Supercapacitors of Nanocrystalline Metal–Organic Frameworks

The high porosity of metal–organic frameworks (MOFs) has been used to achieve exceptional gas adsorptive properties but as yet remains largely unexplored for electrochemical energy storage devices. This study shows that MOFs made as nanocrystals (nMOFs) can be doped with graphene and successfully incorporated into devices to function as supercapacitors. A series of 23 different nMOFs with multiple organic functionalities and metal ions, differing pore sizes and shapes, discrete and infinite metal oxide backbones, large and small nanocrystals, and a variety of structure types have been prepared and examined. Several members of this series give high capacitance; in particular, a zirconium MOF exhibits exceptionally high capacitance. It has the stack and areal capacitance of 0.64 and 5.09 mF cm^–2, about 6 times that of the supercapacitors made from the benchmark commercial activated carbon materials and a performance that is preserved over at least 10000 charge/discharge cycles

Three-Dimensional Metal-Catecholate Frameworks and Their Ultrahigh Proton Conductivity

A series of three-dimensional (3D) extended metal catecholates (M-CATs) was synthesized by combining the appropriate metal salt and the hexatopic catecholate linker, H₆THO (THO^6– = triphenylene-2,3,6,7,10,11-hexakis­(olate)) to give Fe­(THO)·Fe­(SO₄) (DMA)₃, Fe-CAT-5, Ti­(THO)·(DMA)₂, Ti-CAT-5, and V­(THO)·(DMA)₂, V-CAT-5 (where DMA = dimethylammonium). Their structures are based on the <b>srs</b> topology and are either a 2-fold interpenetrated (Fe-CAT-5 and Ti-CAT-5) or noninterpenetrated (V-CAT-5) porous anionic framework. These examples are among the first catecholate-based 3D frameworks. The single crystal X-ray diffraction structure of the Fe-CAT-5 shows bound sulfate ligands with DMA guests residing in the pores as counterions, and thus ideally suited for proton conductivity. Accordingly, Fe-CAT-5 exhibits ultrahigh proton conductivity (5.0 × 10^–2 S cm^–1) at 98% relative humidity (RH) and 25 °C. The coexistence of sulfate and DMA ions within the pores play an important role in proton conductivity as also evidenced by the lower conductivity values found for Ti-CAT-5 (8.2 × 10^–4 S cm^–1 at 98% RH and 25 °C), whose structure only contained DMA guests