Optimal Cell Performance Research Articles

Analysis of the clamping effects on the passive direct methanol fuel cell performance using electrochemical impedance spectroscopy

The clamping effects on a passive direct methanol fuel cell (DMFC) performance have been analysed using electrochemical impedance spectroscopy (EIS). The stainless steel bolts of size M 6×0.75mm with a length of 50mm have been used for clamping the cell. The passive DMFC performance was conducted for different combinations of clamping bolt torque and methanol concentrations. It is found that the cell performance decreases with under and over uniform clamping bolt torque, and it is maximum at a particular clamping bolt torque. It is concluded from the EIS study that both the ohmic and mass transfer resistance decides the optimum clamping bolt torque of the passive DMFC. The EIS study also reveals that the non-uniform clamping bolt torque deteriorates the DMFC performance due to increase of the ohmic resistance and mass transfer resistance as well. The effects of bolt configurations on the cell performance have also been discussed. In this study, eight bolt configurations passive DMFC under 8.0Nm uniform clamping bolt torque produces optimum cell performance at 4 molar methanol concentrations. It is therefore recommended to decide clamping bolt torque accurately during assembling of the passive DMFC.

Experimental Study of Silver Cathode for Electrochemical Deoxygenation of Seawater for Enhanced Oil Recovery

Seawater injection into reservoirs is a common method to enhance oil recovery. In order to avoid corrosion in pipes, the oxygen has to be removed from the seawater. This study focuses on the use of silver cathodes in electrochemical cells for oxygen removal, and the physical parameters that affect the efficiency of this process. Three electrochemical cells have been constructed and tested with packed bed cathodes made up of pure silver particles and silver plated brass spheres. Experimental results showed that silver was a suitable cathode material for oxygen removal. The most important parameter for optimizing cell performance was the depth of the cathode chamber. In addition, the thickness of the silver plating is also an important parameter to adjust since a too-thin layer results in erosion giving rise to galvanic corrosion between brass and silver, which reduces the efficiency of the cell.

Correlation between morphology and device performance of pBTTT:PC71BM solar cells

Phenyl-C71-butyric acid methyl ester (PC71BM) could intercalate between the side-chains of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene (pBTTT) creating a stable co-crystal structure, so optimal solar cell performance was obtained at high PC71BM concentrations promoting phase separated electron conductive pathways. Neutron reflectivity, with the application of magnetic contrast variation, was used to investigate the concentration profile of PC71BM within the active layer. And this profile was found to be homogeneous through the film thickness. Small angle neutron scattering was utilized to find there is amorphous PC71BM even at 50wt% of fullerene while previously it was believed that all fullerene was consumed to form co-crystals when its concentration is below 75wt%. These fullerene molecules evolve into approximately 15nm sized agglomerates to improve the electron transport when their concentration is above 75wt%. Thermal annealing gives these agglomerates mobility to form micrometer sized crystals causing a decrease of device performance. These findings can therefore correlate the morphology, especially in terms of fullerene agglomerates, vertical concentration profile and percolating structure they formed, with the device performance and provide valuable guidance for optimal morphology design of polymer: fullerene solar cells.

Experimental determination of optimal clamping torque for AB-PEM Fuel cell

<span lang="EN-GB">Polymer electrolyte Membrane (PEM) fuel cell is an electrochemical device producing electricity by the reaction of hydrogen and oxygen without combustion. PEM fuel cell stack is provided with an appropriate clamping torque to prevent leakage of reactant gases and to minimize the contact resistance between gas diffusion media (GDL) and bipolar plates. GDL porous structure and gas permeability is directly affected by the compaction pressure which, consequently, drastically change the fuel cell performance. Various efforts were made to determine the optimal compaction pressure and pressure distributions through simulations and experimentation. Lower compaction pressure results in increase of contact resistance and also chances of leakage. On the other hand, higher compaction pressure decreases the contact resistance but also narrows down the diffusion path for mass transfer from gas channels to the catalyst layers, consequently, lowering cell performance. The optimal cell performance is related to the gasket thickness and compression pressure on GDL. Every stack has a unique assembly pressure due to differences in fuel cell components material and stack design. Therefore, there is still need to determine the optimal torque value for getting the optimal cell performance. This study has been carried out in continuation of deve­lopment of Air breathing PEM fuel cell for small Unmanned Aerial Vehicle (UAV) application. Compaction pressure at minimum contact resistance was determined and clamping torque value was calcu­la­ted accordingly. Single cell performance tests were performed at five different clamping torque values i.e 0.5, 1.0, 1.5, 2.0 and 2.5 N m, for achieving optimal cell per­formance. Clamping pressure distribution tests were also performed at these torque values to verify uniform pressure distribution at optimal torque value. Experimental and theoretical results were compared for making inferences about optimal cell perfor­man­ce. A clamp­ing torque value of 1.5 N m was determined experimentally to be the best for getting optimal performance as well as uniform pressure distribution for this specific fuel cell.</span>

