Enhanced Hydrogen Storage Properties and Reversibility of LiBH4

Subscriber access provided by University of Winnipeg Library

Energy, Environmental, and Catalysis Applications

Enhanced hydrogen storage properties and reversibility of LiBH4 confined in two-dimensional Ti3C2 Lei Zang, Weiyi Sun, Song Liu, Yike Huang, Huatang Yuan, Zhanliang Tao, and Yijing Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b02327 • Publication Date (Web): 22 May 2018 Downloaded from http://pubs.acs.org on May 22, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Enhanced hydrogen storage properties and reversibility of LiBH4 confined in two-dimensional Ti3C2 Lei Zang,† Weiyi Sun, † Song Liu, †Yike Huang, † Huatang Yuan, † Zhanliang Tao,*, †,‡ and Yijing Wang *, †,‡ †

Key Laboratory of Advanced Energy Materials Chemistry (MOE), College of Chemistry,

Nankai University, Tianjin 300071, P. R. China. ‡

Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Nankai University, Tianjin 300071, P. R. China.

Keywords: Hydrogen storage, lithium borohydride, Ti3C2, confinement, destabilization.

ABSTRACT: LiBH4 is of particular interest as one of the most promising materials for solidstate hydrogen storage. Herein, LiBH4 is confined into a novel 2D layered Ti3C2 MXene through a facile impregnation method for the first time to improve its hydrogen storage performance. The initial desorption temperature of LiBH4 is significantly reduced, and the de-/rehydrogenation kinetics are remarkably enhanced. It is found that the initial desorption temperature of LiBH4@2Ti3C2 hybrid decreases to 172.6 °C and releases 9.6 wt% hydrogen at 380 °C within 1 h, whereas pristine LiBH4 only releases 3.2 wt% hydrogen under identical conditions. More

ACS Paragon Plus Environment

1

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 22

importantly, the dehydrogenated products can partially rehydrogenate at 300 °C and under 95 bar H2. The nano-confined effect caused by unique layered structure of Ti3C2 can hinder the particles growth and agglomeration of LiBH4. Meanwhile, Ti3C2 could possess superior effect to destabilize LiBH4. The synergetic effect of destabilization and nanoconfinement contributes to the remarkably lowered desorption temperature and improved de-/rehydrogenation kinetics.

INTRODUCTION LiBH4 has been widely considered as one of the most potential solid-state hydrogen storage materials owing to its high volumetric hydrogen densities (121 kg H2/m3) and gravimetric hydrogen densities (18.5 wt%).1, 2 Unfortunately, sluggish reaction kinetics, high thermodynamic stability and undesirable rehydrogenation conditions severely hinder its practical applications. Practically, the initial desorption temperature of pure LiBH4 is approximately exceeding 400 °C3, 4

and the dehydrogenation products can only be rehydrogenated at a rigorous condition of 35

MPa H2 and 600 °C.5, 6 These harsh de-/rehydrogenation conditions are essentially attribute to the strong ionic and covalent bonds between the constituent elements.7 To overcome these barriers, various attempts have been taken to improve the hydrogen storage properties of LiBH4, including partial anion/cation substitution,8, 9, addition of dopants 10, 11 reactant destabilization12, 13 and nanoconfinement14, 15. Among these strategies, addition of dopants is one of the most effective ways that has been extensively explored. It is based on mixing LiBH4 with other elements or compounds which can either weaken the strong ionic bond between Li+ and (BH4)-16-17 or result in more stable dehydrogenation products formed,18 thus decrease the enthalpy change of dehydrogenation. Among various dopants, Ti-based compounds exhibit excellent activity in decreasing the initial desorption temperature and improving the


