Open Circuit Voltage Measurements Research Articles

Synthesis and Testing of BCZY/LNZ Mixed Proton–electron Conducting Composites for Fuel Cell Applications

A composite of BaCe0.6Zr0.2Y0.2O3–δ and Li2O:NiO:ZnO was investigated for fuel cell applications. The composite was successfully synthesized and its phase stability was confirmed at temperatures up to 900°C. The influence of sintering and pressing aids on density was also investigated. Electrical properties were measured. DC electrical conductivity was about 8•10-4 S/m at 845K. Open circuit voltage measurements in wet hydrogen have shown that the composite can be used in single layer fuel cells.

Long-term evaluation of solid oxide fuel cell candidate materials in a 3-cell generic short stack fixture, part I: Test fixture, sealing, and electrochemical performance

A generic solid oxide fuel cell stack test fixture was developed to evaluate candidate materials and processing under realistic conditions. A NiO–YSZ anode-supported YSZ electrolyte cell with a composite cathode was used to evaluate the long-term stability of a sealing system, alumina coating, Ce-modified (Mn,Co)-spinel coating, ferritic stainles steel AISI441 interconnect metal, and current collectors. A 3-cell short stack was assembled and tested in constant current mode for 6000 h at 800 °C. Part I of the work addresses the stack fixture design, cell components, sealing system, cell performance, and post-mortem analysis. Parts II and III will discuss microstructure evolution, interfacial reactions, and degradation mechanisms. During 6000 h of testing, the top cell showed very low degradation (∼1.4% kh−1), while the middle and bottom cells exhibited much higher degradation after ∼2000 h. The rapid cell degradation was correlated to the open circuit voltage measurements and was attributed to glass seal failure, probably due to unbalanced stress conditions. Post-mortem analysis showed a characteristic yellowish color around the glass seal, suggesting formation of SrCrO4. Overall the developed stack test fixture was demonstrated as a simple and useful tool for evaluation of SOFC candidate materials in realistic conditions.

Study of Inx(O,OH,S)y buffer layer effect on CIGSe thin film solar cells

Inx(O,OH,S)y buffer layer has been applied to Cu(In,Ga)Se2(CIGSe) solar cell by chemical bath deposition (CBD). The cell efficiency was observed to be dependant on film growth mode of Inx(O,OH,S)y buffer layer, which was affected by the CBD conditions such as sulfur chemical concentration and deposition time. The fabricated solar cell showing higher conversion efficiency was observed to have non-porous and uniform texture of buffer, whereas the lower conversion efficiency cells were found to have fibrous texture or detached texture of buffer. The fibrous texture and the detached texture induced high series resistance and lower shunt resistance, respectively, which all resulted in lower cell efficiency with reduced fill factor. External quantum efficiency and temperature dependence of open circuit voltage measurements revealed that the lower efficiency cells suffered from higher interface recombination loss due to the related defects.

Factors Affecting the Performance of Single Chamber Microbial Fuel Cell Using a Novel Configuration

In this study, the single chamber microbial fuel cell (MFC) with annular configuration and spiral anode geometry is proposed for future large-scale applications. Dairy wastewater containing complex organic matter was used as substrate. Factors affecting power generation and internal resistance of this MFC such as substrate injection, electrode surface area, and substrate concentration were investigated to elucidate the effects of the MFC configuration and operating conditions on its performance. The results show that with decreasing anode surface area output current is reduced. With decreasing anode surface area from 2×63 to 2×38 cm, output current is reduced about 34%. In measurement of open circuit voltage, replacement of old wastewater by fresh ones the open circuit voltage significantly increased. Also, enhancement of wastewater concentration shows an increase in the MFC power density. The MFC which was fed with wastewater with lower COD had a shorter batch time than that of the higher wastewater COD.

All-Organic Sulfonium Salts Acting as Efficient Solution Processed Electron Injection Layer for PLEDs

