Revisiting Self-Discharge of Nanoporous Electrodes—Insights from Multilayered Graphene Membrane-Based Electrodes

Self-discharge (SD) of nanoporous electrodes is a phenomenon of spontaneous voltage drop when an electrode is placed in the open circuit state. It is not only a persistent challenge for the community of electric double-layer capacitors but also has plagued the development of other electrochemical systems owing to the dissipation of both electronic and ionic charges at the electrode/electrolyte interface. However, the intricate interplay of diverse interfacial electrochemical processes, involving ions, solvents, and host nanoporous materials, complicates the elucidation of the SD mechanism of nanoporous electrodes. The complex nanostructure and surface chemistry of typically used carbon-based nanoporous materials, such as activated carbon, add further complexity to the mechanism analysis. In this work, taking a series of additive-free and highly conductive multilayered graphene-based membranes with varied slit sizes as a platform, we revisit the SD of nanoporous electrodes. By leveraging a widely-used hybrid SD model, our fitting results suggest a predominant role of the kinetic process of activation-controlled Faradaic reactions during the SD of multilayered graphene membrane-based electrodes even under different testing conditions, encompassing varied slit sizes and different aqueous electrolytes. However, subsequent experiments on charging voltage-dependent SD and chemical characterization exclude the commonly deemed activation-controlled reactions, including carbon oxidation and water electrolysis, implying the involvement of previously unidentified activation-controlled processes. Our findings shed new light on the SD at the electrode/electrolyte interface and underscore the need to refine the existing hybrid SD model to accommodate these novel observations in nanoporous material.