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Li–Mg–B–H reactive hydride composite (RHC) has attracted extensive attention over the past decades for its extremely high hydrogen storage capacity (11.5 wt%). But the sluggish desorption kinetics for the second step dehydrogenation reaction need to be further improved. Herein, short rod-like TMTiO 3 (TM = Co, Ni) bimetallic oxides, which contain two kinds of transition metal elements, were synthesized and introduced into Li–Mg–B–H RHC for the first time. The NiTiO 3 exhibits excellent catalytic effect on the hydrogen desorption kinetic performance of Li–Mg–B–H RHC, and the incubation period for the second step dehydrogenation reaction is eliminated completely by reducing the apparent activation energy for the generation of MgB 2 from 296 kJ/mol to 269 kJ/mol. The NiTiO 3 doped Li–Mg–B–H RHC can desorb about 9.0 wt% H 2 without obvious attenuation of kinetic performance in five cycles. Mechanism analyses reveal that the in-situ generated nano-sized MgNi 3 B 2 and TiB 2 species (∼5 nm) both meet the critical value (< 10%) of the edge-to-edge matching model (5.77% for MgNi 3 B 2 and 2.22% for TiB 2), which play a significant role in supporting the nucleation of MgB 2. Meanwhile, the extremely fine MgNi 3 B 2 and TiB 2 heterogeneous nucleation sites can inhibit the excessive growth for a single crystal nucleus of MgB 2. The heterogeneous nucleation and grain refinement mechanisms caused by the novel bimetallic oxide could provide alternative insights into designing an in-situ generated nano-sized catalytic hydrogen storage system with enhanced kinetics and cyclic stability for hydrogen-fueled applications. Image 1 • Short rod-like NiTiO 3 eliminates the incubation period of dehydrogenation. • In-situ generated MgNi 3 B 2 and TiB 2 nano-species support the nucleation of MgB 2. • Fine MgNi 3 B 2 and TiB 2 nucleation sites cause the grain refinement of MgB 2. [ABSTRACT FROM AUTHOR]

ZrCo alloy has been considered as a tritium storage material to replace uranium for large-scale hydrogen isotope storage and delivery in tritium plant of the magnetic confinement nuclear fusion reactor. However, the disproportionation of ZrCo greatly obstructed its aspects to engineering application. A multifaceted understanding about the intrinsic nature of disproportionation reaction, and proposing anti-disproportionation strategies from material design have always been the bottleneck and hotspot in the tritium science and technology field. Herein, we studied the anti-disproportionation properties of Zr(Ti)Co alloy with thin film structure, and the effects of film thickness and Ti substitutions on the anti-disproportionation properties of the films were obtained. Firstly, a series of ZrCo films with different deposited time were prepared by magnetron sputtering instrument. The disproportionation ratio of the 2 h deposited ZrCo film (1.641μm) is 23.9%, and attenuated with the increase of film thickness. It indicates that the anti-disproportionation properties of the film structure is significantly better than that of ZrCo particle (68%). The microtopography analysis shows that the micro stress in the film structure is beneficial to hinder the disproportionation process. However, the hydrogenation reaction is also obviously inhibited in the ZrCo film. In addition, Ti doping can further improve its anti-disproportionation performance (10.3–7.3% for the 2 h deposited Zr 1-x Ti x Co film) without significantly reducing the hydrogen absorption capacities of the ZrCo flims. The anti-disproportionation performance is closely related to the weakened interaction between Zr and H atoms, after Ti doping into the ZrCo flim, leading to the impaired driving force for disproportionation reaction. The study in this work can provide an important reference for the anti-disproportionation modification of ZrCo alloys. • Hydrogen storage performance of ZrCo with film structure were investigated. • Anti-disproportionation behavior of ZrCo film is related to thickness. • Anti-disproportionation properties of ZrCo film is better than that of particles. • The Ti doping improve the anti-disproportionation performance of ZrCo films. • The Ti enhancement mechanism was obtained from the perspective of binding energy. [ABSTRACT FROM AUTHOR]

