Wednesday, 31 May 2017: 10:20
Grand Salon C - Section 15 (Hilton New Orleans Riverside)
Metal Organic Frameworks (MOFs) are crystalline, open-porous materials consisting of metal ions or metal-oxo units coordinated by electron donating organic ligands and possess very high surface area, well defined pore sizes, tailorable structure and permeability to guest molecules. MOFs have been widely used in catalysis, gas separation, drug storage and delivery, imaging and sensing, optoelectronics and molecular sieving. Although these chemical building blocks can participate in electron exchange processes with the likelihood of providing rich fundamental data; utilizing these materials for energy storage application have been limited. In the present study, composites of a Ni-doped MOF with reduced graphene Oxide (rGO) are synthesized in bulk (gram scale) quantities. The composites are composed of rGO sheets which avoid restacking from the physical presence of MOF crystals. Ni in Ni-doped MOF is found to engage in a reversible, efficient, redox reaction shuttling between Ni and Ni(OH)2 in aqueous potassium hydroxide (KOH) electrolyte. Employing electrochemical impedance spectroscopy, we determined the charge transfer resistance to be 184 mΩ for MOF, 74 mΩ for a Ni doped MOF and 6 mΩ for an rGO-Ni-doped MOF composite, but these modifications do not affect the mass transfer resistance. This redox reaction in conjunction with the lowered charge transfer resistance from the introduction of rGO underpin the synergy which dramatically increases the capacitance to 758 F/g in the rGO-Ni-doped MOF composite, when the parent MOF could store only 100 F/g and a physical composite of rGO and Ni-doped MOF could algebraically achieve about 240 F/g. A generic approach of doping MOFs with a redox active metal and forming a composite with rGO transforms an electro-inactive MOF to high capacity energy storage material with energy density of 37.8 Wh/kg at a power density of 227 W/kg. These results can promote the development of high performance energy storage materials from the wide family of MOFs available.