Nafion/sulfated β-cyclodextrin composite membranes for direct methanol fuel cells

Proton-conducting composite membranes based on H⁺-form sulfated β-cyclodextrin (sb-CD) in a Nafion matrix are prepared via the solution-casting method and their methanol permeabilities, proton conductivities, proton diffusion coefficients and cell performances are measured. The methanol permeabilities of the composite membranes increase very slightly with increases in their sb-CD content. As a result of adding sb-CD with its many sulfonic acid groups into the Nafion matrix, the proton conductivities of the composite membranes increase with increases in their sb-CD content. The methanol permeability and proton conductivity results are used to show that the best selectivity of the membranes is that of the NC5 membrane (‘NCx’ denotes a Nafion/sb-CD composite membrane containing x wt.% sb-CD). The proton diffusion coefficients are measured with ¹H pulsed field gradient nuclear magnetic resonance (PFG-NMR) and found to increase with increase in the sb-CD content in the order NC5 > NC3 > NC1 > NC0. Thus the presence of sb-CD in the Nafion membranes increases the proton diffusion coefficients as well as the proton conductivities, ionic cluster size, water uptakes and the ion-exchange capacities (IECs). A maximum power density of 58 mW cm⁻² is obtained for the NC5 membrane. The combination of these effects should lead to an improvement in the performance of direct methanol fuel cells prepared with Nafion/sb-CD composite membranes.     

Co–Ni/WC-AC catalysts for dry reforming of methane: The role of Ni species

To improve the DRM reaction performance of the catalysts, a series of Co–Ni/WC-AC catalysts are prepared by impregnation using WC-AC as the support. The structural features of the fresh and spent catalysts are characterized by BET, XRD, H₂-TPR, XPS and TG. The results show that the introduction of Ni in the 20Co/WC-AC catalyst promotes the conversion of W species to WC. Further, WC enhances the interaction between the active metal and the support. Thus, the activity and sintering resistance of Co–Ni/WC-AC catalysts are improved. It is also found that the introduction of different ratios of Ni has a significant effect on the chemical environment (oxygen environment) on the catalyst surface.10Co–10Ni/WC-AC catalysts showed high surface O_α and O_β contents of 26% and 53%, respectively. The catalyst shows excellent catalytic performance. The conversion of CH₄ and CO₂ is stable at about 84% and 85% at 800 °C.     

Hydrogen production from steam reforming of bioethanol using Cu/Ni/K/γ-Al2O3 catalysts. Effect of Ni

Hydrogen to be used as a raw material in fuel cells or even as a direct fuel can be obtained from steam reforming of bioethanol. The key aim of this process is to maximize hydrogen production, discouraging at the same time those reactions leading to undesirable products, such as methane, acetaldehyde, diethyl ether or acetic acid, that compete with H₂ for the hydrogen atoms. Cu–Ni–K/γ-Al₂O₃ catalysts are suitable for this reaction since they are able to produce acceptable amounts of hydrogen working at atmospheric pressure and a temperature of 300°C. The effect of nickel content in the catalyst on the steam-reforming reaction was analyzed. Nickel addition enhances ethanol gasification, increasing the gas yield and reducing acetaldehyde and acetic acid production.     

Glycerol steam reforming over Ni/mg/γ-Al2O3 catalysts effect of Ni(II) content

The aim of the present work is to analyse the effect of the Ni(II) content for the Ni(II)-Mg(II)/γ-Al₂O₃ catalysts on the textural and structural characteristics of the solid, as well on the catalytic activity and selectivity to H₂ for the steam reforming of glycerol at atmospheric pressure.     

Elaboration and electrochemical characterization of Mg–Ni hydrogen storage alloy electrodes for Ni/MH batteries

