Local Current Distribution Research Articles

Humidity-Induced Degradation Mapping of Pt3Co ORR Catalyst for PEFC by In-Operando Electrochemistry and Ex Situ SAXS.

Understanding the degradation mechanisms of Pt-alloy catalysts is crucial for enhancing their durability. This study investigates the impact of relative humidity on Pt and Pt3Co catalysts using potential-cycling-based accelerated stress tests. Two conditions are investigated: 100% relative humidity on both sides, and a gradient with 30% at the anode and over 100% at the cathode. Pt3Co demonstrates sensitivity, with 77% performance loss and reductions in electrocatalyst surface area. Results demonstrate a 30% decrease in potential loss for Pt catalysts and a 77% increase for Pt3Co catalysts, indicating significant performance degradation in high humidity conditions, with Pt3Co exhibiting greater sensitivity. Measurements of electrochemically active surface area reinforce these findings. Resistance analysis using electrochemical impedance spectroscopy using equivalent circuit modeling reveals a threefold increase in Pt3Co MEAs' cathode charge transfer resistance and mass transport resistance during accelerated stress tests. Local current distribution analysis highlights differences between Pt catalyst and Pt3Co, with the latter displaying dealloying effects. Small-angle X-ray scattering reveals changes in particle and cluster sizes, indicating structural changes. Scanning electron microscopy highlights catalyst and membrane thickness variations, suggesting heterogeneity in Pt3Co. Under humidity gradients, Ostwald ripening plays a significant role in altering the catalyst's Pt3Co structure and subsequently impacting its performance.

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

Proton exchange membrane fuel cell (PEMFC) with dead-ended anode (DEA) suffers from nitrogen diffusion and water accumulation, leading to unstable performance. The core of this paper is to enhance the stability of DEA operation. By coupling the flow field structure with the DEA mode, the factors affecting the stability are explored, the performance degradation mechanism after DEA operation is revealed, and the purging strategy is formulated by combining the energy management with the voltage stability as a prerequisite. The experimental results show that the serpentine flow field is advantageous for maintaining the most stable DEA operation with a minimum voltage recession of 17.01 mV and a voltage undershoot of 11.63 mV. The local current density distribution exhibited a pattern of highest values at anode inlet and lowest at anode outlet, which could be improved by increasing operating pressure and reducing load current density. In this experiment, PCB was innovatively combined to investigate the degradation of each region of PEMFC after 60h of DEA operation. It is found that the most severe performance degradation occurs in anode outlet with a degradation rate exceeding 50%, while the center area has a degradation rate of no more than 20%.

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.

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

Aqueous zinc ion batteries (AZIBs) are an increasingly popular high-safety and eco-friendly energy storage solution. However, the development of high-performance zinc (Zn) anodes remains a formidable challenge, primarily due to dendrite formation and poor reversibility. To address these challenges, this study harnesses the potential of digital light process (DLP) 3D printing technology to fabricate reduced graphite oxide-based 3D gyroid structure (3DP-rGG) as zinc anode frameworks for aqueous zinc batteries. The 3D-printed structure effectively regulates local current density distribution, offering ample nucleation sites and free space for inducing uniform zinc deposition and accommodating diminutive zinc nodules. Consequently, the 3D-printed graphite framework demonstrates remarkable reversibility in zinc plating and stripping processes, resulting in commendable coulombic efficiency and low voltage hysteresis. The full battery with a 3D-printed zinc anode, incorporating a polyaniline-intercalated vanadium oxide cathode (PVO), exhibits high specific capacity and superior long-term cycling stability. Remarkably, the robust 3DP-rGG structure can be reused over ten times without any discernible impact on its electrochemical performance, thereby underscoring the potential of this controllable and efficient fabrication of 3D graphite current collectors as a promising solution to develop reusable 3D frameworks for high-performance metal batteries.

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

The performance of proton exchange membrane fuel cells (PEMFCs) is affected by impurities, and airborne NO2 is a potential factor in the degradation of the performance and durability of PEMFCs. Herein, the effect of 50 ppb ∼ 5 ppm NO2 on PEMFC was investigated by the poisoning strategy of increasing concentration gradient, and the effect of NO2 on the local current density distribution was explored in both galvanostatic and potentiostatic states. The results showed that 2 ppm NO2 caused a significant voltage decay accompanied by an increase in activation impedance and mass transfer impedance. NO2 was decomposed into oxygen atoms and adsorbed NO on the Pt surface, occupying active sites, impeding oxygen reduction reaction, and further hindering mass transfer. Polarization curve results showed more pronounced voltage decay at high current densities. Polarization curve testing and clean air purging were effective in restoring the poisoned PEMFC. Moreover, it was proved that the poisoning effect is more severe in the inlet region, especially in potentiostatic state. Hence, it is suggested to operate in galvanostatic state, which has a positive impact on reducing the uneven performance caused by NO2. This study provides a reference for the prevention of PEMFC poisoning and performance recovery after poisoning.

