石墨烯催化稀土—镁—铝基复合储氢材料动力学及热力学研究

Metal magnesium and magnesium-based alloys have advantages of high hydrogen storage capacity and low raw material cost, which are considered as the most potential materials for on-board hydrogen storage field. However, the poor kinetics and high hydrogen desorption temperature of MgH2 have been restricting its application. Our previous studies show that the hydriding/dehydriding kinetics and thermodynamics can be improved to some extent by melting Mg with Al and RE or milling the Mg-Al alloys with grapheme, however, its mechanism is yet to be further investigated. Therefore, in this project, we will intend to prepare the RE-Mg-Al-based ternary or multicomponent alloys through vacuum induction melting. And then the RE-Mg-Al-based alloys were mechanical milled with grapheme for preparing the nanocrystalline composite hydrogen storage materials with good kinetic performance and low decomposing temperature of the hydrides. The effects of the contents of RE and Al and the technology parameters of vacuum induction melting and mechanical milling on the Mg(Al) solid solution, RE-Mg, Mg-Al and RE-Al intermetallic compounds and microstructure will be further investigated. The phase changes in the hydriding/dehydriding processes will be explored and the hydriding/dehydriding reaction paths will be build. Illuminating the improvement mechanism of hydriding/dehydriding kinetics and thermodynamics of the RE-Mg-Al-based composite hydrogen storage materials catalyzed by grapheme. It provides the theory basis for preparing the Mg-based hydrogen storage alloy with excellent hydrogen absorption and desorption performances.

金属镁及其合金吸氢量大、成本低廉，是最具潜力的车载储氢材料。但极差的动力学性能和较高的放氢温度限制了其实际应用。我们前期研究证实，通过将金属镁与铝、稀土元素合金化，以及与纳米石墨粉混合球磨对镁基合金吸放氢动力学及热力学性能有一定的改善作用，但其机理尚待进一步研究。在此基础上，本项目拟先通过真空感应熔炼制备高镁含量的稀土—镁—铝三元或多元合金。然后将稀土—镁—铝合金与石墨烯混合球磨，制备具有优异动力学性能并且氢化物稳定性较低的纳米晶储氢复合材料。深入研究稀土元素、金属铝含量以及熔炼+球磨工艺对Mg(Al)固溶体，稀土—镁、镁—铝和稀土—铝金属间化合物及微观结构的影响。探索吸放氢过程中各相的变化，并构建吸放氢反应路径。阐明石墨烯催化的RE-Mg-Al复合储氢材料动力学及热力学改善机理。为制备具有优异吸放氢性能的镁基贮氢合金提供理论依据。

金属镁及其合金吸氢量大、成本低廉，是最具潜力的车载储氢材料。但极差的动力学性能和较高的放氢温度限制了其实际应用。通过将金属镁与铝、稀土元素合金化，以及与纳米石墨粉混合球磨对镁基合金吸放氢动力学及热力学性能有一定的改善作用。本项目通过真空感应熔炼制备高镁含量的稀土-镁-铝三元或多元合金。然后将合金与石墨烯混合球磨，制备具有优异动力学性能并且氢化物稳定性较低的纳米晶储氢材料，详细研究了其储氢性能。适量A1与Mg合金化能明显改善合金的储氢动力学，归因于合金内部包括Mg相、Mg17Al12相和Mg2A13相在内的多相结构的生成。但过量的Al反而不利，因为随着A1含量增加，合金中Mg17Al12相的晶粒尺寸增加，晶界数量减少，氢原子的扩散通道随之减少。Mg100-yAly (y = 10、20、30、40)合金的放氢活化能(Edea)分别为157.65、159.12、169.07、169.58 kJ/mol。NdxMg90-xAl10 (x = 2、5、8、10)合金的Edea值分别为117.24、81.03、79.01和78.12 kJ/mol。脱氢动力学改善与晶界数目的增加和Mg相体积的减小有关。Mg95-xAl5Yx (x = 0-5)合金的Edea值从155.562降低到79.622 kJ/mol，初始分解温度降低40.2 K。球磨合金为纳米晶结构，主要由Mg相和Al相或Mg17Al12相组成。具有多孔片层结构的催化剂Tm@C (Tm= Fe、Co、Cu)对球磨Mg-Al-Y合金的储氢性能具有显著的提高。主要归因于这几个方面：提高球磨效率和合金颗粒/晶粒细化；引入大量的缺陷(活性位点)；负载的过渡金属(具有高电负性和多价性)或其衍生物纳米颗粒。Mg91Al5Y4 + Fe@C (0、2、5、8 wt.%)复合材料随着Fe@C含量从0增加到8 wt.%，Edea从92.23降低到84.51 kJ/mol。.通过对本项目研究，掌握了高镁含量稀土-镁-铝+石墨烯的纳米晶储氢复合材料的制备方法，探讨了稀土元素、金属铝含量以及球磨工艺对Mg(Al)固溶体，稀土-镁、镁-铝和稀土-铝金属间化合物及微观结构的影响，以及吸放氢过程中各相的变化，并构建吸放氢反应路径。阐明了石墨烯催化的RE-Mg-Al复合储氢材料动力学及热力学改善机理。为制备优异吸放氢性能的镁基储氢合金提供理论依据。