Mol H2 Research Articles

Biorefinery Approach for H2 and Acids Production Based on Uncontrolled pH Fermentation of an Industrial Effluent

In this work, the feasibility of uncontrolled pH acidogenic fermentation of industrial organic effluent from corn-bioethanol production was studied and modelled by using a Monod-based mathematical model. In order to do that, several tests were carried out at different initial pH values, ranging from 4 to 6. The experimental data showed a pH reduction during the fermentation process due to the generation of short-chain acids. When starting at initial pH of 5.0 and 6.0, the substrates were fully fermented reaching final pH s over 4 units in both cases and a final undissociated fatty acid concentration of about 80 (mmol·L−1) in both cases. Regarding fermentation at an initial pH of 4, the pH decreased to 3.5 units, and the organic substrates were not fully fermented due to the stoppage of the fermentation. The stoppage was caused by the very acidic pH conditions. The biomass showed an uncoupled growth as the operating conditions became more acidic, and, finally, the biomass growth was zero. Regarding the generation of fermentation products, in general terms, the highest economical value of products was obtained when fermenting at an initial pH of 5. More specifically, acetic acid was the acid that presented the highest yield at an initial pH value of 4. Butyric yield showed the highest values at initial pH values of 5 and 6. The highest H2 yield (1.1 mol H2·mol−1 dextrose) was achieved at an initial pH value of 5. Finally, the experimental data were modelled using a Monod-based model. From this model, the value of the main kinetics and stoichiometric parameters were determined.

Exploring the Enhanced Catalytic Activity of Pt Nanoparticles Generated on the Red Phosphorus/Graphitic Carbon Nitride Binary Heterojunctions in the Photo-assisted Hydrolysis of Ammonia Borane.

Ammonia borane (AB) holds great promise for chemical hydrogen storage, but its slow dehydrogenation kinetics under ambient conditions requires a suitable catalyst to facilitate hydrogen production from AB. Here, we fabricated binary red phosphorus/graphitic carbon nitride (RP/g-CN) heterojunctions decorated with Pt nanoparticles (NPs, denoted Pt/RP/g-CN) with a facile ultrasound-assisted two-step protocol as a photo-assisted catalyst for the hydrolysis of AB (HAB). The heterojunction established through intimate P-O-N bonds was proven to have improved photophysical properties such as a lower electron-hole recombination and enhanced visible light utilization compared to the pristine components. With the incorporation of Pt NPs, the optical properties of RP/g-CN heterojunctions were further improved through Schottky junction formation between semiconductors and Pt NPs, enabling a superb hydrogen gas (H2) generation rate of 142 mol H2·mol Pt-1·min-1 under visible light irradiation. Even though g-CN is a well-known host material for many metal NPs, here we discovered that the interaction of Pt NPs with RP in the ternary heterojunction structure is more favorable than that of g-CN, stressing the key role of RP as a support material in the designed ternary heterostructure. The band alignment of the ternary heterojunction catalyst along with the flow of charge carriers was also studied and shown to be a type-II heterojunction structure without hole migration, namely, a complex type-II heterojunction. Several scavenger experiments were also conducted to explain the mechanism of the photo-assisted HAB. To the best of our knowledge, this is the first example of a dual mechanism proposed for the visible light-assisted HAB. While the majority of the H2 was believed to be produced on the Pt NPs surface with the traditional B-N bond dissociation mechanism, the strong oxidizing action of OH• radicals formed by the heterojunction photocatalyst was also speculated to account for the 33% increase in the activity upon visible light irradiation through another mechanism.

