稀有金属(英文版) 2020,39(04),383-391

Dehydrogenation characteristics of ZrC-doped LiAlH₄ with different mixing conditions

Zi-Liang Li Fu-Qiang Zhai Hao-Chen Qiu Qi Wan Ping Li Xuan-Hui Qu

State Key Laboratory for Advanced Metals and Materials, Institute for Advanced Materials and Technology,University of Science and Technology Beijing

Applied Physics Department,Polytechnic University of Catalonia-Barcelona

Research Institute of Energy and Materials Technology,General Research Institute of Nonferrous Metals

作者简介：*Ping Li e-mail:ustbliping@126.com;

收稿日期：11 January 2015

基金：financially supported by the National High Technology Research and Development Program of China (No.2006AA05Z132);the National Natural Science Foundation of China (No.51471054);

Dehydrogenation characteristics of ZrC-doped LiAlH₄ with different mixing conditions

Zi-Liang Li Fu-Qiang Zhai Hao-Chen Qiu Qi Wan Ping Li Xuan-Hui Qu

State Key Laboratory for Advanced Metals and Materials, Institute for Advanced Materials and Technology,University of Science and Technology Beijing

Applied Physics Department,Polytechnic University of Catalonia-Barcelona

Research Institute of Energy and Materials Technology,General Research Institute of Nonferrous Metals

Abstract：

The catalytic effects of ZrC powder on the dehydrogenation properties of LiAlH₄ prepared by designed mixing processes were systematically investigated.The onset dehydrogenation temperatures for the 10 mol% ZrC-doped sample are 85.3 and 148.4℃for the first two dehydrogenation stages,decreasing by 90.7 and 57.8℃,respectively,compared with those of the as-received LiAIH₄.The isothermal volumetric measurement indicates that adding ZrC powder could significantly enhance the desorption kinetics of LiAlH₄.The reaction constant and Avrami index show that the first dehydrogenation stage is controlled by diffusion mechanism with nucleation rate gradually decreasing and the second stage is a freedom nucleation and subsequent growth process.The microstructures and phase transformation characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS) and Fourier transform infrared spectroscopy(FTIR) reveal that the improved desorption behavior of LiAlH₄ is primarily due to the high density of surface defects and embedded catalyst particles on the surface of LiAlH₄ particles during the high-energy mixing process.

Keyword：

Lithium alanate; Zirconium carbide; Doping methods; Dehydrogenation performances; Catalytic mechanism;

Received： 11 January 2015

1 Introduction

The storage of hydrogen in one kind of specific solid states has been considered as the most potential way for realizing the so-called hydrogen energy economy due to its high volumetric hydrogen capacity and relatively perfect safety considerations,compared with other hydrogen storage forms including compressed and liquefied H₂ [ 1, 2, 3, 4, 5, 6] .Among the alternative solid-state hydrogen storage materials,alanate has been in the limelight for the past several years since Bogdanovic and Schwickardi [ 7] conducted the seminal work in improving the hydrogen storage performance of NaAlH₄ by doping TiCl₃.Currently,lithium aluminum hydride (LiAlH₄) is regarded as a potential promising candidate for the practical utility in the new energy automobile due to its relatively larger theoretical hydrogen storage capacity (10.5 wt%H₂).Upon heating,LiAlH₄ gradually decomposes according to the following reactions [ 8, 9] ,

Although Reaction (3) can release 2.6 wt%H₂,it is not considered as feasible released hydrogen content because the initial hydrogen desorption temperature of this stage is above 400℃,which is not significant for practical applications.In the following text,the first two dehydrogenation stages were only considered to analyze the dehydrogenation performance of LiAlH₄.

