钛基MXene及其衍生物增强NaAlH4储氢性能及微观机制

The catalytic activity and stability of active species are directly determined by element composition, chemical property and microstructure of the additives, and then they further affect hydrogen sorption kinetics and cycling stability of NaAlH4. Ti-based transition metal carbide two-dimensional material (MXene) and its derivatives endow some prerequisites to be optimal additives in terms of unique two-dimensional structures and controllable morphologies. In this project, Ti-based MXene with functional groups (f-MXene) and its derivatives of f-MXene@TiO2 will be used as the additives. Simultaneously, the functional groups and theirs defects of f-MXene, and the microstructure of f-MXene@TiO2 will be tailored. And then we will systematically study hydrogen storage performances of NaAlH4 with the different additives. Thereafter, the relationships between the states of active species and functional groups, the defects of f-MXene, and the microstructure of f-MXene@TiO2 will be elucidated by investigating the microstructures of additives and chemical environment of Ti under different absorption/desorption states. In addition, we will theoretically valuate the effect of surface states on the catalytic activity and the thermodynamic and kinetic stability of MXene. Finally, the improved micro-mechanism of hydrogen storage performances of NaAlH4 by adding f-MXene and f-MXene@TiO2 would be clarified. The achievement of this project would not only improve hydrogen storage performance of NaAlH4 and broaden the applications of MXenes, but also provide some new ideas and implications for microstructural design of the complex hydride dopants.

添加剂的元素组成、化学性质和微观结构决定了活性物质的催化活性和稳定性，进而影响其添加后NaAlH4的吸/放氢动力学和循环稳定性，钛基过渡金属碳化物二维晶体（MXene）及其衍生物独特的二维结构和可调控的微观形貌使其有望成为理想的添加剂。本项目拟以带有官能团的钛基MXene（f-MXene）及其衍生物f-MXene@TiO2为添加剂，调控f-MXene官能团和官能团缺陷以及衍生物的微观结构，测试其添加后NaAlH4的储氢性能，表征不同吸/放氢状态下添加剂的微观结构和Ti周围化学环境，明确活性物质存在状态与f-MXene官能团和官能团缺陷及衍生物微观结构的关联性；从理论上探讨MXene表面状态对其催化活性和热/动力学稳定性的影响，阐明f-MXene及其衍生物改善NaAlH4储氢性能的微观机制。本项目的完成可提高NaAlH4储氢性能、拓展MXene应用领域并为配位氢化物添加剂设计提供思路和指导。

添加剂引入是提高NaAlH4储氢性能的有效方法，钛基二维过渡金属碳化物（MXene）及其衍生物独特的二维结构和可调控的微观形貌使其成为理想的添加剂。采用HF或LiF+HCl刻蚀法制备了Ti3C2 MXene，通过NH3气氛热处理、多巴胺包覆热处理和H2S气氛热处理制备了N掺杂Ti3C2、碳包覆Ti3C2和Ti3C2F2-x-ySx(OH)y，充分认识工艺参数（热处理温度、时间和原料比等）对N掺杂量、表面碳层结构和S取代量的影响。采用热处理和醇热方法，制备了C@TiO2/Ti3C2、Ti3C2/A-TiO2和TiO2/C等不同组成和微观结构的Ti3C2 MXene衍生物，研究了制备工艺参数（热处理温度和时间，醇热反应的溶剂组成、诱导剂含量、反应温度和反应时间）对Ti3C2 MXene衍生物微观结构的影响。研究了添加Ti3C2及其衍生物后NaAlH4的储氢性能。添加Ti3C2及其衍生物后NaAlH4的储氢性能明显优于纯的NaAlH4，第一、二步的初始放氢温度和终止放氢温度显著降低，等温放氢速率明显提高，100 °C时的放氢量大于3.0 wt%，且具有较好的循环稳定性。表征不同吸/放氢状态下NaAlH4体系的微观结构，分析Ti3C2 MXene及其衍生物改善NaAlH4储氢性能的微观机制。Ti3C2 MXene及其衍生物作为添加剂不改变NaAlH4的吸/放氢反应，与NaAlH4球磨过程中转化为含Ti活性物质（Ti0、Ti3+、Ti-H、TiN和TiC等）和碳，活性物质间协同作用提高了NaAlH4的吸/放氢性能，如：碳提高Ti0和Ti3+的催化活性和稳定性，Ti-F-Ce提高Ti0的稳定性等。基于以上工作，团队发表了标注基金资助的期刊论文18篇，其中SCI检索论文14篇。获批发明专利4项，申请发明专利1项。参加国内外学术会议17人次。