Chemists have named promising materials for supercapacitors

(ORDO NEWS) — A group of scientists from MIEM HSE, together with colleagues from the Institute of Non-Classical Chemistry in Leipzig, developed a theoretical model of polymerized ionic liquids at the interface with a charged metal electrode.

Using the approaches of polymer physics and theoretical electrochemistry, researchers have shown for the first time how the behavior of the electrical capacitances of polymeric and ordinary ionic liquids differs.

Polymerized ionic liquids (PILs) are a relatively new class of materials that are finding more and more applications in various applications, from the development of new electrolytes to the creation of solar panels.

Unlike conventional ionic liquids, which are liquid organic salts, where cations and anions can move freely, in ILI, cations are usually cross-linked into long polymer chains, and anions move freely. Since recently, PILs, along with ordinary ionic liquids, have been used in the creation of supercapacitors as a filling.

Supercapacitors are devices that store energy in a double electrical layer on the surface of an electrode (for example, platinum, gold, carbon electrodes work). A supercapacitor, compared to, for example, a battery, stores more energy and does it faster. The characteristic that shows how much electricity a supercapacitor can store is called “capacitance”.

The authors of the work for the first time theoretically simulated the behavior of the electric capacitance of the electric double layer that appears in PILs and their solutions at the interface with a charged electrode in supercapacitors.

The scientists also compared the electrical capacitance of PILs with the electrical capacitance of conventional ionic liquids. The result of the study was a new analytical expression for the electric capacitance at low voltages, which can be used in engineering calculations.

Having considered two model cases of interactions of polymerized ions with the electrode surface, the authors found both a quantitative and a qualitative difference between the behavior of the electric capacitance and the behavior of ordinary ionic liquids. Scientists predict a huge increase in electrical capacity for PILs compared to ordinary ionic liquids with the same chemical composition.

The study elucidates for the first time how the presence of chain-linked cations affects the electrochemical properties of an ionic liquid near a charged electrode.

As the authors note, despite the fact that the developed model is a rather rough description of PILs on charged electrodes, even at this stage of the development of the theory, the results obtained can be useful in the development of new supercapacitors, fuel cells, batteries, and solid-state electrolytes.

“We assumed that the charged polymer chains in a polymeric ionic liquid would attract ions to a charged electrode much more easily than in conventional ionic liquids, where the ions are not bound.

This, in turn, should lead to the appearance of large capacitances at the same voltages. Having carried out a rigorous calculation based on a combination of the approaches of theoretical electrochemistry and polymer physics, we were convinced of the correctness of our hypothesis.

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