Hydrogen permeation through a Pd/Ta composite membrane with a HfN intermediate layer

Dense hafnium nitride (HfN) layers were prepared between Pd protection films and a Ta substrate in a composite hydrogen separation membrane to prevent a reaction between the Pd and the substrate at high temperatures. No significant reduction in hydrogen permeation rate was observed for the membrane with 50-nm-thick HfN layers at 873 K through at least 35 h, whereas the specimen without HfN layers rapidly deteriorated within 5 h. Hydrogen permeability of the former specimen was 4 × 10⁻⁹ mol m⁻¹ s⁻¹ Pa^−0.5 at 873 K at steady state. This value was smaller than the initial permeability of Pd-covered Ta before deterioration by an order of magnitude. The measurements of pressure–composition isotherms by using a HfN powder specimen showed that the hydrogen solubility in HfN was sufficiently high and comparable with the solubility in Ta. Therefore, the low permeability observed with the HfN intermediate layers was ascribed to low hydrogen diffusivity in HfN.     

Adsorption and compression contributions to hydrogen storage in activated anthracites

We prepared activated carbons (ACs) that are among the best adsorbents for hydrogen storage. These ACs were prepared from anthracites and have surface areas (S_BET) as high as 2772 m² g⁻¹. Anthracites activated with KOH presented the highest adsorption capacities with a maximum of 5.3 wt.% at 77 K and 4 MPa. Non-linearity between hydrogen uptake at 77 K and pore texture was confirmed, as soon as their S_BET exceeded the theoretical limiting value of (geometrical) surface area, i.e., S_BET > 2630 m² g⁻¹. We separated adsorption and compression contributions to total hydrogen storage. The amount of hydrogen stored is significantly increased by adsorption only at moderate pressure: 3 MPa and 0.15 MPa at 298 and 77 K, respectively. Hydrogen adsorption on ACs at high pressure, above 30 MPa at 298 K and 8 MPa at 77 K, has not interest because more gas can be stored by simply compression in the same tank volume.     

Preparation of activated rectangular polyaniline-based carbon tubes and their application in hydrogen adsorption

Porous materials, especially porous carbon materials, have the most potential as hydrogen adsorbents. In this research, a series of novel rectangular polyaniline tubes (RPTs) are synthesized using hollow carbon nanosphere (HCNS) templates. By changing mass ratios of ammonium persulfate to HCNSs, the sizes of RPTs can be controlled. Chemical activation with KOH gives rise to a large specific surface area (SSA), ranging from 1680 to 2415 m2 g⁻¹, and big pore volumes that range from 1.274 to 1.550 cm³g⁻¹. These observations demonstrate that activated rectangular polyaniline-based carbon tubes ARP-CTs are promising hydrogen adsorbents. Hydrogen uptake measurements show that the highest hydrogen adsorption reaches 5.2 wt% at 5 MPa/77 K and 0.62 wt% at 7.5 MPa/293 K respectively. Notably, the large pore volume can contribute 2.8 wt% to the total hydrogen storage which has approached 8.0 wt% at 5 MPa/77 K.     

Substitutional V–Pd alloys for the membranes permeable to hydrogen: Hydrogen solubility at 150–400 °C

The development of non-palladium membrane for separation of hydrogen from gas mixtures is one of critical challenges of hydrogen energy. Vanadium based materials are most promising for such membranes. The alloying of pure vanadium is crucially important for reduction of hydrogen solubility to an optimal value. Solution of hydrogen in substitutional V-xPd alloys (x = 5, 7.3, 9.7, 12.3, 18.8 at%) was investigated. The pressure–composition-isotherms were obtained in the range of pressure (10–10⁶) Pa, temperature (150–400) °С and concentration of hydrogen, H/M, from 4·10⁻⁴ to 0.6. The alloying of vanadium with palladium was found to reduce the hydrogen solubility substantially greater than the alloying with other elements, e.g. by Ni and Cr. The hydrogen absorption in the V–Pd alloys obeyed Siverts' law including the range of undiluted solution with hydrogen concentration H/M > 0.1. The reduction in the hydrogen solubility due to the alloying of V with Pd was caused mainly by increase in the enthalpy of solution at nearly constant entropy factor. Changes in the gross electronic structure of metal are most probably responsible for the effects of alloying on the hydrogen solubility in the substitutional V–Pd alloys.     

