Local Current Density Distribution Research Articles

Do Binders Form Surface Films on Active Particles in Li-Ion Electrodes? Revealing Nanoscopic Surface Binder Morphology in Graphitic Electrodes Using Chemical Staining and High-Resolution Energy-Selective Backscattered Electron Imaging

Although polymeric binders constitute only a small fraction (< 5% volume) of Li-ion electrodes, they are an essential component of Li-ion batteries, binding otherwise loose active particles to each other and to the current collector. Yet, despite more than 30 years of development of Li-ion batteries, the exact morphology that binders adopt on and around the active particle surfaces in the electrodes remains extremely difficult to assess, similarly to the fraction of active particle surface covered by the binder. It is already well established that binder chemistry strongly influences key battery surface reactions, such as Li insertion/deinsertion or formation of solid electrolyte interface (SEI).1,2 Also, binder chemistry can be a decisive factor in reaching long cycle stability over rapid failure of, for example, silicon-based electrodes.3 Therefore, quantifying surface coverage of the binders on active particles remains the missing piece for fully understanding binder roles in batteries, and can open new avenues for improving lifetime and rate performance of current and next generation electrodes.In this work, we present a newly established method for large-scale, high-resolution imaging and quantification of carboxymethyl cellulose (CMC) and styrene butadiene rubber (SBR) binders in graphitic Li-ion electrodes. The imaging was enabled using highly selective chemical staining of the binders with high atomic number elements that act as excellent contrast agents during backscattered electron (BSE) imaging. Following staining of the binders, we imaged them using a variant of BSE known as energy-selective backscattered electron imaging (EsB), which operates at low beam voltage and can provide nanometer-level resolution by selective energy filtering of backscattered electrons. By acquiring images at different beam voltages, we selectively captured different fine-scale morphological details of the binder on and around the graphite particles. We revealed binder/carbon additive agglomerates, islands of non-dispersed SBR nanoparticles and, for the first time, details of a continuous thin layer formed by CMC and SBR on the graphite surface that spans across the entire graphitic electrode. Using a combination of Monte Carlo simulations and high resolution cross-sectional EsB imaging, we estimated the thickness of this surface film to be only 10 nanometers. Because of such small thickness, the film adopts the morphology of the underlying graphite surface, which is why it cannot be observed using conventional secondary electron imaging, even at very low beam voltages. Using quantitative image analysis, we also characterized electrodes before and after calendering, finding that calendering shatters the previously-continuous binder film, leaving only 30% of graphitic surfaces covered by irregular patches of the binder layer. We also verified our results by analyzing commercial graphitic electrodes used in electric vehicle batteries, finding identical binder morphologies inside these electrodes.Considering the likely impact of binder coverage on e.g. active particle stability, SEI formation or distribution of local current density during electrochemical cycling, we suggest that this new ability to rapidly image and quantify binder coverage on active particle surfaces will open new avenues to optimize Li-ion electrodes, bridging the gaps between the chemistry, processing and performance of binder-active particle interfaces.(1) Fedorova, A. A.; Levin, O. V.; Eliseeva, S. N.; Katrašnik, T.; Anishchenko, D. V. Investigating the Coating Effect on Charge Transfer Mechanisms in Composite Electrodes for Lithium-Ion Batteries. Int. J. Mol. Sci. 2023, 24.(2) Young, B. T.; Nguyen, C. C.; Lobach, A.; Heskett, D. R.; Woicik, J. C.; Lucht, B. L. Role of Binders in Solid Electrolyte Interphase Formation in Lithium Ion Batteries Studied with Hard X-Ray Photoelectron Spectroscopy. J. Mater. Res. 2019, 34, 97–106.(3) Jung, C. H.; Kim, K. H.; Hong, S. H. Stable Silicon Anode for Lithium-Ion Batteries through Covalent Bond Formation with a Binder via Esterification. ACS Appl. Mater. Interfaces 2019, 11, 26753–26763.Figure 1. Combined secondary electron image (left) and color-enhanced EsB image (right) of an internal part of uncalendered graphitic electrode with chemically stained CMC binder (colored green in the EsB image). Figure 1

Magnetic Field Analysis for State of Health Monitoring of PEM Electrolyzer Stacks

