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.     

Hydrogen producing cycles using electricity and heat-hydrogen halide cycles: Electrolysis of HBr

An alternative to water electrolysis or thermochemical water splitting for hydrogen production could be a process using both electricity and heat. The electrolysis of hydrogen halides may be an important step of such hybrid processes. Some preliminary results obtained by electrolyzing concentrated hydrobromic acid with different electrode materials and at different temperatures are presented. High current densities were obtained at 1 V and less with electrodes of noble metals at low bromine concentrations.     

Experimental investigation for novel electrode materials of coal-assisted electrochemical in-situ hydrogen generation: Parametric studies using single-chamber cell

In this study, the functional group contents of coals of different geological ages to be used in hydrogen production by electrolysis were examined by Fourier Transform Infrared Spectroscopy (FT-IR) analysis, and parametric studies were carried out with the coal type with the highest functional group content. In the parametric studies, the effect of Fe²⁺ ions with known catalytic activity in coal electrolysis, the effects of electrode activation, different electrode materials, temperature, coal concentration and distance between electrodes on current density were investigated. Also, long-term performance test was carried out. It was found that, the highest current density values were observed in the presence of Fe²⁺ ions, at the activated Zn/Zn electrode material and at the nearest electrode distance. In addition to these results, it was determined that instead of high temperatures, high current density values can be obtained at relatively low temperatures such as 50°C and lower coal concentrations.     

Porous electrode improving energy efficiency under electrode-normal magnetic field in water electrolysis

The porous electrodes (Ni, Cu) with 110 pores per inch (PPI) are adopted in water electrolysis for hydrogen production under normal-to-electrode magnetic field. The result shows that the voltage drop between electrodes can be reduced up to 2.5% under 0.9 T field, and the electric energy efficiency is improved correspondingly. Based on the numerical simulation method, the micro-magnetohydrodynamic (micro-MHD) convection induced by Lorentz force within the porous structure is found. The results showed that although the apparent current direction is parallel to magnetic field outside the porous electrode, the electric field may be distorted within the porous structure, and the Lorentz force is involved near the rib of the micro structure where the current is not parallel to the magnetic field any more. Micro-MHD plays the role of strengthening the mass transfer and facilitating bubble to eject from the porous structure, which results in the cell voltage decreasing. The combined application of porous electrode and magnetic field should be potential to further improve energy efficiency of water electrolysis for hydrogen production.     

High temperature solid oxide electrolysis cell employing porous structured (La0.75Sr0.25)0.95MnO3 with enhanced oxygen electrode performance

An efficient steam electrolysis process for hydrogen production via a solid oxide electrolysis cell using porous network-like strontium doped lanthanum manganite (LSM)-yttria stabilized zirconia (YSZ) as the oxygen electrode material has been demonstrated. The porous network-like LSM powder was prepared by a nitrate–glycine combustion method. Impedance spectra and voltage-current density curves were measured as a function of cell current density and absolute humidity at 800 °C and 900 °C to characterize the cell performance. The cell area specific resistance (ASR) was 0.26 Ω cm² at 900 °C with 0.5 A/cm² current density and 50% absolute humidity (AH). The hydrogen production rate calculated from the Faraday's law was 362 ml/cm² h at 900 °C with 80 vol.% AH. The cell performance results indicate that the porous network-like LSM–YSZ is a promising oxygen electrode for high temperature electrolysis cells.     

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%.     

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.     

