Degradation Of Cell Components Research Articles

Theoretical Understanding of Effects of Operating Modes on the Performance Durability of Solid Oxide Cells: A Comparison between Potentiostatic and Galvanostatic Operations

In solid oxide cells (SOCs), the choice between galvanostatic (constant current) and potentiostatic (constant voltage) modes does not significantly affect the performance of SOCs as long as the cell components remain unchanged and intact. However, the degradation of cell components, which leads to changes in electrochemical and physical properties of the cell, elevates the importance of the selected operating mode. This paper aims to investigate the effects of galvanostatic and potentiostatic operating modes on the evolving properties of SOCs and their subsequent influence on performance durability. Employing non-equilibrium thermodynamic analysis, a crucial approach for understanding the degradation phenomena within an active electrochemical system, this study aims to provide in-depth insights into how these operating modes affect the longevity and efficacy of SOCs. Key findings include: In cases where oxygen electrode (OE) degradation is accelerated by higher partial pressure of oxygen ( pO2 ), operating under constant voltage electrolysis can mitigate the high pO2 at the OE|electrolyte (OE|EL) interface. Conversely, if OE degradation occurs more rapidly under a lower pO2, constant current electrolysis is more effective in suppressing degradation by achieving a high pO2 at the OE|EL interface. For degradation of the fuel electrode (FE) due to higher pO2, constant current electrolysis is beneficial for more stable performance, which helps maintain low pO2 at the FE|EL interface. When FE degradation is accelerated by lower pO2, constant voltage electrolysis can avert low pO2 at the FE|EL interface. In practical scenarios, more complex degradation mechanisms come into play, especially when pO2 significantly deviates from initial conditions. Degradation in one electrode can influence pO2 in the other electrode, a phenomenon more pronounced in potentiostatic than in galvanostatic electrolysis.

Extreme Fast Charging of High Energy Density Lithium Ion Battery

The demand for high-energy-density batteries using Ni-rich cathodes is increasing due to the continuous expansion of the electric vehicle (EV) market. U.S. Department of Energy has stated the need for extreme-fast-charging (XFC) batteries that achieve an 80% state of charge (SOC) in less than 15 min. However, Ni-rich cathodes tend to lose capacity quickly under XFC conditions, which compromises their structural integrity. In addition, XFC conditions rapidly generate significant heat due to the high current applied to the cell, leading to the degradation of cell components. It is challenging to create Ni-rich cathodes that can withstand XFC conditions while still maintaining maximum energy density and long-term cycling performance. In this study, a cathode called Li[Ni0.92Co0.06Al0.01Nb0.01]O2 (Nb-NCA93) is introduced, which has a high energy density of 869 Wh kg-1. The presence of Nb in the cathode induces grain refinement in its secondary particles, reducing internal stress and preventing heterogeneity of Li concentration during cycling. When used in a full-cell, the Nb-NCA93 cathode reaches full charge within 12 minutes and retains 85.3% of its initial capacity after 1000 cycles, cycled at full depth of discharge. Furthermore, the refined microstructure of the Nb-NCA93 cathode limits heat generation under XFC conditions. References H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater. 2018, 30, 1155 C. S. Yoon, H.-H. Ryu, G.-T. Park, J.-H Kim, K.-H. Kim, Y.-K Sun, J. Mater. Chem. A 2018, 6, 4126 U.-H. Kim, H.-H. Ryu, J.-H. Kim, R. Mücke, P. Kaghazchi, C. S. Yoon, Y.-K. Sun, Adv. Energy Mater. 2019, 9, 1803902

Alkaline membrane water electrolysis performance improvement from high ionic strength anolyte

Low-temperature hydrogen generation using anion exchange membranes electrolysis (AEMEL) uses the advantages of liquid water alkaline electrolysis and proton exchange membrane electrolysis. In this study, liquid water was fed to the anode and the cathode was operated dry. During electrolysis, water diffuses to the hydrogen cathode through the AEM. It was found that the supporting electrolyte in the water-fed anode (i.e., anolyte) plays an important role in the performance of the dry cathode. Alkali cations from the hydroxide-containing anolyte permeate into the membrane and migrate to the cathode during electrolysis delivering water and significantly improving cathode conductivity and kinetics. The alkali ions in the anolyte can be from an inert salt, not hydroxide, which lessen the potential degradation of cell components because the pH is not as high. There is an optimum concentration of neutral alkali salt in the anolyte because the non-electroactive anions in the anolyte lower the concentration of the hydroxide reactant in the anode ionomer.