2

Page 3 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


kinetic properties of LiBH4. For instance, Guo et al. reported that LiBH4-TiF3 sample with mole ratio of 3:1 started to release hydrogen at around 100 °C, and total 5.0 wt% hydrogen was released at 250 °C.11 Yu et al. revealed that the initial dehydrogenation temperature for the LiBH4-4TiO2 mixture was 150 °C and the dehydrogenation capacity achieved 9.0 wt%.19 However, the harsh reversible conditions still hinder the practical application of LiBH4. Confined LiBH4 in porous or nanostructure scaffolds is another effective approach for improving kinetics and reversibility properties.20, 21 The improved de-/rehydrogenation kinetics for nanoconfined LiBH4 is due to the nano grain size and rich grain boundaries, the suppression of the particle agglomeration and growth and sharply shortened diffusion distances of H2 during de-/rehydrogenation process.22, 23 Commonly, the inert mesoporous carbon materials are primarily served as scaffold hosts.24, 25 Although nanosizing resulting from the mesoprous structure of carbon scaffolds is effective on improving de-/rehydrogenation kinetics and reversibility of LiBH4, the problem of high thermodynamic stability still cannot be mitigated. So far, it’s still difficult to satisfy the demand of practical applications of onboard hydrogen storage system with the mentioned methods carried out separately. Thus, it is imperative to find a material which incorporates the synergic effect of destabilization and nanoconfinement to improve the de-/rehydrogenation properties of LiBH4. Very recently, Ti3C2 as a new two-dimensional (2D) layered material has attracted widely attention due to its unique structure and excellent properties.26, 27 Ti3C2 has exhibited significant potential in many fields including catalysis, sensors, conversion, energy storage, gaseous adsorption and electronic devices owing to layered structure, relatively large surface area , remarkable chemical durability and high electroconductivity.28-31 More encouragingly, Liu et al. have introduced the layered Ti3C2 into hydrogen storage system as dopants by ball-milling


3


Page 4 of 22

method and proved it is beneficial for improving the de-/absorption properties of MgH2 and NaAlH4.32, 33 Taking above discussions into consideration, it is reasonable to illustrate that the layered Ti3C2 material can display beneficial influence on enhancing the hydrogen storage performance of LiBH4. The Ti3C2 material could sever as a scaffold host to confine LiBH4 nanoparticles into its particular nano-layered structure. Meanwhile, it could possess superior effect to destabilize LiBH4. Herein, we conducted the first attempt to synthesized LiBH4-supported on Ti3C2 (LBH@xTi3C2) hybrids using a facile impregnation method at room temperature and further investigated their enhanced hydrogen storage properties. The hybrid with mass ratio of 1:2 (denoted as LBH@2Ti3C2) exhibits superior de-/rehydrogenation properties. It starts to release H2 at 172.6 °C and releases 9.6 wt% H2 at 380 °C within 60 min. Moreover, the hybrid realizes partially reversible hydrogen absorption at 300 °C under 95 bar H2. Ti3C2 with 2D layered structure can downsize the hydride and restrain the dehydrogenated products from aggregation and provide lots of active sites acting as dopant. The synergistic effect of nanoconfinement and destabilization guarantees the enhanced hydrogen storage performance of LiBH4. EXPERIMENTAL SECTION Synthesis of the Ti3C2 sample. The Ti3AlC2 powder (98% purity, HWRK Chem Co., LTO) was immersed in hydrofluoric acid (≥ 40%, Macklin) with stirring for 24 h at room temperature, and in a ratio of 1 g MAX powder to 10 mL HF. Then the precipitation was washed with deionized water by centrifuge sedimentation (10 min at 10000 rpm per cycle). When the pH value of the rinsed solution reached approximately 5, the solid was dried under vacuum at 80 °C for overnight.


4

Page 5 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Preparation of LBH@xTi3C2 hybrids. Commercial LiBH4 powder (95%) was purchased from Alfa Aesar and Ti3C2 was pretreated by calcination in flowing Ar atmosphere at 600 °C to remove moisture and other impurities. LBH@xTi3C2 hybrids with different mass ratios (2:1, 1:1, 1:2, 1:3, respectively) were synthesized using a facile impregnation method. To prepare LBH@xTi3C2 hybrids, 60 mg LiBH4 was dissolved in 30 mL ultra-dried tetrahydrofuran (THF) under vigorous stirring for 1 h. A certain amount of as-prepared Ti3C2 samples (30 mg, 60 mg, 120 mg and 180 mg, respectively) were added in the LiBH4-THF solution. The obtained mixtures were vigorously stirred for 6 h and then heated at 70 °C to remove the THF residue. After THF completely evaporation, the micro-nanostructured composites of LBH@xTi3C2 with four loading amounts of LiBH4 were obtained. All the above operations were carried out in an Ar-filled glove box (Mikrouna Co., China) with H2O and O2 oxygen contents below 1 ppm. Characterization. The phases constitution and morphological features of all samples were characterized by X-ray diffraction (XRD, Rigaku Mini FlexII, Cu Kα radiation), X-ray photoelectron spectrometer (XPS, PHI 5000 Versaprobe, ULVAC PHI), transmission electron microscopy (TEM, JEOL JEM-2010FEF) and scanning electron microscopy (SEM, JEOL JSM7500). FTIR spectra were measured by infrared spectrometer at a resolution of 4 cm-1 (FTIR-650, Tianjin Gangdong). The dehydrogenation behaviors were examined by home-made temperature programmed desorption (TPD) system at heating rate of 2 °C min-1 from 30 to 500 °C in 35 mL/min Ar flow. De-/rehydrogenation kinetics propertiess were detected via a Sievertstype isothermal measurement. Rehydrogenation of the samples was carried out under 95 bar initial hydrogen pressure for 24 h at 300 °C. Differential scanning calorimetry (DSC) was performed using a TA apparatus (DSC Q20P) with certain heating rate in a flow of high purity Ar (50 ml min-1).


