A novel nickel electrode with gradient porosity distribution for alkaline water splitting

Electrodes with porous structures are widely used in commercial alkaline water splitting devices. By optimizing the porous structure, the efficiency of alkaline water splitting devices could be evidently promoted. In this work, nickel electrodes with gradient porosity distribution were designed and fabricated through selective laser melting. The effect of gradient porous distribution structure on electrochemical performance of Ni electrode was evaluated. The results showed that with small pores towards counter electrode the prepared Ni electrodes exhibits better anodic performance, and a better cathodic performance is observed with big pores towards the counter electrode. It was considered as joint effect of active specific area and mass transfer. Finally, by applying an electrolysis cell with optimized arrangement, an improvement of 14% electrolysis efficiency is achieved, which shows the potential of Ni electrodes with gradient porosity distribution to be applied in commercial application of hydrogen generation.     

Ni/Fe electrodes prepared by electrodeposition method over different substrates for oxygen evolution reaction in alkaline medium

A series of Ni/Fe electrodes have been prepared by electrodeposition of metal salt precursors on different substrates. The surface morphology, chemical composition and electrochemical characteristics of these electrodes were studied by various physico-chemical techniques such as X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). The electrochemical properties of the electrodes were examined by steady-state polarization curves. First, the influence of features such as Ni/Fe composition and type of substrate for the oxygen evolution reaction (OER) were determined by electrochemical techniques in a conventional 3-electrodes cell. The overpotential for the OER is lower for the electrodes with the higher concentrations of Ni. The electrodes with a Ni/Fe composition of 75/25 wt.% electrodeposited on steel mesh and/or 75/25 and 50/50 wt.% on nickel foam result in the most active configurations for the OER. These electrodes were further tested as anodes for alkaline water electrolysis during at least 70 h. In order to understand their activity and stability, the used electrodes were also characterized by SEM and compared to the fresh electrodes. Among the compositions and substrates examined, the Ni50Fe50-Nf electrode exhibited the lowest overpotential (2.1 V) for the OER and the higher stability as anode in an alkaline water electrolysis cell.     

Noble fabrication of Ni–Mo cathode for alkaline water electrolysis and alkaline polymer electrolyte water electrolysis

Among the catalysts for hydrogen evolution reaction (HER) in alkaline media, Ni–Mo turns out to be the most active one. Conventional preparations of Ni–Mo electrode involve repeated spraying of dilute solutions of precursors onto the electrode substrate, which is time-consuming and usually results in cracking and brittle electrodes. Here we report a noble fabrication of Ni–Mo electrode for HER. NiMoO₄ powder was synthesized and used as the precursor. After reduction in H₂ at 500 °C, the NiMoO₄ powder layer was converted to a uniform and robust electrode containing metallic Ni and amorphous Mo(IV) oxides. The distribution of Ni and Mo components in this electrode is naturally uniform, which can maximize the interaction between Ni and Mo and benefit the electrocatalysis. The thus-obtained Ni–Mo electrode exhibits a very high catalytic activity toward the HER: the current density reaches 700 mA/cm² at 150 mV overpotential in 5 M KOH solution at 70 °C. This new fabrication method of Ni–Mo electrode is not only suitable for alkaline water electrolysis (AWE), but also applicable to the alkaline polymer electrolyte water electrolysis (APEWE), an emerging technique for efficient production of H₂.     

Application of green hydrogen with theoretical and empirical approaches of alkaline water electrolysis: Life cycle-based techno economic and environmental assessments of renewable urea synthesis

Alkaline water electrolysis which is the most commercialized and mature technology of water electrolysis was researched to improve performance by the Korea Institute of Energy Research (KIER). In line with the trend of energy shift, renewable urea production through hydrogen production from alkaline water electrolysis was proposed in this work. To validate the process modeling of renewable urea production and hydrogen performance analysis with I–V curves was assessed. Economic and life cycle assessments were conducted to provide quantitative guidelines for renewable urea production. Absolutely, the influential factor of unit urea production cost was hydrogen from alkaline water electrolysis and environmental assessment results as well. Moreover, the guidelines for renewable urea production were provided through cost estimation and life cycle assessment. In summary, hydrogen production from alkaline water electrolysis had a significant impact on urea production and for this reason, research on alkaline water electrolysis should continue for further development.     

