Capacitive behavior of amorphous and crystalline RuO2 composite electrode fabricated by spark plasma sintering technique

This study is intended to determine if the capacitive properties are improved when a specific amount of crystalline ruthenium oxide (c-RuO2) is added to an amorphous hydrous ruthenium oxide (a-RuO2) 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-RuO2 electrode is augmented by adding 5–20 wt.% of c-RuO2 which is less capacitive, but more electron-conductive than a-RuO2. The capacitance fades when more than 20 wt.% of c-RuO2 is added because the less capacitive nature of c-RuO2 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-RuO2 content. The fact that c-RuO2 is composed of smaller particles than a-RuO2 seems to be related to the maximum σ value for a certain c-RuO2 content of the composite electrode.

► Binderless fabrication of RuO2 pseudocapacitor electrode by spark plasma sintering. ► Addition of crystalline RuO2 to amorphous one improves the capacitive behavior. ► Amorphous:crystalline = 95:5 composite RuO2 electrodes show the best performance. ► High electronic conductivity at this composition results in the above improvement.