5


Page 6 of 22

Results and Discussion The phases constitution and structure information of the as-prepared Ti3C2 were obtained by XRD and SEM. As shown in Figure. 1, XRD analysis proves the formation of Ti3C2, which is achieved by selectively etching of Al from Ti3AlC2. It is obviously that the strongest diffraction peak of Ti3AlC2 at 2θ=39° belonging to Al disappears while the (002) and (004) peaks are broadened and shift to lower angles.33, 34 As we can see from the embedded SEM image, the asprepared Ti3C2 is effectively separated and exhibits an accordion-like multilayer morphology. EDS analysis (Figure. S1) further indicates that the obtained product is mainly composed of Ti and C with the thoroughly removing of Al. In addition, the small amount of F and O elements are

Figure 1. XRD curves of as-prepared Ti3C2, Ti3AlC2 and the embedded SEM image of Ti3C2. resulting from the substitution of Al with F and OH. The detailed SEM and TEM images with different magnifications of bulk Ti3AlC2 powders and prepared Ti3C2 are displayed in Figure. S2-3. It can be clearly observed that the open nanolayered structure of Ti3C2 is derived from dense stacked layered structure of initial Ti3AlC2 bulk.


6

Page 7 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The LBH@xTi3C2 hybrids with different mass ratios were prepared by a facile impregnation method at room temperature. The dehydrogenation behaviors of pure LiBH4 and LBH@xTi3C2 hybrids were investigated by TPD measurements and the results were displayed in Figure. 2(a). The onset desorption temperature (referred to Tonset) and peak temperature (referred to Tmax), as two characteristic temperatures in the TPD curves, are chosen to evaluate the dehydrogenation properties of LBH@xTi3C2 hybrids. For pure LiBH4, there is a weak desorption peak locating at about 296 °C, corresponding to the melting point of LiBH4. The main dehydrogenation process starts at above 400 °C and Tmax reaches at 485.6 °C, which is generally identical with the results from previous reports. With the increasing content of the Ti3C2 scaffold, a remarkable drop in the dehydrogenation temperature can be found. In particular, When the mass ratio of LiBH4 and Ti3C2 is 1:2, the Tonset respectively decreases to 172.6 °C, about 220 °C lower than that of pristine LiBH4.There are two characteristic desorption peaks in the curve of LBH@2Ti3C2 hybrid with the Tmax occurring at 278.4 °C and 322.8 °C, respectively. The quantitative dehydrogenation capacities of LBH@xTi3C2 hybrids were calculated only on the basis of LiBH4 and the results were shown in Figure. 2(b). we can see that pure LiBH4 slowly decomposes from approximately 300 °C and thedehydrogenation process accelerates appreciably at about 400 °C, with a final release about 7.8 wt% H2 at 500 °C. More encouragingly, the dehydrogenation capacities of all LBH@xTi3C2 hybrids gradually increase with the increasing addition amount of Ti3C2. Among them, the LBH@2Ti3C2 hybrid releases 11.3 wt% H2, possessing the maximum desorption capacity. However, the hydrogen amount of LBH@3Ti3C2 hybrid decreases rapidly. It


7


Page 8 of 22

Figure 2. (a) Thermal desorption curves and (b) hydrogen desorption capacity curves of LBH@Ti3C2 hybrids with different mass ratios (heating at 2 °C min-1). is because the amount of LiBH4 is so small that the hydrogen desorption signal is too weak to detect. The characteristic dehydrogenation properties of all the above-mentioned samples are displayed in Table S1. Taking overall consideration of the hydrogen desorption temperature and hydrogen desorption capacity, the LBH@2Ti3C2 hybrids were selected for further investigations. To further explore the remarkable influence of Ti3C2 on the desorption thermodynamics and kinetics properties of LiBH4, the DSC curves of the LBH@2Ti3C2 hybrids were measured with various heating rates. As a contrast, pure LiBH4 was also measured and corresponding curve was shown in Figure. S4. It is obvious that LiBH4 displays three endothermic behaviors in the DSC curve. The first endothermic peak around 119.6 °C assigns to the polymorphic transformation of LiBH4 (from orthorhombic to hexagonal phase); the melting point of LiBH4 is correspongding to the second endothermic peak at 288.2 °C; and the third endothermic peak centered at 470.3 °C can be safely assigned to the main desorption reaction of LiBH4. Interestingly, the nanoconfined LBH@2Ti3C2 sample displays weaker melting peak with a lower


