Raney Nickel Electrodes Research Articles

Bridging the Gap between Laboratory and Industrial Scale Electrochemical Characterisation of Raney Ni Electrodes for Alkaline Water Electrolysis

The most mature water electrolysis technology is alkaline electrolysis, where an aqueous solution of KOH is used as the electrolyte. While this technology has been used for decades, there is still a lot of potential to improve the performance of these devices. Much research is focused on the optimisation of the electrodes containing novel catalyst materials that lower the activation energy barrier of the electrolysis process. However, one of the issues described by Ehlers et al.1 is that the current academic electrolysis research is done under conditions that are far from practical (e.g. at low current densities, room temperature, and dilute electrolytes).In this study, we characterise a commercial Raney nickel electrode in various setups using a systematic series of experiments, including a typical laboratory-scale three-electrode setup, two different flow-cell setups and a 10-kW electrolysis stack of 17 cells. In addition to the cell geometry (electrode area ranging from 1 cm2 to 960 cm2), the varied measurement conditions include temperature (ranging from room temperature to 80 degrees Celsius), pressure (from atmospheric pressure to ), electrolyte concentration (from 0.1 M to 30 wt% KOH), and the level of Fe impurities in the electrolyte. The resulting electrochemical data received from different measurement setups and measurement conditions are compared, and insights about the challenges related to correlating laboratory experiments to industrial-scale experiments are provided. Figure 1. Alkaline electrolysis measurement setups with the typical measurement conditions used to study Raney nickel electrodes within this work – a typical laboratory-scale three-electrode setup (a), two different flow-cell setups (b, c) and a 10-kW electrolysis stack of 17 cells (d). Acknowledgements This work was supported by the Applied Research Program of Enterprise Estonia ("Developing and Validating Alkaline Electrolysis Stack Technology with Nanoceramic Electrodes", RE.5.04.22-0109) and by the Estonian Research Council (EAG273 "Highly active electrodes for precious metal free alkaline electrolysers" (1.09.2023−31.08.2024)). References J. C. Ehlers, A. A. Feidenhans’l, K. T. Therkildsen, and G. O. Larrazábal, ACS Energy Lett., 8, 1502–1509 (2023). Figure 1

(Invited) Cost Reduction Strategies in Low Temperature Water Electrolysis with Improved Catalytic Activity

