Contribution of Cations and Anions of Aqueous Electrolytes to the Charge Stored at the Electric Electrolyte/Electrode Interface of Carbon-Based Supercapacitors

摘要

For their use in supercapacitors, aqueous electrolytes of acidic (H2SO4), neutral (Na2SO4, K2SO4), and basic (NaOH, KOH) nature are studied, using two microporous binder-free and self-standing carbon cloths as electrodes. The carbon cloths show similar porosities and specific surface areas but different contents in surface oxygen groups. The working potential window and the specific capacitance associated with the cations and anions are measured. From these parameters, the charges stored by the cations and anions at the electric electrolyte/electrode interface are deduced. The charge stored by the cations is higher than that stored by the anions for the three types of electrolytes. The differences between cations and anions are higher for the acidic and basic electrolyte than for the neutral electrolyte and also higher for the carbon cloth with the highest content in surface oxygen groups. The charge stored by the cations follows the sequence H3O+ > Na+ or K+ from the basic electrolytes > Na+ or K+ from the neutral electrolytes. The charge stored by the anions follows the sequence SO42– > HSO4– > OH–. The results here reported provide a better understanding on the electric double layer of carbon-based supercapacitors. Those results are also of interest for asymmetric and hybrid supercapacitors.