Optimization of the Geometric Design of Silicon Solar Cells under Concentrated Sunlight

The optimization of silicon solar cells is presented. The desired performance characteristics of a solar cell include a high conversion efficiency and a large power output through optimal grid contact design with minimal power losses under concentrated sunlight. Both square and rectangular shapes of linear grid contact patterns are considered for silicon solar cells with constraints on design parameters. The optical and ohmic losses are noted in computing the conversion efficiency and power output, which influence the structure and size of the solar cell and the grid contact design. In the optimization of solar cell performance, the various power losses caused by grid contact that influence the solar cell size, geometry of the fingers, busbars, and spacing between the metal grid lines are also considered. The proposed methodology permits the design of the solar cell for optimal cell performance even when some of the parameters, such as the size of the cell or the geometry of the fingers, are prespecified.

Identification of metabolic engineering targets for the enhancement of 1,4-butanediol production in recombinant E. coli using large-scale kinetic models

Rational metabolic engineering methods are increasingly employed in designing the commercially viable processes for the production of chemicals relevant to pharmaceutical, biotechnology, and food and beverage industries. With the growing availability of omics data and of methodologies capable to integrate the available data into models, mathematical modeling and computational analysis are becoming important in designing recombinant cellular organisms and optimizing cell performance with respect to desired criteria. In this contribution, we used the computational framework ORACLE (Optimization and Risk Analysis of Complex Living Entities) to analyze the physiology of recombinant Escherichia coli producing 1,4-butanediol (BDO) and to identify potential strategies for improved production of BDO. The framework allowed us to integrate data across multiple levels and to construct a population of large-scale kinetic models despite the lack of available information about kinetic properties of every enzyme in the metabolic pathways. We analyzed these models and we found that the enzymes that primarily control the fluxes leading to BDO production are part of central glycolysis, the lower branch of tricarboxylic acid (TCA) cycle and the novel BDO production route. Interestingly, among the enzymes between the glucose uptake and the BDO pathway, the enzymes belonging to the lower branch of TCA cycle have been identified as the most important for improving BDO production and yield. We also quantified the effects of changes of the target enzymes on other intracellular states like energy charge, cofactor levels, redox state, cellular growth, and byproduct formation. Independent earlier experiments on this strain confirmed that the computationally obtained conclusions are consistent with the experimentally tested designs, and the findings of the present studies can provide guidance for future work on strain improvement. Overall, these studies demonstrate the potential and effectiveness of ORACLE for the accelerated design of microbial cell factories.

Fabrication and characterization of Ni-SSZ/SSZ/LSM-SSZ anode-supported SOFCs by tape casting and single-step co-sintering techniques

In this work, Ni-10 % Sc2O3-stabilized ZrO2 (SSZ)/SSZ/La0.8Sr0.2MnO3-δ (LSM)-SSZ anode-supported solid oxide fuel cells (SOFCs) have been successfully prepared by tape casting and single-step co-sintering procedures. The structure contains Ni-SSZ anode substrate and Ni-SSZ anode functional, dense SSZ electrolyte, LSM-SSZ cathode functional, and LSM-SSZ cathode layers were successfully prepared at 1250, 1300, and 1350 °C, respectively. The microstructures of the single cells were examined by SEM. There were some close pores in electrolyte of Cell-1250, and the cathode particle size obviously increased in Cell-1350. Therefore, Cell-1300 showed the optimal cell performance, the maximum power density attained 920 mW cm−2 at 800 °C. The impedance analysis demonstrated that the co-sintered temperatures have effects on not only the polarization resistance R P of a single cell but also its overall ohmic resistance R S . The results indicate that the tape casting and single-step co-sintering methods are both time saving and feasible for the development of anode-supported SOFCs.

Ultrathin Cu2O as an efficient inorganic hole transporting material for perovskite solar cells.

We demonstrate that ultrathin P-type Cu2O thin films fabricated by a facile thermal oxidation method can serve as a promising hole-transporting material in perovskite solar cells. Following a two-step method, inorganic-organic hybrid perovskite solar cells were fabricated and a power conversion efficiency of 11.0% was achieved. We found that the thickness and properties of Cu2O layers must be precisely tuned in order to achieve the optimal solar cell performance. The good performance of such perovskite solar cells can be attributed to the unique properties of ultrathin Cu2O, including high hole mobility, good energy level alignment with CH3NH3PbI3, and longer lifetime of photo-excited carriers. Combining the merits of low cost, facile synthesis, and high device performance, ultrathin Cu2O films fabricated via thermal oxidation hold promise for facilitating the developments of industrial-scale perovskite solar cells.