Understanding Improved Lifetimes of Lithium-Metal Batteries with LiPF6 Carbonate Electrolyte Modified By Phosphorus Pentoxide

Lithium metal anodes offer the possibility of a ten-fold increase in capacity versus standard intercalation anodes such as graphite. However, to date, there has been limited success using commercially available liquid electrolytes for batteries with lithium metal anodes. A critical issue in LiPF6 carbonate electrolytes results from the reaction of trace water (<100 ppm) with PF5, which is in equilibrium with the PF6 - anion, to produce hydrofluoric acid (HF) and difluorophosphoric acid. These reaction products contribute to lithium passivation, transition-metal leaching and subsequent particle cracking at the cathode, and degradation of cell components. Furthermore, HF begins an autocatalytic degradation cycle, so if not removed, can continually decompose the carbonate solvents in a self-sustaining cycle.Here, we demonstrate the effectiveness of a simple and scalable modification procedure of 1M LiPF6 ethylene carbonate (EC)/diethylcarbonate (DEC) (50/50 v/v) electrolyte to greatly enhance performance of lithium-metal batteries. Phosphorus pentoxide (P2O5) added to commercial, battery-grade electrolyte performs the dual functions of both scavenging HF and H2O, while also generating chemical species that promote formation of a beneficial, POxFy-rich SEI layer upon cycling. In commercial-scale pouch cells (0.4 Ah), performance using the modified electrolyte is vastly superior, with 87.7% capacity retention at >230 cycles and minimal hysteresis, to that of the cell with as-received electrolyte, which failed after approximately 30 cycles. Electrodes harvested after 30 cycles in the commercial electrolyte yielded cracked cathode particles and transition metal migration to the anode surface, while these were not seen with the modified electrolyte, corroborating the performance enhancement resulting from HF scavenging. Rigorously quantitative, liquid-state 19F, 31P, 1H, and 13C NMR of the modified electrolyte proves complete removal of residual HF in addition to revealing a plethora of new fluorophosphate species, while two-dimensional 19F{31P} correlation experiments were used to confidently establish signal assignments. These fluorophosphate moieties make up the anodic surface layer that promotes smooth and uniform lithium electrodeposition, further enhancing performance. Understanding the relationship between electrolyte speciation and electrochemical performance is crucial for careful design of electrolyte additives, and in particular, multi-functional materials such as P2O5 offer simple but highly effective improvements to resultant electrolyte formulations.Overall, we achieve enhanced operation of lithium-metal batteries using a P2O5-modified LiPF6 carbonate electrolyte as a result of HF and H2O removal, alongside formation of favorable SEI-forming species. Through NMR, we quantitatively established speciation of this electrolyte to better understand the improved performance and elucidate the major reaction pathways. Reference: Zhang, J., et al. Performance Leap of Lithium Metal Batteries in LiPF6 Carbonate Electrolyte by a Phosphorus Pentoxide Scavenger. (Under review, 2022)

A review of accelerated stress tests dedicated to proton exchange membrane fuel cells – Part I: Fuel cell component level

Various research are currently done about fuel cells. They can concern the application context, the fuel cell technology by itself or the socio-economic bolts. This paper deals with fuel cells stack testing and especially the accelerated stress testing. Long and expensive ageing tests are performed to study the behavior of the fuel cell with the aim of making it as robust as possible versus permanent degradation over time. Accelerated stress tests should provide results faster as classical ageing tests, thus inducing cost reduction. This paper reviews fuel cell component degradation, including degradation mechanisms, and the accelerated stress tests dedicated to all the constituting components (catalyst layer, membrane, gas diffusion layer and bipolar plates). Obviously, the harmonized accelerated stress tests given by the Department of Energy (DoE) are presented but all other recent accelerated test protocols proposed in the literature are also reviewed. In addition, several tables are given to detail operating conditions, specimen, characterization planning and a degradation rate that will be relevant and helpful to converge with an optimal AST solution.

Coupling Experiment and Modelling to Characterize and Predict Performances of PEMFC

