Synthesis and characterization of Chitosan‑Avocado seed starch hydrogels as electrolytes for zinc‑air batteries

Abstract

The application of innovative batteries is considered a plausible option to overcome the need to store energy. Current investigations focus on improving electrolytes in solid or gel states. Biopolymers are an excellent choice for gel electrolytes. In addition, polymer blends offer a high amorphous system compared to a single polymer improving its properties. In the present work, gel polymeric electrolytes (GPEs) were synthesized based on chitosan and starch. Chitosan and starch are compatible, and they served as a polymer host due to their high structural strength and low crystallinity degree. Moreover, epichlorohydrin was employed as a chemical crosslinker to create a reasonable degree of swelling of 12 M KOH solution. Hydrogels of different compositions were structurally and electrochemically characterized by ATR-Fourier Infrared Spectroscopy (ATR-FTIR), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and Cyclic Voltammetry (CV). The electrolyte film with the highest conductivity values was CS:A 3:3 embedded in 12 M KOH solution, which reached a conductivity of 0.027 S·cm− 1 at room temperature. Structural characterization of chitosan-starch membranes showed an enhanced thermal stability and decrease in crystallinity degree due to the reticulation and absorption of KOH. The cyclic voltammetry study showed a quasi-reversible behavior of the GPEs during the redox processes. Finally, GPEs were tested in Zn-air batteries, with a maximum power density of 8.82 mW·cm− 2 for CS:A 3:3 Sw at 25 °C. The present study suggests that chitosan-starch GPEs can be good candidates to support the sustainable energy transition.