Overcoming the Trade-Off between Optical Transmittance and Areal Capacitance of Transparent Supercapacitors for Practical Application.

It is substantially challenging for transition metal oxide nanoparticle (NP)-based electrodes for supercapacitors to achieve high transparency and large capacity simultaneously due to the inherent trade-off between optical transmittance (T) and areal capacitance (CA ). This study demonstrates how this trade-off limitation can be overcome by replacing some electrode NPs with transparent tin oxide (SnO2 ) NPs. Although SnO2 NPs are non-capacitive, they provide effective paths for charge transport, which simultaneously increase the CA and T550nm of the manganese oxide (Mn3 O4 ) NP electrode from 11.7 to 13.4 mF cm-2 and 82.1% to 87.4%, respectively, when 25 wt% of Mn3 O4 are replaced by SnO2 . The obtained CA values at a given T are higher than those of the transparent electrodes previously reported. An energy storage window fabricated using the mixed-NP electrodes exhibits the highest energy density among transparent supercapacitors previously reported. The improved energy density enables the window to operate various electronic devices for a considerable amount of time, demonstrating its applicability in constructing a reliable and space-efficient building-integrated power supply system.

RuO2 Thin Films Electrodeposited on Polystyrene Nanosphere Arrays: Growth Mechanism and Application to Supercapacitor Electrodes.

Two-dimensionally (2D) arrayed polystyrene (PS)/ruthenium oxide (RuO2) core/shell nanospheres are successfully prepared by the electrodeposition of RuO2 nanoparticles on a hexagonal close-packed PS monolayer. This nanosphere structure is entirely different from the structure previously reported for other transition metal oxides electrodeposited on the PS nanosphere arrays. The different growth behavior is analyzed, and a possible deposition mechanism is proposed based on the morphological evolution and photoelectron spectroscopy measurements. As an electrode for supercapacitors, this 2D arrayed nanosphere structure exhibits superior capacitive properties such as significantly large areal capacitance, tight binding with current collectors, and retarded saturation of the capacitance, compared to a planar RuO2 film electrode.

Preparation of superhydrophobic, long-neck vase-like polymer surfaces.

Polymer surfaces comprising nanopillars with various geometries were prepared by nanoimprinting the surface using anodic aluminium oxide templates. In particular, a simple fabrication method for long-neck vase-like stepped nanopillars was established, and the surface showed considerable enhancement in the water contact angle, for example from 95.7° to 150.6° for the polystyrene surface. This enhanced hydrophobicity could be explained by the desirable reduction in the area of the solid-liquid interface and reduced sticking between the nanopillars.

Supercapacitive Properties of 3D-Arrayed Polyaniline Hollow Nanospheres Encaging RuO2 Nanoparticles.

A major limitation of polyaniline (PANi) electrodes for supercapacitors is the slow rate of ion transport during redox reactions and the resultant easy saturation of areal capacitance with film thickness. In this study, three-dimensionally (3D)-arrayed PANi nanospheres with highly roughened surface nanomorphology were fabricated to overcome this limitation. A hierarchical nanostructure was obtained by polymerizing aniline monomers on a template of 3D-arrayed polystyrene (PS) nanospheres and appropriate oxidative acid doping. The structure provided dramatically increased surface area and porosity that led to the efficient diffusion of ions. Thus, the specific capacitance (Csp) reached 1570 F g-1, thereby approaching a theoretical capacitance of PANi. In addition, the retention at a high scan rate of 100 mV s-1 was 77.6% of the Csp at a scan rate of 10 mV s-1. Furthermore, 3D-arrayed hollow PANi (H-PANi) nanospheres could be obtained by dissolving the inner PS part of the PS/PANi core/shell nanospheres with tetrahydrofuran. The ruthenium oxide (RuO2) nanoparticles (NPs) were also encaged in the H-PANi nanospheres by embedding RuO2 NPs on the PS nanospheres prior to polymerization of PANi. The combination of the two active electrode materials indicated synergetic effects. The areal capacitance of the RuO2-encaged PANi electrode was significantly larger than that of the RuO2-free PANi electrode and could be controlled by varying the amount of encaged RuO2 nanoparticles. The encagement could also solve the problem of detachment of RuO2 electrodes from the current collector. The effects of the nanostructuring and RuO2 encagement were also quantitatively analyzed by deconvoluting the total capacitance into the surface capacitive and insertion elements.

Effective surface oxidation of polymer replica molds for nanoimprint lithography.

In nanoimprint lithography, a surface oxidation process is needed to produce an effective poly(dimethylsiloxane) coating that can be used as an anti-adhesive surface of template molds. However, the conventional photooxidation technique or acidic oxidative treatment cannot be easily applied to polymer molds with nanostructures since surface etching by UV radiation or strong acids significantly damages the surface nanostructures in a short space of time. In this study, we developed a basic oxidative treatment method and consequently, an effective generation of hydroxyl groups on a nanostructured surface of polymer replica molds. The surface morphologies and water contact angles of the polymer molds indicate that this new method is relatively nondestructive and more efficient than conventional oxidation treatments.