In situ activation of cobalt cathodes in alkaline water electrolysis

The hydrogen evolution reaction (HER) on polished pure cobalt cathodes in 30 w/o KOH at 70°C in the presence of dissolved metallic impurities has been investigated in constant current and potential modes combined with the potential-sweep method. Potentiostatic tests show that the cell current decreases with time during the first 1000 s, which is tentatively attributed to the penetration of atomic hydrogen into the metal lattice. The deposition of copper, iron and zinc, observed after several hours' incubation significantly influences the Tafel parameters for HER.Marked improvement in the electrocatalytic activity of the cathode in the presence of dissolved sodium molybdate is ascribed mainly to the deposition of molybdenum on the electrode surface, which lowers the Tafel slope and considerably increases the exchange-current density. The current increase is observed after an incubation period which is closely related to the concentration of dissolved sodium molybdate, whereas the rate of current increase with time is largely influenced by the applied potential.     

Electrocatalytic activation of ruthenium electrodes for the Cl2 and O2 evolution reactions by anodic/cathodic cycling

Ruthenium electrodes subjected to an anodic/cathodic potential cycling regime from 0.06 to 1.4E _H develop a changed state of surface oxidation in comparison with that observed in the initial sequence of potentiodynamic sweeps. The cycling effect is analogous to that known at iridium electrodes but here refers to monolayers. The kinetics of Cl₂ and O₂ evolution of these two types of oxidized surfaces were studied by steady-state polarization experiments. Current densities for Cl₂ evolution at the cycled Ru surface oxide areca 30 times greater than those at the original oxidized Ru surface. Oxygen evolution current densities are increased byca 8 times. The effect is a true electrocatalytic one since the real area of the Ru surfaces remains constant withinca 5%. The mechanisms of Cl₂ or O₂ evolution appear to remain unchanged, so the electrocatalytic effects observed are tentatively attributed to a change of potential range over which Ru(III) and Ru(IV) oxidation states arise in the oxide film causing modification of electron transfer rates or adsorption of ions and intermediates.Based on a report to Hooker Chemicals and Plastics Corp., Research Centre, Niagara Falls, NY, July 1976, on a research project supported by Hooker Research Center at the University of Ottawa, 1974–76.Where part of this work (on O₂ evolution electrocatalysis) was carried out by MV.     

Electrocatalytic activities of metal electrodes in anodic oxidation of hydrazine in alkaline solution

The electrocatalytic activities of various metals and alloys in the anodic oxidation of hydrazine in alkaline solution have been studied by means of palladium membrane method in which the contact side of the membrane was electrodeposited with a thin layer of the electrocatalytic metals. The electrode materials studied can be divided into two groups. In the first group, platinum, rhodium, cobalt, cobalt—phosphor and cobalt—boron, anodic current of hydrogen oxidation on the diffusion side decreased remarkably with an increase of the electro-oxidation of hydrazine on the contact side. The anodic oxidation of hydrazine occurs through the preliminary stepwise dehydrogenation on this group metals.On the other hand, the amount of sorbed hydrogen in the palladium, gold, nickel and nickel—phosphor electrodes increased with an increase of the electro-oxidation of hydrazine on the contact side. Thus, the anodic oxidation of hydrazine on the latter group metals may proceed through the anodic formation of the intermediate radicals which readily decompose into hydrogen and the related compounds.     

碱性电解槽隔膜的研究进展

碱性电解槽制氢需要一种隔膜将H、Ｏ隔离开。文章概述了隔膜材料的选择,对国内外隔膜的发展进行了综述,并详细介绍了石棉隔膜、改性石棉隔膜、非石棉隔膜、聚苯硫醚隔膜、聚砜类隔膜的性能及其优缺点。     

In situ activation of cathodes during alkaline water electrolysis by dissolved iron and molybdenum species

In situ activation on polished pure Co, Fe, Ni and Pt cathodes by the dissolution of molybdenum in 30 wt % KOH at 70°C was investigated at 100 mA cm^–2. The effect of adding molybdate to the electrolyte to reactivate hydrogen discharge depends on the concentration of dissolved iron. The deposition of Mo on the substrate takes place only in the presence of this metallic impurity. The best improvement of the hydrogen evolution reaction is reported when iron alone is dissolved in the electrolyte. The nature of the changes occurring on the cathode surfaces during hydrogen evolution was demonstrated by scanning electron microscopy and X-ray microanalysis.     

