Operating alkaline water electrolysers above 100 degrees C improves electrolyte conductivity and reaction kinetics significantly. To examine alkaline water electrolysis in this area in more detail a high-temperature pressurized test rig is designed and constructed. Nickel (Ni) foam electrodes coated with Raney nickel (Raney Ni) or nickel manganese (NiMn) and expanded Ni mesh electrodes coated with nickel(II) oxide (NiO) are utilized and the effect of electrolyte flow rate, electrode structure, pressure and temperature variation on the cell performance at temperatures up to 130 degrees C and pressures up to 16 bar are investigated. At the maximum current density of 1.67 A/cm2, 110 degrees C and 16 bar the electrode combination of Raney Ni coated Ni foam as cathode and NiO coated expanded Ni mesh electrode as anode attain the best outcome with a cell voltage of 2.29 V. In a 70 h duration test three-dimensional (3D) Ni foam electrodes with Raney Ni cathode and NiMn anode catalyst show a moderate cell degradation of 9.26 mu V/h.

Proton exchange membrane (PEM) water electrolysis stands out as a promising technology for producing green hydrogen production by using intermittent renewable energy sources like wind or solar. Moreover, the growing demand for green energy and decarbonization has intensified interest in PEM water electrolysis, making it essential to compile and assess the technology status and advancements. Therefore, this chapter comprehensively discusses state-of-the-art PEM water electrolysis technology and its cell components level. Additionally, it delves into the current technical status, challenges, and advancements made in the development of essential components for PEM water electrolysis. Furthermore, we outline our vision for future research and development initiatives aimed at advancing PEM water electrolysis technology.

Open cell metallic foams are suitable for a wide range of applications as materials for filters, catalyst supports for heterogeneous catalysis and electrodes in batteries, fuel cells and electrolyzers due to their excellent heat and mass transfer, low pressure drop, good electrical conductivity and high chemical resistance. The foam can be produced in a wide range of pure metals like nickel, iron, silver and copper. Depending on the application, high high-temperature, oxidation and corrosion resistance can be achieved by a patented powder metallurgical alloying process in industrial scale.In the current paper, results for applications of NiFeCrAl foam as catalyst for Steam Methane Reforming and silver foam for the formaldehyde synthesis are discussed. Another focus is on the application as electrode material in electrolysis. Electrochemical investigations show that modified nickel foam exhibit a much lower overvoltage than nickel sheets and thus the operating costs of electrolyzers can be significantly reduced.

Journal Article Quantification of Hydrogen in Metals Applying Neutron Imaging Techniques Nikolay Kardjilov, Nikolay Kardjilov Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109, Berlin, Germany Corresponding author: kardjilov@helmholtz-berlin.de Search for other works by this author on: Oxford Academic Google Scholar André Hilger, André Hilger Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109, Berlin, Germany Search for other works by this author on: Oxford Academic Google Scholar Henning Markötter, Henning Markötter Bundesanstalt für Materialforschung und -Prüfung, Unter Den Eichen 87, 12205, Berlin, Germany Search for other works by this author on: Oxford Academic Google Scholar Axel Griesche, Axel Griesche Bundesanstalt für Materialforschung und -Prüfung, Unter Den Eichen 87, 12205, Berlin, Germany Search for other works by this author on: Oxford Academic Google Scholar Robin Woracek, Robin Woracek European Spallation Source ESS ERIC, SE-221 00, Lund, Sweden Search for other works by this author on: Oxford Academic Google Scholar Felix Heubner, Felix Heubner Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, Branch Lab Dresden, Winterbergstraße 28, 01277, Dresden, Germany; Search for other works by this author on: Oxford Academic Google Scholar Lars Röntzsch, Lars Röntzsch Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, Branch Lab Dresden, Winterbergstraße 28, 01277, Dresden, Germany; Search for other works by this author on: Oxford Academic Google Scholar Mirco Grosse, Mirco Grosse Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, Eggenstein-Leopoldshafen 76344, Germany Search for other works by this author on: Oxford Academic Google Scholar Ingo Manke, Ingo Manke Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109, Berlin, Germany Search for other works by this author on: Oxford Academic Google Scholar John Banhart John Banhart Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109, Berlin, GermanyTechnische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 28, Issue S1, 1 August 2022, Page 1666, https://doi.org/10.1017/S1431927622006638 Published: 01 August 2022

