Tunable capacitance in all-inkjet-printed nanosheet heterostructures

Heterostructures constructed from two-dimensional (2D) building blocks have shown promise for field-effect transistors, memory devices, photosensors and other electronic applications. 2D nanosheet crystals are typically constructed into multilayer heterostructures using layer-by-layer methods, which cannot be used to fabricate large-scale and thick heterostructures, due to the time-consuming nature and low efficiency of the process. An alternative approach to deposit different 2D materials in the controllable fashion is by inkjet printing. Here we show the fabrication of supercapacitors based on 2D heterostructures by inkjet printing Ti₃C₂T_x MXene nanosheets as electrodes, followed by inkjet printing graphene oxide nanosheets as solid-state electrolyte. The free water molecules trapped between graphene oxide sheets facilitate proton movement through the layered solid electrolyte. The as-made heterostructures show high areal capacitance, good cycling stability and high areal energy and power densities comparable with existing printed supercapacitors. Moreover, the specific capacitance can be increased further by addition of liquid electrolytes.