Fabrication of flexible micro-supercapacitor array with patterned graphene foam/MWNT-COOH/MnOx electrodes and its application

We report on the facile fabrication of an all-solid-state flexible planar-type micro-supercapacitor (MSC) array with micropatterned hybrid electrodes of graphene foam (GF)/COOHfunctionalized multi-walled nanotubes (MWNT-COOH)/MnOx and its application as a power source to operate various micro-light emitting diodes (l-LEDs) and a SnO₂ nanowire (NW) UV sensor. Composite electrodes of GF/MWNT-COOH/MnOx were simply micropatterned via reactive ion etching (RIE) with a metal mask, and used as current collectors as well as active materials. Polyvinyl alcohol-H3PO4 was used as the solid-state electrolyte. The use of the composite film electrodes increased the area specific capacitance ∼11 times compared to the MSC with just patterned GF electrodes. After 104 charge/discharge cycles, 89.5% of the initial capacitance was maintained. Furthermore, very stable performance was observed over 103 bending of the whole MSC on a polyethersulfone substrate with capacitance retention of 95.5%. For the first time, we could directly measure the UV-induced photocurrent through a SnO₂ NW sensor powered by 4 MSCs connected in parallel. Fast response to UV pulses was detected for a time of more than 10 min. This work demonstrates the high application potential of our MSCs using patterned electrodes of GF/MWNT-COOH/ MnOx to self-powered flexible electronic devices including NW-based sensors.