A zero-dimensional, non-isothermal analytical framework was developed to assess solid oxide fuel cell (SOFC) performance across a broad range of operating conditions. The model integrates the anode, electrolyte, interlayers, and cathode, while resolving the distinct physicochemical processes within each layer. Electrochemical impedance spectroscopy (EIS), followed by distribution of relaxation times (DRT) analysis, was implemented to probe relevant cell polarization resistances under open-circuit and load conditions. The modeling framework couples mass and charge transport, electrochemical reactions, and non-isothermal heat transfer, with multilayer discretization applied to capture localized material properties and operating conditions. It enables the estimation of electrolyte ionic conductivity and total ohmic resistance by accounting for microstructural and geometric parameters, while also quantifying activation energies, exchange current densities, and gas-diffusion-related polarization resistances. Simulations were conducted for an SOFC operating on pure hydrogen with varying oxygen concentrations at 700 °C, 660 °C, 620 °C, and 580 °C. The results were validated against experimental data. The analysis revealed that ohmic overpotential dominates total cell losses, even at high current densities, underscoring the importance of minimizing ionic resistance to improve overall SOFC performance.

The energy transition requires flexible technologies to maintain grid stability, and electrolyzers are playing an increasingly important role in meeting this need. While previous studies often question the dynamic capabilities of large-scale alkaline electrolyzer systems, we assess their potential to provide balancing services using real manufacturer data. Unlike common approaches, we propose the decoupling between the total electrolyzer power and a smaller fractions of power actually offered on balancing markets. Adapting an existing methodology, we analyze alkaline electrolyzer systems and extend the assessment to Germany and Europe. Our results show that large-scale electrolyzers are technically capable of delivering fast-response balancing services, with significantly lower dynamic requirements than previously assumed. The planned electrolyzers in Germany could cover the entire balancing capacity market, potentially saving around 13

Degradation of the cathode catalyst layer (CCL) limits the durability of polymer electrolyte membrane fuel cells (PEMFCs) by reducing the electrochemically active surface area and impairing oxygen transport. These cooccurring effects are difficult to disentangle with standard electrochemical diagnostics. In this study, we used impedance-based analysis to quantify the individual contributions of catalyst and carbon support degradation in PEMFCs subjected to accelerated stress tests (ASTs): low-potential cycling (0.6-0.95 V, 55 000 cycles) and highpotential cycling (1.0-1.5 V, 50 000 cycles). In-operando electrochemical impedance spectroscopy under H2/air and impedance data analysis using the distribution of relaxation times and transmission line modeling were combined with complementary diagnostic techniques. This approach separated the ohmic, charge transfer, CCL ionomer, and mass transport resistances and tracked their evolution during ASTs. Low-potential cycling increased the charge transfer resistance by 29-56%, consistent with a loss of active surface area. High-potential cycling resulted in increased charge transfer, mass transport, and ohmic resistances, with a 77% reduction in CCL thickness, indicating severe carbon corrosion and collapse of the CCL structure. The resulting framework provides a practical tool to screen cathode materials and operating strategies by quantitatively linking specific degradation modes to electrochemical loss processes.

Concentration-related changes of the Nernstian voltage inevitably contribute to the resistance observed during DC operation of solid oxide cells. In electrochemical impedance spectroscopy (EIS), concentration losses arising from gas diffusion and gas conversion often overlap with electrochemical polarization processes, which is particularly true for high-capacitance mixed-ionic–electronic conducting electrodes, complicating the interpretation of impedance spectra and extracted activation energies. This work presents a comprehensive in-operando methodology to deconvolute gas diffusion and gas conversion resistances in electrolyte supported cells with screenprinted electrodes. Gas diffusion losses are quantified using an extended inert-diluent variation approach, enabling the determination of an effective microstructure parameter and prediction of diffusion resistances at arbitrary operating conditions. An alternative method based on replacing hydrogen/steam with carbon monoxide/carbon dioxide is introduced to access the same parameter, applicable to electrodes exhibiting a separable low-frequency concentration feature, such as nickel / yttria stabilized zirconia (Ni/YSZ). Furthermore, a novel approach for determining gas conversion resistances is presented, avoiding reliance on idealized analytical models, and enabling accurate prediction of concentration losses over a wide range of gas compositions and temperatures. The combined prediction of diffusion and conversion losses accurately reproduces the total concentration impedance over a broad steam partial pressure range and outperforms existing analytical approaches. The methodology is demonstrated on a commercial full cell, containing a nickel / gadolinia-doped ceria (Ni/GDC) fuel electrode, allowing reliable extraction of intrinsic activation energies even in the presence of increased, setup-induced concentration losses.

