High Rate Capacity through Redox Electrolytes Confined in Macroporous Electrodes

The capacitive characteristics of a model macroporous electrode, comprised of vertically aligned carbon nanotubes, with a relatively large volume /unit mass (of ∼40 cm 3 /g) are discussed. The faradaic characteristics of the capacity were evidenced through a voltage plateau in the galvanostatic discharge experiments. It is shown that the confinement of electrolyte within the spacing between the nanostructures with respect to an appropriate choice of the voltage scan rate yields a regime where both high capacity and rate capability may be realized. Additionally, the absence of diffusional processes allows for large capacitance retention even at discharge current densities of the order of 200 mA/cm 2 . For 1M K 3 Fe(CN) 6 , the maximum observed capacity was found to be ∼26 mAh/cm 3 (normalized to the pore volume) or 0.28 mAh/cm 2 (normalized to the projected area of the electrode) and it was noted that the capacity could be cycled at very high rates for 5000 cycles.