Capacitive behavior of amorphous and crystalline RuO 2 composite electrode fabricated by spark plasma sintering technique

Abstract

This study is intended to determine if the capacitive properties are improved when a specific amount of crystalline ruthenium oxide (c-RuO 2) is added to an amorphous hydrous ruthenium oxide (a-RuO 2) electrode fabricated by the spark plasma sintering technique. For at the cyclic voltammetry scan rates higher than 10 mV s −1, the capacitance of a highly pseudo-capacitive, but less electron-conductive a-RuO 2 electrode is augmented by adding 5–20 wt.% of c-RuO 2 which is less capacitive, but more electron-conductive than a-RuO 2. The capacitance fades when more than 20 wt.% of c-RuO 2 is added because the less capacitive nature of c-RuO 2 prevails. The proximate cause of this phenomenon is the electronic conductivity, σ, of the composite electrode as we observe a maximum in σ at around a 5–20 wt.% c-RuO 2 content. The fact that c-RuO 2 is composed of smaller particles than a-RuO 2 seems to be related to the maximum σ value for a certain c-RuO 2 content of the composite electrode.