Xiuzhen Qian

Synthesis of Ni(OH)2/RGO pseudocomposite on nickel foam for supercapacitors with superior performance

A unique structure consisting of two kinds of Ni(OH)2 layers on the top and the bottom, respectively, of the same reduced graphene oxide (RGO) layer has been designed and synthesized through a facile hydrothermal process. The lower layer of Ni(OH)2, covered with a thin RGO film, is transformed in situ from the surface of a Ni foam substrate through the redox reaction of elemental Ni and graphene oxide (GO), while the upper layer of Ni(OH)2 nanoflakes from Ni ions in the solution is vertically assembled on the top surface of the RGO of the lower RGO/Ni(OH)2 layer. This composite can be regarded as combining RGO with a “pseudocomposite” of Ni(OH)2 material because the upper and lower Ni(OH)2 layers are different in morphology, particle size, and Ni2+ source. The bottom layer mainly acts as a rough support, while the upper Ni(OH)2 is suitable to act as the main active material for supercapacitor electrodes. The lower layer of Ni(OH)2/RGO, however, plays key roles in forming the aligned structure and in the subsequent cycling stability. The composite film has a high areal mass loading of 4.7 mg cm−2, and superior supercapacitor performance. It features a specific capacitance of up to 15.65 F cm−2 (i.e., 3328.7 F g−1) at a current density of 7 mA cm−2 (1.5 A g−1) and a capacity retention of 90.6%, even after 5000 cycles at the high rate of 20 mA cm−2 (4.3 A g−1), indicating that it has a promising application as an efficient electrode for high-performance supercapacitors.

Hydrothermal growth of MnO2/RGO/Ni(OH)2 on nickel foam with superior supercapacitor performance

A MnO2/reduced graphene oxide (RGO)/Ni(OH)2 composite with arrays of mushroom-headed needle-like nanostructures on its top surface was designed and directly grown on nickel foam through a one-pot hydrothermal process without the addition of any source of extra Ni ions. Based on the redox reaction of elemental Ni and graphene oxide (GO), along with electrostatic forces between Mn ions from the solution and GO, there was good contact and strong interaction between the different components, as well as between the active materials and the Ni substrate. Hence, the as-synthesized MnO2/RGO/Ni(OH)2 composite can be utilized as a supercapacitor electrode with a high areal mass loading of 5.4 mg cm−2. It exhibits superior performance: 17.8 F cm−2 (i.e., 3296.9 F g−1) at 7 mA cm−2 (1.3 A g−1), as well as a capacity retention of 90.2%, even after 5000 cycles at 20 mA cm−2 (3.7 A g−1).

Vertically oriented Ni3S2/RGO/Ni3S2 nanosheets on Ni foam for superior supercapacitors

A unique sandwich structure of Ni3S2/RGO/Ni3S2 consisting of Ni3S2 nanosheets was designed and constructed on nickel foam (NF) by a one-step hydrothermal process. The lower Ni3S2 layer was converted in situ from the Ni foam substrate, while the upper Ni3S2 layer with vertical nanosheets resulted from Ni2+ ions in the solution. This Ni3S2/RGO/Ni3S2/NF nanocomposite was directly utilized as a supercapacitor electrode, which possessed a high areal mass loading of 5.2 mg cm−2, and superior performance: a specific capacitance of up to 16.82 F cm−2 (i.e., 3234.62 F g−1) at a current density of 20 mA cm−2 (3.85 A g−1) and 90% retention of the initial capacitance after 1000 cycles at the high rate of 100 mA cm−2 (19.23 A g−1).

A facile one-step route to synthesize the three-layer nanostructure of CuS/RGO/Ni3S2 and its high electrochemical performance

A three-layer nanostructure of a CuS/reduced graphene oxide (RGO)/Ni3S2 composite was in situ grown on nickel foam (NF) through a one-step hydrothermal-assisted process. During this process, the bottom Ni3S2 layer and middle RGO layer were simultaneously formed through the redox reaction of the Ni element on the foam surface of NF with GO and subsequent vulcanization. The upper CuS layer, consisting of sphere and fiber-like blocks, was converted from Cu2+ adsorbed by electrostatic forces and then well anchored on the RGO surface. The binder-free CuS/RGO/Ni3S2 electrode delivered high specific capacitance (10 494.5 mF cm−2 at a current density of 40 mA cm−2, i.e., 1692.7 F g−1 at 6.5 A g−1). It also exhibited an excellent cycling stability with ca. 91.5% of the initial capacitance retention after 4000 charge–discharge cycles at a current density of 100 mA cm−2. The good electrochemical performance and simple accessibility prove that this CuS/RGO/Ni3S2 composite is a promising material for supercapacitor applications.

