Open Circuit Voltage Measurements Research Articles

Well-matched dual photoelectrodes regulated cathodic photoelectrochemical aptasensing capability: Elucidating the role of photoanode in enhancing the sensing signal

To screen well-matched photoelectrodes is highly desirable for achieving efficient signal amplification of the dual-photoelectrode photoelectrochemical (PEC) system. However, the role of photoanode in the characteristic signal amplification remains unclear. In this study, an integrated PEC system was developed by employing well-matched ZnIn2S4/Bi2S3 photoanode and BiOBr-Au nanoparticles (NPs) photocathode. ZnIn2S4/Bi2S3 with super light-harvesting property and Z-scheme electron transfer pathway, served as the photoanode to continuously inject electrons into the photocathode under visible light, resulted in a 69 times enhanced photocurrent signal than that of conventional PEC system. More importantly, a systematic discussion of photoanode in enhancing the sensing signal was presented through the experimental measurements of Mott-Schottky and open-circuit voltage. Using ofloxacin (OFL) as a model target, an aptasensor was constructed for its potential sensing applications, and the possible reaction mechanism of OFL were also conducted. The proposed aptasensor demonstrated the capability to detect concentrations of OFL ranging from 0.1 pM to 5 nM, achieving a detection limit of 47 fM (S/N = 3). Moreover, the aptasensing platform exhibited advantages of high sensitivity, good anti-interference and repeatability. This study proposed insights in understanding the role of photoanode for designing more efficient dual-photoelectrode PEC aptasensors for precise monitoring of other environmental pollutants.

Thermoelectric properties of InGaN/GaN superlattices structure with high indium composition quantum dots

High indium composition InGaN is a promising material for thermoelectric harvesting application, which can work at high temperature and extreme environments. Due to the strong composition segregation, high indium composition InGaN material usually forms localized quantum dots, which advantageously enhances the thermoelectric (TE) properties. In this research, the two-dimensional InGaN/GaN superlattices (SLs) structured TE material with high In composition of 35% quantum dots is first grown and characterized. Using open-circuit voltage measurement, the Seebeck coefficient (S) exhibits a high value of −571 μV/K. Analysis indicates this relatively high S value is related to the increased density of electron states near the Fermi level induced by the reduced dimensionality, resulting in a power factor of 11.83 × 10−4W/m·K2. The dense boundary between InGaN quantum dots also increases the interface phonon scattering, thereby suppressing the heat transportation and leading to a low thermal conductivity (k) value of 19.9 W/m·K. As a result, a TE figure of merit (ZT) value of 0.025 is demonstrated in the sample. This work first clarifies the impact of embedded quantum dots in InGaN/GaN SLs structure on TE properties. It is very conductive for the design and fabrication of low-dimensional GaN based TE device.

Dual boosting of the built-in polarization field in the BiFeO3/ZnS heterostructure for water purification: Effects of Z-scheme heterostructure and corona poling

In this study, we have designed a novel 1D-0D lead-free Z-scheme heterostructure of BiFeO3–ZnS (BFO/ZnS) using an isoelectric point-assistant annealing method for piezocatalytic reactions. The open circuit voltage measurements exhibited a greater internal electric field for BFO/ZnS (90/10) than for individual components, causing its excellent piezocatalytic performance for MTZ antibiotics, organic dyes oxidation, and Cr(VI) reduction. BFO/ZnS (90/10) was treated by corona poling to boost its polarization, resulting in the highest remanent polarization and dielectric constant. Piezocatalytic experiments demonstrated that BFO/ZnS (90/10; poled) can degrade 99% of RhB by 9 min ultrasonic vibration with kapp = 0.44 min−1, which is 2.5, 5.5, and 16.3 times greater than those of BFO/ZnS (90/10), BFO, and ZnS, respectively. Also, the efficiency of piezodegradation for MTZ, Cr(VI), MO, and MB over BFO/ZnS (90/10; poled) was found to be 74.5% (90 min), 84.6% (60 min), 95.3% (40 min), and 97.2% (30 min), respectively. This outstanding piezocatalytic performance of BFO/ZnS (90/10; poled) is ascribed to the enhanced built-in polarization field due to the Z-scheme heterostructure and corona poling treatment. As supported by PL and EIS analysis, the stronger built-in electric field can effectively separate and transmit the charge carriers, causing excellent piezocatalytic activity.

