Advanced processing and characterization of Nafion film for solid state electrochromic devices

Here, we present the processing and the characterization of a suitable Nafion film with the certain thickness of 8 μm used as electrolyte layer in a novel solidstate EC device fabricated at room temperature (RT) on a single substrate (both glass and plastics) with an architecture based on a substrate/ITO/WO3/Nafion-film/ITO configuration. In particular, we focused on the morphological characteristics, proton conductivity and water molecular dynamics of Nafion film in order to provide insight into the EC behavior of these novel devices. EIS analysis performed over a wide range of RH and temperature, showed good proton conductivity values (e.g. 4.42 ×10−3 S cm−1 at 30 °C and 50% RH), suitable for practical EC operation. At the same time, high values of water self-diffusion coefficients (D) and the spinlattice relaxation times (T1) were measured by NMR spectroscopy, proving a similar behavior as well as the same proton conduction mechanism with that observed for thicker Nafion membrane (50 μm thick) prepared by solution casting. These findings were confirmed by the water uptake measurements since both the film and the membrane showed a water uptake value of about 24 wt%