Understanding heat generation during charging processes of electrical double layer (EDL) systems is crucial for electrochemical technologies in practical scenarios. Existing kinetic models, attributing heat to ionic transports, however, fail to capture experimentally observed thermal behaviors in EDLs. Herein, we employ constant-potential molecular simulations to investigate heat generation in aqueous systems under nonquasistatic processes. Atomic-scale analyses via a modified kinetic equation reveal that the water-induced electric current, neglected in existing models, is essential to heat generation in both the bulk electrolyte and EDLs. In the bulk, heat deviates from Joule heating, attributed to the nonmonotonic reorientation of water dipoles driving non-Ohmic currents; within EDLs, heat exhibits damped endothermic and exothermic oscillations, originating from water reorientation that induces alternating electric fields and unidirectional currents. These findings unveil an underappreciated mechanism of heat generation governed by solvent dynamics and establish a kinetic framework for exploring thermal behavior in EDL systems.

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• Batteries
• Electrostatic double-layer capacitors
• Interface & surface thermodynamics
• Liquid-solid interfaces
• Water
• Molecular dynamics