Electrolysis In Alkaline Solution Research Articles

Modeling of hydrogen release during electrolysis of alkaline solution

Electrochemical processes of electrolysis of solutions belong to heterogeneous processes, their most intensive development and flow occurs at the interface, namely at the contact line between the metal electrode and the liquid electrolyte. The paper describes an algorithm for solving the objective of calculating hydrogen evolution during electrolysis of alkaline electrolyte in one-dimensional approximation. This numerical algorithm makes it possible to predict the hydrogen yield, to find the rates of constants in electrode processes, as well as we calculate the concentrations of substances involved in electrode processes and their spatial distribution. The algorithm consists of two blocks. The first block is an independent objective to find rate constants of processes. Kinetic objectives make it possible to find rate constants of near-electrode processes and to estimate contributions of near-electrode processes. The second block is the solution of initial-boundary and boundary value objectives in the “one-dimensional” approximation. The difference schemes for solving these objectives are constructed by the integrointerpolation method on a uniform grid, and an explicit difference scheme is used for solving the initial-boundary objectives of the charged particle balance. Calculation of the amount of separated gas showed good convergence both at the cathode (hydrogen) and at the anode (oxygen). The calculation of the spatial ones showed characteristic gradients, i.e., rather qualitative convergence.

Recent Development of Nickel-Based Electrocatalysts for Urea Electrolysis in Alkaline Solution.

Recently, urea electrolysis has been regarded as an up-and-coming pathway for the sustainability of hydrogen fuel production according to its far lower theoretical and thermodynamic electrolytic cell potential (0.37 V) compared to water electrolysis (1.23 V) and rectification of urea-rich wastewater pollution. The new era of the “hydrogen energy economy” involving urea electrolysis can efficiently promote the development of a low-carbon future. In recent decades, numerous inexpensive and fruitful nickel-based materials (metallic Ni, Ni-alloys, oxides/hydroxides, chalcogenides, nitrides and phosphides) have been explored as potential energy saving monofunctional and bifunctional electrocatalysts for urea electrolysis in alkaline solution. In this review, we start with a discussion about the basics and fundamentals of urea electrolysis, including the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER), and then discuss the strategies for designing electrocatalysts for the UOR, HER and both reactions (bifunctional). Next, the catalytic performance, mechanisms and factors including morphology, composition and electrode/electrolyte kinetics for the ameliorated and diminished activity of the various aforementioned nickel-based electrocatalysts for urea electrolysis, including monofunctional (UOR or HER) and bifunctional (UOR and HER) types, are summarized. Lastly, the features of persisting challenges, future prospects and expectations of unravelling the bifunctional electrocatalysts for urea-based energy conversion technologies, including urea electrolysis, urea fuel cells and photoelectrochemical urea splitting, are illuminated.

Foam Synthesis of Nickel/Nickel (II) Hydroxide Nanoflakes Using Double Templates of Surfactant Liquid Crystal and Hydrogen Bubbles: A High-Performance Catalyst for Methanol Electrooxidation in Alkaline Solution.

This work demonstrates the chemical synthesis of two-dimensional nanoflakes of mesoporous nickel/nickel (II) hydroxide (Ni/Ni(OH)2-NFs) using double templates of surfactant self-assembled thin-film and foam of hydrogen bubbles produced by sodium borohydride reducing agent. Physicochemical characterizations show the formation of amorphous mesoporous 2D nanoflakes with a Ni/Ni(OH)2 structure and a high specific surface area (165 m2/g). Electrochemical studies show that the electrocatalytic activity of Ni/Ni(OH)2 nanoflakes towards methanol oxidation in alkaline solution is significantly enhanced in comparison with that of parent bare-Ni(OH)2 deposited from surfactant-free solution. Cyclic voltammetry shows that the methanol oxidation mass activity of Ni/Ni(OH)2-NFs reaches 545 A/cm2 gcat at 0.6 V vs. Ag/AgCl, which is more than five times higher than that of bare-Ni(OH)2. Moreover, Ni/Ni(OH)2-NFs reveal less charge transfer resistance (10.4 Ω), stable oxidation current density (625 A/cm2 gcat at 0.7 V vs. Ag/AgCl), and resistance to the adsorption of reaction intermediates and products during three hours of constant-potential methanol oxidation electrolysis in alkaline solution. The high-performance electrocatalytic activity of Ni/Ni(OH)2 nanoflakes is mainly derived from efficient charge transfer due to the high specific surface area of the 2D mesoporous architecture of the nanoflakes, as well as the mass transport of methanol to Ni2+/Ni3+ active sites throughout the catalyst layer.