Mg–Ni hydrogen storage alloy electrodes with composition of Mg–33, 50, 67 Ni at. % in amorphous phase were prepared by means of mechanical alloying (MA) process using a planetary ball mill. The electrochemical hydrogen storage characteristics and mechanisms of these electrodes were investigated by electrochemical measurements, X–ray diffraction (XRD) and scanning electron microscope (SEM) analyses. The relationship between alloy composition and electrochemical properties was evaluated. In addition, optimum milling time and composition of Mg–Ni hydrogen storage alloy with acceptable electrochemical performance were determined. XRD results show that the alloys exhibit dominatingly amorphous structures after milling of 20 h. The electrochemical measurements revealed that the discharge capacity of Mg₃₃Ni₆₇ and Mg₆₇Ni₃₃ alloy electrodes reached a maximum when alloys were prepared after 20 h of milling time (260 and 381 mAhg^?1, respectively). The maximum discharge capacity of Mg₅₀Ni₅₀ alloy was observable after 40 h milling (525 mAhg^?1). It was also found that the cyclic stability of the alloys increased with increasing Ni content. Among these alloys, the amorphous Mg₅₀Ni₅₀ alloy presents the best overall electrochemical performance. In this paper, electrode process kinetics of Mg₅₀Ni₅₀ alloy electrode was also studied by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The impedance spectra of electrodes were measured at different depths of discharge (DODs). The observed spectra were fit well with the equivalent circuit model used in the paper. The electrochemical parameters calculated from electrochemical impedance were also compared. The electrochemical discharge and cyclic performance of 20, 40 and 60 h milled Mg₅₀Ni₅₀ alloy electrodes were demonstrated by the fitted charge transfer resistance and Warburg impedance obtained at various DODs. It was further observed that the controlling-step of the discharge process changed from a mixed rate-determining process at lower DODs to a mass-transfer controlled process at higher DODs. The fitted results demonstrated that charge–transfer resistance (R_ct) increased with DOD. The R_ct of 40 h milled Mg₅₀Ni₅₀ alloy (29.27 Ω) was lower than that of 20 h (41.89 Ω) and 60 h milled alloys (92.43 Ω) at fully discharge state.     

Ni/CeO2/ZSM-5 catalysts for the production of hydrogen from the pyrolysis–gasification of polypropylene

The production of hydrogen from the two-stage pyrolysis–gasification of polypropylene using a Ni/CeO₂/ZSM-5 catalyst has been investigated. Experiments were conducted on CeO₂ loading, calcination temperature and Ni loading of the Ni/CeO₂/ZSM-5 catalyst in relation to hydrogen production. The results indicated that with increasing CeO₂ loading from 5 to 30 wt.% for the 10 wt.% Ni/CeO₂/ZSM-5 catalyst calcined at 750 °C, hydrogen concentration in the gas product and the theoretical potential hydrogen production were decreased from 63.0 to 49.8 vol.% and 50.4 to 21.6 wt.%, respectively. In addition, the amount of coke deposited on the catalyst was reduced from 9.5 to 6.2 wt.%. The calcination temperature had little influence on hydrogen production for the catalyst containing 5 wt.% of CeO₂. However, for the 10 wt.% Ni/CeO₂/ZSM-5 catalyst with a CeO₂ content of 10 or 30 wt.%, the catalytic activities reduced when the calcination temperature was increased from 500 to 750 °C. The SEM results showed that large amounts of filamentous carbons were formed on the surface of the catalysts. The investigation of different Ni content indicates that the Ni/CeO₂/ZSM-5 ((2-10)-5-500) catalyst containing 2 wt.% Ni showed poor catalytic activity in relation to the pyrolysis–gasification of polypropylene according to the theoretical potential H₂ production (7.2 wt.%). Increasing the Ni loading to 5 or 10 wt.% in the Ni/CeO₂/ZSM-5 ((2-10)-5-500) catalyst, high potential hydrogen production was obtained.     

Reliability of hydrogen sensing based on bimetallic Ni–Pd/graphene composites

Graphene-supported nickel–palladium (Ni–Pd) bimetallic nanoparticles (Ni–Pd/Gr) were synthesized using a simple chemical method, followed by a post-thermal annealing process. The characteristics of resistivity-type hydrogen (H₂) sensors composed of Pd–Gr composites (with small amounts of Ni added to the Pd nanoparticles (Pd NPs)) were investigated in detail. Pd NPs with various amounts of Ni embedded into the Pd lattice were synthesized by varying the molar ratios of the Ni/Pd precursors. The results from this work indicate that the addition of Ni not only enhances performance, but also reduces the hysteresis behavior of the Pd–Gr composite based H₂ sensors. H₂ was detectable from 1 to 1000 ppm based on a rapid recovery response with suitable Ni/Pd percentages. At the optimal Ni/Pd percentage of 7% (Ni/Pd ∼7%), sensors showed a small enhancement of sensitivity, fast recovery, and minimum hysteresis effect. From our experiment, the addition of Ni to Pd NPs results in a reduction of the hysteresis effect and reliability on H₂ sensors based on Pd–Gr composites.     

