硼氢化锂(LiBH4)的储氢性能及机制研究

IMR OpenIR

	硼氢化锂(LiBH4)的储氢性能及机制研究
	方占召
学位类型	博士
导师	成会明 ; 王平
	2011
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	储氢材料硼氢化锂热力学动力学 Hydrogen Storage Material Libh4 Thermodynamics Kinetics
摘要	"配位金属硼氢化物因具有高氢含量而成为当前储氢材料领域的研究热点。本工作选取硼氢化锂(LiBH4)这一颇具代表性的轻金属配位硼氢化物为研究对象，采用调整材料成分、调制纳米结构等多种方法，重点围绕解决LiBH4热力学稳定性过高、反应动力学缓慢等关键问题开展研究，在提高LiBH4及相关体系的储/放氢性能和深化机制认识方面取得了多项积极进展。此外，还采用LiBH4及相关硼氢化物为起始原料成功制备出数个具有优异低温放氢性能的新型氢化物材料。体系成分调整方面： (1) 研究发现：少量添加TiCl3或TiF3均可显著改善LiBH4体系的综合储/放氢性能；相比之下，TiF3的改性效果更佳，其机制在于TiF3的阴/阳离子分别具有改善LiBH4热力学和动力学性能的效果。该研究发现为协调改善LiBH4等配位金属硼氢化物的综合储/放氢性能揭示了一条新途径；(2) 首次制备出了（Li、Ca）双阳离子配位金属硼氢化物，并围绕其热分解行为开展了深入研究；该工作为发展高性能多元硼氢化物储氢材料奠定了实验基础。纳米结构调制方面： (1) 采用球磨法制备了多个LiBH4/C复合材料体系。研究发现：碳材料可有效改善LiBH4的综合储/放氢性能，且其改性效果在很大程度上取决于碳材料的结构；在所研究的碳材料中，制备态单壁纳米碳管（SWNTs）的改性效果最佳，其机制在于纳米结构碳和碳管制备过程中引入的过渡金属纳米颗粒分别具有结构调制和催化作用；(2) 采用化学浸渍方法将LiBH4装填入活性炭纳米孔中。研究结果表明：调制材料纳米相结构，可在大幅度提高LiBH4吸/放氢动力学的同时，改善材料的热力学性质。该实验发现证明了氢化物颗粒纳米化是改善材料储/放氢性能的有效途径。相关材料制备方面： (1) 采用3LiBH4/TiF3计量比混合物为起始原料，原位制得了硼氢化钛Ti(BH4)3，并首次准确表征了其热分解行为和分子动力学特征。该项研究结果为探索过渡金属硼氢化物的储氢应用潜力提供了新的研究思路；(2) 以NaBH4和NH4F为起始原料，采用机械球磨法结合液氨提纯成功制备了硼烷氨化合物（[(NH3)2BH2](BH4)）。该化合物可于温和温度下快速、高容量放氢，是一种颇具储氢应用潜力的新型化学氢化物。上述研究成果为丰富和发展配位金属硼氢化物储氢的基础理论提供了实验依据，同时也将为开展相关含硼氢化物储氢材料研究提供借鉴和指导。"
其他摘要	"Complex borohydrides have recently received considerable interest as potential hydrogen storage media owing to their extremely high hydrogen capacity, among which lithium borohydride (LiBH4) is a leading candidate. Currently, the main obstacle of LiBH4 system is that the reversible dehydrogenation of LiBH4 is greatly restricted by the problematic H-exchange kinetics and thermodynamics. In this work, we mainly focus on addressing these problems via tailoring material composition, modifying particle nanostructure and developing new material systems. Systematic experimental studies have resulted in considerable progresses in both improving the reversible dehydrogenation properties of LiBH4-based hydrogen storage systems and developing better understanding of the underlied reaction mechanisms. Material Composition Tailoring: (1) The reversible dehydrogenation properties of LiBH4 can be markedly improved by mechanically milling with small amounts of TiCl3 or TiF3. Particularly, TiF3 exhibits a superior promoting effect to its analogue TiCl3. Mechanism study shows that the observed promoting effect of TiF3 should be understood from the combined effects of functional cation (Ti2+, kinetic modification) and anion (F-, thermodynamic modification). This finding may lay a new conceptual basis for the design and synthesis of novel hydrogen storage systems with favorable kinetics and thermodynamics. (2) A dual-cation (Li, Ca) borohydride was developed via mechanically milling the 1:1 LiBH4/Ca(BH4)2 mixture and examined with respect to their thermal decomposition behaviors. This finding exemplified the effectiveness of manipulation of dual-cation combination in tuning the de/rehydrogenation properties of ionic light-weight borohydrides. Paticle Nanostructure Modification: (1) Various LiBH4/C composites were prepared via mechanical milling method. Experimental results show that the carbon additives could improve the H-exchange kinetics and H-capacity of LiBH4 to some extent. Mechanism study shows that the observed promoting effect of the carbon additives should be correlated with their viaried structures. Additionally, as-prepared SWNT was found to possess more pronounced promoting effects on the reversible dehydrogenation reactions of LiBH4 due to both the catalytic effect of metal nanoparticles or their borides and the nano-confinement effect of carbon nanotubes. (2) LiBH4 nanoparticles (~2 nm) were readily prepared via being incorporated into an activated carbon (AC) scaffold using a chemical impregnation method. Thus-prepared LiBH4/AC sample was found to significantly improve both the hydrogen sorption kinetics and thermodynamics, compared to the bulk hydride. This finding demonstrates that creating nanophase hydrides using nanoporous scaffolds is a promising route to improve the hydrogen storage properties of LiBH4. Related Materials Preparation: (1) 3LiBH4/TiF3 mixture possessed superior dehydrogenation performance. Mechanism study shows that it should be associated with the in situ formation and rapid decomposition of Ti(BH4)3. This finding shows the potential of transition metal borohydrides for hydrogen storage applications. (2) Mechanically milling a 1:1 NaBH4/NH4F powder mixture, followed by extraction with liquid NH3, provides a simple, efficient, easily practiced and high-yield solid-phase synthesis route of [(NH3)2BH2](BH4) (DADB for short). Furthermore, DADB could discharge hydrogen under moderate temperature conditions, and therefore, is regarded as a potential chemical hydride for hydrogen storage applications. Clearly, these findings have contributed to enhancing H-storage properties of LiBH4 and to deepening the mechanistic understandings of the LiBH4 system. Furthermore, two related borohydride systems with high hydrogen content were developed. These findings may guide the following research efforts on other related borohydride systems."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64279
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	方占召. 硼氢化锂(LiBH4)的储氢性能及机制研究[D]. 北京. 中国科学院金属研究所,2011.