International Journal of Hydrogen Energy

Published by Elsevier
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This paper deals with the electrochemical production of hydrogen by depolarizing the oxygen evolution reaction using human feces and urine, which contains 30-40% bacteria and yeast. The electroactivity of graphite, tungsten carbide, perovskite and RuO2-coated Ebonex (Ti4O7) as anode materials are compared. The scale-up of the process in a laboratory-scale three-dimensional packed bed cell is discussed.
 
It is shown that the performance of a gas fuelled spark ignition engine can be enhanced considerably when relatively small amounts of hydrogen are present with methane. This improvement in performance which is especially pronounced at operational equivalence ratios that are much leaner than the stoichiometric value, can be attributed largely to the faster and cleaner burning characteristics of hydrogen in comparison to methane. Through analytical simulation of engine performance, the addition of hydrogen is considered through its production in-situ on board the engine by electrolysis of water with the necessary energy supplied from engine power. It is shown that when the work energy required for the production of hydrogen by electrolysis is taken into account, the range of viable operation of such an engine is very narrow. This would render the whole concept of in situ hydrogen production through water electrolysis uneconomical in conjunction with engine operation, even though the presence of additional oxygen produced with the hydrogen tends, in principle, to improve engine performance beyond that observed with hydrogen addition
 
The objective of this work was to compare the hydriding kinetics of Mg2Ni with that of Mg1.9Al0.1Ni and study the influence of the initial hydrogen pressure on the hydriding kinetics in the two-phase (α–β) region of the Mg2−xAlxNi (x=0,0.1) alloys. Experiments were carefully performed under the initial hydrogen pressure ranging from 0.275 to and isothermal condition. The obtained hydrogen absorption kinetic curves were fitted using various rate equations to reveal the mechanism of the hydriding process. It was found that the three-dimensional diffusion process dominated the hydrogen absorption. The experimental investigation suggested that increase of the initial hydrogen pressure resulted in an acceleration of hydriding transformed fraction and the kinetic characteristics of Mg2Ni alloy was improved by substituting Al for Mg due to difference in hydride structure, particle size.
 
In this paper, the effects of both Co substitution and annealing treatment on the structures and electrochemical properties of La0.7Mg0.3Ni2.45-xCo0.75+xMn0.1Al0.2(x=0.00,0.15,0.30) hydrogen storage alloys have been studied. X-ray diffraction (XRD) analyses show that the main phases of all of the alloys are (La,Mg)Ni3 phase (PuNi3-type structure) and LaNi5 phase (CaCu5-type structure). Electrochemical investigations show that increasing Co content and annealing treatment can considerably enhance the cyclic stability of the alloy electrodes. For La0.7Mg0.3Ni2.15Co1.05Mn0.1Al0.2 alloy, the value of C100/Cmax was only 65.5% at its as-cast, however, the value reached 80.5% after an annealing treatment of . The maximum discharge capacity of the alloy electrodes increased by annealing treatment and decreased slightly when Co content increased from x=0.00 to 0.30 at its as-cast state. But the exchange current density (I0), the limiting current density (IL) and the diffusion coefficient of hydrogen (D) of the alloy electrodes decreased, leading to a corresponding reduction of the high rate dischargeability (HRD), with increasing Co content and annealing treatment.
 
The phase structures and electrochemical properties of alloys were investigated by the general electrochemical techniques and X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer and emission spectrochemical analysis. Nickel added into V2.1Ti alloy plays a key role in the performance of the new alloys, due to the formation of a continuous TiNi-based secondary phase in the form of a three-dimensional network around the main phase. Though the hydrogen absorbed by the alloy reduces with the increase of nickel content, the actual electrochemical discharge capacity and the high-rate discharge capability are improved noticeably. Among the studied alloys, V2.1TiNi0.5 with a good combination of the main phase and the secondary phase has the best overall electrochemical performance.
 
Ba0.5Sr0.5Co1−yFeyO3−δ (y = 0.1–0.9) (BSCF) oxides have been evaluated as cathode materials for intermediate solid oxide fuel cells with La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) as electrolyte. The increase of iron content in BSCF materials results in an increase of the area-specific resistance (ASR), e.g. 0.04, 0.08 and 0.13 Ω cm2 for compositions with y = 0.2, 0.4 and 0.6 respectively at 1073 K. The influence of iron content in BSCF oxides on the unit cell volume via high temperature X-ray diffraction, the overall electrical conductivity and the thermal expansion coefficient (TEC) has also been investigated. The lattice cell parameters for the BSCF series increase as a function of the temperature and exhibit a non-linear behaviour, with a sudden increase at around 673 K due to the loss of lattice oxygen, which in turn is caused by the reduction of Co4+ and Fe4+ to lower oxidation states. This was determined by O2 temperature-programmed desorption and thermogravimetric analysis. Such oxygen non-stoichiometry results in a significant thermal expansion and conductivity change for all compositions at the same temperature.
 