Ni/La2O3 and Ni/MgO–La2O3 catalysts for the decomposition of NH3 into hydrogen

The decomposition of NH₃ for hydrogen production was studied using Ni/La₂O₃ catalysts at varying compositions and temperatures prepared via surfactant-templated synthesis to elucidate the influence of catalyst active metal content, support composition and calcination temperature on the catalytic activity. The catalytic performance of all samples was studied between 300 and 600 °C under atmospheric pressure. The catalytic activity of the sample were as follows: 10Ni/La₂O₃-450 > 10Ni/La₂O₃-550 > 10Ni/La₂O₃-650 ≈ 10Ni/La₂O₃-750 ≈ 10Ni/La₂O₃-850. The excellent activity (100%) of 10Ni/La₂O₃-450 could be due to the high surface area, basicity strength and concentration of surface oxygen species of the catalyst as evidenced by BET, CO₂-TPD and XPS. In addition, to adjust the activity of the catalyst support, the molar ratios of Mg and La were varied (1:1, 3:1, 5:1, 7:1 and 9:1). The 5Ni/5MgLa (5:1 M ratio) was found to be the most active (100%) relative to other Ni/MgLa formulations. Furthermore, the Ni content in the Ni/5MgLa sample was adjusted between 10 and 40 wt%. Increasing the Ni content of the catalysts increased NH₃ conversion with the 40 wt% Ni formulation demonstrating complete NH₃ conversion at 600 °C and a high gas hourly space velocities (GHSV) (30,000 mL∙h⁻¹∙g_cat⁻¹).     

Preparation and electrochemical properties of composite LaNix/Ni–S–Co alloy film

The composite LaNi_x/Ni–S–Co film with considerable stability and high HER activity (η₁₅₀ = 70 mV, 353 K) was obtained by molten salt electrolysis combined with aquatic electrodeposition. LaNi_x film was prepared by galvanostatic electrolysis at 100 mA cm⁻² under 1273 K. The results showed that the La³⁺ ions could be reduced on the nickel cathode and the LaNi_x film could form, i.e. La³⁺ + 3e + xNi = LaNi_x (x = 5 or 3) at ca. −0.6 V, which is much lower than that of the decomposition potential of lanthanum, due to the strong depolarization effect of nickel. Furthermore, compared with the traditional amorphous Ni–S film, the composite LaNi_x/Ni–S–Co film could absorb large amount of H atoms, which would be oxidized and avoid the dissolution of the Ni–S–Co film under the state of open-circuit effectively and increase the HER activity.     

Ni/a-Si肖特基势垒太阳电池

在非晶硅电池的三种基本形式中,M/a-Si肖特基势垒结构发展得最早,曾一度领先,但由于它的开路电压受所用金属功函数的限制,加之存在稳定性问题,因而缺乏足够的竞争力。针对这些问题,已经开展了广泛的研究。 我们发现,不稳定性主要来自M/a-Si肖特基结的退化,而这种退化过程不仅受外界环     

Metallic Ni monolith–Ni/MgAl2O4 dual bed catalysts for the autothermal partial oxidation of methane to synthesis gas

A dual bed catalyst system consisting of a metallic Ni monolith catalyst in the front followed by a supported nickel catalyst Ni/MgAl₂O₄ has been studied for the autothermal partial oxidation of methane to synthesis gas. The effects of bed configuration, reforming bed length, feed temperature and gas hourly space velocity on the reaction as well as the stability are investigated. The results show that the metallic Ni monolith in the front functions as the oxidation catalyst, which prevents the exposure of the reforming catalyst in the back to the very high temperature, while the supported Ni/MgAl₂O₄ in the back functions as the reforming catalyst which further increases the methane conversion by 5%. A typical 5 mmNi monolith–5mmNi/MgAl₂O₄ dual bed catalyst exhibits methane conversion and hydrogen and carbon monoxide selectivities of 85.3%, 91.5% and 93.0%, respectively, under autothermal conditions at a methane to oxygen molar ratio of 2.0 and gas hourly space velocity of 1.0 × 10⁵ h⁻¹. The dual bed catalyst system is also very stable.     

