Density Functional Theory Study On The Effect Of Polyelectrolyte Coating On Capacitor Energy Storage And Salinity Energy Extraction

Clean and renewable new energy is the primary choice to solve global energy demand and green production capacity.Supercapacitors are the key energy storage devices for stable energy transport on new energy extraction,but their energy density is generally low.It is an important breakthrough direction that how to further improve the energy density of supercapacitors on the field and the scope of its application.Polyelectrolyte coating on the electrode surface can greatly improve the energy storage performance(ESP)of supercapacitors.However,the underlying microscopic mechanism remains unclear.In this paper,the effect of the electrode surface of polyelectrolyte(PE)coating microstructure on the energy density and capacitance of supercapacitors is investigated by polymer density functional theory,and the effect of polyelectrolyte coating on salinity energy extraction is explored by the capacitive mixing(Cap Mix),which provides a theoretical basis for the design and regulatory of highperformance supercapacitors.The main contents of this paper are as follows:(1)This research focuses on the selection of PE coating material electrode material that can affect the storage density of supercapacitors,and explores the microscopic mechanism by polymer density functional theory.It is found that the coating effect of polyelectrolyte plays a key role in the energy storage of supercapacitors.When PE coating and electrode carry the same charged sign,the energy density can be increased.In this case,PE coating can increase the adsorption capacity of free ions through electrostatic attraction.When the PE coating carries an opposite charge to the electrode,the energy density will be suppressed due to electrostatic repulsion.In addition,it is meaningless to discuss capacitance trends without specifying operating conditions.In many practices,when the surface voltage is fixed,the effect of PE coating on capacitance is very similar to energy density.On the contrary,when the surface charge density is fixed,the effect of PE coating on capacitance is opposite to that of energy density.(2)This research focuses on the process of spontaneous mixing of seawater and freshwater,the Gibbs free energy of the whole system becomes smaller,and released the energy due to the change of free energy can be extracted by the Cap Mix.We explore the effect of PE coating microstructure on salinity energy extraction.It was found that when the chain length coating and the grafting density of PE coating on the surface increased,the polyelectrolyte microstructure formed on the electrode surface was beneficial to improve the salt differential energy and reduce the operating voltage.With the increase of PE coating chain length and grafting density,salt ions density from seawater and fresh water on the electrode surface increases,and the extracted salinity energy shows a nonlinear increasing trend.In summary,this paper illustrates the microscopic mechanism of the polymer coating on the electrode surface is illustrated by the polymer density functional theory,reveals the interface microstructure and thermodynamic properties of macroscopic physics of the polyelectrolyte coating,and provides a theoretical basis for the optimization of the energy density on supercapacitors and the extraction of salinity energy.