Fine-Tuned Nanoporous Supercapacitor Electrode Materials from Renewable Natural Precursors

Wednesday, May 14, 2014
Grand Foyer, Lobby Level (Hilton Orlando Bonnet Creek)
E. Redondo, E. Goikolea, J. Carretero-González, J. Ségalini, A. Navarro-Suárez, and R. Mysyk (CIC Energigune)
Reducing the cost and maximizing the volumetric capacitance are the most critical attributes of current market demand in materials for electrochemical capacitors. The better affordability of electrode materials can be provided by an increased use of renewable biomass precursors instead of traditional fossil precursors of nanoporous carbons such as coals and pitches. The volumetric capacitance can be maximized by fine-tuning synthetic methodology, enabling control over the density of electrode materials through textural properties such as pore size distribution. Renewable natural precursors are generated in abundance, often being industrial waste materials, and are already known to be a source of nanoporous carbons with well-developed microporosity and low admixture content. This has stimulated the present work on alternative carbon precursors with a focus on the optimization of synthetic parameters, primarily targeting high volumetric capacitance and cost-related parameters such as an amount of activating agents and temperature.
Optimum synthesis conditions were defined by thoroughly varying synthesis parameters such as temperature, amounts of an activating agent, etc. Good control over textural properties was enabled through small variations in the synthesis procedures, resulting in a series of microporous carbons displaying gradual changes in pore size distribution within narrow limits. A range of prepared electrode materials exhibited the ion-sieving effect, which is detrimental to supercapacitor operation. Consequently, cost-effective synthesis conditions (the minimum loading of an activating agent and the lowest synthesis temperature) were defined to avoid the ion-sieving effect and provide a volumetric capacitance as high as 150 F.cm-3 per electrode in aqueous electrolyte and 60 F.cm-3 in organic electrolyte with good rate capability (e.g. 90% capacitance retention at a current density of 9 A.g-1 in organic electrolyte) and cycling characteristics. The whole data set generated in the course of refining the synthesis conditions can be used as a guide for adjusting the porosity of the materials to novel electrolytes.