金属硼氢化物中纳米催化相和约束碳原位引入对其储氢性能的影响及其作用机理研究

Metal borohydrides possess high hydrogen storage density. They are a type of highly potential hydrogen storage materials of fuel cells for vehicles. However, their hydrogen desorption/absorption temperatures are comparatively high and their reversibility is low. Present enhancement on their hydrogen storage properties is limited and the mechanism of the hydrogen storage processes is not clear yet. Related recent work of the present applicant shows that a new structure of porous morphology and in situ formed nano-TiO2, which improves evidently the hydrogen storage of calcium borohydride, is formed, when Ti(OEt)4 is introduced combining a heat treatment. Based on our previous related research work, liquid metal organic compounds are proposed to be introduced in metal borohydrides in the present proposal, which aims to form nano-catalysts in situ in the borohydrides, and to form a porous structure in the borohydrides. Moreover, a thermal solvent reaction method is combined to in situ introduce carbon scaffold in order to confine the borohydrides into nano-size. Metal borohydride composites with porous structure, nano-catalysts in situ formed, nano-size confined borohydride, which possess high hydrogen storage capacity, superior kinetics and favorable reversibility, are expected to be obtained. Correlation between phase composition, structure, morphology and hydrogen storage properties of the borohydride composites are going to be systematically investigated. Effect and mechanism of the nano-catalysts, the confinement of borohydride to nano-size and the porous structure on the hydrogen storage properties of the borohydrides are expected to be revealed. The developed metal borohydride materials, their fabrication technology, the mechanism and theories of the hydrogen desorption/absorption processes, which are expected to be achieved in the work of the project, are hopefully able to provide novel approaches and theories for the further investigation and development of hydrogen storage materials with high capacity.

金属硼氢化物储氢密度高，是一类极具潜力的车载燃料电池氢源材料，但其吸放氢温度较高，可逆条件苛刻。目前对其储氢性能改善研究效果有限，机理尚未明确。申请人在近期研究中通过在硼氢化钙中引入Ti(OEt)4并结合热处理，获得了一种能明显提高其储氢性能的具有纳米TiO2弥散分布的多孔复合材料新结构。在已有研究基础上，本项目拟通过向金属硼氢化物中添加液态金属有机物，原位引入纳米催化相，结合采用溶剂-热反应原位引入碳载体对硼氢化物进行纳米约束的方法，制备具有多孔结构、纳米催化相及氢化物纳米约束结构的兼具高容量和良好动力学性能及可逆性的复合硼氢化物储氢材料。系统研究体系的相组成、结构、形貌与其储氢性能的相关性，揭示催化相、纳米约束、多孔结构对硼氢化物储氢材料储氢性能的影响及其作用机理。本项目研究获得的材料及其制备技术和相关吸放氢过程机理及理论可望为高容量储氢材料体系的进一步研究和开发提供新的实践方法和理论依据。

轻金属硼氢化物储氢容量高，是一类极具潜力的车载燃料电池氢源材料，但其吸放氢温度高，可逆条件苛刻，阻碍了其实际应用。项目以LiBH4和Ca(BH4)2等轻金属硼氢化物为主要研究对象，通过多相多结构复合体系设计，高效催化相和高活性相的先进制备及引入，构建具有碳约束结构的复合材料等方法，显著提高了材料的储氢性能。研究了不同的制备参数对获得材料的结构和形貌的影响及其影响规律，研究了组分、结构对材料吸放氢热力学、动力学、可逆性和循环性能等的影响及其影响机理。通过项目实施，获得了多种基于LiBH4和Ca(BH4)2的高性能复合储氢材料新体系，通过多相间的相互作用，优化了体系的反应路径，显著提高了体系的储氢性能，获得的一种基于硼氢化物的三元复合体系分别在320和370 °C开始和结束放氢，放氢温度区间窄，放出 8.1 wt% H2，吸氢可逆率达到94%，10次循环后的放氢量达6.2 wt%；获得了一种以二维结构的Mxene Ti3C2相为催化相前驱体的基于2LiBH4+MgH2复合体系的高效纳米Ti基催化相及其引入方法，体系具有优异的吸放氢循环性能，在350 ºC/10 MPa氢压下等温吸氢，5 min内完成吸氢，达到9.1 wt% 的吸氢量，在15个吸放氢循环中，放氢动力学性能几乎没有衰退，放氢容量保持率达到90%以上；采用纳米CoO和NiO作为催化剂，有效降低了Ca(BH4)2+4LiNH4体系的放氢温度；通过在LiBH4中球磨引入聚氯乙烯(PVC)和石墨烯气凝胶，获得了具有碳约束作用的硼氢化物/碳复合材料，由于改变了体系吸放氢途径或缓解了吸放氢过程中材料团聚，有效提高了LiBH4的储氢性能；在Ca(BH4)2中通过高能球磨结合NH4Cl，合成了新一种具有无定型结构的Ca-B-N-H化合物，体系具有低至60 °C的起始放氢温度，在150 °C的放氢温度下，就能够释放出约4.5 wt%H2。研究和阐明了上述储氢材料体系性能提高的机理和相关高效催化剂的作用机理。研究结果对于进一步开展高性能硼氢化物储氢材料的研究，促进其实用化具有重要的实践和理论指导意义。