The optimization of anion exchange membrane water electrolyzers (AEMWEs) relies on active, stable catalysts and well-designed catalyst layers. This study investigates the impact of tumbler ball milling on a nickel-iron layered double hydroxide (Ni3Fe-LDH) catalyst for the oxygen evolution reaction (OER). Milling reduced catalyst clusters from 1-100 mu m to 30 nm, increasing the geometrical surface area by 8.8-fold. Optimized solvent compositions and dispersing times enhanced catalyst dispersion stability. Tailoring the electrode structure reduced internal electronic resistances and charge-transfer resistances of the membrane electrode assembly. The optimized electrode exhibited outstanding single-cell performance, reaching 1.83 V at 2 A cm- 2 with stable durability of 1000 h and a minor degradation rate of 62 mu V h- 1. This work presents a scalable approach to NiFe-LDH catalyst treatment and dispersion control, demonstrating the importance of research and optimization across scales to improve performance and support the practical advancement of hydrogen technologies.

The progress of energy conversion devices such as fuel cells or electrolyzers is critical for integration of green hydrogen into the energy system. However, the catalyst layer (CL) poses a significant challenge to both technologies as their performance and durability depend on the nature of the CL produced. In most studies, the CL structure remains unknown or is presented superficially. Methods to access and quantify the CL structure are limited but necessary to enable advanced CL architectures, such as low iridium loadings in polymer electrolyte membrane water electrolysis (PEMWE). The path to progress involves advancing our understanding of the production-structure-property triangle (PSPT) for the CL. Proper implementation of quality control measures can lead to reduced production costs and increased longevity of the technologies. The objective of this study is to investigate the production-structure relationship by analyzing the impact of different production variables on the formed structure and quantifying the physical characteristics of CLs. The fabrication of CLs involved the use of an ultrasonic spray coater, with an in-depth exploration of different machine parameters. A confocal laser scanning microscope is used to analyze the produced CLs to obtain surface texture parameters (STPs) corresponding to a microscopy image. Additionally, image features (IFs) were extracted from the obtained images by using the PyRadiomics library. Correlation between the STPs and IFs is evaluated with Pearson correlation. Analysis of 89 CLs and 443 microscopy images showed that the 19 standardized STPs reduce to three non-redundant descriptors, each of which is reproduced by a specific image feature, yielding a compact and instrument-independent parameter set for CL quality control.

Electrocatalysts support crucial industrial processes and emerging decarbonization technologies, but their design is hindered by structural and compositional changes during operation, especially at application-relevant current densities. Here we use operando X-ray spectroscopy and modelling to track, and eventually direct, the reconstruction of iron sulfides and oxides for the oxygen evolution reaction. We show that inappropriate activation protocols lead to uncontrollable Fe oxidation and irreversible catalyst degradation, compromising stability and reliability and precluding predictive design. Based on these, we develop activation programming strategies that, considering the thermodynamics and kinetics of surface reconstruction, offer control over precatalyst oxidation. This enables reliable predictions and the design of active and stable electrocatalysts. In a NixFe1-xS2 model system, this leads to a threefold improvement in durability after programmed activation, with a cell degradation rate of 0.12 mV h-1 over 550 h (standard operation: 0.29 mV h-1, constrained to 200 h), in an anion exchange membrane water electrolyser operating at 1 A cm-2. This work bridges predictive modelling and experimental design, improving the electrocatalyst reliability for industrial water electrolysis and beyond at high current densities.