Improved cathodes for industrial electrolytic hydrogen production

Reduced overpotentials for the generation of hydrogen by alkaline water electrolysis can be achieved with a.c. activation of porous Ni electrodes. Reductions of 50–60 mV were attained which would contribute towards reducing costs in commercial pure hydrogen production by electrolysis.     

Intermetallics as advanced cathode materials in hydrogen production via electrolysis

Intermetallics phases along Mo–Pt phase diagram have been investigated as cathode materials for the production of hydrogen by electrolysis from water KOH solutions, in an attempt to increase the electrolytic process efficiency. These materials were compared with conventional cathodes (Fe and Ni), often used in the alkaline electrolysis, and also with the intermetallic Ti–Pt. An significant upgrade of the electrolytic efficiency using intermetallics in pure KOH electrolyte was achieved in comparison with conventional cathode materials.     

Electrolytic splitting of saline water: Durable nickel oxide anode for selective oxygen evolution

Increasing generation of renewable electricity offers a source of green electric power, which can be exploited for the sustainable production of hydrogen through the electrolysis of water. Scarcity of fresh water resources promotes the search for electrode materials, which could be used for splitting of saline water into hydrogen and oxygen without formation of hazardous chlorine compounds, and also withstand highly aggressive chloride medium. In the present study we demonstrate that nickel oxide layer formed by means of simple spray-pyrolysis technique on conductive glass substrate can be used as corrosion resistant and 100% O₂-selective anode for the electrolysis of alkaline (pH 14) chloride solution. Dimensional stability and durability of the anode is secured by the absence of metallic phase, whereas selectivity towards oxygen evolution and absence of chloride oxidation is shown to be controlled thermodynamically. The obtained experimental evidence that hydrogen peroxide is formed as intermediate in oxygen evolution reaction under conditions investigated has led to new mechanistic insights and the mechanism of Ni(IV)-mediated electrocatalytic oxidation of water molecules in alkaline chloride medium has been proposed.     

Electrocatalytic properties of Ti2Ni/Ni-Mo composite electrodes for hydrogen evolution reaction

A composite electrode as hydrogen cathodes composed of Ti₂Ni hydrogen absorbing alloys and a Ni-Mo electrocatalyst was prepared for alkaline water electrolysis. The electrocatalytic properties of hydrogen evolution reaction (HER) are carried out in a 30 wt% KOH solution at 70 °C. The surface morphology and chemical composition of the cathode were also examined. The experimental results show that the composite cathode has a low hydrogen overpotential (ca. 60 mV at 70 °C in 30 wt% KOH) and excellent stability under conditions of continuous electrolysis and intermittent electrolysis with power interruption shutdown. The stability mechanism of the cathode against intermittent electrolysis is discussed.     

Nickel/Cobalt nanoparticles for electrochemical production of hydrogen

The electrolytic production of hydrogen (POH) from alkaline water electrolysis is at the forefront of technology for alternative energy sources of the future. The present work evaluates the improvement of electro-catalytic activity (ECA) on Ni electrodes for the POH by electrodeposition of cobalt (Co). Tests were conducted in alkaline solution and the ECA of Ni and Ni–Co electrodes for the POH were compared using alternative and direct current techniques. Tafel polarization tests exemplified a significant improvement in the ECA of the bimetallic electrode (Ni–Co) compared with the Ni-electrode. Besides, the bimetallic electrode required less input overpotential energy (η) for the given POH rate under constant current density. Electrochemical impedance spectroscopy (EIS) revealed a significant increase in the number of electrochemical active sites and changed the surface morphology following the electrodeposition of Co over Ni electrodes.     