Hydrogen storage in ordered and disordered phenylene-bridged mesoporous organosilicas

Novel hexagonal Periodic Mesoporous Organosilicas (PMOs) and Disordered Mesoporous Organosilicas (DMOs) were synthesized by hydrolysis of 1,4-bis(trialkoxylsilyl) benzene precursor in alkaline aqueous solutions of different alkyl-trimethyl ammonium cations and evaluated for their hydrogen storage capacity. The PMO materials exhibit regular hexagonal pore arrangement and specific surface area between 640 and 782 m² g⁻¹ whereas the DMO materials have specific surface area that lies between 650 and 910 m² g⁻¹. The storage capacity of the materials is discussed in terms of number of molecules per surface unit. The materials exhibit a reversible hydrogen excess surface adsorption capacity up to 2.10 wt% at 6 MPa and 77 K. DFT calculations were performed to define the binding strength of hydrogen with the pore walls indicated an interaction energy value of −0.55 Kcal mol⁻¹, higher than the interaction energy value of hydrogen with a single benzene or a benzene incorporated in the IRMOR-1 walls. Grand Canonical Monte Carlo (GCMC) simulations showed that no hydrogen molecule can be inserted inside the wall structure of the materials.     

Hydrogen permeation behavior of Nb30Ti35Ni35−xCox (x = 0…35) alloys containing high fractions of eutectic

The hydrogen permeability of cast Nb₃₀Ti₃₅Ni_35−xCo_x (x = 0…35) alloys is found to increase with the Co content, induced by the tailored microstructures containing high fractions of eutectic and less primary phase. Among the cast alloys, Nb₃₀Ti₃₅Co₃₅ consisting entirely of eutectic exhibits the highest permeability, particularly 2.65 × 10⁻⁸ mol H₂ m⁻¹ s⁻¹ Pa^−0.5 at 673 K. This permeability is further increased to 3.58 × 10⁻⁸ mol H₂ m⁻¹ s⁻¹ Pa^−0.5 by aligning eutectic grains perpendicularly to the membrane surface using directional solidification. The high permeability is attributed to the high hydrogen solubility and diffusivity in alloys. Our work demonstrates that hydrogen permeable alloys containing high fractions of eutectic may exhibit high permeability by adequately optimizing morphology, volume fraction and alignment of the bcc-Nb phase in the eutectic as the pathways for hydrogen permeation.     

Scale-up activation of carbon fibres for hydrogen storage

In a previous study, we investigated, at a laboratory scale, the chemical activation of two different carbon fibres (CF), their porosity characterization, and their optimization for hydrogen storage [1]. In the present work, this study is extended to: (i) a larger range of KOH activated carbon fibres, (ii) a larger range of hydrogen adsorption measurements at different temperatures and pressures (i.e. at room temperature, up to 20 MPa, and at 77 K, up to 4 MPa), and (iii) a scaling-up activation approach in which the obtained activated carbon fibres (ACF) are compared with those from laboratory-scale activation. The prepared samples cover a large range of porosities, which is found to govern their ability for hydrogen adsorption. The hydrogen uptake capacities of all the prepared samples have been analysed both in volumetric and in gravimetric bases. Thus, maximum adsorption capacities of around 5 wt% are obtained at 77 K, and 1.1 wt% at room temperature, respectively. The packing densities of the materials have been measured, turning out to play an important role in order to estimate the total storage capacity of a tank volume. Maximum values of 17.4 g l⁻¹ at 298 K, and 38.6 g l⁻¹ at 77 K were obtained.     

Superior hydrogen storage properties of MgH2–10 wt.% TiC composite

The hydrogen storage performance of MgH₂–10 wt.% TiC composite was investigated. The additive TiC nanoparticle led to a pronounced improvement in the de/hydrogenation kinetics of MgH₂. The composite could dehydrogenate 6.3 wt.% at 573 K while the milled MgH₂ only released 4.9 wt.% of hydrogen at the same condition. The improvement came from that the activation energy of dehydrogenation was decreased from 191.27 kJ mol⁻¹ to 144.62 kJ mol⁻¹ with the TiC additive. The MgH₂–10 wt.% TiC composite also absorbed 6.01 wt.% (or 5.1 wt.%) of hydrogen under 1 MPa H₂ at 573 K (or 473 K) in 3000 s. Even at 1 MPa H₂ and 373 K, it could absorb 4.1 wt.% of hydrogen, but milled MgH₂ could not absorb hydrogen at this condition. Additionally, the composite had good cycling stability, and its hydrogen capacity only decreased 3.3% of the first run after 10 de/hydrogenation cycles. The improved hydrogen storage properties were explained to the TiC particles embedded in the MgH₂, which provided the pathways for the hydrogen diffusion into the MgH₂–10 wt.% TiC composite.     

