Open Circuit Voltage Measurements Research Articles

Unwinding Entangled Degradation Mechanisms in Solid Oxide Electrolysis Cells Through Electrode Modifications and Impedance Analysis

AbstractIn the renewable energy scenario, energy storage is of essence. In this context, power‐to‐liquid (PtL) and power‐to‐gas (PtG) concepts have attracted large attention, where the use of solid oxide electrolysis cells (SOECs) has a huge potential, due to their high conversion efficiencies. However, performance and durability of these cells still need to be improved for a large‐scale commercialization of the SOEC technology. It is often difficult to identify the various loss and degradation mechanisms limiting the cell performance and durability. This paper contributes to this scientific discussion, by providing a careful analysis of the degradation mechanisms occurring in three different cells during long‐term H2O and CO2 co‐electrolysis, at 1,200 mV. Electrochemical impedance spectroscopy (EIS) is measured before, during and after the electrolysis operation, and is utilized to address the individual electrode degradation mechanisms and the development of leaks through the electrolyte. Moreover, the leak rates under open circuit voltage (OCV) measurements were compared. In addition, microstructural analysis of the electrodes and electrolytes is related to the electrochemical findings to contribute to the discussion on the interdependency of the degradation mechanisms.

Investigation of electronic transport mechanisms in Sb2Se3 thin-film solar cells

Electronic transport mechanisms in Sb2Se3 thin-film solar cells were investigated using temperature-dependent current-voltage (J-V) measurements. Sb2Se3 thin films were deposited via the vapor transporting deposition method using a double-temperature-zone tubular furnace system, and comparative studies were performed for Sb2Se3 films formed on substrates located at three different positions away from the furnace center. The device efficiency varied from 3.83 to 6.24%. First, structural properties obtained by X-ray diffraction, Raman and scanning electron microscopy measurements verified the optimal Sb2Se3 film quality for the cell with the highest efficiency. Then, temperature-dependent saturation current and open-circuit voltage (Voc) measurements revealed that the dominant carrier recombination occurred in the CdS/Sb2Se3 interface region, which possibly influenced the Voc for all cells: the highest Voc for the optimal Sb2Se3 cell was at least partly due to it having the lowest CdS/Sb2Se3 interface recombination rate. Finally, the reverse bias current relationship revealed that non-ohmic shunt current (space-charge-limited current, SCLC) plays an important role in affecting the performance of solar cells, as lower-efficiency cells had higher non-ohmic shunt current.

Influence of Rare Earths Addition on the Properties of Al–Li Alloys

Aluminum alloys are considered one of the best choices as structural material for aerospace applications, guaranteeing lightweight and strength at the same time. In this work Al–Li alloys with 6% (wt %) of Li are used. To increase further the strength of the material, new alloys are produced by adding different quantities (0.01, 0.05, 0.1, and 0.5 wt %) of rare earths (Nd, Y, Ce, Pr). The microstructure of the samples is examined using scanning electron microscope (SEM). The improvement of the mechanical properties is measured by means of Vickers hardness tests. Also the corrosion resistance of the alloys is evaluated with open circuit voltage (OCV) measurements. At the same time, the thermophysical properties are measured as well, at various temperatures, from 80 to 500°C. The results show that an increase in the Rare Earth (RE) content causes an increase in the mechanical properties and a reduction in the thermal conductivity. Regarding the corrosion resistance, a maximum in the corrosion properties can be found for 0.05% of RE.

Thermoelectric Photosensor Based on Ultrathin Single-Crystalline Si Films †.

Ultrathin Si films have a reduced thermal conductivity in comparison to Si bulk due to phonon scattering at the surfaces. Furthermore, the small thickness guarantees a reduced thermal mass (in the µJ/K range), which opens up the possibility of developing thermal sensors with a high sensitivity. Based on these premises, a thermoelectric (TE) microsensor based on ultrathin suspended Si films was developed and used as a thermal photosensor. The photoresponse of the device was evaluated with an argon laser (λ = 457 nm) with a variable power ranging from 0 to 10 mW in air at atmospheric pressure, with laser diodes at 406 nm, 520 nm and 638 nm wavelengths, and fixed powers in high vacuum conditions. The responsivity per unit area, response time (τ) and detectivity (D*) of the device were determined in air at ambient pressure, being 2.6 × 107 V/Wm2, ~4.3 ms and , respectively. Temperature differences up to 30 K between the central hot region and the Si frame were achieved during open-circuit voltage measurements, with and without laser diodes. During illumination, the photogeneration of carriers caused a slight reduction of the Seebeck coefficient, which did not significantly change the sensitivity of the device. Moreover, the measurements performed with light beam chopped at different frequencies evidenced the quick response of the device. The temperature gradients applied to the thermoelectric Si legs were corrected using finite element modeling (FEM) due to the non-flat temperature profile generated during the experiments.

