Rate Of Hydrogen Reduction Research Articles

Monodisperse silver nanocubes composite Ag@C/SrTiO3 photocatalytic decomposition of water for hydrogen reduction

Metal-induced photocatalysis has been a relatively effective strategy for the efficient use of solar energy. In this paper, highly efficient and stable Ag@C/SrTiO3 photocatalysts were prepared by compounding silver nanocubes wrapped with few layers graphite with strontium titanate materials. We obtained silver nanocubes with a uniformly dispersed size of about 35 nm by varying the surface energy of silver and inducing the preferential binding of PVP on the (100) crystal plane with the help of selective adsorption of chloride ions on the different crystal planes of silver. As obtained under the characterisation of UV–visible absorption spectra, the material has a broad visible light absorption (450–900 nm). The Ag@C/SrTiO3 has a hydrogen reduction rate of up to 457.5 μmol g−1·h−1 under simulated sunlight, which is ∼200 % higher than the SrTiO3 and ∼900 % higher than the sliver. Moreover, the catalyst was stable, still producing 93.5 % hydrogen after three cycles of testing, and the photocatalyst structure did not change as known from the XRD data of the material before and after testing. The present work demonstrates the feasibility of rational design of efficient and stable silver-based photocatalysts.

Hydrogen reduction of spent lithium-ion battery cathode material for metal recovery: Mechanism and kinetics.

Hydrogen reduction is becoming a promising method for recycling lithium-ion battery cathode materials. However, the reaction mechanism and kinetics during hydrogen reduction are unclear, requiring further investigation. Therefore, non-isothermal and isothermal reduction experiments were conducted to evaluate the temperature dependence of the hydrogen reduction kinetics using simultaneous thermogravimetric and differential thermal analysis equipped with mass spectrometry. XRD and SEM were used to characterize the reduction products to understand the underlying reduction mechanisms. The hydrogen reduction profile could be divided into three main stages: decomposition of cathode materials, reduction of the resultant nickel and cobalt oxides, and reduction of LiMnO2 and residual nickel and cobalt oxides. The hydrogen reduction rate increased with increasing temperature, and 800°C was the optimum temperature for separating the magnetic Ni-Co alloy from the non-magnetic manganese oxide particles. The apparent activation energy for the isothermal tests in the range of 500–700°C was 84.86 kJ/mol, and the rate-controlling step was the inward diffusion of H2(g) within each particle. There was an downward progression of the reduction through the material bed for the isothermal tests in the range of 700–900°C, with an apparent activation energy of 51.82 kJ/mol.

Lithium/bismuth co-functionalized phosphotungstic acid catalyst for promoting dinitrogen electroreduction with high Faradaic efficiency

Ammonia occupies a significant standing in the global economy. As a promising alternative to the energy-intensive Haber-Bosch process, electrochemical nitrogen reduction could achieve sustainable ammonia synthesis. However, the attractive alternative suffers from the bottleneck of insufficient activity and low electron selectivity. Here, we report an efficient electrocatalyst using phosphotungstic acid as platforms to anchor bismuth species on the 4-fold hollow site and anchor lithium species on the 3-fold hollow site, which reaches high ammonia yield rates of 61 ± 1 μg h −1 mg cat. −1 and Faradaic efficiencies of 85% ± 2% at −0.1 V versus reversible hydrogen electrode (RHE). Experiments and theoretical calculations reveal that the Bi δ+ species can promote the activation and hydrogenation of nitrogen at adjacent unsaturated tungsten active sites, and the incorporated lithium species reduce the hydrogen reduction rate in undesired water splitting. This synergistic functionalization of bismuth and lithium species contributes to the high-efficient catalyst. Li/Bi species are anchored on phosphotungstic acid by impregnation Li/Bi species synergistically contribute to the activation of nitrogen Li species are favorable to inhibit the competitive hydrogen evolution reaction Li/Bi species teamwork achieves a high Faradic efficiency for aqueous ammonia synthesis Electrochemical nitrogen reduction could achieve sustainable ammonia synthesis as a promising alternative to the energy-intensive Haber-Bosch process. Liao et al. design Li/Bi co-functionalized phosphotungstic acid by precisely anchoring Bi and Li species, where Bi δ+ species facilitate nitrogen reduction and Li species suppress competitive hydrogen evolution reaction. The cooperation promotes electrocatalytic nitrogen reduction to ammonia with, to the best of our knowledge, record Faradic efficiencies for aqueous systems.