In the past few decades, many improvements have been achieved regarding the PEMFCs components, the cell/stacks design as well as the architecture of the overall system. Hence, the level of maturity of PEMFC systems recently became sufficient to enable their commercialization for automotive applications (FCEV Miraï by Toyota, FCEV Nexo by Hyundai, etc.). However, despite great initial performance, PEMFC systems still suffer technological limitations, such as their initial cost and overall durability in real life operation, which prevents widespread industrial deployment. Some of these limitations can be overcome by combining experiments and modelling to characterize and better understand the behaviour of the carbon-supported platinum (Pt/C) electrocatalyst, its utilization/effectiveness in PEMFC catalyst layers and to be able to predict the performance and durability of PEMFC. This should help making the most relevant choices to accelerate the development processes of PEMFC.In this work, physico-chemical and electrochemical measurements are performed from the scale of the raw Pt/C materials up to the complete catalyst layer, to gather as much information as possible on the catalytic layer micro-structure and its operating properties. Coupling experiments in classic RDE and in PEMFC differential-single cell (1.8 cm² under high reactant stoichiometry) enables to fully characterize the electrochemical properties and behaviour of our materials. These different measurements are performed under various ideal and well-controlled operating conditions: cell temperature (T), relative humidity (RH), partial pressure of O2 (PO2 ) were chosen to be relevant and to dissociate and characterize as much as possible the different electro-chemical mechanisms involved in the catalyst layers of PEMFC. In parallel; several models have been developed to simulate one or combined mechanisms leading to the performance [1] and degradation of cell components[2], [3]. In fact, models aim at isolating and quantifying the contribution of each mechanism by choosing relevant operating conditions. Based on our experimental work and data sets, the behaviour of the Pt/C electrocatalysts has been studied in order to introduce new electrocatalytic features and especially the Pt surface oxide formation and reduction which is linked to Pt surface state. This preliminary step was then further developed into, a complete performance model for the O2 reduction reaction at the cathode to better describe the physical and electrochemical phenomenon involved in 0D and 1D catalyst layers during fuel cell operation. In this new description, the position of the main adsorption/desorption peaks are well captured by the simulation compared to experiment keeping complete physical meaning.This work has partially received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No. 875025 (FURTHER-FC project). This Joint Undertaking receives support from the European Union’s Horizon 2020 Research and Innovation programme, Hydrogen Europe and Hydrogen Europe Research.[1] B. Randrianarizafy, P. Schott, M. Chandesris, M. Gerard, and Y. Bultel, “Design optimization of rib/channel patterns in a PEMFC through performance heterogeneities modelling,” International Journal of Hydrogen Energy, vol. 43, no. 18, pp. 8907–8926, May 2018, doi: 10.1016/j.ijhydene.2018.03.036.[2] T. Jahnke, G. A. Futter, A. Baricci, C. Rabissi, and A. Casalegno, “Physical Modeling of Catalyst Degradation in Low Temperature Fuel Cells: Platinum Oxidation, Dissolution, Particle Growth and Platinum Band Formation,” J. Electrochem. Soc., vol. 167, no. 1, p. 013523, Nov. 2019, doi: 10.1149/2.0232001JES.[3] G. Maranzana, A. Lamibrac, J. Dillet, S. Abbou, S. Didierjean, and O. Lottin, “Startup (and Shutdown) Model for Polymer Electrolyte Membrane Fuel Cells,” J. Electrochem. Soc., vol. 162, no. 7, pp. F694–F706, 2015, doi: 10.1149/2.0451507jes. Figure 1

Evaluation of Trihalide Ion’s Ability As Redox Mediators in Lithium Oxygen Batteries

Redox mediators have been intensively studied for increasing the energy efficiency and cycle life of lithium oxygen(Li-O2) batteries by reducing the high overpotential, which induces degradation of cell components. Lithium halides have been explored as representative redox mediators in Li-O2 batteries because of their low redox potential under 3.6 V. However, there is still controversy about the proper form of halide materials as redox mediators to decompose the discharge product of Li-O2 batteries, lithium peroxide (Li2O2). Therefore, we conducted quantitative analyses such as UV–Vis and GC-MS to confirm the ability of different halide materials to decompose Li2O2 as redox mediators in Li-O2 batteries. By controlling the byproducts during discharge and exempting the misunderstandings when using commercial Li2O2 powder, we clearly demonstrated that triiodide (I3 −) and tribromide (Br3 −) have sufficient ability to decompose Li2O2 in Li-O2 batteries. [1] W.-J. Kwak, D. Hirshberg, D. Sharon, M. Afri, A.A. Frimer, H.-G. Jung, D. Aurbach and Y.-K.Sun, Energy Environ. Sci. 2016, 9, 2334. [2] W.-J. Kwak, D. Hirshberg, D. Sharon, H.-J. Shin, M. Afri, J.-B. Park, A. Garsuch, F.F. Chesneau, A.A. Frimer, D. Aurbach and Y.-K. Sun, J. Mater. Chem. A 2015, 3, 8855. [3] W.-J. Kwak, H. Kim, H.-G. Jung, D. Aurbach and Y.-K. Sun, J. Electrochem. Soc. 2018, 165, A2274.