Polarization curves in PEM water electrolyzers are typically considered to consist of contributions from electrochemical equilibrium, reaction kinetics, and transport phenomena for both charge and mass. However, breaking down these contributions can be difficult due to limited experimental data, making it challenging to accurately resolve each component. To mitigate this underdetermination, models are employed to provide insight into the specific contributions. A common approach assumes that, at low current densities, reaction kinetics adhere to the Tafel equation. By fitting the iR-corrected polarization curves, Tafel slopes can be derived, with deviations at mid- and high-current densities often attributed to mass transport effects. Yet, given the complexities of porous electrodes and necessary simplifications, it remains uncertain whether this traditional method is entirely applicable. In this study, we introduce a statistical method for voltage breakdown analysis that does not assume adherence to the Tafel equation for reaction kinetics. We hypothesize that the precise gas concentration within the catalyst layers is unknown but must exceed that in the flow fields, in accordance with mass transport principles. Mass transport should, therefore, result in a concentration increase in the catalyst layer with higher production rates. Additionally, we assume that increasing the cathode gas pressure in a PEM water electrolyzer minimally impacts the kinetic overpotentials of both the oxygen and hydrogen evolution reactions. Consequently, when cathode flow field gas concentration varies across otherwise identical experiments, we anticipate systematic shifts between polarization curves. These shifts should align with both transport laws and the Nernst equation. By correcting the iR-free cell voltage based on mass transport effects, reaction kinetics—potentially displaying a Tafel slope—can be unveiled without presupposing it. Surprisingly, our experimental data reveals that the overpotential attributed to reaction kinetics aligns closely with a Tafel slope across the full current density range (R² > 0.999). This approach reduces the unexplained overpotential by 90% and reveals a slightly steeper Tafel slope (+5%) compared to conventional methods. Additionally, the calculated increase in gas concentration within the catalyst layer agrees with transport laws, predicting a gas pressure increase of approximately 380 mbar·cm²·A⁻¹, indicating a transport resistance intermediate between those of membranes and porous transport layers and pointing to the catalyst layer as a source. While these findings are unexpectedly precise and potentially groundbreaking, they contradict initial assumptions, necessitating a careful re-evaluation and further discussion.

The two-phase flow behavior inside a zero-gap alkaline electrolysis cell is investigated using operando neutron radiography. The cell was operated with a highly concentrated potassium hydroxide solution. The two-phase flow is evaluated at different electrolyte volume flows, current densities, and temperatures. The amount of gas inside the parallel flow channels is identified and the gas bubble velocity over the channel's length and time is evaluated depending on the different operating conditions. The gas bubble motion requires a high degree of temporal resolution. At the Institut Laue Langevin, a high frame rate of 50 fps was achieved using the NeXT (Neutron and X-Ray Tomograph) neutron imaging instrument, which is fed by the world's most powerful neutron source. This study demonstrates the importance and limitations of high temporal and spatial resolution in neutron radiography for the investigation of two-phase flow in electrochemical flow cells.

Understanding the sheet resistance of porous electrodes is essential for improving the performance of polymer electrolyte membrane (PEM) water electrolyzers and related technologies. Despite its importance, existing methods often fail to provide reliable and comprehensive data, especially for porous materials with complex morphologies and non-uniform thicknesses. This study introduces a robust and straightforward method for determining the sheet resistance of porous electrodes using a novel probe concept based on industrial printed circuit board (PCB) technology. This probe measures resistance across ten distances, ranging from 250 µm to 2500 µm, enabling local mapping of resistance. The study focuses on the sheet resistance of key components in PEM water electrolyzers, including the gas diffusion layer (GDL), porous transport layer (PTL), and catalyst layers deposited on a membrane. Additionally, an image-processing-based method is presented to obtain the thickness distribution of the studied catalyst layers, facilitating a detailed analysis of the electrical in-plane resistivity with thickness variations. Overall, this methodology has the potential to expedite material integration and bridge the gap between electrode engineering and single-cell testing, thereby advancing the development of PEM water electrolyzers.

Electrocatalysts support crucial industrial processes and emerging decarbonization technologies, but their design is hindered by structural and compositional changes during operation, especially at application-relevant current densities. Here we use operando X-ray spectroscopy and modelling to track, and eventually direct, the reconstruction of iron sulfides and oxides for the oxygen evolution reaction. We show that inappropriate activation protocols lead to uncontrollable Fe oxidation and irreversible catalyst degradation, compromising stability and reliability and precluding predictive design. Based on these, we develop activation programming strategies that, considering the thermodynamics and kinetics of surface reconstruction, offer control over precatalyst oxidation. This enables reliable predictions and the design of active and stable electrocatalysts. In a NixFe1-xS2 model system, this leads to a threefold improvement in durability after programmed activation, with a cell degradation rate of 0.12 mV h-1 over 550 h (standard operation: 0.29 mV h-1, constrained to 200 h), in an anion exchange membrane water electrolyser operating at 1 A cm-2. This work bridges predictive modelling and experimental design, improving the electrocatalyst reliability for industrial water electrolysis and beyond at high current densities.