Synergistic Functionalization for Promoting Dinitrogen Electroreduction with High Faradaic Efficiency

Electrochemical nitrogen reduction is suffering from the bottleneck of poor activity and low electron selectivity. Herein, we precisely synthesize an efficient electrocatalyst using phosphotungstic acid as a platform to anchor Bi species on the four-fold hollow site and associate with Li species on the three-fold hollow site. The well-designed catalyst shows a significant eNRR performance with an ammonia yield rate of 61 ± 1 μg h-1 mgcat.-1 and a recorded Faradaic efficiency of 85 ± 2% at -0.1 V vs. RHE. Isotopic labeling verifies that N atoms of formed NH4+ originate from N2. In situ experiments and theoretical calculations reveal that the Biδ+ species could promote the effective activation and hydrogenation of dinitrogen molecules at the adjacently unsaturated W active sites, and the incorporated Li species reduce the hydrogen reduction rate in the undesirable water splitting. This synergistic functionalization of Bi and Li species contributes to the high-efficient catalyst.

Reaction Mechanism and Process Control of Hydrogen Reduction of Ammonium Perrhenate

The preparation of rhenium powder by a hydrogen reduction of ammonium perrhenate is the only industrial production method. However, due to the uneven particle size distribution and large particle size of rhenium powder, it is difficult to prepare high-density rhenium ingot. Moreover, the existing process requires a secondary high-temperature reduction and the deoxidization process is complex and requires a high-temperature resistance of the equipment. Attempting to tackle the difficulties, this paper described a novel process to improve the particle size distribution uniformity and reduce the particle size of rhenium powder, aiming to produce a high-density rhenium ingot, and ammonium perrhenate is completely reduced by hydrogen at a low temperature. When the particle size of the rhenium powder was 19.74 µm, the density of the pressed rhenium ingot was 20.106 g/cm3, which was close to the theoretical density of rhenium. In addition, the hydrogen reduction mechanism of ammonium perrhenate was investigated in this paper. The results showed that the disproportionation of ReO3 decreased the rate of the reduction reaction, and the XRD and XPS patterns showed that the increase in the reduction temperature was conducive to increasing the reduction reaction rate and reducing the influence of disproportionation on the reduction process. At the same reduction temperature, reducing the particle sizes of ammonium perrhenate was conducive to increasing the hydrogen reduction rate and reducing the influence of the disproportionation.

Nanocrystalline nickel–cobalt electrocatalysts to generate hydrogen using alkaline solutions as storage fuel for the renewable energy

Generation of hydrogen using an electrocatalyst is valuable research field for the energy conversion and storage of the renewable energies. Electroplating of nanocrystalline metals and their alloys thin film is auspicious for the conversion and storage of the energy in the form of hydrogen fuel during water electrolysis. In this work, we electroplated the nanocrystalline Ni–Co alloys of different Co% using natural compounds such as gluconate and cysteine via the galvanostatic-ultrasonication conditions. The electroplated Ni–Co alloys have been characterized using energy dispersive X-ray, X-ray diffraction and scanning electron microscopy, to determine their elemental composition, crystal lattice system and surface morphology, respectively. The morphological structure of the electroplated Ni–Co alloys varies from dense and lustrous to granular. The electroplated Ni–Co alloys arranged in the face centred cubic or hexagonal closed packaged depending on the Co%. The electroplated NiCo alloys arranged in the small unit cell which enhances electron transfer and boosts the rate of hydrogen reduction. The electrocatalytic activity of the electroplated Ni–Co cathodes towards hydrogen reduction reaction was investigated using cathodic polarization and electrochemical impedance spectroscopy, EIS, dipped in 1.0 M KOH solution. The electroplated Ni–50Co cathode displays the superior electrocatalytic activity and the lowest overpotential for the hydrogen evolution reaction than bulk Ni.