Effective ionic Seebeck component suppression in mixed ion-electron conductor via chemical treatment

By employing time-dependent open-circuit voltage measurement, we demonstrate that a redundant ionic Seebeck component in the mixed ion-electron conducting polymer PEDOT:PSS can be suppressed by simple chemical treatments. The suppression of ionic Seebeck can be attributed to both increase in electronic conductivity and reduction in ionic conductivity, which results in a significant increase in the ratio of electronic-to-ionic conductivity. The thermogravimetric analysis and thickness swelling test confirm that PEDOT:PSS film becomes less or non-hygroscopic after treatment. Low hygroscopicity in the PEDOT:PSS film effectively cuts off the moisture-assisted ion conducting channel, consequently the ionic conductivity becomes extremely low and the ionic Seebeck component is suppressed even at a high humidity (90% RH) condition. The chemical treatment turns out to be a highly promising method to eliminate ionic Seebeck component in the mixed ion-electron conducting polymers and thus to generate consistent thermovoltage for the practical thermoelectric application.

A Novel Multiple Correction Approach for Fast Open Circuit Voltage Prediction of Lithium-Ion Battery

This paper proposes a novel fast open circuit voltage prediction approach for Lithium-ion battery, which is potential to facilitate a convenient battery modeling and states estimation in the energy storage system. Open circuit voltage measurement suffers from a long relaxation time (several hours, even days) to reach the thermodynamic equilibrium of the battery. On the basis of the feedback control theory, the proposed multiple correction approach utilizes the constrained nonlinear optimization of the power function in each curve fitting step. The voltage measurement in a short period is divided into several segments to correct the voltage prediction multiple times with the feedback errors after each curve fitting. The similarity between the shape of the power function and the variation of the terminal voltage during the relaxation time is utilized. The proposed method can speed up the time-consuming open circuit voltage measurement and predict the open circuit voltage with high accuracy. Experimental tests on a LiFePO4 battery prove the validation and effectiveness of the proposed method in accurately predicting the open circuit voltage within a very short relaxation time (less than 15 min).

Transient analysis of luminescent coupling effects in multi-junction solar cells

We investigate the luminescent coupling (LC) effects in a four-junction GaInP/GaAs//GaInAsP/GaInAs concentrator solar cell based on transient open-circuit voltage (Voc) measurements under monochromatic illumination. Photocurrent generation in the non-absorbing GaInAs bottom subcell due to LC from upper subcells shows superlinear behavior with increasing light intensity. Along with this, a Voc enhancement is observed and quantified for illumination intensities that span almost six orders of magnitude. The Voc increase is explained and studied using a series-connected diode model including subcell shunt resistances, capacitances, and LC effects. The impact of unilluminated subcells on the subcell Voc determination is discussed for multi-junction solar cells. Finally, in the analysis of the LC generated photocurrent, namely, the coupling factor from the GaInAsP to the non-absorbing GaInAs subcell, a characteristic dependency on bias voltage is shown and explained by a result of competing photo- and electroluminescence mechanisms.

Performance of post-hidrothermally treated xerogel TiO2 dye-sensitized solar cell (DSSC) and its nanostructure characteristic

Dye-sensitized solar cell (DSSC) is one of photovoltaic solar cells, which is very favorable as alternative renewable energy source to anticipate the diminishing the fossil fuel due to its low-cost, ease of production and eco-friendliness. This work is aimed to investigate the correlation between TiO2 nanostructure properties i.e.: crystallite size, surface area, band gap energy to obtain the optimum parameter for best performance as DSSC prototype. At this study, TiO2 nanoparticles were synthesized via sol-gel process using titanium tetra-n-butoxide, ethanol, hydrochloric acid and deionized water with the ratio of (0.4 : 0.83 : 1 and 1.39) respectively upon sol preparation. The followed with multi-step calcinations to obtain anatase phase and post-hydrothermal process with various temperatures (100, 120, and 150 ˚C). As comparison, TiO2 of P25 Degussa was used and also assembled to make DSSC. The X-ray diffraction, BET (Brunauer-Emmett-Teller) and UV-Vis DRS (diffuse reflectance spectroscopy) tests were taken to characterize the samples. The performance of DSSC was investigated using open voltage circuit (Voc) measurement. The characterization results of synthesis powder shows indication at temperature 150ºC was optimum process of post-hydrothermal with crystallite size 10.55 nm, surface area 95.38 m2/grams, and band gap energy 3.16 eV. Nevertheless, the open circuit voltage (VOC) measurement reveals that the DSSC fabricated with post-hydrothermal at temperature process 120˚C provide the highest voltage (250 mV).