Analyzing PEM electrolyzer polarization curves via voltage breakdown analysis involves decomposing contributions from underlying processes, typically based on the assumption of reaction kinetics that may be expressed by means of the Tafel equation. When extrapolating the corresponding straight line to high current densities, there is a discrepancy between the measurement and model, which is often attributed to mass transport resistance. In addition to the qualitative description of this mass transport resistance, a consistent quantification is difficult to obtain from the measurement results. Accordingly, the approach to the breakdown analysis of the polarization curves is strongly based on assumptions that evade experimental verification. In this study, an alternative statistical method is introduced that permits the falsifiability of the standard approach. By means of experiments at different hydrogen partial pressures and a subsequent data fit, it is possible to extract the kinetic behavior without prior specification. The results indicate that behavior corresponding to the Tafel equation cannot be proven wrong. In addition, transport coefficients can be evaluated that fall between those of membranes and porous transport layers, indicating that the catalyst layer predominantly contributes to the mass transport resistance.

Water electrolysis will be an essential element of the future energy system, with hydrogen serving as a climate-friendly energy storage medium. To make electrolyzers suitable for market penetration at scale, the cost of manufacturing megawatt electrolyzers must be minimized, with no detrimental effects to their performance and lifetime. Here we show a facile and cost-effective manufacturing method to produce one-piece Ti-based bipolar plates. Low-cost and commercially and readily available feedstock materials (blank sheets, expanded metals and nonwovens) are positively joined using an innovative welding process, diffusion bonding. This approach reduces the contact resistances that can occur with multi-part bipolar plates by around 75%, reducing the number of components and therefore significantly simplifying stack assembly. Ex-situ tests on the contact pressure distribution on the active cell surface reveal a homogeneous pattern with values of about 3.75 MPa ( +/- 1.25 MPa). In a first proof-of-concept, a five-cell short stack with a 100 cm2 active cell area, average cell voltages of 1.71 V at 2 A cm-2 could be achieved using our new stack concept.(c) 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

The development of catalysts for an economical and efficient oxygen evolution reaction (OER) is critical for clean and sustainable energy storage and conversion. Nickel-iron-based (NiFe) nanostructures are widely investigated as active OER catalysts and especially shape-controlled nanocrystals exhibit optimized surface structure and electronic properties. However, the structural control from amorphous to well-defined crystals is usually time-consuming and requires multiple stages. Here, a universal two-step precipitation-hydrothermal approach is reported to prepare a series of NiFe-based nanocrystals (e.g., hydroxides, sulfides, and molybdates) from amorphous precipitates. Their morphology and evolution of atomic and electronic structure during this process are studied using conclusive microscopy and spectroscopy techniques. The short-term, additive-free, and low-cost method allows for the control of the crystallinity of the materials and facilitates the generation of nanosheets, nanorods, or nano-octahedra with excellent water oxidation activity. The NiFe-based crystalline catalysts exhibit slightly compromised initial activity but more robust long-term stability than their amorphous counterparts during electrochemical operation. This facile, reliable, and universal synthesis method is promising in strategies for fabricating NiFe-based nanostructures as efficient and economically valuable OER electrocatalysts.

Commercialized implementations of anion exchange membrane water electrolysis (AEMWE) require stable operation at high current density. To achieve this, ohmic, electrochemical and concentration polarizations are supposed to be exceedingly suppressed. Among all crucial materials, porous electrodes with catalyst coatings extensively affect the above polarizations, which are highly sensitive to specific mechanical pressure for cell assembly. However, the imposed mechanical pressure and its effects on cell performance are rarely reported in AEMWE cells. Here, quantitative characterizations of mechanical pressure and its effects on i) physical properties of catalyst coated electrodes and ii) corresponding single-cell performance are comprehensively investigated. First, the imposed mechanical pressure on membrane electrode assembly (MEA) is controlled by different total thickness gaps between anode/cathode and poly-tetra-fluoroethylene (PTFE) gaskets (Delta d = 0, 100, 200, 300 mu m). Second, the above resulted distributions of mechanical pressure are quantitatively studied by a mechanical pressure tracking method. Third, the influence of the mechanical pressure on the physical properties of the electrodes and cell performance are demonstrated. It is proved that the mechanical pressure of ca. 0.5 MPa is comprehensively beneficial for suppressing internal resistance (R omega) and charge transfer resistance (Rct), with slightly increased mass diffusion resistance (Rmd) and hydrogen crossover. This study unveils the intrinsic effects of mechanical pressure on cell performance and provides critical insights into baseline benchmarking and single cell even stack optimization.