However,the harsh terms for re-/dehydrogenation of LiAlH₄,such as the high thermodynamic stability,poor reversibility and slow desorption kinetics,have severely obstructed its popularization in hydrogen storage systems.In recent years,a great deal of researches have been undertaken to solve this problem,including improving the surface and kinetics by ball milling [ 10, 11] ,reacting with other metal/complex hydride (destabilization system) [ 12, 13, 14, 15] and doping with catalyst [ 3, 4, 5, 16, 17, 18, 19] .Meanwhile,reducing the particle size of hydrides to nanoscale was shown an effective approach to improve their physicochemical properties in the past few years [ 20, 21, 22, 23] .Adding catalyst as one of the most effective ways in improving the dehydrogenation performance of LiAlH₄ has attracted great attentions in the past years.Recently,a study by Rangsunvigit et al. [ 24] presents that carbon aerogels (CAs) have significant effects on the hydrogen desorption behavior of LiAlH₄.Rafi et al. [ 18] reported the superior catalytic effects of nano-sized TiC on enhancing the hydrogen storage properties of LiAlH₄.Theoretically,thermodynamic constraints of reversibility will make NaAlH₄ a more promising hydrogen storage material for onboard application,compared with LiAlH₄ and Mg(AlH₄)₂ [ 25, 26] .Nevertheless,recent study proved that the re-/dehydrogenation can be improved simultaneously through doping [ 26, 27, 28, 29] ,e.g.,partial reversibility was realized under the conditions of 9.5×10⁶ Pa H₂ and 165℃by doping nano-sized TiC catalyst [ 18] and the dehydrogenated LiAlH₄+TiCl₃ sample (LiH+Al) can be partially recharged to LiAlH₄ in low-boiling dimethyl ether under1×10⁷ Pa H₂ pressure even at room temperature [ 30, 31] .Kojima et al. [ 32] investigated the catalytic effects of TiCl₃,ZrCl₄,VCl₃,NiCl₂ and ZnCl₂ separately and established their catalytic activity in the following order:TiCl₃>ZrCl₄>VCl₃>NiCl₂>ZnCl₂;meanwhile,LiAlH₄ reacted with the transition metal chlorides ZrCl₄ with various byproducts (Al₃Zr,Al,LiCl and H₂) generated.Under this background,ZrC exhibits the prominent potential as a catalyst to advance the hydrogen storage properties of LiAlH₄.To the best knowledge,few studies have been reported on LiAlH₄ doped with ZrC catalyst.

In this study,the dehydrogenation properties of ZrC-doped LiAlH₄ by different mixing processes were investigated by utilizing a pressure-composition-temperature(PCT) apparatus,thermogravimetry (TG) and differential scanning calorimetry (DSC).The catalytic mechanism wasalso demonstrated.

2 Experimental

2.1 Reagents and sample preparation

All the raw materials were obtained commercially.LiAlH₄(≥93%pure,Alfa-Aesar) was mixed with ZrC powder(≥99%,～3μm,Sigma Aldrich Co.) in a glove box filled with high-purity Ar in order to avoid oxidation and moisture.In order to obtain optimal distributions of catalyst and crystallite size of LiAlH₄,perse preparation methods were adopted.All the samples with and without ZrC powder were prepared and the doping conditions are listed in Table 1.For the S3-S6 and S8-S9 samples,LiAlH₄ (typically 1.5 g) was mixed with designed mole fractions of ZrC powder,and then,these mixtures were loaded into stainless milling vials (5 cm in diameter,quenching) with identical ball-to-powder weight ratio of 20:1.Subsequently,ball milling was carried out in a high-energy Spex (QM-3B) mill at a rotating rate of1200 r·min^-1 for different time.After every 10 min of milling,the 5-min delay was introduced for cooling the samples.

2.2 Characterization

The dehydrogenation measurements were made in a Sieverts-type PCT equipment (General Research Institute Nonferrous Metal,Beijing,China).The details of the apparatus are given in previous researches [ 19, 33] .About0.4 g of sample was loaded into a sample vessel in the glove box and then heated to 300℃at 5℃·min^-1 under a vacuum condition.All the temperature-pressure and timepressure data were documented,and the curves for the dehydrogenation process were drawn by Origin software(Origin 8.0).During the heating process,the desorption amounts and temperature data for all samples were documented,and then,the values were converted for pure LiAlH₄ with the elimination of various impurities;the detailed calculation formula is as follows:

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Table 1 Preparation conditions of samples for dehydrogenation properties test

whereφ_mat represents dehydrogenation rate, is H₂mass,m_d is the mass of doped material,and m_c is the mass of catalyst.In the meanwhile,all the values in wt%are talking about in the present study on materials basis [ 5] .