Investigation of Faradaic Contributions from Bipolar Plates to Areal Current Density in Vanadium Redox Flow Batteries

All-vanadium redox flow batteries (VRFBs) have been identified as a promising technology for bridging the gap to integrating renewables onto grids as well as improving grid-level power generation efficiency. VRFBs are prime candidates for this role on account of their modularity, scalability, and relatively high performance. [1] There are still, however, many design parameters that can be more highly optmized to improve and specialize the aspects of this technology. Capacity fade is a parasitic loss that occurs in all electrochemical enery storage systems and is one of the parameters that can be most improved in VRFBs. Fading capacity is due to a host of variables in the system, such as membrane permeability and electroactive species concentration.[2] Degradation of cell components (electrodes and membranes) can also contribute to capacity decay in the form of increased overpotentials throughout the systems operating range. The kinetics at the negative electrode (V(II) ↔ V(III)) are generally understood to be more sluggish than at the positive electrode [3] as well as being less stable (i.e. degrading more rapidly with respect to time). Several high performance materials have been identified for the negative electrode [4] [5], however extended cycling data on the order of years is uncommon in the literature. Mitigation of this degradation on this time scale is one such optimization that can improve voltage efficiency and mitigate capacity fade. In this work we present our most recent experimental work in which the Faradaic current that can be supported by the plates is quantified on different sets of VRFB hardware and isolated from the current on the combined plates with GFD 2.5 mm carbon felt electrodes. For this work symmetric cells were utilized, to isolate crossover effects, in conjunction with electrochemical impedance spectroscopy and polarization curves to quantify the contributions from the different processes at each overpotential. Likewise, experiments were also performed on a symmetric cell where the plates served as the electrodes to quantify the parallel contribution. The data were assessed via statistical tests in order to determine significance. The results of this study show that, graphitic bipolar plates can support 35-50% of the current density on the negative electrode at low overpotentials and 20 and 30% at higher overpotentials. The open circuit impedance data also show that the ASR of the cell with felt electrodes is increasing at a rate of around 25 mΩ cm2 min−1 at this stage in the electrode’s life. This degradation is nonlinear and asymptotes to a stable ASR, however, this implies that the percentage measured in this context is smaller than the steady state percentage. These combined results suggests a material oriented approach to improving the bipolar plate material in order to achieve a more stable negative electrode.

Verification for trihalide ions as redox mediators in Li-O2 batteries

Redox mediators have been intensively studied for increasing the energy efficiency and cycle life of Li-O2 batteries by reducing the high overpotential, which induces degradation of cell components. Lithium halides have been explored as representative redox mediators in Li-O2 batteries because of their low redox potential under 3.6 V. However, there is still controversy about the proper form of halide materials as redox mediators to decompose the discharge product of Li-O2 batteries, lithium peroxide (Li2O2). Therefore, we conducted quantitative analyses such as UV–Vis and GC-MS to confirm the ability of different halide materials to decompose Li2O2 as redox mediators in Li-O2 batteries. By controlling the byproducts during discharge and exempting the misunderstandings when using commercial Li2O2 powder, we clearly demonstrated that triiodide (I3−) and tribromide (Br3−) have sufficient ability to decompose Li2O2 in Li-O2 batteries.

General Stress-Strength Interference and Gamma Process Combined Method for Space Solar Cell Components Reliability Analysis

Space solar cell components always suffered from the complex and hostile space environment. The reliability of space solar cell components is important to ensure the mission success of space satellites. However, the current research mostly focuses on solar cells' degradation mechanisms. There is less research based on the performance parameters of space solar cell component's degradation to analyze its reliability. Therefore, a reliability analysis method based on the method of modeling the performance degradation of space solar cell components is proposed. By combining general stress-strength interference model and Gamma process, the reliability model of space solar cell components is established. The accelerated degradation test based on the equivalent particle dose is performed to simulate the radiation influence and verify the proposed method. Compared with the displacement damage dose method, the proposed method can further develop the reliability analysis based on performance degradation analysis. Moreover, the cover glass and interconnection are also taken into account together to form a completed component analysis. Through analyzing the cover glass and interconnection experiment results, the cover glass can affect the component reliability; whereas, the interconnection has little influence at the particle radiation condition. Based on the proposed method, the reliability is easier to calculate with the degradation of output power.

