Characterizing Biopolymer Electrolytes in Zinc–Air Batteries: Challenges, Best Practices, and a Robust Workflow Guiding Future Research Paths

ABSTRACT Bio‐based gel polymer electrolytes (GPEs) are emerging as promising components for rechargeable zinc–air batteries (ZABs), combining electrochemical functionality, mechanical adaptability, and sustainability. Yet, progress in this area is increasingly limited not only by materials design, but also by the lack of rigorous and application‐relevant characterization workflows. This critical, practice‐oriented review assesses the characterization strategies used for bio‐based GPEs in ZABs, focusing on relevant, recent studies reported between 2021 and 2026. Methods are grouped into six categories: mechanical and rheological characterization, electrochemical analysis and cell‐level testing, spectroscopic techniques, microscopy and nanoscale imaging, thermal analysis, and bulk physicochemical characterization. Rather than merely cataloguing methods, the review examines what each technique can reliably reveal, the key parameters controlling data quality, and the limitations imposed by conditions specific to ZAB operation, including highly alkaline environments, dynamic electrode interfaces, and the soft, heterogeneous nature of biopolymer networks. Recurring inconsistencies in experimental practice and reporting are highlighted, and best‐practice recommendations, methodological adaptations, and emerging approaches are discussed. Overall, the review provides a workflow‐oriented framework linking formulation, structure, interfacial behavior, and electrochemical performance, underscoring that better electrolytes require better characterization to enable more rigorous evaluation and accelerate the rational development of next‐generation sustainable GPEs for ZABs.