Yingru Li

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.

Highly Compressible Macroporous Graphene Monoliths via an Improved Hydrothermal Process

An improved hydrothermal process is developed to fabricate macroporous graphene monoliths (MGMs) using a soft template of organic droplets. The MGMs are constructed from closed-cell distorted spherical pores. This unique microstructure makes MGMs that have low weight densities, good electrical conductivities, and excellent elasticity with rapid recovery rates.

A Flexible UV–Vis–NIR Photodetector based on a Perovskite/Conjugated‐Polymer Composite

A lateral photodetector based on the bilayer composite film of a perovskite and a conjugated polymer is reported. It exhibits significantly enhanced responsivity in the UV-vis region and sensitive photoresponse in the near-IR (NIR) region at a low applied voltage. This broadband photodetector also shows excellent mechanical flexibility and improved environmental stability.

High-Performance Strain Sensors with Fish-Scale-Like Graphene-Sensing Layers for Full-Range Detection of Human Motions.

Strain sensors with large stretchability, broad sensing range, and high sensitivity are highly desirable because of their potential applications in electronic skins and health monitoring systems. In this paper, we report a high-performance strain sensor with a fish-scale-like graphene-sensing layer. This strain sensor can be fabricated via stretching/releasing the composite films of reduced graphene oxide and elastic tape, making the process simple, cheap, energy-saving, and scalable. It can be used to detect both stretching and bending deformations with a wide sensing range (up to 82% strain), high sensitivity (a gauge factor of 16.2 to 150), ultralow limit of detection (<0.1% strain), and excellent reliability and stability (>5000 cycles). Therefore, it is attractive and promising for practical applications, such as for the full-range detection of human motions.

Three-dimensional porous graphene/polyaniline composites for high-rate electrochemical capacitors

We report an electrochemical co-deposition method to prepare three-dimensional (3D) porous composites of reduced graphene oxide (rGO) and polyaniline (PANI) with pores vertically oriented on the surfaces of current collectors and used as an electrode material for electrochemical capacitors (ECs). These composites showed much higher areal specific capacitances and greatly improved rate capability than those of PANI. Typically, the rGO/PANI composite film with a thickness of 150 μm exhibited a high areal specific capacitance (Ca, 67.2 mF cm−2), small relaxation time constant (τ0, 316 ms) and good electrochemical stability, promising for the fabrication of a high-rate EC.

Reduced Graphene Oxide Membranes for Ultrafast Organic Solvent Nanofiltration

Solvated reduced graphene oxide (S-rGO) membranes are stable in organic solvents, and strong acidic, alkaline, or oxidative media. They show high rejections to small molecules with charges the same as that of S-rGO coatings or neutral molecules larger than 3.4 nm, while retaining their high permeances to organic solvents.

Size Fractionation of Graphene Oxide Sheets via Filtration through Track‐Etched Membranes

Graphene oxide (GO) fractionation is achieved by size-exclusive passing of GO sheets through size-defined pores of track-etched membranes, which separate the GO sample into three portions with narrow size distributions. The method reported can be used for the performance improvement of graphene-based materials.

A graphene wrapped hair-derived carbon/sulfur composite for lithium–sulfur batteries

A hair-derived carbon/sulfur composite was prepared via a facile melt-diffusion strategy and successively wrapped with reduced graphene oxide (rGO) sheets by electrostatic self-assembly. This composite was used as the sulfur electrode for lithium–sulfur (Li–S) batteries, exhibiting high capacity, good rate capability, and excellent cyclability. The electrode containing 69.0% (by weight, wt%) sulfur delivered an initial discharge capacity of 1113.2 mA h g−1 and 989.2 mA h g−1 after 300 cycles at a current density of 0.2 C with an average coulombic efficiency of 99.3%. Its capacity retention at 2 C was measured to be 62% with respect to the capacity achieved at 0.2 C. The high-performance of this electrode in Li–S batteries can be attributed to the porous carbon infrastructure, inherent nitrogen-doping and graphene protection. Taking into account the low-cost of raw materials and easy scalable processes, this work features a promising approach to prepare sulfur/carbon composites for high-performance Li–S batteries.

High-Quality Graphene Ribbons Prepared from Graphene Oxide Hydrogels and Their Application for Strain Sensors.

Reduced graphene oxide (rGO) ribbons with arbitrary lengths were prepared by dry spinning of the hydrogels of graphene oxide (GO) formed via thermal annealing GO dispersions, and followed by chemical reduction. These rGO ribbons are flexible, having ultrahigh tensile strengths of 582 ± 17 MPa, ultrahigh fracture energies of 18.29 ± 2.47 MJ m(-3), high conductivities of 662 ± 41 S cm(-1), and an extremely large breakdown current density of about 11,500 A cm(-2). Strain sensors based on the meshes of these ribbons showed sensitive recoverable responses to different tensile strains with excellent cycling stability, promising for the applications in wearable devices.

An ultrahigh-rate electrochemical capacitor based on solution-processed highly conductive PEDOT:PSS films for AC line-filtering

Alternating current (AC) line-filters are widely used to attenuate the leftover AC ripples in line-powered devices. However, the commercialized aluminum electrolytic capacitors (AECs) have low specific capacitances, making them usually the largest components in the electronic circuits of miniaturized, portable and/or flexible electronics. Herein, we report a scalable wet-process to fabricate an electrochemical capacitor (EC) using sulfuric acid treated commercially available poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (AT-PEDOT:PSS) as an electrode material and graphite foil as the current collector. It exhibited high areal (994 μF cm−2) and volumetric (16.6 F cm−3) specific capacitances at 120 Hz, ultrahigh-rate frequency response (phase angle = −83.6° at 120 Hz) with a short resistor–capacitor time constant of 0.15 ms, and an excellent electrochemical stability. Therefore, it is promising to replace AECs for AC line-filtering, and their performance is superior to those of the state-of-the-art ECs for this purpose.