Chun Xian Guo

Layered graphene/quantum dots for photovoltaic devices.

To meet the increasing demand of clean energy the harvesting of electricity from solar incident photons with high efficiency at economically viable cost is needed. Quantum dot (QD) based solar cells are poised to play a leading role in this revolution owing to their potential in exceeding the Shockley–Queissar limit, their size-tuned optical response, and their efficient multiple carrier generation. 6] A major challenge in developing high-performance QD solar cells is the effective separation of photogenerated electron–hole pairs and the transfer of the electrons to the electrode. Strategies that have been tried include the introduction of nanomaterials with a suitable band energy as efficient acceptors. Carbon, an environmentally friendly and inexpensive material, exists in a variety of nanostructures ranging from insulator/semiconducting diamond to metallic/semimetallic graphite, conducting/semiconducting fullerenes, and single-walled carbon nanotubes (SWNTs), 10] and recently has been widely used in QD solar cells. Particularly, SWNTs 12] and stacked-cup carbon nanotubes have been used as efficient acceptors to enhance photoinduced charge transfer for improved performance because of their unique one-dimensional nanostructure and appropriate band energy. However, the efficiency of carbon nanomaterial based QD solar cells reported so far is still low (incident photon-to-charge-carrier conversion efficiency (IPCE) 5 % and photocurrent response 0.4 mAcm 2 under light illumination of 100 mWcm ), which is still some distance from the requirement for the next generation of solar cells. Graphene, a new class of two-dimensional carbon material with single-atom-thick layer features different from balllike C60 and one-dimensional carbon nanotubes, has attracted attention in recent years. As a result of its high specific surface area for a large interface, high mobility up to 10000 cm V 1 s , and tunable band gap, graphene should be a very promising electron acceptor in photovoltaic devices. In this work, a novel layered nanofilm of graphene/QDs was constructed from all aqueous solutions to fabricate a photovoltaic device using graphene as acceptor, demonstrating the best performance (IPCE of 16% and photoresponse of 1.08 mAcm 2 under light illumination of 100 mWcm ) in all reported carbon/QD solar cells. For a better understanding of the mechanism of the graphene in improving the performance of the device, the graphene/QDs and SWNT/QDs photovoltaic devices are compared. The fabrication of the layered graphene/QDs device is shown schematically in Figure 1. Chemically reduced graphene was used not only because of its unique properties

One-step and high yield simultaneous preparation of single- and multi-layer graphene quantum dots from CX-72 carbon black

A facile, low cost and high yield method has been developed to prepare single- and multi-layer graphene quantum dots (GQDs) from XC-72 carbon black by chemical oxidation. The single-layer GQDs are demonstrated to be excellent probes for cellular imaging, while the multi-layer GQDs may offer great potential applications in optoelectronic devices.

A self-assembled hierarchical nanostructure comprising carbon spheres and graphene nanosheets for enhanced supercapacitor performance

A self-assembly approach is used to fabricate a hierarchical nanostructure using functionalized carbon spheres as nano-spacers to separate graphene nanosheets. The nanostructure significantly enhances capacitance of a graphene supercapacitor by more than 70%, while providing a universal method to self-assembling various carbons into hierarchical structures for energy conversion/storage systems.

Graphene/carbon cloth anode for high-performance mediatorless microbial fuel cells.

Graphene was electrochemically deposited on carbon cloth to fabricate an anode for a Pseudomonas aeruginosa mediatorless microbial fuel cell (MFC). The graphene modification improved power density and energy conversion efficiency by 2.7 and 3 times, respectively. The improvement is attributed to the high biocompatibility of graphene which promotes bacteria growth on the electrode surface that results in the creation of more direct electron transfer activation centers and stimulates excretion of mediating molecules for higher electron transfer rate. A parallel bioelectrocatalytic mechanism consisting of simultaneous direct electron transfer and cell-excreted mediator-enabled electron transfer was established in the P. aeruginosa-catalyzed MFC. This study does not only offer fundamental insights into MFC reactions, but also suggests a low cost manufacturing process to fabricate high power MFCs for practical applications.

CeO2 nanoparticles/graphene nanocomposite-based high performance supercapacitor

CeO(2) nanoparticles/graphene nanocomposite is fabricated by depositing CeO(2) nanoparticles onto three-dimensional graphene material and its supercapacitor performance is further investigated. The nanocomposite shows a high specific capacitance and power density, demonstrating a strong synergistic effect possibly contributed from improved conductivity of CeO(2) and better utilization of graphene.

