Novel Nanosized Perovskite: SOFCs Application

 Beijing University of Science and Technology researchers and their team (Huang et al.) have surveyed the synthesis of nanoporous perovskite metal oxides and their applications. They discussed various synthesis methods for the preparation-nanoporous perovskite metal oxides and used it for various useful applications.

In general Perovskite metal oxides (ABX₃), here A-site is an alkaline, earth-alkaline or lanthanide element and B-site preferably with a transition metal. ABX₃ structure tolerates very large distortion with respect to the ideal cubic symmetry and X = O, Cl, Br, F (ex: CaTiO₃). Among the five compositional flexibilities of ABO₃, the major response in experimental and predicted (theoretical) reports are done in (A¹⁺B⁵⁺O₃), (A²⁺B⁴⁺O₃), and (A³⁺B³⁺O₃), In reality, of the 2346 kinds of possible ABO₃ composition only about 265 have been obtained experimentally [1]. Tolerance factor and stability are playing a vital role in their application scenarios.

Pena et al., have reported that nanoporous perovskite metal oxides have attracted extensive attention due to its superior performance with special morphological properties. Perovskite-type metal oxides were widely used in various fields for a variety of applications owing to their extraordinary compositions and structures targeted with physical and chemical properties. Besides their composition and structure, the morphology of perovskite oxides has a great influence on their physicochemical properties. Although numerous methods are available for the development of the preparation of nanoporous materials, the design of particle size, surface morphology, composition, and porosity of the nanostructured materials with multi-metallic oxides is still a challenging one [2].

 Synthesis Methods

Huang et al., and his research team further discussed various synthesis methods for the preparation of nanoporous perovskite metal oxides. They highlighted with extensive and special care in morphology, properties, and superior performances. Basically, the synthesis methods for the preparation of nanoporous perovskite oxides employed are as follows:

• Soft-template
• Hard-template
• Colloidal-crystal-template
• Electrospinning
• Hydrothermal method

Among these preparation methods with features and disadvantages, Huang et al., have reported that the hydrothermal methods were the best-suited one for the synthesis of nanoporous perovskite metal oxides.based on titanates [3]. In this method, they used nanoporous perovskite oxides based on titanates, such as SrTiO₃, BaTiO₃, PbTiO₃ [4]. The main strategy which they used was the nanoporosity design of titanate-based perovskite oxides (e.g., SrTiO₃) are TiO₂ or layered protonated titanate with a template as well as without any soft templates. Hence, this method was widely used for the preparation of nanocrystals because of its several advantages like easy control, low energy consumption, low air pollution, high yield, and has the ability to create crystalline phases with good quality of unstable at the melting point [5]. At the same time in other methods, it is difficult to increase the surface area and control the pore structure due to the high calcination temperature with a small portion of the metal-based precursor. Finally, they concluded that each of these synthesis methods has its own advantages, as well as limitations. They found that soft-template and colloidal-crystal-template methods are relatively easier to operate and scale-up. A structural and composition of Perovskite with facile route still needs to be developed with some novel techniques or strategies to obtain for uniform or stable nanoporous metal oxide structures.

Figure 1. Nanoporous perovskite metal oxides towards SOFCs

 (Image credit to  SNB Team).

Some special points should be taken into account during the synthesis of nanoporous perovskite metal oxides due to its high temperature for crystallization and complex multi-metal ions composition which is as follows:

• To obtain pure-phase perovskite oxides, the multi-metal cations should be homogeneously dispersed during the entire process.
• Organic chelating agents, like citric acid and acetic acid is widely used in the synthesis of nanoporous perovskite oxides.
• The formation of pure-phased perovskite oxides with high calcination temperatures lead to the poor thermal stability of the nanoporous structures.
• The formation of pure-phased perovskite oxides with relatively low temperatures lead to the decomposition of organic molecules due to a large amount of heat released.

Applications of SOFCs

Placement of the variety of suitable cations inclusion in A site or B site position of the single perovskite (ABX₃). Single Perovskite metal oxides are widely used in photocatalysis, energy storage, and conversion, etc. Among them, energy storage applications play a vital role in recent years. Today, energy storage and conversion are of great importance to the sustainable world. It is widely applied in electrochemical oxygen reduction reaction(ORR) catalysts mainly for potential applications in energy storage and other conversion fields, especially in Solid Oxide Fuel Cells (SOFCs) and metal-air batteries. Energy storage applications mainly include solid oxide fuel cells. SOFCs received much the attraction of interest owing to their high efficiency, versatility, cleanness, and chemical-to-electrical energy conversion. High-operating temperatures (e.g., 800-1000^oC) with commercial, SOFCs will lead to the strict requirements of the electrode and its interconnected materials. Hence, special care with more effect should be taken for the development of low-temperature SOFCs. Therefore it is believed that the reduction in the cost of materials is essentially required for cell fabrication with improving reliability and operational life. However, if we reduce the operating temperature that would have result in increased interfacial polarization resistances between electrolytes and electrodes. Hence, by traditional, the development of these electrode materials will exhibit outstanding properties and they found this is a conventional route for improving the performance and durability of SOFCs[6].

Further challenges of nanoporous perovskite oxides

Perovskite metal oxides possess good stability, although there some challenges too which should be taken into account are as follows:

• The nanoscale geometry does facilitate to chemical attack and also with other degradation phenomena with an increased surface area.
• When the nanoporous structure exhibits good crystallinity, its increased order of nanoporous structure somewhat mitigates its stability concerns.
• Preparation of nanoporous perovskite oxides to support in situ metal nanoparticles with its stability of the nanoporous structure at such high calcination temperatures.

Our SNB Team recommended this research article to help the reader to know about the synthesis and application of nanoporous perovskite metal oxides due to their high surface areas with unique physicochemical properties. In addition, the synthesis of three-phase compositionally flexible of ABX3, capable to develop multi-component equiatomic high entropy perovskites. The structural features and tolerance factor changes in inorganic nanoscaled perovskites will give a suitable for a delightful performance. Indeed, special concern on nanoporous structure stability should be paid to enhance their performance over the full range of applications during preparation and applications, element doping, ionic-electronic conductivity, and surface modification of perovskite metal oxides.

References

[1] W. J. Yin, et al., Energy Environ. Sci., 12, 442, (2019).

[2] M. A. Pe˜naet al., Chem. Rev., 101, 1981  (2001).

[3] X. Huanget al.,Chem. Sci., 9, 3623 (2018).

[4] G. Xu, et al., J. Mater. Chem. A., 3, 547 (2015).

[5] W. Shi, et al., Chem. Soc. Rev., 42, 5714 (2013).

[6] A. J. Jacobson, Chem. Mater., 22, 660 (2010).

Blog Written By

Dr. Y. Sasikumar

School of Materials Science and Engineering, 

Tianjin University of Technology, China

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Dr. A. S. Ganeshraja

Dr. S. Chandrasekar

Dr. K. Rajkumar

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Dr. S. Thirumurugan