Solvent-free and in situ synthesis of three-dimensional covalent organic frameworks thin films on Zn anodes for Zn–air batteries

Direct synthesis of three-dimensional covalent organic frameworks (3D COFs) thin film on substrates is paramount important to their practical application in devices. Here, solvent-free and in situ synthesis of 3D COFs thin films on Zn substrates by thermal evaporation technique are proposed. Two 3D COFs thin films (i.e., TAM-Tp and TAM-BPDA) are constructed by tetrakis(4-aminophenyl)methane (TAM), 1,3,5-triformylphloroglucinol (Tp), and 4,4′-biphenyldicarboxaldehyde (BPDA). The crystallinity of 3D COFs thin films can rival their powders synthesized by the grinding coupled with hydrothermal methods. In particular, TAM-Tp thin film shows superior transporting ability of hydroxide ions and remarkable suppression for Zn dendrites as compared to TAM-BPDA thin film. Therefore, the assembled quasi-solid state and aqueous Zn–air batteries (ZABs) with TAM-Tp thin films exhibit high power densities (63.8 mW cm−2 and 111.6 mW cm−2) and long cyclic lifespans (58 h and 600 h).