8

Page 9 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (a) DSC profiles and (b) Kissinger plots of LBH@2Ti3C2 hybrid. peak temperature instead of the sharp melting peak of pure LiBH4, owing to the increasing disorder of LiBH4 confined in Ti3C2 scaffold as well as the interaction between LiBH4 and the surface of Ti3C2 layered structure.35 The two endothermic peaks located at about 300-350 °C can be assigned to the dehydrogenation process of LBH@2Ti3C2 sample. The values of activation energies (Ea) of the dehydrogenation process have been calculated by Kissinger’s method.36 Figure. 3(b) displays the Kissinger's plots of the two desorption processes of the LBH@2Ti3C2 hybrid. The values of Ea were calculated to be 94.44 and 98.27 kJ mol-1 respectively by fitting the slope of the data points. These results are about 50% lower than that of pure LiBH4 reported by Li et al. (187±24 kJ mol-1).37 It suggests that the desorption kinetics properties of LiBH4 achieved a remarkable enhancement by confinement into layered Ti3C2. Figure. 4 displays SEM images of LBH@2Ti3C2 sample. It is obvious that the Ti3C2 scaffold host always keeps the layered structure before and after dehydrogenation, indicating a super structural stability during the dehydrogenation process. Differently, nanosize LiBH4 particles


9


Page 10 of 22

Figure 4. SEM images of (a) Ti3C2, (b, c) LBH@2Ti3C2 hybrid before dehydrogenation and (d) after dehydrogenation. support on the surface and between interlayers of Ti3C2 scaffold for the LBH@2Ti3C2 sample compared with the smooth surface of pure Ti3C2. The corresponding TEM results (Figure. S5) prove the phenomenon and the particles size remain nearly unchanged after dehydrogenation. EDS images (Figure. 5) present that the elements Ti, C and B distribute homogeneously in the LBH@2Ti3C2 sample, which indicates LiBH4 uniform loading on the Ti3C2 scaffold host. To explore the reaction mechanism of LBH@2Ti3C2 hybrid during the dehydrogenation process, XPS analysis of pure Ti3C2 and LBH@2Ti3C2 sample after dehydrogenation were conducted. As seen in Figure. 6(a), the characteristic peaks suggest that the Ti 2p spectrum of pure Ti3C2 can be fitted into four sets of 2p1/2-2p3/2 spin-orbit doublets at 455.0/463.1 eV, 456.0/461.2 eV and458.7/464.8 eV, which can be well assigned to Ti-C, Ti2+, Ti4+ (TiO2),


10

Page 11 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. EDS mapping results of the LBH@2Ti3C2 hybrid. respectively.38 The existing of TiO2 can be assigned to the interaction between Ti3C2 and -OH introduced during HF treatment of MAX phase.39 It is obvious that the shape of the Ti 2p spectra has greatly changed after full dehydrogenation of LBH@2Ti3C2 sample. The peaks assigned to Ti0 (453.6/459.7 eV) and Ti3+ (456.8/463.6 eV) were observed while the peaks of TiO2 and Ti-C disappeared. Meantime, the results in C 1s spectrum (shown in Figure. 6(b)) also proved the broken of Ti-C bond after dehydrogenation of LBH@2Ti3C2 sample. It demonstrates that a chemical reaction occurs between LiBH4 and Ti3C2 during the dehydrogenation process. Ti element are reduced from high valence state to low valence state by strong reducing agent LiBH440, so that the Ti-C bonds break and metallic Ti and Ti3+ species emerge. The active Ti formed in situ can weaken the strong ionic bond between Li+ and (BH4)-.41 More importantly, the


11


Page 12 of 22

Figure 6. XPS spectra for (a) Ti 2p, (b) C 1s of Ti3C2 and LBH@2Ti3C2 composite after dehydrogenation. results forcefully proves that the confined Ti3C2 carrier itself can also act as the active dopant, which achieve the synergic effect of destabilization and nanoconfinement to improve the dehydrogenation properties of LiBH4. To better explore the desorption kinetics of LBH@2Ti3C2 sample, the isothermal desorption experiments were carried out at different holding temperatures (300 °C, 350 °C and 380 °C). In contrast, the desorption behaviors of pristine LiBH4 were also measured under the uniform conditions (Fig. S6). As can be seen from Figure. 7(a), the results show that the LBH@2Ti3C2 sample released 8.2, 11.3 and 12.6 wt% H2 at 300, 350 and 380 °C, respectively. However, the total hydrogen desorption amount of LiBH4 is only 0.9, 2.9 and 5 wt% under the same conditions. Notably, the LBH@2Ti3C2 sample releases 9.6 wt% H2 at 380 °C within 1 h, whereas the pure