The time-domain Cartesian multipole expansion of electromagnetic fields

Time-domain solutions of Maxwell’s equations in homogeneous and isotropic media are paramount to studying transient or broadband phenomena. However, analytical solutions are generally unavailable for practical applications, while numerical solutions are computationally intensive and require significant memory. Semi-analytical solutions (e.g., series expansion), such as those provided by the current theoretical framework of the multipole expansion, can be discouraging for practical case studies. This paper shows how sophisticated mathematical tools standard in modern physics can be leveraged to find semi-analytical solutions for arbitrary localized time-varying current distributions thanks to the novel time-domain Cartesian multipole expansion. We present the theory, apply it to a concrete application involving the imaging of an intricate current distribution, verify our results with an existing analytical approach, and compare the proposed method to a finite-difference time-domain numerical simulation. Thanks to the concept of current “pixels” introduced in this paper, we derive time-domain semi-analytical solutions of Maxwell’s equations for arbitrary planar geometries.

Design and Development of Flow Fields with Multiple Inlets or Outlets in Vanadium Redox Flow Batteries

In vanadium redox flow batteries, the flow field geometry plays a dramatic role on the distribution of the electrolyte and its design results from the trade-off between high battery performance and low pressure drops. In the literature, it was demonstrated that electrolyte permeation through the porous electrode is mainly regulated by pressure difference between adjacent channels, leading to the presence of under-the-rib fluxes. With the support of a 3D computational fluid dynamic model, this work presents two novel flow field geometries that are designed to tune the direction of the pressure gradients between channels in order to promote the under-the-rib fluxes mechanism. The first geometry is named Two Outlets and exploits the splitting of the electrolyte flow into two adjacent interdigitated layouts with the aim to give to the pressure gradient a more transverse direction with respect to the channels, raising the intensity of under-the-rib fluxes and making their distribution more uniform throughout the electrode area. The second geometry is named Four Inlets and presents four inlets located at the corners of the distributor, with an interdigitated-like layout radially oriented from each inlet to one single central outlet, with the concept of reducing the heterogeneity of the flow velocity within the electrode. Subsequently, flow fields performance is verified experimentally adopting a segmented hardware in symmetric cell configuration with positive electrolyte, which permits the measurement of local current distribution and local electrochemical impedance spectroscopy. Compared to a conventional interdigitated geometry, both the developed configurations permit a significant decrease in the pressure drops without any reduction in battery performance. In the Four Inlets flow field the pressure drop reduction is more evident (up to 50%) due to the lower electrolyte velocities in the feeding channels, while the Two Outlets configuration guarantees a more homogeneous current density distribution.

Multifunctional Double Layer Based on Regional Segregation for Stabilized and Dendrite‐Free Solid‐State Li Batteries

AbstractThe Li dendrite problem triggered by the inhomogeneous deposition of Li and the reduction of Li+ in the electrolyte has seriously hindered the practical application of garnet‐based solid‐state batteries. To address this issue, a multifunctional double layer (MDL) based on the phenomenon of segregation during welding is introduced between the garnet and the Li anode. BiLi3/LiCl3 interlayer with a double‐layer structure is constructed by modulating the cooling rate. The LiCl3 enriched on the electrolyte side exhibits extremely low electronic conductivity, effectively blocking electrons and preventing electrolyte attack. On the anode side, the BiLi3‐enriched layer regulates local current distribution, ensuring uniform deposition/exfoliation of Li and preventing dendrite formation at the interface. Furthermore, this welding‐based preparation method achieves a strong and secure connection between the metal electrode and the ceramic electrolyte. Hence, this Li|LLZTO‐MDL|Li battery with double‐layer special structural interfacial modification can realize a high critical current density of 2.9 mA cm−2 and can be stably cycled for more than 10 000 h at 0.3 mA cm−2.