Abstract Hydrogen GT-SOFC cycles for aviation can offer a step change in efficiency and NOx. The SOFC contributes electrical power, but is also integrated within the GT cycle to receive air and return hot gases. This paper introduces normalised coupling parameters and integration constraints to perform a systematic thermodynamic exploration of GT-SOFC cycles with three main outcomes: a) impacts of SOFC integration on the GT cycle gas composition and thermodynamics, b) the potential of different cycles from SOFC integration, c) universal coupling maps for the cycle potential. The overall efficiency change was found a nearly unique function of the electrical degree of hybridisation (DoHel) due to the high electrothermal potential of the SOFC, while the main enabler of high DoHel - high efficiency is combining low GT specific power with high SOFC specific power. Within the investigated range of air utilisation and cell voltage, low specific power cycles can have Specific Fuel Consumption (SFC) reduction up to -55.7% with optimised Overall Pressure Ratio (OPR) and up to -53% with constrained OPR=10 due to SOFC technology. High specific power cycles can have SFC reduction up to -30% with optimised OPR and up to -14.1% with constrained OPR, when comparing against H2GT cycles with same TET and optimised OPR. With constrained OPR, low specific cycles reach higher efficiencies than high specific power cycles. When AU=0.1, OPR-constrained high specific power cycles perform worse than the H2GT cycle with optimised OPR, and increasing AU should be a priority.

A pulse-fitting methodology for time-domain analysis of lithium-ion battery impedance is presented and systematically extended to address automotive-relevant measurement constraints under controlled test conditions, including non-ideal current profiles, limited stabilization times, measurement noise, low sampling frequencies, and SOC-dependent OCV contributions. Since no universally applicable test pulse exists for large-format automotive lithium-ion cells, pulse-based diagnostics require evaluation methods that remain robust under application-specific excitation conditions. In this work, a pulse-fitting methodology for time-domain analysis of lithium-ion battery impedance is systematically extended. The approach models the voltage response to current pulses using a physically motivated RC network, enabling the extraction of diffusion-related time constants without relying on frequency-domain techniques. Key enhancements include numerical convolution for non-ideal current profiles, incorporation of a dynamic open-circuit voltage, Tikhonov regularisation, and weighting and scaling strategies to improve robustness against noise and low sampling frequencies. Furthermore, a quadratic programming solver is introduced to increase stability for ill-conditioned problems, and an extrapolation method is proposed to account for insufficient voltage stabilization times. The methodology is validated using both synthetic and experimental pulse data, demonstrating reliable access to low-frequency impedance characteristics. The results highlight the potential of the approach for advanced state estimation and model development.

Under technically relevant air-fed polymer electrolyte membrane fuel cell (PEMFC) operation, the low-frequency impedance response is shaped by overlapping oxygen-transport processes along the cathode channel and through the porous gas diffusion layer (GDL), microporous layer (MPL), and cathode catalyst layer (CCL). Local ionomer hydration and liquid-water accumulation further modify these transport processes. In this study, these low-frequency contributions are resolved locally using an along-the-channel segmented PEMFC by combining sequential segment-wise electrochemical impedance spectroscopy (EIS) with subsequent distribution of relaxation times (DRT) analysis. Targeted variations in inert gas, cathode stoichiometry, current density, and relative humidity were evaluated together with along-the-channel current-density distributions, allowing two distinct low-frequency processes, PLF1 and PLF2, to be separated over the investigated operating window. The results show that the relaxation frequency of the lower low-frequency peak, PLF1, depends primarily on channel-gas velocity. Its polarization contribution is additionally influenced by oxygen depletion and oxygen transport along the channel. The higher low-frequency peak, PLF2, is governed mainly by local through-plane oxygen transport through the GDL, MPL, and CCL and responds strongly to the effective oxygen diffusion coefficient, local oxygen availability, local current density, and water-modified transport conditions in the porous cathode. These findings establish a mechanistic distinction between a predominantly channel-related low-frequency contribution and a predominantly local through-plane oxygen-transport contribution in the porous cathode, providing a physically informed basis for interpreting low-frequency impedance signatures under technically relevant PEMFC operating conditions.

