Electrochemical Reconstruction of Co_<i>x</i>Ni_1–<i>x</i>-MOF-74 Microfibers: Influence of Atomic Ratio on Morphological Evolution

Understanding the interplay between metal-node stability and electrochemical conditions is essential for designing metal–organic framework (MOF) derivatives with tailored morphologies through electrochemical reconstruction. Here, we synthesized high-aspect-ratio CoxNi1–x-MOF-74 microfibers with varying Co2+ to Ni2+ atomic ratios and investigated their electrochemical reconstruction in alkaline electrolyte within a pre-OER potential range. The atomic ratio significantly influences the morphological evolution of the MOFs during electrochemical cycling. Co-MOF-74 experiences substantial corrosion, losing its initial microfiber morphology and transforming into nanosheets. However, the incorporation of Ni2+ into MOF-74 improve its stability against electrooxidation. Notably, the derivatives of Co0.75Ni0.25-MOF-74 exhibit a unique hollow microfiber morphology, resulting from the complete dissolution of the MOF core while retaining a bimetallic hydroxide shell. As the Ni2+ content increases, CoxNi1–x-MOF-74 transforms into core–shell microfibers, where the hydroxide forms on the surface while residual MOF remains in the core. Operando Raman analysis reveals asynchronous oxidation of Co2+ and Ni2+, further supporting the role of the dissolution-redeposition mechanism in driving morphological transformation. This electrochemical reconstruction strategy can be extended to producing other bimetallic hydroxide-oxyhydroxide materials, providing essential insights into the design of bimetallic MOF derivatives with unique and tunable morphologies for various applications.