A cobalt-based layered MOF material for supercapacitor applications

Metal-organic frameworks (MOFs) have been identified as promising electrode materials that increase energy densities in supercapacitors. Importantly, a greater level of understanding of charge storage mechanisms and transport behavior within these materials will facilitate improved design strategies. Here, we present results from the synthesis and characterization of a cobalt-based layered metal−organic framework (Co-LMOF) {[Co(Hmt)2(tfbdc)(H2O)2]·(H2tfbdc)·(EtOH)2}n (H2tfbdc = 2,3,5,6-tetrafluoroterephthalic acid; Hmt = hexamethylenetetramine). Electrochemical measurements were performed with Co-LMOF/Carbon Black/PTFE electrodes that demonstrated that this material indeed shows notable performance potential as a supercapacitor electrode despite electrically insulating behavior determined experimentally and from density of states calculations. Nickel foam and carbon-based current collectors were used to distinguish Co-LMOF redox behavior from double layer and current collector contributions. We also cross-correlated findings from solid state NMR, quasi-elastic neutron scattering, and theoretical modeling to gain new insights into the dynamics of the water and ethanol present in this material. This information was coupled with characterization tools of nitrogen gas sorption, X-ray diffraction, thermal gravimetric analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy. Finally, electrode degradation was evaluated for 10 k galvanostatic charge-discharge cycles with FTIR, Raman and energy dispersion X-ray spectroscopy.