Song Tianfu, Lei Huanyu, Cai Feng, Kang Yu, Yu Haifeng, Zhang Liqun
School of Material Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
School of Material Science and Engineering, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Peking University, Beijing 100871, China.
ACS Appl Mater Interfaces. 2022 Jan 12;14(1):1940-1949. doi: 10.1021/acsami.1c19819. Epub 2021 Dec 20.
Molecular solar thermal fuels (MOSTs), especially azobenzene-based MOSTs (Azo-MOSTs), have been considered as ideal energy-storage and conversion systems in outer or confined space because of their "closed loop" properties. However, there are two main obstacles existing in practical applications of Azo-MOSTs: the solvent-assistant charging process and the high molar extinction coefficient of chromophores, which are both closely related to the π-π stacking. Here, we report one efficient strategy to improve the energy density by introducing a supramolecular "cation-π" interaction into one phase-changeable Azo-MOST system. The energy density is increased by 24.7% (from 164.3 to 204.9 J/g) in Azo-MOST with a small loading amount of cation (2.0 mol %). Upon light triggering, the cation-π-enhanced Azo-MOST demonstrates one gravimetric energy density of about 56.9 W h/kg and a temperature increase of 8 °C in ambient conditions. Then the enhanced mechanism is revealed in both molecular and crystalline scales. This work demonstrates the huge potential of supramolecular interaction in the development of Azo-MOST systems, which could not only provide a universal method for enhancing the energy density of solar energy storage but also balance the conflicts between molecular design and the condensed state for phase-changeable materials.
分子太阳能热燃料（MOSTs），尤其是基于偶氮苯的MOSTs（Azo-MOSTs），因其“闭环”特性而被视为外层或受限空间中理想的能量存储和转换系统。然而，Azo-MOSTs的实际应用存在两个主要障碍：溶剂辅助充电过程和发色团的高摩尔消光系数，这两者都与π-π堆积密切相关。在此，我们报告了一种有效的策略，即通过将超分子“阳离子-π”相互作用引入一个可相变的Azo-MOST系统中来提高能量密度。在阳离子负载量较小（2.0 mol%）的Azo-MOST中，能量密度提高了24.7%（从164.3 J/g提高到204.9 J/g）。在光触发下，阳离子-π增强的Azo-MOST在环境条件下表现出约56.9 W h/kg的重量能量密度和8°C的温度升高。然后在分子和晶体尺度上揭示了增强机制。这项工作展示了超分子相互作用在Azo-MOST系统开发中的巨大潜力，这不仅可以为提高太阳能存储的能量密度提供一种通用方法，还可以平衡分子设计与可相变材料凝聚态之间的矛盾。