Development of durable and efficient electrodes for large-scale alkaline water electrolysis

A new type of electrodes for alkaline water electrolysis is produced by physical vapour depositing (PVD) of aluminium onto a nickel substrate. The PVD Al/Ni is heat-treated to facilitate alloy formation followed by a selective aluminium alkaline leaching. The obtained porous Ni surface is uniform and characterized by a unique interlayer adhesion, which is critical for industrial application. IR-compensated polarisation curves prepared in a half-cell setup with 1 M KOH electrolyte at room temperature reveals that at least 400 mV less potential is needed to decompose water into hydrogen and oxygen with the developed porous PVD Al/Ni electrodes as compared to solid nickel electrodes. High-resolution scanning electron microscope (HR-SEM) micrographs reveal Ni-electrode surfaces characterized by a large surface area with pores down to a few nanometre sizes. Durability tests were carried out in a commercially produced bipolar electrolyser stack. The developed electrodes showed stable behaviour under intermittent operation for over 9000 h indicating no serious deactivation in the density of active sites.     

Graphene oxide modified non-noble metal electrode for alkaline anion exchange membrane water electrolyzers

This paper reports the performance of a graphene oxide modified non noble metal based electrode in alkaline anion exchange water electrolyzer. The electrolytic cell was fabricated using a polystyrene based anion exchange membrane and a ternary alloy electrode of Ni as cathode and oxidized Ni electrode coated with graphene oxide as anode. The electrochemical activity of the graphene oxide modified electrode was higher than the uncoated electrode. The anion exchange membrane water electrolyzer (AEMWE) with the modified electrode gave 50% higher current density at 30 °C with deionised water compared to that of an uncoated electrode at 2 V. Performance was found to increase with increase in temperature and with the use of alkaline solutions. The results of the solid state water electrolysis cell are promising method of producing low cost hydrogen.     

Electrochemical characterization of a NiCo/Zn cathode for hydrogen generation

Hydrogen is considered to be the most promising candidate as a future energy carrier. One of the most used technologies for the electrolytic hydrogen production is alkaline water electrolysis. However, due to the high energy requirements, the cost of hydrogen produced in such a way is high.In continuous search to improve this process using advanced electrocatalytic materials for the hydrogen evolution reaction (HER), high area NiCo/Zn electrodes were prepared on AISI 304 stainless steel substrates by electrodeposition. After preparing, the alloys were leached of to remove part of the zinc and generate a porous layer (type Raney electrodes). The presence of a thin Ni layer between the substrate and the Raney coating favour the adherence of the latter. The porous NiCo/Zn electrode was characterized by SEM, EDX, confocal laser microscopy, and electrochemical impedance spectroscopy. HER on this electrode was evaluated in 30 wt.% KOH solution by means of polarization curves, hydrogen discharge curves, and galvanostatic tests. Results show that the developed electrode presents a most efficient behaviour for HER when comparing with the smooth Ni cathode. The high electrode activity was mainly attributed to the high surface area of the developed electrode.     

Development and testing of a novel catalyst-coated membrane with platinum-free catalysts for alkaline water electrolysis

A stable, platinum-free catalyst-coated anion-exchange membrane with a promising performance for alkaline water electrolysis as an energy conversion technology was prepared and tested. A hot plate spraying technique used to deposit electrodes 35 or 120 μm thick on the surface of an anion-selective polymer electrolyte membrane. These thicknesses of 35 and 120 μm corresponding to the catalyst load of 2.5 and 10 mg cm⁻². The platinum free catalysts based on NiCo₂O₄ for anode and NiFe₂O₄ for cathode were used together with anion selective polymer binder in the catalyst/binder ratio equal to 9:1. The performance of the prepared membrane-electrode assembly was verified under conditions of alkaline water electrolysis using different concentrations of liquid electrolyte ranging from 1 to 15 wt% KOH. The electrolyser performance was compared to a cell utilizing a catalyst-coated Ni foam as the electrodes. The prepared membrane-electrode assembly stability at a current load of 0.25 A cm⁻² was verified by a 72-hour electrolysis test. The results of the experiments indicated the possibility of a significant reduction of the catalyst loading compared to a catalyst-coated substrate approach.     

