High energy density transparent and flexible asymmetric supercapacitor based on a transparent metal hydroxides@graphene micro-structured film via a scalable gas-liquid diffusion method

Faradaic transition-metal-oxide/hydroxide (TMH) materials are critical for high-performance supercapacitors. However, the preparation of transparent micro-structured TMH electrodes is a great challenge and has become the bottleneck restricting the performance of transparent flexible supercapacitors. Here, Ni(OH)2 nanosheets and amorphous FeOOH nanowires were simply synthesized as micro-structured transparent films through a scalable gas-liquid diffusion method at the air-solution interface. The microstructures are enwrapped in graphene shells (Ni@Gr-TF and Fe@Gr-TF) for increasing rapid 3D electron/ion transport pathways, alleviating the exfoliation and dissolution of active materials into the electrolyte, and extending the potential window of the FeOOH cathode to −1.25-0 V. An asymmetric transparent and flexible supercapacitor (ATFS) based on Ni@Gr-TF//Fe@Gr-TF exhibited a transmittance of 52.3% at 550 nm, a high specific capacity of 17.42 mF cm−2 at 0.2 mA cm−2 (one order higher than the maximum value reported for a transparent graphene membrane), an energy density of 0.67 mWh cm−3 based on the entire device (comparable with nontransparent devices) as well as a high capacity retention (85.1%) after a long cycle life of 20 000 cycles.