The expected increase in the number of installed PEM electrolyzers during their industrialization in the upcoming years highlights the need for suitable non-destructive diagnostic methods for state of health monitoring and anomaly detection to ensure reliability and durability while reducing lifetime costs. The inner electrical current density distribution significantly impacts the efficiency and lifetime of a PEM electrolyzer stack. During operation, various degradation phenomena and inhomogeneities, including inhomogeneous water and cooling management, starvation effects, contact pressure, and delamination, influence its electric conductivity and current density distribution. These, in turn, affect the generated vectorial magnetic field distribution inside and outside the stack.This work examines the use of non-destructive magnetic field analysis (MFA) to identify changes in the outer magnetic field distribution and, thus, local current density distributions within PEM electrolyzer stacks. The magnetic field distribution is analyzed in all three spatial directions to trace electrical currents and identify electrical defects during different operating conditions. Accordingly, signatures in magnetic field images allow for the distinction between normal and abnormal system behavior. For initial investigations, creating a parameterized stack model using the finite element method (FEM) enabled the analysis of different stack geometries and their outer magnetic fields. The following examinations evaluated the effect of electric inhomogeneities on the magnetic field signatures, showing unique patterns depending on defect location and current density distribution. Both results were used to determine resolution limits, which enable the development of suitable sensor hardware and measurement concepts for industrial operating conditions. These concepts were initially tested and validated using a test stack designed to emulate the electrical behavior of an operational PEM electrolyzer stack without electrochemical reactions. Figure 1 shows one stylized measurement plane, along with the Bx, By, and Bz magnetic field component scans of the test stack in a non-defective state. Following these measurements, artificial defects are induced. After repeated experiments with an electrochemical operating stack, the work presents, compares, and discusses the resulting magnetic fingerprints of both stacks. Additionally, an overview of expected resolvable current-related defects is provided.Magnetic field simulations and measurements conducted on a PEM electrolyzer test stack show systematic differences depending on defect location and current density distribution, resulting in characteristic magnetic field images. In addition, comparative experiments with an operating stack are presented and discussed, determining the potential and limitations of the method. Furthermore, enhancing Magnetic Field Analysis for industrial applications using machine learning methods will be assessed. These initial results suggest that MFA is potentially useful as a non-destructive diagnostic state of health monitoring method for industrial PEM electrolyzer stacks. Figure 1

Overvoltage Analysis of the Heterogeneous-Structure Effect of PEMFC Cathodes

Catalyst layer (CL) design of polymer electrolyte membrane fuel cells (PEMFCs) requires an understanding of the contribution of each physicochemical process to overvoltage. In this study, the effect of the heterogeneous CL structure on the overvoltage of each process was numerically analyzed. Using a previously validated model [1], a heterogeneous CL structure was constructed based on the fabrication conditions of an actual CL. The Pt catalyst was distributed, and the effective diffusion coefficients of oxygen and vapor and the effective conductivities of protons and electrons were calculated locally based on the void, ionomer, and carbon structures. For comparison, a homogeneous CL structure with an averaged local Pt content, effective diffusion coefficients, and effective conductivities was constructed. Subsequently, the reaction and mass transport were calculated using the heterogeneous and homogeneous models, followed by overvoltage separation based on local power losses. Figure 1 shows the local current density distributions and overvoltage differences of the two models calculated at a cell temperature (Tcell) of 80 °C, relative humidity (RH) of 50%, and an oxygen partial pressure (pO2) of 0.2 atm. The local current density in heterogeneous model has a discrete distribution, while that in homogeneous model has a continuous distribution. Although the activation overvoltage is smaller in the heterogeneous model, the overvoltage difference is relatively small. In contrast, the overvoltages of oxygen and proton transport are larger in the heterogeneous model. Furthermore, these mass transport-related overvoltages increase with increasing current density. In this contribution, the effect of the heterogeneous CL structure on each overvoltage will be comprehensively discussed by varying the operating conditions.Reference[1] A. Tanaka, G. Inoue, K. Nagato, and M. Nakao, Available at SSRN: http://dx.doi.org/10.2139/ssrn.4745148. Figure 1

Effects of Contact Loss at Electrolyte/Negative Electrode Interface on Current Density Distribution in Solid-State Batteries

Cyclic volume changes and non-uniform electrodeposition/stripping, among other cycling-induced chemo-mechanical degradation of lithium metal and lithium-alloy solid state batteries, lead to contact loss between the anode and the solid electrolyte separator. Operando experiments have shown accelerated short-circuiting behavior due to contact loss in “anode-free” solid-state batteries. Simulations have shown the relationship between active area fraction and the ratio of effective conductivities in regular-shape active area configurations. Through modeling experiments using imputed active contact area of lithium-metal negative electrode batteries, we quantify the effects of this contact loss. Specifically, we (1) quantify the interfacial resistance due to this contact loss, (2) show non-uniform local current density distribution such that evaluation of what area fraction has current exceeding critical current densities is possible, and (3) show non-uniform reaction distribution at the positive electrode. This work sheds light on the tradeoffs in the design of solid state batteries within the context of contact loss.

