Scientists develop new model of electric double layer

The new model takes into account a wide range of ion-electrode interactions and predicts the charge storage capacity of the device. The model’s theoretical predictions are consistent with the experimental results. Data on electric double layer (EDL) behavior can help develop more efficient supercapacitors for portable electronics and electric vehicles. The study was published in ChemPhysChem.

Many devices store energy for future use, the most well-known example being batteries. It can consistently release energy and maintain stable output, regardless of existing conditions and loads, until fully discharged.

In contrast, supercapacitors deliver power in pulses rather than a continuous flow. If a battery is like a jar that gradually stores energy for long-term use, a supercapacitor is like a bucket that can be quickly filled and emptied. This means that supercapacitors can store energy for short periods of time and release it instantly in large bursts.

The power of a supercapacitor depends on its internal resistance, which is significantly higher. This allows supercapacitors to operate at very high currents, almost similar to a short circuit. Such systems are useful when fast, powerful charging is required and are used in vehicles, emergency power systems, small equipment, etc. This effect is made possible by the storage of energy in the supercapacitor via the electric double layer (EDL).

A capacitor’s ability to store charge is determined by the area of ​​its plates, the distance between them, and the type of dielectric used. Because the electrolyte layer between the supercapacitor plates is only a few nanometers thick and the porous coating on the electrodes provides a large surface area, supercapacitors can significantly exceed conventional capacitors in terms of stored energy. Masu.

In real-world situations, the electric double layer is influenced by chemical interactions that occur at the quantum level. Therefore, to improve the efficiency of electrical devices, it is essential to study both the properties of the electric double layer and the factors that influence it.

Scientists from HSE MIEM and the Semyonov Research Center for Chemical Physics developed a model that describes the electric double layer at the interface between the electrode and the electrolyte solution, using the modified Poisson-Boltzmann equation for calculations.

The model takes into account the specific interactions between the ions and with surrounding water molecules, the effect of the electric field on the dielectric properties of the water, and the limited space available to the ions at the electrode surface. This enabled a detailed description of the differential capacitance profile, which measures how effectively the EDL can store charge in response to changes in voltage. The higher the differential capacitance, the more charge a layer can hold with a small voltage change.

In this study, aqueous solutions of sodium perchlorate (NaClO4) and potassium hexafluorophosphate (KPF6) were investigated at the interface with a silver electrode. The resulting model successfully predicted the structure of the electric double layer and provided insight into the capacitance behavior at different ionic solution concentrations. An important achievement was the successful application of this model to mixtures of said electrolytes, demonstrating the versatility and suitability of the model for predicting the behavior of complex electrochemical systems.

“Our theoretical predictions are in perfect agreement with experimental data. This is important because quantifying differential capacitance during experiments is not easy and requires meticulous and time-consuming steps.” comments Yuri Budkov, Principal Researcher at the MIEM HSE Institute of Computational Physics. and one of the authors of the paper. This model allows prediction of differential capacitance behavior under conditions where experimental data is difficult or impossible to obtain.

This is the first in a series of studies aimed at developing a comprehensive theory of electric double layers at metal-electrolyte interfaces with relevance to real-world systems. In the future, the authors plan to extend the model to include the most common systems with stronger ion-electrode interactions.

“Such models will be able to account for additional factors that influence the behavior of modern electrochemical devices. It is important for the development of capacitors,” Budkov said. .