Revisiting Self-Discharge of Supercapacitors with Multilayered Graphene Membrane as a Model Nanoporous Electrode

Self-discharge in electrochemical energy storage systems, particularly in electric double-layer capacitors, poses significant challenges due to the spontaneous dissipation of stored charges at electrode/electrolyte interfaces, which compromises device performance and energy efficiency. Despite decades of research, the underlying mechanisms of self-discharge remain a subject of debate. In this study, we use multilayered graphene-based membranes with adjustable nanoslit sizes as an additive-free electrode material platform to revisit the self-discharge in nanoporous electrodes. By integrating a hybrid self-discharge model with a comprehensive electrochemical characterization, we identified activation-controlled Faradaic reactions as the primary driver of self-discharge, but ruled out traditionally suggested reactions like carbon oxidation and water splitting in carbon-based electric double-layer capacitors with aqueous electrolytes. Furthermore, the observed ion identity-dependent self-discharge underscores the pivotal role of electrolyte ions in self-discharge, highlighting this overlooked aspect in the conventional hybrid model. Our findings highlight the inherent challenges in studying self-discharge and the need to further develop advanced research methods and models to address this enduring problem.