Biopolymer Electrolyte Membranes (BioPEMs) for Sustainable Primary Redox Batteries

The proliferation of portable electronic devices has resulted in an increase of e-waste that is generated after their use. One of the most hazardous components in e-waste are batteries, due to their content of heavy metals and toxic chemicals. Fuel cells and redox flow batteries have been recognized as more sustainable alternatives to Li-based batteries for powering portable applications. Although they provide comparable energy and power densities, they still face some challenges because they rely on proton exchange membranes based on nonenvironmentally friendly, high-priced perfluorosulfonic acid copolymers that require energy-intense manufacturing and recycling procedures. In this work, eco-friendly and sustainable biopolymer electrolyte membranes (BioPEMs) are synthesized from biopolymers like chitosan, cellulose, and starch. These BioPEMs bring forth advantages in performance, sustainability, and cost. Additionally, they present good chemical and mechanical stability, high ionic conductivity in the same order of magnitude as Nafion membranes. Two alternatives of cellulose–chitosan based BioPEMs are successfully applied into primary redox batteries using benign eco-friendly redox chemistries, delivering open circuit voltages above 0.75 V and power output up to 2.5 mW cm⁻². These results demonstrate BioPEMs capability to improve biodegradable batteries in sectors requiring a transient electrical energy, such as environmental monitoring, agriculture, or packaging.