Machine learning methods help accurate estimation of the hydrogen solubility in biomaterials

This study investigates the hydrogen solubility in five industrially relevant biochemicals, i.e., eugenol, furfural, furan, allyl alcohol, and furfuryl alcohol. Gene expression programming, three different artificial neural networks, and least-squares support vector regression (LS-SVR) are checked in this regard. The ranking analysis employing seven well-known statistical criteria confirmed that the LS-SVR is the most accurate model for the given purpose. The developed LS-SVR is superior to the Peng-Robinson, Soave-Redlich-Kwong, and perturbed-chain statistical associating fluid theory thermodynamic-based correlations proposed in the literature. The LS-SVR model predicts hydrogen solubility in the considered biochemicals with the relative absolute deviation of 1.91%, mean squared error of 6.4 × 10^?7, and regression coefficient of 0.99924. Both experimental and modeling observations approved that furan has the maximum tendency to absorb hydrogen molecules. A pure simulation analysis indicates that the maximum hydrogen solubility of 0.11 (mole fraction) can be absorbed by furan at pressure = 14.93 MPa and temperature = 402 K.     

Analyses of hydrogen distribution around fatigue crack on type 304 stainless steel using secondary ion mass spectrometry

Secondary Ion Mass Spectrometry (SIMS) analyses were carried out on type 304 austenitic stainless steel. On annealed specimen exposed to hydrogen (10 MPa, 358  K), Element Depth Profiles SIMS mode was able to describe quantitatively the hydrogen profile content computed by the Fick’s law. Based on SIMS analyses on the wake of a fatigue crack (propagation in hydrogen gas at 0.6 MPa and RT), it was possible to compute an apparent diffusivity and solubility in the crack tip region. The apparent solubility and diffusivity in the deformed regions were two times and five orders of magnitude higher than the ones on annealed material, respectively. High hydrogen content was found around the crack tip, where the plastic deformation was well developed (pronounced slip activity). The high apparent diffusivity is presumed to result from enhanced hydrogen transport induced by cyclic plastic activity at the crack tip.     

Magnesium alloy-graphite composites with tailored heat conduction properties for hydrogen storage applications

Melt-spun magnesium alloys that contain catalytically active constituents have become attractive hydrogen storage materials due to their ultra-fine and homogeneous microstructure and their excellent (de-)hydrogenation characteristics. However, their heat conduction properties have to be improved for practical applications. For this purpose, composites of melt-spun magnesium alloys and expanded natural graphite (ENG) were examined in this work. Melt-spun flakes were mixed with different amounts of up to 25.5 wt.% ENG. These mixtures were compacted to cylindrical pellets using compaction pressures up to 600 MPa. For comparison, pellets of pure magnesium hydride and ENG were equally processed. All sets of specimens were investigated regarding their thermal conductivities in radial and axial direction, their microstructure and phase fractions. It was found that the heat transfer characteristics can be tailored in a wide range, e.g. the thermal conductivity of magnesium alloy-ENG compacts were tuned from 1 up to 47 W m⁻¹ K⁻¹. For the system MgH₂-ENG, the thermal conductivity can be adjusted from 1 up to 43 W m⁻¹ K⁻¹. Therefore, a hydrogen storage material with homogeneous heat transfer properties can be anticipated which only slightly depend on the hydrogenated fraction.     

Synthesis and hydrogen storage studies of metal−organic framework UiO-66

Metal−organic framework UiO-66 has high chemical and thermal stability. However, it is difficult to produce such Zr-based MOFs with good crystalline morphology. Here, highly pure metal−organic framework UiO-66 has been synthesized at low temperature (50 °C). The as-synthesized sample has been characterized by X-ray diffraction, thermogravimetric analysis, nitrogen adsorption, and scanning electron microscopy. Its hydrogen-storage capacity has been measured by means of an Intelligent Gravimetric Analyser. The results showed that UiO-66 was synthesized in octahedral crystals of well-defined sizes (150−200 nm) and had a high specific surface area (1358 m²/g). The as-synthesized UiO-66 showed a significant hydrogen uptake even at a moderate pressure, which increased to 3.35 wt% at 77 K and 1.8 MPa. A grand canonical Monte Carlo simulation (GCMC) has been employed to calculate the adsorption of hydrogen in UiO-66. The result of this simulation provided a theoretical foundation for the experimental results.     

