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, hRuO2NRGT indicates pseudocapacitive hydrous RuO2 (hRuO2) 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 RuO2 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 30.6 μW at 75 μA and 1.23 μW at 5 μA.