Mg1.5Al0.5−xZrxNi (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) type alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that Zr facilitated the amorphization of Mg2Ni phase, while Al retarded the amorphization of this phase. The increase in the Zr content was observed to bring about significant improvement in the discharge capacities at all the ball milling durations. The stepwise replacement of Al with Zr, however, caused considerable reduction in the initial discharge capacities of the alloys. Despite the adverse effect of Al on the initial discharge capacity, it prevented the rapid degradation of Mg2Ni phase with the charge/discharge cycles. When the beneficial effects of Zr and Al were combined by designing Mg1.5Al0.5−xZrxNi type alloys, Mg1.5Al0.2Zr0.3Ni alloy was found to have the highest discharge capacity at almost all the charge/discharge cycle steps. Among the obtained capacity retaining rates, Mg1.5Al0.4Zr0.1Ni alloy had the best performance. This alloy has kept at least 50% of its initial discharge capacity at 20th cycle. The analysis by the electrochemical impedance spectroscopy revealed that the charge transfer resistances of Al-rich alloys were low at high depth of discharges. This observation was attributed to the formation of the porous unstable Mg(OH)2 layer due to the intercalation of Al2O3 layers, which have the high rate of solubility in strongly basic solutions, and thus the exposition of the underlying electrocatalytically active Ni sites.
 
The structure and electrochemical properties of hydrogen storage alloys were studied systematically. X-ray powder diffraction and Rietveld analyses indicate that all the alloys mainly consist of the (La,Mg)Ni3 phase and the LaNi5 phase. The Co7W6 phase and the separate W phase are formed with increasing x. Electrochemical studies show that the maximum discharge capacity decreases monotonously from 355.5 mAh/g (x=0) to 319.5 mAh/g (x=0.15) with increasing x due to the formation of new phases Co7W6 and W which cannot absorb hydrogen. However, the cycling stability is markedly improved, that is, after 150 charge/discharge cycles, the discharge capacity retention increases from 51.8% (x=0) to 61.5% (x=0.1). In addition, as x=0.05, the alloy electrode exhibits the optimum kinetics property.
 
The high temperature deformation behaviors of Ti-6Al-4V alloy and the alloy hydrogenated with 0.3 wt%H were studied. Comparing with the unhydrogenated alloy, the hydrogenated alloy exhibited higher plasticity and lower flow stress. The possibilities of hydrogen-induced plasticity were attributed to the effect of hydrogen on dislocation density, stacking fault energy in starting microstructure and dislocation mobility, dynamic recrystallization during high temperature deformation. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
 
In order to identify competitive ion-conducting materials in ceria-carbonates composite electrolytes, M-NLCO (M = Ce0.8Sm0.2O2-δ (SDC), Ce0.8Gd0.2O2-δ (GDC), Ce0.8Y0.2O2-δ (YDC); NLCO = 0.53Li2CO3–0.47Na2CO3) sintered at different temperatures (600° C, 625° C, 650° C, 675° C and 700° C) have been prepared and characterized. It is found that independent of systems, the 675° C-sintered composites in M-NLCO always present the highest conductivities because of the best NLCO distribution and interfacial microstructures. Moreover, among three composites (sintered at 675° C), the total (σt) and grain boundary (σgb) conductivities measured at 600° C are ranked as: SDC-NLCO (, ) ﹥ GDC-NLCO (, ) ﹥ YDC-NLCO (, ), which is attributed to ionic-radius compatibility between the dopant and the host as well as the NLCO distribution and interfacial microstructures. It can be concluded that ionic-radius compatibility between the dopant and the host, NLCO distribution and interfacial microstructures have important effects on improving ionic conductivities for ceria-carbonates composite electrolytes.
 
The dehydrogenation reaction of the 0.6LiBH4-0.4Mg(BH4)2 eutectic system was investigated by Temperature-Programmed-Desorption and Pressure-Composition-Isotherm methods, in the range of 25–540 °C and 0.1–150 bar of p(H2). A sequence of four decomposition steps was found by TPD measurements; they occur at 235, 315, 365 and 460 °C for p(H2) = 3 bar, with a clear T decrease with respect to pure LiBH4 and Mg(BH4)2. In the PCI experiments, the first two steps could not be resolved but appeared merged in a single process. The amounts of H2 release at each step and the ΔrH and ΔrS values derived from van’t Hoff plots were analyzed and compared with known results for relevant possible reactions. A scheme of interpretation was then proposed for all four processes. In particular, a fraction of LiBH4 and Mg(BH4)2 would react together in the range of 300–350 °C according to 2LiBH4 + Mg(BH4)2 → 2B + 2LiH + MgB2 + 7H2, thus explaining the quite large H2 yield therein observed. The first and fourth steps correspond to decompositions of pure remaining Mg(BH4)2 and LiBH4, respectively, and the third one to dehydrogenation of MgH2 produced in the first step.Highlights► We study dehydrogenation of the Li-Mg borohydride eutectic by TPD and PCI methods. ► The H2 release below 400 °C is larger than for the weighted average of end members. ► LiBH4 is shown to partly decompose at unusually low temperature. ► A multi-step reaction model accounts for results from van’t Hoff plots and H2 yields.
 
Pd0.5NixSe(0.5−x) electrocatalysts with different chemical composition, X = 0.25, 0.35, 0.45, were synthesized by a NaBH4 reduction of PdCl2, NiCl2 and SeO in a THF solution and evaluated for the oxygen reduction reaction (ORR) in acid media by electrochemical techniques of rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE). The electrocatalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and CO adsorption/stripping. The relation of Se to Ni in the samples has a profound effect on the nature of the cathode catalytic activity toward the oxygen reduction process, enhanced as the Se content in the electrocatalysts was reduced. Electrochemical results show that the ORR takes place by a multi-electron charge transfer process (n = 4e−) with the formation of less than 1% of hydrogen peroxide. The enhanced activity was attributed to the high active surface area deduced from CO adsorption/stripping analysis. The research activities are reported within the focus on the activity-stability of the bimetallic chalcogenides electrocatalysts.
 