12

Page 13 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


LiBH4 released only 3.2 wt% H2 within the same time. The enhanced desorption kinetics properties probably attribute to the particle size reduction of LiBH4 resulting from confinement within the open layered nanostructure and destabilization causing by in situ formed Ti. For the

Figure 7. (a) Dehydrogenation kinetic curves of LBH@2Ti3C2 hybrid (calculated according to the weight of LiBH4); (b) FTIR spectra of pure LiBH4, Ti3C2 , LBH@2Ti3C2 hybrid and corresponding dehydrogenated products. sake of further understanding of the reaction mechanism, FTIR spectra of pure LiBH4, Ti3C2, LBH@2Ti3C2 hybrid and its dehydrogenated products after isothermal desorption process were proceeded and displayed in Figure. 7(b), typical vibrations characteristic peaks of B-H bonds are observed at 2224, 2291, 2385 and 1123 cm-1, indicating the emergence of LiBH4 in the LBH@2Ti3C2 hybrid and the dehydrogenated products. Notably, the intensities of B-H bonds gradually weaken with the heating temperature increment and almost disappear until heated at 380 °C, which attributes to the dehydrogenation process of LiBH4. In order to examine the reversibility of LBH@2Ti3C2 hybrid, the de-/rehydrogenation process of LBH@2Ti3C2 hybrid


13


Page 14 of 22

Figure 8. Dehydrogenation cycle profiles of the LBH@2Ti3C2 hybrid. was further investigated for three cycles. As can be seen from Figure. 8, the LBH@2Ti3C2 hybrid released 10.6 wt% H2 for the first dehydrogenation cycle at 350 °C. Rehydrogenation of the hybrid was conducted at 300 °C under 95 bar H2 for 24 h. Then about 6.5 wt% H2 could be released at 350 °C within 6 h for the second dehydrogenation cycle, and only 5.5 wt% H2 was released after three cycles. It is obvious that the rehydrogenation pressure and temperature of LBH@2Ti3C2 hybrid are significantly lower than than that of pristine LiBH4 (35 MPa and 600 °C) even 10 MPa and 400 °C for LiBH4 with some dopants reported previously.3-6, 42 The improved reversibility properties for nanoconfined LiBH4 are attributed to the nanosizing particle of LiBH4, sharply reduced diffusion distances and the super destabilization activity caused by the Ti-containing defect sites. Unfortunately, the LBH@2Ti3C2 hybrid still suffers from severe cyclic capacity degradation. The hydrogen reversible capacity reduces 48% after three cycles. To investigate the possible mechanism about this phenomenon, SEM images of product after three dehydrogenation cycles were detected and displayed in Figure. 9. Unfortunately, a certain extent particle growth and agglomeration still occur in spite of the particle size of LiBH4 is below


14

Page 15 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 9. SEM image of product after three dehydrogenation cycles and the inset of its magnified view. 100 nm. Although it can confine LiBH4 into the interlayer of Ti3C2, the particle agglomeration phenomenon is unavoidable in the horizontal layered surface of Ti3C2. It is probably the main reason of cyclic capacity degradation. Conclusions In summary, the two-dimensional layered Ti3C2 was prepared by selective exfoliation of the Al element from the Ti3AlC2 raw material using HF solution. And then the LBH@Ti3C2 hybrids were synthesized by incorporating LiBH4 into the layer structure of Ti3C2 using a facile impregnation method. The initial desorption temperature of LBH@2Ti3C2 hybrid is decreased to 172.6 °C with the main desorption peaks at 278.4 and 322.8 °C, indicating significant reduction compared with pure LiBH4. Meanwhile, the sample shows excellent desorption kinetics, with 9.6wt% H2 liberated from LiBH4 at 380 °C within 1 h. More encouragingly, the values of Ea are reduced to be 94.44 and 98.27 kJ mol-1, which are reduced by around 50% in comparison with pure LiBH4. More attractively, the dehydrogenated sample can achieve a partial reversibility