The performance of uranium as a hydrogen storage material has attracted much attention. Herein, the hydrogen absorption properties of depleted uranium in impure hydrogen containing He, Ar, CH 4 , N 2 , CO, CO 2 and O 2 were studied by PVT method and XPS analysis. When these impurity gases were mixed in H 2 at low concentrations (0.1%∼1.5%), their behavior can be classified into three categories. The He, CH 4 and Ar were chemically inert to the activated uranium powder under room condition. These three gases inhibited the absorption kinetics during the whole stage by hindering the diffusion of H 2 molecules, showing a blanketing effect. The N 2 and O 2 did not affect the absorption kinetics but reduced the capacity by forming nitrides and oxides. The poisoning effect of N 2 was weaker than that of O 2. The CO and CO 2 not only affected the hydrogen absorption capacity, but also strongly inhibited the absorption kinetics. These two gases are chemically adsorbed on the uranium surface to form passivation layers, thus inhibiting the adsorption and dissociation of H 2 molecules and the diffusion of H atoms. The poisoning and retardation effect of CO 2 were much stronger than that of CO. The above conclusions are important to further study the reactivity of mixed gas with uranium, and can also be used as a reference for other hydrogen storage systems. [Display omitted] • The absorption of impure hydrogen by uranium was investigated. • Seven common impurity gases correspond to three kinds of mechanisms. • Blanketing effect inhibits the dynamics process. (He, CH 4 , Ar). • Poisoning effect reduces the hydrogen absorption capacity. (N 2 , O 2). • CO and CO 2 show poisoning & retardation effect. [ABSTRACT FROM AUTHOR]

Pd film has been endowed with the hydrogen selective permeation capability and widely used for hydrogen separation via a series of complex processes. Clarifying the exact relationship between permeating mechanism and hydrogen pressure exponent (n) is of great significance to optimize the purification performance, adequate exploration toward which is nevertheless insufficient. In this work, Pd membrane-based hydrogen permeation was divided into seven steps according to the "dissociation-diffusion" principle. The effect of each step on permeation flux with and without considering external mass transfer process was quantified by mathematical and physical models, in which the relationship between n value and the flux-limiting mechanism was deeply analyzed. The calculation suggested that desorption-limiting mechanism acting as leading role would result in n value to be 0, while external mass transfer dominating the permeation would make n value to be 1. When n value was between 0 and 0.5, desorption and diffusion processes would impose combined impact on the permeation (ignoring external mass transfer) and desorption might have more weight as n approaching to 0. On the other hand, taking external mass transfer into account, desorption-limiting and external mass transfer-limiting mechanism would work together as 0 < n < 1. The closer n approaching to 1, the more significant of external mass transfer mechanism. In addition, the influences of Pd film thickness, ΔP variation and mass transfer coefficient on n value were also elucidated systematically. [Display omitted] • Pd membrane-based hydrogen permeation was divided into seven steps according to the "dissociation-diffusion" principle. • The effect of each step on permeation flux was quantified by mathematical and physical models. • The relationship between n value and the flux-limiting mechanism was deeply analyzed. • Effect of external mass transfer process on flux-limiting mechanism was displayed. [ABSTRACT FROM AUTHOR]

