Metal-organic framework formation by [Fe4S4] clusters offers promising electrochemical performance

Abstract

[Fe₄S₄] clusters have served as molecular batteries and charge transfer centers in many biosystems. However, their potential as electrode materials has been overlooked amidst the ever-increasing studies on various materials in the search for efficient battery compositions. To evaluate their electrochemical efficiency as electrode materials, we focused on the use of two important oxidation states, [Fe₄S₄]²⁺ and [Fe₄S₄]⁰, in a series of Li-, Na-, K-, Mg-, Ca-, and Zn-ion batteries. We also assessed the effect of metal–organic framework (MOF) formation on their performance by studying [Fe₄S₄]²⁺-1,4-benzenedithiolate MOF (BMOF) and its carboxylate-based counterpart (CMOF). Our model-based Density Functional Theory (DFT) calculations indicated that oxidation of the cluster to [Fe₄S₄]²⁺ and MOF formation significantly improve the electrochemical efficiency of the cluster. Among the studied electrode materials and metals, the BMOF combination with Mg⁰ and Zn²⁺ presented the best electrochemical performance. Notably, our periodic calculations indicated an open circuit voltage of 4.32 V for the Zn²⁺-BMOF system, suggesting a promising performance for BMOF compared to other cathode/negative electrode materials. Our atomic and electronic structure analyses indicated that intercalation is the underlying electrochemical mechanism.