Ti-Cr-Mn-Fe-based alloys optimized by orthogonal experiment for 85 MPa hydrogen compression materials

https://doi.org/10.1016/j.jallcom.2021.161791Get rights and content

Highlights

  • The effect of Ti, Mn, and Fe on hydrogen storage performance was systematically investigated by orthogonal analysis.

  • Ti-Cr-Mn-Fe-based alloys were developed for the final-stage hydrogen compression.

  • Ti1.08Cr1.3Mn0.2Fe0.5 exhibits a theoretical dehydrogenation pressure over 85 MPa below 373 K.

Abstract

The development of hydrogen storage alloys possessing high plateau pressures for three-stage metal hydride hydrogen compressors (MHHCs), is critically significant for the safe and high-efficiency re-/charging of H2 in hydrogen refueling stations (HRSs). Herein, Ti-Cr-Mn-Fe-based alloys (Ti1.04+xCr2−y-zMnyFez, x = 0.02, 0.04, 0.06, y = 0.2, 0.3, 0.4, z = 0.5, 0.6, 0.7) synthesized by vacuum arc melting, with the single structure of C14 Laves and uniform element distribution, enable the final-stage compression units up to 85 MPa for MHHCs. It is demonstrated that both unit cell volume and maximum hydrogen capacity (Cmax) increase by the rising amount of Ti or decreasing Mn and Fe in the Ti-Cr-Mn-Fe-based alloys, whereas the dissociation pressures and plateau hysteresis (Hf) at 223 K are reduced correspondingly, according to the orthogonal results. Meanwhile, as the over-stoichiometric amount of Ti increases, so does the plateau slope (Sf) of the Ti-Cr-Mn-Fe-based alloys. Under the optimized conditions conducted by the orthogonal results, Ti1.08Cr1.3Mn0.2Fe0.5 exhibits comprehensively considerable hydrogen absorption/desorption properties, rendering it possible to be one of the most promising final-stage compression materials. Notably, the dehydrogenation enthalpy and entropy for Ti1.08Cr1.3Mn0.2Fe0.5 is determined to be 22.3 ± 0.3 kJ/mol and 117.8 ± 1.0 J/(mol K), respectively, with a corresponding hydrogen absorption pressure of 14.00 ± 0.52 MPa at 298 K and a dehydriding pressure of 89.19 ± 3.21 MPa at 363 K. Furthermore, the values of Cmax, Hf,andSf are evaluated as 1.83 ± 0.01 wt%, 0.33 ± 0.01, and 0.72 ± 0.03, respectively, at 223 K.

Introduction

Continuously rising concerns over the dwindling resources of conventional energy and the environmental issues of burning fossil fuels have promoted great efforts on the development of hydrogen fuel cell vehicles (HFCVs) powered by clean and renewable hydrogen energy [1], [2], [3], [4], [5], [6], [7]. To ensure a sufficient energy supply for long-distance transport of HFCVs, the state-of-the-art 70 MPa hydrogen tank proposed by Toyota [8], possesses a hydrogen density of 5.7 wt%. Therefore, the development of efficient hydrogen compressors with reliable safety and ultrahigh output pressure will be of crucial importance to construct hydrogen refueling stations (HRSs) [4], [9], [10], [11], [12], [13].

In 1970, Wiswall and Reilly firstly proposed a metal hydride hydrogen compressor (MHHC) using TiFe alloy as the hydrogen compression material [14]. MHHCs possess numerous advantages that merit their hydrogen storage applications, including reliable safety, environmental friendliness, high-efficiency hydrogen purification, and low maintenance costs [15], [16], as opposed to the traditional mechanical hydrogen compressors in most in-service HRSs. The wide application of MHHCs is, however, restricted by the high operating temperatures and low dehydrogenation pressure of the hydrogen compression materials. A schematic representation of the proposed three-stage MHHC is shown in Fig. 1, which is composed of high-density hydrogen storage units and three kinds of hydrogen compression materials. Not only can the integrated system theoretically release H2 above 85 MPa below 373 K (100 ℃) with the circulating water acting as a heat transfer medium, but also it meets the demands of pressurization for each stage. In this case, the primary, intermediate, and final stages enable long tube trailers, hydrogen fuel cell busses, and cars to be effectively charged with hydrogen, respectively [17], [18].

