Pyridinium salt ionic liquid is a salt compound composed of pyridine cyclic cations and inorganic or organic anions, which is liquid at room temperature or near room temperature. Pyridinium salt ionic liquid is a new kind of soft functional materials, which has many unique advantages such as high vapor pressure, low melting point, wide liquid flow and designable structure. Traditional synthesis methods of pyridinium salt ionic liquid include one-step synthesis and two-step synthesis. Compared with one-step synthesis, two-step synthesis can synthesize more diversified pyridinium salt ionic liquid, and has been widely used by researchers. In addition, many new synthesis methods have been developed in recent years, including ultrasonic synthesis, microwave synthesis and others.
Figure 1. Synthesis of pyridinium salt ionic liquids.
- Dye-sensitized solar cell: Dye-sensitized solar cell is a new kind of solar cell, which is favored by scientists all over the world for its high efficiency and low cost. At present, dye-sensitized solar cells reported are based on organic solvent electrolytes containing inorganic or organic iodized salt/iodine units. Although this kind of dye-sensitized solar cell has high photoelectric conversion efficiency, it has some problems, such as easy selection, easy leakage, difficult packaging and poor long-term stability of the cell, which seriously affect the practical application of this kind of photo optimization technology. However, pyridinium salt ionic liquid can be used as electrolyte solution of dye-sensitized solar cell, and its contact performance with electrode is good. The assembled dye-sensitized solar cell has high photoelectric conversion efficiency and good long-term stability, and the photoelectric conversion efficiency could be greatly improved.
- Perovskite type solar cell: Pyridinium salt ionic liquid is an important additive for perovskite solar cells, which plays an important role in obtaining high quality perovskite film during the use of perovskite solar cells. For example, cyano-pyridine salt ionic liquids are formed by designing specific chemical structures in which cyano-groups are attached to pyridine rings. The strong polarity of cyanide group is beneficial to the morphology control of perovskite film growth and the preparation of larger grain size. At the same time, cyanide group and pyridine cation synergism can passivate the internal defects of perovskite film very well, and the prepared perovskite film has good fluorescence properties. Furthermore, through the design of anionic, hydrophobic ionic liquid additives can be obtained, which can effectively block water and oxygen to the perovskite film. Therefore, more stable perovskite film can be prepared. Finally, the photoelectric efficiency and device stability of perovskite solar cells using the additive are improved.
- Others: In addition to the above applications, due to the excellent chemical and thermal stability of pyridinium salt ionic liquid, it can be used as electrolyte of lithium ion battery or fuel cell, which will greatly improve the safety of battery. In addition, pyridinium salt ionic liquid can be recycled and reused, which is environmentally friendly.
Common pyridinium salt ionic liquid include 1-ethylpyridine hydrochloride, 1-ethylpyridine hydro bromate, 1-propyl pyridine hydrochloride, 1-butylpyridine hydrochloride, 1-pentyl pyridine tetrafluoroborate, 1-octylpyridine hydro iodate, 1-decyl pyridine hydrochloride and others.
- Tankov I, Mitkova M, Nikolova R, et al. n-Butyl Acetate Synthesis in the Presence of Pyridinium-Based Acidic Ionic Liquids: Influence of the Anion Nature[J]. Catalysis Letters, 2017, 147(9):1-11.