Development of Inverse-Opal-Structured Charge-Deficient Co₉S₈@nitrogen-Doped-Carbon to Catalytically Enable High Energy and High Power for the Two-Electron Transfer I⁺/I^- Electrode.

Abstract

The iodine (I) electrode involving two-electron transfer chemistry by converting between I⁺ and I^-, has the potential to deliver theoretically doubled capacity and higher working voltage platforms, thus achieving higher energy density. However, owing to the slow kinetics of the cascade two-electron transfer reactions, the system suffers from large overpotentials and low power density, especially at high working currents and low temperatures. Here, an inverse-opal-structured cobalt sulfide@nitrogen-doped-carbon (Co₉S₈@NC) catalyst with unique charge-deficient states is developed to promote the reaction kinetics of the I^-/I⁺ electrode. The charge-deficient Co₉S₈@NC catalyst not only enables strong physicochemical adsorption with the iodine species but also significantly reduces the activation energy and interfacial charge transfer resistance of the cascade I⁺/I⁰/I^- conversion reaction. Consequently, the prototypical Zn‖I⁺/I⁰/I^- battery equipped with the Co₉S₈@NC catalyst can deliver a high energy density of 554 Wh kg^-1 and a stable cycle life of 5000 cycles at 30 °C. Moreover, at a subzero temperature of -30 °C, the battery can exhibit enhanced kinetics and a high power density of 1514 W kg^-1, high energy density of 485 Wh kg^-1.