Autophagy mediates calcium-sensing receptor-induced TNFα production in human preadipocytes

Obesity is a major current public health problem worldwide due to the severe co-morbid conditions that this disease entails. The development of obesity-related cardiometabolic disorders is in direct association with adipose tissue inflammation that leads to its functional impairment. Activation of the Calcium-Sensing Receptor (CaSR) in adipose tissue contributes to inflammation and adipose dysfunction. Autophagy, a process of cell component degradation, is closely related to inflammation in many diseases, however, whether autophagy is associated with CaSR-induced inflammation remains unknown. Using LS14 and SW872 preadipose cell lines as well as primary human preadipocytes, we show that CaSR activation with the allosteric activator cinacalcet induces autophagosome formation. Cinacalcet-induced LC3II content elevation was precluded by knockdown of the CaSR and enhanced by CaSR overexpression, indicating a specific effect. Autophagy inhibition using 3-methyladenine prevented CaSR-induced TNFα production, indicating that autophagy contributes to CaSR-induced inflammation in human preadipocytes. Our results suggest that modulation of CaSR-induced autophagy is an attractive target in obese inflamed adipose tissue, to prevent the development of diseases triggered by adipose dysfunction. We describe a novel mechanism and possible new target to modulate and prevent adipose inflammation and hence the resulting disease-generating adipose tissue dysfunction.

Lifetime Prediction of a Polymer Electrolyte Membrane Fuel Cell under Automotive Load Cycling Using a Physically-Based Catalyst Degradation Model

One of the bottlenecks hindering the usage of polymer electrolyte membrane fuel cell technology in automotive applications is the highly load-sensitive degradation of the cell components. The cell failure cases reported in the literature show localized cell component degradation, mainly caused by flow-field dependent non-uniform distribution of reactants. The existing methodologies for diagnostics of localized cell failure are either invasive or require sophisticated and expensive apparatus. In this study, with the help of a multiscale simulation framework, a single polymer electrolyte membrane fuel cell (PEMFC) model is exposed to a standardized drive cycle provided by a system model of a fuel cell car. A 2D multiphysics model of the PEMFC is used to investigate catalyst degradation due to spatio-temporal variations in the fuel cell state variables under the highly transient load cycles. A three-step (extraction, oxidation, and dissolution) model of platinum loss in the cathode catalyst layer is used to investigate the cell performance degradation due to the consequent reduction in the electro-chemical active surface area (ECSA). By using a time-upscaling methodology, we present a comparative prediction of cell end-of-life (EOL) under different driving behavior of New European Driving Cycle (NEDC) and Worldwide Harmonized Light Vehicles Test Cycle (WLTC).

Influence of Ca Doping on the Performance of Ruddlesden-Popper Oxides Sr3.2-XCaxLn0.8Fe1.5Co1.5O10-δ as Cathode Materials for It-SOFCs

Solid oxide fuel cell (SOFC) is an attractive electrochemical device for energy conversion with high efficiency and fuel flexibility at high operating temperatures (~1000 °C). Current operating temperatures of SOFC technology limit its wide commercialization due to the selection of materials used and degradation of cell components. This challenge has generated enormous interest in SOFCs operating at intermediate temperatures (600 – 800 oC). However, the catalytic activity of the conventional La1-xSrxMnO3 perovskite cathode drops significantly at temperatures < 800 °C. Mixed ionic-electronic conducting perovskites are widely investigated as cathodes for SOFCs due to their high catalytic activity for oxygen reduction reaction (ORR) at intermediate operating temperatures. Cobalt-based perovskite oxides exhibit good mixed ionic-electronic conductivity and catalytic activity at 600 – 800 oC, but they suffer from a huge thermal expansion mismatch between the electrolyte and electrode. Another class of materials with mixed ionic and electronic conducting property and catalytic activity for ORR is the perovskite-related intergrowth oxides belong to the Ruddlesden-Popper (R-P) series. Here we present R-P oxides of the n = 3 series Sr3.2-xCaxLn0.8Fe1.5Co1.5O10-δ with x = 0 and 0.4 and Ln = La, Pr, and Nd as potential cathodes for intermediate temperature SOFCs. Specifically, the effects of Ca substitution for Sr on the crystal chemistry, oxygen content, thermal expansion coefficient (TEC), and electrocatalytic activity in SOFC are presented. The substitution of Ca for Sr in Sr3.2-xCaxLn0.8Fe1.5Co1.5O10-δ enhances the stability of phase at the operating temperatures and decreases the amount of oxygen loss on heating. Comparing different lanthanides with and without Ca in Sr3.2-xCaxLn0.8Fe1.5Co1.5O10-δ, the Ln = Nd samples exhibit superior cathode performance which is ascribed to the high concentration of oxygen vacancies. Among the different compositions studied, the composite cathode Sr2.8Ca0.4Nd0.8Fe1.5Co1.5O10-δ + GDC exhibits an enhanced performance with good phase stability due to high oxygen vacancy concentration and enhanced oxide-ion transport.