Enhanced CO₂ Detection Using Potentiometric Sensors Based on PIM‐1/DBU Imidazolate Membranes

AbstractA novel potentiometric sensor for carbon dioxide (CO2) detection utilizing a composite membrane of Polymer of Intrinsic Microporosity (PIM‐1) and 18‐diazabicyclo[5.4.0]undec‐7‐ene imidazolate (DBU‐imidazolate) is presented. The high surface area and gas permeability of PIM‐1, combined with the chemical affinity and ion‐exchange properties of DBU‐imidazolate, contribute to enhanced CO2 sensitivity and selectivity. The research objectives included the synthesis of PIM‐1 and DBU‐imidazolate, the preparation of composite membranes, and the evaluation of their performance as CO2 sensors. Solvent casting and impregnation methods are employed to prepare the membranes, which are characterized using Thermal Gravimetric Analysis (TGA), and Field Emission Scanning Electron Microscopy (FESEM). CO₂ absorption tests and Electrochemical Impedance Spectroscopy (EIS) are conducted to assess the sensors' performance. The PIM‐1/DBU‐imidazolate membrane exhibited high efficiency in CO₂ capture and release. Open circuit voltage (OCV) measurements are performed under varying concentrations of CO2 exposure and cycles of adsorption/desorption. Results show that the membrane achieves steady state faster at higher CO2 concentrations, with a logarithmic relationship between CO2 concentration and voltage variation, indicating potential for CO2 detection in human environments. These results confirm the sensor's ability to detect varying CO2 concentrations, highlighting its potential for reliable and efficient CO2 monitoring in environmental and industrial applications.

Online estimation of state-of-charge using auxiliary load

Numerous approaches and methodologies have been established for online (while the load is supplied) estimation of the State-of-Charge of Lithium-ion cells and batteries. However, as battery load consumption fluctuates in real time because of delivered device operations, obtaining a precise online state of charge estimation remains a challenging task. This work proposes a new technique for online open circuit voltage measurement to estimate state of charge of batteries. This novel technique proposes the addition of an auxiliary regulated load that may be utilized to temporarily force specifically defined forms of the battery's current curve under particular conditions, which results in improving and simplifying online open circuit voltage computations. The effectiveness of the proposed technique was successfully validated through several experimental tests. The acquired findings demonstrated its efficiency with an acceptable online state of charge estimation accuracy. Typically, an estimation error of less than 2% was recorded in most tests, while the error was less than 1% when the battery’s state of charge was high.

Temperature-dependent hysteresis model for Li-ion batteries

The increasing importance of accurate battery state estimations in advanced Battery Management Systems (BMS) underscores the need for precise modelling of battery behaviour and characteristics. While equivalent circuit models are widely utilized for their low computational demands, they face challenges in maintaining precision and adaptability during dynamic conditions, posing a persistent concern for future advancements. This study focuses specifically on the battery hysteresis effect, a complicating factor in the modelling and estimation processes. Open circuit voltage (OCV) measurements and parameter identification for equivalent circuit models were conducted on prevalent Li-ion battery technologies, namely nickel-manganese–cobalt (NMC) and lithium-iron-phosphate (LFP). The experimental results indicate the hysteresis effect becomes more significant with lower temperatures. In this paper, a battery model covering the temperature influence on the hysteresis effect is proposed. The proposed model exhibits an average root mean square error of less than 13 mV. The model holds promise for application in modern battery management systems, offering an enhancement to state-of-charge estimation methodologies.