Electrochemical hydrogen production from water electrolysis using ionic liquid as electrolytes: Towards the best device

Electrodes constructed with different electroactive materials such as platinum (Pt), nickel (Ni), 304 stainless steel (SS) and low carbon steel (LCS) have been tested in water electrolysis using 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF₄). All experiments were performed at room temperature using a classical Hoffman's cell operating at atmospheric pressure and at different cathodic potentials. For the electrodes studied herein, in the presence of a 10 vol.% solution of BMI.BF₄ in water, current densities (j) in the range 10–42 mA cm⁻² were observed, with overall hydrogen production efficiencies (experimental/theoretical hydrogen production ratio) between 82 and 98%. The highest j values obtained with Pt, Ni, SS and LCS electrodes were 30, 12, 10 and 42 mA cm⁻², respectively, and all efficiencies were in the 85–99% range. These comparative results show that the LCS electrocatalyst constitutes an attractive alternative for the technological production of high purity hydrogen by water electrolysis reaction since the LCS electrode gave j and efficiencies as high as those observed with platinum electrodes.     

Characterization of infiltrated (La0.75Sr0.25)0.95MnO3 as oxygen electrode for solid oxide electrolysis cells

Porous strontium doped lanthanum manganite (LSM)-yttria-stabilized zirconia (YSZ) composite has been made by an impregnation method as oxygen electrodes for solid oxide electrolysis cells. X-ray diffraction and SEM results showed that LSM powders with well-crystallized perovskite phase uniformly distributed in the porous YSZ matrix. Impedance spectra and voltage-current density curves were measured as a function of absolute humidity at different temperatures to characterize the cell performance. The LSM infiltrated cell has an area specific resistance (ASR) of 0.20 Ω cm² at 900 °C at open circuit voltage with 50% absolute humidity (AH), which is relatively lower than that of the cell with LSM-YSZ oxygen electrode made by a conventionally mixing method. Electrolysis cell with LSM infiltrated oxygen electrode has demonstrated stable performance under electrolysis operation with 0.33 A/cm² and 50 vol.% AH at 800 °C.     

The stability of NiCoZn electrocatalyst for hydrogen evolution activity in alkaline solution during long-term electrolysis

The long-term stability of NiCoZn coating for hydrogen evolution reaction (HER) was investigated in 1 M KOH solution under 100 mA cm⁻² current density at room temperature. The effect of electrolysis on the corrosion behavior of NiCoZn coating was also studied. The alloy prepared on a copper electrode (Cu/NiCoZn) was etched in a concentrated alkaline solution (30% NaOH) to produce a porous and electrocatalytic surface suitable for use in the HER. The bulk and surface compositions of coating before and after alkaline leaching were determined by atomic absorption spectroscopy (AAS) and energy dispersive X-ray (EDX) analysis. The surface morphologies of freshly prepared and aged electrodes were investigated by scanning electron microscopy (SEM). Their catalytic activity towards the HER was assessed by recording cathodic current–potential curves and electrochemical impedance spectroscopy (EIS) techniques. It was found that the NiCoZn coating has a compact and porous structure. The long-term operation at 100 mA cm⁻² current density showed that the electrochemical activity of Cu/NiCoZn electrode increased slightly with increasing electrolysis time. The activation of electrode related to the removal of any existing corrosion products and accumulations from the pores and formation of cracks during hydrogen gas evolution. The corrosion tests showed that the corrosion resistance of Cu/NiCoZn electrode changed after electrolysis.     

PEM water electrolysis cells with catalyst coating by atomic layer deposition

The limited annual mining capacity and high costs of platinum metal group catalysts (PMG) are confining the production of hydrogen from PEM electrolysis. Therefore, a significant reduction of catalyst needs is crucial to reduce system costs and increase production capacity. This study demonstrates the feasibility of a PEM water electrolysis cell design using porous transport electrodes (PTE) with catalyst coating by atomic layer deposition (ALD) and operation in 1 mol/L sulphuric acid at 60 °C. Though the catalyst loading has been reduced to 0.12 mg/cm² iridium on the anode and 0.28 mg/cm² platinum on the cathode, a current density of 168 mA/cm² and mean high mass activity of 1400 A/g iridium could be achieved at 1.7 V. The characterization of three high loading PTE cells is combined with a detailed overpotential analysis from polarization curve fits and demonstrates a reproducible cell setup. Further analysis steps show an increasing cell performance with increasing coating cycle numbers and the consistency of the anode performance in the three electrode setup with the complete cell. The ALD coated PTE design turns out to be a promising candidate for catalyst loading reduction in PEM electrolysis.     

