Mesostructure-Dependent Capacitive Performance in Two-Dimensional Conductive Metal–Organic Framework Films: Effects of Crystallite Orientation and Aggregation Morphology

Performance of two-dimensional conductive metal-organic frameworks (MOFs) in supercapacitor applications relies not only on their intrinsic structural properties but also on their mesostructures related to the size, shape, orientation, and aggregation morphology of crystallites assembled on a current collector. Nevertheless, the influence of crystallite orientation and aggregation morphology on the capacitive behavior remains poorly understood. Herein, the capacitive performance of dense face-on, sparse face-on, and edge-on Cu₃(HHTP)₂ (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) films, with controlled thicknesses and distinct crystallite morphologies, was systematically investigated in an aqueous electrolyte (3 M KCl). Face-on films showed a positive correlation between areal capacitance and thickness, indicating efficient electron and ion transport along their vertically aligned [001] channels. Although sparse face-on films exhibited a lower volumetric capacitance (98 F cm^-3) than dense films (205 F cm^-3), their isolated rod-like crystallites facilitated lateral interlayer ion diffusion, notably accelerating capacitive kinetics. Conversely, edge-on films displayed increasing areal capacitance only up to a limited thickness (883 nm), beyond which ion diffusion was impeded by a dense base layer formed by lateral intergrowth of vertically aligned sheet-like crystallites. Interestingly, despite featuring much shorter [001] channels, edge-on films showed slower capacitive kinetics than face-on films of comparable thicknesses, which was attributed to their more geometrically heterogeneous surface.