We present impedance spectra and related Distribution of Relaxation Times (DRT) analysis of pressurized PEM water electrolysis (PEMWE) single cells obtained with a newly developed test bench, including an incremental (zero-gradient) cell for homogeneous operating conditions. The setup enables reproducible electrochemical impedance spectroscopy (EIS) measurements over technically meaningful operating parameter ranges. DRT analysis reveals that current density variations (0.01-7 A cm- 2) show significant issues with the common approach of attributing an electrochemical process to a fixed relaxation frequency. We demonstrate that individual peaks significantly shift their relaxation frequency from the mHz-range at low current densities (0.01 A cm- 2) up to the kHz-range at 7 A cm- 2. We show variations of current density, temperature, pressure, and water flow rate, which reveal five capacitive and one low-frequency inductive peaks. Our findings emphasize the importance of detailed operating parameter variations for accurately assigning and modeling electrochemical processes in PEMWE cells.

The accumulation of hydrogen and oxygen within the flow channels of proton exchange membrane water electrolysis cells results in increased gas fractions and pronounced two-phase flow effects at higher current densities. Spatially resolved segmentation along the channel permits investigation of such gradients but necessitates complex hardware. In this study, a simplified method is introduced to emulate local gas production in an incremental cell through controlled injection of well-defined amounts of hydrogen and oxygen into the respective inlet streams. The impact of the gas-to-water ratio on ohmic resistance and polarization phenomena is examined using electrochemical impedance spectroscopy combined with subsequent distribution of relaxation times analysis. This reveals membrane dehydration effects as well as an impact on activation-related losses on the cathode side. A detailed comparison between an incremental (zero gradient) cell and an along-the-channel cell demonstrates a good overall performance correlation. In the medium current density region (2-3 A cm-2), the along-the-channel cell shows significantly increased polarization losses, which might be attributed to contamination from ion release from the CCM and/or mass transport issues.

Pressurization of solid oxide cells promises higher performance in the SOFC-mode, whereas downstream pressurization of the product gas is simplified in the SOEC-mode. The impact of pressurization on the SOEC-performance is hardly investigated. It is well known that the common dual side pressurization will increase the open circuit voltage (OCV) by the pO 2 at the air side whereas differential pressure only at the fuel side will not impact OCV and avoid an operating voltage offset. Detailed studies about the impact of pressure on the individual electrochemical processes at air and fuel electrode are rare. To evaluate the impact of pressurization on cell level, a single cell test bench, enabling pressurized operation without the need for a pressure vessel and thus significantly simplifying pressurized tests, has been developed [1]. This test bench is featuring impedance analysis of different types of incremental (1 cm²) cells in a temperature range from 300 to 900°C so far with H 2 /H 2 O fuels and O 2 /N 2 oxidant mixtures. To evaluate gas diffusion losses, different inert gases (N 2 , He) can be added [2]. In this contribution the impact of pressure on OCV and cell performance in SOFC and SOEC mode for a pressure range from atmospheric to 10 bar is presented. Detailed analyses of the pressure dependency of electrochemical processes at air and fuel electrode are performed. By means of impedance spectroscopy and the subsequent impedance data analysis by the distribution of relaxation time (DRT) [3], the impact of pressure on the different peaks in the DRT and the correlation to the related electrochemical processes is shown. [1] C. Grosselindemann, M. Dorn, F.M. Bauer, M. Seim, D. Ewald, D. Esau, M. Geörg, R. Rössler, A. Pundt, A. Weber, Pressurized single cell testing of solid oxide cells, Journal of Power Sources, 614 (2024) 12. [2] C. Grosselindemann, N. Russner, S. Dierickx, F. Wankmüller, A. Weber, Deconvolution of Gas Diffusion Polarization in Ni/Gadolinium-Doped Ceria Fuel Electrodes, Journal of The Electrochemical Society, 168 (2021). [3] A. Leonide, V. Sonn, A. Weber, E. Ivers-Tiffée, Evaluation and modeling of the cell resistance in anode-supported solid oxide fuel cells, Journal of the Electrochemical Society, 155 (2008) B36-B41. Figure 1