Tritium target is of crucial importance in relation to the development of neutron generator apparatus. However, the prevalent Ti target is now suffering from the intricate procedures for activation, limited tritium content at room temperature (RT) and poor ability to fix the helium. Herein, a succession of new type ZrCo(Ti) alloy targets were designed and fabricated by magnetron sputtering. Firstly, the influence of technological parameters (types of substrate, sputtering temperatures, sputtering time and annealing temperatures) on the assemblage and also the hydrogen storage properties of the ZrCo films were systemically studied. The results show that high sputtering temperature is benefit to acquiring high crystallinity of ZrCo films, but the substrates seem to have no significant effect on that. The thickness and grain size of ZrCo film are both positively related to the sputtering time. However, the hydrogen uptake capacities (0.14 wt%~0.79 wt%) for all the prepared ZrCo films are relatively low. After that, the composition and microstructure of the ZrCo films were further regulated and optimized. On the one hand, Zr 1-x Ti x Co films were constructed by introduction of Ti element, achieving a higher hydrogen absorption capacity (~0.7 wt%), but with weak thermal stability in the subsequent hydrogen desorption process (~80% of hydrogen escaped at 500 °C). On the other hand, the surface of the ZrCo film was modified by a thin layer of Ti, forming a serious of double-layer ZrCo/Ti films. The ZrCo/Ti composite films not only achieve extremely high hydrogen storage capacity (1.85 wt%), but also maintain strong thermal stability (only 15.7% of hydrogen escaped at 500 °C). These findings related to the ZrCo(Ti) films in this paper provide crucial reference for the development of tritiated ZrCo film targets, and spark inspiration even for the design of other new-type tritiated film target. • The influence of sputtering parameters on ZrCo films are revealed. • The crystallinity of ZrCo film can be improved when deposited at 800 °C. • The thickness and grain size are positively related to the sputtering time. • Zr 1-x Ti x Co shows similar hydrogen capacity but faster dynamics to ZrCo film. • ZrCo/Ti film exhibits high hydrogen capacity and strong thermal stability. [ABSTRACT FROM AUTHOR]

ZrCo 1− x Mn x ( x = 0–0.1) alloys for tritium storage were prepared by induction levitation melting under an argon atmosphere. The effect of Mn substitution for Co on the alloy microstructure, initial activation behavior, hydrogen storage kinetics and thermodynamics was investigated. The results show that the ZrCo 1− x Mn x ( x = 0, 0.025, 0.05) alloys have a single phase of ZrCo, while ZrCo 1− x Mn x ( x = 0.075, 0.1) alloys consist of a main phase of ZrCo and a secondary phase of ZrMn 2 . It is observed that the initial activation time (uptake to 95% of saturated hydrogen capacity) decreases from 63.73 h to 0.24 h as the Mn content increases from x = 0 to x = 0.1. However, Mn substituted for Co is determined to result in disproportionation during activation and a loss in hydrogen capacity. For increasing Mn content in the alloy, the plateau width for Pressure-Composition-Temperature (P-C-T) curve is shortened, while the plateau pressure remains mostly unchanged. DSC measurements were also performed to investigate the thermal stability of the ZrCo 1− x Mn x system. [ABSTRACT FROM AUTHOR]

Fast heat and mass delivery with high cycling stability of the core component, hydrogen storage bed, in SDS are essential for the operation of the future tritium factory in ITER project. However, the aforementioned properties are still perplexing in large-capacity ZrCo bed, especially for that with secondary containment structure required by the actual tritium operation in the future. Herein, the performance including heating, cycling and cooling with two different size ZrCo beds (loading of ZrCo are 200 g and 2000 g respectively) were systematically studied. The experimental data shows that the maximum heating ability of the middle-size/full-scale storage bed are both about 10 °C/min, and the maximum hydrogen absorption capacity of these ZrCo beds are 44.6 L/405.5 L, respectively. Besides, hydrogen pressure and hydrogen retention during the following desorption can affect the cycling performance of the ZrCo bed. The use of transfer pump can reduce the pressure of the bed during the hydrogen desorption process (operated at 500 °C), which inhibits the disproportionation reaction of the ZrCo alloy. However, the degree of hydrogen pressure reduction in two the types of ZrCo bed are different. As a result, the cycling capacity of the middle-size bed (93.4%, lower hydrogen pressure) is higher than the full-scale bed (68.7%, higher hydrogen pressure) after 10 cycles. When the transfer pump was not used and operated at lower temperature (350 °C), the beds cannot release hydrogen completely, and partial hydrogen atoms are retained in the ZrCo alloy. The middle-size bed still maintains a hydrogen storage capacity of 94.5% after 10 cycles, while 75.9% of the hydrogen storage capacity remained for the full-scale bed. Therefore, the increase of hydrogen surplus in ZrCo alloy is helpful to improve its cycling stability. At last, the cooling performances of the beds under 10 different cooling methods were studied. Among the cooling methods, the best cooling rate was achieved by filling nitrogen in the secondary containment cavity and flowing water passing through the cooling circuit of the bed. This work will provide a crucial reference for the design and optimization of the subsequent operation technology of SDS in ITER. • Thin double-layered annulus ZrCo bed with secondary containment cavity is manufactured. • Real-time pumping transfer helps to improve the circulation stability of the ZrCo bed. • Keep remaining H in the ZrCo is benefits to improve its cycling stability. [ABSTRACT FROM AUTHOR]