15


Page 16 of 22

under much moderate conditions (95 bar H2, 300 °C). The improved hydrogen storage performance results from the synergistic effect of nanosized LiBH4 confined into unique Ti3C2 layered structure and destabilization activity caused by the Ti-containing defect sites. More studies are required to investigate the reaction mechanism connected with destabilization and confinement. Our attempt indicates the probability of exploring novel nanoporous materials with high catalytic activity for enhancing the hydrogen storage performance of LiBH4. ASSOCIATED CONTENT Supporting Information. EDS spectrum of the as-prepared Ti3C2 sample; SEM images of Ti3AlC2 and Ti3C2; TEM images of Ti3AlC2 and Ti3C2; Details of TPD dehydrogenation curves of pure LiBH4 and LBH@Ti3C2 hybrids with different ratios; DSC profile of pure LiBH4; TEM images of LBH@2Ti3C2 hybrid before and after dehydrogenation; Dehydrogenation kinetic curves of pure LiBH4 at 300, 350 and 380 °C. AUTHOR INFORMATION Corresponding Author * E-mail: [email protected] (Y. J. Wang). * E-mail: taozhl @nankai.edu.cn (Z. L.Tao). Notes The authors declare no competing financial interest. ACKNOWLEDGMENT


16

Page 17 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


We greatly appreciate the financial support by NSFC (51571124, 51571125 , 51471089, 51501072), 111 Project (B12015), MOE (IRT13R30). REFERENCES (1) Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim, J. O’Keeffe, M. Hydrogen Storage in Microporous Metal-Organic Frameworks. Science 2003, 300, 1127-1129. (2) Chen, J.; Kuriyama, N.; Xu, Q.; Takeshita, H. T.; Sakai, T. Reversible Hydrogen Storage via Titanium-Catalyzed LiAlH4 and Li3AlH6. J. Phys. Chem. B 2001, 105, 11214-11220. (3) Orimo, S.; Nakamori, Y.; Eliseo, J. R.; Züttel, A.; Jensen, C. M. Complex Hydrides for Hydrogen Storage. Chem. Rev. 2007, 107, 4111-4132. (4) Liu, Y. F.; Zhang, Y.; Zhou, H.; Zhang, Y.; Gao, M. X.; Pan, H. G. Reversible Hydrogen Storage Behavior of LiBH4-Mg(OH)2 Composites. Int. J. Hydrogen Energy 2014, 39, 7868-7875. (5) Mao, J.; Guo, Z.; Leng, H.; Zhu, W. Guo, Y.; Yu, X. B.; Liu, H. Reversible Hydrogen Storage in Destabilized LiAlH4-MgH2-LiBH4 Ternary-Hydride System Doped with TiF3. J. Phys. Chem. C 2010, 114, 11643-11649. (6) Chen, P.; Xiong, Z. T.; Lou, J. Z.; Lin, Z. Y.; Tan, K. L. Interaction of Hydrogen with Metal Nitrides and Imides. Nature 2002, 420, 302-304. (7) Miwa, K.; Ohba, N.; Towata, S. First-Principles Study on Lithium Borohydride LiBH4. Phys. Rev. B 2004, 69, 245120. (8) Nickels, E. A.; Jones, M. O.; David, W. I. F.; Johnson, S. R.; Lowton, R. L.; Sommariva, M. Tuning the Decomposition Temperature in Complex Hydrides: Synthesis of a Mixed Alkali Metal Borohydride. Angew. Chem. 2008, 120, 2859-2861; Angew. Chem. Int. Ed. 2008, 47, 2817-2819.