Experimental investigation on operational stability and its influencing mechanisms for PEMFC with dead-ended anode

Experimental investigation on operational stability and its influencing mechanisms for PEMFC with dead-ended anode

Design of Lithium Metal Anode and Other High-Capacity Alloy Anodes Solid-State Batteries in Context of Contact Loss between Anode and Solid Electrolyte Separator

Cyclic volume changes and non-uniform electrodeposition/stripping, among other cycling-induced chemo-mechanical degradation of lithium metal and lithium-alloy solid state batteries, lead to contact loss between the anode and the solid electrolyte separator[1, 2]. In-operando experiments have shown ac-celerated short-circuiting behavior due to contact loss in “anode-free” solid-state batteries[2]. Simulations reveal the relationship between active area fraction and the ratio of effective conductivities in made-up active area configurations[3]. Through modeling experiments using imputed active con-tact area of lithium-metal anode batteries, we quantify the effects of this contact loss in terms of accelerated chemo-mechanical degradation and de-creased rate capability. Specifically, we (1) quantify the interfacial resistance due to this contact loss, (2) show non-uniform local current density distribution such that local current densities could exceed lithium filament growth critical current densities, (3) show uniaxial stress inhomogeneity due to non-uniform reaction at the anode/separator interface, and (4) show non-uniform reaction distribution at the positive electrode.Besides allowing for the optimization of designs to minimize contact loss, our work sheds light on tradeoffs in the design of solid electrolyte separators.

A Large-Scale Fabrication of Flexible, Ultrathin, and Robust Solid Electrolyte for Solid-State Lithium-Sulfur Batteries.

All-solid-state lithium metal batteries (ASSLMBs) are considered as the most promising candidates for the next-generation high-safety batteries. To achieve high energy density in ASSLMBs, it is essential that the solid-state electrolytes (SSEs) are lightweight, thin, and possess superior electrochemical stability. In this study, a feasible and scalable fabrication approach to construct 3D supporting skeleton using an electro-blown spinning technique is proposed. This skeleton not only enhances the mechanical strength but also hinders the migration of Li-salt anions, improving the lithium-ion transference number of the SSE. This provides a homogeneous distribution of Li-ion flux and local current density, promoting uniform Li deposition. As a result, based on the mechanically robust and thin SSEs, the Li symmetric cells show outstanding Li plating/stripping reversibility. Besides, a stableinterfacecontact between SSE and Li anode has been established with the formation of an F-enriched solid electrolyte interface layer. The solid-state Li|sulfurized polyacrylonitrile (Li|SPAN) cell achieves a capacity retention ratio of 94.0% after 350 cycles at 0.5 C. Also, the high-voltage Li|LCO cell shows a capacity retention of 92.4% at 0.5 C after 500 cycles. This fabrication approach for SSEs is applicable for commercially large-scale production and application in high-energy-density and high-safety ASSLMBs.

Multiscale study of reactive transport and multiphase heat transfer processes in catalyst layers of proton exchange membrane fuel cells

Improving the performance of proton exchange membrane fuel cells (PEMFCs) requires deep understanding of the reactive transport processes inside the catalyst layers (CLs). In this study, a particle-overlapping model is developed for accurately describing the hierarchical structures and oxygen reactive transport processes in CLs. The analytical solutions derived from this model indicate that carbon particle overlap increases ionomer thickness, reduces specific surface areas of ionomer and carbon, and further intensifies the local oxygen transport resistance (Rother). The relationship between Rother and roughness factor predicted by the model in the range of 800-1600 s m-1 agrees well with the experiments. Then, a multiscale model is developed by coupling the particle-overlapping model with cell-scale models, which is validated by comparing with the polarization curves and local current density distribution obtained in experiments. The relative error of local current density distribution is below 15% in the ohmic polarization region. Finally, the multiscale model is employed to explore effects of CL structural parameters including Pt loading, I/C, ionomer coverage and carbon particle radius on the cell performance as well as the phase-change-induced (PCI) flow and capillary-driven (CD) flow in CL. The result demonstrates that the CL structural parameters have significant effects on the cell performance as well as the PCI and CD flows. Optimizing the CL structure can increase the current density and further enhance the heat-pipe effect within the CL, leading to overall higher PCI and CD rates. The maximum increase of PCI and CD rates can exceed 145%. Besides, the enhanced heat-pipe effect causes the reverse flow regions of PCI and CD near the CL/PEM interface, which can occupy about 30% of the CL. The multiscale model significantly contributes to a deep understanding of reactive transport and multiphase heat transfer processes inside PEMFCs.