Nanotitania supported ruthenium(0) nanoparticles as active catalyst for releasing hydrogen from dimethylamine borane

We reports the ex situ preparation of nanotitania supported ruthenium(0) nanoparticles (NPs) and their catalytic testing in dehydrogenation of dimethylamine borane (DMAB) in toluene solvent. Ru0/TiO2 NPs are prepared following a 2-step process: Ru3+ ions are first impregnated from the aqueous solution on titania nanopowder and then, reduced by aqueous solution of sodium borohydride. The prepared Ru0/TiO2 NPs are dried, bottled under inert N2 gas atmosphere, and used for characterization by XRD (X-ray powder diffraction), TEM (transmission electron microscopy), ICP-OES (inductively coupled plasma optical emission spectroscopy) and XPS (X-ray photoelectron spectroscopy). Ru0/TiO2 NPs with various Ru loadings are tested as catalysts in hydrogen generation from DMAB and the Ru0/TiO2 (0.48% wt. Ru) with an average diameter of 6.7 ± 1.3 nm is found to have the highest initial turnover frequency value of 1700 h−1 for the release of 1.0 mol H2 per mole of DMAB at 60 °C. Results of the recyclability test indicate quite high durability of Ru0/TiO2 NPs in dehydrogenation of DMAB.

Thermodynamic improvement of lithium hydrides for hydrogen absorption and desorption by incorporation of porous silicon

Lithium is a popular lightweight material in the field of energy storage because of its hydrogen-binding properties and electrochemical advantages. The high hydrogen uptake capacity (∼12.6 wt%) of lithium hydride (LiH) is limited by the major thermodynamic constraint of requiring a higher temperature (∼700 °C) for desorption at 0.1 MPa. Incorporating a third element that creates Li phases during LiH dehydrogenation can help overcome thermodynamic constraints. This study involves modifying the hydrogen storage properties and thermodynamic characteristics of LiH through mechanical alloying with porous silicon (PS). Pressure composition isotherms measure the reversible hydrogen storage capacity (∼3.39 wt%) of LiH-PS alloy at different temperatures. The energy of hydrogen interaction is quantified by isosteric heat of absorption, which provides the enthalpy change in the reaction system. Hydrogen absorption and desorption enthalpies of 94.5 kJ (mol H2)−1 and 114.9 kJ (mol H2)−1 demonstrate the lowest energy demand among previously reported LiH alloys. The energy of hydrogen interaction is quantified by isosteric heat of absorption, which provides the enthalpy change in the reaction system. The hydride decomposition of the alloy indicates the possible range of hydrogen desorption.

Phase Equilibria, Solidified Microstructure, and Hydrogen Transport Behaviour in the V-Ti-Co System.

At present, the V-Ti-Co phase diagram is not established, which seriously hinders the subsequent development of this potential hydrogen permeation alloy system. To this end, this article constructed the first phase diagram of the V-Ti-Co system by using the CALculation of PHAse Diagrams (CALPHAD) approach as well as relevant validation experiments. On this basis, hydrogen-permeable VxTi50Co50-x (x = 17.5, 20.5, …, 32.5) alloys were designed, and their microstructure characteristics and hydrogen transport behaviour were further studied by XRD, SEM, EDS, and so on. It was found that six ternary invariant reactions are located in the liquidus projection, and the phase diagram is divided into eight phase regions by their connecting lines. Among them, some alloys in the TiCo phase region were proven to be promising candidate materials for hydrogen permeation. Typically, VxTi50Co50-x (x = 17.5-23.5) alloys, which consist of the primary TiCo and the eutectic {bcc-(V, Ti) and TiCo} structure, show a high hydrogen permeability without hydrogen embrittlement. In particular, V23.5Ti50Co26.5 exhibit the highest permeability of 4.05 × 10-8 mol H2 m-1s-1Pa-0.5, which is the highest value known heretofore in the V-Ti-Co system. The high permeability of these alloys is due in large part to the simultaneous increment of hydrogen solubility and diffusivity, and is closely related to the composition of hydrogen permeable alloys, especially the Ti content in the (V, Ti) phase. The permeability of this alloy system is much higher than those of Nb-TiCo and/or Nb-TiNi alloys.

