Fullerene-impregnated IRMOFs for balanced gravimetric and volumetric H2 densities: A combined DFT and GCMC simulations study

This paper aimed to study the effects of fullerene (C₆₀) impregnation on the isoreticular metal-organic framework (IRMOF) materials MOF-650 (ZnO₄ nodes were connected to azulenedicarboxylate linkers), MOF-5(ZnO₄ nodes were connected to benzenedicarboxylate linkers), and IRMOF-10 (ZnO₄ nodes were connected to biphenyldicarboxylate linkers) for H₂ storage, these IRMOFs had similar structures but different pore volumes and organic linkers. Density functional theory (DFT) and grand canonical monte Carlo (GCMC) calculations indicated that C₆₀ plays an important role in balancing the gravimetric and volumetric H₂ densities of the IRMOFs. The C₆₀@IRMOFs revealed improved volumetric density when H₂ was undersaturated but reduced gravimetric density under H₂ saturation. The saturated gravimetric H₂ density of the IRMOFs was decided by the free volume. At 77 K, C₆₀@MOF-650 had a gravimetric H₂ density of 5.3 wt% and volumetric H₂ density of 42 g/L under 10 bar, and C₆₀@IRMOF-10 had a gravimetric H₂ density of 7.4 wt% and volumetric H₂ density of 43 g/L under 18 bar. These values nearly meet the United States Department of Energy (DOE) gravimetric and volumetric H₂ density ultimate targets (gravimetric H₂ density, 6.5 wt%; volumetric H₂ density, 50  g/L) under ambient pressures. Among the studied IRMOFs, C₆₀@MOF-650 and C₆₀@IRMOF-10 demonstrated the best H₂ storage properties at 233 and 298 K.     

Tuning the hydrogen storage properties of MOF-650: A combined DFT and GCMC simulations study

Combined density functional theory and grand canonical monte Carlo (GCMC) calculations were performed to study the electronic structures and hydrogen adsorption properties of the Zn-based metal-organic framework MOF-650. The benzene azulenedicarboxylate linkers of MOF-650 were substituted by B atoms, N atoms, and boronic acid B(OH)₂ linkers, and the Zn atoms were substituted by Mg and Ca atoms. The calculated electronic densities of states (DOSs) of MOF-650 showed that introduction of B atoms reduces the band gap but damages the structure of MOF-650. Introduction of single N bonds cannot provide active electrons to attract H₂ molecules. Thus, substitutions of B and N into MOF-650 are not suggested. B(OH)₂ substitute in MOF-650 decreased its band gap, slightly improved its hydrogen storage ability and made H₂ molecules more intensively distributed besides organic linkers. GCMC calculations were carried out by estimating the H₂ storage amount of the pure and modified MOFs at 77 and 298 K and from 1 bar to 20 bar. B(OH)₂ linker and Mg/Ca co-doped MOF-650 showed increased H₂ adsorption by approximately 20 wt%. The adsorption of H₂ around different bonds showed the order N–C < C = C < B–C < C–O < B–O.     

Experimental and principal component analysis studies on minimum oxygen concentration of methane explosion