Towards reusable 3D-printed graphite framework for zinc anode in aqueous zinc battery

Towards reusable 3D-printed graphite framework for zinc anode in aqueous zinc battery

Study on the effect of NO2 impurity gas on the performance and local current density distribution of PEMFC

Study on the effect of NO2 impurity gas on the performance and local current density distribution of PEMFC

Fault Detection and Identification for Polymer Electrolyte Membrane Fuel Cell Stack by External Magnetic Field

Many technological locks prevent the deployment of Proton Exchange Membrane Fuel Cell (PEMFC). Particularly for vehicle applications, cost and durability represent two of the most significant challenges to achieve clean, reliable, and cost-effective PEMFC systems. Solving these shortcomings will be a great opportunity for a decisive breakthrough towards mass-diffusion of the current PEMFC technology. The long-term electrical performance losses are associated to either the degradation of the MEA constitutive materials or due to specific operating conditions (flooding, drying, etc.). In perspective, local current density distribution may support stack-level degradation analyzes as well as effective stack control to mitigate the consequences of degradation due to load cycles (electrochemical, thermal, mechanical and humidity effects) or faults.External magnetic field measurement (MFM) shows a high potential in PEMFC non-invasive diagnosis. Thus, 2D and 3D current distributions and their anomalies in the fuel cell can be identified independent of the size of the causing fault.To perform this local characterization, the external magnetic field measurement will enable to model the current density in stationary conditions over the cell surface and for the different cells of the stack. This methodology requires the complementary development of magnetic field techniques and inverse models.In this work, this challenge is tackled by using tailored defective MEAs and specific operating conditions (flooding, drying, ...) to characterize, how local and overall performances of the MEA are affected and to identify the signatures of the various anomalies. Figure 1

Using Magnetic Field Analysis for Localizing Defects of Fuel Cell & Electrolyzer Components

Production capacities of electrolysis and fuel cell technologies are expected to increase significantly in the upcoming years, reducing costs of stack components through numbering-up. To ensure reliability and durability and reduce costs along the manufacturing process, developing suitable in-line non-destructive diagnostic methods for quality control becomes essential for their industrialization.In both fuel cell and electrolyzer stacks, the main components' electrical resistance and current density distribution greatly influence stack efficiency and longevity. Here, the flowing electric current generates a magnetic field depending on its strength and direction. Potential defects caused by the manufacturing process, including cracks, defective welding spots, coating adhesion issues, delamination, and contamination, influence the components' electric conductivity and current density distribution and hence the magnetic field distribution.This work investigates non-destructive diagnostic methods using magnetic field analysis (MFA) to identify changes in the magnetic field distribution and, thus, local electrical resistance and current density distributions of fuel cell and electrolyzer components. The methods used are magnetic field imaging (MFI) and Eddy Current Testing (ECT). MFI analyzes the magnetic field distribution in all three spatial directions to trace electrical currents and identify electrical defects, creating a magnetic field signature that can potentially distinguish between functional and non-functional components along the manufacturing process. ECT measures variations in local conductivity by inducing eddy currents in the sample through an alternating magnetic field generated by a sender coil. These eddy currents create a detectable magnetic field in a receiver and are affected by defects and changes in electrical conductivity. Therefore, the method can characterize sheet resistance and material homogeneity through electrical anisotropy in electrically conductive components.In initial experiments, ECT measurements on coated and uncoated hollow embossed stainless steel bipolar half plates showed systematic differences depending on quality characteristics resulting in unique patterns and inhomogeneities which require further investigation. Furthermore, experiments with both methods on other stack components will be presented and discussed. In addition, their in-line capability will be assessed and evaluated. However, these first promising results imply that MFA is potentially useful as an in-line, non-destructive diagnostic method for quality control.

Unraveling the Coupling Effect between Cathode and Anode toward Practical Lithium-Sulfur Batteries.