The synchronous differential scanning calorimetry/thermogravimetry (DSC/TG,NETZSCH ST A 449C) measurements were taken a under a high-purity (99.99%) Ar flow of50 ml·min^-1.About 5 mg of sample was loaded into an alumina crucible in the glove box.Heating runs were performed at the heating rate of 6 K·min^-1 from 35 to 300℃,respectively.The microstructure was examined by a field emission scanning electron microscope (FESEM,FESEM-6301F).The as-prepared samples were dispersed on conductive adhesive supported by an aluminum block,and the preparation process was carried out inside the glove box and then transferred into the FESEM chamber using a seal box.Fourier transform infrared spectroscopy (FTIR) analyses of the pure and doped samples were conducted using a Bruker Vector 22 FTIR spectrometer.The FTIR spectra were recorded from 750 to 2000 cm^-1 with a spectral resolution of4 cm^-1.XRD analysis was performed on an X-ray diffractometer (XRD,MXP21VAHF) with Cu Kαradiation,40 kV,200 mA at room temperature.The X-ray intensity was tested over the 2θangle ranging from 10℃to 80°with a scanning velocity of 0.02°per step.X-ray photoelectron spectroscopy(XPS) experiments were made on an ultra-high vacuum(UHV) chamber with the base pressure of 3×10^-13 MPa,equipped with a PerkinElmer PHI-5300 XPS spectrometer.

3 Results and discussion

3.1 Hydrogen storage performance

Figure 1a presents the non-isothermal dehydrogenation results for S1-S6 samples after high-energy ball milling(HEM) for 60 min.The two plateau regions correspond to the dehydrogenation reactions (Reactions (1) and (2)).It is clear that the dehydrogenation of LiAlH₄ is significantly enhanced through doping ZrC powder.For S1 sample,it starts to desorb H₂ at about 172.3 and 234.1℃for the first two stages with 6.61 wt%hydrogen released.Meanwhile,the onset dehydrogenation temperature of S2 sample shows a slight decrease by 42.5 and 35.6℃without any reduction in the dehydrogenation amount.All the ZrC-doped LiAlH₄ samples (S3-S6) initiate their dehydrogenation process at 118.9,110.0,96.0 and 85.3℃,while the second stage of those samples starts at 173.6,172.4,167.5 and148.4℃,respectively,which are much lower than those of pure samples (S1 and S2).The results reveal that ZrC powder exhibits superior catalytic effect by reducing the onset dehydrogenation temperature without loss of hydrogen content.Moreover,the relatively high ZrC addition level could cause catalytic effect more efficiently.

Figure 1b shows the thermal desorption performances of S1,S2,S5,S7-S9 samples.As can be seen in Fig.1b,the first two desorption stages of S7 sample initiate at 129.8and 198.5℃,respectively,which reduce by 23.1 and16.0℃compared with that of the as-milled LiAlH₄,indicating that ZrC powder could facilitate the decomposition process of LiAlH₄ just by hand-shaking mixing(SM).The onset desorption temperatures (Reactions (1)and (2)) of S5,S8 and S9 samples are all around 104.3 and160.7℃with infinitesimally small difference,illustrating that only 0.5-h ball milling could make the excellent catalytic effect for the 5 mol%ZrC-doped hydrogen storage materials.This phenomenon could be explained by the fact that the distribution of catalyst and the amount of the surface defect could reach maximum attainable level after milling for 30 min.However,the reversibility of dehydrogenated S5 sample cannot be observed under 8.0 MPa H₂ at 150,200 and 250℃,respectively.So,the possible way of improving the low formation enthalpy of LiAlH₄ [ 34] will be further investigated in our further work.

Fig.1 Non-isothermal dehydrogenation profiles of S1-S6 samples a and thermal desorption profiles of S1,S2,S5,S7-S9 samples b

