Planar ultracapacitors of miniature interdigital electrode loaded with hydrous RuO₂ and RuO₂ nanorods

Planar ultracapacitors of miniature interdigital electrode are prepared, using the standard technologies of photolithography and reactive sputtering. The ultracapacitor is denoted by its deposition sequence, for example, hRuO ₂NRGT indicates pseudocapacitive hydrous RuO₂ (hRuO ₂) and RuO₂ nanorods (NR) are grown on an interdigital stack layer of gold (G) and titania (T). The connection between structure and performance is studied through contrasting the hRuO₂NRGT capacitor with other capacitors built on a less conducting stack layer or without hydrous RuO₂ filling the gaps between the nanorods. The stack layer can be a major source of cell resistance. For instance, a buffer layer of titania could be utilized between the capacitive RuO₂ and the Au current collector to overcome the delamination problem. But the less conductive titania also makes its cyclic voltammograms (CV) elliptical and tilted, and causes a pronounced IR drop during the cell discharging. In contrast, CV of the hRuO₂NRGT capacitor on a conductive stack layer takes the shape of horizontal rectangle, and its discharge curve shows no sign of IR drop. Filling hydrous RuO ₂ into the gap reduces the cell resistance between nanorods, improves the discharge performance as well. The power output of hRuO₂NRGT, with the two resistances minimized, is 30.6μWat 75μA and 1.23μWat 5μA.