Nanocombing Effect Leads to Nanowire-Based, in-Plane, Uniaxial Thin Films.

The fabrication of thin films comprising ordered nanowire assemblies with emerging, precisely defined properties and adjustable functionalities enables highly integrated technologies in the fields of microelectronics and micro system technology, as well as for efficient power generation, storage, and utilization. Shear force, theoretically, is deemed the most promising method for obtaining in-plane, uniaxial thin films comprising nanowires. The success depends largely on the assembly process, and uniform structural control throughout multiple length scales can be achieved only if a rational strategy is executed. Here, we report that in shearing processes dopants such as lyotropic cellulose nanorods can give rise to the uniaxial alignment of V2O5· nH2O nanowires. Our systematic study indicates that this finding, namely, the nanocombing effect, can be a general principle for the continuous production of uniaxial thin films comprising densely packed nanowires varying in chemical composition and aspect ratios. Conversion of the V2O5· nH2O constituents via in situ oxidative polymerization leads to in-plane, uniaxial polyaniline (PANI) thin films with anisotropic electric and optical properties, which are otherwise difficult to fabricate due to the poor processability of PANI. The uniaxial PANI thin films can be utilized to fabricate flexible gas sensors for distinguishing various analytes, including similar homologues such as methanol and ethanol. We expect the methodology to be applied to a broad spectrum of synthetic and biogenic nanowires for the integration of their collective properties in high-performance electronic devices.

A Hydrogel of Ultrathin Pure Polyaniline Nanofibers: Oxidant-Templating Preparation and Supercapacitor Application.

Although challenging, fabrication of porous conducting polymeric materials with excellent electronic properties is crucial for many applications. We developed a fast in situ polymerization approach to pure polyaniline (PANI) hydrogels, with vanadium pentoxide hydrate nanowires as both the oxidant and sacrifice template. A network comprised of ultrathin PANI nanofibers was generated during the in situ polymerization, and the large aspect ratio of these PANI nanofibers allowed the formation of hydrogels at a low solid content of 1.03 wt %. Owing to the ultrathin fibril structure, PANI hydrogels functioning as a supercapacitor electrode display a high specific capacitance of 636 F g-1, a rate capability, and good cycling stability (∼83% capacitance retention after 10,000 cycles). This method was also extended to the preparation of polypyrrole and poly(3,4-ethylenedioxythiophene) hydrogels. This template polymerization method represents a rational strategy for design of conducing polymer networks, which can be readily integrated in high-performance devices or a further platform for functional composites.

Three-Dimensional Printing of Polyaniline/Reduced Graphene Oxide Composite for High-Performance Planar Supercapacitor.

We apply direct ink writing for the three-dimensional (3D) printing of polyaniline/reduced graphene oxide (PANI/RGO) composites with PANI/graphene oxide (PANI/GO) gel as printable inks. The PANI/GO gel inks for 3D printing are prepared via self-assembly of PANI and GO in a blend solvent of N-methyl-2-pyrrolidinone and water, and offer both shaping capability, self-sustainability, and electrical conductivity after reduction of GO. PANI/RGO interdigital electrodes are fabricated with 3D printing, and based on these electrodes, a planar solid-state supercapacitor is constructed, which exhibits high performance with an areal specific capacitance of 1329 mF cm-2. The approach developed in this work provides a simple, economic, and effective way to fabricate PANI-based 3D architectures, which leads to promising application in future energy and electric devices at micro-nano scale.

A high-performance electrochemical supercapacitor based on a polyaniline/reduced graphene oxide electrode and a copper(ii) ion active electrolyte.

Active electrolyte enhanced supercapacitors (AEESCs) have received increasing attention because of their large specific capacitance and easy fabrication process. The better matching between the active electrolyte and the counter electrode and the slow self-discharge rate are the challenges of this type of supercapacitor. In this paper, a novel AEESC with polyaniline/reduced graphene oxide hydrogel (PANI/RGOHG) as the anode and Cu(ii) ions as the cathodic active electrolyte is constructed. Experimental results demonstrate that the electrode potentials of PANI and Cu(ii) can match perfectly, thus the device has a wide working voltage range. Because of the large specific capacitance of both PANI and Cu(ii), a high average specific capacitance of a single electrode of 1120 F g-1 at 2.6 A g-1 is achieved. Meanwhile, self-discharge is also suppressed because the reduction product of Cu(ii) is immobilized on the electrode. These results demonstrate that the performance of AEESCs strongly depends on the choice of a suitable electrode material, and also reveal that Cu(ii) is a promising cathodic active electrolyte for AEESCs.

Benzoyl Peroxide as an Efficient Dopant for Spiro-OMeTAD in Perovskite Solar Cells.

Although organic small molecule spiro-OMeTAD is widely used as a hole-transport material in perovskite solar cells, its limited electric conductivity poses a bottleneck in the efficiency improvement of perovskite solar cells. Here, a low-cost and easy-fabrication technique is developed to enhance the conductivity and hole-extraction ability of spiro-OMeTAD by doping it with commercially available benzoyl peroxide (BPO). The experimental results show that the conductivity increases several orders of magnitude, from 6.2×10-6  S cm-1 for the pristine spiro-OMeTAD to 1.1×10-3  S cm-1 at 5 % BPO doping and to 2.4×10-2  S cm-1 at 15 % BPO doping, which considerably outperform the conductivity of 4.62×10-4  S cm-1 for the currently used oxygen-doped spiro-OMeTAD. The fluorescence spectra suggest that the BPO-doped spiro-OMeTAD-OMeTAD layer is able to efficiently extract holes from CH3 NH3 PbI3 and thus greatly enhances the charge transfer. The BPO-doped spiro-OMeTAD is used in the fabrication of perovskite solar cells, which exhibit enhancement in the power conversion efficiency.

Phase-Separated Polyaniline/Graphene Composite Electrodes for High-Rate Electrochemical Supercapacitors.

Polyaniline/graphene hydrogel composites with a macroscopically phase-separated structure are prepared. The composites show high specific capacitance and excellent rate performance. Further investigation demonstrates that polyaniline inside the graphene hydrogel has low rate performance, thus a phase-separated structure, in which polyaniline is mainly outside the graphene hydrogel matrix, can enhance the rate performance of the composites.