Efficient hydrogen production in single-chamber microbial electrolysis cell with a fermentable substrate under hyperalkaline conditions

Hydrogen production from food waste is of great significance for energy conversion and pollution control. The aim of this study was to investigate the glucose fermentation from food waste and hydrogen (H2) production in the single-chamber microbial electrolysis cell (MEC) under hyperalkaline conditions. Single-chamber MECs were tested with 1 g/L glucose as substrate under different pH values (i.e., 7.0, 9.5, and 11.2) and applied voltages (i.e., 0.8, 1.2, and 1.6 V). With pH increase from 7.0 to 11.2, H2 production with methanogenesis inhibition was significantly improved in the MEC. At pH of 11.2, the maximum current density reached 180 ± 9 A/m3 with the H2 purity of 93.3 ± 1.2% and average H2 yield of 7.72 ± 0.23 mol H2/ mol glucose under 1.6 V. Acetate from glucose fermentation was the largest electron sink within 12 h. Methanobacterium alcaliphilum dominated the archaeal communities with the relative abundance of > 99.0% in the cathodic biofilms. The microbial communities and mcr A gene copy numbers analyses showed that high pH enhanced the acetate production from glucose fermentation, inhibited syntrophic acetate-oxidizing with hydrogenotrophic methanogenesis in the anodic biofilms, and inhibited hydrogenotrophic methanogenesis in the cathodic biofilms. Our results of hyperalkaline conditions provide a feasible way to harvest H2 efficiently from fermentable substrates in the single-chamber MEC.

Scalable Synthesis of Oxygen Vacancy-Rich Unsupported Iron Oxide for Efficient Thermocatalytic Conversion of Methane to Hydrogen and Carbon Nanomaterials.

Thermocatalytic methane decomposition (TCMD) involving metal oxides is a more environmentally friendly and cost-effective strategy for scalable hydrogen fuel production compared to traditional methane steam reforming (MSR), as it requires less energy and produces fewer CO/CO2 emissions. However, the unsupported metal oxide catalysts (such as α-Fe2O3) that would be suited for this purpose exhibit poor performance in TCMD. To overcome this issue, a novel strategy was developed as a part of this work, whereby oxygen vacancies (OVs) were introduced into unsupported α-Fe2O3 nanoparticles (NPs). Systematic characterization of the obtained materials through analytical techniques demonstrated that mesoporous nanostructured unsupported α-Fe2O3 with abundant oxygen vacancies (OV-rich α-Fe2O3 NPs) could be obtained by direct thermal decomposition of ferric nitrate at different calcination temperatures (500, 700, 900, and 1100 °C) under ambient conditions. The thermocatalytic activity of the resulting OV-rich α-Fe2O3 NPs was assessed by evaluating the methane conversion, hydrogen formation rate, and amount of carbon deposited. The TCMD results revealed that 900 °C was the most optimal calcination temperature, as it led to the highest methane conversion (22.5%) and hydrogen formation rate (47.0 × 10-5 mol H2 g-1 min-1) after 480 min. This outstanding thermocatalytic performance of OV-rich α-Fe2O3 NPs is attributed to the presence of abundant OVs on their surfaces, thus providing effective active sites for methane decomposition. Moreover, the proposed strategy can be cost-effectively scaled up for industrial applications, whereby unsupported metal oxide NPs can be employed for energy-efficient thermocatalytic CH4 decomposition into hydrogen fuel and carbon nanomaterials.

Phase evolution, hydrogen storage thermodynamics, and kinetics of ternary Mg98Ho1.5Fe0.5 alloy

Rare earth elements and transition metals have been found to improve the hydrogen storage characteristics of magnesium-based alloys. This study investigated the Mg-Ho-Fe (MHF) ternary alloy prepared using the vacuum induction melting technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), pressure-composition-temperature (PCT), and differential scanning calorimetry (DSC) were used to analyze the alloy's phase transitions, microstructure, thermodynamics, and kinetic properties. The results reveal that the Mg98Ho1.5Fe0.5 alloy forms a solid solution with Ho and Fe in the magnesium matrix. Upon hydrogen absorption, the activated alloy transforms into a mixture of Mg/MgH2 phases and nanoscale HoH2 phases. Notably, only the MgH2 phase decomposes during hydrogen desorption, while the HoH2 phase remains unchanged, exhibiting a positive catalytic effect. The alloy demonstrates excellent hydrogen absorption kinetics, achieving a capacity of 5.56 wt% H2 within 10 min at 360 °C, owing to the combined catalytic effects of Ho and Fe. The activation energy for hydrogen desorption is found to be 135.87 kJ/mol, which is lower than that of the activation energies of pure MgH2 and MgFe alloys, indicating an enhancement in desorption kinetics. Moreover, the enthalpy and entropy changes for hydrogen absorption and desorption are determined to be –70.51 kJ/mol H2, –125.62 J/(K·mol) H2, 72.83 kJ/mol H2, and 128.95 J/(K·mol) H2, respectively. Furthermore, it is worth noting that the thermodynamic properties of the alloy are improved due to the catalytic effect of Ho and Fe.