Investigating the transient electrical behaviors in PEM fuel cells under various platinum distributions within cathode catalyst layers

The spatial distribution of platinum (Pt) within the cathode catalyst layer (CCL) is vital for the electrochemical reactions and mass transport in fuel cells. Though important, the transient effects of these distributions are seldom explored. This study examines the impact of Pt distribution on transient electrical behaviors, including voltage and local current distribution (LCD) uniformity, using a transient, two-dimensional, two-phase, non-isothermal fuel cell model that incorporates catalyst agglomerate. Three Pt distribution types are investigated: uniform, MPL-side biased, and PEM-side biased. Results indicate a voltage undershoot occurs during current loading. Compared to the homogeneous CCL, PEM-side bias reduces this undershoot by 12.5% due to shortened proton transfer paths and decreased ohmic loss, while MPL-side bias increases it by 18.8% due to the inverse effect. Additionally, Pt distribution affects both oxygen transport and reaction resistance within the agglomerate, influencing LCD uniformity. Under loading conditions, gradient CCLs show inferior LCD uniformity than homogeneous ones. Peak non-uniformity values of 0.22, 0.59, and 0.71 are observed for homogeneous, MPL-biased, and PEM-biased CCLs, respectively. From the perspective of voltage and LCD uniformity, the MPL-side biased CCL is not found to enhance dynamic characteristics, whereas the PEM-side bias improves voltage undershoot but at the cost of LCD uniformity. This study provides a novel perspective on fuel cell dynamics, emphasizing the transient effects of Pt distribution and their potential for optimizing dynamic performance by adjusting the Pt gradient.

Practical potential of suspension electrodes for enhanced limiting currents in electrochemical CO2 reduction.

CO2 conversion is an important part of the transition towards clean fuels and chemicals. However, low solubility of CO2 in water and its slow diffusion cause mass transfer limitations in aqueous electrochemical CO2 reduction. This significantly limits the partial current densities towards any desired CO2-reduction product. We propose using flowable suspension electrodes to spread the current over a larger volume and alleviate mass transfer limitations, which could allow high partial current densities for CO2 conversion even in aqueous environments. To identify the requirements for a well-performing suspension electrode, we use a transmission line model to simulate the local electric and ionic current distributions throughout a channel and show that the electrocatalysis is best distributed over the catholyte volume when the electric, ionic and charge transfer resistances are balanced. In addition, we used electrochemical impedance spectroscopy to measure the different resistance contributions and correlated the results with rheology measurements to show that particle size and shape impact the ever-present trade-off between conductivity and flowability. We combine the modelling and experimental results to evaluate which carbon type is most suitable for use in a suspension electrode for CO2 reduction, and predict a good reaction distribution throughout activated carbon and carbon black suspensions. Finally, we tested several suspension electrodes in a CO2 electrolyzer. Even though mass transport limitations should be reduced, the CO partial current densities are capped at 2.8 mA cm-2, which may be due to engineering limitations. We conclude that using suspension electrodes is challenging for sensitive reactions like CO2 reduction, and may be more suitable for use in other electrochemical conversion reactions suffering from mass transfer limitations that are less affected by competing reactions and contaminations.

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.

A magnetic-assisted construction of functional gradient interlayer for dendrite-free solid-state lithium batteries

Garnet-based solid-state Li batteries are considered as important candidates of the next generation batteries due to their potentially high energy density and reliable safety, however the Li dendrite issue is a serious impediment to their further development. Herein, a functional gradient interlayer (FGIL) is introduced at the interface between the garnet and Li anode, which is formed by the in-situ reaction of molten Li with FeF3 assisted by a magnetic force. The FGIL not only reduces the interfacial impedance, evens out the local current distribution, and prevents the growth of Li dendrites on the electrode surface, but also blocks electron transport and prevents the formation of "Li filaments" inside the electrolyte. Consequently, the Li|LLZTO-FGIL|Li cells have a critical current density of up to 2.3 mA cm−2 and exhibit stable cycling for more than 3400 h at 0.3 mA cm−2.

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 the Effects of Cascading Accelerated Stress Tests (ASTs) on the Localized Electrochemical Performance Degradation in Polymer Electrolyte Fuel Cells (PEFCs)

