The Properties of Carbons Derived through the Electrolytic Reduction of Molten Carbonates under Varied Conditions: Part I. A Study Based on Step Potential Electrochemical Spectroscopy

Abstract

Carbons have been produced through the electrolytic reduction of molten alkali metal carbonate salts under a range of conditions. The resultant carbons consist of both graphitized and amorphous phases. The carbon surface has also been shown to be heavily functionalized with oxygen containing groups. Their charge storage capabilities as electrochemical capacitor materials have been investigated using cyclic voltammetry and step potential electrochemical spectroscopy (SPECS). Trends in carbon performance with electrodeposition conditions have been identified, and carbons with a specific capacitance as high as 375 F.g −1 have been obtained at scan rates of 10 mV.s −1 . With respect to temperature of carbon deposition, carbon electrodeposited at 500 • C has been identified as the best electrical double layer capacitor type material, and as a superior material for pseudocapacitive applications. The performance of a control activated carbon has been compared with the electrodeposited carbons, and it has been shown that, when electrodeposited at low current densities, the resultant carbon performance is superior to the activated carbon.

Optimized Electrolytic Carbon and Electrolyte Systems for Electrochemical Capacitors

“…Phases of this form have been stated to correspond to graphitic carbon by previous groups . These phases are apparently present in low concentrations and are slightly more prevalent towards the edges of particles, which is consistent with what is expected in carbons electrodeposited at low temperatures and current densities based on previous results . The observable concentration of graphitic phases in these carbons is lower than that which has been observed in previously synthesized carbons in molten carbonate systems, which is likely due to the manner of synthesis being chosen to produce carbon with increased amorphous character.…”

“…[31,39,42,43] The research presented here continues from the work of this group, [27,28] which has shown how temperature, current density, substrate, and electrolyte variation influences the morphology of carbonate derived carbons, and how these morphological changes relate to aqueous supercapacitive performance in the materials. [27,28] This has indicated that electrochemical performance in aqueous systems is at its highest for materials showing elevated amorphous character, which contributes to increased double layer formation, [28] and high oxygen functionalization, which leads to high pseudo-capacitance. [28] These carbons may be produced through the electroreduction of molten carbonates at low temperatures [23][24][25]28,[29][30][31] or at low current densities relative to the geometric surface area of the working electrode.…”

“…One potential method of achieving this is the synthesis of carbons through the electrolytic reduction of molten carbonate salts. [4,5,9,[23][24][25][26] This method of carbon synthesis has received considerable interest in recent years, both by this group [26][27][28] and a range of further…”

“…[27,28] This has indicated that electrochemical performance in aqueous systems is at its highest for materials showing elevated amorphous character, which contributes to increased double layer formation, [28] and high oxygen functionalization, which leads to high pseudo-capacitance. [28] These carbons may be produced through the electroreduction of molten carbonates at low temperatures [23][24][25]28,[29][30][31] or at low current densities relative to the geometric surface area of the working electrode. [28,30,37] Based on these previous results, the work presented here investigates an optimized carbonate-derived carbon and electrolyte system for aqueous electrochemical capacitors.…”

“…[28] These carbons may be produced through the electroreduction of molten carbonates at low temperatures [23][24][25]28,[29][30][31] or at low current densities relative to the geometric surface area of the working electrode. [28,30,37] Based on these previous results, the work presented here investigates an optimized carbonate-derived carbon and electrolyte system for aqueous electrochemical capacitors. In the context of this paper the investigated carbon is referred to as the optimized carbon, and the desired carbonelectrolyte system is referred to as the optimized system.…”