Gas explosion has always been one of the leading disasters in chemical and mining industries, causing tremendous considerable casualties and property damage. It is very effective to control ignition parameters to prevent explosion accidents. To intensively investigate the impacts of C₂H₆/C₂H₄/CO/H₂ mixtures on CH₄ explosion, we added C₂H₆/C₂H₄/CO/H₂ mixtures with different ratios (samples 1–4) and different volume fractions ([mixture] = 0–2.0 vol%) to CH₄/air([CH₄] = 7.0, 9.5 and 11.0 vol%) for measurement of the flammability limit and minimum oxygen concentration (MOC) for CH₄ explosion in a 20-L spherical vessel. Changes of flammability limits of CH₄ were obtained with the addition of C₂H₆/C₂H₄/CO/H₂ mixtures at room temperature (18–22 °C) and pressure (1 atm). The experimental data about MOC of CH₄ explosion were examined by principal component analysis (PCA). On the basis of experimental results, multiple regression models were established to determine the influences of principal components on MOC of CH₄ explosion. The results clearly indicated that the impacts of organic and inorganic combustible gases on flammability limits of CH₄ were significantly different. The involvement of sample 1 and sample 2 (main component is organic flammable gas) increased the explosive hazard degree (F value) of CH₄ by 43.18% and 45.45%, respectively. However, it was increased by 15.91% and 4.55%, respectively after adding sample 3 or sample 4 (main component is inorganic flammable gas). Additionally, the required MOC for CH₄ explosion was increased with the increase of C₂H₆/C₂H₄/CO/H₂ mixtures, and they showed a quadratic parabola relationship. Moreover, the linear expressions between the concentrations of C₂H₆, C₂H₄, CO and H₂ and the MOC of CH₄ explosion were achieved by PCA. Based on these analyses, it is indicated that the effects of C₂H₆, C₂H₄ and CO were increasingly significant on MOC while H₂ was just the opposite from the oxygen-rich state to the stoichiometric state and fuel-rich state for CH₄/air mixture. The results presented in this paper can provide theoretical reference for the prevention and control of multiple flammable gas explosion.     

Hydrogen trapping: Synergetic effects of inorganic additives with cobalt sulfide absorbers and reactivity of cobalt polysulfide

The biphasic product CoS₂ + Co(OH)₂ obtained by oxidation of cobalt sulfide is known to trap hydrogen at room temperature and low pressure according to a balanced reduction equation. Adding various inorganic compounds to this original absorber induces their reduction by hydrogen in the same conditions at a significant rate: (i) excess cobalt hydroxide is reduced to metallic cobalt; (ii) nitrate ions are reduced to ammonia; (iii) sulfur and sodium thiosulfate are reduced to H₂S or NaHS and Na₂S, respectively. Without a hydrogen absorber these inorganic compounds are not reduced by H₂, suggesting synergetic effects involving H₂ and the hydrogen absorber. Amorphous cobalt polysulfide, CoS₅, is also reduced by hydrogen at room temperature and releases H₂S gas. In the presence of a base to neutralize H₂S gas, the reaction rate is initially slower than with the CoS₂ + Co(OH)₂ mixture due to the higher stability of polysulfide chains but the H₂ trapping yield is improved, making CoS₅ a good candidate for H₂ trapping.     

Photocatalytic H2 production from water splitting employing depolymerized cellulose through LiCl activation as sacrificial agent

We report a facile approach of depolymerizing cellulosic biomass by a physical pressing intensified inorganic salt hydrolysis (PIISH) process, in which inorganic ion (e.g. Li⁺) as an activation agent can be drilled into the outlayers of cellulose particles so as to break down the hydrogen bonds in cellulose, and the fragments detached from bulk cellulose could be further converted to glucose or other soluble carbohydrates by in situ formed LiOH or HCl catalyzed hydrolysis. The particle size, morphology and surface structure of microcrystalline cellulose are markedly changed which have been observed by a series of physicochemical characterization of PIISH treated cellulose. The cellulose depolymerization was related to the applied pressure and the type of inorganic ions, and about 4.5% cellulose was converted into glucose using LiCl salt at 20–30 MPa pressing. Platinized TiO₂ prepared by different approaches has been characterized and screened for photocatalytic H₂ production utilizing the cellulose decomposed products as sacrificial agents under UV light irradiation. The apparent quantum efficiencies in 5 h and 35 h for H₂ production under 365 ± 10 nm irradiation are about 6.12% and 2.36%. This facile approach has been applied for depolymerizing cellulosic biomass resources for solar driven H₂ production.     