Proton exchange membrane water electrolysis (PEMWE) technology is especially advantageous for green H2 production as a clean energy vector. During the water electrolysis process, the oxygen evolution reaction (OER) requires a large amount of iridium (2-3 mgIr cm−2) as catalyst. This material is scarce and expensive, representing a major bottleneck for large-scale deployment of electrolyzers. Recently, Retuerto et al. have synthesized different Ir double perovskites (Sr2CaIrO6) with the Ir atoms in a high oxidation state (Ir6+/5+) 1 and their catalytic activity was extensively investigated. Specifically, a Ca-based double perovskite (Sr2CaIrO6) has showed the highest OER activity similar to those of Ir or Ir oxides-based catalysts while being stable for the OER in half cell measurements. We report the development of a membrane electrode assembly taking advantage of the high activity of the Sr2CaIrO6 catalyst that has only 0.2 mgIr cm−2, around 10 times lower compared to what it is used in the anodes of commercial PEMWE, showing superior performance and stability. The morphology/structure of the developed anode and Sr2CaIrO6 catalyst, before and after operation in PEMWE, were extensively characterized by X-ray diffraction (XRD, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge structure (XANES). We discuss in this contribution how the finding of this work can provide a strategy to lower the Ir content in commercial PEMWE.Anion exchange membrane water electrolysis (AEMWE) combines the advantages of proton exchange membrane water electrolysis (PEMWE), i.e., high current density while maintaining high efficiency and fast dynamic response with the advantages of alkaline water electrolysis (AWE), i.e., low-cost materials. However, AEMWE technology is still depends on a supporting electrolyte and its durability is low. In this regard, the German Aerospace Center (DLR) is developing novel approaches and cell components. Raney-nickel electrodes were developed via vacuum plasma spraying, reaching performance and stability comparable to SoA MW size PEMWE. The electrodes were further refined, switching to lower cost atmospheric plasma spraying while maintaining high performance. Studying the effect of supporting electrolyte concentration it was found, that lowering the ohmic resistance is by far the largest challenge for high performance AEMWE, especially at low KOH concentrations and electrode kinetics are less impactful. Moreover, a 17% efficiency uplift was achieved by applying a carefully tuned, thermally sprayed, nickel-based macro porous layer (MPL) onto a traditional mesh porous transport layer. Both ohmic and mass transport resistances were found to be lowered by the MPL. FIB-SEM and µCT analysis revealed an ideal structure, i.e., 30-40% porosity, almost exclusively open pores, and a broad pore size distribution2. In a fundamental study3, the mechanism of the OER activity was investigated as well as the effect of trace amounts of iron in Ni(OH)2. X-ray diffraction (XRD) and Thermogravimetric analysis (TGA) TGA analysis lead to the conclusion, that iron stabilized the α-Ni(OH)2which is the most active. CV analysis showed that an important redox switching step is also accelerated by Fe-doping. M. Retuerto, L. Pascual, J. Torrero, M. A. Salam, Á. Tolosana-Moranchel, D. Gianolio, P. Ferrer, P. Kayser, V. Wilke, S. Stiber, V. Celorrio, M. Mokthar, A. S. Gago, K. A. Friedrich, M. A. Peña, J. A. Alonso, D. G. Sanchez, S. Rojas, Highly Active and Stable OER Electrocatalysts Derived from Sr2MIrO6 for Proton Exchange Membrane Water Electrolyzers. Nat. Commun. 2022, 13, 7935. Razmjooei, F.; Morawietz, T.; Taghizadeh, E.; Hadjixenophontos, E.; Mues, L.; Gerle, M.; Wood, B. D.; Harms, C.; Gago, A. S.; Ansar, S. A.; Friedrich, K. A., Increasing the performance of an anion-exchange membrane electrolyzer operating in pure water with a nickel-based microporous layer. Joule 2021, 5 (7), 1776-1799. Wang, L.; Saveleva, V. A.; Eslamibidgoli, M. J.; Antipin, D.; Bouillet, C.; Biswas, I.; Gago, A. S.; Hosseiny, S. S.; Gazdzicki, P.; Eikerling, M. H.; Savinova, E. R.; Friedrich, K. A., Deciphering the Exceptional Performance of NiFe Hydroxide for the Oxygen Evolution Reaction in an Anion Exchange Membrane Electrolyzer. ACS Applied Energy Materials 2022, 5 (2), 2221-2230.

Room temperature, fast fabrication of square meter-sized oxygen evolution electrode toward industrial alkaline electrolyzer

NiFe-based electrode materials exhibit great promise for next-generation efficient oxygen evolution reaction (OER) electrocatalysts in alkaline medium, but they are difficult to be scaled up for large-area fabrication and are lack of robust research under real industrial conditions. Here we present a rapid, room-temperature sulfuration strategy that transforms stainless steel meshes into highly active and stable oxygen evolution electrodes. Such method is easy to be scaled up to produce square meter-sized stainless steel electrodes (1 m × 1 m) with NiFeCr-containing trimetal sulfides on the surface. In a standard three-electrode cell, the sulfurated stainless steel electrode exhibits 7.2 times higher OER activity than the corresponding stainless steel, and possesses remarkable catalytic stability for over 1000 h at the current density range of 100–200 mA cm−2. During the OER, the Cr and S species are demonstrated to be easily detached from the electrode surface, and the in situ formed γ-(Fe,Ni)OOH is found to be the electrocatalytic active phase. Furthermore, we integrate the sulfurated stainless steel electrode into an industrial alkaline electrolyzer as the anode (400 cm2). Our results demonstrate that the electrolyzer based on the sulfurated stainless steel electrode exhibits a better catalytic activity than the electrolyzer based on the Raney nickel electrode, a widely-adopted electrode in commercial water–alkali electrolyzers, and delivers a catalytic current of c.a. 300 mA cm–2 for over 120 h under the industrial catalytic conditions (30% KOH, 80 °C).

