Yiqing Sun

Graphene based new energy materials

Graphene, a one-atom layer of graphite, possesses a unique two-dimensional (2D) structure, high conductivity and charge carrier mobility, huge specific surface area, high transparency and great mechanical strength. Thus, it is expected to be an ideal material for energy storage and conversion. During the past several years, a variety of graphene based materials (GBMs) have been successfully prepared and applied in supercapacitors, lithium ion batteries, water splitting, electrocatalysts for fuel cells, and solar cells. In this review, we will summarize the recent advances in the synthesis and applications of GBMs in these energy related systems. The challenges and prospects of graphene based new energy materials are also discussed.

Three-dimensional self-assembly of graphene oxide and DNA into multifunctional hydrogels.

Graphene and its functionalized derivatives are unique and versatile building blocks for self-assembly to fabricate graphene-based functional materials with hierarchical microstructures. Here we report a strategy for three-dimensional self-assembly of graphene oxide sheets and DNA to form multifunctional hydrogels. The hydrogels possess high mechanical strength, environmental stability, and dye-loading capacity, and a exhibit self-healing property. This study provides a new insight for the assembly of functionalized graphene with other building blocks, especially biomolecules, which will help rational design and preparation of hierarchical graphene-based materials.

Ultrahigh-rate supercapacitors based on eletrochemically reduced graphene oxide for ac line-filtering.

The recent boom in multifunction portable electronic equipments requires the development of compact and miniaturized electronic circuits with high efficiencies, low costs and long lasting time. For the operation of most line-powered electronics, alternating current (ac) line-filters are used to attenuate the leftover ac ripples on direct current (dc) voltage busses. Today, aluminum electrolytic capacitors (AECs) are widely applied for this purpose. However, they are usually the largest components in electronic circuits. Replacing AECs by more compact capacitors will have an immense impact on future electronic devices. Here, we report a double-layer capacitor based on three-dimensional (3D) interpenetrating graphene electrodes fabricated by electrochemical reduction of graphene oxide (ErGO-DLC). At 120-hertz, the ErGO-DLC exhibited a phase angle of −84 degrees, a specific capacitance of 283 microfaradays per centimeter square and a resistor-capacitor (RC) time constant of 1.35 milliseconds, making it capable of replacing AECs for the application of 120-hertz filtering.

Nanoporous nitrogen doped carbon modified graphene as electrocatalyst for oxygen reduction reaction

Nanoporous nitrogen doped carbon was used to modify the surfaces of graphene sheets by carbonizing a mixture of graphene oxide and phenol–melamine–formaldehyde (PMF) pre-polymer in the presence of a soft template (F127). The resulting graphene based composite sheets (G-PMFs) have a sandwich structure with one graphene layer and two nanoporous nitrogen-doped carbon layers. G-PMFs have large specific surface areas of 190 to 630 m2 g−1 and exhibited high electrocatalytic activity, good durability and high selectivity for the oxygen reduction reaction. The performance of the Zn–air fuel cell with a G-PMF anode was tested and found to be comparable to that of the Zn–air cell with a commercial Pt/C anode. Thus, these metal-free catalysts are promising for applications in practical fuel cells.

Highly conductive and flexible mesoporous graphitic films prepared by graphitizing the composites of graphene oxide and nanodiamond

Flexible mesoporous graphitic films with high conductivities were prepared by graphitizing the composite films of graphene oxide (GO) and nanodiamond (ND). After graphitization, ND was changed into onion-like carbon (OC) and GO was reduced to conductive graphene. In the graphitic films, OC nanoparticles were sandwiched between thermally reduced graphene oxide (or graphene) sheets, which not only prevented the aggregation of graphene sheets, but also formed mesopores. The maximum specific surface area of the porous graphitic films was measured to be around 420 m2 g−1 and the diameters of their pores were mostly in the range of 2–11 nm. Furthermore, they are highly conductive with conductivities in the range of 7 400 to 20 300 S m−1. These films are flexible and can be mechanically shaped into the desired structures. Thus, they can be directly used as the electrodes of supercapacitors without the addition of a polymer binder or a conductive additive. The supercapacitors showed a long cycling life and their specific capacitance was optimized to be 143 F g−1 at a discharge rate of 0.2 A g−1.

Antimony-Doped Tin Oxide Nanorods as a Transparent Conducting Electrode for Enhancing Photoelectrochemical Oxidation of Water by Hematite

We report the growth of well-defined antimony-doped tin oxide (ATO) nanorods as a conductive scaffold to improve hematites photoelectrochemical water oxidation performance. The hematite grown on ATO exhibits greatly improved performance for photoelectrochemical water oxidation compared to hematite grown on flat fluorine-doped tin oxide (FTO). The optimized photocurrent density of hematite on ATO is 0.67 mA/cm(2) (0.6 V vs Ag/AgCl), which is much larger than the photocurrent density of hematite on flat FTO (0.03 mA/cm(2)). Using H2O2 as a hole scavenger, it is shown that the ATO nanorods indeed act as a useful scaffold and enhanced the bulk charge separation efficiency of hematite from 2.5% to 18% at 0.4 V vs Ag/AgCl.