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Highly Conducting Bombyx mori Silk Fibroin-Based Electrolytes Incorporating Glycerol, Dimethyl Sulfoxide and [Bmim]PF6

Publication . Fernandes, Tânia C. D.; Gonçalves, Helena M R; Paz, Filipe A. A.; Sousa, Joana F. M.; Valente, Artur J. M.; Silva, Maria M.; Zea Bermudez, Verónica de; Pereira, Rui F. P.

Green, transparent and flexible electrolyte films composed of a Bombyx mori silk fibroin (SF) host biopolymer doped with glycerol (G), dimethyl sulfoxide (DMSO, D) and 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim]PF6) ionic liquid (IL), were synthesized. The materials were represented by the notation SF@GD@ILx (x = 15, 20 and 30 is the mass ratio of SF/[Bmim]PF6 in %). SF@, SF@G, SF@D and SF@GD samples were also prepared. DMSO was found to play a dual-role, acting as solvent of [Bmim]PF6, and enhancing ionic conductivity. DMSO, alone or combined with [Bmim]PF6, led to the increase of the mean roughness and induced the formation of more ordered Silk II conformations (β-sheets). No structural modifications were detected in the SF@GD@ILx samples upon increasing the temperature up to 100 °C. The highest ionic conductivity was exhibited by the IL-rich sample SF@GD@IL30 (1.07 and 4.61 mS cm−1, at 22 and 100 °C, respectively). In the [Bmim]PF6-doped electrolytes "free" and coordinated PF6− ions coexist. The weight losses occurring below 200 °C involved essentially the release of adsorbed water and DMSO. The suitable mechanical properties, high ionic conductivity and good electrochemical stability suggest that these electrolytes are attractive candidates for application in electrochemical devices.

2020Journal article

Open access

Proton conducting electrolytes composed of chondroitin sulfate polysaccharide and citric acid

Publication . Santos, Filipe M.; Barbosa, Paula C.; Pereira, Rui F.P.; Silva, M. Manuela; Gonçalves, Helena M R; Nunes, Sílvia C.; Figueiredo, Filipe L.; Valente, Artur J.M.; Zea Bermudez, Verónica de

Novel electrolytes composed of chondroitin sulfate A (CSA) and citric acid (CA) have been prepared using a clean, safe, and fast route. These electrolytes exhibit different physical-chemical properties, depending on the amount of CA. For X > 82.3%, where X is the mass ratio, in %, of CA/(CA + CSA), whitish polycrystalline powders result. Lower amounts of CA leads to the production of translucent, amorphous films, sticky for X = 75.6 and 82.0, brittle for X < 43.6 and crack-free, self-standing for 43.6 < X < 75.6%. The results obtained provide evidence that, at low pH, strong hydrogen bonding interactions take place between the anionic sulfonic and carboxylic groups of CSA and CA. CA exerts a key role, acting as a cross-linker and proton source, while simultaneously influencing sample morphology. At room temperature the highest ionic conductivity is achieved at X = 60.8%. A significant enhancement of the ionic conductivity of this sample occurs with the increase of relative humidity (RH) (from 3.1 × 10−7 to 3.7 × 10−2 S cm−1 30% for RH = 30 and ~100%, respectively).

2020Journal article

Open access