Photocatalytic hydrogen production was investigated over ZnS1−x−0.5yOx(OH)y–ZnO using sulfide ion (Na2S–Na2SO3) as an electron donor from NaCl saltwater. NaCl can affect markedly the activity for photocatalytic hydrogen production, depending on NaCl concentration. When NaCl concentration is lower, the activity is lower than that in pure water, whereas when NaCl concentration is higher, the activity is higher than that in pure water. NaCl decreases not only the surface charge of ZnS1−x−0.5yOx(OH)y–ZnO but also the surface hydration. When ZnS1−x−0.5yOx(OH)y–ZnO was impregnated with the electron donor (Na2S–Na2SO3), ZnO was transformed partly into ZnS. The impregnated ZnS1−x−0.5yOx(OH)y–ZnO exhibits higher activity than the non-impregnated one. The possible mechanisms were discussed.Graphical abstractWhen NaCl concentration is lower, the activity is lower than that in pure water, whereas when NaCl concentration is higher, the activity is higher than that in pure water. The impregnated photocatalyst (with Na2S–Na2SO3) exhibits much higher activity than non-impregnated one.Highlights► ZnS1−x−0.5yOx(OH)y–ZnO as photocatalyst and Na2S–Na2SO3 as electron donor. ► Effect of NaCl concentration on photocatalytic H2 evolution. ► The photocatalytic activity increases markedly in concentrated NaCl saltwater. ► The photocatalyst impregnated with Na2S–Na2SO3 exhibits higher activity.
 
The kinetics of hydrogen absorption by magnesium bulk is affected by two main activated processes: the dissociation of the H2 molecule and the diffusion of atomic H into the bulk. In order to have fast absorption kinetics both activated processed need to have a low barrier. Here we report a systematic ab initio density functional theory investigation of H2 dissociation and subsequent atomic H diffusion on TM (= Ti, V, Zr, Fe, Ru, Co, Rh, Ni, Pd, Cu, Ag)-doped Mg(0001) surfaces. The calculations show that doping the surface with TMs on the left of the periodic table eliminates the barrier for the dissociation of the molecule, but the H atoms bind very strongly to the TM, therefore hindering diffusion. Conversely, TMs on the right of the periodic table do not bind H, however, they do not reduce the barrier to dissociate H2 significantly. Our results show that Fe, Ni and Rh, and to some extent Co and Pd, are all exceptions, combining low activation barriers for both processes, with Ni being the best possible choice.
 
Rhodobacter sphaeroides O.U. 001 (concentration of inoculum-0.36 g dry wt/l) and brewery wastewaters were applied in photobiogeneration of hydrogen under illumination of 116 W/m2. The best results were obtained with filtered wastewaters sterilized at 120 °C for 20 min and maximal concentration of waste in medium equal 10% v/v. The main product in generated biogas was hydrogen (90%). After sterilization the amount of generated hydrogen was tripled (from 0.76 to 2.2 l H2/l medium), whereas waste concentration of 10% v/v resulted in the best substrate yield (0.22 l H2/l of waste). Under these conditions the amount of generated hydrogen was 2.24 l H2/l medium and light conversion efficiency reached value of 1.7%. The modified Gompertz equations served in modeling of the kinetics of the studied process.
 
Waste water from a distillery was used as the electron donor for photoproduction of hydrogen by Rhodobacter sphaeroides O.U. 001. Hydrogen production by free cells was observed only at 5 and 10% waste water (diluted with tap water) yielding a maximum of 500 μl H2 (in 144 h) at 10% concentration. Calcium alginate immobilization of cells enhanced hydrogen photoproduction two–three fold and hydrogen evolution was observed after varying lag periods at all the concentrations of waste water tested. Semicontinuous culturing of R. sphaeroides was demonstrated in a 3.6 l photobioreactor harvesting 1 l of culture every day amounting to 2 g dry wt. Hydrogen production was demonstrated for 12 days using immobilized cells with 10% waste water in a 3.6 l photobioreactor under light/dark cycles.
 
Photoproduction of hydrogen and substrate conversion efficiency by resting cells of a photosynthetic purple non-sulfur bacterium Rhodobacter sphaeroides O.U. 001 varied with the gas phase of the assay. Both exogenous and endogenous substrates could support photoproduction of hydrogen by this organism. Substrate conversion efficiency of more than 100% was observed when Ar, Ar + 10% H2 and Ar + 10% N2 + 10% H2 were gas phases. This excess substrate conversion efficiency is attributed to hydrogen production from endogenous substrates. Dinitrogen (100%) and air in the gas phase totally inhibited hydrogen production. Hydrogen production was maximum in the presence of 10% H2 in the gas phase. However, 100% H2 atmosphere inhibited hydrogen production partially.
 
The kinetics and the effects of various parameters on hydrogen production by Rhodobacter sphaeroides O.U. 001 were investigated in a batch column photobioreactor. In particular, the effect of the inoculum age and the implementation of a light–dark cycle illumination scheme for emulating natural sunlight have been investigated in detail. The possibility of using yeast extract to replace the rather expensive vitamin mixture in the medium was also studied.The results show that hydrogen production is decreased when the initially inoculated bacteria have a high culture age. Exposure of the bacterial culture to light–dark cycles increased the amount of hydrogen compared to continuous illumination, all other parameters remaining the same. Similarly, the use of yeast extract to replace the vitamins increased the growth and hydrogen production rates, however, with a slight reduction in the total amount of gas produced and the hydrogen fraction in the evolved gas.
 
