Xiang Duo, Gu Changdong, Xu Haoran, Xiao Gang
State Key Laboratory of Clean Energy Utilization, College of Energy Engineering, Zhejiang University, Hangzhou, Zhejiang, 310027, China.
State Key Laboratory of Silicon Materials, College of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang, 310027, China.
Small. 2021 Jul;17(29):e2101524. doi: 10.1002/smll.202101524. Epub 2021 Jun 17.
Thermochemical energy storage (TCES) materials have emerged as a promising alternative to meet the high-temperature energy storage requirements of concentrated solar power plants. However, most of the energy storage materials are facing challenges in redox kinetics and cyclic stability. Iron-doped manganese oxide attracts raising attention due to its non-toxicity, low cost, and high energy capacity over 800 °C. However, there are few investigations on the reversibility enhancement of the redox reaction from the microstructural-evolution-mechanism point of view. Herein, bixbyite-type (Mn Fe ) O is synthesized and extruded into honeycomb units, which can maintain an 85% initial capacity after 100 redox cycles. It is also found that a self-assembled core-shell MnFe O @Mn Fe O structure forms during the reduction step, and then transforms into a homogeneous solid solution of (Mn Fe ) O in the following oxidation step. During the reduction step, shells are formed spontaneously from the Mn Fe O with the MnFe O as cores due to the lower surface energy, which facilitates the oxygen adsorption and dissociation during subsequent oxidation step. Through the density functional theory calculation, it is revealed that the lower formation energy of oxygen vacancies in the shell contributes to the improvement of oxygen diffusion rate. This study can provide a guideline to design prospective materials for high-temperature TCES.
热化学储能（TCES）材料已成为满足聚光太阳能发电厂高温储能需求的一种有前景的替代方案。然而，大多数储能材料在氧化还原动力学和循环稳定性方面面临挑战。铁掺杂的氧化锰因其无毒、低成本以及在800℃以上具有高能量容量而受到越来越多的关注。然而，从微观结构演化机制的角度对氧化还原反应可逆性增强的研究很少。在此，合成了方铁锰矿型（Mn Fe）O并将其挤压成蜂窝单元，在100次氧化还原循环后仍能保持85%的初始容量。还发现，在还原步骤中形成了自组装的核壳结构MnFe O@Mn Fe O，然后在随后的氧化步骤中转变为（Mn Fe）O的均匀固溶体。在还原步骤中，由于表面能较低，以MnFe O为核，由Mn Fe O自发形成壳层，这有利于后续氧化步骤中的氧吸附和解离。通过密度泛函理论计算表明，壳层中氧空位的形成能较低有助于提高氧扩散速率。该研究可为设计用于高温TCES的前瞻性材料提供指导。
