Photo-annealed electrospun TiO2 nanofibers as ion-storage layer for self-rechargeable Zn-based electrochromic energy storage device

Developing a self-rechargeable transparent electrochromic energy storage device (EESD) is highly demanding for advancing electrochromic technology and energy harvesting capabilities. In this study, we introduce a roomtemperature photo-annealing method to fabricate electrospun titanium oxide (TiO2) nanofibers, serving as an ion-storage layer (ISL) on the counter electrode. By monitoring the composition and morphology of the precursor before and after ultraviolet/ozone irradiation, we confirm the formation of oxide nanostructures in electrospun TiO2 nanofibers, which enhances ion transport in the fabricated EESDs. The structural and surface properties of the photo-annealed ISL are comprehensively analyzed using various characterization techniques. Enhanced electrochromic performances are evidenced through cyclic voltammetry, spectroelectrochemical measurements, and charge storage assessments. The Zn-based EESDs with ISL (ISL Zn-EESDs) display rapid electrochemical kinetics, high charge-storing capacities, and long lifespans, with open-circuit potential of 1.2 V, optical contrast of 77 %, discharge capacity of 92 mA h/g, coloration efficiency of 58.63 cm2/C, and 99.9 % efficiency retention up to 250 cycles in both flat and bent states. Furthermore, the practical viability of the ISL Zn-EESDs is demonstrated by powering an LED lamp for several minutes. This approach highlights the potential of ISL ZnEESDs for developing flexible smart windows, opening up a range of promising applications.