Rhodobacter sphaeroides O.U.001 is a purple non-sulfur bacterium producing hydrogen under photoheterotrophic conditions. Hydrogen is produced by Mo-nitrogenase enzyme and substantial amount of H2 is reoxidized by a membrane-bound uptake hydrogenase in the wild type strain. To improve the hydrogen producing capacity of the cells, a suicide vector containing a gentamicin cassette in the hupSL genes was introduced into R. sphaeroiodes O.U.001 and the uptake hydrogenase genes were destroyed by site directed mutagenesis. The correct integration of the construct was confirmed by uptake hydrogenase activity measurement, PCR and subsequent sequence analysis. The wild type and the mutant cells showed similar growth patterns but the total volume of hydrogen gas evolved by the mutant was 20% higher than that of the wild type strain. This result demonstrated that the hydrogen produced by the nitrogenase was not consumed by uptake hydrogenase leading to higher hydrogen production.
 
Rhodobacter sphaeroides O.U.001 is one of the candidates for photobiological hydrogen production among purple non-sulfur bacteria. Hydrogen is produced by Mo-nitrogenase from organic acids such as malate or lactate. A hupSL in frame deletion mutant strain was constructed without using any antibiotic resistance gene. The hydrogen production potential of the R. sphaeroides O.U.001 and its newly constructed hupSL deleted mutant strain in acetate media was evaluated and compared with malate containing media. The hupSL−R. sphaeroides produced 2.42 l H2/l culture and 0.25 l H2/l culture in 15 mM malate and 30 mM acetate containing media, respectively, as compared to the wild type cells which evolved 1.97 l H2/l culture and 0.21 l H2/l culture in malate and acetate containing media, correspondingly. According to the results, hupSL−R. sphaeroides is a better hydrogen producer but acetate alone does not seem to be an efficient carbon source for photoheterotrophic H2 production by R. sphaeroides.
 
The effect of pH, temperature, light intensity and concentration of carbon source/e− donor and nitrogen source on the regulation of biomass yield and photoproduction of hydrogen (the fuel of the future) by a purple non-sulfur photosynthetic bacterium, Rhodobacter sphaeroides O.U. 001, was studied. The importance of culture density and age on the hydrogen photoproduction is also discussed.
 
Onset of simultaneous hydrogen photoproduction in Rhodobacter sphaeroides O.U. 001 occurred during the early stationary phase of growth. The studies on the regulation of onset of hydrogen photoprodaction during growth by pH and glutamate suggest that these parameters affect the total and rates of hydrogen evolution rather than the onset, except at pH 7.5.
 
In the present study, expression levels of nitrogenase encoding nifH and control genes nifA and prrA were examined at different physiological conditions in Rhodobacter sphaeroides O.U.001. In addition to variations in expression levels, changes in hydrogen production and growth were also investigated in response to different concentrations of ammonium source, acetate and aerobic conditions.In the present study, increasing concentration of ammonium chloride was found to be caused decrease in hydrogen production. Glutamate containing medium had the capacity for higher hydrogen production. Hydrogen production was observed even in aerobic conditions. The expression levels of nifH and nifA genes decreased with the increasing concentrations of ammonium chloride. Although the expression of nifA was present in the highest concentrations of NH4Cl under anaerobic conditions, no expression was observed under aerobic conditions of the same culture conditions. This was likely due to transcriptional level inhibition of nitrogenase in the presence of ammonium ion. Negative correlation was observed between the expression levels of prrA gene and its target, nifA gene.
 
Rhodobacter sphaeroides O.U.001 was grown in media with different concentrations of molybdenum and iron to study the expression level of nifD and nifK genes coding for the large subunit of Mo-nitrogenase and hupS gene coding for the small subunit of uptake hydrogenase. Hydrogen productions under the same growth conditions were also evaluated. Increasing concentrations of the molybdenum and iron stimulated hydrogen production and the highest total hydrogen accumulation was achieved in sodium molybdate (0.84 l H2/l culture at ) and 0.1 mM ferric citrate (1.14 l H2/l culture at ) containing media. Maximal expressions of nifD and nifK were observed from the late log phase until the mid-stationary phase of growth and hupS expression was seen as soon as the hydrogen was produced in the cells. Moreover, nifK, nifD and hupS expressions were significantly reduced in the molybdenum and iron starved cells.
 
Rhodobacter sphaeroides O.U.001 is a photosynthetic non-sulfur bacterium which produces hydrogen from organic compounds under anaerobic conditions. Halobacterium salinarum is an archaeon and lives under extremely halophilic conditions (4 M NaCl). H. salinarum contains a retinal protein bacteriorhodopsin in its purple membrane which acts as a light-driven proton pump. In this study the Rhodobacter sphaeroides O.U.001 culture was combined with different amounts of packed cells of H. salinarum S9 or isolated purple membrane fragments in order to increase the photofermentative hydrogen gas production. The packed cells of H. salinarum have the ability to pump protons upon illumination due to the presence of bacteriorhodopsin. The proton gradient produced may be used for the formation of ATP or protons may be used for H2 production by R. sphaeroides. Similar to intact cells purple membrane fragments may also form vesicles around certain ions and may act like closed systems.The hydrogen production experiments were carried out using 400 ml water-jacketed-glass column stirred photobioreactors. In combined systems 10–200 nmol of bacteriorhodopsin was used. Hydrogen gas production was enhanced by four- to sixfold in combined systems of H. salinarum packed cells with R. sphaeroides O.U.001 cell. Stirring both increased the total gas produced and enhanced the rate of hydrogen production. The light energy conversion efficiency was increased from 0.6% to 2.25% in combined systems.
 
