N-doped few-layered graphene-polyNi complex nanocomposite with excellent electrochromic properties

A new nanocomposite was obtained through the incorporation of N-doped few-layered graphene (N-FLG) into films of the electroactive polymer poly[Ni(3-Mesalen)] (poly[1]). The nanocomposite, N-FLG@poly[1], prepared by in situ electropolymerization, showed similar electrochemical responses to pristine poly[1], but with more well-defined redox peaks and higher current intensities, in compliance with larger electroactive surface coverage. N-FLG incorporation did not affect the electronic structure of poly[1], but decreased in 12% the molar extinction coefficient of the charge transfer band between metal and oxidized ligand, which is a promising advantage since this band is related to polymer degradation. The N-FLG@poly[1] showed multi-electrochromic behaviour (yellow in reduced state and green/russet in oxidized states) and revealed excellent improvement in electrochromic performance compared to original poly[1], specifically an increase of 71% in electrochemical stability (loss of 2.7% in charge after 10 000 switching cycles). Furthermore, nanocomposite formation decreased the switching time for oxidation (reduction) τ = 9 s (11 s) and improved the optical contrast (ΔT = 35.9%; increase of 38%) and colouration efficiency (η = 108.9 cm2 C−1; increase of 12%), for a representative film of coverage Γ = 296 nmol cm−2. The excellent electrochromic performance improvements are attributed to the alternative conducting pathways and to morphological modifications induced by N-FLG.