MPPT Algorithm Based on PV Cell Temperature, Using Open Circuit Voltage Measurement, Combined With PV Cell Cooling

As an increase of Photovoltaic (PV) cell temperature originates a negative effect, the application of a PV cell cooling system allows a performance improvement. Therefore, the present work aims to investigate the performance of a PV module transformed into a Photovoltaic/Thermal (PV/T) module, producing electrical and thermal energy simultaneously, while concurrently establishing a cooling system for the PV cells. The PV conversion efficiency is affected by modifications of the operation conditions particularly the ones concerning PV cell temperature and radiation due to the displacement of the system Maximum Power Point (MPP). In the present work the Maximum Power Point Tracking (MPPT) is performed using an algorithm based exclusively on PV cell temperature information with the particularity that the temperature measurements are perform without the use of any temperature sensors. The studied system performance is compared to a conventional PV using the same MPPT algorithm. The results show that the cooling system associated to the MPPT temperature based algorithm provides a bigger energy output leading to higher economic savings. In addition, it can help simplifying the MPPT algorithm by allowing the use of slower dynamic.

Fabrication and Characterization of Dye-Sensitized Solar Cell using Chemically Grown ZnS Nanoparticles

In this work, we have fabricated dye-sensitized solar cell (DSSC) based on chemically grown ZnS nanoparticles with three different source of dye namely Gerbera jamesonii, Rosa indica and Acalypha wilkesiana leaves extract. Anthocyanin, a kind of natural dye found in the leaves of plants and flowers was used as photosensitizers in preparing dye-sensitized solar cell. The optical properties of anthocyanin present in three dyes were also studied. Morphological properties have been studied by atomic force microscopy on ZnS film as well as on ZnS film with dye. The current-voltage characteristics of the dye-sensitized solar cell had been studied in light condition. The DSSC is characterized by the measurement of open circuit voltage, short circuit current density; efficiency and fill factor. The efficiency of three dye solar cell is different and it is maximum for Acalypha wilkesiana leaves extract dye.

Relationship between bandgap grading and carrier recombination for Cu(In,Ga)Se2-based solar cells

To understand the effect of bandgap grading on carrier recombination for Cu(In,Ga)Se2 (CIGS)-based solar cells in detail, samples with different bandgaps at the CIGS surface were fabricated by changing the Ga/(Ga + In) (GGI) ratio from 0.4 to 0 at the third stage of the conventional three-stage growth process. Optoelectronic characterizations, such as photoluminescence, temperature-dependent open-circuit voltage measurement and light-intensity-dependent current–voltage measurement, indicate that the photo-generated carriers move rapidly towards the location of the bandgap minimum, and the carrier recombination occurs mainly at this location. From simulation using a one-dimensional solar cell capacitance simulator (SCAPS-1D), a single-grade sample with the smallest bandgap on the surface of CIGS showed high recombination current at the surface, while the location of the maximum recombination current moved from the surface to the bulk for double-grade samples. This study suggests that controlling the bandgap grading is one way of suppressing recombination at the interface in CIGS-based solar cells.

A fully integrated autonomous power management system with high power capacity and novel MPPT for thermoelectric energy harvesters in IoT/wearable applications

This paper reports a fully integrated autonomous power management system for thermoelectric energy harvesting with application in batteryless IoT/Wearable devices. The novel maximum power point tracking (MPPT) algorithm does not require open circuit voltage measurement. The proposed system delivers 0.5 mA current with 1 V regulated output based on simulations, which is the highest output current for a fully integrated converter reported in the literature for ultra-low voltage applications, to the best knowledge of the authors. Regulated 1 V output can be achieved for load range >2 kΩ, and input voltage range >140 mV. The circuit has been implemented in UMC-180nm standard CMOS technology and simulated.