Herein we introduce the all-organic triphenylsulfonium (TPS) salts cathode interfacial layers (CILs), deposited from their methanolic solution, as a new simple strategy for circumventing the use of unstable low work function metals and obtaining charge balance and high electroluminescence efficiency in polymer light-emitting diodes (PLEDs). In particular, we show that the incorporation of TPS-triflate or TPS-nonaflate at the polymer/Al interface improved substantially the luminous efficiency of the device (from 2.4 to 7.9 cd/A) and reduced the turn-on and operating voltage, whereas an up to 4-fold increase in brightness (∼11 250 cd/m(2) for TPS-triflate and ∼14 682 cd/m(2) for TPS-nonaflate compared to ∼3221 cd/m(2) for the reference device) was observed in poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-2,1',3-thiadiazole)] (F8BT)-based PLEDs. This was mainly attributed to the favorable decrease of the electron injection barrier, as derived from the open-circuit voltage (Voc) measurements, which was also assisted by the conduction of electrons through the triphenylsulfonium salt sites. Density functional theory calculations indicated that the total energy of the anionic (reduced) form of the salt, that is, upon placing an electron to its lowest unoccupied molecular orbital, is lower than its neutral state, rendering the TPS-salts stable upon electron transfer in the solid state. Finally, the morphology optimization of the TPS-salt interlayer through controlling the processing parameters was found to be critical for achieving efficient electron injection and transport at the respective interfaces.

Synthesis of Highly-Ordered TiO<sub>2</sub> through CO<sub>2</sub> Supercritical Extraction for Dye-Sensitized Solar Cell Application

Dye-sensitized solar cell (DSSC) is one of the very promising alternative renewable energy sources to anticipate the diminishing in the fossil fuel reserves in the next few decades and to make use of the abundance of intensive sunlight energy in tropical countries like Indonesia. TiO2 nanoparticles have been used as the photo electrode in DSSC because of its high surface area and allow the adsorption of a large number of dye molecules. In the present study, TiO2 aerogel have been synthesized via sol-gel process with water to inorganic precursor ratio (Rw) of 2.00, followed with subsequent drying by CO2 supercritical extraction (SCE). As comparison, the TiO2 xerogel was also prepared by conventional drying and annealing. Both types of gels were subjected to conventional and multi-step annealing. The resulting nanoparticles in aerogel and xerogel have a band-gap energy of 3.10 and 3.04 eV, respectively. The open circuit voltage (Voc) measurement reveals that the DSSC fabricated with aerogel provided a higher voltage (21,40 mV) than xerogel (1,10 mV).

Advancements in OCV Measurement and Analysis for Lithium-Ion Batteries

Incremental open-circuit voltage (OCV) curves and low-current charge/discharge voltage profiles of a lithium-ion (Li-ion) battery are compared and evaluated for optimizing measurement time and resolution. Since these curves are often used for further analysis, minimizing kinetic contributions is crucial for approximating battery OCV behavior. In this context, an incremental OCV measurement is characterized by state of charge (SOC) intervals and relaxation times. Various constant low C-rates, SOC intervals, and relaxation times are tested for approximating OCV behavior. Differential capacity and voltage analysis is used to check whether the main electrode features can be resolved satisfactorily. An interpolation method yields additional data points for the differential analysis of incremental OCV curves. It is shown that incremental OCV measurements are suitable for an approximation of battery OCV behavior, rather than low current-voltage profiles. Furthermore, extrapolation of voltage relaxation enables the estimation of fully relaxed OCV.

Synthesis of Highly-Ordered TiO<sub>2</sub> through CO<sub>2</sub> Supercritical Extraction for Dye-Sensitized Solar Cell Application

Dye-sensitized solar cell (DSSC) is one of the very promising alternative renewable energy sources to anticipate the diminishing in the fossil fuel reserves in the next few decades and to make use of the abundance of intensive sunlight energy in tropical countries like Indonesia. TiO2 nanoparticles have been used as the photo electrode in DSSC because of its high surface area and allow the adsorption of a large number of dye molecules. In the present study, TiO2 aerogel have been synthesized via sol-gel process with water to inorganic precursor ratio (Rw) of 2.00, followed with subsequent drying by CO2 supercritical extraction (SCE). As comparison, the TiO2 xerogel was also prepared by conventional drying and annealing. Both types of gels were subjected to conventional and multi-step annealing. The resulting nanoparticles in aerogel and xerogel have a band-gap energy of 3.10 and 3.04 eV, respectively. The open circuit voltage (Voc) measurement reveals that the DSSC fabricated with aerogel provided a higher voltage (21,40 mV) than xerogel (1,10 mV).

