LAUSR

Porous crystalline covalent organic frameworks (COFs) suffer from the difficulty of forming crystalline thin films, which hinders their application in membrane devices. Here, a strategy is developed for forming highly crystalline 2D COFs thin films via unique in situ thermal evaporation followed by solvent vapor annealing. Two different COFs are selected containing 1,3,5-triformylphloroglucinol (Tp), ionic triaminoguanidine hydrochloride (TGCl), and neutral 2,2'-bipyridine-5,5'-diamine (Bpy) monomers because of their common use in energy storage devices. The results show that the condensation rate between the monomers of Tp and ionic TGCl is faster than that of Tp and Bpy during the solvent vapor annealing, which leads to a homogeneous ionic TpTGCl crystalline thin film whereas the neutral TpBpy thin film consists of crystalline islands. AFM nanoindentation revealed a high stiffness of the ionic TpTGCl thin film compared to the neutral TpBpy thin film. Using polycrystalline TpTGCl and TpBpy thin films, Zn-air batteries (ZABs) are produced by covering Zn plates with the ionic TpTGCl (TpTGCl/Zn) and neutral TpBpy (TpBpy/Zn) thin films as anodes. As produced, TpTGCl/Zn-based ZAB exhibits a long cycle life of 91 h due to the high hydroxide ion conductivity and the Zn dendrites suppression.