This paper presents a novel scalable electrode fabrication process suitable for large alkaline water electrolysers. Laser structuring technology is applied, and a large-scale development of active Ni-based cathodes is demonstrated. The most active electrode shows an overpotential of 104 mV at a current density of 300 mA cm-2 for the hydrogen evolution reaction at the end of the accelerated durability test protocol. Large 400 x 600 mm2 electrodes have been fabricated for the first time, and the electrodes thus fabricated are compared with state-of-theart electrodes in an industrial alkaline electrolyzer. Within the test period, the laser-structured Ni electrodes significantly outperformed the comparison electrodes. This impressively high activity is attributed to the existence of Ni oxide adjacent to the metallic Ni reaction sites.

The hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) occurring at the Raney-Ni mesh electrode in 30 wt.-% aqueous KOH solution were studied in the absence (silent) and presence of ultrasound (408 kHz, ∼54 W, 100% acoustic amplitude) at different electrolyte temperatures (T = 25, 40 and 60 °C). Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) experiments were performed to analyse the electrochemical behaviour of the Raney-Ni electrode under these conditions. Under silent conditions, it was found that the electrocatalytic activity of Raney-Ni towards the HER and the OER depends upon the electrolyte temperature, and higher current densities at lower overpotentials were achieved at elevated temperatures. It was also observed that the HER activity of Raney-Ni under ultrasonic conditions increased at low temperatures (e.g., 25 °C) while the ultrasonic effect on the OER was found to be insignificant. In addition, it was observed that the ultrasonic effect on both the HER and OER decreases by elevating the temperature. In our conditions, it is suggested that ultrasound enhances the electrocatalytic performance of Raney-Ni towards the HER due to principally the efficient gas bubble removal from the electrode surface and the dispersion of gas bubbles into the electrolyte, and this effect depends upon the behaviour of the hydrogen and oxygen gas bubbles in alkaline media.

Electrochemical energy conversion technologies play a crucial role in space missions, for example, in the Environmental Control and Life Support System (ECLSS) on the International Space Station (ISS). They are also vitally important for future long-term space travel for oxygen, fuel and chemical production, where a re-supply of resources from Earth is not possible. Here, we provide an overview of currently existing electrolytic energy conversion technologies for space applications such as proton exchange membrane (PEM) and alkaline electrolyzer systems. We discuss the governing interfacial processes in these devices influenced by reduced gravitation and provide an outlook on future applications of electrolysis systems in, e.g., in-situ resource utilization (ISRU) technologies. A perspective of computational modelling to predict the impact of the reduced gravitational environment on governing electrochemical processes is also discussed and experimental suggestions to better understand efficiency-impacting processes such as gas bubble formation and detachment in reduced gravitational environments are outlined.

1 Institute for Manufacturing Technology, Technische Universität Dresden, George-Baehr-Str. 3c, 01069 Dresden, Germany *Corresponding author: robert.baumann1@tu-dresden.de 2 Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM, Branch Lab Dresden, Winterbergstr. 28, 01277 Dresden, Germany 3 Fraunhofer-Institut für Werkstoffund Strahltechnik IWS, Winterbergstr. 28, 01277 Dresden, Germany

Hydrogen production using water electrolysers equipped with an anion exchange membrane (AEM), a pure water feed and cheap components such as platinum group metal-free catalysts and stainless steel bipolar plates (BPP) can challenge proton exchange membrane (PEM) electrolysis systems as the state of the art. For this to happen the performance of the AEM electrolyzer must match the compact design, stability, H-2 purity and high current densities of PEM systems. Current research aims at bringing AEM water electrolysis technology to an advanced level in terms of electrolysis cell performance. Such technological advances must be accompanied by demonstration of the cost advantages of AEM systems. The current state of the art in AEM water electrolysis is defined by sporadic reports in the academic literature mostly dealing with catalyst or membrane development. The development of this technology requires a future roadmap for systematic development and commercialization of AEM systems and components. This will include basic and applied research, technology development & integration, and testing at a laboratory scale of small demonstration units (AEM electrolyzer shortstacks) that can be used to validate the technology (from TRL 2-3 currently to TRL 4-5). This review paper gathers together recent important research in critical materials development (catalysts, membranes and MEAs) and operating conditions (electrolyte composition, cell temperature, performance achievements). The aim of this review is to identify the current level of materials development and where improvements are required in order to demonstrate the feasibility of the technology. Once the challenges of materials development are overcome, AEM water electrolysis can drive the future use of hydrogen as an energy storage vector on a large scale (GW) especially in developing countries.