(Invited) Battery Safety across Different Use-Cases

Battery Safety has been discussed at length in the literature. Recently, the use of mathematical models to describe failure mechanisms and propagation modes within battery modules and packs has become more prevalent. Detailed models that represent thermal events from ohmic heating [1] to component-wise reaction heats, [2] gradual degradation of cell components, [3] plating of lithium leading to internal short circuits,[4] failure of welded joints,[5] venting of the cell via the crimp or the can walls,[6] mechanical deformation have been developed.[7] This presentation will highlight the utility of physics-based models to discuss a few practical questions posed during the design process. We begin by attempting to present an electrochemical definition of a short circuit that is consistent across different failure modes. This section of the presentation will explore in detail the origin of failure within a cell. With our mathematical derivation, we identify parameters that govern the evolution of failure under a few key scenario, including an internal-short and mechanical crush. Next, we discuss different experimental approaches to measure these parameters and issues associated with the different measurement techniques. The second part of the presentation will cover modeling tools for propagation of failure across a module. We will discuss the influence of different trigger mechanisms and compare the amounts of heat released across the different modes. The set of case-studies presented include gradual degradation of the interface, to ultra-high strain rate deformation scenario. We will present a methodology to distinguish between gradual deformation across prolonged periods of time and severe degradation across fewer use-cycles. These results are particularly relevant in designing duty cycles for different applications and to monitor how safety evolves as a function of the aging profile of the battery. Finally we conclude with a generic map (Fig. 1) of the heat evolution versus dissipation rates that summarizes the various case-studies discussed in the presentation. This approach enables us to compare different cell designs for a given module requirement, determine packaging and/or spacing requirements as well as design of cooling loads that help mitigate the risk of failure propagation for a given design.

Influence of Perfluorinated Additives on ORR and Performance of High Temperature PEM Fuel Cells

High Temperature PEM Fuel Cells (HTPEMFC) typically operate in the temperature range of 100-200°C while Low Temperature PEM Fuel Cells (LTPEMFC) operate below 100°C. Due to the higher operating temperature, HTPEMFCs benefit from several advantages over LTPEMFCs, including enhanced electrode kinetics, increased tolerance to impurities in the fuel feed and improved heat and water management. However, there are also many challenges preventing their large-scale implementation. Some of the issues related to the increased temperature of operation include corrosion of catalyst and support, degradation of cell components, and difficulties in selecting a viable polymer electrolyte membrane where applicable. Currently, polymer membranes filled (doped) with a low vapor pressure acid, such as concentrated phosphoric acid, are used as electrolytes in HTPEMFCs operating in the 140-200°C temperature range. The acid bound to the membrane molecules acts as the ionic conductor in the electrolyte, while the free or “unbound” acid functions as the ionic conductor in the electrodes. In order to form triple phase boundaries in the electrode, the free acid must be in contact with the catalyst particles, and as a result the oxygen has to dissolve in and diffuse through the acid film to reach the catalyst site. This can result in significant mass transport losses in the cathode due to the low solubility and diffusivity of oxygen in concentrated phosphoric acid. With the use of phosphoric acid, additional issues affecting cell performance arise due to phosphate adsorption on the Pt catalyst, migration of acid during operation and the loss of acid from the stack. The performance losses resulting from the mass transport losses and anion adsorption on Pt are two major issues affecting the development of HTPEMFC technology as they necessitate the use of higher Pt catalyst loading compared to state of the art LTPEMFCs in order to match their performance, which increases the stack cost significantly [1-4]. The effect of perfluorinated carbon compounds on improving the oxygen solubility and diffusivity in phosphoric acid is well documented [5, 6]. In this study, pottasium nonafuorobutanesulfonate (C4F9SO3K) and potassium perfluorohexanesulfonate (C6F13SO3K) will be used to modify the phosphoric acid prior to doping the electrolyte membrane in order to analyze the effect of the additive on ORR kinetics and fuel cell performance. The modified electrolytes are also expected to exhibit less anion adsorption on the Pt surface. Polarization curves, Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) will be used to evaluate the effect of varying the concentration and type of additive on cell performance, the ECSA and mass transport resistance in the cathode catalyst layer. A drawback to using additives is that the wetting angle of the modified acid on PTFE increases significantly, leading to electrode flooding issues at higher additive concentrations in the acid. So, optimization of the wet-proofing of the electrode by controlling the PTFE content in the catalyst layer will also be studied.