Monolithic Selenium/Silicon Tandem Solar Cells

Selenium is experiencing renewed interest as a promising candidate for the wide bandgap photoabsorber in tandem solar cells. However, despite the potential of selenium-based tandems to surpass the theoretical efficiency limit of single-junction devices, such a device has never been demonstrated. In this study, we present the first monolithically integrated selenium/silicon tandem solar cell. Guided by device simulations, we investigate various carrier-selective contact materials and achieve encouraging results, including an open-circuit voltage of Voc=1.68V from suns-Voc measurements. The high open-circuit voltage positions selenium/silicon tandem solar cells as serious contenders to the industrially dominant single-junction technologies. Furthermore, we quantify a pseudo fill factor of more than 80% using injection-level-dependent open-circuit voltage measurements, indicating that a significant fraction of the photovoltaic losses can be attributed to parasitic series resistance. This work provides valuable insights into the key challenges that need to be addressed for realizing higher efficiency selenium/silicon tandem solar cells. Published by the American Physical Society 2024

Qualitative and quantitative diagnosis of internal hydrogen leakage in fuel cell based on air flowrate control and open-circuit voltage measurements

Internal hydrogen leakage faults in fuel cells can cause severe performance loss and safety risks. The aim of this study is to achieve qualitative and quantitative diagnoses of internal leakage in fuel cell based on air flowrate control and transient voltage measurements. The hydrogen crossover characteristics of a fault-free and defective fuel cell are both investigated, and the effectiveness of the diagnosis method is evaluated by comparing and analyzing the results before and after the leakage fault introduction. The results suggest that hydrogen leakage failure inside fuel cell is dominated by convection processes. In airflow interruption tests, where the fuel cell is operated under open-circuit conditions with given anode overpressures, the fall time of the cell voltage is used as a qualitative measure of internal hydrogen leakage, and fault occurrence can be recognized by a considerable decrease in this indicator. Through cyclic staircase flowrate sweep tests, we obtain good estimates of internal leakage rates in the defective fuel cell. These diagnostic methods can be performed directly under hydrogen/air conditions, and there is no need for additional power source equipment dedicated to generating excitation signals for fuel cell, giving them great potential in on-board applications.

(Invited) Effect of Temperature on Lithium-Ion Battery Voltage Response and How to Model It in the Mechanistic Modeling Approach

The ongoing usage of lithium-ion cells and packs in both stationary and mobile applications necessitates comprehensive tools and models to diagnose and prognose cell performance onboard. One of the main tasks of a battery management system is to infer the state of charge (SOC) and state of health (SOH) of batteries. SOC estimation is usually done by relating a measured relaxation voltage to a stored SOC versus open circuit voltage (OCV) curve. The latter is dependent on the cell SOH and its degradation path. Therefore, both an accurate OCV and relaxation measurement are necessary for state estimation and it is essential to consider how they vary with temperature to ensure accuracy.This study aims at an exploration of the impact of temperature on relaxation and cell’s kinetics and how the voltage response at different temperatures can be simulated using the mechanistic modeling framework by tuning two parameters, the ohmic resistance increase and the rate degradation factor. The mechanistic modeling framework is using electrode half-cell data to synthesize the terminal voltage of battery cells based on the individual electrode potentials. Although proven valid in the quantification of degradation modes, path dependence of aging and cell-to-cell variations, the application of this modeling framework has been restricted so far mostly to voltage profiles recorded at room temperature and low rates. To be used in deployed battery management systems, this limitation should preferably be overcome to enable on-board diagnostics from medium to high rates and at any temperature.

In-Situ Quantification of the Ageing Dynamics in Lithium-Ion Cells up to Failure-Near Conditions

Implementing end-of-life (EOL) lithium-ion batteries from automotive applications in stationary energy storages is of utmost relevance for a sustainable handling of scarce resources. Beneficial from an economic and ecological perspective, such second-life applications urgently require a guarantee for safe operation. Unlike the state of health (SOH), defined by classical performance indicators such as capacity and voltage, the state of safety (SOS) of an aged battery cannot be assessed straightforward. Its determination requires a plethora of cells to be tested which is a particular challenge for new technologies with limited access to EOL batteries.For providing cells with a defined SOH at a reasonable timescale, we herein propose a novel method of greatly accelerating the ageing process of lithium-ion batteries. In a preliminary test series, lithium-ion NMC pouch cells are exposed to incrementally increasing temperatures, current rates and/or states of charge (SOC), until thermal runaway is induced. In this manner, the critical state in proximity to cell failure is spotted for individual and combined stress parameters. Based on this knowledge, cell-specific test parameters for heavily accelerated ageing are developed. In this protocol, electrical abuse conditions are defined by over/under charging and high current rates. Typically, the cells are cycled utilizing a depth of discharge above 100 %.The accelerated aging dynamics under these critical conditions are monitored by systematic capacity, open circuit voltage and electrochemical impedance spectroscopy (EIS) measurements. This enables a comparative assessment of the electrical behaviour, following conventional vs. heavily accelerated ageing. Such knowledge will in turn help to define the threshold to which cyclic ageing can be accelerated without changing the characteristic degradation mechanisms of lithium-ion batteries.