Fabrication and characterization of gold nanoparticle-loaded TiO2 nanotube arrays for medical implants.

Au nanoparticles (AuNPs) are successfully assembled on TiO2 nanotube (TN) arrays through electrochemical deposition technology to improve the surface characteristics of TN arrays as an implant material. The loading amount of AuNPs can be controlled by adjusting the deposition time of electrochemical deposition. The effect of the amount of the loaded AuNPs on surface roughness and surface energy is systematically investigated on the basis of various characterizations. Results show that the increase in the loading amount of AuNPs on the TN arrays can increase surface roughness and decrease surface energy. Potentiodynamic polarization tests indicate that AuNP-modified TNs possess a higher corrosion resistance than unmodified TNs. Corrosion resistance increases as the amount of the loaded AuNP increases. In vitro cell culture tests are performed on the basis of cell morphology observations and MTT assays. Osteoblast cell adhesion and proliferation ability on the AuNP-modified TN surface are greater than those on the unmodified TN surface. The sample fabricated at the deposition time of 90s exhibits an optimum cell performance. This work can provide a new platform to develop the surface chemistry of TN arrays and to fabricate titanium-based implant materials to enhance bioactivity.

Influence of Intermixed Donor and Acceptor Domains on the Ultrafast Charge Generation in Bulk Heterojunction Materials

Understanding how intermixed domains and pure domains in bulk heterojunction (BHJ) thin films affect charge generation and recombination in polymer solar cells (PSCs) is important to further improve PSC device performance. We control the proportion of intermixed domains and pure domains in an amorphous polymer and fullerene BHJ thin films by varying the fullerene concentration. By studying these thin films with ultrafast spectroscopy, we found that the coherent ultrafast charge generation process is nonexistent in this BHJ system due to the lack of pure polymer domains. We also found that the BHJ thin film with 100% intermixed domains begins charge recombination immediately after the initial charge generation process, while the BHJ thin film with pure fullerene domains showed an additional slow excitonic charge generation process before a slower charge recombination takes place. These results clearly demonstrate that pure domains are important for optimal BHJ solar cell performance.

Multiphysics Simulation of the Bromine Cathode: Cell Architecture and Electrode Optimization

A multiphysics model of a flow battery fibrous cathode was designed in COMSOL. A seven level parametric study was performed to determine the effect of a variety of physical and chemical parameters on overall cell performance. It was found that kinetic factors dominate the operation and performance however certain morphological properties, such as fiber diameter, porosity and anisotropy, could be modified to optimize cell performance. It was also found that further optimization could be performed on engineering parameters such as the electrode thickness and design of the flow distributor. Due to the strong dependence on porosity, future studies will take into account membrane compression.

Modeling of Ni Diffusion Induced Austenite Formation in Ferritic Stainless Steel Interconnects

Interconnect plates, made of ferritic type stainless steel, are widely used in planar solid oxide fuel cell (SOFC) or electrolysis cell (SOEC) stacks. These interconnect plates serve as current collector and separator for the neighboring fuel and oxygen electrode compartments of two adjacent cells. An intimate contact between the cell component and the interconnect (IC) plate is therefore essential to ensure optimum cell and stack performance. During stack production and operation, inter-diffusion across the cell – IC interface takes place, which under certain circumstances introduces adverse effects on the electrical, mechanical, and corrosion properties of the IC plates. One representative example is diffusion of nickel from the Ni/YSZ fuel electrode or from the Ni contact component into the IC plate, while iron and chromium from the steel diffuse in the reverse direction. Diffusion of Ni into the steel causes transformation of the ferritic BCC phase into the austenitic FCC phase in the interface region, accompanied with changes in volume and in mechanical and corrosion properties of the IC plates. Very few studies have been devoted to investigate this process experimentally. In this work, kinetic modeling of the inter-diffusion between Ni and FeCr based ferritic stainless steel was conducted, using the CALPHAD (CALculation of PHAse Diagrams) approach with the DICTRA software. The kinetics of inter-diffusion and austenite formation was explored in full detail, as functions of steel composition, thickness of Ni contact component or IC plate, temperature and time. The simulation was further validated by comparing with previously obtained experimental results. Growth of the austenite phase in commercial interconnect materials such as Crofer 22 APU and Crofer 22H was predicted under practical SOFC and SOEC operation conditions. The present work provides a proper account of the thermodynamics and kinetics of Ni-IC inter-diffusion and in addition provides input to further analysis of associated changes in the mechanical and corrosion properties of the IC plates.