17


Page 18 of 22

(9) Ravnsbæk, D.; Filinchuk, Y.; Cerenius, Y.; Jakobsen, H. J.; Besenbacher, F.; Skibsted, J. A Series of Mixed-Metal Borohydrides. Angew. Chem. 2009, 121, 6787-6791; Angew. Chem. Int. Ed. 2009, 48, 6659-6663. (10) Tu, G. P.; Xiao, X. Z.; Jiang, Y. Q.; Qin, T. Composite Cooperative Enhancement on the Hydrogen Desorption Kinetics of LiBH4 by Co-Doping with NbCl5 and Hexagonal BN. Int. J. Hydrogen Energy 2015, 40, 10527-10535. (11) Guo, Y. H.; Yu, X. B.; Gao, L.; Xia, G. L;. Guo, Z. P.; Liu, H. K. Significantly Improved Dehydrogenation of LiBH4 Destabilized by TiF3. Energy Environ. Sci. 2010, 3, 464-469. (12) Vajo, J. J.; Skeith, S. L.; Mertens, F. Reversible Storage of Hydrogen in Destabilized LiBH4. J. Phys. Chem. B 2005, 109, 3719-3722. (13) Mao, J. F.; Wu, Z.; Chen, T. J.; Weng, B. C.; Xu, N. X.; Huang, T. S. Improved Hydrogen Storage of LiBH4 Catalyzed Magnesium. J. Phys. Chem. C 2007, 111, 12495-12498. (14) Gross, A. F.; Vajo, J. J.; Atta, S. L. V.; Olson, G. L. Enhanced Hydrogen Storage Kinetics of LiBH4 in Nanoporous Carbon Scaffolds. J. Phys. Chem. C 2008, 112, 5651-5657. (15) Fang, Z. Z.; Wang, P.; Rufford, E.; Kang, X. D.; Lu, G. Q.; Cheng, H. M. Kinetic- and Thermodynamic- Based Improvements of Lithium Borohydride Incorporated into Activated Carbon. Acta. Mater. 2008, 56, 6257-6263. (16) Hagemann, H.; Longhini, M.; Kaminski, J. W.; Wesolowski, T. A.; Černy, R.; Penin, N.; Sørby, M. H.; Hauback, B. C.; Severa, G.; Jensen, C. M. LiSc(BH4)4: A Novel Salt of Li+ and Discrete Sc(BH4)4- Complex Anions. J. Phys. Chem. A 2008, 112, 7551-7555. (17) Kim, C.; Hwang, S. J.; Bowman Jr, R. C.; Reiter, J. W.; Zan, J. A.; Kulleck, J. G.; Kabbour, H.; Majzoub, E. H.; Ozolins, V. LiSc(BH4)4 as a Hydrogen Storage Material: Multinuclear High-


18

Page 19 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Resolution Solid-State NMR and First-Principles Density Functional Theory Studies. J. Phys. Chem. C, 2009, 113, 9956-9968. (18) Bösenberg, U.; Doppiu, S.; Mosegaard, L.; Barkhordarian, G.; Eigen, N.; Borgschulte, A.; Jensen, T. R.; Cerenius, Y.; Gutfleisch, O.; Klassen, T.; Dornheim, M.; Bormann, R. Hydrogen Sorption Properties of MgH2-LiBH4 Composites. Acta. Mater. 2007, 55, 3951-3958. (19) Yu, X. B.; Grant, D. M; Walker, G. S. Low-Temperature Dehydrogenation of LiBH4 through Destabilization with TiO2. J. Phys. Chem. C 2008, 112, 11059 -11062. (20) de Jongh, P. E.; Allendorf, M.; Vajo, J. J.; Zlotea, C. Nanoconfined Light Metal Hydrides for Reversible Hydrogen Storage. MRS Bull. 2013, 38, 488-494. (21) Nielsen, T. K.; Besenbacher, F.; Jensen, T. R. Nanoconfined Hydrides for Energy Storage. Nanoscale 2011, 3, 2086-2098. (22) Bérubé, V.; Radtke, G.; Dresselhaus, M.; Chen, G. Size Effects on the Hydrogen Storage Properties of Nanostructured Metal Hydrides: A Review. Int. J. Energy Res. 2007, 31, 637-663. (23) Berube, V.; Chen, G.; Dresselhaus, M. Impact of Nanostructuring on the Enthalpy of Formation of Metal Hydrides. Int. J. Hydrogen Energy 2008, 33, 4122-4131. (24) Ngene, P.; Verkuijlen, M. H. W.; Barre, C.; Kentgens, A. P. M.; de Jongh, P. E. Reversible Li-Insertion in Nanoscaffolds: A Promising Strategy to Alter the Hydrogen Sorption Properties of Li-Based Complex Hydrides. Nano Energy 2016, 22, 169-178. (25) Shao, J.; Xiao, X. Z.; Huang, X.; Zhai, B.; Li, S. Q.; Ge, H. W.; Wang, Q. D.; Chen, L. X. Enhanced Hydrogen Storage Capacity and Reversibility of LiBH4 Nanoconfined in the Densified Zeolite-Templated Carbon with High Mechanical Stability. Nano Energy 2015, 15, 244-255. (26) M. Naguib, V. N. Mochalin, M. W. Barsoum, Y. Gogotsi, 25th Anniversary Article: MXenes: A New Family of Two-Dimensional Materials. Adv. Mater. 2014, 26, 992-1005.


