Abstract
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 Ti3C2Tx 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.
Highlights
Two-dimensional heterostructures with vertical stacking configurations are useful for a vast range of applications due to their exciting properties, such as superconductivity, magnetism and optoelectronic properties[1,2]
The thickness of MXene and graphene oxide (GO) nanosheets were determined by atomic force microscopy (AFM) to be around 1.5 nm and 1 nm, respectively, indicating a unilamellar structure for both types (Supplementary Fig. S1a,b)
To prepare a printable GO ink, Triton X-100 was added to the water-based graphene oxide ink in order to optimize the ink surface tension[10]
Summary
Two-dimensional heterostructures with vertical stacking configurations are useful for a vast range of applications due to their exciting properties, such as superconductivity, magnetism and optoelectronic properties[1,2]. Mechanical exfoliation of three-dimensional layered compounds followed by dry transfer of each 2D nanosheet onto a substrate is still the main technique for vertical 2D heterostructure fabrication[4]. The advantage of this technique is that atomically thin high-quality heterostructures can be realized on a small scale. We used a water-based additive-free MXene ink to inkjet print electrodes and current collectors on polyimide substrates, and a water-based GO ink to inkjet-print the solid-state electrolyte Both sandwiched supercapacitors (SSCs) and micro-supercapacitor devices (MSCs) were printed on flexible polyimide substrates (Fig. 1). The addition of aqueous electrolytes led to an enhancement of CA, due to the improved ionic conductivity of the electrolyte resulting from the presence of additional ions and a liquid phase
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