Pd (II) decorated conductive two-dimensional chromium-pyrazine metal-organic framework for rapid detection of hydrogen

The utilization of H₂ for versatile application has demanded highly selective, low cost and rapid hydrogen sensors that are proficient in sensing H₂ near flammability limit. In this report, Cr^IIICl₂(pyrazine)₂ MOF with negatively charged pyrazine linkers in its structure is used for the stabilization of Pd (II) via charge transfer interactions. This material design turned an innocent MOF into selective hydrogen sensor that can respond (through decrease in resistance under dynamic sensing setup) to H₂ in 5–7 s with a detection range of 0.25%–1% H₂ concentration. A correlation of H₂ sensing characteristics and the structure-property relationship is established using density functional theory (DFT) calculations. The calculations suggested that near fermi level in Pd^II@CrPy, the bandwidth increases upon interaction with H₂ thereby the phase space for electron delocalization increases leading to better carrier mobility. This new approach not only yields novel sensing properties but also enables limited usage of precious metal to develop cost-effective sensors.     

A DFT study on enhanced adsorption of H2 on Be-decorated porous graphene nanosheet and the effects of applied electrical fields

The adsorption of the hydrogen molecule on the pure porous graphene nanosheet (P-G) or the one decorated with Be atom (Be-G) was investigated by the first-principle DFT calculations. The Be atom was adsorbed on the P-G with a binding energy of ?1.287 eV to successfully establish the reasonable Be-G. The P-G was a poor substrate to interact weakly with the H₂, whereas the Be-G showed a high affinity to the adsorbed H₂ with an enhanced adsorption energy and transferred electrons of ?0.741 eV and 0.11 e, respectively. A molecular dynamics simulation showed that the H₂ could also be adsorbed on the Be-G at room temperature with a reasonable adsorption energy of ?0.707 eV. The interaction between the adsorbed H₂ and the Be-G was further enhanced with the external electrical fields. The applied electrical field of ?0.4 V/Å was found to be the most effective to enhance the adsorption of H₂ on the Be-G with the modified adsorption energy and the improved transferred electrons being ?0.708 eV and 0.17 e, respectively. Our study shows that the Be-G is a promising substrate to interact strongly with the H₂ and could be applied as a high-performance hydrogen gas sensor, especially under the external electrical field.     

H2 physisorption in fluorinated MOF-74: The role of fluorine from the perspective of electronic structure calculations

Fluorine has been shown to be a promising candidate of H₂ physisorption center. First-principles calculations reported here provide a fundamental insight into the role of fluorine in H₂ physisorbing performance of a fluorinated metal-organic framework Mg-MOF-74. When a fluorine atom caps an open metal site of the framework, the fluorine p states weakly interact with the linker states so that they are highly localized, a inducing highly charged fluorine center. Meanwhile, the fluorine substituent on the aromatic ring of the organic linker has its p states strongly interacting with the linker states. Therefore, the fluorine p states become so dispersive that the fluorine site is weakly charged. The ab initio molecular dynamics (AIMD) simulation demonstrates that the highly charged capping fluorine acts as a dominating adsorption center that can attract four H₂ molecules. The binding strengths of the H₂ molecules with the capping fluorine are higher than with the organic linker of the original framework by up to 3.9 kJ/mol. Whereas, the weakly charged fluorine substituent does not act as a dominating adsorption center. In this case, the AIMD simulation produces similar adsorption positions as those in the original framework. Although the fluorine substituent shows some contribution to the H₂ affinity, it indirectly reduces the host–guest binding strengths by reducing the electron density on the π bonds of the aromatic ring as well as delocalizing the electron density on oxygen atoms. Consequently, the H₂ affinity of the linker fluorinated framework is weaker than that of the original framework by up to 3.0 kJ/mol.     

Effects of temperature and limestone on sulfur release behaviors during fluidized bed gasification