High Valence M-Incorporated PdCu Nanoparticles (M = Ir, Rh, Ru) for Water Electrolysis in Alkaline Solution.

The high-valence metal catalysts show extraordinary talent in various electrochemical reactions. However, there is no facile method to synthesize high-valence noble metal-based materials. Herein, we synthesized the different high valence noble metal M-incorporated PdCu nanoparticles (M = Ir, Ru, Rh) by the assistant of Fe3+ and exhibit excellent performance for water electrolysis. In 0.1 M KOH, the OER and HER mass activities of Ir16-PdCu/C were 50.5 and 16.5 times as much as PdCu/C, and achieved a current density of 10 mA cm-2 at 1.63 V when worked for overall water splitting. DFT calculation revealed that the incorporating of high valence Ir could optimize the binding energy of the intermediate products, and promote the evolution of oxygen and hydrogen. Ex situ XPS shows that the huge amount of oxidized Ir (V) formed in OER could promote the formation of O-O bonds.

Designed controllable nitrogen-doped carbon-dots-loaded MoP nanoparticles for boosting hydrogen evolution reaction in alkaline medium

Abstract The development of inexpensive, highly active, and stable non-precious metal catalysts is the key to efficient H2 production by the electrolysis of water. Based on initial theoretical predictions, we report the design and synthesis of N-doped, defect-containing, carbon-dots (CDs)-loaded molybdenum phosphide (MoP/CDs) nanoparticles using CDs with different N contents. This optimized composite material performed outstandingly in the hydrogen evolution reaction (HER), with an overpotential of 70 mV at a current density of 10 mA cm−2 with a 1.0 M KOH electrolyte. N doping changed the electronic arrangement around the reaction site, promoting the adsorption of HER intermediates. Increasing the N content further activated the adjacent C atoms to detach due to the more negative C vacancy formation energies resulting in a defect site with lost atoms and changed bond lengths. The introduction of defects increases the number of dangling bonds adjacent to reaction sites and reduces site coordination numbers, changing their electrocatalytic activity. Results show that N-doped and defect-containing MoP/CDs nanoparticles have excellent H2 production performance during the electrolysis of alkaline solution. These findings open a new area of application of heteroatom-doped CDs and provide new ideas for the design of efficient carbon-semiconductor composite HER catalysts.

Morphology-Controllable Synthesis of Zn-Co-Mixed Sulfide Nanostructures on Carbon Fiber Paper Toward Efficient Rechargeable Zinc-Air Batteries and Water Electrolysis.

It remains an ongoing challenge to develop cheap, highly active, and stable electrocatalysts to promote the sluggish electrocatalytic oxygen evolution, oxygen reduction, and hydrogen evolution reactions for rechargeable metal-air batteries and water-splitting systems. In this work, we report the morphology-controllable synthesis of zinc cobalt mixed sulfide (Zn-Co-S) nanoarchitectures, including nanosheets, nanoplates, and nanoneedles, grown on conductive carbon fiber paper (CFP) and the micronanostructure dependent electrochemical efficacy for catalyzing hydrogen and oxygen in zinc-air batteries and water electrolysis. The formation of different Zn-Co-S morphologies was attributed to the synergistic effect of decomposed urea products and the corrosion of NH4F. Among synthesized Zn-Co-S nanostructures, the nanoneedle arrays supported on CFP exhibit superior trifunctional activity for oxygen reduction, oxygen evolution, and hydrogen evolution reactions than its nanosheet and nanoplate counterparts through half reaction testing. It also exhibited better catalytic durability than Pt/C and RuO2. Furthermore, the Zn-Co-S nanoneedle/CFP electrode enables rechargeable Zn-air batteries with low overpotential (0.85 V), high efficiency (58.1%), and long cycling lifetimes (200 cycles) at 10 mA cm-2 as well as considerable performance for water splitting. The superior performance is contributed to the integrated nanoneedle/CFP nanostructure, which not only provides enhanced electrochemical active area, but also facilitates ion and gas transfer between the catalyst surface and electrolyte, thus maintaining an effective solid-liquid-gas interface necessary for electrocatalysis. These results indicate that the Zn-Co-S nanoneedle/CFP system is a low cost, highly active, and durable electrode for highly efficient rechargeable zinc-air batteries and water electrolysis in alkaline solution.