Green and active hydrogen production from hydrolysis of ammonia borane by using caffeine carbon quantum dot-supported ruthenium catalyst in methanol solvent by hydrothermal treatment

Here, carbon quantum dot (CQD) supported Ru nanoparticles from the caffeine in methanol or water by the hydrothermal method were synthesized for the first time to produce hydrogen (H2) by hydrolysis of ammonia borane(NH3BH3) and their catalytic activities were investigated. The chemical compositions and morphology structures of this caffeine carbon dot-supported Ru catalysts were carefully characterized by UV, PL, TEM, FTIR, and ICP/OES analyses. Well-dispersed Ru nanoclusters with ∼1.81 nm particle size on CQD by the hydrothermal method in methanol medium showed very good catalytic performance. The turnover frequency (TOF) obtained for H2 production from the catalytic hydrolysis of 5% NH3BH3 with CQD supported Ru catalyst obtained by the hydrothermal method in methanol and water was found to be 361 and 1895 mol H2 min−1 mol−1, respectively. The activation energies (Ea) for NH3BH3 hydrolysis with the same catalysts were measured as 33.32 and 27.80 kJmol-1, respectively.

A high-productivity PSA process configuration for H2 purification

This work proposes a 10-bed pressure swing adsorption (PSA) process configuration for H2 production, which allows extended purification time using purge tanks to completely regenerate the adsorption beds. Meanwhile, it divides the ten beds into two series at the purge step to improve the process stability. The process was simulated using the commercial software Aspen Adsorption, and evaluated by means of performance indicators and profiles of variables. It is proved that the purge tank can improve considerable flexibility in designing PSA configuration and significantly boost productivity. In addition, this work investigated the effect of the purge-to-feed (P/F) ratio and the tank volume. The novel configuration applied for H2 production from steam methane reforming (SMR) at 22 bar can provide 99.9918%-purity H2 with 87.63% recovery, and productivity up to 7.82 mol H2/(kgads⋅h). Compared to the direct coupling of the two adsorption beds at the purge step in the reported process, the production capacity increases by 50%.

Magnetically isolable Pd(0) nanoparticles supported on surface functionalized Fe3O4 for hydrogen generation via ammonia borane hydrolysis

AbstractPd(0) nanoparticles supported on surface functionalized magnetite (Fe3O4/SiO2‐NH2/HB@Pd) were prepared as catalyst for hydrolysis of ammonia borane (AB). The obtained magnetic nanocomposite material was seperated from the reaction media through a permanent magnet and characterized by FT‐IR, XRD, SEM‐EDX, TEM, ICP‐OES and XPS techniques. 100 mg Fe3O4/SiO2−NH2/HB@Pd nanocomposite with Pd metal content of 6.00±0.14 catalyzed the hydrolysis of 10 mM AB at 25 °C with 100 % yield. The presented work includes the effect of catalyst amount and temperature on the rate of the hydrolysis reaction of AB. As a result of the kinetic studies, the activation energy (Ea) for the Fe3O4/SiO2−NH2/HB@Pd catalyzed AB hydrolysis reaction was calculated as 34±1 kJ.mol−1, and the TOF value was calculated as 133 mol H2.(mol Pd(0).h)−1. The designed heterogenous magnetic nanocomposite catalyst demonstrated significant catalytic activity for AB hydrolysis reaction at 25 °C.