Concerning the third stage of the MMHC, the final-stage hydrogen compression materials are required to compress H2 from 40 MPa to 85 MPa below 373 K (100 ℃). TiCr2 was first studied by Brookhaven National Laboratory in 1978 [19], [20], [21], revealing that it had three allotropes, namely the MgZn2 phase of hexagonal structure (C14), the MgCu2 phase of cubic structure (C15), and the MgNi2 phase of hexagonal structure (C36) [22]. As early as 1980, Johnson et al. [20] observed that two plateau pressures occurred in the PCI curve of TiCr1.9 with C14 structure at − 78 ℃, and the alloy only possessed a single plateau with the temperature rising. In comparison with conventional LaNi5, TiCr2 holds a much larger capacity and higher equilibrium pressure, rendering it promising in the field of high-pressure hydrogen compression. The enhancement of hydrogen storage properties for TiCr2 can often be achieved by alloying and non-stoichiometric ratio. For example, the substitution upon the A-side of TiCr2 with Zr [23] or Sc [24] can improve its activation performance and hydrogen capacity. On the other hand, the partial substitution of the B-side with V [25], [26], [27], Mn [28], Fe [29], [30], [31], [32], [33], W [34], or Mo [25] can tune the plateau pressure, which is realized by adjusting the relationship between elastic modulus and unit cell volume [28], [35]. Furthermore, elements Mn and Fe are often used in the substitution of partial Cr to increase the plateau pressures on the premise of holding a considerable capacity for TiCr2-based alloys, due to their smaller atomic radius than chromium [29], [36]. Corgnale et al. [37] designed a two-stage hybrid compressor with a compression ratio of 45, where Ti1.1CrMn could release 45 MPa hydrogen at 413 K. Wang et al. [38], [39] reported that both (Ti0.97Zr0.03)1.1Cr1.6Mn0.4 and Ti1.1Cr1.5Mn0.4V0.1 alloys held a dehydrogenation pressure over 45 MPa below 373 K as well as a considerable hydrogen capacity when serving as the second stage of compressors. Li et al. [40], [41] demonstrated that the dehydrogenation pressure of a double-stage MHHC employing Ti0.8Zr0.2Cr0.95Fe0.95V0.1 alloy was up to 74.5 MPa at 423 K. Under the nearly same temperature (430 K), the desorption pressure of TiCr1.55Mn0.2Fe0.2 prepared by Guo et al. [42] could reach 100 MPa according to Van’t Hoff equation. Also, orthogonal analysis was utilized in the optimization of Ti-Zr-Cr-Fe-based alloys by Li et al. [43], where (Ti0.85Zr0.15)1.05Cr1.1Fe0.9 could theoretically release 45.5 MPa hydrogen at 363 K with usable capacities of 1.4 wt%. Though great progress has been made in hydrogen compression materials, the output pressures of in-service MHHCs are still too low (< 85 MPa) below 373 K, which makes them unsuitable for the practical application in final-stage units.

Notably, some Ti-Cr-Mn-Fe-based alloys, generally used for high-pressure hybrid hydrogen vessels, may satisfy the pressure requirement of the final stage. Chen and Li et al. [29], [30], [31], [32] synthesized a series of Tix(CrMnFe)2 alloys, and they found that the component (Ti, Mn, and Fe) showed a marked effect on the hydrogen storage properties of the alloys, giving rise to a theoretical dehydrogenation pressure of 85 MPa at 341 K for TiCr1.1Mn0.3Fe0.6. Moreover, Yao et al. [44] proposed that the addition of rare-earth elements (La, Ce, Ho) toward Ti1.02Cr1.1Mn0.3Fe0.6 could improve its activation performance. Liu et al. [45] reported that the plateau slope of Ti1.02Cr1.1Mn0.3Fe0.6 could be significantly relieved after annealing treatment under 1123 K for 5 h. To the best of our knowledge, however, there have hitherto been no explorations on an 85 MPa three-stage MHHC below 373 K, with Ti-Cr-Mn-Fe-based alloys used as the hydrogen compression materials. Herein, we systematically investigated the microstructure and hydrogen storage performance of the Ti-Cr-Mn-Fe-based alloys, especially focusing on the effect of substituting Cr by Mn and Fe and the over-stoichiometric ratio of Ti, according to an orthogonal experiment. Under the optimized conditions predicted by orthogonal analysis, as-received Ti1.08Cr1.3Mn0.2Fe0.5 showed the best overall hydrogen properties, thus making it possible to be one of the promising final-stage compression materials.

Section snippets

Composition design

In this work, the specific composition of Ti1.04+xCr2−y-zMnyFez was determined by three-factor and three-level orthogonal experiments. The parameter settings of the three factors and three levels are shown in Table S1, which lists three main factors, namely the contents of Ti, Mn, and Fe (marked as A, B, and C, respectively), and three levels representatively based on previous studies [29], [30]. Table S2 presents the compositions of nine samples simplified by an orthogonal table.

Sample preparation

Alloy ingots

Structure characterization

Rietveld refinements of the XRD patterns for the Ti-Cr-Mn-Fe-based alloys before and after PCI measurement are shown in Fig. 2 and Fig. S1, respectively. The structure of the as-prepared alloys is determined as the single phase of C14-type Laves (space group P63/mmc, No. 194), indicating that Mn and Fe successfully occupy the site of partial Cr with the phase structure being unchanged for the TiCr2 matrix [29], [30], [42]. Moreover, the single-phase structure after dehydrogenation displays that

Conclusion

In summary, the effects of Ti, Mn and Fe on the crystallographic characteristics and hydrogen storage properties of Ti1.04+xCr2−y-zMnyFez (x = 0.02, 0.04, 0.06, y = 0.2, 0.3, 0.4, z = 0.5, 0.6, 0.7) have been investigated by orthogonal experiment in this work. A single C14 Laves structure and a uniform element distribution could be obtained for all prepared alloys. With the increase of over-stoichiometric Ti and the decrease of substitution amount of Mn and Fe toward Cr, the unit cell volumes (V

CRediT authorship contribution statement

Zhuoya Peng: Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing – original draft. Quan Li: Methodology, Validation, Investigation. Jiangyong Sun: Writing – review & editing, Supervision. Kang Chen: Writing – review & editing. Wenbin Jiang: Resources, Methodology. Hui Wang: Project administration. Jiangwen Liu: Visualization. Liuzhang Ouyang: Conceptualization, Funding acquisition, Supervision. Min Zhu: Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was financially supported by the National Key Research and Development Program of China (No. 2019YFB1505101), National Natural Science Foundation of China Projects (No. 51771075), the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No. NSFC51621001) and the Project Supported by Natural Science Foundation of Guangdong Province of China (2016A030312011).

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