3.2 Dehydrogenation kinetics investigation

In order to analyze the kinetics of dehydrogenation of pure and ZrC-doped LiAlH₄,the isothermal dehydrogenation performances of S1,S3,S4 and S5 samples were measured.As can be seen in Fig.2,the curves for the doped samples show a two-step decomposition feature (StagesⅠandⅡ)corresponding to the two reaction stages of LiAlH₄.Figure 2a displays the isothermal dehydriding kinetics measurements of S1 sample at 145℃and S5 sample at 115,130and 145℃.Within 180 min,the dehydrogenation capacities of the LiAlH₄/ZrC composite at 115,130 and 145℃are4.08 wt%,5.48 wt%and 5.62 wt%,respectively.In contrast,the as-received LiAlH₄ exhibits poor desorption kinetic with only 1.39 wt%H₂ released at 145℃for 180 min.Consequently,the LiAlH₄ presents considerable dehydrogenation kinetics improvement by adding 5 mol%ZrC powder,compared with pristine LiAlH₄.Figure 2b shows the isothermal dehydrogenation kinetics of S1,S3,S4 and S5samples at 130℃.It can be seen that adding 1 mol%,2 mol%and 5 mol%ZrC cause LiAlH₄ to release as much as4.27 wt%,4.57 wt%and 5.48 wt%H₂ within 3 h at 130℃,indicating the increasing improvement in the desorption kinetics of LiAlH₄ with catalyst amount increasing.Therefore,the dehydrogenation kinetics of pure LiAlH₄ could be significantly improved by adding ZrC powder.

The data of isothermal dehydrogenation of S5 sample at115,130 and 145℃were further analyzed by JohnsonMehl-Avrami-Kologoromov (JMAK) theory [ 35, 36, 37] upon the first-order reaction.

where t is the time,αis the percent conversion of LiAlH4 at the time of t,k is the reaction rate constant,and n is the Avrami index.The variables t andαare based on the isothermal dehydrogenation kinetics of S5 sample at 115,130 and 145℃.The linear fitted curves of the typical master plots ln[-ln(1-α)]versus lnt are shown in Fig.2c,d,which yields the values of n and k.Table 2 gives the reaction constant and Avrami index of the first two dehydrogenation stages which are calculated from the linear plots in Fig.2c,d.As can be seen in Table 2,the reaction rate constant of the first two desorption stages increases gradually,while the Avrami index of the first stage is between 2.16 and 2.36 when temperature increases from 115 to 145℃,indicating that the hydrogendesorption process of Reaction (1) is controlled by diffusion mechanism with nucleation rate gradually decreasing within this temperature range.In the meanwhile,the Avrami index of Reaction (2) is below0.5,signifying that this dehydrogenation stage is a freedom nucleation and the subsequent growth process at the temperature range of 115-145℃.Analyzing the isothermal dehydrogenation kinetics of as-received LiAlH₄ at 145℃,its kinetic model corresponds to the Mampel unimolecular law formulated through random nucleation [ 18] :

Fig.2 Isothermal dehydrogenation kinetics of samples:a S1 sample at 145℃and S5 sample at 115,130 and 145℃;b S1,S3,S4 and S5samples at 130℃;linear fitted curves of the first two dehydrogenation stages of S5 sample at 115,130 and 145℃:c StageⅠand d StageⅡ

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Table 2 Reaction constant (k) and Avrami index (n) of the first two dehydrogenation stages based on isothermal dehydrogenation kinetics of S5 sample at 115,130 and 145℃

From the above analyses,the desorption process of asreceived LiAlH₄ was controlled mainly by random nucleation,while the diffusion rate limitations predominate over random nucleation through doping ZrC particles.The results clearly indicate that the doped ZrC particles act as nucleation site during the decomposition process.

3.3 Thermal analysis

Figure 3a presents the DSC curves of pure LiAlH₄ (S1 and S2) and LiAlH₄+5 mol%ZrC (S5) composite.It is obvious that the DSC curve of as-received LiAlH₄ includes four characteristic peaks:two endothermic peaks and two exothermic peaks.On the basis of the order of rising temperature,the peaks correspond to the interaction of LiAlH₄ with surface hydroxyl impurities,melt of LiAlH₄ [ 38] ,decomposition of liquid LiAlH₄ (Reaction (1)) and decomposition of Li₃AlH₆ (Reaction (2)) [ 39] ,respectively.However,the situation changes if the pure LiAlH₄was ball-milled under the high-energy mode for 60 min,i.e.,the exothermic peak disappears,attributing to the fact that the decomposition of LiAlH₄ in the phase boundary occurs before its reaction with surface hydroxyl impurities.Combined with TG results,the peaks (exothermic and the second endothermic peaks) locating at 143.2 and 216.2℃

correspond to the first two decomposition processes,respectively.The first endothermic peak,which is inconspicuous in the curve,indicates the melting of the undecomposed LiAlH₄.For S5 sample,the number of thermal peak is reduced to only two.The first thermal event starts at97.6℃followed with an exothermic peak at 127.8℃and the second one initiates at 161.8℃followed with an endothermic peak at 195.6℃,which correspond to the decomposition process of solid-state LiAlH₄ and Li₃AlH₆,respectively [ 3, 27, 34, 40, 41, 42] .This phenomenon could be explained that the decomposition reaction occurs on the surface prior to the reaction with surface hydroxyl impurities and without LiAlH₄ left at the melting point.