Electrolyzer cells are a way of converting and storing excess energy and releasing it again if needed. Beside Li-ion-based batteries, this technique would enable to overcome the intermittent day-dependent availability of electricity (like solar or wind power). The power density and the amount of raw materials needed for the assembly of such cells can be improved through optimized manufacturing processes, especially the sintering process of the electrodes. The sintering process is crucial for the overall performance of an electrolyzer cell. The electrical conductivity as well as the media distribution inside the pores during cell operation needs to be tuned. Hereby, nickel particles are sintered on a nickel substrate. Different substances such as binder and surfactant, are added to the Ni(OH)2 before the sintering process is started. Ni(OH)2 will be reduced to Ni, resulting in an additional Ni coating on the Ni substrate. Material densification, decrease of the porosity and active surface are the most relevant factors during this process. To meet all the requirements a well-balanced sintering process in mandatory. A sufficient electrical conductivity requires well detached particles, while an optimal media transport requires more and large pores. Both can be met by using nickel particles with a defined size distribution of the particle diameters, and a balanced sintering process which significantly affects the conductivity and pores sizes. Moreover, remaining oxidized Ni, which is not an electrochemically active material, decreases the active surface of the sintered material. This study focuses on the two-phase flow system through newly developed porous nickel materials. Therefore, imaging techniques are combined with electronic measurements and simulations. To characterize these materials results were taken from focused Ion beam (FIB), synchrotron tomography and neutron radiography. Typical structures are coated meshes, foams or expanded metals. The structure of nickel particles was analyzed in 3D using machine learning algorithms for image segmentation. In-operando measurements were performed at the neutron source BER II at Helmholtz-Zentrum Berlin, Germany. Different electric loads and materials were tested in order to obtain additional information to the electronical measurements in terms of media distributions, see figure 1. The authors gratefully thank the German Federal Ministry for Economic Affairs and Energy (BMWi, Project AEL3D, grant number 03ET6063B) for financial support. Figure 1

Porous electrodes for alkaline water electrolysis were prepared by spark plasma sintering, a short-time sintering technique, in combination with a space holder method. After removal of the space holders, highly porous layers of polycrystalline Ni and of a nanocrystalline Ni-Fe alloy were obtained on a metallic substrate. Both porosity and thickness of the electrocatalytic layers can be controlled by the space holder volume content and the sintering process conditions, for example, the applied pressure and temperature. The active surface of the electrode can be increased significantly by a roughness factor of up to 1,120 determined by double layer charging. The porous layers are efficient towards oxygen evolution reaction (OER), whereas activity is greatly influenced by the chemical composition. The porous Ni-Fe electrodes exhibit an extremely low OER-overpotential of 230 mV at 0.3 A cm(-2) in highly concentrated KOH (29.9 wt.-%) at 333 K. Beside the high surface area, the efficiency of the porous Ni-Fe layer is characterized by a high intrinsic activity resulting in a low Tafel slope of around 23 mV dec(-1) at low and 50 mV dec(-1) at high current densities as well as a high turnover frequency (TOF) of approximately 3.4 s(-1) at 0.3 V. The porous Ni electrodes have a lower intrinsic activity with higher Tafel slopes and lower TOF. Moreover, an excellent stability and activity under realistic operating conditions of intermittent electrolysis (up to 1 A cm(-2)) for 100 h was proven for the porous Ni-Fe electrode. (C) 2019 Elsevier Ltd. All rights reserved.