Ceramic diaphragms for advanced alkaline water electrolysis

Chemically stable and physically strong, but relatively expensive diaphragms with low electrical surface-specific resistance have been developed for alkaline water electrolysis intended to work at temperature around and above 120°C at increased current densities and yet reduced cell voltage. These diaphragms are made of a porous cermet produced from ceramic particles (group 2A titanates) and NiO by reductive sintering. Two versions of such cermets have been investigated: a nickel net-supported diaphragm and a diaphragm which is supported by two porous metal electrodes.Paper presented at the meeting on Materials Problems and Material Sciences in Electrochemical Engineering Practice organised by the Working Party on Electrochemical Engineering of the European Federation of Chemical Engineers held at Maastricht. The Netherlands, September 17th and 18th 1987.     

Ohmic potential drop during alkaline water electrolysis

Advanced alkaline water electrolysis may be an attractive method of producing hydrogen in the future. Large energy losses in water electrolysis are caused by evolution of gas bubbles. The main aim of this investigation is to obtain a dimensionless correlation for the increase of ohmic resistance between working electrode and diaphragm due to the presence of gas bubbles. The ohmic potential drop across the solution layer between diaphragm and working electrode, distance from the rear of the working electrode to the back wall of the compartment of the working electrode, the height in the electrolytic cell, the electrode type, nature of the electrode surface and of the gas evolved. From the experimental results the dimensionless correlation has been deduced as

where ΔR_wm^* denotes the increase in resistance of solution layer between diaphragm and working electrode due to bubbles, divided by the resistance of this layer in absence of bubbles, Re Reynolds number, h^* reduced height in the electrolytic cell, d_wm^* reduced distance between the working electrode and the diaphragm, n empirical experimental constant depending on nature of electrode surface, nature of gas evolved and whether or not the bubbles can enter a chamber behind the working electrode, K empirical constant depending on nature of both electrode surface and gas evolved. A remarkable result is that ΔR_wm^* is independent of current density in the current density range from 1–10 kA m^?2.     

Hydrogen evolution on electrodeposited nickel-cobalt-molybdenum in alkaline water electrolysis

The hydrogen evolution reaction (HER) was conducted on nickel-cobalt-molybdenum electrodes in a 30 wt% KOH solution at temperatures from 298 to 353 K. These nickel- and cobalt-based ternary materials were electrodeposited on a stainless steel screen, initially at a current density of 0.5 A cm⁻² and subsequently at 2 A cm⁻². They showed good adhesion to the substrate, high surface roughness and they enhanced the HER in water electrolyssi compared with nickel, cobalt, nickel-molybdenum and cobalt-molybdenum deposited electrodes, having comparable or even higher deposit loadings. The HER enhancement on the ternary materials with respect to nickel-molybdenum and cobalt-molybdenum was attributable to their large surface area. On the ternary materials, two Tafel slopes were distinguished on the HER polarization in the low and high HER overpotential ranges. However, no conventionally proposed relation between TAfel slope and temperature was found; the transfer coefficient increased with temperature under the experimental conditions.     

In situ activation of nickel cathodes by sodium molybdate during alkaline water electrolysis at constant current

The nickel cathode undergoes significant deactivation at 100 mA cm^–2 in 30 wt% KOH at 70°C containing KOH metallic impurities. The time dependence of the potential reveals two distinct regions: the first due to hydrogen absorption, while the Tafel parameters, charge transfer resistance and double-layer capacitance remain fairly constant; the second due to the electrodeposition of metallic impurities as manifested by SEM pictures, EDX analysis and cyclic voltammograms. The resulting deactivation is due mainly to the increase in the Tafel slope, although the electrode impedance reveals a significant increase in electrode roughness. The hydrogen discharge at 100 mA cm^–2 in 30 wt% KOH containing 4mm sodium molybdate largely attenuates the deactivation process owing to hydrogen absorption and the deposition of impurities. Thein situ activation is ascribed to the formation of a spongy molybdenum-base deposit on the nickel cathode during the first day of water electrolysis.     