Fabrication of High Performing and Durable Nickel-Based Catalyst Coated Diaphragms for Alkaline Water Electrolyzers

In this work, a catalyst coated-diaphragm (CCD) for classical alkaline electrolysis was prepared by the blade-coating method, using Raney nickel as HER catalyst and a Zirfon® (AGFA Perl UTP 500) diaphragm. Our best CCD reduced the overvoltage in an alkaline single cell by 270 mV at 300 mA cm−2 compared to the benchmark, mainly due to the higher catalytic activity and surface area of the Raney nickel electrode. The new electrode system also showed a low degradation rate of 22 μA cm−2 h−1 after 1000 h at a cell voltage of 2 V. The gas purity tests showed that the CCD has hydrogen in oxygen contamination well below the lower explosion limit, even at low current densities. Therefore, we propose the use of our novel CCD architecture for atmospheric alkaline electrolyzers, which have a partly separated electrolyte cycle.

A Powder Metallurgy Route to Produce Raney-Nickel Electrodes for Alkaline Water Electrolysis

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/cm² 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.

Electrochemical characterization of Raney nickel electrodes prepared by atmospheric plasma spraying for alkaline water electrolysis

A Raney Ni electrode was prepared by the simple and economical atmospheric plasma spraying method. It showed excellent performance for hydrogen evolution reaction (HER), as indicated by a Tafel slope of 54mV/dec and overvoltage of 108mV at 300mA/cm2. The Ni–Al alloy coating contained a NiAl phase, which has a very slow Al leaching rate in alkaline solution. H2 heat treatment of the electrode enhanced the uniformity of Al distribution in the coating and adhesion of the coating to the substrate. However, the HER performance did not improve and the electrode was rendered more structurally vulnerable to deactivation.

Deactivation Mechanisms of Atmospheric Plasma Spraying Raney Nickel Electrodes

Major current research trends in alkaline electrolysis are targeted toward improving efficiency, extending the durability and decreasing the price of the electrolyzer units. The novel atmospheric plasma spraying (APS) production method for Raney nickel coatings demonstrated good efficiency for the hydrogen evolution reaction (HER). The research work performed focused on the investigation of the degradation/deactivation mechanisms of these APS electrodes. The formation of hydrides was recognized as a key contributor toward cathode deactivation and to prevent it, in-situ activation in the electrolyte as well as hydrides oxidation, through controlled switching of the cell potential were carried out. Both techniques showed some effect in suppressing the deactivation process but failed to eliminate it completely. The APS Raney nickel cathodes also presented good stability for variable load operations during the cycling.

Evaluation of Raney nickel electrodes prepared by atmospheric plasma spraying for alkaline water electrolysers

The work describes the evaluation of Raney nickel electrodes prepared by the technique of atmospheric plasma spraying (APS). The APS Raney nickel layers of 30 μm, 100 μm and 300 μm thicknesses were characterised prior to and post-chemical activation by SEM. Following further electrochemical activation, the performance of these layers towards hydrogen evolution reaction (HER) were evaluated using potentiodynamic Tafel analysis and electrochemical impedance spectroscopy (EIS) in 30% KOH solutions over the temperature range 30 °C–80 °C. Large surface area increases, in relation to smooth nickel, were obtained for these layers following activation and these were also confirmed from cyclic voltammetry measurements. The analysis of the data indicated that of the 3 thicknesses examined, the best electrocatalytic activity towards HER was obtained for 100 μm sample, with an efficiency (based on the Higher Heating Value for H2) equal to 96% at a current density of 300 mA cm−2 and temperature of 70 °C.

ChemInform Abstract: Electrocatalytic Hydrogenation Using Precious Metal Microparticles in Redox-Active Polymer Films.

Glassy carbon felt electrodes have been modified by electrodeposition of poly(pyrrole-viologen) films (derived from N,N{prime}-dialkyl-4,4{prime}-bipyridinium salts), followed by electroprecipitation of precious metal (Pt, Pd, Rh, or Ru) microparticles. The resulting electrodes have been proved to be active for the electrocatalytic hydrogenation of conjugated enones (2-cyclohexen-1-one, cryptone, carvone, isophorone), styrene, and benzonitrile in aqueous media (pH 1). Despite low loadings of metal catalysts, high electric and products yields and a long term stability of these cathodes have been observed. The influence of the metal loading and the polymer structure on the catalytic efficiency as well as the selectivity obtained according to the metal catalyst used have been studied. Comparison with results previously reported for other catalytic cathodes like Pt/Pt, Pd/C, or Raney nickel electrodes proves the high efficiency of these metal microparticles within redox polymer film based electrodes.

