Incorporating electrospun nanofibers of TEMPO-grafted PVDF-HFP polymer matrix in viologen-based electrochromic devices

A novel polymer, denoted as TP-X, is synthesized by grafting 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) onto the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) backbone. TP-X was electrospun into a nanofibrous polymer matrix and introduced into viologen-based electrochromic devices (ECDs). Heptyl viologen (HV) was chosen as the electrochromic material and TEMPO was added as the stable redox couple in the ECDs in this study. The results show that the addition of TP-X nanofibers (TP-X NF) effectively reduced the aggregation of HV and the grafted TEMPO moieties provide the extended surface area for electron transfer. The reduction in viologen aggregation led to outstanding stability and the extended electron transfer surface area resulted in fast write-erase response for ECDs with TP-X NF polymer matrix. The optimized ECD containing the TP-10 NF showed fast write-erase response times of 2.3 and 1.5 s for bleaching and coloring at 605 nm, respectively. More importantly, the incorporation of TP-10 NF gave improved stability of the ECDs, which retained more than 83% of its initial transmittance change at 605 nm after 10,000 operation cycles, as compared to the conventional solution-type ECD (27.3%). This study provides a potential polymer matrix to be utilized in various electrochemical applications for pursuing decent performance and reliable stability.