Cell-to-cell variation beyond parameter analysis — Identification and correlation of processes in Lithium-Ion Batteries using a combined distribution of relaxation times analysis

Cell-to-cell variations inside a battery pack can result in inhomogeneities, leading to an accelerated, uneven aging. Until today these variations are solely quantified by parameter-based studies, which only offer a limited interpretability. To tackle this inconclusiveness, cell-to-cell variations and their effects on the electrode processes of lithium-ion batteries are investigated in this work. For this purpose 92 cells are characterized by impedance, pulse, and pseudo open-circuit voltage measurements, and the data obtained is compiled as publicly available data set. The data is examined by a holistic distribution of relaxation times analysis, comprising complementary distribution of relaxation times approaches. This enables a reliable identification of process variations between cells. First, the confidence intervals of both the raw data and the distribution of relaxation times are examined. Subsequently, the individual processes, their characteristic time constants, and their polarization are determined. The analysis reveals that a normal distribution only applies in one of the examined cases and can even be excluded in four cases. Finally, a correlation analysis is conducted, allowing the categorization of the identified processes into cell winding, electrochemical interface processes, and solid-state diffusion. The potential physicochemical reasons behind are discussed and the work thus contributes to a deeper understanding of cell-to-cell variations.

A New Ignition Source for the Determination of Safety Characteristics of Gases

Safety characteristics are used to keep processes, including flammable gases, vapors, and combustible dusts, safe. In the standards for the determination of safety characteristics of gases and vapors, the induction spark is commonly used. However, classic transformers are hard to obtain, and replacement with new electronic transformers is not explicitly allowed in the standards. This article presents the investigation of five gases that are normally used to calibrate devices for the determination of safety characteristics, the maximum experimental safe gap (MESG), with an electronic transformer, and the values are compared to the ones that are obtained with the standard transformer. Additionally, calorimetric measurements on the net energy of both ignition sources were performed as well as open-circuit voltage measurements. It is concluded that the classic type of transformer can be replaced by the new type obtaining the same results for the MESG and introducing the same amount of energy into the system.

On-Road Experimental Campaign for Machine Learning Based State of Health Estimation of High-Voltage Batteries in Electric Vehicles

The present study investigates the use of machine learning algorithms to estimate the state of health (SOH) of high-voltage batteries in electric vehicles. The analysis is based on open-circuit voltage (OCV) measurements from 12 vehicles with different mileage conditions and focuses on establishing a correlation between the OCV values, the energy stored in the battery, and the battery SOH. The experimental campaign was conducted at the Hyundai Motor Europe Technical Center GmbH (Germany), and the data collection process took advantage of the ETAS Integrated Calibration and Application Tool (INCA) and the ETAS Measure Data Analyzer (MDA) software. Six machine learning algorithms are evaluated and compared, namely linear regression, k-nearest neighbors, support vector machine, random forest, classification and regression tree, and neural network. Among the evaluated algorithms, random forest (RF) exhibits the best performance in predicting the state of health of high-voltage batteries, both for the OCV and the capacity (C) estimation. Specifically, if compared to the worst algorithm (i.e., linear regression), RF achieves a remarkable improvement with a reduction of 96% and 97% in the mean absolute error for the OCV and the C estimation, respectively. Furthermore, the comparison highlighted the main differences in the performance, complexity, interpretability, and specific features of the six algorithms. The findings of the present study will contribute to the development of efficient maintenance strategies, thus reducing the risk of unexpected battery failures.

