Rapid 3D Printing of Nanoporous Microsupercapacitor Electrodes Using Projection Two-Photon Lithography

Abstract

Despite their high power density, microsupercapacitors (MSCs) are impractical for many energy storage applications due to their limited energy density. Their energy density can be increased by shaping the electrodes into 3D structures with high specific surface area (SSA). Direct printing of nanoporous 3D electrodes is a promising approach for achieving high SSA. However, conventional nanoscale 3D printing is too slow due to point-by-point processing. Here, we have employed the projection two-photon lithography technique to fabricate nanoporous 3D electrodes via a rapid layer-by-layer mechanism. The 3D MSC electrodes are engineered as an array of nanoporous polymeric micropillars that are printed with customizable spacing and count over a 0.25 cm² area. After printing, these micropillars are conformally coated with titanium nitride to form conductive 3D electrodes, which exhibit a specific capacitance of 361 μF/cm². This is two orders of magnitude higher than the capacitance of the flat surface and exceeds the capacitance of both traditional bare electrodes, such as single-wall carbon nanotubes (< 100 μF/cm²), and electrodes produced by photo-polymerization 3D printing (˜200 μF/cm²). As our work demonstrates that high energy density 3D electrodes can be rapidly fabricated, it significantly expands the utility of MSCs as miniaturized energy storage devices.