Impedance spectroscopy and the subsequent impedance data analysis by the distribution of relaxation times (DRT) [1] are powerful tools to analyze electrochemical devices, which have hardly been applied in the field of low temperature PEM water electrolysis. In this contribution an impedance based analysis of PEM water electrolyzer cells will be presented. The fundamental analyses of electrochemical processes in full cells was performed with an incremental (2 cm²) cell approach, ensuring homogeneous operating conditions over the entire electrode area and thus prevent the blurring of different electrochemical processes in the spectrum. To consider gradients in temperature, gas to liquid ratio and current density, unavoidable in any kind of technical scale stack, impedance spectroscopy was applied to a segmented along the channel (ATC) cell [2]. To deconvolute the different processes in the cell and evaluate their operating parameter dependencies, impedance spectra were measured for operating parameter variations of current density, differential pressure, temperature, anode water flow rate and cell compression. The DRT analysis of the spectra revealed up to 5 capacitive processes that could be attributed to proton transport in the ionomer, charge transfer kinetics and mass transport related losses at anode and cathode. Additionally, inductive low frequency processes were observed, lowering the internal resistance essentially at high current densities and low temperatures [3, 4]. The detailed analysis with up to 22 steps for each parameter variation revealed a strong frequency dependency of some processes, preventing the common DRT process assignment by fixed relaxation frequencies. Furthermore, it was observed that inductive phenomena at low frequencies can overlap with capacitive mass transport processes and annihilate each other. Regarding the segmented cell, a good correlation in impedance spectra was achieved. Impacts of gradients in temperature and gas to liquid ratio could be resolved, but strong gradients in current density were only observed for small educt water flows close to the stoichiometric water level resulting in rather high gas to liquid ratios [5]. Even under such conditions, impedance spectroscopy made it possible to determine the causes for lowered current densities. In this contribution, results of the impedance based analysis will be presented and critical features in impedance measurements and data analysis of PEM water electrolyzer cells will be discussed. [1] E. Ivers-Tiffée, A. Weber, Evaluation of electrochemical impedance spectra by the distribution of relaxation times, Journal of the Ceramic Society of Japan, 125 (2017) 193-201. [2] N. Hensle, S. Metz, A. Weber, T. Smolinka, A Segmented Along the Channel Test Cell for Locally Resolved Analysis at High Current Densities in PEM Water Electrolysis, Journal of The Electrochemical Society, 171 (2024). [3] N. Hensle, D. Brinker, S. Metz, T. Smolinka, A. Weber, On the role of inductive loops at low frequencies in PEM electrolysis, Electrochemistry Communications, 155 (2023) 6. [4] D. Brinker, N. Hensle, J. Horstmann de la Viña, I. Franzetti, L.V. Bühre, U.A. Andaluri, C. Menke, T. Smolinka, A. Weber, Inductive loops in impedance spectra of PEM water electrolyzers, Journal of Power Sources, 622 (2024) 14. [5] N. Hensle, T. Lickert, N. Winterholler, T. Smolinka, A. Weber, Water starvation phenomena in a segmented along the channel PEM water electrolysis cell, Journal of Power Sources, 654 (2025).

