二维层状过渡金属催化剂的可控制备及其对金属氢化物储氢性能的影响

Light-metal hydrides, including MgH2 and NaAlH4, have been regarded as the most important high-capacity hydrogen storage materials due to their high hydrogen storage capacity and good reversibility. However, their hydrogen absorption/desorption operating temperature is high, and the reaction rate is slow. Doping catalysts is an effective approach for improving hydrogen absorption/desorption properties of light-metal hydrides. Unfortunately, the activities of the existing catalysts are too limited to meet the requirements of the practical applications. To solve this problem, we propose a new strategy to improve hydrogen absorption/desorption properties of light-metal hydrides by developing 2D-layer transition metal compounds (e.g. MXene) as catalysts in this project. Increased catalytic activities is desired because of their unique layer morphology and high specific surface area. The controllable preparation techniques of the 2D-layer transition metal catalysts and their effects on hydrogen storage behaviors of light-metal hydrides including MgH2 and NaAlH4 will be systematically studied. The critical factors to determine the formation of layer-like transition metal catalysts will be identified, and the relationship between composition, structure, morphology and catalytic activity will be indicated. Moreover, the catalytic mechanism of the 2D-layer transition metal compounds will be revealed. Based on the above studies, the new 2D-layer transition metal catalysts with higher activities will be designed and developed, which can further reduce the operating temperature and enhance reaction rate for hydrogen storage in light-metal hydrides including MgH2 and NaAlH4. The studies present in this project will build a solid foundation for the practical applications of hydrogen-based energy.

MgH2和NaAlH4等轻金属氢化物具有较高的储氢容量和良好的吸放氢可逆性，是目前高容量储氢材料研究的重点，但其吸放氢温度偏高，速度较慢。催化剂掺杂是改善其吸放氢性能的有效途径，但现有催化剂的活性有限，尚不能满足实际应用的要求。本项目针对这一问题，提出发展二维层状过渡金属化合物MXene作为催化剂改善轻金属氢化物吸放氢性能的研究思路，利用其独特的层状形貌和较高的比表面积，提高过渡金属化合物的催化活性。拟系统研究二维层状过渡金属化合物的可控制备及其对MgH2和NaAlH4等轻金属氢化物吸放氢行为的影响，查明影响层状过渡金属催化剂形成的关键因素，掌握其成分、结构、形貌与催化活性的关系，揭示相关的催化作用机理。在此基础上，设计催化活性更为优异的二维层状过渡金属催化剂，进一步降低MgH2和NaAlH4等轻金属氢化物的吸放氢工作温度，提高其吸放氢速率，为氢能的实际应用奠定基础。

本项目重点围绕MgH2和NaAlH4等轻金属氢化物的催化改性开展研究工作，成功合成了Ti-Al-C、Nb-Al-C、Cr-Al-C、Ti-Nb-Al-C、Ti-V-Al-C、Ti-Al-N等二维MAX相化合物及其相应的MXene化合物，系统研究了其结构、形貌和催化活性，显著降低了MgH2和NaAlH4等轻金属氢化物储氢材料的吸放氢温度，提高了其吸放氢速率，揭示了催化活性物种，阐明了催化作用机理。在此基础上，发展了一种碳负载超细纳米过渡金属化合物催化剂的可控制备方法，进一步提高了过渡金属催化剂的催化活性，降低了MgH2和NaAlH4等轻金属氢化物的吸放氢工作温度。其中NbTiC催化的MgH2的放氢起始温度降低到了195°C，在250 °C下等温放氢，可以在30 min内放出5.9 wt% H2。放氢产物在50 °C下保温16 min能吸收4.0 wt%氢气。氮掺杂Nb2O5改性的MgH2，起始放氢温度降低了170 °C，总放氢量保持在6.3 wt%，放氢样品在70 °C即可完全氢化。无定形碳负载超细纳米Ti改性的NaAlH4储氢体系，放氢起始温度仅为50 °C，放氢量可达5.05 wt%，放氢样品室温即可吸氢，随温加热至90 °C时，可完全氢化，在140 °C放氢，100 °C/100 bar H2吸氢时，样品100个循环后容量保持率仍有97%。理论计算显示，Ti团簇的出现，不仅弱化了Al-H键，而且促进了氢扩散，从而改善了NaAlH4的吸放氢性能。相关成果对于发展催化改性的轻金属氢化物储氢体系具有重要的推动作用。发表论文27篇，录用待发表1篇，获授权专利6项，受理2项，培养毕业研究生7名。