Wenjing Yuan

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.

Graphene-based gas sensors

Graphene materials have been widely explored for the fabrication of gas sensors because of their atom-thick two-dimensional conjugated structures, high conductivity and large specific surface areas. This feature article summarizes the recent advancements on the synthesis of graphene materials for this purpose and the techniques applied for fabricating gas sensors. The effects of the compositions, structural defects and morphologies of graphene-based sensing layers and the configurations of sensing devices on the performances of gas sensors will also be discussed.

High-performance NO2 sensors based on chemically modified graphene.

Covalently grafting reduced graphene oxide (rGO) sheets with sulfophenyl or ethylenediamine groups can produce chemically modified graphene (CMG) for fabricating high-performance gas sensors. The NO(2) sensors based on these CMGs exhibit sensitivities 4 to 16 times higher than that of a sensor based on rGO. They also show excellent selectivity and repeatability without the aid of UV-light or thermal treatment.

The edge- and basal-plane-specific electrochemistry of a single-layer graphene sheet

Graphene has a unique atom-thick two-dimensional structure and excellent properties, making it attractive for a variety of electrochemical applications, including electrosynthesis, electrochemical sensors or electrocatalysis, and energy conversion and storage. However, the electrochemistry of single-layer graphene has not yet been well understood, possibly due to the technical difficulties in handling individual graphene sheet. Here, we report the electrochemical behavior at single-layer graphene-based electrodes, comparing the basal plane of graphene to its edge. The graphene edge showed 4 orders of magnitude higher specific capacitance, much faster electron transfer rate and stronger electrocatalytic activity than those of graphene basal plane. A convergent diffusion effect was observed at the sub-nanometer thick graphene edge-electrode to accelerate the electrochemical reactions. Coupling with the high conductivity of a high-quality graphene basal plane, graphene edge is an ideal electrode for electrocatalysis and for the storage of capacitive charges.

A high-performance three-dimensional Ni–Fe layered double hydroxide/graphene electrode for water oxidation

Water oxidation to evolve oxygen is the key step in water splitting and is related to a variety of energy systems. Here, we report a facile electrodeposition process to immobilize nickel–iron layered double hydroxide (Ni–Fe LDH) nanoplates on three-dimensional electrochemically reduced graphene oxide (3D-ErGO) for water oxidation. This Ni–Fe LDH/3D-ErGO electrode has a three-dimensional interpenetrating network with Ni–Fe nanoplates uniformly decorated on graphene sheets. It has an electrochemically active surface area (EASA) 3.3 times that of conventional planar electrodes. The open porous structure of this electrode also makes its EASA fully accessible to the electrolyte for water oxidation and easy release of oxygen gas. This electrode can be directly used for catalysing the oxygen evolution reaction (OER) in alkaline media without using a binder and conductive additive, exhibiting a small overpotential of 0.259 V and a low Tafel slope of 39 mV dec−1. It outperforms the precious IrO2 catalyst in activity, kinetics, and electrochemical stability.

Performance enhancement of a graphene–sulfur composite as a lithium–sulfur battery electrode by coating with an ultrathin Al2O3 film via atomic layer deposition

A graphene–sulfur (G–S) composite was conformally coated with an ultrathin Al2O3 film via atomic layer deposition (ALD) and used as the cathode of a lithium–sulfur (Li–S) battery. The G–S composite cathode with an ALD-Al2O3 coating delivered a high specific capacity of 646 mA h g−1 after 100 charge–discharge cycles at 0.5 C, and this value is about twice that of the bare G–S composite. The rate capability and coulombic efficiency of the G–S composite electrode were also greatly increased. The ALD-Al2O3 coating worked as an artificial barrier to suppress the dissolution of polysulfides and alleviate the shuttle effect; thus, it effectively improved the performance of a G–S composite cathode in a Li–S battery.

Ultrasensitive and selective nitrogen dioxide sensor based on self-assembled graphene/polymer composite nanofibers.

Reduced graphene oxide (rGO) sheets were self-assembled onto the surfaces of electrospun polymer nanofibers to form an ultrathin coating. These rGO/polymer composite nanofibers were used to fabricate nitrogen dioxide (NO2) sensor. This sensor can be performed at room temperature, and it exhibited a high sensitivity of 1.03 ppm(-1) with excellent selectivity and good reversibility. Furthermore, the limit of detection was experimentally measured to be as low as 150 ppb, and this value is much lower than the threshold exposure limit proposed by American Conference of Governmental Industrial Hygienists (200 ppb).

Solution-Processed PEDOT:PSS/Graphene Composites as the Electrocatalyst for Oxygen Reduction Reaction

Composites of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and reduced graphene oxide (rGO) have been prepared by solution mixing and applied as electrocatalysts for oxygen reduction reaction (ORR) after treatment with concentrated H2SO4. The blending of rGO induces the conformational change of PEDOT chains from benzoid to quionoid structure and charge transfer from rGO to PEDOT. H2SO4 post-treatment can remove part of insulating PSS from the surface of the PEDOT:PSS/rGO composite film, resulting in a significant conductivity enhancement of the composite. This synergistic effect makes the H2SO4-treated PEDOT:PSS/rGO composite a promising catalyst for ORR. It exhibits enhanced electrocatalytic activity, better tolerance to a methanol crossover effect and CO poisoning, and longer durability than those of the platinum/carbon catalyst.