Gaseous sulfur is released during fluidized bed coal gasification, and control the yield of gaseous sulfur or the conversion between gaseous organic sulfur and inorganic sulfur at source is necessary, because it can economically satisfy the requirements of industrial production and protect the environments. In this study, sulfur release behaviors of a middle-sulfur coal called Guizhou coal were quantitatively determined through controlled experiments in a lab-scale fluidized bed during oxygen rich-steam gasification. The measured gaseous sulfur species were H₂S, SO₂, COS and CS₂. The effects of temperature (850^OC-950^OC) and limestone (Ca/S = 2) on the sulfur release behaviors were investigated. Among the above four gaseous sulfur, the yield of H₂S is the highest, followed by COS, while only less than 1.5% of sulfur in coal is released as SO₂ and CS₂. With the increase in temperature, the yield of H₂S increases while that of SO₂ decreases, and the change of COS yield and CS₂ yield is not obvious. The molar ratio of H₂S/COS increases with increasing temperature, which is qualitatively matched by thermodynamic analysis. The addition of limestone reduces the released sulfur but not change the distribution of gaseous sulfur forms. Meanwhile, the molar ratio of H₂S/COS increases after adding limestone, while the trend with temperature of H₂S/COS does not change. The removal rate of H₂S is between 23% and 28%, which increases with temperature. The distributions of sulfur in bottom char and fly ash are similar. The main sulfur species in the bottom char is organic sulfur, and thiophene dominates the organic sulfur. The increase of temperature and the addition of limestone will both promote the increase of inorganic sulfur content, and the decrease of organic sulfur content.     

A DFT study of H2 adsorption on lithium decorated 3D hybrid Boron-Nitride-Carbon frameworks

Based on density functional theory (DFT) and first-principles molecular dynamics (MD),a new 3D hybrid Boron-Nitride-Carbon–interconnected frameworks (BNCIFs) consisting of organic linkers with Li decoration is created and optimized. Firstly, Li adsorption behaviors on several BNC_xcomplexes are investigated and compared systematically. The results indicate C substitution of N atom in pure BN layer could improve the metal binding energy effectively. Secondly, the BNC layer (BNC_NN) is chosen to model the frameworks of BNCIFs. The average binding energy of adsorbed Li atoms on BNCIFs is 3.6 eV which is much higher than the cohesive energy of bulk Li and avoids the Li clustering problem. Finally, we study the H₂ adsorptions on the Li decorated BNCIFs by DFT. Every Li atom could adsorb four H₂ molecules with an average binding energy of 0.24 eV. The corresponding gravimetric and volumetric storage capacities are 14.09 wt% and 126.2 g/L respectively overpassing the published 2020 DOE target. The excellent thermal stability of 160H₂@40Li@BNCIFs is also proved by MD. This nanostructure could be served as a promising hydrogen storage medium at ambient conditions.     

In situ fabrication of cross-linked PEO/silica reverse-selective membranes for hydrogen purification

Targeting at hydrogen purification, cross-linked organic–inorganic reverse-selective membranes containing poly(ethylene oxide) (PEO) are fabricated in situ by using functional oligomers (O,O′-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol: Jeffamine^® ED-2003) with a high content of PEO and epoxy-functional silanes (3-glycidyloxypropyltrimethoxysilane: GOTMS). Changes in physicochemical properties due to varying silica content have been characterized; including a great decline in melting temperature; an improvement in glassy and degradation temperature, and the suppression of PEO crystallinity. The strong affinity between quadrupolar CO₂ and polar ethylene oxide (EO) groups enhances the CO₂/H₂ separation performance of hybrid membranes, which can be further tuned by controlling the organic/inorganic ratio. The organic–inorganic hybrid membrane with 90 wt% of ED-2003 demonstrates an appealing CO₂ permeability of 367 Barrer with an attractive CO₂/H₂ selectivity of 8.95 at 3.5 atm and 35 °C. The transport performance trend with composition variations is explained by analyzing the calculated solubility and diffusivity based on the solution-diffusion mechanism. Moreover, CO₂ permeability increases with applied pressure in pure gas tests because of CO₂ plasticization phenomena, which is beneficial for CO₂/H₂ separation. Attributing to CO₂ plasticization and CO₂ dominant sorption, the mixed gas test results of the membrane containing only 25 wt% ED-2003 show greatly improved CO₂/H₂ selectivity of 13.2 with CO₂ permeability of 148 Barrer at 35 °C compared to pure gas results. Interestingly, at a stipulated CO₂ pressure, the inherent tension in cross-linked networks maintains the CO₂ permeability stable with the time. The cross-linked organic–inorganic membranes with enhancements in mechanical and thermal properties are promising for industrial-scale hydrogen purification.     

