Ruili Liu

A hybrid-assembly approach towards nitrogen-doped graphene aerogel supported cobalt nanoparticles as high performance oxygen reduction electrocatalysts

As a novel electrocatalyst for oxygen reduction reaction (ORR), nitrogen-doped graphene aerogel supported cobalt nanoparticles (Co-NGA) is archived by a hybrid-assembly of graphene oxide (GO), o-phthalonitrile and cobalt acetate and the following thermal treatment. The hybrid-assembly process successfully combines the ionic assembly of GO sheets and Co ions with the coordination between o-phthalonitrile and Co ions, which can be converted to nitrogen doped carbon and Co nanoparticles in the pyrolysis process under nitrogen flow. Remarkable features of Co-NGA including the macroporous graphene scaffolds, high surface area, and N/Co-doping effect can lead to a high catalytic efficiency for ORR. As the results, the composites pyrolyzed at 600°C (Co-NGA600) shows excellent electrocatalytic activities and kinetics for ORR in basic media, which are comparable with those of Pt/C catalyst, together with superior durability.

Highly photoluminescent nitrogen-rich carbon dots from melamine and citric acid for the selective detection of iron(III) ion

A facile one-step hydrothermal strategy to fabricate nitrogen-rich carbon dots (N-rich CDs) with melamine and citric acid as the precursors has been successfully developed. The as-prepared N-rich CDs exhibit a uniform quasi-spherical morphology, high N content of about 24 wt% and very strong photoluminescence (PL) with a high quantum yield of ∼42%. Additionally, the PL emission of these N-rich CDs can be stabilized in a wide pH range from 4.0 to 11.0. More importantly, the N-rich CDs can be utilized as the label-free PL sensors for the highly selective and sensitive detection of Fe3+ ions in aqueous solution with a very low detection limit of 142 nM.

A facile biomass based approach towards hierarchically porous nitrogen-doped carbon aerogels

Nitrogen-doped carbon aerogels with hierarchically porous architectures (NHCAs) are prepared via hydrothermal treatment of cantaloupes and the following activation with potassium hydroxide. The porous structure of the obtained NHCAs can be easily tuned by adjusting the activation temperature. Among the samples, the one activated at 800 °C (NHCA-800) exhibits the highest specific surface area of 1778 m2 g−1 and the best electrochemical performance as both the electrode for a supercapacitor and the electrocatalyst for the oxygen reduction reaction, which is due to the co-existence of large amount of micro- and mesopores in NHCA-800.

Strongly coupled polyaniline/graphene hybrids with much enhanced capacitance performance

To enforce the interactions between polyaniline (PANI) and graphene, a facile strategy is developed in this work to fabricate the strongly coupled hybrids of PANI nanofibers and graphene (named as PAGs) by introducing different diamines to functionalize graphene oxide. As the electrode material in a two-electrode supercapacitor (SC), the ethylenediamine-functionalized hybrid (PAG-EDA) deliveries an excellent volumetric specific capacitance of 810Fcm(-3) at 5mVs(-1). The SC also manifests high cycling stability by maintaining 84.4% of the initial capacitance after 10,000 cycles. More importantly, PAG-EDA renders the SC to have both high energy density (92.15Whkg(-1)) and high power density (182.28kWkg(-1)), superior to most of the previously reported PANI based SC electrode materials.

Hierarchically porous nitrogen-doped graphene aerogels as efficient metal-free oxygen reduction catalysts

Nitrogen-doped graphene aerogels with hierarchically porous architectures (N-Gs) are fabricated through the co-assembly of graphene oxide and o-phthalonitrile in a solvothermal process and the thermal treatment of the obtained composites at different temperatures. The structural characterizations indicate that both mesopores and macropores exist in the monolithic N-Gs. More importantly, the architectures, porosities and compositions show obvious dependence on the thermal treatment temperature. As the metal-free catalyst for oxygen reduction reaction in basic media, the sample thermally treated at 750°C shows the best catalytic performances among the three N-Gs, which is owing to its advantages in the surface areas and content of active N species.

Perylene diimide-diamine/carbon black composites as high performance lithium/sodium ion battery cathodes

The electrochemical performances of three in situ synthesized composites of perylene diimide-diamine and carbon black (PDI-DA/CBs) and their mechanically mixed analogs are compared as the cathode materials in both lithium ion batteries (LIBs) and sodium ion batteries (SIBs). Benefiting from the fabrication strategy and variable structures, the composite containing ethylene diamine units exhibits an excellent reversible capacity of ∼100 mA h g−1 at an ultrahigh current density of 5.0 A g−1 in LIBs and a high capacity over 90 mA h g−1 at 2.0 A g−1 in SIBs.

Universal route to fabricate facile and flexible micro-supercapacitors with gold-coated silver electrodes

Currently, microsupercapacitors (MSCs) are considered as a promising strategy to solve the energy problems of micro-scale devices. Due to complex fabrication processes and high costs, innovative techniques need to be developed to micro-fabricate and integrate MSCs on chips. In this paper, for the first time, a facile, cost-effective and universal route to fabricate flexible Ag@Au MSCs was proposed. This technique combines a surface ion-exchange (SMIE) process with immersion plating. The commercially-available polyimide film was first treated with SMIE, followed by immersion plating. Via this method, the pristine polyimide is finally turned into gold coated silver electrodes. The whole fabrication is cleanroom-free and environmentally friendly. With this novel patterning and slicing method, a new route for simple and scalable fabrication of MSCs may fulfill a wide variety of applications. As demonstrations, two types of MSCs have also been fabricated. Coated with MWNTs, MSCs were examined in an electrolyte. For sandwiched MSCs, high cycling properties enable MSCs to work at a scan rate up to 10 V s−1. The maximum phase angle is above −75°. For planar MSCs, the scan rate is easily over 100 V s−1. The mechanical flexible testing indicated that the SMIE Ag@Au electrodes are sufficiently robust.

Highly Uniform Carbon Sheets with Orientation-Adjustable Ordered Mesopores

A soft-hard template-assisted method toward the unconventional free-standing ordered mesoporous carbon sheets (OMCSs) with uniform hexagonal morphology is developed by applying MgAl-layered double hydroxide (MgAl-LDH) as the hard template, triblock copolymer F127 as the soft template, and phenolic resols as the carbon sources. It is found that the surface of MgAl-LDH can induce the morphology variation of resol-F127 monomicelles, leading to the formation of vertically or horizontally aligned mesopore arrays in the OMCSs, which can in turn determine their electrochemical energy storage behaviors in supercapacitors with different configurations. In an all-solid-state supercapacitor with two face-to-face electrodes, an OMCS with vertical mesopores manifests the best performance among the samples. By contrast, in a micro-supercapacitor with in-plane film-like electrodes, an OMCS with horizontal mesopores delivers higher energy/power densities than the other OMCSs, which are also comparable to the state-of-the-art supercapacitors based on ordered mesoporous carbons. The achievement of uniform carbon sheets with orientation-adjustable mesopore arrays can help elucidate their electrochemical storage mechanism and allow the optimization of the performances according to the device configuration, thus providing a powerful tool for the manipulation of energy storage devices on the nanoscale.