Shirui Guo

Hydrous Ruthenium Oxide Nanoparticles Anchored to Graphene and Carbon Nanotube Hybrid Foam for Supercapacitors

In real life applications, supercapacitors (SCs) often can only be used as part of a hybrid system together with other high energy storage devices due to their relatively lower energy density in comparison to other types of energy storage devices such as batteries and fuel cells. Increasing the energy density of SCs will have a huge impact on the development of future energy storage devices by broadening the area of application for SCs. Here, we report a simple and scalable way of preparing a three-dimensional (3D) sub-5 nm hydrous ruthenium oxide (RuO2) anchored graphene and CNT hybrid foam (RGM) architecture for high-performance supercapacitor electrodes. This RGM architecture demonstrates a novel graphene foam conformally covered with hybrid networks of RuO2 nanoparticles and anchored CNTs. SCs based on RGM show superior gravimetric and per-area capacitive performance (specific capacitance: 502.78 F g−1, areal capacitance: 1.11 F cm−2) which leads to an exceptionally high energy density of 39.28 Wh kg−1 and power density of 128.01 kW kg−1. The electrochemical stability, excellent capacitive performance, and the ease of preparation suggest this RGM system is promising for future energy storage applications.

Intertwined nanocarbon and manganese oxide hybrid foam for high-energy supercapacitors.

Rapid charging and discharging supercapacitors are promising alternative energy storage systems for applications such as portable electronics and electric vehicles. Integration of pseudocapacitive metal oxides with single-structured materials has received a lot of attention recently due to their superior electrochemical performance. In order to realize high energy-density supercapacitors, a simple and scalable method is developed to fabricate a graphene/MWNT/MnO2 nanowire (GMM) hybrid nanostructured foam, via a two-step process. The 3D few-layer graphene/MWNT (GM) architecture is grown on foamed metal foils (nickel foam) via ambient pressure chemical vapor deposition. Hydrothermally synthesized α-MnO2 nanowires are conformally coated onto the GM foam by a simple bath deposition. The as-prepared hierarchical GMM foam yields a monographical graphene foam conformally covered with an intertwined, densely packed CNT/MnO2 nanowire nanocomposite network. Symmetrical electrochemical capacitors (ECs) based on GMM foam electrodes show an extended operational voltage window of 1.6 V in aqueous electrolyte. A superior energy density of 391.7 Wh kg(-1) is obtained for the supercapacitor based on the GMM foam, which is much higher than ECs based on GM foam only (39.72 Wh kg(-1) ). A high specific capacitance (1108.79 F g(-1) ) and power density (799.84 kW kg(-1) ) are also achieved. Moreover, the great capacitance retention (97.94%) after 13 000 charge-discharge cycles and high current handability demonstrate the high stability of the electrodes of the supercapacitor. These excellent performances enable the innovative 3D hierarchical GMM foam to serve as EC electrodes, resulting in energy-storage devices with high stability and power density in neutral aqueous electrolyte.

Centimeter-scale high resolution metrology of entire CVD grown graphene sheets

A high-throughput metrology method for measuring the thickness and uniformity of entire large-area chemical vapor deposition-grown graphene sheets on arbitrary substrates is demonstrated. This method utilizes the quenching of fluorescence by graphene via resonant energy transfer to increase the visibility of graphene on a glass substrate. Fluorescence quenching is visualized by spin-coating a solution of polymer mixed with fluorescent dye onto the graphene then viewing the sample under a fluorescence microscope. A large-area fluorescence montage image of the dyed graphene sample is collected and processed to identify the graphene and indicate the graphene layer thickness throughout the entire graphene sample. Using this metrology method, the effect of different transfer techniques on the quality of the graphene sheet is studied. It is shown that small-area characterization is insufficient to truly evaluate the effect of the transfer technique on the graphene sample. The results indicate that introducing a drop of acetone or liquid poly(methyl methacrylate) (PMMA) on top of the transfer PMMA layer before soaking the graphene sample in acetone improves the quality of the graphene dramatically over immediately soaking the graphene in acetone. This work introduces a new method for graphene quantification that can quickly and easily identify graphene layers in a large area on arbitrary substrates. This metrology technique is well suited for many industrial applications due to its repeatability and flexibility.

Tuning Electron Transport in Graphene-Based Field-Effect Devices using Block Co-polymers

Graphene possesses many remarkable properties and shows promise as the future material for building nanoelectronic devices. For many applications such as graphene-based field-effect transistors (GFET), it is essential to control or modulate the electronic properties by means of doping. Using spatially controlled plasma-assisted CF(4) doping, the Dirac point shift of a GFET covered with a polycrystalline PS-P4VP block co-polymer (BCP) [poly(styrene-b-4-vinylpyridine)] having a cylindrical morphology can be controlled. By changing the chemical component of the microdomain (P4VP) and the major domain (PS) with the CF(4) plasma technique, the doping effect is demonstrated. This work provides a methodology where the Dirac point can be controlled via the different sensitivities of the PS and P4VP components of the BCP subjected to plasma processing.

Toxicology Study of Single-walled Carbon Nanotubes and Reduced Graphene Oxide in Human Sperm

Carbon-based nanomaterials such as single-walled carbon nanotubes and reduced graphene oxide are currently being evaluated for biomedical applications including in vivo drug delivery and tumor imaging. Several reports have studied the toxicity of carbon nanomaterials, but their effects on human male reproduction have not been fully examined. Additionally, it is not clear whether the nanomaterial exposure has any effect on sperm sorting procedures used in clinical settings. Here, we show that the presence of functionalized single walled carbon nanotubes (SWCNT-COOH) and reduced graphene oxide at concentrations of 1–25 μg/mL do not affect sperm viability. However, SWCNT-COOH generate significant reactive superoxide species at a higher concentration (25 μg/mL), while reduced graphene oxide does not initiate reactive species in human sperm. Further, we demonstrate that exposure to these nanomaterials does not hinder the sperm sorting process, and microfluidic sorting systems can select the sperm that show low oxidative stress post-exposure.