Hydrogen Reduction of a Black Nickel Oxide Ore in a Fluidized-Bed Reactor without Sticking

A black nickel oxide powder, one of the commercial nickel oxide ores, was reduced by hydrogen gas in a batchtype fluidized-bed reactor in a temperature range of 350 to 500 °C and in a residence time range of 5 to 120 min. The hydrogen reduction behavior of the black nickel oxide was found to be somewhat different from that of green nickel oxide ore. For the black nickel oxide, the maximum temperature (below which nickel oxide particles can be reduced without any agglomeration) was significantly lower than that observed for the green nickel oxide. In addition, the best curve fittings of the Avrami model were obtained at higher values of the overall rate constant “k” and at lower values of the exponent “m”, compared to those values for the green nickel oxide. It may be inferred from these results that the hydrogen reduction rate of the black nickel oxide is faster than that of the green nickel oxide in the early stages, but the situation reverses in the later stages. For the black nickel oxide ore, in spite of the low temperature sintering, it was possible to achieve a high degree fluidized-bed reduction at lower temperatures and at lower gas consumption rates than was possible for the green nickel oxide. In this regard, the use of black nickel oxide is expected to yield a benefit if its ore price is sufficiently lower than that of the green nickel oxide.

CFD analysis of the effect of different PAR locations against hydrogen recombination rate

Many studies have been conducted on the performance of a passive autocatalytic recombiner (PAR), but not many have focused on the locations where the PAR is installed. During a severe accident in a nuclear reactor containment, a large amount of hydrogen gas can be produced and released into the containment, leading to hydrogen deflagration or a detonation. A PAR is a hydrogen mitigation method that is widely implemented in current and advanced light water reactors. Therefore, for this study, a PAR was installed at different locations in order to investigate the difference in hydrogen reduction rate. The results indicate that the hydrogen reduction rate of a PAR is proportional to the distance between the hydrogen induction location and the bottom wall.

Analysis of the Hydrogen Reduction Rate of Magnetite Concentrate Particles in a Drop Tube Reactor Through CFD Modeling

A computational fluid dynamics (CFD) approach, coupled with experimental results, was developed to accurately evaluate the kinetic parameters of iron oxide particle reduction. Hydrogen reduction of magnetite concentrate particles was used as a sample case. A detailed evaluation of the particle residence time and temperature profile inside the reactor is presented. This approach eliminates the errors associated with assumptions like constant particle temperature and velocity while the particles travel down a drop tube reactor. The gas phase was treated as a continuum in the Eulerian frame of reference, and the particles are tracked using a Lagrangian approach in which the trajectory and velocity are determined by integrating the equation of particle motion. In addition, a heat balance on the particle that relates the particle temperature to convection and radiation was also applied. An iterative algorithm that numerically solves the governing coupled ordinary differential equations was developed to determine the pre-exponential factor and activation energy that best fit the experimental data.

Voltammetric currents of the reduction of hydrogen ions from monoprotic acids. The effect of water dissociation

In the present work we report on the results of numerical simulation of the voltammetric currents of the hydrogen ions reduction from aqueous solutions of monoprotic acids. Diffusion and migration of the components of solution are taken into account, as well as homogenous chemical reaction of water dissociation. Calculations show that for small overvoltage the rate of the electrode reaction of hydrogen ion reduction is close to that in binary solutions. For large overvoltage, the rate of hydrogen reduction is higher than it might be expected for a binary acid. The concentration of the hydroxyl ion near the electrode substantially exceeds its concentration in the volume and has a maximum at a small distance from the metal surface. These effects result from the joint action of migration and a fast chemical reaction of water dissociation. In aqueous solutions of a strong acid with an excess of the supporting electrolyte, the effect of water dissociation reaction on the rate of hydrogen ion reduction is insignificant.

The negative-difference effect during the localized corrosion of magnesium and of the AZ91HP alloy

Galvanostatic tests with pure magnesium and with the AZ91HP alloy were performed in NaCl solutions, and the volume of hydrogen evolved during the tests was measured. In order to examine the negative-difference effect, a concept was developed to separate the hydrogen evolution (H.E.) on the passive surface and the H.E. inside the pits. An analysis of the volumetric data showed that the current density of H.E. inside the pits is much higher for Mg than for the AZ91HP alloy. With the assumption, that the ratio between the hydrogen reduction rate and the rate of the anodic metal dissolution, expressed by the factor k, does not change with the polarization, a k value of ca. 0.5 for pure Mg was found, while for the AZ91HP alloy this value was only ca. 0.3.

