Controlled Chemical Vapor Deposition for Synthesis of Nanowire Arrays of Metal–Organic Frameworks and Their Thermal Conversion to Carbon/Metal Oxide Hybrid Materials

Abstract

Metal–organic frameworks (MOFs) can serve as high-surface-area templates to generate hierarchically ordered nanoporous carbon electrodes for high-performance supercapacitor devices. Here we describe a simple chemical approach to synthesize dense three-dimensional (3D) arrays of core–shell ZnO@ZIF-8 and Co(CO3)0.5(OH)·0.11H2O@ZIF-67 nanowires on a conductive carbon cloth. Annealing the core–shell structures at high temperatures converted the MOF shell into a composite of nanoporous carbon (NC) mixed with conductive metal oxides. The conformal nature of the MOF-coating process generates a NC film with continuous conductive paths from the outer surfaces of the nanowires down to the flexible carbon electrode. Carbonization of ZIF-67 transforms the material into conductive sp2 type carbon mixed with Co3O4 nanostructures. Because Co3O4 is a faradic metal oxide with a high theoretical capacitance, these Co3O4/NC hybrid heterostructure arrays are a promising candidate material for use in an electrochemical superc...