Cycling stability of ZrCo–H system is extremely important for the long-term operation of the storage and delivery system (SDS) in ITER. Herein, the optimal cycling operation parameters were systematically investigated. It indicates that various parameters, such as hydrogen pressure, temperature, composition, and stoichiometric ratio of H atoms, will all affect the cycling performance of the ZrCo–H system significantly. The decline rate of the hydrogen capacity of the ZrCo–H system is positively correlated with the hydrogen pressure. The experimental result shows that 54% of hydrogen capacity decreases under 28.1 kPa hydrogen pressure, while 30% of attenuation is obtained when the pressure is decreased to 8.1 kPa after 14 cycles. In terms of temperature, the lowest cycling attenuation can be maintained at about 25% after 14 cycles when the dehydrogenation temperature at 550 °C. The effects of doping elements, Hf and Ti, on the cycling stability of ZrCo–H system are also compared. The Zr 0.8 Ti 0.2 Co sample exhibits higher cycling capacity than ZrCo and Zr 0.8 Hf 0.2 Co samples. The extremely excellent behavior can be achieved when all ZrCo alloys are continuously evacuated during the hydrogen release process, and the attenuation of only 1.1% is observed for Zr 0.8 Ti 0.2 Co after 15 cycles. Besides, the cycling attenuation is related to residual stoichiometric ratio of H atoms in ZrCo alloy during the cycling test. When the residual H atoms proportion exceeds 1 in ZrCo during dehydrogenation, hydrogen cycling capacity hardly fades. The XRD results reveal that the disproportionation of ZrCo is directly associated with the cycling degradation, yielding the more stable products of ZrCo 2 and ZrH 2 , However, the disproportionation can be avoided during the cycling process by controlling the stoichiometric ratio of H atoms remained in ZrCo above 1. This study demonstrates that the cycling performance of ZrCo can be substantially improved when the operation parameters are properly adjusted, which provides a significant important reference for durable running of SDS in ITER. • Relationship between cyclic property and operation parameters of ZrCo is revealed. • Residual H ratio above 1 in ZrCo after desorption indeed improves cyclic stability. • Cycling capacity retention ratio maintains at ~99% for the optimized parameter. [ABSTRACT FROM AUTHOR]

