Developing bimetallic FeM–organic frameworks based on ferroalloy trinuclear clusters for high-performance supercapacitors

Abstract

Alloying is an effective method to enhance the properties of materials, as evidenced by the addition of a second metal in steelmaking to create iron alloys. Inspired by this, the introduction of analogous inorganic building units into metal–organic frameworks (MOFs) is hypothesized to improve their porous environment, framework charges, and redox performance. However, accurately incorporating multiple metals into homo-metallic MOFs poses a significant challenge, unlike the relatively straightforward process in iron alloys. Heterometallization of MOFs not only modulates the pore characteristics of the parent MOFs but also results in materials with exceptional stability and reversibility in electrochemical reactions. In this study, by leveraging the exceptional compatibility of metals within trinuclear clusters, a sequence of alloy-like [M₃O(O₂C)₆] structures (M₃ = Fe₂Mn, Fe₂Co, Fe₂Ni) were successfully synthesized, yielding a robust Fe/M-MOF ({Fe₂MO(DCPB)₂(H₂O)₂}, (M = Mn, Co, Ni)) material family. In particular, due to the synergistic effects of multi-metallic active sites, the Fe₂M (with M = Mn, Co, Ni) ternary alloy-like cluster-based materials ({Fe₂MO(DCPB)₂(H₂O)₂} (M = Mn, Co, Ni), DCPB = 3,5-di(4′-carboxyphenyl)benzoic acid) exhibit exceptional stability and high specific capacitances. The Fe-MOF, Fe/Mn-MOF, Fe/Co-MOF, and Fe/Ni-MOF demonstrate high specific capacitances of 268, 752, 1145, and 1210 F g⁻¹ at 1 A g⁻¹, respectively. An asymmetric solid-state device, Fe/Ni-MOF//AC, also achieves a high energy density and long cycling life. This strategy of using a multi-alloy-like building block has the potential for the precise design of MOFs and the development of advanced electrode materials for supercapacitors and energy storage systems.