A hydrogen producing strain F.P 01 was newly isolated from cow dung sludge in an anaerobic bioreactor. The strain F.P 01 was a mesophilic and facultative anaerobic bacterium, which exhibited gram-negative staining in both the exponential and stationary growth phases, and a regular long rod-shaped bacteria with the size of 0.6–0.9 μm × 1.2–2.5 μm, and also could biodegrade a variety of carbohydrates such as glucose, xylose, maltose, etc. The effects of important process parameters on hydrogen producing of F.P 01 were further investigated from hydrogen fermentation of maltose by strain F.P 01, including substrate concentration, medium pH, etc. And the results showed that hydrogen production potential and hydrogen production rate from maltose of this strain F.P 01 was180 mLH2/g-maltose and 4.0 mLH2/h, respectively. The corresponding hydrogen concentration of 58–73% was also be observed. Both butyric acid and acetic acid as main by-product was left in the reactor.
 
Cell growth and substrate degradation kinetics of newly isolated Enterobacter cloacae IIT-BT 08 were investigated with the help of Monod model. The values of μmax, KS and YX/S of the cell were 0.568 h−1, 3.658 g l−1 and 0.0837, respectively, using glucose as a substrate. The simulated profiles of the substrate concentration and cell mass concentration had significant variance with respect to the experimental values. This might be due to the substrate inhibition as the product is a gas. A modified Andrew’s model for substrate inhibition was suggested and found to have good resemblance with the experimental results. In other studies, hydrogen production was found to be growth associated.
 
The effects of treating the alloy powder of an electrode with 6 M sodium hydroxide solution containing y M (y = 0.0, 0.005, 0.01, 0.02, 0.03, 0.05) sodium borohydride (NaBH4) on the kinetics of hydrogen evolution reaction (HER) at the Mm(B5)1.15 hydride electrode (Mm = cerium-rich mischmetal; B5 = Ni3.6Co0.7Mn0.4Al0.3) are described. Several kinetic parameters are considered, including Total, Volmer and Tafel overpotentials, exchange current densities and activation energies of the elementary reactions. Such parameters are investigated by measuring the overpotential decay immediately after the interruption of an applied cathodic current. The effects of NaBH4 treatment and temperature on the mechanism of the HER are analysed on the basis of the dependence of the Volmer and Tafel overpotentials on current density. The effect of the NaBH4 concentration on the performance of the hydrogen storage alloy as a negative electrode material in nickel-metal hydride batteries and/or alkaline fuel cells is discussed from the standpoint of relative velocity of the elementary reactions.
 
Effect of annealing at up to 1400 K under argon pressure up to 1.2 GPa on hydrogen — plasma — etched and hydrogen — implanted Czochralski or FZ silicon was investigated by SIMS, X — ray, TEM, electrical, infrared and photoluminescence methods. External stress during annealing of hydrogen — containing Si results in suppression of hydrogen out — diffusion but in its pronounced diffusion into sample depth, in stress — stimulated creation of small bubbles, thermal donors and crystallographic defects but in preventing of sample splitting.
 
The deuterium thermal desorption of various YFe2Dx (x = 1.3, 2.5, 3.5, 4.2) compounds has been studied using differential scanning calorimetry (DSC) and thermal desorption (TD) experiments. These studies show that the number of desorption peaks increases with the deuterium content. In order to understand the origin of this multipeak behaviour, in situ neutron diffraction experiments during thermal desorption have been performed from 290 K to 680 K on YFe2D4.2. Upon heating, a multipeak TD spectrum is observed. It relates to the existence of several YFe2Dx phases with different stabilities. The rate limiting step of this thermal desorption has been therefore attributed to several successive phase transformations rather than to different types of interstitial sites as proposed in previous TD models reported for C15-Laves phase compounds.
 
Classical physical laws predict that atomic hydrogen may undergo a catalytic reaction with certain species, including itself, that can accept energy in integer multiples of the potential energy of atomic hydrogen, m·27.2 eV, wherein m is an integer. The predicted reaction involves a resonant, nonradiative energy transfer from otherwise stable atomic hydrogen to the catalyst capable of accepting the energy. The product is H(1/p), fractional Rydberg states of atomic hydrogen called “hydrino atoms,” wherein n = 1/2, 1/3, 1/4,…, 1/p (p ≤ 137 is an integer) replaces the well-known parameter n = integer in the Rydberg equation for hydrogen excited states. Each hydrino state also comprises an electron, a proton, and a photon, but the field contribution from the photon increases the binding rather than decreasing it corresponding to energy desorption rather than absorption. Since the potential energy of atomic hydrogen is 27.2 eV, two H atoms formed from H2 by collision with a third, hot H can act as a catalyst for this third H by accepting 2·27.2 eV from it. By the same mechanism, the collision of two hot H2 provide 3H to serve as a catalyst of 3·27.2 eV for the fourth. Following the energy transfer to the catalyst an intermediate is formed having the radius of the H atom and a central field of 3 and 4 times the central field of a proton, respectively, due to the contribution of the photon of each intermediate. The radius is predicted to decrease as the electron undergoes radial acceleration to a stable state having a radius that is 1/3 (m = 2) or 1/4 (m = 3) the radius of the uncatalyzed hydrogen atom with the further release of 54.4 eV and 122.4 eV of energy, respectively. This energy emitted as a characteristic EUV continuum with a cutoff at 22.8 nm and 10.1 nm, respectively, was observed from pulsed hydrogen discharges. The continua spectra directly and indirectly match significant celestial observations.
 