Effect of Ni/Al atomic ratio of mesoporous Ni–Al2O3 aerogel catalysts on their catalytic activity for hydrogen production by steam reforming of liquefied natural gas (LNG)

Mesoporous Ni–Al₂O₃ (XNiAE) aerogel catalysts with different Ni/Al atomic ratio (X) were prepared by a single-step sol-gel method and a subsequent CO₂ supercritical drying method. The effect of Ni/Al atomic ratio of mesoporous XNiAE aerogel catalysts on their physicochemical properties and catalytic activity for steam reforming of liquefied natural gas (LNG) was investigated. Textural properties and chemical properties of XNiAE catalysts were strongly influenced by Ni/Al atomic ratio. Nickel species were highly dispersed on the surface of XNiAE catalysts through the formation of surface nickel aluminate phase. In the steam reforming of LNG, both LNG conversion and hydrogen yield showed volcano-shaped curves with respect to Ni/Al atomic ratio. Average nickel diameter of XNiAl catalysts was well correlated with LNG conversion and hydrogen yield over the catalysts. Among the catalysts tested, 0.35NiAE (Ni/Al = 0.35) catalyst with the smallest average nickel diameter showed the best catalytic performance. The highest surface area, the largest pore volume, the largest average pore size, and the highest reducibility of 0.35NiAE catalyst were also partly responsible for its superior catalytic performance.     

Preparation of Ni–Cu/Mg/Al catalysts from hydrotalcite-like compounds for hydrogen production by steam reforming of biomass tar

Ni–Cu/Mg/Al bimetallic catalysts were prepared by the calcination and reduction of hydrotalcite-like compounds containing Ni²⁺, Cu²⁺, Mg²⁺, and Al³⁺, and tested for the steam reforming of tar derived from the pyrolysis of biomass at low temperature. The characterizations with XRD, STEM-EDX, and H₂ chemisorption confirmed the formation of Ni–Cu alloy particles. The Ni–Cu/Mg/Al bimetallic catalyst with the optimum composition of Cu/Ni = 0.25 exhibited much higher catalytic performance than the corresponding monometallic Ni/Mg/Al and Cu/Mg/Al catalysts in the steam reforming of tar in terms of activity and coke resistance. The catalyst gave almost total conversion of tar even at temperature as low as 823 K. This high performance was related to the higher metal dispersion, larger amount of surface active sites, higher oxygen affinity, and surface modification caused by the formation of small Ni–Cu alloy particles. In addition, the Ni–Cu/Mg/Al catalyst showed better long-term stability than the Ni/Mg/Al catalyst. No obvious aggregation and structural change of the Ni–Cu alloy particles were observed. The coke deposition on the Ni–Cu/Mg/Al catalyst was approximately ten times smaller than that on the Ni/Mg/Al catalyst, indicating good coke-resistance of the Ni–Cu alloy particles.     

Thermocatalytic decomposition of methane over mesoporous Ni/xMgO·Al2O3 nanocatalysts

This paper describes a facile method to produce mesoporous nanostructure Ni/Al₂O₃, Ni/MgO, and Ni/xMgO.Al₂O₃ (x: MgO/Al₂O₃ molar ratio) catalysts prepared by “one-pot” evaporation-induced self-assembly (EISA) method with some modifications for investigating in the thermocatalytic decomposition of methane. Detailed characterizations of the material were performed with X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and N₂ adsorption/desorption, hydrogen temperature-programmed reduction (H₂-TPR), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and temperature-programmed oxidation (TPO). The characterizations demonstrated that the synthesized catalysts with various MgO/Al₂O₃ molar ratios possessed mesoporous structure with the high BET area in the range of 216.79 to 31.74 m² g^?1. The effect of different surfactants and calcination temperatures on the characterizations and catalytic activity of the catalysts were also examined in details. The experimental results showed that the catalysts exhibited high catalytic potential in this process and the 55 wt.% Ni/2 MgO·Al₂O₃ catalyst calcined at 600^οC possessed an acceptable methane conversion (～60%) under the harsh reaction conditions (GHSV = 48000 (mL h^?1 g_cat^?1)).     