Ab initio study of hydrogen adsorption on Zn2(NDC)2(diPyTz) metal-organic framework decorated with alkali and alkaline earth metal cations

We have studied effect of alkali and alkaline earth metal cations (Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺) decoration on hydrogen adsorption of the organic linker of Zn₂(NDC)₂(diPyTz) by employing three cluster models: diPyTz:mLi⁺ (m = 1–4), diPyTz:mLi⁺:nH₂ (m = 0,1,2 and n = 1–5) and diPyTz:1M⁺:1H₂ (M⁺ = Na⁺, K⁺, Be²⁺, Mg²⁺) complexes, using density functional theory (DFT) and second-order Moller–Plesset perturbation theory (MP2). The calculated binding energies show that decoration of the organic linker with alkali and alkaline earth metal cations enhanced H₂ interaction with diPyTz when compared with the pristine diPyTz. The atomic charges were derived by Mulliken, ChelpG and ESP methods. Finally, the atoms in molecules theory (AIM) were also applied to get more insight into the nature of the interaction of diPyTz and Li⁺. Results of AIM analysis show that N–Li⁺ bond in diPyTz organic linker's complex appears as shared electron interaction.     

18O/16O isotope exchange for yttria stabilised zirconia in dry and humid oxygen

The oxygen surface kinetics and mechanism of oxygen interaction between oxygen from the gas phase and yttria-stabilised zirconia nano-sized powder have been studied by pulse ¹⁸O/¹⁶O isotope exchange (PIE) in dry (O₂) and humid (mixture O₂ + H₂O with pH₂O = 2.6 kPa at T = 22 °C) oxygen atmospheres in comparison with micro-sized powder. Dependences of the heterogeneous oxygen exchange rate (r_H) in the temperature range from 550 to 900 °C, and oxygen partial pressure range in the carrier gas and pulses of 5–19% have been obtained. It has been established that the presence of water causes a decrease in the heterogeneous oxygen exchange rate due to the presence of strongly bound hydroxyl groups in the nanopores of the sample. Differences between the mechanisms of isotopic exchange for dry and humid atmospheres have been found in this temperature range (550–700 °C). The observed differences are associated with the interaction of the gas phase and hydroxyls in the adsorbed layer of the oxide. An original method for the separation of the contributions of three types of oxygen exchange for dry and humid atmospheres has been proposed.     

Quantification of “delivered” H2 by a volumetric method to test H2 storage materials

We set up and validated a volumetric method to quantify the amount of hydrogen “delivered” after saturation of a solid material as adsorber at different pressures (up to 100 kg_f/cm²) and temperatures (down to 77 K). This is the practically most relevant datum to quantify the effectiveness of an adsorbent for the present application. A complementary dynamic method has been also developed to take into account the reversibility of adsorption and to assess in at least a semi-quantitative way the strength of interaction between H₂ and the adsorbent. The method has been applied to compare the hydrogen storage capacity of some significant different carbon-based materials (two active carbons and one graphite), as supplied or after thermal treatments under oxidising or reducing conditions. The best results, ca. 7 wt% H₂ “delivered”, were achieved after saturation at 77 K, 20 kg_f/cm² with an active carbon with ca. 3000 m²/g of apparent specific surface area. The thermal treatments, almost always inducing a drop in surface area, showed effective only for saturation at 273 K, in particular the oxidising procedure. This was correlated to the formation of surface oxidised species, likely carboxylic groups, which improved the interaction strength between H₂ and the adsorbent.     

