Synergistic Donor-Acceptor Effect in Conductive Covalent Organic Frameworks of Polyphthalocyanines for Aqueous Zn-I₂...

The development of materials with sufficient electrical conductivity and electroactivity is crucial for advancing their application in energy storage; however, integrating feasible electron transport properties and redox activity in a material remains a significant challenge. Here, we report two conjugated COFs constructed with fully aromatic linkages, namely poly-zinc phthalocyanine (pZnPc) and poly-zinc naphthalocyanine (pZnNPc), which exhibit distinct degrees of π-conjugation, endowing them with good electrical conductivity. Iodine incorporation further induces remarkable conductivity increases up to two orders of magnitude with 1 S m^-1 for pZnPc and 0.15 S m^-1 for pZnNPc, along with a 200% enhancement in the electroactivity of iodine (I₂). Spectroscopic analyses and density functional theory (DFT) calculations reveal that the host-guest charge-transfer interaction between the COFs and I₂ allows the formation of an electron donor-acceptor system, which synergistically facilitates electron transport to improve the electrical conductivity of the system and lowers the reaction barrier for the iodine redox reaction, consequently suppressing the shuttling of the I₃ ^-/I₅ ^- intermediates. As a result, the host-guest complex material I₂@pZnPc as a cathode in aqueous Zn-I₂ batteries delivers a high specific capacity of 234.4 mAh g^-1, close to the theoretical limit of I₂, meanwhile offering excellent cycling stability of over 40,000 cycles.