Zwitterionic Engineering of Vinylene-Linked Covalent Organic Frameworks for Superior Protonic Electrolytes

Solid protonic electrolytes are a promising avenue for advanced solid-state proton batteries, offering enhanced safety, long-term cycling stability, and high energy density. However, achieving high proton conductivity under ambient conditions remains a formidable challenge. In this study, we demonstrate a highly robust zwitterionic vinylene-linked covalent organic framework (COF) engineered with sulfobetaine functionalities that promote efficient proton dissociation and migration, enabling superior proton conduction under ambient conditions and setting a new benchmark in the COF field. The solid protonic electrolyte comprising phosphoric acid-modified zwitterionic COFs achieved the highest proton conductivity (5.34 × 10^-2 S cm^-1) under ambient conditions among all reported COF-based protonic electrolytes, along with incredible long-term stability. Furthermore, solid-state proton batteries assembled using the solid electrolyte delivered a record-high specific capacity (108.5 mAh g^-1 at 1.0 A g^-1), good cycling durability (90% capacity retention after 2000 charge-discharge cycles at 1.0 A g^-1), and excellent rate capability. This study presents a viable and effective strategy for constructing high-performance COF-based protonic electrolytes tailored for advanced solid-state proton battery technologies.