Photovoltaic Response of Heterojunction Photodiode based on Ba0.8Sr0.2TiO3 Nanorod Film

The BST/Si photodiode has been effectively synthesized by growth BST on the p-type Si (100) substrate utilizing the hydrothermal process. Screen printing was used to prepare TiO2 film deposited on Si substrate, then immersing TiO2 film in Ba(OH)2 and Sr(OH)2 solution to fabricate BST/Si photodiode using a hydrothermal process. The BST film was studied using XRD, FESEM, and reflection spectra. The band gap was calculated for a BT film using the reflection methods. Hall measurement confirmed the n-type conductivity of BST film. Curie temperature of the BST film was observed at 87 °C according to DC measurement. The dark and illuminated (J-V) characteristics of the BST/Si photodiode have been measured under simulated AM1 conditions using a Xenon lamp. The Shockley-Read- Hall recombination caused unequal electron and hole capture rates that dominated the I-V characteristics resulting in an absence of classic superposition phenomena. The open circuit voltage (Voc) measurement is carried out to know the recombination mechanism in an open circuit. The BST/Si film showed more conductivity after increasing illuminating power density, which qualifies it for photovoltaic applications.

Identification and Fast Measurement Method of Open-circuit Voltage

Accurate measurement of the open-circuit voltage (OCV) promotes state of charge (SOC) accuracy. In this study, three transformation methods are employed to make the OCV identifiable, and factors affecting the accuracy of OCV identification are investigated. Furthermore, a fast OCV measurement method is proposed. The results show that the forward difference transformation and the adaptive differential evolution algorithm are more suitable for OCV identification. The accuracy of OCV identification is affected by pulse characteristics, sampling frequency, C-rate, and resting time between pulses. Positive-negative (PN) pulses of equal amplitude are more suitable for OCV identification than hybrid pulse power characteristics. A method for fast OCV measurement is developed based on the relationship between the identification error of the OCV and the number of PN pulses. A total of 57 PN pulses with an amplitude of 2 C are used to realize accurate OCV identification at various charge/discharge states, C-rate, and SOC, with an average error of −0.03% (about 1 mV). The proposed method only needs to obtain the battery voltage and current to achieve a fast measurement of OCV, which also serves as a foundation for an accurate estimation of the battery state.

An improved Fractional MPPT Method by Using a Small Circle Approximation of the P–V Characteristic Curve

This paper presents an analytical solution to the maximum power point tracking (MPPT) problem for photovoltaic (PV) applications in the form of an improved fractional method. The proposal makes use of a mathematical function that describes the relationship between power and voltage in a PV module in a neighborhood including the maximum power point (MPP). The function is generated by using only three points of the P–V curve. Next, by using geometrical relationships, an analytical value for the MPP can be obtained. The advantage of the proposed technique is that it provides an explicit mathematical expression for calculation of the voltage at the maximum power point (vMPP) with high accuracy. Even more, complex calculations, manufacturer data, the measurements of short circuit current (iSC) and open-circuit voltage (vOC) are not required, making the proposal less invasive than other solutions. The proposed method is validated using the P–V curve of one PV module. Experimental work demonstrates the speed in the calculation of vMPP and the feasibility of the proposed solution. In addition, this MPPT proposal requires only the typical and available measurements, namely, PV voltage and current. Consequently, the proposed method could be implemented in most PV applications.

Li pre-doping technique using perforated electrodes for the cells with a rubber-derived sulfur composite cathode

We attempted to develop a disassembly- and reassembly-free Li pre-doping technique using perforated electrodes in order to develop Li-ion batteries containing a rubber-derived sulfur composite cathode. The Li pre-doping of the anodes was performed using perforated electrodes by external shorting between the anodes and Li metal electrodes provided on both end parts of the stacked electrodes within the cell, in which the degree of the Li pre-doping could be determined by the open circuit voltage measurement between the anodes and Li metal electrodes. The Li pre-doping of the graphite anodes in the cell composed of rubber-derived sulfur composite cathodes and graphite anodes was successfully conducted using this technique without disassembly and reassembly of the cell. After the Li pre-doping treatment, a stable charge-discharge was achieved between the rubber-derived sulfur composite cathodes and Li pre-doped graphite anodes. The Li pre-doping technique using the perforated electrodes was demonstrated to be applied even for practical 5 Ah cell. Furthermore, the Li pre-doping of the SiO anodes could be achieved in the cell composed of the perforated rubber-derived sulfur composite cathodes and SiO anodes, in which the cell showed a stable cycling performance and excellent charge-discharge rate performance.

