Cerium(IV)-Based Metal–Organic Framework Nanostructures Grown on 3D-Printed Free-Standing Membranes and Their Derivatives for Charge Storage

Shaping the nanoporous metal–organic frameworks (MOFs) into processable monoliths or membranes while preserving their crystalline structures and functions is crucial for various applications, and additive manufacturing (or 3D printing) allows the programable fabrication of objects with customizable sizes and shapes. Herein, 3D-printed polymeric hydrogels with adjustable shapes are prepared with the use of cellulose nanocrystals (CNCs) as the rheology modifier for printing, and the CNCs present in the hydrogels with enriched hydroxyl groups on their surfaces are further utilized to initiate the crystal growth of a redox-active cerium-based MOF. MOF crystals uniformly grown on the surface of 3D-printed free-standing membranes are thus obtained, and such MOF growth is feasible on size-adjustable 3D-printed objects. As a demonstration, the membranes with the MOF are further carbonized at various temperatures to prepare the MOF-derived membranes composed of nanosized ceria and nitrogen-doped carbon, and the resulting membranes serve as the free-standing electrodes for supercapacitors. Cyclic voltammetric and galvanostatic charge–discharge measurements are used to examine the charge-storage performances of the membranes, and the capacitive contributions originating from the redox reaction of ceria and non-Faradaic processes of the porous carbon are quantified, respectively. The findings here provide a strategy to integrate the functional MOF and the 3D-printing technique to fabricate size-adjustable MOF-based monoliths and membranes, which have the potential for a range of applications.