With a recent shift in focus from light-duty to heavy-duty vehicle applications, the durability and performance targets for polymer electrolyte fuel cells (PEFCs) have become even more stringent and challenging to achieve; for example, a net power output of 2.5 kW/g-PGM (1.07 A/cm2 current density) at 0.7 V is required after 25,000 hour-equivalent accelerated stress test (AST) [1]. Generally, different ASTs are designed to evaluate Pt electrocatalyst and support durability; for example, a square-wave (SW) AST with H2/N2 between 0.6 V to 0.95 V vs. reversible hydrogen electrode (RHE) targets Pt catalyst and a separate triangular-wave (TW) AST with a higher potential range (1 – 1.5 V vs. RHE) assesses the durability of carbon-based supports [2]. Recently, many studies [3]–[7] have revealed the heterogeneous nature of cathode catalyst layer degradation under different ASTs. Fuel cell electric vehicles are typically subjected to an enormous number of load/unload and start/stop cycles during regular operation. Though there is a considerable body of literature discussing the isolated effects of load/unload and start/stop cycles on durability and performance, there is a dearth of studies exploring the effects of cascading load/unload and start/stop cycles, a scenario more relevant to actual automotive conditions. In the present study, a segmented cell along with ex-situ Pt particle size mapping (through micro-X-ray diffraction) is used to understand the effects of cascading a DoE square-wave AST (0.6 V to 0.95 V vs. RHE) and a triangular-wave (1 – 1.5 V vs. RHE) on the durability and performance of a PEFC.The membrane electrode assemblies (MEAs) are subjected to two cascade ASTs. The first one involves 15k cycles of SW AST followed by 2.5k cycles of TW AST (referred to as Pt-followed-by-carbon, PtfCC, AST) and the other one involves 2.5k cycles of TW AST followed by 15k cycles of SW AST (referred to as Carbon-followed-by-Pt, CCfPt, AST). Multiple in-situ and post-mortem ex-situ techniques are used to obtain particle size distribution and spatial degradation profiles. Preliminary results indicate that the performance losses at the end-of-life (EOL) depend on the cascade order; PtfCC AST leads to higher losses compared to CCfPt AST in wet polarization conditions. The local current distributions are also strongly impacted by the cascade order during the aging process. Figure 1 shows the polarization performance of the samples at the beginning, middle (following the first AST), and the end-of-life of cascade ASTs.

Electrochemical Performance of a Spatially Distributed ECPrOx Reactor

In this contribution a spatially distributed Electrochemical Preferential Oxidation (ECPrOx) reactor is evaluated and the influence of the temperature, CO inlet concentration, feed flow rate and relative humidity on the polarization curve, the local current distribution and the CO outlet concentration, selectivity and conversion are investigated. For that, six different cases are studied under galvanostatic and potentiostatic operation. For Galvanostatic operation, it was observed that depending on the operation conditions, the bifurcation point as well as the frequency and amplitude of the oscillations can be modified. Additionally, several spatiotemporal profiles of the local current density were found. For potentiostatic operation, the spatiotemporal profiles are constant with time, however they are affected by the anode overvoltage. Finally, after the bifurcation point, the temporal averaged anode overvoltage and the CO outlet concentration is always lower for galvanostatic control.

Direct visualization of electronic transport in a quantum anomalous Hall insulator.

A quantum anomalous Hall (QAH) insulator is characterized by quantized Hall and vanishing longitudinal resistances at zero magnetic field that are protected against local perturbations and independent of sample details. This insensitivity makes the microscopic details of the local current distribution inaccessible to global transport measurements. Accordingly, the current distributions that give rise to transport quantization are unknown. Here we use magnetic imaging to directly visualize the transport current in the QAH regime. As we tune through the QAH plateau by electrostatic gating, we clearly identify a regime in which the sample transports current primarily in the bulk rather than along the edges. Furthermore, we image the local response of equilibrium magnetization to electrostatic gating. Combined, these measurements suggest that the current flows through incompressible regions whose spatial structure can change throughout the QAH regime. Identification of the appropriate microscopic picture of electronic transport in QAH insulators and other topologically non-trivial states of matter is a crucial step towards realizing their potential in next-generation quantum devices.

Insight into mechanism of boosted oxygen reduction reaction in mixed-conducting composite cathode of solid oxide fuel cell via a novel open-source pore-scale model

Composite engineering is one of the most practical strategies for mitigating thermo-mechanical instability in state-of-the-art cobalt-based mixed ionic-electronic conducting electrodes for solid oxide cells. Nevertheless, the mechanism underlying improved performance and durability of composite electrodes is not substantially examined and understood. Pore-scale modeling can effectively bridge the gap between material property, microstructure discovery, and performance evaluation. However, most of the previous pore-scale models are built on in-house codes or commercial software that is closed-source to the public, limiting customization and community involvement. Here we report for the first time a microstructure-resolved 3D pore-scale model based on an open-source Lattice Boltzmann library, implementing a well-validated electrochemical module that considers gas, ion and electron transport, as well as electrochemical reaction at triple-phase-boundary (TPB) and double-phase-boundary (DPB). The pure La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and 50/50 vol% composite LSCF/GDC (Gd-doped ceria) cathodes are reconstructed using focused ion beam-scanning electron microscopy and then are investigated under various current densities, temperatures, oxygen concentrations, and thicknesses. Results reveal the advantages of boosted TPB density and ionic conductivity outweigh the disadvantages of lower DPB density and electronic conductivity for the composite cathode. Furthermore, the composite cathode performs better at low temperatures and low oxygen concentrations due to the presence of more macropores, the stable bulk ion conductivity of GDC, and higher TPB density. Local current distribution at active sites indicates a thickness of 20 to 40 μm is favorable for reduced overpotential and moderate reaction homogeneity.