Toward binder-free electrochemical capacitor electrodes of vanadium oxide-nanostructured carbon by supercritical fluid deposition: Precursor adsorption and conversion, and electrode performance

Electrochemical capacitor electrodes were fabricated by depositing an ultra-thin layer of vanadium oxide on a high conducting, large specific surface area (SSA) materials (substrates) using a supercritical fluid adsorption-calcination method. The high SSA materials included binder free single walled carbon nanotube-activated carbon (SWCNT-AC) composites and the traditional electrode of activated carbon-carbon black-polymer binder (AC-CB-binder). The uptake of the organometallic precursor for the oxide (vanadium (III) acetylacetonate) on the substrates were investigated and related to their SSA. Precursor uptakes up to 54.7 wt% of the initial carbon substrate was achieved. Calcination conditions for converting the precursor to oxide and electrochemical properties of the electrodes were thoroughly investigated. The V₂O₅, which showed extremely high specific pseudo-capacitance (>1000 F g^-1 at 100 mV s^-1), greatly enhanced the overall electrode performances. Conversely, the V ₂O₅ pseudo-capacitance was better utilized in the SWCNT-AC substrate, particularly at high working speeds, because of the significantly higher electrical conductivity. For example, the SWCNT-AC-V₂O ₅ composite (weight ratio 40:60) had its volumetric capacitance doubled, comparing to the ∼50% increase in the AC-CB-binder sample at 100 mV s^-1.