Microplotter Printing of a Miniature Flexible Supercapacitor Electrode Based on Hierarchically Organized NiCo2O4 Nanostructures

The hydrothermal synthesis of a nanosized NiCo₂O₄ oxide with several levels of hierarchical self-organization was studied. Using X-ray diffraction analysis (XRD) and Fourier-transform infrared (FTIR) spectroscopy, it was determined that under the selected synthesis conditions, a nickel-cobalt carbonate hydroxide hydrate of the composition M(CO₃)_0.5(OH)·0.11H₂O (where M-Ni²⁺ and Co²⁺) is formed as a semi-product. The conditions of semi-product transformation into the target oxide were determined by simultaneous thermal analysis. It was found by means of scanning electron microscopy (SEM) that the main powder fraction consists of hierarchically organized microspheres of 3-10 μm in diameter, and individual nanorods are observed as the second fraction of the powder. Nanorod microstructure was further studied by transmission electron microscopy (TEM). A hierarchically organized NiCo₂O₄ film was printed on the surface of a flexible carbon paper (CP) using an optimized microplotter printing technique and functional inks based on the obtained oxide powder. It was shown by XRD, TEM, and atomic force microscopy (AFM) that the crystalline structure and microstructural features of the oxide particles are preserved when deposited on the surface of the flexible substrate. It was found that the obtained electrode sample is characterized by a specific capacitance value of 420 F/g at a current density of 1 A/g, and the capacitance loss during 2000 charge-discharge cycles at 10 A/g is 10%, which indicates a high material stability. It was established that the proposed synthesis and printing technology enables the efficient automated formation of corresponding miniature electrode nanostructures as promising components for flexible planar supercapacitors.

Facile Co-Electrodeposition Method for High-Performance Supercapacitor Based on Reduced Graphene Oxide/Polypyrrole Composite Film

A facile co-electrodeposition method has been developed to fabricate reduced graphene oxide/polypyrrole (rGO/PPy) composite films, with sodium dodecyl benzene sulfonate as both a surfactant and supporting electrolyte in the precursor solution. The introduction of rGO into the PPy films forms porous structure and enhances the conductivity across the film, leading to superior electrochemical performance. By controlling the deposition time and rGO concentration, the highest area capacitance can reach 411 mF/cm² (0.2 mA/cm²) for rGO/PPy films, whereas optimized specific capacitance is as high as 361 F/g (0.2 mA/cm²). All of the composite films exhibit excellent rate capability (at least 175 F/g at the current density of 12 mA/cm²) compared with pure PPy film (only 12 F/g at the current density of 12 mA/cm²). The rGO/PPy composite exhibits excellent cycling stability that maintains 104% of its initial capacitance after cycling for 2000 cycles and 80% for 5000 cycles. The two-electrode solid-state supercapacitor (SC) based on rGO/PPy composite electrodes demonstrates good rate performance, excellent cycling stability, as well as a high area capacitance of 222 mF/cm². The solid-state planar SC based on the rGO/PPy composite exhibits an area capacitance of 9.4 mF/cm², demonstrating great potential for fabrication of microsupercapacitors.