The production of hydrogen or electrical energy using solid oxide cell (SOC) technology requires stacks comprising numerous SOCs with large active areas. Operation at high conversion rates and large current densities is desired to obtain high efficiencies and reduce CapEx costs for these stacks. Such operating conditions generate significant gradients in internal temperature and local gas composition. Since they are the determining factors regarding cell degradation and thus stack lifetime, their precise knowledge is essential for efficient, but safe operation of a stack. As experimental investigation of the local conditions is challenging or even impossible, spatially resolved models are required and employed. Reliable simulations require adequate model parametrization and extensive validation through comparison of simulated and measured results. In this work a spatially resolved 3D stack model based on previous works [1,2] is developed and implemented in COMSOL Multiphysics v.6.2 [3]. The model comprises multiple cells with technically relevant dimensions of 11 x 11 cm² active area and explicit domains of all cell layers as well as ribs and channels of the interconnects. All relevant physical processes are implemented and coupled in this multiphysics FEM model. Experimental parametrization and validation of the model is conducted at different scales. Parameters used for modelling the performance of a state-of-the-art SOC [4] are determined according to an established experimental procedure [5], utilizing electrochemical impedance spectroscopy and subsequent equivalent circuit modelling on button cells with 1 cm² active area. The results are applied to parameterize an OCV minus losses model that was validated by comparing simulated and measured current voltage curves at various operating conditions. To account for the impact of temperature differences within the stack [6,7], a full parametrization is conducted at three operating temperatures. This revealed temperature dependencies of multiple parameters. Incorporating these dependencies results in changes in the magnitude of the calculated activation overpotentials (without spatial resolution) at both electrodes of up to 50%. Since large activation overpotentials are often considered as a driver for degradation effects this is expected to improve the accuracy of models describing such phenomena (cf. Figure 1). A significant impact of the derived dependencies on total cell performance is observed only at low operating temperatures (cf. Figure 1), due to the exponential decrease of the activation overpotential with temperature. The experimentally parametrized and validated approach to model the charge transfer current density is incorporated in the spatially resolved 3D stack model. The distribution of temperature, overpotentials and current density in the large active area cells is investigated for technically relevant operation conditions (cf. Figure 2). In these investigations, the derived temperature dependencies are considered. Further, it is identified whether the recommended limits of the operating range of the cells are also satisfied locally. Temperature profiles in SOCs vary significantly between fuel cell and electrolysis mode due to the differing sign of the reaction heat of the electrochemical reaction (exothermic resp. endothermic). Hence, operating points at both fuel cell and electrolysis operation are investigated. The results of the spatially resolved 3D model are compared to measurements of cells exhibiting a larger active area. As an upcoming task, the spatially resolved 3D stack model will be validated by measurements on a short stack consisting of cells with 121 cm² active area. The validated model is then employed to conduct parameter studies determining the impact of individual cell and stack parameters on the overall stack performance as well as on local conditions in the stack. [1] H. Geisler, A. Kromp, A. Weber, E. Ivers-Tiffée, J. Electrochem. Soc. 161 (2014), 6, F778 [2] N. Russner, S. Dierickx, A. Weber, R. Reimert, E. Ivers-Tiffée, J. Power Sources . 451 (2020), 227552 [3] COMSOL Multiphysics v.6.2. COMSOL AB, Stockholm, Sweden. www.comsol.com (accessed 2025-01-31). [4] Elcogen AS (2024) Product sheet elcoCell® [5] A. Leonide, Y. Apel, E. Ivers-Tiffee, ECS Trans. 19 (2009), 20, 81–109 [6] M. Peksen, Int. J. Hydrogen Energy . 36 (2011), 18, 11914–11928 [7] M. Navasa, X.-Y. Miao, H. L. Frandsen, Int. J. Hydrogen Energy . 44 (2019), 41, 23330–23347 Figure 1