Electromotive force characterization of secondary battery cells using estimated electrolyte molality

Abstract Existing methods for electromotive force (EMF) characterization that make use of readily available data, such as terminal voltage and applied current, require a significant time commitment and a constant temperature environment. Both linear interpolation and extrapolation rely on state-of-charge (SOC) calculation by Coulomb-counting which only serves to reduce the accuracy of the resulting EMF-SOC curve(s). A battery management system requires accurate EMF-SOC data for periodic recalibration otherwise it cannot apply proper charge control. This paper presents an alternative concentration-based method for EMF characterization and the key lies in the fact that molality is not influenced by temperature. A modified version of the Nernst equation and temperature-compensated open-circuit voltage measurements are used to estimate the molality when the cell is at rest. During operation, the energy into or out of the cell is mapped to changes in the estimated molality to calculate the EMF as the cell charges or discharges. The concentration-based method is verified using experimental data from valve-regulated lead-acid cells and its EMF curves are compared to those of linear interpolation and extrapolation. The proposed method has less stringent practical requirements and validation results indicate a significant improvement in accuracy and applicability over the existing methods.

Successive-approximation algorithm for estimating capacity of Li-ion batteries

This paper proposes a capacity estimation algorithm for Li-ion batteries (LIBs) using the successive approximation method. Model-based capacity estimation method can be applied to a variety of current profiles because the capacity is calculated from state of charge (SOC) estimated accurately using the functional relationship between open circuit voltage (OCV) and the SOC. However, with aging, the OCV-SOC table changes, which worsens the estimation accuracy. Therefore, additional experiments are necessary to compensate the errors whenever the capacity should be identified. To overcome this restriction, this paper proposes an algorithm for estimating both the capacity and the corresponding OCV-SOC table based on the preliminary OCV-SOC tables obtained from other batteries. The capacity and the table are updated successively based on the prior capacity estimate. This work proposes two algorithms for voltage characteristics: OCV measurement and SOC estimation cases. The former uses the measured OCV to calculate the SOCs directly, while the latter estimates the SOCs using a dual extended Kalman filter (DEKF). Aging data from five LIB packs are analyzed, and the capacity estimation errors are less than 2.2% for the OCV measurement case and 3.06% until 20% loss of capacity estimate for SOC estimation case.

Impact of air‐light exposure on the electrical properties of Cu(In,Ga)Se2 solar cells

AbstractThe impact of air‐light exposure of bare Cu(In,Ga)Se2 layers is investigated by measuring the performance of completed solar cells. Solar cells formed from air‐light–exposed absorbers reveal inferior cell parameters by about 10% regarding open circuit voltage, fill factor, and efficiency compared with cells from nonilluminated absorbers. Time‐dependent and temperature‐dependent open circuit voltage measurements give reasons that the solar cell impairment by air‐light exposure of the bare absorbers is due to interface recombination. Interface states are detected by admittance spectroscopy. Heat‐light soaking of complete solar cells—having formerly degraded interfaces—recovers the solar cell parameters up to the nondegraded levels. Paradoxically, both the air‐light–induced degradation of bare absorbers and the revision of cell parameters after light annealing go along with a light‐induced segregation of sodium at the Cu(In,Ga)Se2 surface and Cu(In,Ga)Se2/CdS interface, respectively.

Electrothermal Feedback and Absorption-Induced Open-Circuit-Voltage Turnover in Solar Cells

A solar panel gets hot as it works up on the roof, yet photoinduced self-heating is often ignored when characterizing lab-sized samples. The authors present their understanding of the turnover effect in measurements of open-circuit voltage versus light intensity (Suns-${V}_{O\phantom{\rule{0}{0ex}}C}$ curves), which is identified as a unique feature of all semiconductor-based solar cells. This effect is explained in terms of electrothermal feedback arising when the incident irradiation heats up the device. The authors' model fully explains the experimental data, and allows one to determine key device parameters such as the ideality factor and the band gap from a single measurement.

