Recently, the team, led by Professor Wu-Qin Pei at School of Chemistry and Chemical Engineering, Beijing Institute of Technology, has made phased achievements in the field of energy storage technology. The research findings entitled “Tremendous enhancement of heat-storage efficiency for Mg(OH)2-MgO-H2O thermochemical system with addition of Ce(NO3)3 and LiOH” was published online in Nano Energy (https:///doi.org/10.1016/j.nanoen. 2020.105603) on 18th December. Meng-Tian Li and Ya-Ting Li, graduate students at School of Chemistry and Chemical Engineering, Beijing Institute of Technology, are co-first authors, and BIT is the only author unit.

Increased fossil fuel consumption leads to the air pollution and greenhouse gas emission, while thermal energy is indispensable to industrial and agricultural production and everyday life of residents and in great demand. Failure to get the utmost use of thermal energy in the process of industrial production is not only a waste of energy, but also causing more emission of pollutant. The solar energy is a kind of inexhaustible clean energy, but this energy has far not yet been effectively used due to its fluctuating nature. With the application of energy storage technology, not only industrial waste heat can be recycled and reused ,but also technical conditions can be provided for the expansion and effective use of solar energy. Chemical heat storage technology uses the reversible thermal chemical reaction to store and release the thermal energy. In this way, heat can be stored for a lang time, which overcomes the technical bottleneck of sensible heat storage (molten salt)----huge heat loss and low energy density in the process of heat storage. Thus, the research of chemical heat storage technology has been thriving in these years.(In February 2020, Ministry of Education, National Development and Reform Commission and National Energy Administration joint together to formulate, print and distribute Disciplinary Development Action Plan for Energy Storage Technology (2020-2024), proposing that several undergraduate majors, sub-disciplines and inter-disciplines about energy storage technology will be added in about 5 years to promote the construction of a number of colleges of energy storage technology (including research institutes), construct innovative platforms where production and education of energy storage technology are combined, promote the development of the key part of this technology to reach the world’s leading level, form a number of technical specification and standards and effectively promote the energy revolution and the development of energy internet.

Fig.1 (a) Isothermal kinetic curves of pure Mg(OH)2 and MgCeLi-x-y composites at 270℃;

(b)Plots comparing the maximum conversion rate and conversion time of pure Mg(OH)2 and MgCeLi-x-y composites at 270℃.

Magnesium hydroxide (Mg(OH)2) and calcium hydroxide (Ca(OH)2) are promising heat storage materials to be applied at moderate-temperature and high-temperature. Through and hydration processes, they store and release heat respectively. However, because of the low rate of heat storage and release and the poor cycle performance, Mg(OH)2 and Ca(OH)2 can’t be put in practice use. To solve these problems, after years’ hard work, the author finally finds the fact that cerium nitrate (Ce(NO3)3) and lithium hydroxide (LiOH) can catalyze the hydroxide dehydration with high efficiency in a synergistic manner, and improve the heat storage and release cycle performance. For example, the isothermal kinetics experiment (TG) of magnesium hydroxide has turned out that materials containing 8% Ce(NO3)3 and 6% LiOH can dehydrate within 14 minutes, with the conversion rate up to 99%. Under the same condition, the conversion rate of pure Ca(OH)2 can only reach 21% within 300 minutes, while the heat storage rate of the new materials is improved by about 92 times.(Fig.1a and Fig.1b)

Fig.2 Relationship between maximum conversion rate, maximum conversion time and cycle times of pure Mg(OH)2 and MgCeLi-x-y composites.

Figure 2 presents the outcome of the cycle performance experiment of heat storage and release. After 20 continuous cycles of heat storage, the heat storage efficiency can still reach 88%, and heat can be stored for 60 minutes. The two statistics prove the stability property of the material, and thus the research and development of relevant heat storage and release devices and technology can be carried out.

Fig.3 HRTEM image for dehydration product of MgCeLi-8-6.

Fig.4 X-ray photoelectron spectra of MgCeLi-8-6: (a) XPS survey spectrum, (b) XPS of Ce 3d.

Through the study of constitution and microstructure of the material by analysis and testing techniques like SEM, HRTEM, XRD and XPS, the catalytic mechanism of enhancement of heat storage efficiency and the influence on the material structure brought by the additives are preliminarily revealed (Fig.3 and Fig.4). According to the experimental data of kinetics of dehydration, the author deduces the potential kinetic mechanism function and kinetic equation (F.1 and F.2). The kinetic equation can support the subsequent numerical simulations and heat storage devices design. The test and calculation outcomes of the activation energy in dehydration prove that activation energy (E) and Ln A can be reduced by 51% and 50% (Fig. 5). Thus, cerium nitrate and lithium hydroxide can significantly improve the heat storage and release performance of magnesium hydroxide by reducing the activation energy and influence on the material microstructure.

Fig.5 Activation energy of dehydration reaction of pure Mg(OH)2 and MgCelI-8-6 composite materials.

After more than 5 years of research on hydroxide chemical heat storage technology, the team not only has researched and developed heat storage materials with excellent performance (having declared relevant patent technology); meanwhile, relevant evaluation parameter in the field of heat storage and release has been established and effective test method has been built.

More about the author:

Qin-Pei Wu, a professor at School of Chemistry and Chemical Engineering, Beijing Institute of Technology. He gained his Ph. D. degree from King’s College of London. His research focuses on Energy Storage and Bioactive Molecules. Thermochemical heat storage includes enhancing heat storage rate of brucite and lime as well as the reversibility of energy storage and release. Molecular design and synthesis of heterocyclic compounds and nucleosides as inhibitors toward Hepatitis C virus and herpes viruses. More than 50 articles have been published in SCI，including Chemical Engineering Journal、ACS Nano、Nano Energy、Journal of Energy Storage、Journal of Medicinal Chemistry、Medicinal Chemistry、European Journal of Medicinal Chemistry and Advanced Synthesis & Catalysis.

Meng-Tian Li, received her bachelor’s degree in Chemical Engineering and Technology from Wuhan University of Science and Technology in 2018. In the same year, she joined in the team of Qin-Pei Wu in September and carried out the research on efficient moderate-temperature and high-temperature materials.

Ya-Ting Li，graduated from Changchun University of Science and Technology. In the same year, she joined in the team of Qin-Pei Wu in September and carried out the research on the efficient heat storage technology and has published 3 papers as the first author in SCI. She is now taking office in Liming Research & Design Institute of Chemical Industry CO., LTD.