Synthesis, structure, and catalytic behavior for hydrogen evolution of a binuclear triazendio-palladium(I) complex

The reaction of 1,3-bis[(2-chloro)benzene]triazene (HL) and PdCl2 affords a binuclear triazenido-palladium complex, [Pd2L2], which has been determined by X-ray crystallography. Investigations show that this palladium complex can serve as a catalyst for both electrochemical and photochemical driven hydrogen evolution. Under an overpotential (OP) of 837.6 mV, 535 moles of hydrogen per mole of catalyst per hour (mol H2/mol catalyst/h) is afforded from an electrolysis of a neutral buffer with [Pd2L2]. With blue light (λ = 469 nm) irradiation, together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H2A) as a sacrificial electron donor, [Pd2L2] can catalyze hydrogen generation with a turnover number (TON) of 15130 moles H2 per mol of catalyst (mol of cat−1) during 48 h irradiation in a heterogeneous environment. The average value of apparent quantum yields (AQYs) is as high as 33.91%.

Zirconium nitride intermetallic diffusion barriers enable stable hydrogen permeation in palladium–vanadium composite membranes

Zirconium nitride (ZrN) is explored as a hydrogen permeable, intermetallic diffusion barrier for stable, high temperature operation of composite palladium-vanadium membranes for hydrogen purification. ZrN was deposited by reactive sputtering, and the properties and performance of films deposited in the metallic and compound mode were compared. Screening experiments using Pd-based sandwich structures showed that ZrN does not significantly impede H permeation until its thickness is increased above 40 nm. Stable hydrogen permeabilities up to >6 × 10−8 mol H2 m−1 s−1 Pa−0.5 were obtained in Pd|ZrN|V|ZrN|Pd composite membranes at operating temperatures of T = 400–450 °C, with superior performance obtained from ZrN deposited in the metallic mode. Long term stability (>200 h) was obtained and the structural integrity post-testing was confirmed by XRD and TEM imaging. Compositional profiling showed that oxygen originating in the V foil segregates to the ZrN–V interface but does not impede flux, and the transient behavior observed is attributed to this. Zirconium nitride decomposes at T > 450 °C, leading to rapid Pd–V interdiffusion and loss of permeability. However, with perfect selectivity and permeabilities up to 4X greater than Pd, these membranes are a promising cost effective alternative for hydrogen purification operations at 350–450 °C.

Energy recovery from agro-forest wastes through hydrothermal carbonization coupled with hydrothermal co-gasification: Effects of succinic acid on hydrochars and H2 production

Aiming to upgrade agro-forest wastes into value-added solid and gaseous fuels in the present investigation, hydrothermal carbonization (HTC) of spruce (SP), canola hull (CH), and canola meal (CM) was optimized in terms of operating conditions, maximizing the higher heating value of hydrochars. The optimal operating conditions were achieved at HTC temperature, reaction time, and solid-to-liquid ratio of 260 °C, 60 min, and 0.2 g mL−1, respectively. At the optimum condition, succinic acid (0.05–0.1 M) was used as HTC reaction medium to investigate the effects of acidic medium on the fuel characteristics of hydrochars. The succinic acid assisted HTC was found to eliminate ash-forming minerals e.g., K, Mg, and Ca from hydrochar backbones. The calorific values, H/C and O/C atomic ratios of hydrochars were in the range of 27.6–29.8 MJ kg−1, 0.8–1.1, and 0.1–0.2, respectively, indicating the biomass upgrading into coal-like solid fuels. Finally, hydrothermal gasification of hydrochars with their corresponding HTC aqueous phase (HTC-AP) was assessed. Gasification of CM resulted in a relatively high H2 yield of 4.9–5.5 mol kg−1 followed by that for SP with 4.0–4.6 mol H2 per kg of hydrochars. Results suggest that hydrochars and HTC-AP have a great potential for H2 production via hydrothermal co-gasification, while suggesting HTC-AP reuse.