Lanthanum strontium manganite (LSM)-based air electrodes are applied in solid oxide cells for high-temperature operations (800 degrees C-1000 degrees C), offering chemical and microstructural stability despite relatively lower performance. This work focuses on impedance study of hexis electrolyte supported cells with LSM air electrodes and Nickel/Gadolinia-doped Ceria (Ni/GDC) fuel electrodes. Electrochemical impedance spectroscopy and distribution of relaxation times (DRT) were employed to analyze performance-limiting processes in single cells with a 1 cm2 active electrode area. This analysis identified losses across five frequency ranges (5 DRT peaks), with no clear correlation to operating parameters. To deconvolute the processes and isolate loss mechanisms in both air and fuel electrodes, symmetrical cells were studied across a wide range of temperatures and air/fuel compositions. These measurements allowed for the separation of air and fuel electrode processes, development of a meaningful equivalent circuit model, and extraction of the model parameters using complex non-linear least squares fitting. These parameters were applied to build a 0-dimensional nonlinear DC performance model, which showed excellent agreement with the measured current-voltage data. The findings revealed that, in contrast to cells with mixed-conducting LSCF air electrodes, cell performance is limited by the LSM air electrode.

The utilization of Solid Oxide Fuel Cells (SOFC) in aviation necessitates lightweight high power density cells and stacks feasible for pressurized operation. Performance increases can be realized at various levels by optimizing materials, electrodes, cells and stack designs [1]. However, another considerable high-impact lever to increase the power density are the operating conditions, which is targeted in this work. In a previous study [2], a zero-dimensional performance model was transferred to an isothermal one-dimensional model along the gas channel. This shall be extended towards adiabatic and pressurized conditions as well as constant fuel and air utilization in this work. Thus, an established 0D dc performance model [3, 4] was parameterized for a high-performance anode-supported cell by means of impedance spectroscopy and the subsequent distribution of relaxation times (Fig. 1 a). Microstructural parameters were extracted by a three-dimensional FIB-SEM reconstruction (Fig. 1 b, fuel support not shown) and included to the parameterization. The derived equivalent circuit model from Ref. [3] could be applied (Fig. 1 c) and was validated by current-voltage characteristics, where the experimental data of the small scale (1 cm 2 ) cell is in excellent agreement with the 0D model, as exemplary shown in Figure 1 d. This validated 0D approach was integrated into a 1D along the channel model that calculates the performance along the cell length, as schematically shown in Figure 2 a and b. The iterative determination of the current density within the segment using the 0D approach enables to calculate the amount of converted gas, providing the gas composition entering the next segment. The overall air ( AU ) and fuel utilization ( FU ) are kept constant by iteratively adjusting the inlet molar flows n in . Furthermore, a constant cell voltage U cell approach is applied. In comparison to previous isothermal models [3], the temperature increase along the cell was considered by implementing adiabatic conditions based on an enthalpy balance of each segment (Fig. 2 c). Pressurized operation indispensable for airborne applications was implemented in the model as well. We will examine the validity of the developed 1D model by a comparison with a 2D FEM model [5]. Simulation results of pressurized operation will be placed to the context of recent experimental results [6]. Our modelling approach results in rather low computation times (< 10 s) enabling systematic variations of operating conditions like gas inlet temperature, pressure, cell voltage and gas utilizations. In this study, the model is applied to evaluate advantageous operating conditions for airborne applications considering coupling of hydrogen powered SOFC and gas turbine in an integrated power and propulsion system. Performance limitations due to operating conditions such as the fuel utilization will be discussed. References: P. Nehter, H. Geisler, V. Ahilan, S. Friedl, O. Rohr, A. Walter, C. Metzner, K. Zimmermann, ECS Trans. , 111 (6), (2023) 143 D. Klotz, J. P. Schmidt, A. Weber, E. Ivers-Tiffée, J. Power Sources , 259 , (2014) 65-75 A. Leonide, Y. Apel, E. Ivers-Tiffee, ECS Trans. , 19 (20), (2009) 81 C. Grosselindemann, N. Russner, S. Dierickx, F. Wankmüller, A. Weber, J. Electrochem. Soc. , 168 , (2021) 124506 N. Russner, S. Dierickx, A. Weber, R. Reimert, E. Ivers-Tiffée, J. Power Sources , 451 , (2020) 227552 C. Grosselindemann, M. Dorn, F. M. Bauer, M. Seim, D. Ewald, D. Esau, M. Geörg, R. Rössler, A. Pundt, A. Weber, J. Power Sources , 614 , (2024) 234963 Figure 1 Figure 2