Fuel cells/electrolyzers are efficient and clean electrochemical devices that convert chemical energy directly into electricity and vice versa. They have attracted sustainable attention over the past decade from multiple experimental and numerical studies. However, detailed experimental investigations are typically expensive and challenging for providing a number of operating conditions and designs. Computational analysis offers an alternative approach for these studies. With the steadily increasing high-performance computing resources available, the limitations of numerical simulations have substantially decreased. This contribution details on the design choice and code structure of modern electrochemical devices, which have been implemented as a versatile C++ library named openFuelCell2 within the open-source platform OpenFOAM, allowing for large-scale parallel calculations to be performed. The solver considers the major transport phenomena in a typical electrochemical device, including fluid flow, heat and mass transfer, species and charge transfer, and electrochemical reaction. This enables the numerical simulations on popular electrochemical devices, such as fuel cells and electrolyzers, to be conducted. The paper also describes the domain decomposition, and parallel performance issues, as well as future applications.

Anion exchange membrane water electrolysis (AEMWE) is an attractive method for green hydrogen production. It allows the use of non-platinum group metal catalysts and can achieve performance comparable to proton exchange membrane water electrolyzers due to recent technological advances. While current systems already show high performances with available materials, research gaps remain in understanding electrode durability and degradation behavior. In this study, the performance and degradation tracking of a Ni3Fe-LDH-based single-cell is implemented and investigated through the correlation of electrochemical data using chemical and physical characterization methods. A performance stability of 1000 h, with a degradation rate of 84 mu V h-1 at 1 A cm-2 is achieved, presenting the Ni3Fe-LDH-based cell as a stable and cost-attractive AEMWE system. The results show that the conductivity of the formed Ni-Fe-phase is one key to obtaining high electrolyzer performance and that, despite Fe leaching, change in anion-conducting binder compound, and morphological changes inside the catalyst bulk, the Ni3Fe-LDH-based single-cells demonstrate high performance and durability. The work reveals the importance of longer stability tests and presents a holistic approach of electrochemical tracking and post-mortem analysis that offers a guideline for investigating electrode degradation behavior over extended measurement periods. Transitioning industrial processes toward renewable energy is vital for decarbonization. Green hydrogen, generated via anion exchange membrane water electrolysis (AEMWE) offers cost-effective, efficient hydrogen production. While recent research has improved AEMWE components, long-term durability and comprehensive electrode studies are lacking. This study investigates a Ni3Fe-LDH-based single-cell's 1000 h operation, tracking anode degradation, and establishing correlations with overall cell stability.image

Due to water uptake, the polymer membrane of polymer electrolyte membrane water electrolyzers (PEMWE) swells, increases in thickness and so induces swelling pressure. The water content in the membrane and catalyst coated membrane (CCM), respectively, defines the protonic conductivity, which has a significant impact on the performance of a PEMWE. In order to ensure the gas tightness of the PEMWE and increase the thermal and electrical connectivity between the different layers, the entire electrolyzer is compressed. Whether and in which way the swelling of the CCM is influenced by applying pressure or influences the surrounding layers is investigated in this study using a special compression device and X-ray computer tomography (CT). CT scans were carried out and the resulting cross-sectional images analyzed. Five different compression pressures between 0.36 and 1.63MPa were applied for the dry (28°C, atmospheric humidity) and wet (28°C, surrounded by liquid water) states. The thickness change of the CCM and adjacent porous transport layers (PTL) was then measured. Due to the compression pressure, the thickness of the CCM decreased by 5%. For lower pressures, the carbon paper PTL compensates more of the swelling than the titanium felt PTL. For higher pressures, the ratio is inverse.

Green hydrogen is a key solution for reducing CO2 emissions in various industrial applications, but high production costs continue to hinder its market penetration today. Better competitiveness is linked to lower investment costs and higher efficiency of the conversion technologies, among which polymer electrolyte membrane electrolysis seems to be attractive. Although new manufacturing techniques and materials can help achieve these goals, a less frequently investigated approach is the optimization of the design point and operating strategy of electrolyzers. This means in particular that the questions of how often a system should be operated and which cell voltage should be applied must be answered. As existing techno-economic models feature gaps, which means that these questions cannot be adequately answered, a modified model is introduced here. In this model, different technical parameters are implemented and correlated to each other in order to simulate the lowest possible levelized cost of hydrogen and extract the required designs and strategies from this. In each case investigated, the recommended cost-based cell voltage that should be applied to the system is surprisingly low compared to the assumptions made in previous publications. Depending on the case, the cell voltage is in a range between 1.6 V and 1.8 V, with an annual operation of 2000-8000 h. The wide range of results clearly indicate how individual the design and operation must be, but with efficiency gains of several percent, the effect of optimization will be indispensable in the future. (c) 2022 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/).

