Reduced Faradaic Contributions and Fast Charging of Nanoporous Carbon Electrodes in a Concentrated Sodium Nitrate Aqueous Electrolyte for Supercapacitors.

ABSTRACT: The Faradaic processes related to electrochemical water reduction at the nanoporous carbon electrode under negative polarization are reduced when the concentration of aqueous sodium nitrate (NaNO₃) is increased or the temperature is decreased. This effect enhances the relative contribution of ion electrosorption to the total charge storage process. Hydrogen chemisorption is reduced in aqueous 8.0?m NaNO₃ due to the low degree of hydration of the Na⁺ cation; consequently, less free water is available for redox contributions, driving the system to exhibit electrical double-layer capacitive characteristics. Hydrogen adsorption/desorption is facilitated in 1.0?m NaNO₃ due to the high molar ratio. The excess of water shifts the local pH in carbon nanopores to neutral values, giving rise to a high overpotential for dihydrogen evolution in the latter. The dilution effect on local pH shift in 1.0?m NaNO₃ can be reduced by decreasing the temperature. A symmetric activated carbon cell assembled with 8.0?m NaNO₃ exhibits a high capacitance and coulombic efficiency, a larger contribution of ion electrosorption to the overall charge storage process, and a stable capacitance performance at 1.6?V.

SUBMITTER: Abbas Q 

PROVIDER: S-EPMC6774286 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature