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

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 supercapacitor device. The Co₃O₄/NC hybrid electrodes had good performance and exhibited a high areal capacitance of 1.22 F·cm^-2 at 0.5 mA·cm^-2. Conformal deposition of MOFs via the chemical vapor method offers a promising new platform to design conductive, ultrahigh surface area electrodes that preserve the 3D morphology for applications in supercapacitors and electrocatalysis.