Nanocrystalline Nickel-based alloys were investigated as catalysts for the oxygen evolution reaction(OER) at industrial operation conditions for alkaline water electrolysis. Different alloys were prepared by rapid solidification and subsequent high-energy milling. Regarding OER activity, the best efficiency was obtained for a nanocrystalline Ni-Fe alloy in 29.9 wt.% KOH at 298 K. However, at elevated temperature (333 K), comparable activities were determined in short-term experiments for nanocrystalline Ni-Fe and Ni alloys as well as for polycrystalline Ni. This initially incomprehensible outcome can be explained by the incorporation of Fe, which is present as impurity in the reagent grade KOH solution, into the NiOOH anode surface layer. However, after a long-term operation, the nanocrystalline Ni-Fe alloy shows a significantly better activity, in particular, at altering current density of up to 1 A cm(-2). As a result, the nanocrystalline Ni-Fe alloy exhibits a very high efficiency and excellent long-term activity (375 mV overpotential at 0.3 A cm(-2)) after 95 h of operation at different loads. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

A powder metallurgy route is described as a promising route to produce highly active Raney-Ni electrodes. An expanded Ni mesh was used as metallic substrate on the surface of which Raney-Ni phases were produced via a heat-treatment step using Al powder at different loads. The overpotential at -300 mA/cm(2) as well as the active surface area were determined to evaluate the electrodes. The results reveal that a high Al loading is necessary to achieve a stable electrode and a high activity for the hydrogen evolution reaction. (c) The Author(s) 2019. Published by ECS.

Nanocrystalline Fe60Co20Si10B10, prepared by ball milling atomised powder, was studied as a hydrogen evolution reaction catalyst for alkaline water electrolysis. Two application-oriented aspects of this material were studied: (i) Surface activation of the catalyst (cyclic voltammetry and leaching in 1 mol dm(-3) potassium hydroxide) and (ii) the composition of a catalyst layer (ratio of the amount of catalyst to the polymer binder). Polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene with DABCO functional groups (PSEBS-CM-DABCO) was used as an anion-selective binder. The catalytic activity of the material was evaluated by means of Tafel analysis and by recording load curves under alkaline water electrolysis conditions. The results revealed that both activation procedures increase the activity of the Fe60Co20Si10B10 catalyst by almost 50% compared to as-received material. The most suitable ratio of catalyst to binder was determined as 70: 30. The catalyst remained stable and active in the stability test performed. (c) 2019 Elsevier Ltd. All rights reserved.

Solid-state hydrogen storage in metal hydrides offers highest volumetric energy storage densities and low working gas pressures at the same time. Recently developed metal hydride composites (MHC) consist of a hydride-forming metal alloy and a secondary phase, typically graphite, to realize form-stable composites and short loading and unloading times (<5 min). Hydride formation causes a volume expansion of the storage material. Thus, it is mandatory to characterize this behavior for the sake of system safety. This work focuses on the in-operando characterization of the volume expansion of MHC that could trigger mechanical stresses acting on the walls and internal assemblies of the storage container. MHC with different metal particle shapes (flakes and powder) were studied. In-operando neutron imaging of axially freely expanding MHC was applied to analyze the time-resolved and spatial concentration of hydrogen, reaction fronts and the evolution of volume expansion and stability of the MHC. Stress measurements revealed that stresses of up to 330% of the respective operating gas pressure occur for confined MHC. Both techniques combined deliver crucial information and implications for the design of safe (according to ISO 16111), efficient and dynamic metal hydride storage systems.

Hydrogen production by alkaline water electrolysis has attracted great attention due to the feasibility of large scale H-2 production and the use of non-precious electrode materials. In particular, efficient electrodes towards the hydrogen evolution reaction (HER) consist of porous or skeletal Ni-based catalysts. In this contribution, a unique surface processing technique using a femtosecond (fs) laser pulse process was utilized to enlarge the surface area of Ni aiming to enhance significantly the HER-activity. Fs laser structured Ni surfaces were processed using different laser process parameters (e.g. fluence, spot size and scan line overlap). Surface morphology was studied by scanning electron microscopy. Under the chosen process conditions arrays of conical surface structures were obtained, which are significantly covered by redeposited particles using a fluence far above the ablation threshold. Electrochemical investigations (CV, EIS, steady-state polarization curves) conducted in 29.9 wt.-% KOH at 333 K (industrial conditions) point out that the fs laser structured electrodes reveal a high and adjustable surface area with a roughness factor between 6 and 73. The roughness of the fs laser structured surfaces has a significant impact on the HER leading to a reduced overpotential (eta(300) = 280 mV, reduction by approximately 45 % compared to smooth Ni). In fact, the results clearly show the feasibility of the fs laser pulse technique for processing highly structured electrodes without affecting the intrinsic HER-activity significantly. (C) 2017 Elsevier Ltd. All rights reserved.