Two-Dimensional Metal-Organic Framework for Supercapacitors: Thickness-Dependent Charge Storage Mechanisms

Additive-free active materials are desirable for energy storage devices as they reduce processing complexity and eliminate variability from binders or conductive additives. We report the synthesis of a highly stable, two-dimensional copper-based metal-organic framework (CuMOF) film with a tunable thickness. The exceptional adhesion of CuMOF films to electrode surfaces enables a binder-free fabrication approach, addressing a key challenge in energy storage applications, particularly in electrode design. The film exhibits a columnar morphology with well-defined grain boundaries and a high surface area, making it optimal for supercapacitor applications. Electrochemical characterization on glassy carbon electrodes yielded an areal capacitance of 2.9 mF/cm² at a scan rate of 1 mV/s using a ∼160 nm thick CuMOF film. We investigated films as thin as 2.4 nm, where the capacitance is predominantly governed by electrical double-layer effects, highlighting the interplay between the film structure and electrochemical behavior. Thus, CuMOF films offer practical applicability, advancing efficient binder-free energy storage.