Interfacial kinetics of hydrogen with liquid slag containing iron oxide

Interfacial kinetics on the hydrogen reduction of liquid Fe t O in Fe t O-M x O y slag (M x O y = CaO, SiO2, Al2O3, and TiO2) has been studied at 1673 K. Because the rate of hydrogen reduction was very fast, the rate was controlled by gas-phase mass transfer under most of the experimental conditions. The effect of CaO or SiO2 addition on the interfacial chemical reaction rate of hydrogen reduction was empirically evaluated as a function of the ferrous-ferric ratio in the slag. The observed interfacial chemical reaction rates in Fe t O-CaO and Fe t O-SiO2 slags showed reasonable agreement with the estimated values. Most of the available literature data on the reduction rate of liquid iron oxide by solid carbon, hot metal, and reducing gases were also reviewed and compared with the results of the present work. It was found that the rate of hydrogen reduction of liquid iron oxide slag is much faster than that with other reducing agents such as solid carbon, carbon dissolved in the liquid iron, and CO gas.

Influence of Gangue Species on Hydrogen Reduction Rate of Liquid Wustite in Gas-conveyed Systems.

A laboratory scale fine particles-gas conveyed system was utilized to measure the hydrogen reduction rates of liquid wustite containing gangue such as 14.5 mol%CaO, 18.2 mol%SiO2, or 5.15 mol%A2O3 at 1773 K. The N2-H2 mixture having various flow rates and compositions was flowed downward through a cylindrical reactor maintained isothermally and a batch of spherical wustite particles (mean dia.; 58 μm) was concurrently fed into the reactor at a small constant rate and reduced in a hot zone. The reduction process was found to proceed in such a manner that a single metallic iron sphere was formed in the center of a wustite droplet. Rate analysis was made according to one dimensional mass balance equations for particles and gas in an isothermal steady moving bed. Under relatively small reducing potentials, it was concluded that the major fraction of overall reaction resistance is attributable to chemical reaction. The obtained chemical reaction parameters were found to be two orders of magnitudes larger than those in previous CO reduction. CaO raised the parameter, SiO2 lowered it, and Al2O3 did not affect it, relative to gangue-free one. Under higher reducing potentials, the reduction process was estimated to include an appreciable diffusion resistance in the liquid particle.

Analysis of rate of hydrogen reduction of porous wustite pellets basing on zone-reaction models.

Porous wustite pellets were reduced with hydrogen at 900°C, and reduction curves, position of reaction zone and local fractional-reduction profiles were measured.Basic equations for the grain model were re-examined and solved as they were (unsteady numerical solution), and under quasi-steady (quasi-steady numerical one) and moreover linearization approximations (quasi-steady analytical one). When rate parameter values are selected suitably in each case, measured reduction curves and reaction zone behavior are comparatively well reproduced by the calculated results. Thiele's modulus is about 10-14 under the present experimental conditions and reaction fashion differs much from the one for unreacted-core shrinking model.When the unsteady numerical solution is calculated, reducible oxygen density is divided by M to reduce the computation time; the error at M≤2000 is within a permissible range, although the solution most faithful to the basic equations is obtained at M=1. Comparison between the unsteady and the quasi-steady numerical solutions shows that the latter is an approximate solution having rather good accuracy. The quasi-steady analytical solution is better than the others from practical viewpoint, because its computation time is the shortest and degree of agreement between the measured and the calculated results is much the same among the three.

硫酸銅水溶液の水素加圧還元による銅微粉末製造法の研究

Hydrogen reduction of acidic copper sulfate solution was studied to obtain fine copper powder suitable for conductive paste. Reaction rate of hydrogen reduction of cupric ion to cuprous (Cu2++1/2H2→Cu++H+) was catalytically enhanced twice by addition of 0.1g/l Bi3+Coarse copper powder (>10μm) was obtained with further hydrogen reduction of cuprous ion to metallic copper (Cu++1/2H2→Cu0 +H+), because of some heterogeneous nature of the reaction.Fine copper powder (about 2μm) was obtained only by disproportionation of cuprous ion to metallic copper and cupric ion (2Cu→Cu0+Cu2+), which occurs by means of cooling the Cu+solution. The cooling rate and Cu+ion concentration determine size and shape of the powder. Experiments using a continuous autoclave resulted in oxidation resistant powder consisted of single crystals of about 5μm in size.