Catalyst Degradation in High Temperature Proton Exchange Membrane Fuel Cells Based on Acid Doped Polybenzimidazole Membranes

AbstractDegradation of carbon supported platinum catalysts is a major failure mode for the long term durability of high temperature proton exchange membrane fuel cells based on phosphoric acid doped polybenzimidazole membranes. With Vulcan carbon black as a reference, thermally treated carbon black and multi‐walled carbon nanotubes were used as supports for electrode catalysts and evaluated in accelerated durability tests under potential cycling at 150 °C. Measurements of open circuit voltage, area specific resistance and hydrogen permeation through the membrane were carried out, indicating little contribution of the membrane degradation to the performance losses during the potential cycling tests. As the major mechanism of the fuel cell performance degradation, the electrochemical active area of the cathodic catalysts showed a steady decrease in the cyclic voltammetric measurements, which was also confirmed by the post TEM and XRD analysis. A strong dependence of the fuel cell performance degradation on the catalyst supports was observed. Graphitization of the carbon blacks improved the stability and catalyst durability though at the expense of a significant decrease in the specific surface area. Multi‐walled carbon nanotubes as catalyst supports showed further significant improvement in the catalyst and fuel cell durability.

Intercomparison of Temperature Sensors for Outdoor Monitoring of Photovoltaic Modules

Solar cells' temperature is a very important parameter that affects performance of photovoltaic (PV) modules since main electrical parameters of PV cells and modules are temperature dependent regardless the technology. The present study evaluates and compares different sensor types and mountings for long term outdoor temperature monitoring of PV modules along with a standardized method for determination of cell's temperature from open-circuit voltage. For that purpose, a special multicrystalline silicon PV module with miniature in situ Pt1000 temperature sensors was used for reference temperature measurement. On the back side of the PV module different temperature sensors were attached, including thermocouple (TC), platinum Pt1000 (PT) and digital temperature sensors DS18B20 (DS). All sensors except one were covered by a 1 cm thick insulation block. The whole setup was mounted on the outdoor PV testing site and all temperatures were monitored for several days with selection of different environmental conditions. On the basis of measurement results, deviations of different temperature sensors are investigated and compared to temperature calculated from open-circuit voltage measurement according to standard EN 60904-5. Among sensors attached at the back side, covered PT and TC sensors deliver the best results in range of 1–2 °C of lower temperature in average; while the covered DS sensor gives additional 1–2 °C underestimated temperature values. The worst measurement results demonstrate the PT sensor without insulation. All temperature sensors exhibit similar and adequate time response regarding the thermal capacitance of the PV module. DS sensors, although showing somewhat worse results, offer great advantages if several temperatures have to be acquired simultaneously and require very simple data acquisition equipment. They feature comparable measurement accuracy than commonly used Pt1000 temperature sensors if they are covered by insulation with 10 mm thick walls in lateral direction to avoid micro-environmental changes.

Electrochemical open circuit voltage (OCV) characterization of SOFC materials

In this paper, we are reporting an extensive characterization, by means of open circuit voltage measurements, of Ce0.8Gd0.2O2, La0.9Sr0.1Ga0.8Mg0.2O3, and La2Mo0.6W1.4O9 oxide-ions and BaCe0.8Y0.2O3 and BaCe0.55Zr0.3Y0.15O3 proton-conducting electrolyte materials for solid oxide fuel cell (SOFC) applications. This simple and common technique, well known for a long time in the electrochemical study of solid oxide fuel cells, has been here proposed for the electrical characterization of these ceramic materials, in order to define their ionic transport numbers, the maximum voltage performances, the thermal and chemical stability, and also to suggest the ideal temperature range for different applications, as in the electrochemical devices, sensors, and SOFC field. In the paper, controlled and reproducible working conditions have been applied in a wide range of temperature, by means of ultrapure gas (H2 and O2), under operational conditions found in real SOFC devices and, mainly, without the usual problems related to the chemical compatibility, the depolarization efficiency, and the high current density required to the electrode materials in the design of a more efficient SOFC device.

Influence of the dye molecular structure on the TiO2conduction band in dye-sensitized solar cells: disentangling charge transfer and electrostatic effects

We report a thorough theoretical and computational investigation of the effect of dye adsorption on the TiO2 conduction band energy in dye-sensitized solar cells that is aimed at assessing the origin of the shifts induced by surface adsorbed species in the position of the TiO2 conduction band. We thus investigate a series of working dye sensitizers and prototypical surface adsorbers and apply an innovative approach to disentangle electrostatic and charge-transfer effects occurring at the crucial dye–TiO2 interface. We clearly demonstrate that an extensive charge rearrangement accompanies the dye–TiO2 interaction, which amounts to transfer of up to 0.3–0.4 electrons from the dyes bound in a dissociative mode to the semiconductor. Molecular monodentate adsorption leads to a much smaller CT. We also find that the amount of CT is modulated by the dye donor groups, with the coumarin dyes showing a stronger CT. A subtle modulation of the semiconductor conduction band edge energy is found by varying the nature of the dye, in line with the experimental data from the literature obtained by capacitance and open circuit voltage measurements. We then decompose the total conduction band shift into contributions directly related to the sensitizer properties, considering the effect of the electric field generated by the dye on the semiconductor conduction band. This effect, which amounts to ca. 40% of the total shift, shows a linear correlation with the TiO2 conduction band shifts. A direct correlation between the dye dipole and the observed conduction band shift is retrieved only for dyes of similar structure and dimensions. We finally found a near-exact proportionality between the amount of charge transfer and the residual contribution to the conduction band shift, which may be as large as 60% of the total shift. The present findings constitute the basis for obtaining a deeper understanding of the crucial interactions taking place at the dye–semiconductor interface, and establish new design rules for dyes with improved DSC functionality.