For applications of solid oxide cells (SOCs), the ceramic single-cells consisting of fuel electrode, electrolyte and air electrode, are integrated into a stack using metallic interconnectors, which can lead to increased contact resistance and chromium poisoning. In a previous study [1], the electrochemical performance of 1 cm² single cells using stack-like metallic flow fields fabricated from Crofer 22 APU steel, both with and without a cerium-cobalt (CeCo) coating was investigated. Performance and loss mechanisms were analyzed using IV-characteristics, electrochemical impedance spectroscopy, and distribution of relaxation times (DRT) analysis. Based on this, the impact of un- and CeCo-coated metallic flow fields on the structural and chemical evolution of LSCF/GDC composite air electrodes was examined via (scanning) transmission electron microscopy ((S)TEM) in this work. Here, STEM imaging and energy-dispersive X-ray spectroscopy (EDX) was performed using a Tecnai OSIRIS ChemiStem TEM. TEM samples were prepared with a Helios G4 FX dual-beam instrument. The preparation of the comparably large TEM-sample required stabilization between the layers as shown in figure 1 (a) and 2 (a). Uncoated interconnectors exhibited significant performance degradation due to increased contact losses and air electrode polarization, attributed to Cr-oxide scale formation and Cr-poisoning. STEM-EDX analysis revealed Cr-poisoning as the driver of SrCrO₄ formation in the air electrode as shown in figure 1 in the LSCF layer. In addition, Cr is present in LSCF as well as GDC (figure 2). In contrast, CeCo-coated interconnectors demonstrated enhanced performance, driven by reduced contact losses and the effective suppression of Cr-evaporation, mitigating degradation and achieving substantial improvements in electrochemical performance [1]. References: C. Grosselindemann, M.J. Reddy, H. Störmer, D. Esau, M. Dorn, F.M. Bauer, D. Ewald, L. Wissmeier, J. Froitzheim, A. Weber, J. Electrochem. Soc. , 171 , 054508 (2024). Figure 1

This paper presents a methodology to compare different layouts of a solid oxide fuel cell (SOFC) system, focusing on component integration and constraints for low-emission aircraft propulsion. The SOFC system is a subsystem of an Integrated Power and Propulsion System (IPPS) fueled by hydrogen and tightly coupled with a micro gas turbine (mGT). The methodology presented here is applied to the case study of a mGT-SOFC and will later help to define the SOFC system layout for the 1MW+ IPPS of the FlyECO project. Due to the low power density of current SOFCs designed for stationary applications, technology projections are used to explore a scenario of entry into service in 2050. Parametric analyses have been performed to consider possible future developments and performance opportunities on the basis of anticipated increases in SOFC power density, which so far could only be implemented on a laboratory scale. Different SOFC system layouts are defined by assuming different aircraft operating conditions (take-off and cruise) as design point, due to the important impact of ambient pressure and temperature in-flight variation on the SOFC system, the related components and the overall performance. To maximize the synergy between SOFC and mGT, all layouts are based on a pressurized SOFC and include a heat exchanger for heat recovery and flow pre-heating. The system performance exploration is carried out with the W-TEMP software, varying the hybridization factor of the mGT-SOFC system between 5% and 20%, and comparing its performance to a baseline H-2-fueled mGT. The results obtained for this performance exploration report details on the coupling aspects between the micro gas turbine and the SOFC system and show clearly the advantages of mGT-SOFC integration in terms of net efficiency and production of water, which can be used in the combustion chamber of the mGT to limit the formation of NOx. In conclusion, a procedure to preliminary estimate the mass of the main components in each layout is also presented, to assess how different choices in the design of the mGT-SOFC can affect its weight.