Electrocatalytic Hydrogenation and Hydrogenolysis of Aromatic Halides by Raney Nickel in the Presence of Different Surfactants

Abstract Electrocatalytic hydrogenolysis and hydrogenation of 4-halophenols, 4-chloroaniline and chloronitrobenzene have been investigated in aqueous media using different surfactant agents on two kinds of cathodes investigated on, Raney nickel electrode and carbon electrode.

Electrocatalytic hydrogenation of alkyl-substituted phenols in aqueous solutions at a Raney nickel electrode in the presence of a non-micelle-forming cationic surfactant

The electrocatalytic hydrogenation (ECH) of 2,6-dimethylphenol and 2-tert-butylphenol was performed at RaNi cathodes in aqueous buffers containing various amounts of didodecyldimethylammonium bromide (DDAB). Without surfactant, 2,6-dimethylcyclohexanol, 2-tert-butylcyclohexanone and 2-tert-butylcyclohexanol were obtained, at 65 °C, with very low yields. The surfactant effect on the yields, the selectivity of the reaction and the diastereoisomeric composition of alkylcyclohexanols produced was studied in acidic and basic solutions in relation to the substrate adsorption. At pH 9 the efficiency of the hydrogenation reaction was significantly improved by low amounts of DDAB, which led to an increase of the alkylcyclohexanols formation. In particular, cis-2-tert-butylcyclohexanol was obtained with a high diastereoselectivity.

Alkaline fuel cell: carbon nanobeads coated with metal catalyst over porous ceramic for hydrogen electrode

The development of a hydrogen electrode using a porous ceramic coated with carbon nanobeads for an alkaline fuel cell (AFC) is reported. This electrode can provide necessary strength and porosity to enable hydrogen to diffuse without allowing electrolyte to percolate inside the electrode. Various catalysts (Pt, Ni, Co and Fe) are electrochemically dispersed over the carbon nanobeads to examine their performance in the alkaline fuel cell. Turpentine oil has been used as a precursor for preparing the carbon nanobeads by a chemical vapour deposition technique. Scanning electron microscopic and transmission electron microscopic images show that the carbon nanobeads have sizes between 500 and 650 nm and are spread uniformly over the entire ceramic substrate. X-ray diffraction (XRD) patterns indicate that the nanobeads are graphitic in nature. Thus, the electrode is highly conductive. The current–voltage characteristics and chronopotentiometry of a half cell (i.e. hydrogen electrode coated with different electrocatalysts) and a full cell (using both hydrogen and oxygen electrodes) with 30% KOH solution are measured. About 93% of the theoretical hydrogen dissociation voltage is obtained with Ni and Pt catalyst. All other metals (Co and Fe) give a lower voltage. Ni-coated carbon nanobeads deposited over a ceramic oxide can be used in place of Raney nickel electrode as their characteristics are similar to those of a platinum electrode.

Electrocatalytic Hydrogenation of Indigo : Process Optimization and Scale-Up in a Flow Cell

The industrial feasibility of the electrocatalytic hydrogenation of indigo on Raney nickel electrodes as a suspension in an aqueous medium has been studied in a divided flow cell. The attempt was made to establish optimized conditions in the system, and a scale-up in indigo concentration to 10 g/L was achieved. Increasing pH can enhance the reduction rate and a maximum conversion has been found by optimizing current density and temperature. The reaction rate is clearly enhanced in the presence of ultrasonic waves and organic solvents. Methanol is among the best cosolvents and was used in concentrations of 10 vol %. With Raney nickel electrodes an optimized current efficiency of 13% could be reached at 95% conversion. This value was enhanced to 19% by using electrodes doped with platinum particles. © 2002 The Electrochemical Society. All rights reserved.

Electrocatalytic hydrogenation of phenol in aqueous solutions at a Raney nickel electrode in the presence of cationic surfactants

The electrocatalytic hydrogenation (ECH) of phenol at a Raney nickel cathode was studied in aqueous solutions. At 30 °C, without surfactants, cyclohexanol was obtained with low or medium yields. The best results were observed in alkaline solutions (pH 9). At pH 2 the efficiency of the hydrogenation reaction is significantly improved by low amounts of didodecyldimethylammonium bromide (DDAB). This surfactant effect is studied in relation to the substrate and hydrogen adsorption phenomena.