Photo-fermentative hydrogen gas production from dark fermentation effluent of acid hydrolyzed wheat starch with periodic feeding

Hydrogen gas production by photo-fermentation of dark fermentation effluent of acid hydrolyzed wheat starch was investigated at different hydraulic residence times (HRT = 1-10 days). Pure Rhodobacter sphaeroides (NRRL B-1727) culture was used in continuous photo-fermentation by periodic feeding and effluent removal. The highest daily hydrogen gas production (85 ml d⁻¹) was obtained at HRT = 4 days (96 h) while the highest hydrogen yield (1200 ml H₂ g⁻¹ TVFA) was realized at HRT = 196 h. Specific and volumetric hydrogen formation rates were also the highest at HRT = 96 h. Steady-state biomass concentrations and biomass yields increased with increasing HRT. TVFA loading rates of 0.32 g L⁻¹ d⁻¹ and 0.51 g L⁻¹ d⁻¹ resulted in the highest hydrogen yield and formation rate, respectively. Hydrogen gas yield obtained in this study compares favorably with the relevant literature reports probably due to operation by periodic feeding and effluent removal.     

A versatile strategy towards semi-interpenetrating polymer network for proton exchange membranes

A universal method to prepare proton exchange membrane (PEM) with semi-interpenetrating polymer network (semi-IPN) via a versatile crosslinker 1,3-benzenedisulfonyl azide (1,3-BDSA) is proposed. Sulfonyl azide groups can react with any polymer with carbon-hydrogen bonds via hydrogen abstraction. Polyvinylidene fluoride (PVDF) and perfluorosulfonic acid (PFSA) polymer are selected as two precursors for semi-IPN. When 1,3-BDSA is heated to a sufficiently high temperature it can form the nitrene and connect with PVDF via hydrogen abstraction reaction, recombination, or CH-bond insertion. The crosslinking structure of PVDF is formed, and semi-IPN is constructed in the presence of PFSA at the same time. The mechanical properties, degree of crosslinking, water uptake, and proton conductivity of semi-IPN membranes are investigated. Compared with pure PFSA membrane, the mechanical properties and the dimensional stability of the semi-IPN membranes are improved significantly. The tensile strength of the composite membrane (27.2 MPa) is much higher than that of PFSA membrane (10.1 MPa). The maximum power density of the composite membrane can reach 382 mW cm⁻² at 940 mA cm⁻². Sulfonyl azide based crosslinkers can be used to prepare semi-IPN or IPN PEMs from any paired polymers with carbon–hydrogen bonds.     

Nanoscale cobalt doped carbon aerogel: microstructure and isosteric heat of hydrogen adsorption

The incorporation of nanoscale Co particles (with sizes from a few nanometres) into porous carbon aerogels (CAs) was investigated. Elemental maps of the nanoscale metal particles embedded within CA were obtained using energy filtered transmission electron microscopy. The microstructure of Co doped carbon aerogels was further investigated using small angle X-ray scattering and nitrogen adsorption at 77 K. The isosteric heat of adsorption (Qst) was investigated as a function of hydrogen uptake at temperatures from 77 K to 110 K over the pressure range of 0-0.25 MPa. The isosteric heat of adsorption at low H₂ concentration for Co doped CA (9.0 kJ mol⁻¹) was found to be higher than for pure CA (5.8 kJ mol⁻¹).     

Simultaneous coproduction of hydrogen and methane from sugary wastewater by an “ACSTRH–UASBMet” system

A two-phase “ACSTR_H–UASB_Met” system has been investigated at the stepwise decreased HRT for the simultaneous production of hydrogen and methane in this study. Hydrogen could be continuously produced from the two-phase hydrogen fermentation of sugary wastewater in ACSTR and effluents from hydrogen fermentation were converted into methane in UASB reactor. At optimum conditions (HRT_H: 5 h, HRT_Met: 15 h), the highest hydrogen production rate of 5.69 (±0.06) mmol L⁻¹ h⁻¹ was obtained from sugary wastewater and methane was continuously produced from effluents of hydrogen fermentation with a production rate of 3.74 (±0.13) mmol L⁻¹ h⁻¹. The total bioenergy recovery by coproduction of hydrogen and methane from sugary wastewater reached 19.37 W and a total of 92.41% of substrate was converted to the biogas (hydrogen and methane) with two-phase anaerobic fermentation.     