For the purpose of further investigating the thermal decomposition properties of LiAlH₄ with and without catalyst,Fig.3b,c presents TG and its corresponding derivative (dTG) profiles of S1,S2 and S5 samples within the temperature range of 35-300℃at a heating rate of5℃.min^-1.It is clear that the samples present a distinguished two-stage dehydrogenation feature within this temperature range.Through simultaneously analyzing TG and dTG profiles,the S1,S2 and S5 samples begin to lose weights at 153.0,130.6 and 92.7℃for the first stage,respectively.Then weight lose in the second stage starts at226.1,186.0 and 162.5℃,respectively.During the first two stages,the weights lose of the three samples are7.94 wt%,7.34 wt%and 7.15 wt%,respectively.The onset dehydrogenation temperature measured by DSC is slightly lower than that tested by PCT,which is on account of the different dehydrogenation atmosphere and heating rate for the tested samples [ 42] .

Fig.3 DSC profiles a,TG profiles b and dTG profiles c of Sl,S2 and S5 samples within temperature range of 35-300℃at heating rate of3℃min^-1

3.4 Catalytic mechanism

SEM images shown in Fig.4 provide information on particle shape and their distribution.The particles of the asreceived LiAlH₄ show irregular surface profile.However,the shape of as-milled LiAlH₄ changes into regular globular particles and their particle size reduces from～40 to～15-20μm.Figure 4c and e presents the SEM images of S7 and S5 samples,respectively.Microscopically,the two doped samples have uneven surface and the initial particles break into smaller particles (～10-15μm).Figure 4d,f shows the FESEM images of LiAlH₄+5 mol%ZrC after hand-shaking and mechanical ball milling,respectively.It is discernible in the micrographs that ZrC particles have different distribution between the two samples.For S7sample,the catalyst particles seem to be distributed randomly and numerous isolated granules exist with absolutely no adhesion on the LiAlH₄ particles.In contrast,the ZrC particles are on the surface or embed in the LiAlH₄matrix with a more homogeneous distribution,indicating that substantial surface modifications have occurred after ball milling doped with ZrC.From the above analyses on microstructure,it is reasonable to conclude that numerous of surface defects and high density of embedded catalyst particles are created on the LiAlH₄ particles,which can introduce a large amount of reaction nucleation sites and hydrogen diffusion channels for the dehydrogenation process,contributing to the improvement in the hydrogen desorption performance of LiAlH₄.

In order to further determine the phase transition of LiAlH₄ during the ball milling process,the FTIR measurements of S1,S2,S5,S8 and S9 samples were taken,as shown in Fig.5.As reported in previous studies [ 43, 44] ,the active infrared frequencies (v) of locate in two regions:(1) Li-Al-H bending vibrational modes,v₄ (F2)between 700 and 900 cm^-1,(2) Al-H stretching vibrational modes,v₃ (F2) between 1600 and 1800 cm^-1.Meanwhile,[AlH₆]^3-shows octahedral symmetry with active infrared frequencies between 800 and 900 cm^-1 [ 43, 44] .The spectra in Fig.5 show that the infrared (IR)spectroscopy of as-received LiAlH₄ at around 1774.22 and1648.87 cm^-1 can be ascribed to the v₃ (F2),while the peak at 875.54 cm^-1 corresponds to the v₄ (F2).However,there is a tiny peak at 1432.87 cm^-1 corresponding to the stretching vibrational modes of[AlH₆]^3-,v₃ (F1),indicating that a spot of Li₃AlH₆ exists in as-received sample.Simultaneously,there are four peaks appearing at FTIR spectra of as-milled LiAlH₄ and doped LiAlH₄ samples locating at around 1772.29,1645.01,809.97 and1425.16 cm^-1,respectively.It is obvious that a small shift of the stretching modes to higher frequency is observed due to the strain created [ 43] during ball milling process,which is similar to the result detected by Raman spectroscopy for LiAlH₄ under a static pressure at around 5 GPa [ 45] .

