Li-Al-B-H复合储氢材料的制备及储氢性能研究

Preparation and Hydrogen Storage Propertiesof Li-Al-B-H Composites

硼氢化锂(LiBH_(4))的有效储氢密度可达13.6%(质量分数,下同),是一种具有潜在应用前景的储氢材料。但是,LiBH_(4)的热力学稳定性高,导致其吸放氢温度高,且其吸放氢动力学差,可逆条件苛刻,严重限制了其实际应用。针对这些问题,以普通Al粉(记为“Al”)和纳米Al粉(记为“nano-Al”)作为改性添加剂,采用机械球磨法制备了LiBH_(4)+0.5Al和LiBH_(4)+0.5nano-Al(物质的量之比)这2种Li-Al-B-H复合储氢材料,并通过X射线衍射(XRD)、吸放氢测试、热分析等手段研究了2种Al粉制备的Li-Al-B-H复合储氢材料的微结构和放氢性能。放氢性能研究表明,添加Al后,LiBH_(4)的放氢温度得到降低,且以纳米Al粉构建的Li-Al-B-H复合储氢材料具有比以普通Al粉构建的Li-Al-B-H复合储氢材料更优异的放氢性能和循环性能。放氢产物微结构研究表明,在放氢过程中,LiBH_(4)会与Al发生反应生成AlB_(2)和Li-Al-B相,这是LiBH_(4)吸放氢性能提高的关键。另外,由于纳米Al的颗粒尺寸小,比表面积大,反应界面更多,使得LiBH_(4)+0.5nano-Al放氢后生成的AlB_(2)和Li-Al-B相的量比LiBH_(4)+0.5Al更多,这是LiBH_(4)+0.5nano-Al放氢性能优于LiBH_(4)+0.5Al的原因。研究结果将为进一步理解Li-Al-B-H复合储氢材料的储氢性能和储氢机理提供参考。

Lithium borohydride(LiBH_(4)) is a promising hydrogen storage material due to its large effective hydrogen storage capacity of 13.6wt%. However, the high thermodynamic stability resulting in high hydrogen absorption and desorption temperature, poor hydrogen absorption and desorption kinetics, and harsh reversibility conditions seriously limit its practical application. In response to these problems, two kinds of Li-Al-B-H composites(LiBH_(4)+0.5Al and LiBH_(4)+0.5nano-Al) were prepared by mechanical ball milling method using ordinary Al powder(written as “Al”) and nanoscale Al powder(written as “nano-Al”) as modification additives. The microstructures and hydrogen desorption properties of the Li-Al-B-H composites prepared with different Al powders were studied by means of X-ray diffraction(XRD), scanning electron microscopy(SEM), hydrogen absorption and desorption tests, and thermal analysis. The hydrogen desorption performance study shows that the hydrogen desorption temperature of LiBH_(4)is reduced after adding Al, and the L-Al-B-H composite constructed with nano-Al has better hydrogen releasing performance and cycling performance than the Li-Al-B-H composite constructed with ordinary Al powder. The microstructure study of the hydrogen desorption product shows that during the hydrogen desorption process, LiBH_(4)reacts with Al to form AlB_(2)and Li-Al-B phases, which is the key to the improvement of the hydrogen absorption and desorption performance of LiBH_(4). In addition, due to the smaller particle size, the nano-Al has larger specific surface area and more reaction interfaces, which leads to that the amount of AlB_(2)and Li-Al-B phases generated after LiBH_(4)+0.5nano-Al dehydrogenation is more than that of LiBH_(4)+0.5Al. This is the reason why the hydrogen releasing performance of LiBH_(4)+0.5nano-Al is better than that of LiBH_(4)+0.5Al. This work provides an important reference for further understanding the hydrogen storage performance and hydrogen storage mechanism of Li-Al-B-H hydrogen storage materials.