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 (Co<inf>9</inf>S<inf>8</inf>@NC) catalyst with unique charge-deficient states is developed to promote the reaction kinetics of the I⁻/I⁺ electrode. The charge-deficient Co<inf>9</inf>S<inf>8</inf>@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 Co<inf>9</inf>S<inf>8</inf>@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.