Improved performance of Raney nickel electrode by the addition of electrically conductive materials for hydrogen oxidation reaction

Abstract The performance of Raney Ni electrodes with electrically conductive materials for hydrogen oxidation reaction on an alkaline fuel cell was investigated in 6 M KOH solution at 80°C. The Raney Ni electrodes with carbon black (Vulcan XC-72 and Ketjen black) showed higher performance than Raney Ni electrode without carbon black for hydrogen oxidation. The improved performance of Raney Ni electrode was caused on the enhanced conductivity of electrodes, the increase of electrolyte diffusivity and the enlargement of active sites. When various carbon blacks — Vulcan XC-72 and Ketjen black — with different surface area and conductivity were added, Raney Ni electrode with Vulcan XC-72, which had a relatively large surface area and high conductivity, showed higher performance than that with Ketjen black. When non-porous nickel powder as a conductive material was added, the Raney Ni electrodes with 20% nickel powder showed high performance.

Development of electrode morphologies of interest in electrocatalysis: Part 2: Hydrogen evolution reaction on macroporous nickel electrodes

The current–potential dependence for the hydrogen evolution reaction (HER) was determined on macroporous nickel electrodeposits with roughness factors ranging between 7 and 1700 in alkaline solution. It has been demonstrated that the active electrodic area is conditioned by the presence of occluded hydrogen gas inside the pores. Starting from measurements of the total real surface area and the polarization resistance, the active area for the HER (wetted area) was determined. On the basis of these results, it has been concluded that the electrocatalytic activity is the same for all these electrodeposits. The kinetic parameters corresponding to the Volmer–Heyrovsky–Tafel mechanism were evaluated and critically compared with those previously determined for smooth nickel electrodes in the same experimental conditions. Besides, the apparent electrocatalytic activity was compared with that of a Raney–Nickel electrode.

Electrocatalytic hydrogenation of lignin models at Raney nickel and palladium-based electrodes

The electrocatalytic hydrogenation (ECH) of β-O-4 lignin model compounds has been carried out at constant current at Raney nickel and palladium-based cathodes in aqueous sodium hydroxide solution at temperatures ranging from 25 to 75°C. It was found that the hydrogenolysis of phenolic β-arylethyl-aryl ethers with one β-O-4 linkage takes place at both types of electrodes to give a mixture of phenolic compounds. The ECH of 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-ethanol (model 1) at Raney nickel gives guaiacol (9), acetovanillone (11b), alpha-methylvanillyl alcohol (12b), and products derived from their further hydrogenation. The β-O-4 bond is more difficult to cleave upon replacing one hydrogen of the methylene group of 1 by a hydroxymethyl group (see 2). However, model 4 with two β-O-4 linkages obtained by the introduction of an α-methylvanillyl group at the phenolic position of 1 is hydrogenolysed at the same rate as 1 at Raney nickel. Only the C-O aryl bond attached to the hydroxyethylphenol moiety is cleaved. At palladium, the hydrogenolysis of 1 requires only half of the theoretical amount of electricity due to the generation of chemisorbed hydrogen by dehydrogenation of 1 followed by hydrogenolysis of the resulting ketone. A general reaction scheme is proposed for the ECH of model 1.Key words: Lignins, lignin models, electrocatalytic hydrogenation, Raney nickel electrodes, palladium electrodes.

Development of electrode morphologies of interest in electrocatalysis. Part 1: Electrodeposited porous nickel electrodes

Pure nickel electrodeposits with macropores were prepared from electrolytic solutions of 0.2 M NiCl 2 and NH 4Cl with concentrations varying between 0.25 and 4 M. The effects of the electrodeposition current density and the NH 4Cl concentration on the surface morphology were determined. Surface area, faradaic efficiency and fractal dimension of the cross-section of the electrodeposits were evaluated also. From these results, it was concluded that highly porous metallic matrices can be obtained, with very high roughness factors and excellent mechanical resistance, yet at very high apparent current densities of electrodeposition (5 A cm −2). The use of this type of electrodeposition bath is suggested for the preparation of Raney-Nickel electrodes, in order to improve the accessibility of reactants to the electrode surface.

Electrocatalytic hydrogenation of lignin models at Raney nickel and palladium-based electrodes

Electrocatalytic hydrogenation of lignin models at Raney nickel and palladium-based electrodes

99/00456 Hydrogen oxidation characteristics of Raney nickel electrodes with carbon black in an alkaline fuel cell

99/00456 Hydrogen oxidation characteristics of Raney nickel electrodes with carbon black in an alkaline fuel cell