Ultrashort pulse laser-structured nickel surfaces as hydrogen evolution electrodes for alkaline water electrolysis

In this study, we report on micro- and nanostructured Ni surfaces produced by an ultrashort pulse laser process as cathode materials for the alkaline electrolysis of water. We studied the influence of the laser-induced microstructure and surface morphology as well as a cyclic voltammetric activation process on the electrochemical activity of the hydrogen evolution reaction. Galvanostatic techniques, steady-state polarization curves to attain Tafel parameters and capacitance calculations via electrochemical impedance spectroscopy were used to analyze the electrodes. The analyses reveal that the ultrashort pulse laser process increases the specific surface on formerly flat Ni surfaces. Further, the cyclic voltammetric activation process gives rise to an increased intrinsic activity. Both effects lead to a strongly reduced overpotential value. This work demonstrates that different processes can be combined to dramatically boost the activity of Ni electrodes for the hydrogen evolution reaction.     

Multifunctional Co–B–O@CoxB catalysts for efficient hydrogen generation

The development of efficient and non-noble catalyst is of great significance to hydrogen generation techniques. Three surface-oxidized cobalt borides of Co–B–O@Co_xB (x = 0.5, 1 and 2) have been synthesized that can functionalize as active catalysts in both alkaline water electrolysis and the hydrolysis of sodium borohydride (NaBH₄) solution. It is discovered that oxidation layer and low boron content favor the oxygen evolution reaction (OER) activity of Co–B–O@Co_xB in alkaline water electrolysis. And surface-oxidized cobalt boride with low boron content is more active toward hydrolysis of NaBH₄ solution. An alkaline electrolyzer fabricated using the optimized electrodes of Co–B–O@CoB₂/Ni as cathode and Co–B–O@Co₂B/Ni as anode can deliver current density of 10 mA cm⁻² at 1.54 V for overall water splitting with satisfactory stability. Meanwhile, Co–B–O@Co₂B affords the highest hydrogen generation rate of 3.85 L min⁻¹ g⁻¹ for hydrolysis of NaBH₄ at 25 °C.     

(Fe,Ni)S2@MoS2/NiS2 hollow heterostructure nanocubes for high-performance alkaline water electrolysis

Hollow hybrid heterostructures are regarded to be promising materials as bifunctional electrocatalysts for highly efficient water electrolysis due to their intriguing morphological features and remarkable electrochemical properties. Herein, with FeNi-PBA as both a precursor and morphological template, we demonstrate the rational construct of cost-effective (Fe,Ni)S₂@MoS₂/NiS₂ hollow hybrid heterostructures as bifunctional electrocatalysts for alkaline overall water splitting. Microstructural analysis shows that the hybrid is a kind of hierarchical heterostructure composed of MoS₂/NiS₂ nanosheets/nanoparticles in situ grown on hollow (Fe,Ni)S₂ nanocubes with abundant heterointerfaces, which effectively maximizes the electrochemical active sites to the accessible electrolyte ions, leading to the promoted charge transfer. As expected, the hybrid shows remarkable alkaline electrocatalytic performance, such as hydrogen evolution overpotential of 176 mV and oxygen evolution overpotential of 342 mV at 50 mA cm^?2, as well a cell voltage of 1.65 V at 20 mA cm^?2. Moreover, the stability and durability are greatly enhanced under harsh electrochemical conditions. This study opens a new venue for developing earth-abundant bifunctional electrocatalysts with hollow hybrid heterostructures for alkaline water electrolysis in the future.     