Optimisation of Sb2S3 thin-film solar cells via Sb2Se3 post-treatment

In this work, Sb2S3 thin films are prepared by Vapour Transport Deposition (VTD) and solar cell devices with the superstrate structure of ITO/CdS/Sb2S3/Au are fabricated. In particular, an effective Sb2Se3 post-treatment method is developed for the optimisation of Sb2S3 thin-film cells without modifying the Sb2S3 main structure and phase. A device efficiency of 4.02% is reached by optimising the time of Sb2Se3 post-treatment with the augment of short-circuit current density (Jsc) and fill factor (FF). Comparative studies of the electrical properties, carrier transport, and carrier recombination of cells with and without Sb2Se3 post-treatment are carried out in detail, including current density versus voltage (J-V) measurements under both light and dark conditions, energy-dispersive X-ray spectroscopy (EDX), deep-level transient spectroscopy (DLTS), and open-circuit voltage measurements at various temperatures and light intensity levels. The best-performing cells are Sb2Se3 post-treated cells, which have the least amount of parallel current pathways, the smallest amount of trap-assisted recombination, longer carrier lifetimes, and a benign distribution of elements with S-rich features. This study provides a unique strategy for realising the greater potential of chalcogenide thin-film solar cells.

Effect of current density on membrane degradation under the combined chemical and mechanical stress test in the PEMFCs

This study elucidates the effects of current density on membrane degradation under combined mechanical and chemical stress tests. Relative humidity (RH) cycling tests using hydrogen gas and air are conducted on a polymer electrolyte membrane fuel cell based membrane NRE211 at the open circuit voltage (OCV), 0.05 and 0.3 Acm−2 conditions. The different current density conditions result in different in-plane membrane stresses and H2O2 formation rates during the test. After every 200 RH cycles, membrane integrity is assessed via the hydrogen crossover rate and OCV. Furthermore, catalytic combustion is analyzed during OCV measurement using a thermal imaging method employing high-transmittance glass at the cathode side. The membrane failed after 1600, 1800, and 2200 RH cycles under the OCV condition, 0.05 of 0.3 Acm−2, respectively. The vigorous membrane degradation under OCV conditions can be attributed to higher mechanical stress and H2O2 formation rate. Hotspots created owing to the combustion between the crossover hydrogen and air were successfully captured, with a maximum temperature rise ranging from 15 to 16 °C compared with a given cell temperature of 80 °C. Moreover, a post-mortem analysis (SEM imaging) revealed the presence of pinholes, through-membrane cracks, and membrane thinning at the hotspot locations.

Impact of Proton Activity in PFSA Membranes on Electrochemical Kinetics Using Microelectrodes

Polymer-electrolyte fuel cells and electrolyzers (PEFC&Es) have the potential to play a prominent role in green energy technologies including transportation, chemical manufacturing, and grid-scale energy storage. PEFC&Es have made significant advancements in recent years, largely due to improvements in the catalyst layers, and especially at the ionomer/catalyst interface. However, it is not yet definitively known how this solid-state environment impacts electrochemical kinetics, especially under various operating conditions (e.g., temperature, humidity, etc.). Additionally, it is challenging to probe local conditions at the catalyst/ionomer interface using traditional analytical techniques. In this study, we explore the influence and nature of proton activity in Nafion and 3M ionomers using a specialized microelectrode setup containing a 50 μm platinum microelectrode in a solid-state three-electrode cell for hydrogen oxidation and evolution (HOR&HER) reactions. Proton activity was calculated through open circuit voltage measurements, and was found to increase with increasing water content, mirroring trends in reaction performance. The effect of proton activity on the reactions' kinetics was investigated using semi-empirical fitting with the Butler-Volmer equation, which gives insight into the reaction rate order and possible mechanism for the reactions. This study demonstrates that microelectrodes can be used to probe solid-state kinetics and can also elucidate complex ion interactions within the ionomer at the catalyst/ionomer interface.