Density functional theoretical analysis of micro-adsorption of isotopes of hydrogen molecule and atom by uranium

Tritium, the heaviest among hydrogen isotopes can be safely stored as metal hydride (tritide). The (depleted) uranium metal is being considered in international thermonuclear experimental reactor (ITER) because of its compatible physicochemical properties. The fundamental understanding of U–H isotopes interaction will help in the efficient storage of H isotopes in depleted uranium metal. Hence, density functional theoretical (DFT) analysis has been performed to investigate the micro-adsorption of hydrogen and its isotopic molecules on uranium atom. The geometrical configurations of UX_n, U (X₂)_n and UX₄-(X₂)_n (X = H, D, T; n = 1–9) cluster were analyzed using different DFT functional (PBE, PBEO, M06 and M06-2X). In the case of U-(H₂)₄ and U-(H₂)₅, one H₂ molecule was seen to be dissociated to give UH₂(H₂)₃ and UH₂(H₂)₄ cluster as observed earlier in the experiment. The formation of U (X₂)_n and UX₄-(X₂)_n microclusters was explained by calculating binding enthalpy, natural population analysis and electron density at the bond critical points (BCP). Further, more insights were derived by computing the type of interactions between U and H₂ isotopic molecules. The Kubas interaction of a U atom with a H₂ molecule was identified by an elongation of the H–H bond without breakage and a reduction in its stretching frequency due to binding. The interaction of U and H₂ isotopic molecules was confirmed to be Kubas type of interaction whose strength lies in between the covalent bond of metal hydrides and the van der Waals bond of materials. Further, σ-donation from H₂ to d and f orbitals of U atom and π-back-donation from U to the anti-bonding orbital of H₂, and atoms-in-molecules analysis indicates that the electron density at the bond critical points of the bound H₂ is similar to that of Kubas systems. The Kubas type of interaction suggests that the reversible adsorption of hydrogen molecules might be favored with U metal. From structural and binding enthalpy (BE) analysis, UH₄-(H₂)₈ polyhydride was predicted to be the largest super polyhydride and found to be stable by 8.2 kcal/mol over UH₄-(H₂)₆ polyhydride and thus confirmed its plausibility. To the best of our knowledge UH₄-(H₂)₈ is the largest metal polyhydride ever been reported with twenty hydrogen atoms displaying high gravimetric density of 7.80, 14.47 and 20.21 wt% for H₂, D₂ and T₂ respectively. The present DFT results thus draw further attention for more computational and experimental studies in this important uranium-hydrogen system for efficient reuse of depleted uranium metal as tritium storage material.     

Influence of AlCl3 and oxidant catalysts on hydrogen production from the supercritical water gasification of dewatered sewage sludge and model compounds

Hydrogen has attracted significant attention as a clean energy source. Supercritical water gasification (SCWG) technology can produce hydrogen-rich gas while also disposing of sludge. The hydrogen yield from the SCWG of sludge is greatly increased when catalyzed by AlCl₃. In this paper, a combined catalyst based on AlCl₃ was proposed to further increase the hydrogen yield of SCWG of dewatered sewage sludge (DSS). Analysis of the products from catalytic gasified of DSS and its model compounds were used to propose a catalytic mechanism and reaction pathway of the catalytic SCWG of DSS. Among the combined catalysts used for the SCWG of DSS, 10 wt% AlCl₃–H₂O₂ (mass ratio 8:2) had the best hydrogen production effect, and the hydrogen yield reached 8.88 mol/kg organic matter. This was 14% higher than when catalyzed by 10 wt% AlCl₃. During catalysis with AlCl₃, Al³⁺ reacted with OH⁻ in water and precipitated as Al(OH)₃, which produced an acidic environment in the liquid product. Al(OH)₃ dehydrated to form an AlO(OH) and deposited in the solid product. A small amount of H₂O₂ promoted the steam reforming reaction of organic matter in DSS, which increased the hydrogen yield. H₂O₂ further promoted the hydrogen yield in an acidic environment. The catalytic effect of AlCl₃ was unaffected by H₂O₂. The H⁺ generated by AlCl₃ during catalysis promoted H₂O₂ to further depolymerized organic matter (such as humic substances) in DSS, so that AlCl₃–H₂O₂ catalyzed the SCWG of DSS to further increase the hydrogen yield. The order of hydrogen yield catalyzed by AlCl₃–H₂O₂ was guaiacol > humic acid > glycerol > alanine > glucose. Compared with AlCl₃, AlCl₃–H₂O₂ reduced the hydrogen yield of glucose by nearly 20% and increased the hydrogen yield of humic acid by about 17% (25.81 mol/kg feed).     