Performance of microtubular SOFCs with infiltrated electrodes under thermal cycling

In this research, tubes consisting of a co-extruded dense YSZ electrolyte (∼10 μm) and porous NiO–YSZ anode (∼200 μm) were modified with different cathodes and anode infiltration to investigate the effects on both power and thermal cycling tolerance. Type of cathode (produced by infiltration of LSM into a porous YSZ matrix or by hand-painting of an LSM–YSZ ink), the type of pore former used in the cathode (graphite or poly (methyl methacrylate), PMMA) and the infiltration of the anode (no infiltration, or with infiltration steps using a co-precipitated SDC (Samaria doped ceria) mixture, or Ni–SDC mixture) were investigated as variables. The overall aim of this work is to produce cells that are more tolerant to thermal cycling, without sacrificing power density.Testing at 750 °C with 20 mL/min of dry hydrogen shows that anode infiltration has a particularly advantageous effect on performance, raising the peak power and reducing the degradation in peak power seen after aggressive cycling (100 °C/min heating and cooling rates). Cell power can be improved by LSM infiltration into a porous YSZ layer when the thickness of the YSZ layer is optimised and there is sufficient LSM. Infiltrated cells with cathode thicknesses of 20–40 μm functioned better than those 10–15 μm thick despite having a similar LSM/YSZ weight ratio. This may be due to the additional reaction zone available as a result of the higher LSM mass, suggesting that the reaction zone extends beyond 15 μm from the electrolyte. LSM and SDC infiltrated fine particles (50–100 nm) show good distribution and connectivity in the cathode and anode of the cells respectively. When PMMA is used as the pore former in the porous YSZ matrix, a slightly better cell performance is obtained compared with graphite as the pore former. Monitoring the power variation is found to be a more reliable tool than open circuit voltage (OCV) measurements for studying the effect of thermal cycling on cell stability.

Development of paper based electrodes: From air-breathing to paintable enzymatic cathodes

This work presents the results from the development of bio-cathodes for the application on paper-based biofuel cells. Our main goal here is to demonstrate the possibility of using different designs of air-breathing bio-cathodes and ink-based bio-cathodes for this new type of paper based electrochemical cell. The electrochemical performance for the bio-electrocatalytic oxygen reduction reaction was studied by using open circuit voltage and amperometry measurements, as well as polarization curves to probe the four-electron reduction reaction of ambient oxygen catalyzed by bilirubin oxidase (BOx). The electrochemical measurements showed that all procedures allowed the direct electron transfer from the active site of the bilirubin oxidase to the electrode surface with a limiting current density of almost 500μAcm−2 for an air-breathing BOx cathode and 150μAcm−2 for an ink based BOx cathode. Under a load of 300mV a stable current density was obtained for 12h of continuous operation.

Measurements of Lateral Impedance and Local Characteristics of Solid Oxide Fuel Cells

Lateral impedance and local characteristics of anode-supported solid oxide fuel cells (SOFCs) are studied in this paper. The testing device, which combines the original cell housing with a four-point probe equipment, is set for measuring SOFC single cell. The current collectors on anode and cathode in the original cell housing are, respectively, replaced by four independent probe units. They are not only to collect current, but also become measuring probes. Therefore, the lateral impedance of anode and cathode can be measured. Furthermore, the local characteristics are examined by open circuit voltage (OCV), I-V curve, and electrochemical impedance spectroscopy (EIS) measurements. The results show that the lateral impedance is substantially varied with temperature, the OCV at the center of the cell are higher than the edge, the central location on cell have better performance and lower impedance than the marginal location.

