Guo Ye

Transparent 1T-MoS2 nanofilm robustly anchored on substrate by layer-by-layer self-assembly and its ultra-high cycling stability as supercapacitors

Two-dimensional MoS2 materials have attracted more and more interest and been applied to the field of energy storage because of its unique physical, optical, electronic and electrochemical properties. However, there are no reports on high-stable transparent MoS2 nanofilms as supercapacitors electrode. Here, we describe a transparent 1T-MoS2 nanofilm electrode with super-long stability anchored on the indium tin oxide (ITO) glass by a simple alternate layer-by-layer (LBL) self-assembly of a highly charged cationic poly(diallyldimethylammonium chloride) (PDDA) and negative single-/few-layer 1T MoS2 nanosheets. The ITO/(PDDA/MoS2)20 electrode shows a transmittance of 51.6% at 550 nm and obviously exhibits excellent transparency by naked eye observation. Ultrasonic damage test validates that the (PDDA/MoS2)20 film with the average thickness about 50 nm is robustly anchored on ITO substrate. Additionally, the electrochemical results indicate that the ITO/(PDDA/MoS2)20 film shows areal capacitance of 1.1 mF cm-2 and volumetric capacitance of 220 F cm-3 at 0.04 mA cm-2, 130.6% retention of the original capacitance value after 5000 cycles. Further experiments indicate that the formation of transparent (PDDA/MoS2) x nanofilm by LBL self-assembly can be extended to other substrates, e.g., slide glass and flexible polyethylene terephthalate (PET). Thus, the easily available (PDDA/MoS2) x nanofilm electrode has great potential for application in transparent and/or flexible optoelectronic and electronics devices.

Freestanding flexible polymer films based on bridging of two EDOT units with functionalized chains for use in long-term-stable supercapacitors

Freestanding flexible capacitive materials are ideal for use in bendable electronic devices. However, it is difficult to prepare pure PEDOT films in a freestanding state by chemical and electrochemical methods. Here, we used a simple strategy of introducing alkoxy, ether, ester, and amide chains for bridging two EDOT units to form precursors, which could then be electrodeposited readily to produce freestanding and flexible films. The precursor with the amide group was suitable for obtaining higher-quality films with improved thermal stability, mechanical properties, and capacitive performance. In addition, the asymmetric PBEDTA//PEDOT capacitors exhibited a capacitance retention rate of 98.5% after 5000 cycles, which is higher than those of PBEDTH//PEDOT (92.7%), PBEDTG//PEDOT (80.5%), and PBEDTE//PEDOT (86.8%) capacitors. This result indicates that the polymer films and, in particular, the PBEDTA films, are suitable for use in flexible supercapacitors.

Simple and green synthesis of piperazine-grafted reduced graphene oxide and its application for the detection of Hg(II)

In this paper, piperazine-grafted reduced graphene oxide (NH-rGO) was synthesized via a simple and green two-step procedure: (i) opening of the resulting epoxides of graphene oxide (GO) with piperazine (NH) through nucleophilic substitution; (ii) reduction of GO with ascorbic acid. Its structure and morphology were characterized by scanning electron microscopy and x-ray photoelectron spectroscopy. The NH-rGO modified glassy carbon electrode was explored as an electrochemical sensor for the determination of Hg(II) using a differential pulse anodic stripping voltammetry technique. Hg(II) can be efficiently accumulated and deposited on the surface of a modified electrode by strong coordination chemical bonds formed between Hg(II) and NH. And then the anodic stripping current can be significantly enhanced by rGO with the merits of large specific surface area and high conductivity, which served as a signal amplifier, finally realizing the highly sensitive determination of Hg(II). The experimental parameters including the pH value of the acetate buffer, deposition potential and deposition time were optimized. Under optimal conditions, the developed sensor exhibited a wide linear range from 0.4-12 000 nM with a low limit of detection of 0.2 nM, which is well below the guideline value in drinking water set by the WHO. Moreover, the practical application of this method was confirmed by an assay of Hg(II) in tap water samples with acceptable results.