In situ synchrotron x-ray diffraction study of Zn/Bi2O3 electrodes prior to and during discharge of Zn-air batteries: Influence on ZnO deposition

Zn-based electrodes containing different amount of Bi2O3 have been analyzed by synchrotron XRD during the discharging process of a real Zn/air battery. Bi2O3 is clearly detected for pristine Zn-Bi2O3 based electrodes. However, immersion of Zn-Bi2O3 electrodes in 6 M KOH solution before starting the discharge results in the disappearance of Bi2O3 XRD signature in the pattern and the appearance of new peaks indicating the presence of metallic Bi, regardless of the amount of Bi2O3 initially included in the Zn-Bi2O3 electrodes. This behavior together with Open Circuit Voltage measurements points to a spontaneous reduction of Bi3+ to metallic Bi by the oxidation of Zn to Zn2+. Irrespective of the amount of Bi2O3 present in the negative electrodes, Zn XRD peaks diminish as the discharge proceeds. However, the initial amount of Bi2O3 clearly affect to ZnO and Bi metal XRD peaks. ZnO peaks are observed only for electrodes without Bi2O3 or those containing 6% of Bi2O3. Conversely, ZnO peaks do not appear in the XRD patterns obtained for higher quantities of Bi2O3 electrodes. Besides, in this case metallic Bi peaks are observed during all discharging processes, indicating that Bi remained in the electrode. Finally, SEM and EDX studies support these conclusions.

Fabrication and characterization study of ZnTe/n-Si heterojunction solar cell application

Different thicknesses (150 250 and 350) ±20 nm has been deposited on the glass substrate and nSi wafer to fabricate ZnTe/n-Si heterojunction solar cell by vacuum evaporation technique Structural optical electrical and photovoltaic properties are investigated for the samples. The structural characteristics studied via X ray analyses indicated that the films are polycrystalline besides having a cubic (zinc blende) structure also average diameter and surface roughness calculated from AFM images The optical measurements of the deposited films were performed in different thicknesses to determine the transmission spectrum as a function of incident wavelength in the range of wavelength (4001000) nm and the optical energy gap calculated from the optical absorption spectra was found to reduse with thickness The IV characteristic at (dark and illuminated) and CV measurement for ZnTe/n-Si heterojunction shows the good rectifying behaviour under dark condition. The measurements of opencircuit voltage (VOC) short-circuit current density (JSC) fill factor (FF) and quantum fficiencies of the ZnTe/n-Si heterojunction are calculated for all samples The results of these studies are presented and discussed in this paper.

Covariance controlled state-of-charge estimator of LiFePO4 cells using a simplified hysteresis model

Equivalent circuit model (ECM)-based state-of-charge (SOC) estimation has been considered as one of the most important aspects in battery management system (BMS). However, in case of a lithium iron phosphate (LiFePO4) cell, because of the flatness and hysteresis effect of the open-circuit voltage (OCV) curve, there are inevitable drawbacks directly related to both erroneous SOC information and the slow SOC convergence speed caused by incorrect OCV characteristics. Therefore, this approach gives insight to the design and implementation of the ECM-based SOC estimator that is suitable for an actual LiFePO4 cell. Two approaches for settlement in current OCV issues are as follows. Firstly, through linearization between coordinated charging and discharging OCVs, an OCV hysteresis model can be easily implemented. This model incorporating OCV measurement data is adequately applied to the model-based SOC estimator using the extended Kalman filter (EKF). Secondly, a well-adjusted measurement error covariance controlled in the EKF is used to alleviate an undesired SOC fluctuation that surely results in low BMS performance. This measurement error covariance additionally enables us to provide the fast SOC convergence speed against an inaccurate initial SOC value. This approach has been sufficiently validated by extensive experimental results conducted on LiFePO4 cells that had a rated capacity of 14 Ah by EIG. Consequently, our validation showed the clearness of the proposed work for a reliable SOC estimator of a LiFePO4 cell.

Near ambient pressure X-ray photoelectron - and impedance spectroscopy study of NiO - Ce0.9Gd0.1O2-δ anode reduction using a novel dual-chamber spectroelectrochemical cell

This paper reports an experimental study, where the reduction of NiO-GDC to Ni-GDC is monitored using high temperature (HT) near ambient pressure (NAP) X-ray photoelectron spectroscopy (XPS) in combination with simultaneous impedance spectroscopy (IS). The experiment is carried out using a dual chamber (DC)-HT-NAP-XPS cell designed for membrane electrode studies. The dual chamber measurement cell enables adequate electrochemical feedback, i.e. the possibility of measuring the working electrode potential against a Pt reference electrode in a well-known environment (pO2 = 0.2 bar) and of monitoring the pO2 value on the studied electrode through open circuit voltage (OCV) measurements. Simultaneous changes of electrode impedance and O 1s, Ce 4d and Ni 3p electron binding energies are observed and discussed. The shape of the O 1s photoelectron peak is significantly influenced by the equilibria of Ce4+ ↔ Ce3+ and Ni2+ ↔ Ni0, influenced by pO2, in analysis chamber.