electrodeelectrolyte

An electrode-electrolyte system consists of an electrode in contact with an electrolyte, forming the active region where electrochemical reactions occur. The electrode supplies or accepts electrons, while the electrolyte provides mobile ions that carry charge and maintain electroneutrality. The interface between the solid electrode and the ionic electrolyte, often referred to as the electrode-electrolyte interface, governs charge transfer, mass transport, and stability of the cell.

At the interface, an electric double layer forms, creating a potential difference known as the electrode potential. Charge transfer reactions may be limited by kinetics, described by the exchange current and activation overpotentials. In many systems, a solid-electrolyte interphase (SEI) forms on reactive electrodes, passivating the surface but also consuming electrolyte and affecting performance.

In energy storage and conversion, the electrode-electrolyte interface controls capacity, voltage, rate capability, and cycle life. In batteries, the electrolyte comprises solvents and salts; in electrolysis and sensors, water or organic electrolytes may be used. The choice of electrode material and electrolyte composition, including solvent, salt, and additives, determines electrochemical window, conductivity, and interfacial stability.

Modeling and characterization reveal that the interface is described by electrical double-layer concepts (such as Helmholtz and Gouy-Chapman-Stern models) and by charge-transfer resistance; impedance spectroscopy and cyclic voltammetry probe kinetics and diffusion. Surface-sensitive techniques reveal SEI composition and morphology.

Examples include lithium-ion batteries with graphite anodes in organic carbonate electrolytes with LiPF6; platinum electrodes in acid for fuel cells; and supercapacitors with activated carbons and ionic liquids. Understanding the electrode-electrolyte interface is essential for improving performance and durability of electrochemical systems.