The localized reaction heterogeneity of the sulfur cathode and the uneven Li deposition on the Li anode are intractable issues for lithium-sulfur (Li-S) batteries under practical operation. Despite impressive progress in separately optimizing the sulfur cathode or Li anode, a comprehensive understanding of the highly coupled relationship between the cathode and anode is still lacking. In this work, inspired by the Butler-Volmer equation, a binary descriptor (IBD ) assisting the rational structural design of sulfur cathode by simultaneously considering the mass-transport index (Imass ) and the charge-transfer index (Icharge ) is identified, and subsequently the relationship between IBD and the morphological evolution of Li anode is established. Guided by the IBD , a scalable electrode providing interpenetrated flow channels for efficient mass/charge transfer, full utilization of active sulfur, and mechanically elastic support for aggressive electrochemical reactions under practical conditions is reported. These characteristics induce a homogenous distribution of local current densities and reduced reaction heterogeneity on both sides of the cathode and anode. Impressive energy density of 318Wh kg-1 and 473Wh L-1 in an Ah-level pouch cell can be achieved by the design concept. This work offers a promising paradigm for unlocking the interaction between cathode and anode and designing high-energy practical Li-S batteries.

Interaction phenomena of electrically coupled cells under local reactant starvation in automotive PEMFC stacks

The local current density distribution of polymer electrolyte membrane fuel cells (PEMFCs) can be distorted by various error states. Differences in current density distributions (CDDs) of adjacent cells in a stack are equilibrized by in-plane currents within the sandwiched bipolar plates. Degradation stressors such as detrimental differences in local cell voltage and current density maxima can thus be generated. A novel method was therefore developed to intentionally manipulate CDD profiles by integrating local artificial starvation into only one fuel cell in an assembly. This technique is applied to automotive-sized PEMFCs single cells as well as in 20 cell short-stack to analyze such voltage and current redistribution phenomena. A drastic distortion of local cell voltage is only observed for stacks, which is explained by a supplementary simulation. The local voltage distribution of an electrically coupled fuel cell is therefore calculated by combining CDD measurements with a spatially resolved polarization curve model. The capabilities and limits of a multipoint cell voltage monitoring measurement device are discussed on this basis. The inspected correlation between these two independent online measurement techniques allows to localize such error states with considerable accuracy during operation of automotive sized PEMFC stacks.

Investigating Different Local Polyurethane Coatings Degradation Effects and Corrosion Behaivors by Talaromyces funiculosus via Wire Beam Electrodes.

The degradation effect of mold on the coating in a hot and humid environment is one of the important factors that cause layer failure. Combined with the wire beam electrode (WBE) and the traditional surface analysis technique, the local biodegradation of the coatings and the corrosion behaviors of metal substrates can be characterized accurately by a WBE. Herein, a WBE was used to study the degradation impact of Talaromyces funiculosus (T. funiculosus) isolated from a tropical rainforest environment on the corrosion of polyurethane (PU) coating. After immersion for 14 days, the local current density distribution of the WBE surface can reach ~10-3 A/cm2 in the fungal liquid mediums but maintains ~10-7 A/cm2 in sterile liquid mediums. The |Z|0.01Hz value of the high current densities area (#85 electrode) was 1.06 × 109 Ω cm2 in a fungal liquid medium after 14 days of immersion. After being attacked by T. funiculosus, the degradation of the PU was more severe, and there were wrinkles, cracks, blisters, and even micro-holes distributed randomly on the surface of electrodes. This resulted from the self-corrosion caused by the T. funiculosus degradation of the coating; the corrosion caused by the electric coupling effect of the coating was introduced. Energy dispersive spectroscopy (EDS) and Raman spectra results showed that the corrosion products were flakey and globular, which consisted of γ-FeOOH, γ-Fe2O3, and α-FeOOH.

Experimentally investigation on current density distribution characteristics of hydrogen-oxygen proton exchange membrane fuel cells under dynamic loading

The performance improvement and mitigate degradation of hydrogen-oxygen proton exchange membrane fuel cells (PEMFCs) are of great significance for accelerating the practical application of clean energy and alleviating the energy crisis. In this work, a PEMFC with an active area of 25cm2 was designed based on multilayer printed circuit board technology for high-resolution current density mapping. The characteristics of uneven distribution of local current density under dynamic loading and its influence on performance degradation are further analyzed. The results show that the uneven density distribution at low current density is caused by membrane dehydration and gas starvation, while at high current density, it is caused by the combined effect of gas starvation, and the uneven current density distribution is even worse at high current density. In addition, oxygen starvation causes more worse uneven density distribution than that of hydrogen starvation, and the lowest current density is concentrated near the cathode outlet. What's more, the uneven distribution of local current density led to serious performance degradation, the performance degradation reached 40.03%, the electrochemical active surface area decreased by 31.87% and charge transfer resistance increased by 22.08%. The scanning electron microscope and energy dispersive X-ray spectrometry show that performance degradation is due to the loss of catalysts, especially near the cathode outlet.