Dual-tuning effect of In on the thermodynamic and kinetic properties of Mg2Ni dehydrogenation

Mg₂In_0.1Ni solid solution with an Mg₂Ni-type structure has been synthesized and its hydrogen storage properties have been investigated. The results showed that the introduction of In into Mg₂Ni not only significantly improved the dehydrogenation kinetics but also greatly lowered the thermodynamic stability. The dehydrogenation activation energy (E_a) and enthalpy change (ΔH) decreased from 80 kJ/mol and 64.5 kJ/mol H₂ to 28.9 kJ/mol and 38.4 kJ/mol H₂, respectively. The obtained results point to a method for improving not only the thermodynamic but also the kinetic properties of hydrogen storage materials.     

Influence of sulfate-reducing bacteria,sulfide and molybdate on hydrogen photoproduction by purple nonsulfur bacteria

The interaction between bacterial species is of great importance for H₂ production using microbial consortia or non-sterile conditions. Sulfate reducing bacteria were found in anaerobic starch-hydrolyzing consortium and their inhibitory effect on the following H₂ photoproduction by purple nonsulfur bacteria was shown. This inhibition was clearly demonstrated in the mixed culture of Rhodobacter sphaeroides and Desulfomicrobium baculatum using the synthetic medium. This effect was conditioned by sulfide production rather than H₂ consumption or competition for organic substrate. Actually, the addition of equivalent sulfide concentration brought about the similar effects: inhibition of H₂ production without growth inhibition, cells aggregation, and the increase of carbohydrate content as an alternative way of expenditure of organic acids. In the long-term experiments the average sulfide concentration of about 0.3 mM was detrimental while in short-terms the H₂ production was not inhibited even at 3.2 mM. The protective effect of molybdates against sulfate reducers and sulfide was discussed.     

Enhanced hydrogen gas production from mixture of beer spent grains (BSG) and distiller's grains (DG) with glycerol by Escherichia coli

Escherichia coli perform mixed acid fermentation and produce hydrogen gas (H₂) as one of the fermentation end products. E. coli can ferment sugars like glucose, xylose and alcohols like glycerol. It has been shown that E. coli has the ability to utilize pretreated organic waste (BSG or DG) or mixtures of it with glycerol and H₂ can be produced. H₂ evolution was maximum when the concentration of BSG was 4% and DG - 10% yielding 1.4 mmol L⁻¹ H₂. H₂ evolution was prolonged to ~24–120 h when mixtures of glycerol and DG or BSG wastes were applied. Moreover, in hycE (lacking large subunit of Hyd-3) or hyfG (lacking large subunit of Hyd-4) single mutants H₂ production was absent compared to wild type suggesting that Hyd-3 and Hyd-4 are responsible for H₂ generation. In addition, multiple mutant enhanced cumulative H₂ production ~3–4 fold. Taken together it can be proposed that BSG or DG wastes either together or in mixture with glycerol can be applied to obtain E. coli biomass and produce bio-H₂. The novel data can be used to further control effectively the application of organic waste resources as a feedstock for developing bio-H₂ production technology.     

Enhancement of hydrogen binding affinity with low ionization energy Li2F coating on C60 to improve hydrogen storage capacity

The capacity of hydrogen storage for solid sorbents depends strongly on the binding affinity between hydrogen molecules and solid sorbents. By coating C₆₀ with a low ionization energy material (Li₂F), we obtained an enhanced binding energy and an improved electron transfer between H₂ and hosts. With the first-principles calculations and charge analysis, we found that the orbital interactions play a dominant role in this system and eventually 68H₂ molecules can be stably stored by a C₆₀(Li₂F)₁₂ cluster with a binding energy of 0.12 eV/H₂. The resulting gravimetric and volumetric density of H₂ stored on C₆₀(Li₂F)₁₂ are 10.86 wt% and the 59 g/L through calculations. Our investigation indicates that metals or metal clusters with lower ionization energies would be beneficial to enhance interactions between hydrogen and hosts, and thus, the hydrogen storage capacities for solid sorbents can be greatly improved.