For experiment results obtained in a 2 kW solar concentrator, the FeO production by thermal dissociation of magnetite (Fe3O4) was extrapolated to the 1000 kW solar furnace of Odeillo, France. If this reaction is used in a two step thermochemical water splitting cycle, one can expect an extrapolated value of 137 m3 day−1 hydrogen production when Fe3O4 is dissocated at 2090 K, under an inert atmosphere, during 0.5 min and cooled down by a splat cooling quench technique.
 
Metal–Organic Frameworks (MOFs) have emerged as potential hydrogen storage media due to their high surface area, pore volume and adjustable pore sizes. The large void space generated by cages in MOFs is not completely utilized for hydrogen storage application owing to weak interactions between the walls of MOFs and H2 molecules. These unutilized volumes in MOFs can be effectively utilized by incorporation of other microporous materials such as single walled carbon nanotubes into the pores of MOFs which could effectively tune the pore size and pore volume of the material towards hydrogen sorption. Single walled carbon nanotubes (SWNT) incorporated MIL-101 composite MOF material (SWNT@MIL-101) was synthesized by adding purified single walled carbon nanotube (SWNT) in situ during the synthesis of MIL-101. The powder X-ray diffraction patterns of SWNT@MIL-101 showed the structure of MOF was not disturbed by SWNT incorporation. Hydrogen sorption capacities of MIL-101 was observed to increase from 6.37 to 9.18 wt% at 77 K up to 60 bar and from 0.23 to 0.64 wt% at 298 K up to 60 bar. The increment in the hydrogen uptake capacities of composite MOF materials was attributed to the decrease in the pore size and enhancement of micropore volume of MIL-101 by single walled carbon nanotube incorporation.Highlights► Preparation of hybrid MOF material by incorporation of purified SWNT in MIL-101. ► Utilization of unused space in high surface area MOFs by micropore volume enhancement. ► Enhancement of hydrogen sorption at 77 K and 298 K in MIL-101 by SWNT incorporation. ► DFT calculations of CO2 adsorption isotherms at 273 K in MOF material to confirm ultramicropore formation.
 
Depletion of fossil fuels and environmental considerations have led engineers and scientists to anticipate the need to develop a clean, renewable and sustainable energy system. In general, they agree that in such a system hydrogen will be used as an energy carrier.One of the areas in which hydrogen will be replacing fossil fuels is air transportation, an area that has been under research for several decades. Hydrogen as an energy carrier for use in airplanes has some unique attributes like global availability, safety, minimum pollution and light weight, making it an ideal fuel. This paper briefly reviews hydrogen as a fuel in aviation, compares it with other aviation fuels, and discusses the possible future developments and the goals in this field.
 
The growth potential of the marine Chromatium sp. Miami PBS 1071, a strain of photosynthetic bacteria exhibiting high hydrogen-production capabilities, was studied. This strain, isolated by our laboratory from the subtropical marine environment, grows well at high light intensities (light saturation: 140 μEinstein m−2s−1), high temperatures (optimum: 34°C), salinities normally found in marine environments (optimum: 30‰) and slightly basic pHs (optimum: 7.4–8.1). This strain grows in sulfide concentrations of 0.5–2.5 mM, and oxygen less than 4%. The growth rate in terms of doubling time was 1.75 h, which is one of the fastest rates observed for marine photosynthetic bacteria. Thus, the strain would be well suited for application to a saltwater-based tropical or subtropical outdoor mass-culturing system linked to bio-solar hydrogen-production technologies. This strain cannot utilize carbohydrates for growth but can employ various other carbon and nitrogen compounds. Besides the subject of utilization, the contribution of this work to the study of primary productivity and ecology in tropical and subtropical marine environments is discussed.
 
We tried to improve the H2-sorption properties of Mg by mechanical grinding under H2 (reactive mechanical grinding) at various weight ratios of sample to ball (1/9, 1/27 and 1/45) with 10 wt% Fe2O3. The revolution speed was 250 rpm and the milling time was 2 h. The sample Mg–10 wt% Fe2O3, prepared by milling at the weight ratio of sample to ball 1/45, has the best hydrogen-storage properties. It absorbs 5.56 wt% hydrogen at the first cycle at 593 K under 12 bar H2 for 60 min. Its activation is accomplished after two hydriding–dehydriding cycles. The activated sample absorbs 4.26 wt% hydrogen at 593 K, 12 bar H2 for 10 min. The reactive grinding of Mg with Fe2O3 increases the H2-sorption rates by facilitating nucleation (by creating defects on the surface of the Mg particles and by the additive), by making cracks on the surface of Mg particles and reducing the particle size of Mg and thus by shortening the diffusion distances of hydrogen atoms. Hydriding–dehydriding cycling also increases the H2-sorption rates by creating defects on the surface of the Mg particles, and by making cracks on the surface of Mg particles and reducing the particle size of Mg.
 
