Abstract
In recent years redox flow batteries have been thoroughly examined in an effort to make them more efficient, improve energy density and extend cycle life. Many different components of flow batteries have been investigated including the electrolyte and the electrodes. Carbon aerogels are an ideal candidate for flow battery slurry active materials thanks to their large surface areas and tunable surface functionalities. The carbon aerogels used here are synthesized from a poly-condensation reaction between resorcinol and formaldehyde and are abbreviated RF aerogels. Following a supercritical carbon dioxide (CO₂) drying process they are referred to as carbon aerogels. In order to achieve heightened surface areas they are pyrolyzed, which can be performed at various timeframes and temperatures in order to modify the surface functionalization as well as tuning of the surface area. The effects of different pyrolysis times and temperatures are revealed through both infrared spectroscopy as well as nitrogen porosimetry. Doping the aerogel with ferric (Fe³⁺) ions imparts the ability to store charge in order to store energy. Iron was chosen because it is redox-active, Earth-abundant and not harmful to the environment. The carbon aerogel is doped by soaking in iron chloride (FeCl₃) solutions of various concentrations while stirring. The aerogel adsorption capacities were measured to be 3.79 x 10⁻² (± 3.27 x 10⁻³) moles iron/mole carbon using ultra-violet visible light absorption spectroscopy and atomic absorption spectroscopy. Following successful iron doping, the formal electrode potential of the aerogel electrode was determined to be 0.74 V vs. SHE through the use of cyclic voltammetry. A means of modulating this formal potential by altering the ligand-set, the functional group present on the surface, offered by the aerogel is also discussed.