Surface plasmon resonance imaging of the heterogeneous electric double-layer distribution and its change dynamics

Electric double layer (EDL), the organized distribution of ions and electrons at the solid-liquid interface, is a ubiquitous phenomenon in electrochemical, supercapacitor and field-effect transistor applications. With the development of some new types of supercapacitors and transistors, the detection of EDL lateral distribution at the heterogeneous interface attracts increasing attention. In this paper, we propose a surface plasmon resonance (SPR) imaging method for the lateral EDL distribution detection over millimeter-scale field of vision. We established a model for the first time to describe the relationship between SPR responses and EDL structural changes with ions effective volume fraction, concentration and dielectric constant for different solution. This model converts EDL structure at each position on the interface into SPR images by weighted averaging of ions concentration distribution perpendicular to the interface. Thus, different EDL structures will produce different SPR responses, and the lateral variations of EDL structures across the heterogeneous interface could be mapped by SPR imaging. Furthermore, via continuous imaging, the change dynamics of EDL could be obtained. According to the simulation results, we performed experiments under different potential stimulations with solutions of different ion concentrations and ionic species. The experimental results demonstrated that our method can monitor the EDL change dynamics in real time and map the lateral EDL distribution at the heterogeneous electrode/electrolyte interface. The SPR method can help to improve the understanding of EDL carriers' transport and mobility across the heterogeneous interface, which is crucial for applications in novel transistors and bioanalytical devices.