Cobalt Selenide Nanostructures: An Efficient Bifunctional Catalyst with High Current Density at Low Coverage.

Electrodeposited Co7Se8 nanostructures exhibiting flake-like morphology show bifunctional catalytic activity for oxygen evolution and hydrogen evolution reaction (OER and HER, respectively) in alkaline medium with long-term durability (>12 h) and high Faradaic efficiency (99.62%). In addition to low Tafel slope (32.6 mV per decade), the Co7Se8 OER electrocatalyst also exhibited very low overpotential to achieve 10 mA cm(-2) (0.26 V) which is lower than other transition metal chalcogenide based OER electrocatalysts reported in the literature and significantly lower than the state-of-the-art precious metal oxides. A low Tafel slope (59.1 mV per decade) was also obtained for the HER catalytic activity in alkaline electrolyte. The OER catalytic activity could be further improved by creating arrays of 3-dimensional rod-like and tubular structures of Co7Se8 through confined electrodeposition on lithographically patterned nanoelectrodes. Such arrays of patterned nanostructures produced exceptionally high mass activity and gravimetric current density (∼68 000 A g(-1)) compared to the planar thin films (∼220 A g(-1)). Such high mass activity of the catalysts underlines reduction in usage of the active material without compromising efficiency and their practical applicability. The catalyst layer could be electrodeposited on different substrates, and an effect of the substrate surface on the catalytic activity was also investigated. The Co7Se8 bifunctional catalyst enabled water electrolysis in alkaline solution at a cell voltage of 1.6 V. The electrodeposition works with exceptional reproducibility on any conducting substrate and shows unprecedented catalytic performance especially with the patterned growth of catalyst rods and tubes.

Electrochemical Preparation, Characterization, and Application of a Novel Cathode Material, Mild Steel/Ni/NiZn-Pt, for Alkaline Water Electrolysis

In this study, a mild steel (MS)/Ni/NiZn-Pt electrode was prepared and characterized in view of its possible application as cathode material for the alkaline water electrolysis in alkaline solution. For this purpose, cyclic voltammetry, atomic absorption spectroscopy, cathodic current-potential curves, and electrochemical impedance spectroscopy techniques were used. Corrosion behavior of the electrodes were also evaluated. It was found that the deposition of an under-layer nickel film can enhance corrosion resistance of MS/Ni/NiZn electrode. Alkaline leached MS/Ni/NiZn electrode has good catalytic activity for the hydrogen evolution activity. Moreover, MS/Ni/NiZn-Pt electrode has higher catalytic activity acting by lowering hydrogen overpotential.

Preparation, characterization and application of alkaline leached CuNiZn ternary coatings for long-term electrolysis in alkaline solution

The NiCuZn ternary coating was electrochemically deposited on a copper electrode. Then, it was etched in a concentrated alkaline solution (30% NaOH) to produce a porous and electrocatalytic surface suitable for use in the hydrogen evolution reaction (HER). The surface composition of coating before and after alkaline leaching was determined by energy dispersive X-ray (EDX) analysis. The surface morphologies were investigated by scanning electron microscopy (SEM). The long-term stability of electrode prepared for alkaline water electrolysis was investigated in 1 M KOH solution with the help of cathodic current-potential curves and electrochemical impedance spectroscopy (EIS) techniques. It was found that, the NiCuZn coating has a compact and porous structure with good physical stability. Alkaline leaching process further improved the activity of NiCuZn coating in comparison with binary NiCu deposit for the HER. The long-term operation at −100 mA cm −2 showed good electrochemical stability over 120 h.

The stability of hydrogen evolution activity and corrosion behavior of NiCu coatings with long-term electrolysis in alkaline solution

In this study, NiCu composite coating was electrochemically deposited on a copper electrode (Cu/NiCu) and tested for hydrogen evolution reaction (HER) in 1 M KOH solution for long-term electrolysis with the help of cathodic current–potential curves and electrochemical impedance spectroscopy (EIS) techniques. The bulk and surface composition of the coating was determined using atomic absorption spectroscopy (AAS) and energy dispersive X-ray (EDX) analysis. The surface morphology was investigated by scanning electron microscopy (SEM). The effect of electrolysis on the corrosion behavior of the Cu/NiCu electrode was also reported. It was found that the NiCu coating had a compact and porous structure with good time stability. The HER activity of the coating was stable over 120 h electrolysis and the HER mechanism was not modified during the operation. The corrosion tests showed that the corrosion resistance of the Cu/NiCu electrode changed when a cathodic current was applied to the electrolysis system.