碱性电解水析氢电极的研究进展

电解水制氢将成为未来绿色制氢工业的核心技术。研究新型阴极材料以有效降低阴极过电位,对降低电解水能耗和设备成本、提高生产稳定性和安全性,具有十分重要的现实意义。本文主要对碱性水溶液电解制氢工业的析氢阴极材料进行综述。围绕电极结晶结构设计和尺寸结构设计两个主要的电极发展方向,重点介绍了3类基于电沉积制备技术的Ni基电极材料:合金析氢电极、复合析氢电极、多孔析氢电极。分析了当前析氢电极在实验研发与工业应用中存在的问题。指出采用电沉积法,制备催化活性更高且适用于工业电解环境的多元复合电极材料将是今后析氢电极发展的趋势。     

Lanthanum phosphate-bonded composite nickel electrodes for alkaline water electrolysis

Nickel-powder electrodes bonded with a polymer of lanthanum phosphate were prepared and tested for their performance in water electrolysis of KOH aqueous solutions. Disintegration of the phosphate-bonded electrodes made with spiky filamentary nickel particles is strongly reduced at open circuit potential with LaPO₄ rather than AlPO₄ as the binding material, but the electrocatalytic performance toward hydrogen evolution is practically the same for both materials.On leave from Chemistry Department, University of Warsaw, 02093 Warsaw, Pasteura 1, Poland     

Studies on the anodic and cathodic polarization of amalgams—V. the behaviour of tin amalgams in alkaline solutions

Tin-amalgams of varying concentrations were oxidized galvanostatically in 0·01, 0·10 and 2·00 N NaOH solutions at 25°C. For each amalgam and solution composition a number of constant polarizing currents were used and cyclization was repeated until the oxidation (reduction) features of the amalgam became apparent. Two different oxidation patterns were distinguished. The first describes the behaviour of all amalgams in 0·01, 0·1 N NaOH, and of concentrated amalgams in 2 N NaOH, and the second for the behaviour of dilute tin amalgams in 2 N NaOH solutions.     

Fundamental study of the anodic and cathodic reactions during the electrolysis of a lithium carbonate-lithium chloride melt using a carbon anode

Cyclic voltammetry, in conjunction with the chromatographic analysis of the anode product, has been used to elucidate the reactions occurring during the electrolysis of lithium carbonate-lithium chloride melts. At a carbonate ion concentration of 0.033 mole fraction the peak anodic current densities were 3100 A m^–2 on vitreous carbon and 6900 A m^–2 on graphite with the product being carbon dioxide. The cathodic reduction of carbonate at low concentrations was found to occur at –1.0 V to –1.2 V vs a Ag/Ag(I) reference electrode which is 1.2 V less negative than the potential at which lithium ions were reduced. Voltammetric studies of the reduction of the carbonate ion indicated that the reaction mechanism involved an irreversible charge transfer.     

The anodic and cathodic dissolution of Al and Al-Cu-Mg alloy

Atomic emission spectroelectrochemistry (AESEC) was used to monitor the release of Al from 99.99% aluminum (1199 alloy) and Al, Mg, and Cu from 2024 Al alloy in 30 g/l NaCl electrolyte as a function of pH. The cathodic dissolution of Al was demonstrated and attributed to an increase in the pH at the interface due to the water reduction reaction. The dissolution of Mg was also observed but was a more complex function of current probably depending on the interfacial pH and the Al dissolution rate. The detachment of copper-rich particles was observed as very rapid spectroscopic emission transients (peak width < 10 ms).     

Electrochemical deposition and characterization of NiFe coatings as electrocatalytic materials for alkaline water electrolysis

In this study, nickel (Cu/Ni), iron (Cu/Fe) and nickel-iron (Cu/NiFe) composite coatings with various chemical compositions were electrochemically deposited on a copper electrode and characterized using cyclic voltammetry (CV), atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques in view of their possible applications as electrocatalytic materials for the hydrogen evolution reaction (HER) in an alkaline medium. The electrocatalytic activity of the coatings for the HER was studied in 1 M KOH solution using cathodic current-potential curves and electrochemical impedance spectroscopy (EIS) techniques. The presence of nickel along with iron increases the electrocatalytic activity of the electrode for the HER when compared to nickel and iron coatings individually. The HER activity of the composite coatings depends on the chemical composition of the alloys. The Cu/NiFe-3 electrode (with a molar concentration ratio of Ni²⁺:Fe²⁺ of 4:6 in the plating bath) was found to be the best suitable cathode material for the HER in an alkaline medium under the experimental conditions studied. Furthermore, the electrocatalytic activity of the Cu/NiFe-3 electrode for the HER was tested for extended periods of time in order to evaluate the change in the electrocatalytic activity of the electrode with operation time. The HER was activation controlled and has not been changed after electrolysis. A constant current density of 100 mA cm⁻² was applied to the electrolysis system, and the corrosion behavior of the Cu/NiFe-3 electrode was investigated after different operation times using EIS and linear polarization resistance (LPR) techniques. For comparison, the corrosion behavior of a Cu/NiFe-3 electrode to which current was not applied was also investigated. The corrosion tests showed that the corrosion resistance of the Cu/NiFe-3 cathode changed when a cathodic current was applied to the electrolysis system.     

