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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]

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]