Open-source fuel cell models outmatch commercial codes in many important aspects. By providing the source code, reuse, modification and extension of the model and comparison with other codes becomes possible. With this motivation, we present a three-dimensional, steady-state, non-isothermal proton exchange membrane fuel cell model, implemented in the open-source finite volume library OpenFOAM® . At every stage of implementation, special care was taken to ensure a well documented, organised, and modular structure of the software. The resulting model suite can, and should, be extended with new sub-modules by the user. The main field of application, modelling of fuel cells from an engineering perspective, is demonstrated by simulating two different conventional polymer electrolyte fuel cells, operated at CIEMAT and Forschungszentrum Jülich, respectively.

Alkaline water electrolyzers (AWE) have several advantages over other types of electrolyzers, including their high efficiency and especially their relatively low cost due to the usage of non-precious metal catalysts, such as nickel and iron, for the electrodes. Information about local quantities and physical phenomena such as the formation of gas bubbles, current densities, temperatures or local species concentrations within a running cell are important for their improvement. Multiphysical computational fluid dynamics (CFD) simulations of electrochemical components using detailed three-dimensional models can provide valuable insight on local behaviors and characteristics that are difficult or impossible to measure experimentally. This work extends the CFD library openFuelCell2 1, which has been implemented using the open-source platform OpenFOAM®, to simulate AWE cells. The model considers the major transport phenomena, including two-phase fluid flow, heat and mass transfer, electrochemical reactions, species transfer and charge transfer in the various functional regions of the cell. It employs an Eulerian-Eulerian approach to characterize the behavior of each phase comprising interphase mass transport, momentum exchange and heat transfer. Appropriate mapping functions are used to couple the physically distinct regions together. A Butler-Volmer equation characterizes the electrochemical reactions that are assumed to occur in electrodes of finite thickness. This model is used to simulate a single zero-gap AWE cell, depicted in Fig. 1, for different operating conditions such as varying temperatures and volumetric flow rates. The conducted studies provide insight into the local formation of the created gas phase (bubbles), the distribution of species within the gas and electrolyte and their impact towards the performance of the running cell. These numerically obtained results are compared to in-house available and gathered experimental data. Figure 1 demonstrates that the polarization curves obtained at various temperatures are in good agreement with the experimental data. Figure 1

Physical properties of aqueous KOH solutions are crucialto thedesign and operation of alkaline electrolyzers but have been scarcelyand sometimes unreliably reported. Obtaining published data for variousproperties currently requires time-consuming searches and subsequentinterpretation, interpolation, and extrapolation. This work collatesand critically analyzes published data for a range of physical propertiesrelevant to alkaline electrolysis, including the density, viscosity,conductivity, surface tension, oxygen/hydrogen solubility, oxygen/hydrogendiffusivity, and water vapor pressures of aqueous KOH solutions, asa function of temperature, KOH molarity, and pressure. Correlationfunctions, in the form of excel spreadsheets, have been developedto allow interpolation of the most reliable data and computation ofdesired quantities at specific temperatures, pressures, and KOH concentrations.Composite models incorporating these properties have been developedfor automated computation of (i) diffusive gas crossover and (ii)gas production volumes, including (iii) water vapor content, and associated(iv) dissolved gas concentrations in the liquid electrolyte, as afunction of KOH concentration, temperature, pressure, current density,and separator thickness and porosity. These spreadsheets are providedin the Supporting Information, as tools and reference points for researchersand practitioners in alkaline electrolysis.

This study presents a computational simulation of a zero-gap alkaline water electrolysis cell. The model employed is a three-dimensional, steady-state, non-isothermal, two-phase-flow computational fluid dynamics approach, which has been implemented by means of the OpenFOAM software library. This integration expands the capabilities of the existing libraries within the open-source framework, openFuelCell2, by introducing novel surface and volumetric coupling strategies to connect the dependent quantities over the existing interfaces and different regions. Additionally, the Nernst–Planck equation is incorporated into the two-phase Eulerian–Eulerian framework to describe the behavior of the liquid electrolyte within the cell.The model’s validation in this study is based on experimentally-determined polarization curves for various temperatures and volumetric flow rates. The results obtained show good agreement with the experimentally-acquired data. The implemented model has demonstrated its ability to accurately predict the transport of ions within the electrolyte and assess the influence of the generated gas phase on the local distribution of current density.