Understanding Transport Phenomena in Perfluorosulfonic-Acid Membranes

One of the keys to optimizing polymer-electrolyte-fuel-cell performance is understanding its transport phenomena. This is especially important for the proton-exchange membrane, which helps to control the water management within the cell, an integral aspect for optimal cell performance. Typical fuel-cell membranes are perfluorosulfonic-acid based and are essentially random copolymers that phase separate into hydrophilic domains for water and ion movement supported by a hydrophobic backbone phase. We have previously shown that water transport and uptake at the nano- and macroscale is similar and relatively fast in membranes, especially at higher humidities.1,2 Once water crosses the membrane interface, time-resolved studies show that changes at the nano and macroscale scales occur almost simultaneously. Unlike water incorporation, proton conduction depends not just on the domains but also their interconnectivity. Time-resolved studies such as that in Figure 1, show that unlike the water incorporation, there is more of a time delay due to reorientation of the domains and the transport pathways. In this talk, such issues will be discussed. In particular is the need to explore the structure-function relationships for the transport properties and the critical aspects that the membrane interface plays in controlling transport. In addition to experimental results, a model methodology will be presented to explore proton conductivity. In the model, we propose a macroscopic treatment that utilizes data on the nanoscale relating to membrane morphology and physically relevant phenomena,3 but in a framework that still allows for easy incorporation into cell-level fuel-cell models. Extensions of the analysis and phenomena to the thin-film regime, which is critical for fuel-cell catalyst layers, will also be presented. Acknowledgements We thank Steve Hamrock, Mike Yandrasits, and Greg Haugen at 3M for providing membranes and discussion; This work made use of facilities at the Advanced Light Source (ALS), supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy. This work was funded by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U. S. Department of Energy under contract number DE-AC02-05CH11231. References 1 Gi Suk Hwang, Dilworth Y. Parkinson, Ahmet Kusoglu, Alastair A. MacDowell, and Adam Z. Weber, ACS Macro Letters, 2, 288-291 (2013). 2 Daniel S. Hussey, Dusan Spernjak, Adam Z. Weber, Rangachary Mukundan, Joseph Fairweather, Eric L. Brosha, John Davey, Jacob S. Spendelow, David L. Jacobson, and Rodney L. Borup, J. Appl. Phys., 112, 104906 (2012). 3 Ahmet Kusoglu, Suchol Savagatrup, Kyle T. Clark, and Adam Z. Weber, Macromolecules, 45 (18), 7467-7476 (2012). Figure 1

Study of enhanced photogalvanic effect of Naphthol Green B in natural sunlight

The photogalvanic cells based on Naphthol Green B sensitizer-Fructose reductant-Sodium Lauryl Sulphate surfactant has been studied in natural sunlight. The cell has been found workable in natural sunlight with greatly enhanced optimum cell performance. The 1159.2 μW power, 4500 μA short-circuit current, 1070 mV open-circuit potential, 14.49% efficiency and 240 min storage capacity (as half change time) has been observed in optimum cell fabrication conditions.

A Search for the Optimum Lithium Rich Layered Metal Oxide Cathode Material for Li-Ion Batteries

We report the results of a comprehensive study of the relationship between electrochemical performance in Li cells and chemical composition of a series of Li rich layered metal oxides of the general formula xLi2MnO3·(1-x)LiMn0.33Ni0.33Co0.33O2 in which x = 0,1, 0.2, 0,3, 0.5 or 0.7, synthesized using the same method. In order to identify the cathode material having the optimum Li cell performance we first varied the ratio between Li2MnO3 and LiMO2 segments of the composite oxides while maintaining the same metal ratio residing within their LiMO2 portions. The materials with the overall composition 0.5Li2MnO3·0.5LiMO2 containing 0.5 mole of Li2MnO3 per mole of the composite metal oxide were found to be the optimum in terms of electrochemical performance. The electrochemical properties of these materials were further tuned by changing the relative amounts of Mn, Ni and Co in the LiMO2 segment to produce xLi2MnO3·(1-x)LiMn0.50Ni0.35Co0.15O2 with enhanced capacities and rate capabilities. The rate capability of the lithium rich compound in which x = 0.3 was further increased by preparing electrodes with about 2 weight-percent multiwall carbon nanotube in the electrode. Lithium cells prepared with such electrodes were cycled at the 4C rate with little fade in capacity for over one hundred cycles.

