Nanoscale characterization of the site‐specific degradation of electric double‐layer capacitor using scanning electrochemical cell microscopy

Abstract

Electric double‐layer capacitors (EDLCs) that store electrical energy in the interface between an electrolyte and a solid electrode are favorable energy storage systems that demonstrate high‐power density, excellent cycle stability, and low environmental impact. To increase the operating voltage and improve the capacitance of EDLCs, it is essential to investigate the relationship between the degradation process and structural properties of activated carbon. In the current study, we used scanning electrochemical cell microscopy (SECCM) to assess the site‐specific degradation mechanisms caused by electrolyte decomposition. To simplify the structural properties of activated carbon, we used the highly oriented pyrolytic graphite (HOPG) as a model substrate to distinguish the edge and the basal planes of activated carbon. The mobile and nanoscale electrochemical cell provides local cyclic voltammetry (CV) to examine the difference in the degradation process at the edge and basal planes of HOPG. SECCM's nanoscale electrochemical cell can suppress the impact of capacitive current and can therefore be used to clearly measure the current associated with degradation caused by electrolyte decomposition. SECCM's local CV measurements directly exposed the degradation reaction that occurred at the edge plane in the positive potential range.

Evaluating Analytical Expressions for Scanning Electrochemical Cell Microscopy (SECCM)

“…Sequentially positioning the nanopipette at an array of points across the substrate surface and performing an electrochemical characterization at each point creates a nanoscale electrochemical map. SECCM is used to quantify reactions and processes at a wide variety of electrochemical interfaces with nanoscale spatial resolution, − including corrosion, − phase formation, − surface defect detection, − battery materials, − and electrocatalytic reactions (e.g., hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, etc.) on single particles. − …”

The New Era of High-Throughput Nanoelectrochemistry

“…The local degradation of an electrical double layer capacitor was investigated using HOPG as a substrate, and site-specific electrolyte decomposition was visualized via spatially resolved SECCM cyclic voltammetry measurements. 246 SECCM was further employed to interrogate the electrochemical activity of Fe(CN) 6 3−/4− at boron-doped diamond (BDD). The surfaces of single-crystal particles (Figure 6B) and polycrystalline electrodes were mapped, 247 and the role of BDD surface terminations on the electron transfer rate was identified.…”

“…Characterization of electrochemically heterogeneous surfaces, from the micro- to the nanoscale, is the primary focus of SECCM studies. The local degradation of an electrical double layer capacitor was investigated using HOPG as a substrate, and site-specific electrolyte decomposition was visualized via spatially resolved SECCM cyclic voltammetry measurements . SECCM was further employed to interrogate the electrochemical activity of Fe­(CN) 6 3–/4– at boron-doped diamond (BDD).…”

Five years of scanning electrochemical cell microscopy (SECCM): new insights and innovations

“…Further to this study of pseudocapacitive materials, a study by Kawabe et al was conducted which demonstrated the ability of SECCM to study electric double-layer capacitance on HOPG. 131 The authors were able to measure the degradation of the capacitance at the nanoscale, and measure the increase in the degradation at HOPG edge sites.…”