Hydrogen Permeability of Tectosilicate Glasses for Tank Barrier Liners

The permeation of hydrogen gas was studied in meta-aluminous (tectosilicate) glass powders of Li2O×Al2O3×SiO2 (LAS), Na2O×Al2O3×SiO2 (NAS) and MgO×Al2O3×SiO2 (MAS) systems by pressure loading and vacuum extraction in the temperatures range 210–310 °C. With this method, both the solubility S and the diffusivity D were determined, while the permeability was given by the product SD. For all glasses, S was found to decrease with temperature, while D increased. Since the activation energy of diffusion of H2 molecules exceeded that of dissolution, permeation increased slightly with temperature. When extrapolated to standard conditions (25 °C), the permeability of tectosilicate glasses was found to be only 10-22–10-24 mol H2 (m s Pa)-1, which is 8–10 magnitudes lower than most polymers. Thin glass liners of these compositions are expected to be the most effective barrier for tanks of pressurised hydrogen.

Ensuring consistency in VLE and density modelling of (CO2 + H2) mixtures that are relevant in CCS pipeline transport: fitting BIPs for various EoS implemented in ‘off-the-shelf’ property packages

The impact of impurities in the physical properties of CO2 is now widely acknowledged by industry. In particular, the presence of H2 in CO2 mixtures has a significant effect on the saturation pressure (bubble point) and bulk (liquid) density. Both physical properties are key in the many engineering tasks, for example, in calculating the closed-in tubing head pressure of an injection well or in defining operating pressures to avoid two-phase region in transport systems. If there are large uncertainties in the estimated properties, then, significant design margins will be required making the system less cost-effective.The reliability of Equations of State (EoS) implemented in property packages used in industry is limited to the availability and quality of the experimental data that was used to calibrate the model. For the pair CO2H2, there is lack of validation at conditions of CCS systems. Thus, the performance of EoS is unsatisfactory for many CO2H2 mixtures. An additional complication is that there is large discrepancy not only between models but also between the ‘same’ model implemented across different platforms. For the practitioner, this poses quite a conundrum: ‘What EoS and package should be used?’.In this work, an attempt to homogenize various EoS implemented in commercial software is presented. To calibrate the models, a subset of available of experimental data with content of up to 5%mol of H2 is used. A different subset of data is used to assess the performance of the fitted models. In the parameter estimation problem, the EoS are tuned via Binary Interaction Parameters (BIPs) or departure parameters. To improve liquid density calculations, an additional step is used to regress cubic EoS via volume shift parameters.The resulting optimized EoS can be readily available in commercial simulators, and it is hope that they will be part of a growing databank/toolbox for engineering design activities of CCS systems.

Effects of metal centers of complexes supported by diiminodiphosphines on catalytic activities for electrochemical and photochemical driven hydrogen production

Two complexes, [Co-tn-P2(NCMe)](ClO4)2 1 and [Ni-tn-P2](ClO4)2 2 (tn-P2: N, N’-bis[o-(diphenylphosphino)benzylidene]-1,3-diaminopropane) have been synthesized and characterized. Both serve as electrocatalysts and photocatalysts for hydrogen generation. With 1 or 2, the electrolysis of a neutral buffer can provide 362 and 708 moles of hydrogen per mole of catalyst per hour under an overpotential of 837.6 mV, respectively. With CdS nanorods as a photosensitizer, and ascorbic acid as a sacrificial electron donor, the photolysis of an aqueous solution (pH 4.5) with 1 or 2 can provide 1755 and 2495 moles H2 per mole of catalyst (mol of H2 (mol of cat)−1) during 30 h blue light irradiation. The average apparent quantum yield is 11.04% ([Co-tn-P2(NCMe)](ClO4)2) and 16.77% ([Ni-tn-P2](ClO4)2), respectively. The results show that [Ni-tn-P2](ClO4)2 exhibits a more efficient activity for hydrogen generation than [Co-tn-P2(NCMe)](ClO4)2.

