Zwitterion-Engineered Covalent Organic Frameworks Achieving Record Proton Conductivity for High-Performance Proton Batteries

Abstract

Developing green energy is vital in the dual-carbon era, with proton batteries showing great promise but being limited by the lack of high-performance solid-state protonic electrolytes. Covalent organic frameworks (COFs) are emerging as a promising platform, yet most reported COF-based electrolytes exhibit inferior proton conductivity under ambient conditions. Furthermore, the requirement of excessive guest-acid loading to boost proton conductivity often results in severe electrode corrosion and shortened battery lifetime. Herein, we propose zwitterion engineering as an effective strategy to overcome these limitations, enabling COFs to achieve superior proton conductivity with reduced acid content, thereby facilitating the development of proton batteries with both high specific capacity and long cycle life. Zwitterionic groups are grafted onto a phthalocyanine-based COF through post-synthetic modification, followed by incorporation of methanesulfonic acid to yield a solid-state COF-based protonic electrolyte. The zwitterionic functionalities, possessing strong dipole moment, high dielectric constant, and excellent hydrophilicity, significantly accelerate proton dissociation and migration. Consequently, even with relatively low acid loading, the obtained electrolyte shows an impressive proton conductivity of 8.26 × 10−2 S cm−1 under ambient conditions, surpassing all previously reported COF-based protonic electrolytes. More importantly, when integrated into solid-state proton batteries, it exhibits outstanding electrochemical performance, retaining a capacity of 93.4 mAh g−1 after 5000 charge-discharge cycles at 1.0 A g−1.