Influence of some metal ions on the structure and properties of doped β-PbO2

The lead dioxide active mass of positive lead-acid battery plates is a gel-crystal system with proton and electron conductivity of the hydrated gel zones. This paper discusses the influence of Sn²⁺, Sb³⁺, Co²⁺, Mg²⁺ and Al³⁺ ions, added to the formation electrolyte, upon the stoichiometry, structure and phase composition of the PbO₂ positive active material (PAM) of lead-acid batteries. PAM samples doped with the above metal ions are characterized by: X-ray diffraction (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and chemical analysis. The obtained results show that different metal ions are incorporated in different quantities in the PbO₂ particles. Under the influence of dopants, the stoichiometric coefficient of lead dioxide decreases, i.e. dopants increase the non-stoichiometry of PbO₂. The foreign ions in the formation electrolyte exert strong influence on the microstructure of PAM and change the proportion between crystal and hydrated gel zones in the particles.     

Electrochemical hydrogen storage of ball-milled MmMg12 alloy–Ni composites

MmMg₁₂–Ni amorphous or nanocrystalline composites (Mm: Ce-rich mischmetal) were prepared through the ball-milling method, and their electrochemical hydrogen storage performance was investigated and compared with that of ball-milled CeMg₁₂–Ni composites. It was found that the ball-milled MmMg₁₂–Ni composites had larger initial discharge capacities and better high rate dischargeability. Analysis of electrochemical impedance spectra (EIS) shows that the reaction resistance and hydrogen diffusion resistance of the ball-milled MmMg₁₂–Ni composites are lower as a result of the decrease in Ce content, and thus can contribute to the larger discharge capacity and better high rate dischargeability. Additionally, the cycle performance of the ball-milled MmMg₁₂–Ni composites is better than those of the ball-milled CeMg₁₂–Ni composites. This may be related to the formation of a Nd oxide or Nd(OH)₃ film on surface of the MmMg₁₂ alloys.     

Autothermal reforming of ethanol in a Pd–Ag/Ni composite membrane reactor

The main objective of this project is to study the hydrogen production reaction from oxidative steam reforming of bio-ethanol in the pertinent characteristics of a palladium–silver alloy membrane reactor. The enhancements of hydrogen permeation and of H₂/N₂ permselectivity were studied in a Ni–Pd–Ag ternary alloy membrane, which was fabricated by successive electroless plating of palladium and silver on stainless steel (PSS) supports modified with nickel electroplating. XRD, SEM, and EDS were used to characterize the surface morphology of the membranes. Ethanol–water mixture (n_water/n_ethanol = 1 or 3) and oxygen (n_oxygen/n_ethanol = 0.2 or 0.7) were fed concurrently into the membrane reactor packed with Zn–Cu commercial catalyst (MDC-3). The reaction temperatures were set at temperatures of 593–723 K and pressures of 3–10 atm. The amount of oxygen added in the feed has a significant effect on the steam reforming reaction of ethanol. At high pressures, autothermal reaction of ethanol with no need for external heating to the composite membrane reactor to produce high purity hydrogen was easily processed.     

A study on catalytic activity of modified Ni–Re/Al-SBA-15 catalyst for hydrodenitrogenation of o-toluidine

To elucidate the influence of Al content and effect of Ni loading on the structure and catalytic activity for hydrodenitrogenation reaction of o-toluidine, a series of mesoporous Al-SBA-15 supported Ni–Re sulphided catalysts were prepared. The textural and chemical properties of support and catalyst were analysed using XRD, N₂-sorption studies, DRS UV–Vis, SEM, HRTEM, NH₃-TPD, TPR and XPS. These characterizations indicate that the incorporation of Al content into the SBA-15 framework leads to the formation of moderate acid sites, which shows enhanced catalytic activity. The maximum catalytic activity in 1 wt%Ni-5wt%Re/Al-SBA-15(10) catalyst is due to fine dispersion of Re and Ni over the support, strong metal–support interaction, high degree of sulphidation and more sulphur atoms on the surface.     

Combination of CO2 reforming and partial oxidation of methane to produce syngas over Ni/SiO2 and Ni–Al2O3/SiO2 catalysts with different precursors

Ni/SiO₂ and Ni–Al₂O₃/SiO₂ catalysts were prepared by incipient wetness impregnation using citrate and nitrate precursors and tested with a reaction of combination of CO₂ reforming and partial oxidation of methane to produce syngas (H₂/CO). The catalytic activity of Ni/SiO₂ and Ni–Al₂O₃/SiO₂ greatly depended on interaction between NiO and support. NiO strongly interacted with support formed small nickel particles (about 4 nm for NiSC which is abbreviation of Ni/SiO₂ prepared with Nickel citrate precursor) after reduction. The small nickel particles over NiSC catalysts exhibited a good catalytic performance.