Synthesis, spectroscopic and hydrogen storage studies of mono or bimercury(II) mixed ligand complexes of amines with 2-cyanoamino thiophenolate ligand

Organic heterocyclic compounds play a significant role in coordination chemistry due to their ability to act as donor atoms for coordinating with various metal or metal ions. In this study, particular attention was given to the conversion of the 2-aminobenzothiazole ligand into 2-cyanoaminothiophenolate (LH) through a ring-breaking reaction. This transformation was achieved by reacting 2-aminobenzothiazole with phenyl mercury(II) acetate in the presence of sodium hydroxide, resulting in the formation of the complex [pHHg(LH)]n. During this process, mono-deprotonation of 2-aminobenzothiazole occurred, accompanied by facial carbon-sulfur bond breaking. This complex was used as a synthon to prepare four new mononuclear and binuclear complexes, which were [pHHg(LH)(apmy)2] (apmy= 2-aminopyrimidine) and [PhHg(LH)(bipy)] and [pHHg(LH)(μ-Cl)2Hg(bipy)] and [pHHg(LH)(μ-Cl)2Hg(phen)]. The prepared complexes were characterized using melting point, elemental analysis, FTIR, 1HNMR and 13CNMR. The results showed that the 2-cyanoamino thiophenolate ligand exhibited a monodentate behavior across the thiol sulfur atom, while the nitrile group remained free. The complex [pHHg(LH)(μ-Cl)2Hg(phen)] was used to study its ability to store hydrogen at different temperatures in order to study the thermodynamic parameters (enthalpy and entropy). The study proved that the highest stored value was 1.92 wt.% H2. It was noted that this ratio can be stored at lower pressures as the temperature decreases, proving that the storage is of a physical type with the value of R2= 0.92602 for the Van't Hof plot. The enthalpy value was 0.1131118 (kJ/(mol H2) while the entropy value was 0.60649754 (J/mol H2. K).

Nanoporous oxide coating on carbon paper electrodes to enable bio-hydrogen production in microbial electrolysis cells

To counteract expensive cathodes, a single chamber microbial electrolysis cell (MEC) equipped with nanoporous oxide coating on a carbon paper electrode as a cathode was explored. The performance of the MEC was evaluated based on the chemical oxygen demand (COD) removal efficiency, catalytic activity, and hydrogen production. The obtained results indicated that nanoporous oxide coated carbon electrode with TiO2 achieved maximum H2 yield (3.0 mol H2 mol−1 acetate), followed by ZrO2 and SiO2. In contrast, the uncoated carbon electrode achieved lower hydrogen yield (0.08 mol H2 mol−1 acetate). A maximum COD removal of 82% was achieved from the carbon electrode coated with TiO2 followed by 80.5% from SiO2 and 79% from ZrO2. Additionally, based on linear sweep voltammetry, nanoporous oxide coated electrodes started H2 evolution at a lower potential than the uncoated electrode, thereby exhibiting a higher catalytic rate. This investigation showed that carbon electrodes with nanoporous coating can be one of the economical (low cost) and potential electrodes to be used as a cathode in the MEC for hydrogen production instead of expensive metallic electrodes.

Microstructure and hydrogen transport behaviour of Nb5Ti58Fe35M2 alloy membranes

The dual-phase alloy developed based on Group 5B metals (V, Nb, Ta) is a promising material for hydrogen purification. Especially, Nb-Ti-Fe dual-phase alloys have attracted much attention due to their dual advantages, i.e., low price and good hydrogen permeability. Nevertheless, the challenge of developing higher comprehensive performance alloys in the face of the needs of practical applications remains. To address this need, a series of alloys with the formula Nb5Ti58Fe35M2 (atom %), where M is W, Mo, Cr, Pd, Cu, Al, Co, or Ni, was devised and prepared, and their microstructure characteristics and hydrogen transport properties were investigated. The results show that alloying of different elements will lead to great changes in permeability and hydrogen embrittlement (HE), whereas the structure type is less dependent on element types. Specifically, introducing doping elements W, Mo, Cr, or Co deteriorates the performance, especially the resistance to HE. Similarly, adding Pd, Al, or Ni reduces permeability but increases HE resistance. By contrast, the alloying of Cu improves both hydrogen permeability and hydrogen brittleness. Nb5Ti58Fe35Cu2 shows a high permeability of 4.32 × 10−8 mol H2 m−1s−1Pa−0.5 at 673 K, which is better than our newly developed Nb5Ti60Fe35 alloy. In addition, this paper also demonstrated that a change of phase size and morphology arising from alloying has greater influence on permeability than a change in the orientation relationship (OR) between the phases.