From Mixed-Metal MOFs to Carbon-Coated Core-Shell Metal Alloy@Metal Oxide Solid Solutions: Transformation of Co/Ni-MOF-74 to CoNi@CoNiO@C for the Oxygen Evolution Reaction.

Calcination of the mixed-metal species Co/Ni-MOF-74 leads to the formation of carbon-coated CoNi@CoNiO with a metal core diameter of ∼3.2 nm and a metal oxide shell thickness of ∼2.4 nm embedded uniformly in the ligand-derived carbon matrix. The close proximity of Co and Ni in the mixed-metal Co/Ni-MOF-74 promotes the metal alloying and the formation of a solid solution of metal oxide during the calcination process. The presence of the tightly coated carbon shell prohibits particle agglomeration and stabilizes the CoNi@CoNiO nanoparticles in small size. The CoNi@CoNiO@C derived from Co/Ni-MOF-74 nanocomposites show superior performance for the oxygen evolution reaction (OER). The use of mixed-metal MOFs as precursors represents a powerful strategy for the fabrication of metal alloy@metal oxide solid solution nanoparticles in small size. This method also holds great promise in the development of multifunctional carbon-coated complex core-shell metal/metal oxides owing to the diversified MOF structures and their flexible chemistry.