Maximizing the density of accessible catalytic sites through rational design of self-supported multimetal electrodes that combine high activity, durability, and scalable manufacturing is essential for advancing alkaline water electrolysis (AWE). Herein, we systematically investigated the role of tin, a comparatively underexplored alloying element in AWE, in binary Co–Sn coatings fabricated by one-step electrodeposition onto nickel mesh substrates. Broad variation of the Sn2+/Co2+ concentration ratio (0/1 to 1/1) and deposition current density (30–200 mA cm−2) enabled precise control over alloy composition, phase structure, and surface morphology, establishing clear structure–property–performance relationships for bifunctional hydrogen and oxygen evolution reaction (HER and OER) electrocatalysis. Comprehensive structural, electrochemical, and computational analyses revealed that tin acts primarily as a morphological promoter, drastically increasing electrochemically accessible surface area by up to 5500-fold relative to bare nickel mesh without fundamentally altering the intrinsic activity of Co-rich domains. This extreme enhancement arises from the tin-induced formation of hierarchical porous microstructures that maximize active site exposure. The optimized Co–Sn electrode (Co1Sn0.3-100), balancing composition, porosity, and mechanical integrity, delivered low overpotentials of 161 mV (HER) and 384 mV (OER) at 100 mA cm−2 in 1 M KOH, together with excellent operational stability. When integrated into a zero-gap electrolyzer under industrially relevant conditions (30 wt% KOH, 75 °C), a symmetric Co–Sn configuration outperformed bare nickel mesh by 222 mV at 1 A cm−2. This work establishes morphology-driven surface engineering via controlled Sn alloying as a scalable and generalizable materials design principle for durable, high-performance AWE electrodes.

A novel route to produce Raney-nickel-coated electrodes for industrial alkaline water electrolysis is presented, in which aluminum foil is cold-rolled onto a nickel mesh, followed by heat treatment and selective leaching. This process requires no specialized equipment and shows high potential for cost-effective and scalable fabrication of supported Raney nickel electrodes. Structural analysis with SEM and synchrotron MicroCT confirms the presence of a microporous Raney nickel layer uniformly coating the substrate. Electrochemical characterization reveals superior electrode activity compared to commercial Raney Ni. In 3-electrode setup, overpotentials of 117 mV and 142 mV were recorded at -0.5 A/cm2 and -1 A/cm2, respectively. Used as cathode in a single cell, a stable cell voltage of 1.65 V at 0.5 A/ cm2 after 45 h was measured. A cell voltage of 1.77 V at 1 A/cm2 confirms the excellent activity under industrial conditions.

In an attempt to obtain fully functional cathode materials for zero-gap alkaline water electrolysis, Ni foam substrates with various pore diameters were modified through galvanostatic electrodeposition of Ni-Sn alloys as an easily scalable procedure. To optimize the production process for each substrate, Ni-Sn alloys were electrodeposited at five different constant current densities. The obtained cathodes were primarily subjected to hydrogen evolution in 1 M KOH to evaluate their activity, while the best-performing samples were further investigated in 30 wt % KOH at 70 degrees C in a three- and two-electrode arrangement. Detailed electrochemical impedance spectroscopy analysis of hydrogen evolution reaction (HER) conducted with a three electrode arrangement indicated two semicircles on the Nyquist plots that confirmed that the adsorption of intermediate (H-ads) is potential dependent. Relevant HER parameters such as exchange current density and relaxation time showed exceptional performance of optimized electrodes. During zero-gap single cell tests with bare Ni foam used as the anode, onset voltages for Ni-Sn cathodes were around 1.64 V (for bare foams, 1.99 V), with cell voltage at 1 A cm(-2) being as low as 2.03 V (for bare foams, 2.57 V). The cathodes were also subjected to a long-term stability test, showing excellent activity preservation. Great stability, low cell voltage, and low production cost confirm their suitability for industrial applications. Top-view as well as cross-section electron microscopy analysis have shown that the entire foam surface was evenly covered with Ni-Sn coating. The composition of the investigated coatings was within the range of Ni(1+x)Sn (0 < x < 0.5) metastable phase and practically independent of deposition current density. Aberration-corrected scanning transmission electron microscopy revealed that the so-called metastable phase is in fact the Ni3Sn2 phase, which is shown for the first time for electrodeposited Ni-Sn alloys.