Synthesis of Ni nanoparticles by plasma-induced cathodic discharge electrolysis

Ni nanoparticles were synthesized by plasma-induced cathodic discharge electrolysis in LiCl–KCl–CsCl + NiCl₂ at 573 K under 1 atm of Ar atmosphere. Ni nanoparticles with diameters of around 100 nm were obtained from the melt. It was also confirmed that particles predominantly grow at the surface of the melt, especially the region just under the discharge. Taking into account the above results, a novel type plasma-induced electrolytic cell has been designed and constructed; it operated successfully, a rotating Ni metal disk anode being adopted in order for the formed particles to be quickly removed from the region just under the discharge and be continuously transferred to the inner wall of the cold container. By using this novel type plasma-induced electrolytic cell, Ni nanoparticles with diameters of around 50 nm could be obtained.     

Nanocrystalline ceramic coating on γ-TiAl by bipolar plasma electrolysis (effect of frequency,time and cathodic/anodic duty cycle)

The present work reports the usage of plasma electrolysis for nanocrystalline coating of γ-TiAl alloy by applying pulsed current in an organic electrolyte based on glycerol. Response Surface Methodology (RSM) was applied to optimize the operating conditions for small nanocrystallite sizes of coatings. The levels studied were the ratio of duty cycle of cathodic direction to duty cycle of anodic direction of 0.2–0.4, frequency of pulsed current range between 5 and 15 kHz, and treatment time of 10–30 min. The usage of high applied frequencies and low ratios of duty cycle of cathodic direction to duty cycle of anodic direction and also treatment time is more suitable for achieving lower sizes of complex nanocrystallites. The samples with high height to width ratio of distribution curves of nanocrystallites have simultaneously smaller average sizes of nanocrystallites and lower length to diameter ratio of nanocrystallites.     

钌基碱性电解水制氢催化剂研究进展

碱性电解水具有操作易实现、设备费用低和寿命长的特点,是目前应用最广泛的将可再生资源转化为氢能的技术。但电解水存在能耗高的问题,因此需要高效催化剂提高能量转化效率。钌具有与铂相近的金属-氢键强度,是极具前景的制氢催化剂。综述了近年来钌基催化剂的制备及其碱性电解水制氢反应的最新研究进展。与廉价过渡金属材料相比,钌基催化剂具有优异的电化学活性和稳定性,是一种很有前景的析氢材料。以目前主要研究的钌金属及其合金、钌基磷化物、钌基硫化物、钌基硒化物为代表,分别进行了简要的介绍和评价,最后提出了钌基电催化剂在制氢应用中存在的问题和未来的发展方向。     

Preparation and characterization of thin films of LaNiO3 for anode application in alkaline water electrolysis

LaNiO₃ electrodes were prepared, in the form of thin films on platinum by the methods of spray pyrolysis and sequential coating of mixed metal nitrate solutions followed by thermal decomposition. The films were adherent and of p-type semiconducting. Cyclic voltammetric studies indicated the formation of a quasireversible surface redox couple, Ni(iii)/Ni(ii), on these films before the onset of oxygen evolution in 1 m KOH. The anodic Tafel slopes were 40 and 65 mV decade^–1, on the sprayed LaNiO₃ film and on the film obtained by a layer method, respectively. The reaction order with respect to OH^– was found to be 2.2 on the sprayed oxide film and 1.2 on the layer film. The sprayed oxide film was found to be electrocatalytically more active. It is suggested that the oxygen evolution reaction proceeds on both the film electrodes via the formation of the physisorbed H₂O₂ as an intermediate in the rate determining step.