Surfactant and natural sunlight enhanced Photogalvanic effect of Sudan I dye

Photogalvanic cells (PG) have been extensively studied for solar power and storage at low intensity artificial sunlight. But, PG can be practically significant and applicable in daily life only when they are validated at natural sunlight intensity. Therefore, the present study of photogalvanics of Sudan I-Fructose with efficiency enhancer chemical such as Sodium Lauryl Sulfate (SLS) surfactant in alkaline medium has been used to observe their workable feasibility in natural sunlight with investigation for optimal fabrication parameters. The cell has been found workable in natural sunlight with greatly enhanced optimum cell performance compared to that for reported similar cells. The observed optimum cell performance in terms of maximum power, short-circuit current, open-circuit potential, conversion efficiency and storage capacity (as half change time) is of the order of 1081.1μW, 4200μA, 1048mV, 13.5%, and 31min, respectively.

Low-temperature UV ozone-treated high efficiency radial p-n junction solar cells: N-Si NW arrays embedded in a p-Si matrix

High-efficiency radial p-n junction SiNW solar cells have been realized using UV ozone treatment of n-Si NW arrays embedded in a p-Si matrix structure. This structure provides the advantage of homogeneous and continuous front electrode patterning, which results in a lower series resistance than for core-shell morphology. Surface and bulk recombination is chiefly responsible for degrading cell performance with increased SiNW length in spite of enhanced junction area and improved light-trapping capability. In this study we estimated the critical NW length necessary to obtain optimal cell performance with minimum carrier loss in a simple radial p-n junction solar cell. Further low-temperature UV ozone treatments offer the potential to enhance solar cell properties by passivating, by oxidation, the large number of surface defect states.

Modeling of cell culture damage and recovery leads to increased antibody and biomass productivity in CHO cell cultures.

The development of an efficient and productive cell-culture process requires a deep understanding of intracellular mechanisms and extracellular conditions for optimal product synthesis. Mathematical modeling provides an effective strategy to predict, control, and optimize cell performance under a range of culture conditions. In this study, a mathematical model is proposed for the investigation of cell damage of a Chinese hamster ovary cell culture secreting recombinant anti-RhD monoclonal antibody (mAb). Irreversible cell damage was found to be correlated with a reduction in pH. This irreversible damage to cellular function is described mathematically by a Tessier-based model, in which the actively growing fraction of cells is dependent on an intracellular metabolic product acting as a growth inhibitor. To further verify the model, an offline model-based optimization of mAb production in the cell culture was carried out, with the goal of minimizing cell damage and thereby enhancing productivity through intermittent refreshment of the culture medium. An experimental implementation of this model-based strategy resulted in a doubling of the yield as compared to the batch operation and the resulting biomass and productivity profiles agreed with the model predictions.

Solar energy conversion and storage using naphthol green B dye photosensitizer in photogalvanic cells

Photogalvanic cells are electrochemical devices capable of solar power generation and storage using solution of photosensitizer(s) and reductant(s) in alkali medium. These cells are cheap, renewable, and promising energy devices for the future, provided there electrical performance is further improved. The present study of photogalvanics of Naphthol Green B dye photosensitizer with Fructose as reductant and Sodium Lauryl Suphate as surfactant in alkaline medium was undertaken with aim of finding relatively better combination of chemicals like photosensitizer, reductant and surfactant for further improvement in electrical performance of these cells. This combination of chemicals has shown very impressive and surprisingly very high improvement in cell performance. The optimum conditions for cell have also been observed for optimal cell performance. The maximum power, short-circuit current, open-circuit potential, efficiency and storage capacity (as half change time) has been observed of the order of 422.4 μW, 1850 μA, 1040 mV, ∼10.6%, and 260 min, respectively.

The Effects of Varied Deposition Conditions, Including the Use of Argon, on Thin-Film Silicon Solar Cells Prepared using PECVD

This paper reports the effects of varied deposition conditions on the resultant energy conversion efficiencies of thin-film silicon solar cells. Cells were deposited using an Oxford Instruments PlasmaLab System 100 on to Pilkington TEC-8 TCO glass, and thoroughly investigated using electrical methods. Thin film devices were fabricated using the decomposition of silane gas within a reaction chamber of 13.56 MHz plasma discharge. The deposition conditions, including substrate temperature, gas flow rates, RF power, chamber pressure, and film thickness are all explored to determine the optimum cell performance. A view toward high-efficiency solar structures, including heterojunction with intrinsic thin layer (HIT) and micro-morph cell designs using the same conditions is presented.