Effects of hydrogen recombination poisons on stress corrosion crack initiation and propagation in Al-Zn-Mg alloys

AbstractStress corrosion cracking (SCC) and corrosion behaviour of Al-Zn-Mg alloys have been studied in deaerated 3·5 wt-%NaCl solution at pH 3·5 with and without the hydrogen recombination poisons (HRPs) Na2S.9H2O or Ca3P2. SCC tests were carried out in the range of applied potential from −2150 to −400 mV(SHE) using constant load apparatus equipped with a linear variable differential transformer. The stress corrosion (SC) crack initiation and propagation periods were differentiated by measuring the extension of the gauge length with time. When the NaCl solution contained HRP the anodic dissolution rate decreased, probably due to the adsorption of hydride and/or its reduced phase, and the hydrogen reduction rate decreased due to the inhibition of hydrogen recombination. SC crack initiation and propagation times decreased with increasing HRP concentration, probably due to enhanced hydrogen permeation into the crack tip region. Incipient SCC was initiated preferentially at matrix/intermetallic inclusion int...

Kinetics of electrodeposition of Ni-Sn alloy deposits from an acid chloride bath

Total and partial polarization curves were determined for the deposition of tin and nickel separately as well as for their codeposition from acidic chloride baths. Using a rotating disc electrode system a detailed study of Ni2+, Sn2+ and H+ reduction processes was made, and the results were compared with similar studies on the deposition of such alloys from the same electrolyte with fluoride addition. It was found that for chloride baths the alloy is deposited with a higher polarization than that for the deposition of each metal separately, which is the reverse of the case of deposition from electrolytes containing fluoride ion additions. Furthermore, for coreduction there is a decrease in the hydrogen discharge overvoltage; the rate of hydrogen reduction considerably exceeds the discharge rate of other alloy components, and the hydrogen reduction reaction is diffusion controlled. The tin reduction reaction (for both separate deposition and codeposition) was found to be diffusion controlled, while for nickel reduction in both cases the reaction kinetics are mixed with the activation kinetics dominant. The dependences of current efficiency and of percentage content of tin in the alloy on current density were also investigated. The investigations showed that, although there exists a considerable difference in the electrocrystallization process of Ni-Sn plate from chloride baths and from baths with F- additions, it is possible to choose electrolysis conditions which will allow plates with good properties to be obtained from the bath which contains chloride only.

Determination of the Active Surface of Silica‐gel Supported Co3O4 by Hydrogen Reduction Rate Measurements

AbstractThe method of Mekhandzhiev and Dyakova for the determination of the active surface of supported oxide catalysts, based on the rate of their reduction with gaseous reagents has been applied to silica‐gel supported Co3O4. Different aspects of the interaction of the active phase with the support have been discussed.

各種強電解質水溶液中への水素ガスの溶解

A study on the dissolution behavior of hydrogen gas in aqueous solutions containing strong electrolytes was done to elucidate the dependence of both concentration and effective diameters of electrolyte-constituting ions upon the solubility, as well as the dissolution rate, of hydrogen gas. The main results obtained are as follows:(1) Dissolution rate of hydrogen gas, and its solubility as well, in the aqueous solutions of strong electrolytes decreases with the increase in both the concentration of electrolytes and the effective diameters of electrolyte-constituting ions.(2) Solubility of hydrogen gas in a binary H2 SO4-CuSO4 solution can be estimated as the sum of the solubilities of hydrogen gas in the respective solutions.(3) The value of hydrogen solubility in an aqueous solution containing strong electrolyte can be roughly estimated by taking the concentration of electrolyte and the effective diameter of constituting ions into considerations.(4) The rate of hydrogen reduction of silver from a silver nitrate solution at 50°C and 500 rpm was found to be controlled by the dissolution rate of hydrogen gas in the aqueous solution.

Effect of Compacting and Grinding on the Hydrogen Reduction of Nickel Oxide

Abstract The rate of hydrogen reduction of nickel oxide increases with an increase in the compacting pressure although the bulk density of nickel oxide increases and the surface area does not vary with the pressure. The rate of reduction of nickel oxide which is prepared by the grinding of a single crystal and has a large particle size of 50 μ is higher than that of nickel oxide which is prepared by ignition of nickel sulfate and has small particle size of 0.5 μ. It seems reasonable to conclude that the accelerated reduction is attributed to the crystal distortion which may result from plastic deformation by grinding or compacting.