To obtain highly efficient yet easily produced water-splitting cathodes, Ni-MoO2 composite coatings were electrodeposited at a Ni foam substrate with an open-pore structure, pore size of 450 µm, in a Watts-type bath. The concentration of MoO2 particles (about 100 nm) was varied, while the intensive mixing of the solution was provided by air bubbling with 0.5 L min−1. Electrodeposition was performed at different constant current densities at room temperature. The morphology and composition of the coatings were investigated by SEM and EDS. The hydrogen evolution reaction (HER) was tested in KOH of different concentrations, at several temperatures, in a three-electrode H-cell by recording polarization curves and EIS measurements. The lowest achieved HER overpotential was −158 mV at −0.5 A cm−2. Up-scaled samples, 3 × 3.3 cm2, were tested in a single zero-gap cell showing decreasing cell voltage (from 2.18 V to 2.11 V) at 0.5 A cm−2 over 5 h in 30% KOH at 70 °C with electrolyte flow rate of 58 mL min−1. Compared to pure Ni foams used as both cathode and anode under the same conditions, the cell voltage is decreased by 200 mV, showing improved electrode performance.

The hydrogen evolution reaction (HER) was investigated in 1.0 M KOH at 25 degrees C at Ni foams with different pore sizes (450-1200 & mu;m), and at the Ni-Sn/Ni foam electrodes, where Ni-Sn alloys were electrodeposited from the pyrophosphate-glycine bath using controlled potential coulometry (CPC) technique. The cross-section analysis revealed that rough Ni-Sn alloy covers complete available inner and outer foam surface, while investigated coating composition varied from 62 to 80 at% Ni (20-38 at% Sn). Comparing the HER polarization curves, the overpotential at j =-200 mA cm-2 was 427 mV lower for Ni-Sn samples than for bare Ni foams, while Tafel slopes changed from -120 mV dec- 1 at bare Ni foams to -50 mV dec- 1 for Ni-Sn/Ni foam samples. The lowest overpotential at -100 mA cm-2 achieved is as low as -77 mV. These cathodes could be promising 3D materials for industrial water electrolysis in zero-gap membrane flow cells.

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.

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.

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

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.

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.

For the first time, we report on micro- and nanostructured Ti surfaces produced by ultrashort-pulse laser processing followed by sputter deposition of Pt aiming at efficient cathode electrodes for alkaline water electrolysis. We studied the laser processing-induced surface morphology, the elemental composition of the surface, the specific surface increase, the wetting behavior as well as the activity of the hydrogen evolution reaction. It is demonstrated that ultrashort-pulse laser structuring in combination with thin layer catalyst deposition can dramatically boost the performance of cathodes for the hydrogen evolution reaction due to the enormous increase in specific surface in combination with superhydrophilic and superwetting properties leading to a rapid gas bubble detachment.

In view of alkaline water electrolysis, the activities for the hydrogen evolution reaction of nanocrystalline Fe-based electrode materials were investigated and compared with the activities of polycrystalline Fe and Ni. Electrochemical methods were used to elucidate the overpotential value, the charge transfer resistance and the double layer capacity. Structural properties of the electrode surface were determined with SEM, XRD and XPS analyses. Thus, a correlation between electrochemical and structural parameters was found. In this context, we report on a cyclic voltammetric activation procedure which causes a significant increase of the surface area of Fe-based electrodes leading to a boost in effective activity of the activated electrodes. It was found that the intrinsic activity of activated Fe-based electrodes is very high due to the formation of a nanocrystalline surface layer. In contrast, the activation procedure influences only the intrinsic activity of the Ni electrodes without the formation of a porous surface layer.

The hydrogen evolution reaction (HER) of nanocrystalline Ni-Mo-B alloys was investigated in alkaline solution in comparison with the corresponding crystalline materials and polycrystalline nickel. The nanocrystalline alloys, prepared by melt spinning, were investigated towards the HER in 1 M KOH solution at 298 K. An electrochemical activation procedure (cyclic reduction-oxidation pre-treatment) was used to enhance the apparent HER activity. In case of the crystalline Ni-Mo-B master alloys the origin of the activity can mainly be attributed to an increase of the real surface area (roughening) caused by a dissolution of Mo-containing phases. Interestingly, a roughening of nanocrystalline Ni-Mo-B alloys did not occur, probably, because of the very homogenous and fine microstructure of these materials. The higher HER activity of the nanocrystalline Ni-Mo-B alloys is obviously caused by a higher intrinsic activity of the nanocrystalline Ni-Mo-B alloys and a synergistic effect of Mo. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

In this work different amorphous melt-spun Fe-alloys (Fe82B18, Fe80Si10B10, Fe60CO20Si10B10) were investigated as cathode materials for the alkaline electrolysis of water. In particular, the influence of cobalt as well as the metalloids boron and silicon on the activity for the hydrogen evolution reaction (HER) was studied in 1 M KOH at 298 K using cyclic voltammetric, galvanostatic and polarization techniques. The electrocatalytic activity was evaluated in the view of the overpotential. It was found that cyclic voltammetric techniques can be used to activate the melt-spun Fe-alloys strongly. Different cyclic voltammetric activation procedures are discussed and the influence of the sweep rate and the potential window on the HER activity was elucidated. The experimental data indicate that the addition of metalloids and, most importantly, of cobalt improves the HER activity of the materials. Thus, the overpotential can be reduced by 200 mV compared to polycrystalline Ni. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.