Researchers at Xiamen University (XMU) and their collaborators have revealed how electrical double layers at electrode interfaces dynamically restructure under far-from-equilibrium conditions.
The findings were published online in Nature under the title "Probing far-from-equilibrium dynamics of electrical double layers."
The team, led by XMU's Professors Wang Tao, Zhou Zhiyou, and Sun Shigang, an academician of the Chinese Academy of Sciences, worked with Professor Huang Jun of Forschungszentrum Julich in Germany and Chen Junxiang of the Fujian Institute of Research on the Structure of Matter under the Chinese Academy of Sciences.
The researchers combined time-resolved surface-enhanced infrared absorption spectroscopy with machine-learning molecular dynamics simulations to study electrical double layers under hydrogen evolution reaction conditions.
They found that the inner layer underwent a two-stage restructuring as electrode polarization increased. First, interfacial water changed orientation. With further polarization, cations accumulated near the interface and partially shed their hydration shells, while some water was expelled, causing the inner layer to collapse.
Time-resolved measurements showed that water and ions responded on different timescales. Water reoriented first, while cation accumulation, partial dehydration and inner-layer contraction lagged. When the potential was reversed, the double layer expanded through a different pathway, with concentrated cations rapidly leaving the electrode interface and creating a transient structure with a higher water content.
The restructuring also strengthened the local electric field as dehydrated cations moved closer to the electrode. The team developed a compressible electrical double-layer model that incorporates potential-dependent cation hydration radius and ion-electrode distance to explain these changes.
