New progress in zinc-electric organic cathode research at City University of Hong Kong

On May 24, 2022, Beijing time, the journal Chem published online the latest research results of Professor Zhi Chunyi’s team in the Department of Materials Science and Engineering of the City University of Hong Kong, entitled “Anion Chemistry Enabled Positive Valence Conversion to Achieve a Record High-voltage Organic Cathode for Zinc Batteries”.

The research group found that the combination of sulfur elements, especially selenium and strong electron-absorbing groups, can better stimulate its reactivity, and the resulting selenide triphenylphosphine organic molecules have high discharge voltage, excellent magnification performance and cycle stability.

The application of sulfides in energy storage has been widely explored. Although the sulfide element has a rich valence state transformation, it is often performed in the battery to perform a two-electron negative valence conversion and has a good energy output, which can be attributed to its innate tendency to obtain electrons. However, the redox pair of sulfur elements undergoing positive valence conversion can provide many with a higher redox potential than negative valence conversion, so it is expected to increase the output voltage of the battery. The positive conversion of sulfur elements with high reversibility is difficult to achieve in batteries. For example, the element selenium in a zinc-selenium battery presents only a discharge voltage platform (Se0 to Se2-) of 0.79 V (relative to Zn2+/Zn). Due to the high surface negative charge density of the Se chain, this makes the element Se a natural electron acceptor. Therefore, it is necessary to weaken the surface charge density of the atoms of the sulfur group to promote the reaction between the sulfur element and the anion. In fact, if we can link sulfur atoms to strongly absorbing electron groups or conjugate structures to construct organic sulfur molecules, we can reduce the surface charge density of the three elements. In addition, with the help of suitable anions as strong nucleophilic reagents, the positive conversion of functional groups based on sulfur elements can be achieved.

Recently, professor Zhi Chunyi’s team of the City University of Hong Kong investigated the electrochemical properties of the sulfur element combined with the triphenylphosphine molecule based on the triphenylphosphine molecule, and found that after the combination of the sulfur element, especially selenium, with the strong pull electron group triphenylphosphine, the surface charge density of the sulfur element can be significantly reduced, so as to better achieve the positive price change. The reaction core of this organic molecule, P=Se double bond, has the discharge characteristics of n/p type hybridization, and finally achieves ultra-high discharge voltage (1.96 V) and excellent magnification performance and cycle performance.

The combination of sulfur group elements with strong electron-absorbing groups and reducing their surface charge density can better achieve their binding to anions.

Triphenylphosphine groups are strong electron-absorbing groups that bind to sulfur elements, especially selenium, significantly reducing their surface charge density.

As an organic cathode, triphenylphosphine selenide has an ultra-high discharge voltage, excellent magnification performance and cycle performance.

Mechanically, the reaction core of the organic molecule is the P=Se double bond, and it is an organic molecule with both n and p type transitions, and during the reaction, both P and Se atoms show a reversible valence transition.

The organic electrode also exhibits good self-discharge resistance in addition to excellent kinetic properties. (Source: Science Network)

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