The solvent-free amorphous Mg(BH 4) 2 composite was in-situ synthesized by ball milling LiBH 4 and MgCl 2. It is found that the onset dehydrogenation temperature of the as-synthesized composite is 126.9 °C, which is roughly 156 °C lower than that of pristine Mg(BH 4) 2. The activation energy of the amorphous Mg(BH 4) 2 and pristine Mg(BH 4) 2 for the first dehydrogenation step was calculated as 120.01 kJ/mol and 487.99 kJ/mol, respectively. Hence the kinetics improvement is certified by the lower E a value of the dehydrogenation process. When adding NbF 5 into the composite, the catalyzed composite exhibits better hydrogen storage properties compared to pristine and amorphous Mg(BH 4) 2. The catalyzed composite starts to release hydrogen at proximately 120 °C with a total capacity of 10.04 wt%. The reversibility of the catalyzed composite is also improved. The capacity of the catalyzed composite at the second cycle is 5.5 wt%. For the third and fourth cycles the catalyzed composite can still liberate 4 wt% H 2. Besides, the onset hydrogen desorption temperature during four cycles are extremely lower than those of pristine and amorphous Mg(BH 4) 2. The peaks of the intermediate MgB 12 H 12 is detected by FTIR as the regenerated hydrogenation product in the catalyzed composite. It can be speculated from the detailed analysis that there are mainly three reasons for the improved properties. Firstly, the additive NbF 5 is favorable to enhance the hydrogen storage properties by modifying the dehydrogenation path and producing MgF 2 and NbB 2 as new products. Secondly, the in-situ formation of amorphous Mg(BH 4) 2 is likely to improve the dehydrogenation properties of the samples due to its different reactivity comparing to crystal ones. Finally, LiCl can serve as buffer in the composite and thus improve the dehydrogenation properties. • Amorphous Mg(BH 4) 2 was in-situ synthesized by ball milling. • NbF 5 changes the dehydrogenation path of Mg(BH 4) 2 and produces MgF 2 and NbB 2. • MgB 12 H 12 is regenerated through hydrogenation process in the sample. • The chloride in the sample can serve as buffer during de/rehydrogenation. [ABSTRACT FROM AUTHOR]

Abstract Nowadays, catalytic doping has been regarded as one of the most promising and effective methods to improve the sluggish kinetics of magnesium hydride (MgH 2). Herein, we synthesized Ni/TiO 2 nanocomposite with the particle sizes about 20 nm by an extremely facile solvothermal method. Then, the Ni/TiO 2 nanocomposite was doped into MgH 2 to enhance its reversible hydrogen storage properties. A remarkably enhancement of de/rehydrogenation kinetics of MgH 2 can be achieved by doped with Ni/TiO 2 nanocomposite, compared to that solely doped with Ni or TiO 2 nanoparticles. The hydrogen desorption peak temperature of MgH 2 Ni/TiO 2 is 232 °C, which is 135.4 °C lower than that of ball-milled MgH 2 (367.4 °C). Moreover, the MgH 2 Ni/TiO 2 can desorb 6.5 wt% H 2 within 7 min at 265 °C and absorb ∼5 wt% H 2 within 10 min at 100 °C. In particular, the apparent activation energy of MgH 2 Ni/TiO 2 is obviously decreased from 160.5 kJ/mol (ball-milled MgH 2) to 43.7 ± 1.5 kJ/mol. Based on the analyses of microstructure evolution, it is proved that metallic Ni particles can react with Mg easily to form fine Mg 2 Ni particles after dehydrogenation, and the in-situ formed Mg 2 Ni will transform into Mg 2 NiH 4 in the subsequent rehydrogenation process. The significantly improved hydrogen absorption/desorption properties of MgH 2 Ni/TiO 2 can be ascribed to the synergistic catalytic effect of reversible transformation of Mg 2 Ni/Mg 2 NiH 4 which act as "hydrogen pump", and the multiple valence titanium compounds (Ti4+/3+/2+) which promote the electrons transfer of MgH 2 /Mg. Highlights • Ni/TiO 2 with particle sizes ∼20 nm was synthesized and doped into MgH 2. • MgH 2 Ni/TiO 2 starts to release hydrogen at 190 °C with ∼6.5 wt% H 2. • Enhanced hydrogen storage properties are due to synergistic catalytic mechanism. [ABSTRACT FROM AUTHOR]

