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

Abstract

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 V2O5 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–V2O5 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.