Acidified naphthalene diimide covalent organic frameworks with superior proton conduction for solid-state proton batteries

Proton batteries are emerging as leading candidates for the next generation of energy storage systems, thanks to their high-power density and the abundant availability of protons. However, the development of electrolytes is still in its infancy, which currently limits the overall performance of proton batteries. In this study, we present the first demonstration of a naphthalene diimide covalent-organic framework (PNDI-COF) utilized as a solid-state proton electrolyte, showcasing its potential for promising applications in solid-state proton batteries. Phosphoric acid (PA) molecules were introduced and stabilized within the nanoporous channels of PNDI-COF to yield the solid-state proton electrolyte (PA@PNDI-COF), which showed superprotonic conduction with a wide-temperature range from −30 to 90 °C, with a proton conductivity of 4.2 × 10⁻³ S cm⁻¹ at −30 °C and 3.8 × 10⁻² S cm⁻¹ at 90 °C and ambient humidity, expanded electrochemical stability window (2.9 V, vs. SCE) and stable cycling of the full proton battery (80% capacity retention after 2000 cycles at 1 A g⁻¹), surpassing performance metrics reported for solid-state proton batteries. This study provides valuable insights for designing COF-based proton conductors and solid-state proton battery applications.