Enhanced redox kinetics of iodine electrocatalyzed by cobalt (II) phthalocyanine for high-performance zinc-iodine battery

Zinc-iodine batteries (ZIBs) still suffer from severe shuttle effects and sluggish reaction kinetics of the iodine species, which result in inferior cycle life and unsatisfactory rate performance. Although physical immobilization and chemical adsorption had been used to confine iodine species, the redox kinetics of iodine in ZIBs still needed to be improved. Herein, cobalt (II) phthalocyanines (CoPc) were loaded on actived carbon fiber (ACF) uniformly via π-π interaction and served as I2 support to fabricate CoPc-ACF/I2 cathodes materials of ZIBs. Actived carbon fiber (ACF) as effective catalyst support can achieve high dispersion of cobalt phthalocyanine (CoPc) while maintaining high conductivity of composite, and its favorable porous structure is also conducive to iodine loading. The electrocatalytic effect of CoPc can significantly reduce energy barriers and simultaneously accelerate charge transfer to achieve a faster reaction kinetic process for iodine reduction reactions. In particular, the CoPc-ACF matrix shows a remarkably lower Tafel slope (253.4 mV dec−1) and lower energy barrier (18.04 kJ mol−1) compared with the ACF matrix (395.69 mV dec−1 and 36.25 kJ mol−1) for the iodine redox reaction. Consequently, the CoPc-ACF/I2 cathode delivers a specific capacity of 203.6 mAh g−1 at 0.5 A g−1, an excellent rate capability with 151.4 mAh g−1 achieved even at 15 A g−1, and ultra-stable cycle life over 8000 cycles with 89.2% capacity retention. This work provides fresh insight into the design and development for achieving ZIBs with high performance.