Integrated approach for textile industry wastewater for efficient hydrogen production and treatment through solar PV electrolysis

Combining solar PV based electrolysis process and textile dyeing industry wastewater for hydrogen production is considered feasible route for resource utilization. An updated experimental method, which integrates resource availability to assess the wastewater based hydrogen production with highlights of wastewater treatment, use of solar energy to reduce the high-grade electricity for electrolysis (voltage, electrode materials) efficiency of the process was employed. Results showed that maximum pollutant removal efficiency in terms of conductivity, total dissolved solids, total suspended solids, biological oxygen demand, chemical oxygen demand, hardness, total nitrogen and total phosphorus were obtained from ≅73% to ≅96% at 12 V with steel electrode for pollutant load. The maximum input voltage was found at 3 V for the best efficiency i.e. 49.6%, 67.8% and 57.1% with carbon, steel and platinum electrodes respectively. It was observed that with high voltage (12 V) of the electrolyte the rate of production of hydrogen was higher with carbon, steel and platinum electrodes. However, the increase in the efficiency of the production of hydrogen was not significant with high voltage, may be due to energy loss through heat during extra-over potential voltage to the electrodes. Hence, this integrated way provides a new insight for wastewater treatment and hydrogen energy production simultaneously.     

OER properties of Ni–Co–CeO2/Ni composite electrode prepared by magnetically induced jet electrodeposition

Hydrogen production from water electrolysis with catalysts is a simple, effective, and environmentally friendly way. However, the slow kinetics of the oxygen evolution reaction (OER) directly affects the catalytic efficiency of water electrolysis during hydrogen production. While the high cost of noble metal catalysts limits their engineering applications. Therefore, there is an urgent need to develop an economical and abundant catalyst with efficient OER performance to replace noble metal catalysts to reduce costs. In this work, we propose a method for the preparation of composite catalytic electrodes by magnetically induced jet electrodeposition. Ni–Co–CeO₂/Ni composite electrodes with a unique micro-nano structure and a large specific surface area were rapidly obtained through magnetically induced adsorption of nano-mixed particles. It was found that the Ni–Co–CeO₂/Ni composite electrode deposited by magnetically induced electrodeposition exhibited a lower overpotential of 301 mV@10 mA/cm² when the nano-mixed particle concentration was 2 g/L, and the corresponding Tafel slope was as low as 43.72 mV/dec. The key parameters of overpotential and Tafel slope reach or even outperform the best noble metal electrode in the industry, indicating that the Ni–Co–CeO₂/Ni composite electrode had excellent OER catalytic performance. The study demonstrates that magnetically induced jet electrodeposition provides a new method for the preparation of catalytic electrodes, which has important applications in the electrolysis of water for hydrogen production.     

Experimental studies and modeling of advanced alkaline water electrolyser with porous nickel electrodes for hydrogen production

The commercial hydrogen production by water electrolysis is limited by the high cost of electricity. The production cost can be minimized, if the cell module is operated with the minimum voltage at maximum current density. In the present study, porous nickel electrodes were developed indigenously on an engineering scale and used in an advanced zero gap filter press type bipolar electrolyser to minimize the cell voltage. As the cell voltage–current density characteristic of the cell module is unique feature of its design and the operating parameters, the polarization experiments were carried out using this cell module and the cell voltage–current density characteristics were generated at different operating temperatures. Further, the system is modelled for its electrochemical performance and the parameters accounting for different losses such as Ohmic and activation over potential, were estimated at different temperatures. These different parameters were compared with the data existing in literature and based on the analysis, the present cell module is found to be superior to the existing commercial electrolyzers in terms of energy efficiency.     