Hydrogenation and degradation properties of Mg–10 wt% Ni hydrogen storage alloys were investigated by cyclic hydriding–dehydriding tests. Mg–10 wt% Ni alloy was synthesized by rotation-cylinder method (RCM) under 0.3% HFC-134a/air atmosphere and their hydrogenation and degradation properties were evaluated by pressure-composition-isotherm (PCI) measurement. Hydrogen storage capacities gradually increased following 160 hydriding–dehydriding cycles and thereafter started to decrease. Measured maximum hydrogen capacity of Mg–10 wt% Ni alloy is 6.97 wt% at 623 K. Hydriding and dehydriding plateau pressure were kept constant for whole cycles. Reversible hydrogen capacity started to descend after 280 hydriding–dehydriding cycles. The lamellar eutectic structure of Mg–Ni alloy consists of Mg-rich α-phase and β-Mg2Ni. It is assumed that the lamellar eutectic structure enhances hydrogenation properties.
 
An assessment is presented of hydrogen production using a dedicated central solar receiver system concept coupled to a Mark 13-V2 hybrid thermochemical process. The system which is capable of producing about 106 GJ hydrogen per year was developed at the conceptual level. The total irradiance at normal incidence was taken as a parameter and varied from 1500 to 2500 kWh m−2 y−1 at a location with 30° latitude and 0.1 km altitude. The peak noon irradiance at normal incidence was taken as 0.95 kW m−2 and the mean total sunshine hours as 2333 h y−1.A flow sheet of the solar Mark 13-V2 hybrid process was developed to operate using the intermittent heat supply from the central receiver system and the continuous electric energy supply from outside. It was then evaluated using the models for the central receiver system, the solar receiver and the chemical process.It is found that for 2000 kWh m−2 y−1 total irradiance at normal incidence, the overall efficiency of the solar Mark 13-V2 process is about 21% and that the cost of the solar hydrogen is about $52 GJ−1.
 
The lithium-lithium hydride process serves to generate hydrogen from water efficiently, using the high temperature heat of a nuclear reactor. Thermodynamic analyses show that hydrogen can be produced with an overall thermal efficiency of 48% at conventional HTR outlet temperatures of 950°C. Assuming helium heat of 1300°C, 56% overall thermal efficiency can be achieved.
 
Fermentative hydrogen production was carried out using Clostridium saccharoperbutylacetonicum N1-4 (ATCC 13564). This work investigates the effects of initial substrate concentration, initial medium pH, and temperature. The hydrogen yield was about 3.1 mol (mol glucose)−1 when starting with an initial glucose concentration of 10 gl−1 and initial a pH of 6.0 ± 0.2 at a temperature of 37 °C. The volume of hydrogen produced decreased when higher initial glucose concentrations were applied. The most suitable conditions for hydrogen production in a batch reactor were observed at initial pH 6.0 ± 0.2 and 37 °C.
 
Environmental concerns and depletion in petroleum resources have forced researchers to concentrate on finding renewable alternatives to conventional petroleum fuels. Hydrogen is thought to be a major energy resource of the future due to its clean burning nature and eventual availability from renewable sources. Hydrogen is widely regarded as a promising transportation fuel because it is clean and renewable.The authors manufactured a high accuracy heavy-duty variable compression ratio single cylinder engine to investigate its performance and emissions characteristics. The test engine was run at 1400 rpm with a compression ratio of 8. Spark timing was set to MBT (minimum spark advance for best torque). This paper investigates the effects of hydrogen enriched LPG fueled engine on exhaust emission, thermal efficiency and performance.
 
Lyngbya majuscula CCAP 1446/4 is a N2-fixing filamentous nonheterocystous cyanobacterium that possesses two NiFe hydrogenases: an uptake and a bidirectional hydrogenase. The biosynthesis/maturation of NiFe hydrogenases is a highly complex process requiring several proteins. This work presents the characterization of the hyp cluster in L. majuscula. The hyp genes are located ca. 8 kb upstream from the uptake hydrogenase structural genes, and seem to be transcribed as a single operon, including three other ORFs interspersed throughout the cluster. In addition, the transcriptional start point was identified 21 bp upstream of hypF, and regulatory sequences were recognized within the promoter region. Several ORFs could also be discerned between the hup and the hyp genes. Moreover, hupW, the gene encoding the putative uptake hydrogenase C-terminal endopeptidase was found 1102 bp downstream of hupL. The hydrogenases maturation process and its regulation are discussed for cyanobacteria possessing both or just one hydrogenase.
 
This paper describes six experiments conducted on a 2-liter, 4-cylinder Ford ZETEC internal combustion engine developed to operate on hydrogen fuel. The experiments were conducted to ascertain the effect exhaust gas recirculation (EGR) and a standard 3-way catalytic converter had on NOx emissions and engine performance. All the experiments were conducted at a constant engine speed of and each experiment used a different fuel flow rate, ranging from 0.78 to . These fuel flow rates correspond to a fuel equivalence ratio, Φ, ranging from 0.35 to 1.02 when the engine is operated without using EGR (i.e. using excess air for dilution). The experiments initially started with the engine operating using excess air. As the experiments proceed, the excess air was replaced with exhaust gas until the engine was operating at a stoichiometric air/fuel ratio. The results of these experiments demonstrated that using EGR is an effective means to lowering NOx emissions to less than while also increasing engine output torque.
 