LiBH 4 is a promising hydrogen storage material for its large capacity. However, high desorption temperature, sluggish kinetics and demanding rehydrogenation severely hinder its practical use. Surface functional groups of graphene in many cases are treated as effective approaches to obtain some kinds of excellent properties of energy storage materials. In the current work, a new facile and effective strategy to improve the reversible hydrogen desorption properties of LiBH 4 is proposed by composing with functionalized graphene to form the LiBH 4 –fluorographene composite. The fluorographene (FG) nanosheets are successfully exfoliated from fluorographite (FGi) and composed with LiBH 4 . It is demonstrated that the FG can remarkably improve the hydrogen desorption thermodynamics, kinetics and reversibility of LiBH 4 via reactant destabilization method. An extremely fast hydrogen desorption process with a high capacity of 8.2 wt.% at 148.1 °C is achieved in the LiBH 4 –50FG composite. Further research reveals that the enhancement actually roots in the strengthened interfacial interaction between LiBH 4 and exfoliated FG. Moreover, it is confirmed that the LiBH 4 –40FG composite exhibits a significantly enhanced reversible hydrogen desorption capacity of 7.2 wt.% and LiBH 4 is regenerated. Such enhanced reversible hydrogen desorption properties are ascribed to the strengthened interfacial interactions between LiBH 4 and FG with large surface, as well as the formation of LiH x F 1− x phase. [ABSTRACT FROM AUTHOR]

NbF 5 and eutectic 0.68LiBH 4 –0.32Ca(BH 4 ) 2 were successively infiltrated into highly ordered mesoporous carbon (CMK-3) to obtain a LiBH 4 –Ca(BH 4 ) 2 –NbF 5 @CMK-3 composite. A synergetic effect of nanoconfinement and catalysis on hydrogen desorption properties of the composite was achieved. The onset desorption temperature of LiBH 4 –Ca(BH 4 ) 2 –NbF 5 @CMK-3 is dramatically lower than 120 °C compared with that of as-milled LiBH 4 –Ca(BH 4 ) 2 or LiBH 4 –Ca(BH 4 ) 2 @CMK-3. A hydrogen amount as high as 13.3 wt% can be released within 250 min for LiBH 4 –Ca(BH 4 ) 2 –NbF 5 @CMK-3, compared with only 10.4 wt% for pure LiBH 4 –Ca(BH 4 ) 2 , in which nanoconfinement and catalysis both make some contribution. The cycling hydrogen desorption performance of the composite becomes better likewise due to the addition of NbF 5 . Further microstructure analysis reveals that F − tended to bind with Ca 2+ to form CaF 2 , whereas Nb compound is believed to catalyze the whole system in the form of Nb-based boride (NbB 2 ). [ABSTRACT FROM AUTHOR]

In the process of fermentative bio-hydrogen production, organic matter is degraded into volatile fatty acids and ethanol, and consequently thermodynamic constraints prevent the further spontaneous reactions. Moreover, the anaerobic baffled reactor (ABR) with the advantage of phase separation could realize the acetic acid accumulation via acid-producing bacteria. The microbial electrolysis cell (MEC) could convert the acetic acid into hydrogen furthermore. Considering this, the ABR coupled with MEC has been operated to strengthen the hydrogen production. This study was designed regarding orthogonal experiments to operate the four-compartment ABR with a hydraulic retention time (HRT) = 24 h, influent COD ∼ 4600 mg/L, temperature = 35 ± 1 °C, and discovered the optimal parameters with pH = 7, C/N = 44, and 2-bromoethanesulfonate (BES) concentration = 20 mmol/L to achieve the high acetic acid accumulation of effluent. The single-chamber membranless MEC with carbon anode and Ni-catalyst stainless steel cathode (liquid volume = 85 mL) fed with the ABR effluent with applied voltage = 0.6 V and electric conductivity = 7.45 mS/cm, achieved 99.0 ± 0.3% total COD removal efficiency, 1.31 ± 0.04 m3H2/m3d hydrogen production, 2.78 ± 0.11 mLH2/mgCOD hydrogen yield and 138.63 ± 3.11% electrical energy efficiency. Therefore the ABR-MEC system could overcome the “fermentation barrier” to achieve higher hydrogen production and organic matter degradation. [ABSTRACT FROM AUTHOR]