Recent development in electrocatalysts for hydrogen production through water electrolysis

Hydrogen is a carbon-free alternative energy source for use in future energy frameworks with the advantages of environment-friendliness and high energy density. Among the numerous hydrogen production techniques, sustainable and high purity of hydrogen can be achieved by water electrolysis. Therefore, developing electrocatalysts for water electrolysis is an emerging field with great importance to the scientific community. On one hand, precious metals are typically used to study the two-half cell reactions, i.e., hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, precious metals (i.e., Pt, Au, Ru, Ag, etc.) as electrocatalysts are expensive and with low availability, which inhibits their practical application. Non-precious metal-based electrocatalysts on the other hand are abundant with low-cost and eco-friendliness and exhibit high electrical conductivity and electrocatalytic performance equivalent to those for noble metals. Thus, these electrocatalysts can replace precious materials in the water electrolysis process. However, considerable research effort must be devoted to the development of these cost-effective and efficient non-precious electrocatalysts. In this review article, we provide key fundamental knowledge of water electrolysis, progress, and challenges of the development of most-studied electrocatalysts in the most desirable electrolytic solutions: alkaline water electrolysis (AWE), solid-oxide electrolysis (SOE), and proton exchange membrane electrolysis (PEME). Lastly, we discuss remaining grand challenges, prospect, and future work with key recommendations that must be done prior to the full commercialization of water electrolysis systems.     

Intermetallics as cathode materials in the electrolytic hydrogen production

The intermetallics of transition metals have been investigated as cathode materials for the production of hydrogen by electrolysis from water–KOH solutions, in an attempt to increase the electrolytic process efficiency. We found that the best effect among all investigated cathodes (Hf₂Fe, Zr–Pt, Nb–Pd(I), Pd–Ta, Nb–Pd(II), Ti–Pt) exhibits the Hf₂Fe phase. These materials were compared with conventional cathodes (Fe and Ni), often used in the alkaline electrolysis. A significant upgrade of the electrolytic efficiency using intermetallics, either in pure KOH electrolyte or in combination with ionic activators added in situ, was achieved.The effects of these cathode materials on the process efficiency were discussed in the context of transition metal features that issue from their electronic configuration.     

Electrolysis of black liquor for hydrogen production: Some initial findings

Electrolysis of black liquor, an effluent from paper industry, was carried out and compared with alkaline water electrolysis. Energy efficiency in terms of HHV of hydrogen was found in the range of 84–97% whereas under similar conditions alkaline water electrolysis could not give more than 66% efficiency. Hydrogen evolution in black liquor electrolysis was possible even at an inter electrode potential of 1.17 V but in alkaline water electrolysis there was no hydrogen production below an inter electrode potential of 1.31 V. In addition to this, alkali lignin, amounting to 28–46 mg/mg of hydrogen produced, was separated at anode during black liquor electrolysis, which, on account of its good calorific value, has the potential of significantly improving the overall energy efficiency of the process.     

Enhanced hydrogen production through alkaline electrolysis using laser-nanostructured nickel electrodes

This study describes the fabrication of ultrafast laser-induced periodic nanostructures on Nickel sheets and their use as cathodes in alkaline electrolysis. For the first time, to the best of our knowledge, laser-nanostructured Ni sheets were used as cathode electrodes in a custom-made electrolysis cell at actual, Hydrogen producing conditions, and their efficiency has been compared to the untreated Nickel sheets. The electrochemical evaluation showed higher J_peaks, lower overpotential, and enhanced double-layer capacitance for the nanostructured electrode. A decrease in the Tafel slope was also found for the nanostructured electrode. The hydrogen production efficiency was found to be 3.7 times larger for the laser-nanostructured Nickel electrode, which was also confirmed by current-time measurements during electrolysis. Also, a novel approach is proposed to improve the stability of the current density during electrolysis and, therefore, the hydrogen production process by about 10%.