RGD-Peptide Functionalized Graphene Biomimetic Live-Cell Sensor for Real-Time Detection of Nitric Oxide Molecules

It is always challenging to construct a smart functional nanostructure with specific physicochemical properties to real time detect biointeresting molecules released from live-cells. We report here a new approach to build a free-standing biomimetic sensor by covalently bonding RGD-peptide on the surface of pyrenebutyric acid functionalized graphene film. The resulted graphene biofilm sensor comprises a well-packed layered nanostructure, in which the RGD-peptide component provides desired biomimetic properties for superior human cell attachment and growth on the film surface to allow real-time detection of nitric oxide, an important signal yet short-life molecule released from the attached human endothelial cells under drug stimulations. The film sensor exhibits good flexibility and stability by retaining its original response after 45 bending/relaxing cycles and high reproducibility from its almost unchanged current responses after 15 repeated measurements, while possessing high sensitivity, good selectivity against interferences often existing in biological systems, and demonstrating real time quantitative detection capability toward nitric oxide molecule released from living cells. This study not only demonstrates a facial approach to fabricate a smart nanostructured graphene-based functional biofilm, but also provides a powerful and reliable platform to the real-time study of biointeresting molecules released from living cells, thus rendering potential broad applications in neuroscience, screening drug therapy effect, and live-cell assays.

Construction of one-dimensional nanostructures on graphene for efficient energy conversion and storage

One-dimensional (1D) nanostructures can efficiently scatter incident light, resulting in improved absorption or complete absorption for solar energy conversion and storage. However, 1D nanostructures often lack good conductivity for fast charge transfer and/or transport. A thin-layer coating of graphene gives superior conductivity for improving the charge transport ability while its highly transparency does not deteriorate the light absorption. Thus, construction of 1D nanostructured materials on graphene as an electrode to synergistically boost high-efficiency energy conversion and storage have attracted great attention in recent years. In this feature review, starting with general concepts of 1D nanostructures on a substrate, various advanced methods for the design, fabrication and characterization of different 1D nanostructures comprising inorganic, organic and hybrid materials built on graphene are systematically surveyed. In particular, the significant progress in fabrication strategies, superior nanostructures and unique architectures is discussed, while the excellent electrical, optical, mechanical, and electrochemical properties of the nanostructured composites as well as their important applications in lithium-ion batteries, supercapacitors, solar cells, light-emitting diodes and nanogenerators are also presented. The enhancement mechanisms for the efficient energy conversion and storage are highlighted to elicit scientific insights. The challenges and prospects are also deliberated to spark our future researches. This review provides critical and updated knowledge for researchers to further explore new 1D-structured materials on graphene and their important applications in energy conversion and storage.

Direct electron transfer of glucose oxidase and biosensing of glucose on hollow sphere-nanostructured conducting polymer/metal oxide composite

A hollow sphere-nanostructured conductive polymer/metal oxide composite was synthesized and used to investigate the electrochemical behavior of glucose oxidase, demonstrating a significantly enhanced direct electron transfer ability of glucose oxidase. In particular, the long-standing puzzle of whether enzymatic glucose sensing involves an enzyme direct electron transfer process was studied. The results indicate the mechanism is indeed a glucose oxidase direct electron transfer process with competitive glucose oxidation and oxygen reduction to detect glucose. A glucose biosensor with the glucose oxidase-immobilized nanomaterial was further constructed, demonstrating superior sensitivity and reliability, and providing great potential in clinical applications.

Graphene quantum-dot-doped polypyrrole counter electrode for high-performance dye-sensitized solar cells.

Herein graphene quantum dot (GQD), a graphene material with lateral dimension less than 100 nm, is explored to dope PPy on F-doped tin oxide glass as an efficient counter electrode for high-performance dye-sensitized solar cells (DSSCs). The GQDs-doped PPy film has a porous structure in comparison to the densely structured plain PPy, and displays higher catalytic current density and lower charge transfer resistance than the latter toward I3(-)/I(-) redox reaction. The highest power conversion efficiency (5.27%) for DSSCs is achieved with PPy doped with10% GQDs, which is comparable to that of Pt counter electrode-based DSSCs. This work provides an inexpensive alternative to replace platinum for DSSCs.

Hydrogen storage in a Ni–B nanoalloy-doped three-dimensional graphene material

A three-dimensional graphene material was doped with Ni–B nanoalloys via a chemical reduction process. The graphene doped with Ni (0.83 wt%) and B (1.09 wt%) shows the best hydrogen storage capacity of 4.4 wt% at 77 K and 106 kPa, which is better than that of pristine graphene by three times, and is also excellent among all carbon-based materials. Analysis of hydrogen isotherms and isosteric heat of adsorption suggests that doping with an appropriate amount of Ni–B nanoalloys can result in the dissociative chemisorption of hydrogen molecules by spillover to achieve the high hydrogen storage capacity.