Durability Test of Anode-Supported Solid Oxide Fuel Cell Under Diverse Load Conditions

Solid oxide fuel cells (SOFCs) provide an appealing electrochemical devices to convert chemical energy into electrical power with high efficiency and negligible carbon emissions. For utilizing in a wide spectrum of applications, SOFCs need to prove the operational stability over 40,000 h with less than 10% of power decay [1]. The performance deteriorations of SOFCs are induced by complex factors such as redox cycle [2], carbon deposition [3], S poisoning [4], and Cr poisoning. Therefore, understanding of fundamental degradation mechanisms under various operating conditions are important to improve the lifetime of SOFCs. For past few decades, the durability study of SOFCs has carried out under prolonged periods of time in mainly ‘laboratory conditions’, i.e. constant current operations, well controlled fuel composition, and low level of impurities [5,6]. However, the real operating conditions normally include harsh conditions such as temperature fluctuations, current fluctuations, and fuel and air stop. Especially, the different load conditions can result in accelerating the degradation of cell components because of the local potential and temperature changing. In this research, systematic durability investigations of anode-supported SOFCs are performed under a wide range of operating conditions including load cycle and load trip. In order to understand degradation mechanisms of the cell, various electrochemical investigations are performed such as the current-voltage polarization and electrochemical impedance spectroscopy. The morphology and microstructure of anode-supported cell are examined using field emission scanning electron microscoy and electron probe X-ray microanalyzer. References Y.-S. Chou, J.W. Stevenson, J.-P. Choi, J. Power Sources 250 (2014) 166–173.T. Klemensø, C. Chung, P.H. Larsen, M.Mogensen, J. Electrochem. Soc. 152 (2005) A2186–A2192.Mai, M. Becker, W. Assenmacher, F. Tietz, D. Hathiramani, E. Ivers-Tiffee, D. Stöver, W. Mader, Solid State Ionics 177 (2006) 1965–196H. Yokokawa, T. Horita, K. Yamaji, H. Kishimoto, T. Yamamoto, M. Yoshikawa, Y. Mugikura, K. Tomida, Fuel Cells 13 (2013) 526–535.Hagen, J.V.T. Høgh, R. Barfod, J. Power Sources 300 (2015) 223–228.H. Yokokawa, ECS Trans. 35 (2011) 207–216.T.-H. Lee, K.-Y. Park, J.-T. Kim, Y. Seo, K.B. Kim, S.-J. Song, B. Park, J.-Y. Park, J. Power Sources 276 (2015) 120–132.

Delineating Contributions from Vanadium Crossover and Electrode Degradation to Capacity Decay in Vanadium Redox Flow Batteries

All-vanadium redox flow batteries (VRFBs) are promising candidates for large-scale energy storage thanks to their scalability, relatively high-performance and safety 1. However, wide-spread integration of VRFBs requires mitigation of rapid capacity decay over long-term cycling. There are three major contributors to discharge capacity decay during cycling in VRFBs: 1) undesired transport of vanadium ions and water through the ion-exchange membrane 2) degradation of cell components (predominantly electrodes, and membrane) and 3) gas-generation from side reactions. With careful selection of upper and lower voltage limits for cycling, gas-generation can be mitigated to a great degree. However, capacity decay due to undesired vanadium ion and water crossover along with component degradation is inevitable. It is important to note that the capacity decay over long-term cycling is cumulative and therefore, capacity decay due to vanadium crossover and degradation are combined in cycling experiments making it challenging to distinguish the contribution from these two sources independently. In this work, we will present our latest experimental data focused on delineating contributions from vanadium crossover and electrode degradation. The data include two ion-exchange membranes and two electrodes with different degradation behavior. To this end, we have designed and built a unique facility utilizing multiple electrochemical and flow cells equipped with UV/Vis spectroscopy to measure the vanadium ion crossover in real-time 2-6. To assess the capacity decay due to combined degradation effect of all components, we have developed another diagnostic in which we use a symmetric cell set-up for negative (V(II)/V(III)) and positive (V(IV)/V(V)) sides separately. The degradation diagnostics utilize electrochemical impedance spectroscopy to quantify the contributions of cell overpotential during cycling stemming from charge-transfer, ohmic and mass transport. The results of this study should provide more in-depth insight to optimize VRFBs with enhanced performance and reduced ion-crossover and degradation.

Autophagy in the Vertebrate Inner Ear.

Autophagy is a conserved catabolic process that results in the lysosomal degradation of cell components. During development, autophagy is associated with tissue and organ remodeling, and under physiological conditions it is tightly regulated as it plays a housekeeping role in removing misfolded proteins and damaged organelles. The vertebrate inner ear is a complex sensory organ responsible for the perception of sound and for balance. Cell survival, death and proliferation, as well as cell fate specification and differentiation, are processes that are strictly coordinated during the development of the inner ear in order to generate the more than a dozen specialized cell types that constitute this structure. Here, we review the existing evidence that implicates autophagy in the generation of the vertebrate inner ear. At early stages of chicken otic development, inhibiting autophagy impairs neurogenesis and causes aberrant otocyst morphogenesis. Autophagy provides energy for the clearing of dying cells and it favors neuronal differentiation. Moreover, autophagy is required for proper vestibular development in the mouse inner ear. The autophagy-related genes Becn1, Atg4g, Atg5, and Atg9, are expressed in the inner ear from late developmental stages to adulthood, and Atg4b mutants show impaired vestibular behavior associated to defects in otoconial biogenesis that are also common to Atg5 mutants. Autophagic flux appears to be age-regulated, augmenting from perinatal stages to young adulthood in mice. This up-regulation is concomitant with the functional maturation of the hearing receptor. Hence, autophagy can be considered an intracellular pathway fundamental for in vertebrate inner ear development and maturation.

