Shusheng Xu

A Review on Graphene-Based Gas/Vapor Sensors with Unique Properties and Potential Applications

Graphene-based gas/vapor sensors have attracted much attention in recent years due to their variety of structures, unique sensing performances, room-temperature working conditions, and tremendous application prospects, etc. Herein, we summarize recent advantages in graphene preparation, sensor construction, and sensing properties of various graphene-based gas/vapor sensors, such as NH3, NO2, H2, CO, SO2, H2S, as well as vapor of volatile organic compounds. The detection mechanisms pertaining to various gases are also discussed. In conclusion part, some existing problems which may hinder the sensor applications are presented. Several possible methods to solve these problems are proposed, for example, conceived solutions, hybrid nanostructures, multiple sensor arrays, and new recognition algorithm.

Nanofoaming to Boost the Electrochemical Performance of Ni@Ni(OH)2 Nanowires for Ultrahigh Volumetric Supercapacitors

Three-dimensional free-standing film electrodes have aroused great interest for energy storage devices. However, small volumetric capacity and low operating voltage limit their practical application for large energy storage applications. Herein, a facile and novel nanofoaming process was demonstrated to boost the volumetric electrochemical capacitance of the devices via activation of Ni nanowires to form ultrathin nanosheets and porous nanostructures. The as-designed free-standing Ni@Ni(OH)2 film electrodes display a significantly enhanced volumetric capacity (462 C/cm3 at 0.5 A/cm3) and excellent cycle stability. Moreover, the as-developed hybrid supercapacitor employed Ni@Ni(OH)2 film as positive electrode and graphene-carbon nanotube film as negative electrode exhibits a high volumetric capacitance of 95 F/cm3 (at 0.25 A/cm3) and excellent cycle performance (only 14% capacitance reduction for 4500 cycles). Furthermore, the volumetric energy density can reach 33.9 mWh/cm3, which is much higher than that of most thin film lithium batteries (1-10 mWh/cm3). This work gives an insight for designing high-volume three-dimensional electrodes and paves a new way to construct binder-free film electrode for high-performance hybrid supercapacitor applications.

Morphology Control and Photocatalysis Enhancement by in Situ Hybridization of Cuprous Oxide with Nitrogen-Doped Carbon Quantum Dots

Cuprous oxide (Cu2O) is an attractive photocatalyst because of its visible-light-driven photocatalytic behavior, abundance, low toxicity, and environmental compatibility. However, its short electron diffusion length and low hole mobility result in low photocatalytic efficiency, which hinders its wider applications. Herein, we report an in situ method to introduce nitrogen-doped carbon dots (N-CDs) into Cu2O frameworks. It is interestingly found that the introduction of N-CDs drives the morphology of N-CDs/Cu2O to evolve from rough cube to sphere, and the most encouraging result is that all of the obtained N-CDs/Cu2O composites exhibit better photocatalytic activities than pure Cu2O cubes. The optimal N-CDs/Cu2O photocatalyst is synthesized with 10 mL of N-CDs solution, which shows the best degradation ability (100%, 70 min), far superior to pure Cu2O cubes (∼5%, 70 min) and P25 (∼10%, 70 min). Beside the photodegradation of methyl orange, N-CDs/Cu2O(10) composites also exhibit excellent photocatalytic activities in the photodegradation of methyl blue and rhodamine B. It is demonstrated that the excellent photocatalytic performance of N-CDs/Cu2O composites can be attributed to the highly roughened structure and the suppression of electron-hole recombination as a result of the introduction of N-CDs. These findings demonstrate that the conjugation of CDs is a promising method to improve the photocatalytic activities for traditional semiconductors.

Cobalt-Doping to Boost the Electrochemical Properties of Ni@Ni3S2 Nanowire Films for High-Performance Supercapacitors

Metal sulfides have aroused great interest for energy storage. However, their low specific capacities and inferior rate capabilities hinder their practical applications. In this work, a facile cobalt-doping process is used to boost the electrochemical performance of Ni@Ni3 S2 core-sheath nanowire film electrodes for high-performance electrochemical energy storage. Co ions are doped successfully and uniformly into Ni3 S2 nanosheets through a facile ion-exchange process. The electrochemical properties of film electrodes are improved greatly, and an ultrahigh volumetric capacity (increased from 105 to 730 C cm-3 at 0.25 A cm-3 ) and excellent rate capability are obtained after Co is doped into Ni@Ni3 S2 core-sheath nanowires. A hybrid asymmetric supercapacitor with Co-doped Ni@Ni3 S2 as the positive electrode and graphene-carbon nanotubes as the negative electrode is assembled and exhibits an ultrahigh volumetric capacitance of 142 F cm-3 (based on the total volume of both electrodes) at 0.5 A cm-3 and excellent cycling stability (only 3 % capacitance decrease after 5000 cycles). Moreover, the volumetric energy density can reach 44.5 mWh cm-3 , which is much larger than those of thin-film lithium batteries (1-10 mWh cm-3 ). These results may provide useful insights for the fabrication of high-performance film electrodes for energy-storage applications.

In situ coating nickel organic complexes on free-standing nickel wire films for volumetric-energy-dense supercapacitors

A self-free-standing core-sheath structured hybrid membrane electrodes based on nickel and nickel based metal-organic complexes (Ni@Ni-OC) was designed and constructed for high volumetric supercapacitors. The self-standing Ni@Ni-OC film electrode had a high volumetric specific capacity of 1225.5 C cm-3 at 0.3 A cm-3 and an excellent rate capability. Moreover, when countered with graphene-carbon nanotube (G-CNT) film electrode, the as-assembled Ni@Ni-OC//G-CNT hybrid supercapacitor device delivered an extraordinary volumetric capacitance of 85 F cm-3 at 0.5 A cm-3 and an outstanding energy density of 33.8 at 483 mW cm-3. Furthermore, the hybrid supercapacitor showed no capacitance loss after 10 000 cycles at 2 A cm-3, indicating its excellent cycle stability. These fascinating performances can be ascribed to its unique core-sheath structure that high capacity nano-porous nickel based metal-organic complexes (Ni-OC) in situ coated on highly conductive Ni wires. The impressive results presented here may pave the way to construct s self-standing membrane electrode for applications in high volumetric-performance energy storage.