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(CO 3 ) 0.5 (OH)•0.11H 2 O@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 sp 2 type carbon mixed with Co 3 O 4 nanostructures. Because Co 3 O 4 is a faradic metal oxide with a high theoretical capacitance, these Co 3 O 4 /NC hybrid heterostructure arrays are a promising candidate material for use in an electrochemical supercapacitor device. The Co 3 O 4 /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.

Metal–Organic Framework (MOF)‐Derived Nanoporous Carbon Materials

“…In addition, the porosity of MOFs can be tuned by organic linkers. More interestingly, their structures and functions can be tailored for on‐demand applications through the transition‐metal ions and organic linkers …”

Physical Expansion of Layered Graphene Oxide Nanosheets by Chemical Vapor Deposition of Metal–Organic Frameworks and their Thermal Conversion into Nitrogen‐Doped Porous Carbons for Supercapacitor Applications

“…Inorganic materials such as zinc oxides can be chemically converted into ZIF‐type MOFs in a chemical vapor deposition (CVD) setup (i.e., MOF‐CVD), which results in a large volume expansion of the starting material. Combining this process with graphene should enable researchers to physically expand and maintain the interlayer space between the nanosheets to create more robust nanoporous carbon electrodes with higher surface areas …”

Fabrication of ultra‐small ruthenium nanoparticles on porous modified reduced graphene oxide and its application in solvent‐free oxidation of cyclohexene with molecular oxygen

“…The increasing interest in carbon‐based materials has opened new ways for producing arrays of novel functional nanomaterials due to the discovery of several species (i.e. fullerenes, carbon nanotubes, graphene, mesoporous carbon nitride and MOF‐derived carbons) . Among them, graphene with very thin atomic thickness (0.345 nm) of hexagonally arrayed sp 2 hybridization has attracted wonderful methodical attention in recent years .…”