender LM (2012) Long-range electron transport in Geobacter sulfurreducens biofilms is redox gradient-driven. Proceedings of the National Academy of Sciences of the United States of America 109(38):15467-15472. 9. Strycharz-Glaven SM, Snider RM, Guiseppi-Elie A, & Tender LM (2011) On the electrical conductivity of microbial nanowires and biofilms. Energy & Environmental Science 4:4366-4379.

Changes of the balancing between anode and cathode due to fatigue in commercial lithium-ion cells

The electrode balancing defines the state of charge (SoC) of a lithium-ion cell and is a crucial point considering lifetime and safe operation. The electrode balancing varies during fatigue which results in changes of the individual electrode potentials for fixed (dis-)charge voltages of the full-cell. Therefore the materials are cycled closer or beyond their electrochemical (meta-)stability window. This leads to accelerated degradation reactions or even to safety problems. The origin of the changes in the cell balancing is the limited amount of mobile lithium, which decreases during cycling due to the loss of lithiated active material a), the reduction of accessible lattice sites in the active materials b) and the loss of active lithium outside the electrodes c). In most of the commercial cells a) and b) can be attributed to the cathode, c) occurs due to reactions on the anode surface. Changes in the electrode balancing of three differently fatigued 7 Ah lithium-ion cells are investigated by electrochemical cycling of full- and half-cells, assembled from cell components of the fatigued 7 Ah cells. Based on these results the observed performance drop is assigned to a), b) or c) mentioned above and the capacity losses are quantified.

The Mechanical Insights into Proton/Electron Transfer in Cytochrome C Oxidase Revealed by Direct Modeling of Voltage Changes in Response to Charge Separation

The use of electrometric techniques to study time-dependent membrane potential has been used to elucidate charge motions in membrane proteins, thereby offering mechanistic insights into the function of membrane-bound pumps and transporters. The mean field macroscopic continuum approach is a usual choice of computational methods that allows one to connect the observed voltage changes to the dielectric distance obtained by solving the voltage Poisson-Boltzmann (PB-V) equation. However, correlating the observed voltage changes with the number of transferred charges and distances is challenging since the nature of the dielectric response in a protein-membrane system is complex. Recently, we introduced a new semi-microscopic coarse-graining (CG) of the voltage coupling for membrane proteins, which include the compete electrode, electrolyte, protein, membrane systems. The CG model evaluates the electrogenic events by directly simulating the external charge that flows through electrolyte solution, considering “the changes in the electrolyte distributions” between initial and final configuration of membrane proteins. This model has also provided a new avenue to measure voltage changes in Bacetrial Reactio Center by computing “the changes in electrode potentials” upon electron/proton transfer [Kim I, Charkrabarty S, Brzeninski P and Warshel A (2014) PNAS 111, 11353]. Here, we employs our CG model to give mechanical insights into electron/proton translocation within membrane in Cytochrome c Oxidase. It is found that different proton pathways can give the same elctrogenic results, and the available measurements cannot distinguish between different feasible proton/electron paths in CcO. However, consistency with the paths available upon mutations can provide a powerful insight.

탄소반죽에 쑥 과산화효소를 고정한 과산화수소 감응 바이오센서

A biosensor including the homogenized tissue of mugwort embedded in carbon paste, which senses hydrogen peroxide, was constructed and its electrochemical properties were validated using voltammetry. The good linearity of Hanes-Woolf plot implied that the reduction reaction of substrate was catalyzed by mugwort peroxidase at the electrode surface. Also the small value of symmetry factor, 0.28, indicated that electrochemical kinetics of the sensor is very sensitive to the change of electrode potential. Many experimental results collected above proved that the dissociation of hydrogen peroxide is dependent on the catalytic power of mugwort peroxidase qualitatively and quantitatively at the surface of the mugwort electrode. It is our firm belief that the marketed HRP can be replaced with mugwort tissue.

Metaproteomic evidence of changes in protein expression following a change in electrode potential in a robust biocathode microbiome.

Microorganisms that respire electrodes may be exploited for biotechnology applications if key pathways for extracellular electron transfer can be identified and manipulated through bioengineering. To determine whether expression of proposed Biocathode-MCL extracellular electron transfer proteins are changed by modulating electrode potential without disrupting the relative distribution of microbial constituents, metaproteomic and 16S rRNA gene expression analyses were performed after switching from an optimal to suboptimal potential based on an expected decrease in electrode respiration. Five hundred and seventy-nine unique proteins were identified across both potentials, the majority of which were assigned to three previously defined Biocathode-MCL metagenomic clusters: a Marinobacter sp., a member of the family Chromatiaceae, and a Labrenzia sp (abbreviated as MCL). Statistical analysis of spectral counts using the Fisher's exact test identified 16 proteins associated with the optimal potential, five of which are predicted electron transfer proteins. The majority of proteins associated with the suboptimal potential were involved in protein turnover/synthesis, motility, and membrane transport. Unipept and 16S rRNA gene expression analyses indicated that the taxonomic profile of the microbiome did not change after 52 h at the suboptimal potential. These findings show that protein expression is sensitive to the electrode potential without inducing shifts in community composition, a feature that may be exploited for engineering Biocathode-MCL. All MS data have been deposited in the ProteomeXchange with identifier PXD001590 (http://proteomecentral.proteomexchange.org/dataset/PXD001590).

Changes in SOFC Cathode Crystallographic Structure Induced by Temperature, Potential and Oxygen Partial Pressure Studied Using in-Situ HT-XRD

Porous and monolithic La0.6Sr0.4Co3 −δ, Gd0.15Sr0.85CoO3 −δ and La0.6Sr0.4MnO3 −δ cathodes for intermediate temperature solid oxide fuel cell applications have been studied at different cathode potentials and at different oxygen partial pressures using high-temperature in situ XRD (HT-XRD) method. The kinetic response of the crystallographic structure and lattice parameters on the changes of electrode potential has been correlated with the chronoamperometric data and discussed. Reversible changes in the lattice parameters were observed depending on the temperature (T), electrode potential (E) and oxygen partial pressure (pO2) applied. At fixed T and pO2, the cathode potential noticeably influences the unit cell volume, thus, the oxygen stoichiometry and concentration of vacancies. The La0.6Sr0.4MnO3 -δ cathode does not have remarkable crystallographic changes under comparable conditions. Influence of the cathode potential on the unit cell volume was more pronounced at lower pO2.

The Photovoltaic Effect of CdS Quantum Dots Synthesized in Inverse Micelles and R-Phycoerythrin Tunnel Cavities.

CdS quantum dots (CdS QDs) 4.3nm in diameter synthesized in an AOT/isooctane/water microemulsion and in R-phycoerythrin tunnel cavities (3.5 × 6.0nm) were analyzed for photoelectrochemical properties. The CdS QDs preparations were applied onto a platinum electrode to obtain solid films. Experiments were performed in a two-section vessel, with one section filled with ethanol and the other, with 3M KCl. The sections were connected through an agar stopper. It was found that illumination of the films resulted in a change of the electrode potential. The magnitude of this change and the kinetics of the appearance and disappearance of the photopotential, i.e., the difference between the electrode potential on the light and in dark, depended on the nature of the QD shell. The photovoltaic effect of CdS QDs in R-phycoerythrin, compared to that of CdS QDs in AOT/isooctane micelles, is three to four times greater due to the photosensitizing action of R-phycoerythrin. The photosensitized effect was markedly higher than the photoelectric sensitivity of R-phycoerythrin and had the opposite polarity. Changes in the potential upon turning the light on and off could be observed repeatedly.