From School of Energy and Power Engineering
By Wan Fang, Zhang Jiawei, Jiang Bo
Recently, Prof. Tang Dawei’s research team from School of Energy and Power Engineering, Dalian University of Technology (DUT) has made progress in the research of the oxygen carrier for chemical looping hydrogen generation. Journal of Materials Chemistry A (IF: 11.3), an international authoritative journal of energy materials, published the research results online titled Iron-oxygen covalency in perovskites to dominate syngas yield in chemical looping partial oxidation, used it as the cover article and recommended it as the highlight of the issue.
Chemical looping reforming is an advanced hydrogen production technology featured with carbon dioxide separation. Compared with traditional reforming technology, it greatly reduces the energy consumption of hydrogen purification. At the same time, it decouples the endothermic step from the exothermic step, which helps to introduce solar energy instead of fossil fuel combustion for energy support, thereby reducing the emissions of carbon and nitrogen oxides during the process, and the exergy loss of the system. The development of this technology can provide strong support for the energy system to achieve the goal of "carbon neutrality and carbon peak".
The selection of high-performance oxygen carriers is the key to the development of hydrogen production technology by chemical looping reforming. The oxygen partial pressure of the oxygen carrier directly determines its hydrogen yield. Perovskite oxide (ABO3) is currently the most promising oxygen carrier due to its variable composition and adjustable thermodynamic partial pressure. Nevertheless, the intrinsic relationship between the electronic structure of the perovskite oxygen carrier and the thermodynamic oxygen partial pressure remains elusive, so the current screen of oxygen carriers can only rely on a large number of experiments. Therefore, in order to carry out calculation-assisted oxygen carrier research and development, it is of great significance to develop an effective electronic structure descriptor to indicate the oxygen partial pressure of the oxygen carrier.
This work studied the influence mechanism of the A-site element in the perovskite on the covalency of the B-O bond. It is found that the ionic radius of the A-site element would cause the BO6 octahedron in the perovskite structure to undergo spatial tilting of different degrees, which causes a change in the covalency of the B-O bond in the energy space. This change can be reflected by the B-O bond charge transfer energy. Subsequently, this team explored the influence pattern of the covalency of the B-O bond on the thermodynamic partial pressure of oxygen. The results show that the decrease in the covalency of the B-O bond increases its charge transfer energy, which increases the formation energy of oxygen vacancy and oxygen ion diffusion energy barrier of the oxygen carrier, thereby reducing its oxygen transfer activity and its superficial oxygen activity. The above changes eventually lead to an increase in the thermodynamic partial pressure of oxygen of the oxygen carrier. The work has unveiled the intrinsic relationship between the electronic structure of perovskite and the thermodynamic oxygen partial pressure, and proposed taking the charge transfer energy as an electronic descriptor for evaluating the performance of oxygen carriers, which has laid down the foundation for rapid screening of perovskite oxygen carriers based on machine learning.
The first author of this paper is Jiang Bo, a postdoc from DUT, and the corresponding authors are Assoc.Prof. Li Lin and Prof. Tang Dawei.
This project was funded by the General Program of the National Natural Science Foundation of China and the General Program of the Chinese Postdoctoral Science Foundation.
Editor: Li Xiang