Challenges Considering the Degradation of Cell Components in Commercial Lithium-Ion Cells: A Review and Evaluation of Present Systems.

Owing to the high energy and power density of lithium-ion cells (1200Whkg-1 and 200Whkg-1) and due to their compact design, they are used as energy storage devices in many contemporary mobile applications such as telecommunication systems, notebooks and domestic appliances. Meanwhile their application is not limited only to consumer electronics, they are also standard in hybrid electric (HEVs) and electric vehicles (EVs). However, the profitable application of lithium-ion cells in the automobile industry requires lower costs, lower safety risks, a higher specific energy density and a longer lifetime under everyday conditions. All these aspects are directly or indirectly related to the degradation of the materials in a lithium-ion cell. One possibility for reducing the costs is a second life application of the cells after their usage in (H)EVs. In order to enable this, the safety risks at the end of life of a cell operated in a vehicle have to be reliably predicted. This requires a fundamental knowledge about underlying material degradations during operation. The safety risk of a lithium-ion cell increases during operation because the voltage windows in which the electrodes are cycled shift, resulting in a higher possibility that at least one electrode is operated in a meta- or unstable state. Furthermore, higher impedances due to material degradations lead to increasing heat generation and therefore to an increase in the risk of failure. Higher energy densities can be achieved by raising the end of charge voltage of a cell, causing additional safety risks because many cathode materials tend to decompose at high voltages. Another possibility for achieving higher energy densities is to use nickel-rich or lithium-excess cathode materials, since cathodes are currently limiting the capacity of lithium-ion cells. But these systems show a poor cycling stability (a higher degradation rate). The lifetime of a lithium-ion cell is limited by the degradation of the individual cell components. Although the degradation of materials is the key consideration in achieving lower costs, a higher safety standard, higher energy densities and a longer lifetime, the degradation of the individual cell components in dependence on the operation conditions has hardly been investigated and is poorly understood. The present work reviews known material degradations in commercial lithium-ion cells, shows a way to analyze such degradations in dependence on the operation conditions and describes how these degradation processes lead to observed performance drops.

Passive Mitigation of Capacity Decay in Vanadium Redox Flow Batteries through Asymmetric Cell Configuration

The performance of all-vanadium redox flow batteries (VRFBs) can be significantly improved through improved cell design and material selection. 1 However, there are certain issues yet to be addressed including demonstration of long-term, robust, and stable performance at higher power and efficiency. During the cycling of VRFBs, the capacity of the battery decreases monotonically, and the causes for this loss has yet to be fully studied and understood. The primary contributions to capacity loss are undesired vanadium and water transport through the ion-exchange membrane, degradation of cell components (predominantly electrodes and membrane), and gas-generating side reactions. Appropriate material selection and operating voltage range can greatly reduce degradation and side reactions. However, capacity decay due to vanadium and water transport across the membrane is inevitable. 2-5 Use of thicker membranes and electrolyte rebalancing are partial solutions, but each introduces additional performance losses on the system. Development of new ion exchange membranes with reduced crossover is an active area or exploration with a goal of reduced crossover while maintaining conductivity. However, a little-explored, passive method for decreasing vanadium and water crossover is design of different features that do not necessarily result in any performance loss while reducing the unwanted crossover significantly. In a recent publication from our lab, we studied the effect of the electric field on vanadium crossover and deduced interaction coefficients for quantifying vanadium crossover as a function of state of charge (SoC). As a result, the transport parameters for the solute (vanadium ions) and solvent (water) with and without the effect of electric field and as a function of SoC are now known. 6 In this talk we will report experimental data resulting from investigations into asymmetric cell features designed to passively mitigate the rate of crossover during the cell operation. A unique facility has been designed and built using multiple electrochemical and flow cells to enable real-time quantification of crossover rate. The set-up utilizes UV/Vis spectroscopy in order to assess the vanadium crossover under different operating conditions. The results of this study should provide more in-depth insight to optimize VRFBs with enhanced performance and reduced ion-crossover and pressure drop.