Grid boosters are an elegant option to reduce the grid expansion needed for the energy transition by optimizing it. This study examines how battery grid boosters can be designed more economically and seeks to predict their lifespan for different design variants. In the context of this work, calendar and cycling aging models for battery degradation are applied to the special application of a battery energy storage system, used as a grid booster. The difference to conventional battery systems is the small number of cycles in its lifetime. So smaller capacity degradation is assumed. The calculations predict a lifetime of 25 years, for a grid booster, compared to 15 to 20 years of a conventional system. So already a longer lifespan, as the needed 23 years for amortization, can be reached. The calculations show that by using a lower state of charge and a lower storage temperature in the idle times, the lifespan can be extended and so an increase of economic efficiency can be realized. To aim for a higher return on invest, a dual-use approach is discussed. Through the trade-off between more cycles and lifetime, economic viability can be achieved after 16 years.

Blending of different active materials for lithium-ion electrodes offers great opportunities to combine advantageous properties in order to achieve an overall improved cell performance. While electrochemical models for blend electrodes are readily available, the parametrization remains challenging since the contributions of the two or more blend components are difficult to distinguish and material specific and area specific parameters from literature are not always applicable. Here we present a way to directly extract the charge transfer resistance from a blend electrode using impedance spectroscopy, microstructural analysis and transmission line modeling. To differentiate between the contributions of each active material we make use of the concentration dependence of the exchange current density in intercalation electrodes. We apply and compare two theoretical derivations of concentration-dependent charge transfer kinetics to model the behavior of the two active materials. The first is the common Newman formulation and the second is a thermodynamically more consistent, non-ideal approach. When comparing the two approaches to experimental data, we find a better agreement for the non-ideal approach than for the ideal one. These findings encourage further investigations of non-ideal charge transfer formulations which could improve not only blend electrode- but also single material electrode models.

Proton exchange membrane (PEM) water electrolysis cells can be operated very flexibly and at high current densities. Increasing the current density above today's industrial standard, in combination with low loadings of the catalyst layer, is necessary to become more economical and resource-saving. The water consumption and gas evolution rate are proportional to the current density, leading to a significant difference in the volumetric water-to-gas ratio over the active cell area when operating at high current densities and low water flow rates. This study analyzes industrial-relevant PEM water electrolysis operation at high current densities of up to 7 Acm-(2), measured in a segmented along the channel test cell with a 30 cm channel length. We present locally resolved measurements of current density, temperature, and impedance spectra and discuss variations of operating parameters and porous transport layer microstructure for low-loading catalyst-coated membranes. To achieve a deeper understanding of the observed phenomena, we compare conventional voltage breakdown analysis, done by subtracting ohmic overpotentials through high-frequency resistance measurements, and kinetic overpotential using Tafel analysis with distribution of relaxation times (DRT) and equivalent circuit modeling. At industrially relevant operation with water stoichiometries greater than 50, no relevant mass transport losses or membrane drying effects are observed along the channel. In cases of low stoichiometries, combined with the high heat dissipation of the reaction at high current densities, a significant temperature increase of more than 8 K and a high-frequency resistance reduction along the channel are observed. Investigations using low-loading catalyst-coated membranes and different porous transport layers reveal a high sensitivity of local clamping pressure on the polarization processes but less impact on the high-frequency resistance.

Proton exchange membrane water electrolyzers are typically operated with high water stoichiometry since the water, as a reactant, is also used as cooling agent for heat management. Water starvation phenomena are therefore not a pressing issue. However, in large industrial cell designs with challenging flow distribution, some areas of the cell may not be properly supplied with water. This study investigates water starvation in a segmented test cell with 30 cm long flow field channels. By varying the water flow rate close to the stoichiometric level, local membrane dry-out and mass transport issues are investigated. To achieve this, the distribution of current density, temperature, and impedance are analyzed up to 5 A center dot cm(-2) mean cell current density. Distribution of Relaxation Time is used to analyze the local impedance. Our findings reveal that undersupply of water drastically affects the high frequency resistance coupled with increasing low-frequency capacitive features of the impedance, which we refer to as membrane dry-out due to mass transport limitations. However, mass transport issues, without a significant influence on membrane resistance, seem not to be relevant. By varying the gas pressure, membrane dry-out effects can be reduced which emphasizes the importance of oxygen removal at the anode.