Practical four-electron zinc-iodine aqueous batteries enabled by orbital hybridization induced adsorption-catalysis

The successive I^-/I⁰/I⁺ redox couples in the four-electron zinc-iodine aqueous battery (4eZIB) is plagued by the instability of the electrophilic I⁺ species, which could either be hydrolyzed or be neutralized by the I₃^- redox intermediates. We present an adsorption-catalysis approach that effectively suppresses the hydrolysis of ICl species and also provides an enhanced reaction kinetics to surpass the formation of triiodide ions. We elucidate that the improved stability is attributed to the pronounced orbital hybridization between the d orbitals of Fe-N₄ moieties (atomic Fe supported on nitrogen doped carbon) and the p orbitals of iodine species (I₂ and ICl). Such d-p orbital hybridization leads to enhanced adsorption for iodine species, increased energy barrier for proton detachment from the ICl·HOH intermediate during hydrolysis, and efficient catalysis of the iodine redox reactions with high conversion efficiency. The proposed 4eZIB demonstrates practical areal capacity (>3 mAh cm^-2) with a near-unity coulombic efficiency, high energy density of 420 Wh kg^-1 (based on cathode mass), and long-term stability (over 10,000 cycles). Even at -20 °C, the battery exhibits stable performance for over 1000 cycles with high iodine utilization ratio.