Locally regulating Li+ distribution on an electrode surface with Li-Sn alloying nanoparticles for stable lithium metal anodes.

Despite the fact that lithium metal batteries (LMBs) have the advantage of higher energy density than traditional lithium-ion batteries (LIBs), the development of Li anodes is hindered by the issues of dendritic Li growth and parasitic reactions during cycling, which can cause a coulombic efficiency decrease and capacity decay. Herein, a Li-Sn composite anode is developed by a facile rolling method. The in situ generated Li22Sn5 nanoparticles are uniformly distributed in the Li-Sn anode after the rolling process. The Li22Sn5 nanoparticles on the surface of the electrode exhibit excellent lithiophilicity, reducing the Li nucleation barrier. Multiphysics phase simulation discloses the distribution of local current density around the holes, guiding Li preferentially to deposit back onto the sites of previous Li stripping, and then realizing a controllable plating/stripping behavior of Li on the Li-Sn composite anode. Consequently, the symmetrical cell of Li-Sn||Li-Sn achieves a stable cycling lifetime of more than 1200 h at a current density of 1 mA cm-2 with a fixed capacity of 1 mA h cm-2. Besides, the full cell pairing with the LiFePO4 cathode delivers excellent rate performance and capacity retention after long cycles. This work provides new insight to modify the Li metal for preparing dendrite-free anodes.

Electrodeposition model with dynamic ion diffusion coefficients for predicting void defects in electroformed microcolumn arrays.

Due to the confined mass transfer capability in microchannels, void defects are easily formed in electroformed microcolumn arrays with a high depth/width ratio, which seriously affects the life and performance of micro-devices. The width of the microchannel constantly decreases during electrodeposition, which further deteriorates the mass transfer capability inside the microchannel at the cathode. In the traditional micro-electroforming simulation model, the change of the ion diffusion coefficient is always ignored, making it difficult to accurately predict the size of void defects prior to electroforming experiments. In this study, nickel ion diffusion coefficients in microchannels are tested based on the electrochemical experiments. The measured diffusion coefficients decrease from 4.74 × 10-9 to 1.27 × 10-9 m2 s-1, corresponding to microchannels with a width from 120 to 24 μm. The simulation models of both constant and dynamic diffusion coefficients are established, and the corresponding simulation results are compared with the void defects obtained using micro-electroforming experiments. The results show that when the cathode current densities are 1, 2 and 4 A dm-2, the size of void defects obtained with the dynamic diffusion coefficient model is closer to the experimental results. In the dynamic diffusion coefficient model, the local current density and ion concentration distribution proves to be more inhomogeneous, leading to a big difference in the deposition rate of nickel between the bottom and the opening of a microchannel, and consequently a larger void defect in the electroformed microcolumn arrays. In brief, the ion diffusion coefficient inside microchannels with a different width is tested experimentally, which provides a reference for developing reliable micro-electroforming simulation models.

Electrodeposited 3D lithiophilic Ni microvia host for long cycling Li metal anode at high current density

Electrodeposited 3D lithiophilic Ni microvia host for long cycling Li metal anode at high current density

Local ageing effects of polymer electrolyte fuel cell membrane electrode assemblies due to accelerated durability testing

AbstractAccelerated durability test (ADT) protocols are useful tools to reduce testing time and development costs of automotive polymer electrolyte fuel cell stacks. Established accelerated stress tests allow comparing individual cell components. However, such tests in general do not allow drawing reliable conclusions on the expected lifetime for a complete stack. In this work, we examine the influence of combined stressors on the ageing behavior of individual cell components operated on stack level. We combine known main stressors for mobile fuel‐cell operation such as dynamic load, temperature and humidity cycling or hydrogen/air fronts during start‐up to develop a new accelerated test protocol. It was applied to an automotive 5‐cell short stack for 460 operating hours (OpH). A second stack was operated in a reference long‐term test for 2300 OpH. Several in situ characterization techniques, such as cyclic voltammetry, and recording the local current density distribution were employed. In addition, post‐mortem analyses, such as focused ion beam scanning electron microscopy imaging, was applied in order to better understand the degradation mechanisms. The results presented here provide an excellent basis for the further development of a new ADT protocol, which will accelerate ageing processes in the fuel cell in a realistic way, i.e. leading to similar degradation characteristics as in long term testing.