The two most promising materials for a hydrogen cryo-adsorption tank, activated carbon AX-21_33 and metal-organic framework MOF-177, have been investigated in the pressure range up to 2 MPa and at temperatures from 77 K to 125 K and at room temperature. The total hydrogen storage, including adsorbed hydrogen and gaseous hydrogen, has been determined for both samples. The results were evaluated with respect to the operating conditions of a tank system at cryogenic conditions, assuming a maximum tank pressure of 2 MPa and a minimum back pressure for the hydrogen consumer of 0.2 MPa. AX-21_33 shows a usable capacity of 3.5 wt.% in the case of isothermal operation at 77 K and 5.6 wt.%, if the tank is loaded at 77 K and the temperature is increased by 40 K during unloading. Under the same conditions, MOF-177 has a usable capacity of 6.1 wt.% and 7.4 wt.%, respectively. The results show that the heat of adsorption has a high impact on the amount of hydrogen remaining in a tank after unloading and that the heat management plays a crucial role for the design of a cryogenic tank system.
 
Metal–organic framework (MOF-177) was synthesized, characterized and evaluated for hydrogen adsorption as a potential adsorbent for hydrogen storage. The hydrogen adsorption equilibrium and kinetic data were measured in a volumetric unit at low pressure and in a magnetic suspension balance at hydrogen pressure up to 100 bar. The MOF-177 adsorbent was characterized with nitrogen adsorption for pore textural properties, scanning electron microscopy for morphology and particle size, and X-ray powder diffraction for phase structure. The MOF-177 synthesized in this work was found to have a uniform pore size distribution with median pore size of 12.7 Å, a higher specific surface area (Langmuir: 5994 m2/g; BET: 3275 m2/g), and a higher hydrogen adsorption capacity (11.0 wt.% excess adsorption, 19.67 wt.% absolute adsorption) than previously reported values on MOF-177. Freundlich equation fits well the hydrogen adsorption isotherms at low and high pressures. Diffusivity and isosteric heat of hydrogen adsorption were estimated from the hydrogen adsorption kinetics and equilibrium data measured in this work.
 
Mixed MOF crystals with morphology similar to that of pure MOF-5 and pure MOF-177 were synthesized using two organic solvents: dimethylformamide (DMF) and diethylformamide (DEF). The mixed crystals were characterized with XRD, SEM and TGA for their physical properties and also evaluated for their hydrogen adsorption properties. The XRD and SEM results suggest that the mixed crystals are different from pure MOF-5 and pure MOF-177. The DMF-derived mixed MOF crystals have a slightly higher specific surface area, smaller pore diameter and greater pore volume than those of the DEF-derived crystals, and seem to be a better adsorbent than the DEF-derived crystals, which was confirmed by the higher hydrogen and nitrogen adsorption capacities on the DMF-derived crystals. The hydrogen adsorption capacities on the mixed MOF crystals are lower than those of pure MOF-5 and MOF-177. It was also observed that the hydrogen diffusion time constant increases with hydrogen pressure, and the heat of hydrogen adsorption decreases with adsorbed hydrogen amount on both mixed crystals.
 
An integrated system combining highly efficient III–V solar cells in an optical concentrator system with a polymer electrolyte membrane electrolyser is presented. Hydrogen and oxygen are produced by solar water splitting. The integrated design and the high concentration factor of 500 allow material savings and high system efficiencies. The thermoneutral solar to hydrogen conversion efficiency of a prototype system with an area of was measured outdoor to be 18%.
 
Contemporary models are shown to significantly underestimate the attainable efficiency of solar energy conversion to water splitting, and experimentally a cell containing illuminated AlGaAs/Si RuO2/Ptblack is demonstrated to evolve H2 and O2 at record solar-driven water electrolysis efficiency. Under illumination, bipolar configured and semiconductors generate open circuit and maximum power photopotentials of 1.57 and 1.30 V, well suited to the water electrolysis thermodynamic potential:The EH2O°/photopotential matched semiconductors are combined with effective water electrolysis O2 or H2 electrocatalysts, RuO2 or Ptblack. The resultant solar photoelectrolysis cell drives sustained water splitting at 18.3% conversion efficiencies. Alternate dual bandgap systems are calculated to be capable of attaining over 30% solar photoelectrolysis conversion efficiency.
 
This paper is concerned only with hydrogen fuel cells, and it is suggested that the most likely commercial application will initially be for the propulsion of short-range city traffic, especially buses. For a start, it seems likely that the hydrogen will be stored as a compressed gas, using the latest developments in lightweight pressure vessels, although other methods of hydrogen storage will probably follow, for example metal hydrides. It is suggested that fuel cells are still in an early stage of development, and that considerable improvements should be achieved in the future, as experience is accumulated from the use of fuel cells in space, and other special applications. The use of pure hydrogen in fuel cells probably means that this will provide a new and improved method of energy storage, when compared with conventional storage batteries; and advantage would naturally be taken of the great improvements which are now being made in the design of electrolyzers, which should help to reduce the cost of pure hydrogen, especially in countries such as Canada, which have large reserves of hydro-electric power and a successful nuclear power industry.
 
It is now the 20th anniversary of the beginning of the Hydrogen Energy Movement. Over the 20 years, there have been accomplishments in every front — from the acceptance of the concept as an answer to energy and environment related global problems, to research, development and commercialization. The Hydrogen Energy System has now taken firm roots. Activities towards the implementation are growing.
 
Top-cited authors
Ibrahim Dincer
  • Ontario Tech University
Liejin Guo
  • Xi'an Jiaotong University
Detlef Stolten
  • Forschungszentrum Jülich
Wan Ramli Wan Daud
  • Universiti Kebangsaan Malaysia
Chiu-Yue Lin
  • Feng Chia University