Batch sodium borohydride hydrolysis systems: Effect of sudden valve opening on hydrogen generation rate

A study was undertaken in order to investigate the potential of hydrogen (H₂) generation by hydrolysis of sodium borohydride solution (10 wt% NaBH₄ and 7 wt% NaOH), in batch reactors, operating at moderate pressures (up to ∼1.2 MPa), in the presence of a powdered nickel-ruthenium based catalyst, reused between 311 and 316 times, to feed on-demand a proton exchange membrane fuel cell. A different approach to the testing of the performance of the batch NaBH₄ hydrolysis system is explored, by the quick opening of the reactor release gas valve, to satisfy a sudden H₂ demand; and hydrogen generation rates (HGR) are evaluated by changing catalyst amount, operating pressure and successive refueling. The results have shown the tendency of the studied system to maintain constant the H₂ generation rates, before and after one swift interruption, for single fuel injections (for 2.1 wt% of reused Ni–Ru based catalyst, a maximum value of HGR of 0.61 L(H₂)min⁻¹ g⁻¹(catalyst) at 0.4 MPa, or based on the active metal ruthenium, of 47.5 L(H₂)min⁻¹ g⁻¹(Ru), was achieved). This trend was different in the experiments with successive refueling. The present paper go forward in testing the potential of NaBH₄ system over reused Ni–Ru catalyst after supplying a sudden demand of H₂. Bearing in mind the market of low-power H₂-PEMFCs for portable devices, the herein results are original and useful from an application point of view.     

Bio-hydrogen production from cheese whey powder (CWP) solution: Comparison of thermophilic and mesophilic dark fermentations

Cheese whey powder (CWP) solution was used as the raw material for hydrogen gas production by mesophilic (35 °C) and thermophilic (55 °C) dark fermentations at constant initial total sugar and bacteria concentrations. Thermophilic fermentation yielded higher cumulative hydrogen formation (CHF = 171 mL), higher hydrogen yield (111 mL H₂ g⁻¹ total sugar), and higher hydrogen formation rate (3.46 mL H₂ L⁻¹ h⁻¹) as compared to mesophilic fermentation. CHF in both cases were correlated with the Gompertz equation and the constants were determined. Despite the longer lag phase, thermophilic fermentation yielded higher specific H₂ formation rate (2.10 mL H₂ g⁻¹cells h⁻¹). Favorable results obtained in thermophilic fermentation were probably due to elimination of H₂ consuming bacteria at high temperatures and selection of fast hydrogen gas producers.     

Experimental design as a tool to study the reaction parameters in hydrogen production from photoinduced reforming of glycerol over CdS photocatalyst

The aim of this study was to set the reaction conditions of the photoinduced reforming of glycerol aqueous solution over Pt/hex-CdS under visible light irradiation for enhancement of hydrogen production by using a fractional factorial experimental design followed by a Box–Behnken design. The parameters assessed were irradiation time, mass of photocatalyst, concentration of glycerol, pH and electrolyte concentration (NaCl). The preliminary two-level fractional factorial design (2⁵⁻¹) showed that all of the investigated factors have significant effect in hydrogen production, being pH the most important parameter. The three factors Box–Behnken design showed maximum response for hydrogen production in pH 4.0, 55% glycerol and 1.5 mol L⁻¹ NaCl. The amount of hydrogen obtained under these conditions was 270% higher than our previous result, using the same photocatalyst and electron donor. In the ideal pH, >CdSH₂⁺and >CdOH species are predominant before irradiation, indicating that such species play an important role in the primary steps of the photoelectrochemical mechanism, which served as the basis for proposing a mechanism for hydrogen generation as well as glycerol photooxidation. Based on the surface response [NaCl] × [glycerol], a solution with salinity equivalent to approximately the natural seawater was tested and the result for hydrogen production was comparable to the best condition; besides, under this condition, the solubility of CdS in aqueous solution is reduced.     

Thermophilic dark fermentation of acid hydrolyzed waste ground wheat for hydrogen gas production

Batch dark fermentation experiments were performed to investigate the effects of biomass and substrate concentration on bio-hydrogen production from acid hydrolyzed ground wheat at 55 °C. In the first set of experiments, the substrate concentration was constant at 20 g total sugar L⁻¹ and biomass concentration was varied between 0.52 and 2.58 g L⁻¹. Total sugar concentration was varied between 4.2 and 23.7 g L⁻¹ in the second set of experiments with a 1.5 g L⁻¹ constant biomass concentration. The highest cumulative hydrogen formation (582 mL, 30 °C, 1 atm), formation rate (5.43 mL h⁻¹) and final total volatile fatty acid (TVFA) concentration (6.54 g L⁻¹) were obtained with 1.32 g L⁻¹ biomass concentration. In variable substrate concentration experiments, the highest cumulative hydrogen (365 mL) and TVFA concentration (4.8 g L⁻¹) were obtained with 19.25 g L⁻¹ initial total sugar concentration while hydrogen gas formation rate (12.95 mL h⁻¹) and the yield (200 mL H₂ g⁻¹ total sugar) were the highest with 4.2 g L⁻¹ total sugar concentration.