Deposition of amorphous M1-Ni films using ion-beam sputtering and their electrocatalytic properties

Amorphous M1Ni 2.52 and M1Ni 3.44 films were prepared by ion-beam sputtering on iron substrates. The corresponding crystalline samples were obtained by annealing the amorphous samples. The electrocatalytic properties of the M1-Ni film cathodes for the hydrogen evolution reaction were investigated in 30 wt.% KOH at 70°C. It was found that amorphous samples had better activity than crystalline samples. In addition, the amorphous films had excellent resistance to hydrogen embrittlement, good adhesion to substrates, and good stability after long-term electrolysis in alkaline solution at 200 mA cm −2 and 70°C.

Domain and surface structures of sodium tungsten bronzes, Na xWo 3 (0.4 < x < 1)

Polarized-light microscopic observations have shown that the birefringent, twin-domain structure of metallic sodium tungsten bronze is exhibited by Na-deficient surface films and hence is not, as had been reported elsewhere, a bulk property. The film can be synthesized by anodic electrolysis in alkaline solution. It is chemically inert, translucent, and often laminates to a multiple layer. The domain structure of the film is hypersensitive to lateral stress and to thermal variation, exhibiting a marked change at the phase transition of the substrate through apparent epitaxial coherence. The domain-wall movement is often slow enough to be visible, and the thermally induced domain modulation is occasionally accompanied by audible high-pitched sound. The bulk structure of the substrate exhibits pseudoperiodic subboundaries that are probably caused by growth defects and the segregation of the sodium atoms. The near-surface of the substrate also shows the sodium segregation that tends to precipitate in periodic patterns. Optical and morphological properties of the substrate structures exhibited no detectable change due to thermal variation or external stress.

High efficiency water electrolysis in alkaline solution

Abstract Methods of increasing the efficiency and lowering the capital cost of state-of-the art pressure-type electrolyzers are briefly reviewed. A doubling of current density, accompanied by a halving of the internal resistance, and improved electrode activity are required. The latter may be obtained by catalysis and increases in effective surface area and temperature. An increase in the temperature to 120–130°C appears feasible without giving rise to materials problems provided asbestos separators are not used. All of the above are examined in detail, and it is shown that advanced electrodes with non-precious catalysts will be capable of operating at 1.55 V (I.R. included) at 0.4 A/cm2, 120 C and 30–40 atm., which corresponds to isothermal operation.

水酸化アンモニウム浴中フッ化物添加の影響および二重電解皮膜について

Ammonium hydroxide solution (2.3mol) containing ammonium tartrate (0.1mol), ammonium carbonate (0.1mol), and ammonium fluoride (0.27M mol) was used as an electrolyte for anodizing aluminum in alkaline solution.A thick film (about 15μ) was formed on an aluminum specimen by electrolysis for 30min. under current density of 2Amp/dm2 in this solution.It was found by chemical analysis that the film contained about 1.2% of F- and its density (10μ:1.8mg/cm2) was lower than that of the anodized film in H2SO4 (10μ:2.1mg/cm2). It had a high corrosion resistance to acid (H2SO4 10%) and base (NaOH 10%), but its hardness was not so high.It was supposed by electron microscopic examination of the surface and cross-section that the film had larger pores and cells as compared with the anodized film in H2SO4.The double anodized film, which had been anodized in sulfuric acid after the electrolysis in alkaline solution, had higher corrosion resistance as compared with a double anodized film, which had been electrolyzed in reverse order. It was clearly observed by microscopy that the layer of 2ry oxide film was formed beneath that of 1ry oxide film.

Electrolytic Concentration of Diplogen

WE have recently made some preliminary investigations of the effect of various factors on the efficiency of the concentration of diplogen by electrolysis in alkaline solution. The diplogen-hydrogen ratio at various stages was determined by specific gravity measurements after repeated distillation. These measurements were carried out in pyknometers of 5 c.c. and 25 c.c. capacity with an estimated accuracy of one part in a hundred thousand. In calculating the diplogen concentrations, we have used Lewis's1 value for the specific gravity of pure D2O and Bleakney and Gould's2 estimate of the D/H ratio in ordinary water.