Electrochemical investigation of novel reference electrode Ni/Ni(OH)₂ in comparison with silver and platinum inert quasi-reference electrodes for electrolysis in eutectic molten hydroxide

An efficient and green energy carrier hydrogen (H₂) generation via water splitting reaction has become a major area of focus to meet the demand of clean and sustainable energy sources. In this research, the splitting steam via eutectic molten hydroxide (NaOH–KOH; 49–51 mol%) electrolysis for hydrogen gas production has been electrochemically investigated at 250–300 °C. Three types of reference electrodes such as a high-temperature mullite membrane Ni/Ni(OH)₂, quasi-silver and quasi-platinum types were used. The primary purpose of this electrode investigation was to find a suitable, stable, reproducible and reusable reference electrode in a molten hydroxide electrolyte. Cyclic voltammetry was performed to examine the effect on reaction kinetics and stability to control the working electrode at different scan rate and molten salt temperature. The effect of introducing water to the eutectic molten hydroxide via the Ar gas stream was also investigated. When the potential scan rate was changed from 50 to 150 mV s⁻¹, the reduction current for the platinum wire working electrode was not changed with newly prepared nickel reference electrode that designates its stability and reproducibility. Furthermore, increasing the operating temperature of molten hydroxides from 250 to 300 °C the reduction potential of the prepared nickel reference electrode is slightly positive shifted about 0.02 V. This suggests that it has good stability with temperature variations. The prepared nickel and Pt reference electrode exhibited stable and reliable cyclic voltammetry results with and without the presence of steam in the eutectic molten hydroxide while Ag reference electrode exposed positive shifts of up to 0.1 V in the reduction potential. The designed reference electrode had a more stable and effective performance towards controlling the platinum working electrode as compared to the other quasi-reference electrodes. Consequently, splitting steam via molten hydroxides for hydrogen has shown a promising alternative to current technology for hydrogen production that can be used for thermal and electricity generation.     

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.     

Test of conductor and semiconductor electrocatalysts in high voltage alkaline electrolyzer as production media for green hydrogen

Despite the restricted success of conductor and semiconductor electrodes in solving hydrogen production problems, they provide a promising alternative to expensive conventional electrodes in water electrolysis investigations. Titanium dioxide (TiO₂) and silver (Ag) are widely used as photocatalysts in water splitting systems for hydrogen generation. Though TiO₂ is an inactive chemical semiconductor with poor conductivity, it has not been entirely investigated as an electrocatalyst yet. Two criteria were used to achieve this target: supplying high voltage to overcome the TiO₂ large band gap and immersing it in an alkaline solution to activate its inert surface. For comparison study, Ag noble metal nanoparticles coating was employed as a competitive electrocatalyst. In this regard, the application of Ag and TiO₂ coated on Ti electrodes in a hydrogen production system operated under high voltage was reported. The nanoparticles were synthesized using cost-effective and simple methods based on UV-deposition for Ag nanoparticles and the chemical precipitation method for TiO₂ nanoparticles. Then the synthesized nanoparticles were deposited on the Ti electrodes by simple immersion. The synthesized nanoparticles and coated electrodes were tested by XRD, SEM, and EDS to study their morphology, structure, particle size, and surface composition. Based on these results, TiO₂ nano-powder and coated electrodes exhibited homogenous spheres with a mixture of rutile and anatase phases, the majority being the anatase phase. The Ag-coated Ti substrate possessed a smaller crystallite size compared to TiO₂ coated substrate. To evaluate the performance of Ag/Ti and TiO₂/Ti electrodes toward hydrogen production, H₂ flow rates were measured in a 3.6 M KOH electrolytic solution at 6 V. Hydrogen flow rates obtained for pure Ti, Ag, and TiO₂ electrodes at a steady state were 21, 35, and 37 SCCM (standard cm³/min), respectively. Also, it was found that energy consumption was reduced when the electrodes were coated with nanoparticles. Furthermore, the electrolyzer's performance was assessed by calculating the hydrogen production efficiency and the voltage efficiency. The results showed that using TiO₂ electrodes gave the best hydrogen production and voltage efficiencies of 27% and 23%, respectively. This study brings new insights about Ag and TiO₂ coated electrodes in alkaline water electrolysis at high voltage regarding nanoparticle performance, hydrogen production, system performance, and energy consumption. In addition, minimizing the fabrication and operation costs of hydrogen production is the major enabler for the broad commercialization of water electrolysis devices.     

