All-Solid-State Proton-Based Tandem Structure Achieving Ultrafast Switching Electrochromic Windows

All-solid-state electrochromic devices (ECDs) for smart-window applications currently suffer from limited ion diffusion speed, which lead to slow coloration and bleaching processes. Here, we design an all-solid-state tandem structure with protons as diffusing species achieving an ultrafast switching ECD. We use WO3 as the electrochromic material, while poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) as the solid-state proton source to enable fast switching. This structure by itself exhibits low optical modulation (i.e., difference of on/off transmittance). We further introduce a solid polymeric electrolyte layer on top of PEDOT:PSS to form a tandem structure, which provides Na+ ions to PEDOT:PSS and pump protons there to the WO3 layer through ion exchange. Our new all-solid-state ECD features high optical modulation (>92% at 650 nm), fast response (coloration to 90% in 0.7 s and bleaching to 65% in 0.9 s and 90% in 7.1 s) and excellent stability (<10% degradation after 3000 cycles). Large-area (30×40 cm2) as well as flexible devices are fabricated to demonstrate the great potential for scaling up.

Development of a Chitosan/PVA/TiO2 Nanocomposite for Application as a Solid Polymeric Electrolyte in Fuel Cells

The influence of the incorporation of nanoparticles of titanium oxide (TiO2) at a concentration between 1000 and 50,000 ppm on the physicochemical and mechanical properties of a polymer matrix formed from a binary mixture of chitosan (CS) and polyvinyl alcohol (PVA) at a ratio of 80:20 and the possibility of its use as a solid polymeric electrolyte were evaluated. With the mixture of the precursors, a membrane was formed with the solvent evaporation technique (casting). It was found that the incorporation of the nanoparticles affected the moisture absorption of the material; the samples with the highest concentrations displayed predominantly hydrophobic behavior, while the samples with the lowest content displayed absorption values of 90%. Additionally, thermogravimetric analysis (TGA) showed relatively low dehydration in the materials that contained low concentrations of filler; moreover, differential scanning calorimetry (DSC) showed that the nanoparticles did not significantly affect the thermal transitions (Tg and Tm) of the compound. The ionic conductivity of the compound with a relatively low concentration of 1000 ppm TiO2 nanoparticles was determined by complex impedance spectroscopy. The membranes doped with a 4 M KOH solution demonstrated an increase in conductivity of two orders of magnitude, reaching values of 10−6 S·cm−1 at room temperature in previously dried samples, compared to that of the undoped samples, while their activation energy was reduced by 50% with respect to that of the undoped samples. The voltage–current test in a proton exchange membrane fuel cell (PEMFC) indicated an energy efficiency of 17% and an open circuit voltage of 1.0 V for the undoped compound, and these results were comparable to those obtained for the commercial membrane product Nafion® 117 in evaluations performed under conditions of 90% moisture saturation. However, the tests indicated a low current density in the undoped compound.