Polymerized Melamine Catalyzes Direct I − /I 2 Conversion via ─N═N─ Motif for HighCapacity Zn‐I 2 Batteries

To fundamentally solve low iodine conversion efficiency and severe polyiodide shuttling, a high-performance catalytic organic cathode is developed by in situ polymerizing melamine (MA) on activated carbon (denoted as pMA@AC) for high-capacity Zn-I2 batteries. The pMA@AC cathode exhibits a high capacity of 1.6 mAh cm−2 and an ultra-long lifespan over 20 000 cycles, benefiting the stable pouch cell with 440 mAh and 183 Wh kg−1 after 100 cycles. In/ex situ characterizations coupled with theoretical calculations demonstrate that polymelamine (pMA) catalyzed efficient I−/I2 conversion, suppressing polyiodide formation and avoiding consequent shuttling for high Coulombic efficiency and enhanced lifespan. The high catalytic activity of pMA is attributed to the delocalized 𝝅 electron cloud on ─N═N─ sites, which connect to electron-withdrawing triazine groups, with weaker physicochemical adsorption to I−/I2 than traditional carbon-based catalysts. It thus boosts the formation/desorption of resultant I2 molecules at higher potential for enhanced cycling stability. More importantly, pMA@AC exhibits robust catalytic ability for four-electron I−/I0 /I+ chemistry with 405 mAh g−1 and 10 000 cycles, further strengthening the potential application of such azo compounds for advanced Zn-halogen batteries.