Tae Gwang Yun, Donghyuk Kim, Yong Ho Kim, Minkyu Park, Seungmin Hyun, and Seung Min Han*
Adv. Mater. 2017, 29, 1606728
First published: 22 June 2017
Electrochromic devices have been widely adopted in energy saving applications by taking advantage of the electrode coloration, but it is critical to develop a new electrochromic device that can undergo smart coloration and can have a wide spectrum in transmittance in response to input light intensity while also functioning as a rechargeable energy storage system. In this study, a photoresponsive electrochromic supercapacitor based on cellulose-nanofiber/Ag-nanowire/reduced-graphene-oxide/WO3-composite electrode that is capable of undergoing “smart” reversible coloration while simultaneously functioning as a reliable energy-storage device is developed. The fabricated device exhibits a high coloration efficiency of 64.8 cm2 C−1 and electrochemical performance with specific capacitance of 406.0 F g−1, energy/power densities of 40.6–47.8 Wh kg−1 and 6.8–16.9 kW kg−1. The electrochromic supercapacitor exhibits excellent cycle reliability, where 75.0% and 94.1% of its coloration efficiency and electrochemical performance is retained, respectively, beyond 10 000 charge–discharge cycles. Cyclic fatigue tests show that the developed device is mechanically durable and suitable for wearable electronics applications. The smart electrochromic supercapacitor system is then integrated with a solar sensor to enable photoresponsive coloration where the transmittance changes in response to varying light intensity.