Patterning Islandlike MnO₂ Arrays by Breath-Figure Templates for Flexible Transparent Supercapacitors

Although plenty of active materials could be used as supercapacitor electrodes, only limited ones have been engineered to construct transparent supercapacitors. Specially, it is a great challenge to make opaque metal oxides, which often own high energy density, into transparent films. Here, we demonstrate a novel approach to fabricate transparent MnO₂ films for flexible transparent supercapacitors. By utilizing breath-figure polymer films with ordered pores as template, arrays of MnO₂ islands were electrochemically deposited, with high light transmission. The thickness and interspace distance of MnO₂ island arrays could be adjusted by tuning deposition time so that the capacitance and transparency of the electrodes are changed accordingly. Such island array structure can effectively eliminate the internal stress existing in the composite film to avoid cracks during bending operation. The assembled transparent supercapacitor shows a transmittance of 44% at 550 nm and can yield a high capacitance of 4.73 mF/cm² at a current density of 50 μA/cm², demonstrating high flexibility and stability.