19


Page 20 of 22

(27) Naguib, M.; Kurtoglu, M.; Presser, V.; Lu, J.; Niu, J.; Heon, M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W. Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater. 2011, 23, 4248-4253. (28) Lukatskaya, M. R.; Mashtalir, O.; Ren, C. E.; Dall'Agnese, Y.; Rozier, P.; Taberna, P. L.; Naguib, M.; Simon, P.; Barsoum, M. W.; Gogotsi, Y. Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide. Science 2013, 341, 1502-1505. (29) Peng, Q.; Guo, J.; Zhang, Q.; Xiang, J.; Liu, B.; Zhou, A.; Liu, R.; Tian, Y. Unique Lead Adsorption Behavior of Activated Hydroxyl Group in Two-Dimensional Titanium Carbide. J. Am. Chem. Soc. 2014, 136, 4113-4116. (30) Berdiyorov, G. R. Effect of Lithium and Sodium Ion Adsorption on the Electronic Transport Properties of Ti3C2 MXene. ACS Appl. Surf. Sci. 2015, 359, 153-157. (31) Liu, H.; Duan, C.; Yang, C.; Shen, W.; Wang, F.; Zhu, Z. A Novel Nitrite Biosensor Based on the Direct Electrochemistry of Hemoglobin Immobilized on MXene-Ti3C2. Sens. Actuators Bchem. 2015, 218, 60-66. (32) Liu, Y.; Du, H.; Zhang, X.; Yang, Y.; Gao, M.; Pan, H. Superior Catalytic Activity Derived From a Two-Dimensional Ti3C2 Precursor Towards the Hydrogen Storage Reaction of Magnesium Hydride. Chem. Commun. 2016, 52, 705-708. (33) Wu, R. Y.; Du, H. F.; Wang, Z. Y.; Gao, M. X.; Pan, H. G.; Liu, Y. F. Improvement and Analysis of the Hydrogen-Cerium Redox Flow Cell. J. Power Sources, 2016, 327, 519-525. (34) Naguib, M.; Kurtoglu, M.; Presser, V.; Lu, J.; Niu, J. J.; Heon, M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W. Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater. 2011, 23, 4248-4253.


20

Page 21 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) Shao, J.; Xiao, X. Z.; Fan, X. L.; Zhang, L. T.; Li, S. Q.; Ge, H. W.; Wang, Q. D.; Chen, L. X. Low-Temperature Reversible Hydrogen Storage Properties of LiBH4: A Synergetic Effect of Nanoconfinement and Nanocatalysis. J. Phys. Chem. C 2014, 118, 11252-11260. (36) Kissinger, H. E. Reaction Kinetics in Differential Thermal Analysis. Anal. Chem. 1957, 29, 1702-1706. (37) Li, H. W.; Yan, Y. G.; Akiba, E.; Orimo, S. Improved Dehydrogenation and Rehydrogenation Properties of LiBH4 by Nanosized Ni Addition. Mater. Trans. 2014, 55, 11341137. (38) Han, M. K.; Yin, X. W.; Wu, H.; Hou, Z. X.; Song, C. Q.; Li, X. L.; Zhang, L. T.; Cheng, L. F. Ti3C2 MXenes with Modified Surface for High-Performance Electromagnetic Absorption and Shielding in the X-Band. ACS Appl. Mater. Interfaces 2016, 8, 21011-21019. (39) Rakhi, R. B.; Ahmed, B.; Hedhili, M. N.; Anjum, D. H.; Alshareef, H. N. Effect of Postetch Annealing Gas Composition on the Structural and Electrochemical Properties of Ti2CTx MXene Electrodes for Supercapacitor Applications. Chem. Mater. 2015, 27, 5314-5323. (40) Shao, J.; Xiao, X. Z.; Chen, L. X.; Fan, X. L.; Li, S. Q.; Ge, H. W.; Wang, Q. D. Enhanced Hydriding-Dehydriding Performance of 2LiBH4-MgH2 Composite by the Catalytic Effects of Transition Metal Chlorides. J. Mater. Chem. 2012, 22, 20764-20772. (41) Mo, X. H.; Jiang, W. Q.; Ca, S. L. First-Principles Study on the Dehydrogenation Characteristics of LiBH4 Modified by Ti. Results in Physics 2017, 7, 3236-3642. (42) Y. F. Zhou, Y. F. Liu, W. Wu, Y. Zhang, Gao, M. X.; Pan, H. G. Improved Hydrogen Storage Properties of LiBH4 Destabilized by in Situ Formation of MgH2 and LaH3. J. Phys. Chem. C 2012, 116, 1588-1595.


21


Page 22 of 22

Graphical abstract


22

Enhanced Hydrogen Storage Properties and Reversibility of LiBH4

Recommend Documents