Designing a new process to prepare amphoteric ion exchange membrane with well-distributed grafted chains for vanadium redox flow battery

A combination of radiation grafting technique and solution phase inversion method has been successfully utilized to prepare amphoteric ion exchange membranes (AIEMs) from poly(vinylidene fluoride) (PVDF) powder. First, styrene (St) and dimethylaminoethyl methacrylate (DMAEMA) were grafted into PVDF powder via radiation-induced graft copolymerization. Subsequently, the grafted powder was transferred into film by casting method. Finally the AIEM was obtained by sulfonation and protonation of the grafted film. Micro-FTIR, XPS and TG analyses testified that the grafting and sulfonation of St and DMAEMA units in poly(St-co-DMAEMA) grafts had been carried out as designed. SEM-EDX image of the AIEM indicates the well distribution of the grafted chains across the AIEM. The physicochemical properties of the resulting AIEMs and the conventional AIEMs based PVDF film grafting were comparatively investigated. The AIEMs obtained by this novel process were found to have superior conductivity compared with the AIEMs based PVDF film grafting. Open circuit voltage measurements showed that the vanadium redox flow battery (VRFB) assembled with this new AIEM maintained the value above 1.3 V after a period of 30 h, which was much longer than that with the Nafion117 membrane, suggesting this approach is effective for imparting preferable structure-properties to the membrane for VRFB.

2,3,6,7,10,11-Hexamethoxytriphenylene (HMTP): A new organic cathode material for lithium batteries

We propose a new organic cathode material for rechargeable lithium battery applications: 2,3,6,7,10,11-hexamethoxytriphenylene (HMTP). HMTP is composed of six methoxy functional groups substituted onto a central triphenylene moiety. The cell, incorporating 40wt.% of organic cathode material, exhibits full specific capacity at current densities up to 3C. The main advantage of HMTP as organic cathode material lies in a stable cell performance and negligible self discharge, even though the capacity is lower, ~66mAh/g, compared to other organic cathode materials. Cells with the HMTP cathode showed >95% retention of the initial discharge capacity after 50cycles at 1C and self-discharge was not observed during a full month of open circuit voltage measurements. The latter is due to the fact that the nature of the HMTP radical is fundamentally different from other organic cathode materials' radicals.

Exciton dissociation and charge trapping at poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester bulk heterojunction interfaces: Photo-induced threshold voltage shifts in organic field-effect transistors and solar cells

Photoinduced charge transfer at an electron donor/acceptor interface is one of the most crucial processes in determining the power conversion efficiency of organic solar cell devices. Here, we address exciton dissociation and charge carrier trapping at poly(3-hexylthiophene) (P3HT)/phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction interfaces electrically using a field effect transistor (FET). With a P3HT/PCBM composite film, we elucidated exciton dissociation and charge carrier recombination assisted by localized electronic states at the P3HT/PCBM interface via photoinduced threshold voltage shift measurements with respect to wavelength using FETs in combination with organic solar cell devices. Interestingly, the combination of light coupled with a significant quantity of PCBM within the film was required to observe ambipolar charge transport in P3HT/PCBM FETs. This phenomenon was addressed by filling of electron traps associated with PCBM under illumination and formation of the conducting pathways for both electrons and holes. A high density of carrier traps at the interface suggested by the FET results was confirmed in light intensity dependent short-circuit current (Jsc) and open-circuit voltage (Voc) measurements using solar cell devices.

Planar Double-Sided Anode Supported SOFC—Novel Design

The paper presents the innovative design of a ceramic high temperature solid oxide fuel cell (SOFC) in which the anode consists of two parts: the bottom supportive part with microchannels for fuel distribution and the upper operating part which takes part in the electrochemical reaction in the cell. Both parts of the anode are made of cofired yttrium-stabilized zirconia (Ni/YSZ) foils. Microchannels as well as the manifold for combustion products are engraved mechanically in the isostatic pressed stack of Ni/YSZ foils before their firing. The electrolyte and the cathode are set on the upper functional part of the anode by successive screen printing and firing of the electrolyte paste and the cathode paste. The paper reveals details of the fuel cell processing, test fixture and measurement setup for testing the cells, as well as the results of open circuit voltage and short-circuit current measurements.

Ultra-wide bandwidth piezoelectric energy harvesting

Here, we present an ultra wide-bandwidth energy harvester by exploiting the nonlinear stiffness of a doubly clamped microelectromechanical systems (MEMSs) resonator. The stretching strain in a doubly clamped beam shows a nonlinear stiffness, which provides a passive feedback and results in amplitude-stiffened Duffing mode resonance. This design has been fabricated into a compact MEMS device, which is about the size of a US quarter coin. Based on the open circuit voltage measurement, it is expected to have more than one order of magnitude improvement in both bandwidth (more than 20% of the peak frequency) and power density (up to 2 W/cm3) in comparison to the devices previously reported.