When LiAlH4 was milled for a short time,a small shift(20 cm^-1) of the stretching modes to high frequencies is also observed.This shift may be related to the strain created during milling because a similar shift is observed by Raman spectroscopy for LiAlH₄ under a static pressure(5 GPa),which is in good agreement with the one expected during mechanical milling.Table 3 lists the FTIR active infrared frequencies of S1,S2,S8,S5 and S9 samples.It is clear that the active infrared frequencies of LiAlH₄+5-mol%ZrC samples after ball milling for 0.5,1.0 and 1.5 h shift to higher frequencies compared with that of as-received LiAlH₄.There is not a positive correlation between the shifted wave numbers and the time of ball milling.Meanwhile,there is no further redshift trend presented for the doped LiAlH₄ samples,compared with the as-milled sample.In addition,the intensity of v₃(F1) at around1430 cm^-1 becomes stronger with ZrC particles added,which could be ascribed to the increase in amount of Al-H stretching mode of Li₃AlH₆.Through the above analysis,it is reasonable to conclude that the stability of Al-H bond and Li-Al-H bonds of LiAlH₄ could be decreased by highenergy ball milling.However,this effect reaches the maximum value when ball milling for 0.5 h without any further improvement by increasing milling time.Meanwhile,samples incur partial dehydrogenation and form Li₃AlH₆ during the ball milling process.

Fig.4 SEM images of a Sl,b S2,c S7 and e S5 samples and corresponding FESEM images of d S7 and f S5 samples

Fig.5 FTIR spectra of S1,S2,S8,S5 and S9 samples

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Table 3 FTIR active infrared frequency of S1,S2,S5,S8 and S9samples (cm^-1)

Figures 6 and 7 present XRD patterns of S1,S2 and S5samples before and after dehydrogenation.For S1 and S2samples shown in Fig.6,all diffraction peaks correspond to LiAlH₄ except for the peaks at 51.53°and 62.73°,which correspond to Li₃AlH₆,and the intensity becomes stronger for S2 sample,indicating that LiAlH₄ decomposes during the ball milling process.After ball-milled with 5 mol%ZrC for 1 h,there are some diffraction peaks at 33.04°,38.34°,55.30°and 65.97°corresponding to ZrC (JCPDS No.35-0784),which demonstrates that ZrC particles remain highly stable without any reaction with LiAlH₄ during ball milling process.After that,XRD scans were performed on S1,S2 and S5 samples after dehydrogenation at 250℃for the purpose to determine the phase change during the desorption process,as shown in Fig.7.For S1 and S2samples,XRD patterns present that the dehydrogenated samples consist of Al and LiH as dehydrogenation products and no additional phases are detected,indicating that LiAlH₄ has completed the first two desorption stages when heated up to 250℃.For S5 sample,the dehydrogenated phases consist of not only Al and LiH but also ZrC,confirming the rather high stability of ZrC even heating up to250℃.ZrC is extremely hard,and it is a thermodynamically more stable compound with a high Zr-C bonding strength,which makes it as a stable and high-efficiency grinding material [ 46, 47] and contributes to the improvement in the dehydrogenation properties of LiAlH₄.

Fig.6 XRD patterns of S1,S2 and S5 samples before dehydrogenation

Fig.7 XRD patterns of S1,S2 and S5 samples after dehydrogenation

4 Conclusion

In summary,the dehydrogenation characteristics of ZrC-doped LiAlH₄ in various doping conditions with pure LiAlH₄ were compared.The dehydrogenation properties of LiAlH₄ are significantly improved by doping with ZrC using high-energy ball milling method,and this effect reaches the maximum value when ball milling for 0.5 h without any further improvement by increasing ball milling time.The stability of Al-H bond and Li-Al-H bonds of LiAlH₄ could be decreased by high-energy ball milling.The highly increased surface defects and high density of embedded ZrC particles were created on the LiAlH₄ particles,which can introduce a large amount of reaction nucleation sites and hydrogen diffusion channels for the dehydrogenation process,contributing to the improvement in the hydrogen desorption performance of LiAlH₄.The desorption process of as-received LiAlH₄ was controlled mainly by random nucleation,while the diffusion rate limitations predominate over random nucleation through doping ZrC particles,which clearly indicates that the doped ZrC particles act as nucleation site during the decomposition process.However,the reversibility of LiAlH₄ is not optimized by doping ZrC powder.

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