Alternative cost-effective electrodes for hydrogen production in saline water condition

For the sustainable clean and green energy, hydrogen is considered as one of the prominent renewable energy source which attracted increasing interests in recent years. To produce this, one of the cheapest method is water electrolysis. But several challenges in water electrolysis are, to reduce the maintenance cost, energy consumption and high cost of platinum electrode material. So, in search of an alternative low cost and efficient electrode material, researchers are modifying various metals electrodes to replace the noble metal electrodes. Stainless steel (SS 304) is one of the types of carbon steel material commonly used for various applications. The aim of the work is to explore the stainless steel (SS 304), annealed at high temperature, with and without “hydrogen and argon” environment and tested the samples for hydrogen production in sea water condition (3.5% NaCl). Cr₂O₃ and MnCr₂O₄ spinel oxide formation was observed over the surface of the electrodes after annealing process. From Raman, X-ray Photoelectron Spectroscopy (XPS) and electrochemical measurements it was observed that, the sample prepared under hydrogen and argon environment is stable when compared with the rest of the samples. Decrease in relative amount of chromium oxide was observed for the sample annealed in air environment. The rate of production of hydrogen prepared under “hydrogen and argon” environment is higher and the results are discussed.     

Effect of operating parameters on hydrogen production by electrolysis of water

This paper presents an experimental study of hydrogen production by alkaline water electrolysis using Zinc alloys as materials for cathode. The aim of this study is to select the best alloy for producing hydrogen on testing the effect of some operating parameters. Experiments were conducted on a water electrolysis cell with two electrodes (anode/cathode). Throughout these experiments, we have chosen to use NaOH solution with different concentrations as an electrolyte. Binary alloys: Zn95%Fe5%, Zn90%Fe10%, Zn85%Fe15%, Zn95%Cu5%, Zn90%Cu10%, Zn85%Cu15%, Zn95%Co5%, Zn90%Co10%, Zn95%Cr5% and Zn90%Cr10% (mass %) were prepared as electrodes for the cathode. The effect of electrode composition, the electrolyte concentration, the voltage and amperage applied on volume of hydrogen produced are experimentally investigated. The results showed that the performance of alkaline water electrolysis is significantly affected by these various factors. Indeed, this preliminary study revealed that cathodes elaborated by (Zn95%Cr5%) and (Zn90%Cr10%) (mass %) produce more hydrogen gas than other alloys, in a minimum durations over the range of operating parameters tested.     

Electrode optimization for efficient hydrogen production using an SO2-depolarized electrolysis cell

The hybrid sulfur (HyS) cycle offers an alternative route to hydrogen and sulfuric acid production using the SO₂-depolarized electrolysis (SDE) cell. This work reports the most efficient SDE operation to date at high sulfuric acid concentrations (～60 wt%) achieved through the optimization of operating conditions and cell components. We observed that open porosity in the porous transport media (PTM) plays a significant role in SDE performance as it enables efficient acid removal from the catalyst layer. The combination of membrane electrode assembly (MEA) components, such as Sulfonated Diels Alder Poly (phenylene) (SDAPP) membranes and electrodes prepared using SGL 29BC PTM, and operating conditions (103.4 kPa_gauge at 125 °C) yielded electrolysis potentials <700 mV at 500 mA/cm² and acid concentrations >60 wt%.