3D walnut-shaped TiO2/RGO/MoO2@Mo electrode exhibiting extraordinary supercapacitor performance

Rational architectural design is the key to improve specific capacitance. Herein, we present a facile one-step hydrothermal process for the fabrication of a TiO2/RGO/MoO2 composite with an unprecedented 3D walnut-shaped hierarchical nanostructure, in which amorphous TiO2 is decorated on the RGO (reduced graphene oxide)/MoO2 surface via a Mo-involved in situ growth route on Mo net (TiO2/RGO/MoO2@Mo). This 3D structure coated with ultrafine arched nanorods is a great breakthrough in electrochemical performances of TiO2– or MoO2-based electrodes as it exhibits an extraordinary areal capacitance of 3927 mF cm−2 at 3 mA cm−2 (i.e. 1636 F g−1 at 1.25 A g−1) with only 3.5% capacitance loss after 5000 cycles. Such an excellent performance is benefitted from the following factors: (i) amorphous TiO2 sculptured MoO2 blocky particles supply more active-site accessibility and facilitate the accommodation of volume expansion. (ii) Arched MoO2 nanorods as well as the walnut-shaped spheres of the composite provide electron transfer paths. (iii) RGO is a soft scaffold, which relieves the volume expansion during the charge/discharge processes.

Roe-shaped Ni3(PO4)2/RGO/Co3(PO4)2 (NRC) nanocomposite grown in situ on Co foam for superior supercapacitors

A roe-shaped ternary nanocomposite, Ni3(PO4)2/RGO/Co3(PO4)2 (NRC), was grown in situ on cobalt foam (CoF). The synthesis and loading of NRC on the CoF was completed through a one-step hydrothermal process by immersing the CoF in an aqueous solution of GO and Ni2+ in the presence of H2PO4−, in which the CoF served as the support, reductant and Co source. Three interfaces of Co3(PO4)2/CoF, RGO/Co3(PO4)2, and Ni3(PO4)2/RGO with strong interactions were constructed based on an in situ conversion reaction of Co to Co3(PO4)2, a redox reaction between GO and the CoF, and the electrostatic attraction force of Ni2+ and GO, respectively. The as-synthesized NRC@CoF had a hierarchically porous structure, and directly acted as a supercapacitor electrode and delivered excellent electrochemical performances: a specific capacitance of 10 237.5 mF cm−2 (1137.5 F g−1) at 5 mA cm−2 (0.56 A g−1) with a capacity retention of 117.8% after 14 000 cycles. Furthermore, NRC@CoF-based asymmetric supercapacitors (ASCs) exhibited a specific capacitance of 4845.9 mF cm−2 (115.4 F g−1) at 5 mA cm−2 (0.12 A g−1), and a high energy density of 44.82 W h kg−1 at a power density of 428.6 W kg−1, as well as good cyclic stability (91.9% after 18 000 cycles).

One-pot hydrothermal synthesis of ZnO/RGO/ZnO@Zn sensor for sunset yellow in soft drinks

ZnO/RGO/ZnO nanocomposite was in-situ anchored on Zn foil through a simple one-step hydrothermal approach. Based on the redox reaction between graphene oxide (GO) and Zn foil, and the electrostatic attraction between the negative-charged GO and positive-charged zinc ions, three strong interfaces of ZnO/RGO, RGO/ZnO and ZnO/Zn were simultaneously constructed, which led to improved electron and ion transfer. As-prepared ZnO/RGO/ZnO@Zn directly acted as sensor for amperometric detection of sunset yellow without further assembling, which exhibited an ultrahigh sensitivity of 20.25uAμM-1cm-2, a low limit of detection (3nM), a wide linear detection ranging from 0.01 to 5µM.

Hierarchical FeS/RGO/FeS@Fe foil as high-performance negative electrode for asymmetric supercapacitors

A hierarchical FeS/RGO/FeS composite in situ grown on Fe foil was designed and prepared via an Fe foil-involved one-step hydrothermal route, in which Fe foil acted as the Fe source for the lower FeS layer, reductant of GO and subsequent current collector. The as-prepared FeS/RGO/FeS@Fe showed a high specific capacity of 247.5 C g−1 (206.25 F g−1) and good cyclability with 118% capacity retention after 5000 cycles when directly used as an electrode. Additionally, an asymmetric supercapacitor (ASC) was assembled using Ni(OH)2 and FeS/RGO/FeS@Fe as the positive electrode and negative electrode, respectively. This ASC exhibited maximum power density and energy density of 20 000 W kg−1 and 34.07 W h kg−1, respectively, suggesting that FeS/RGO/FeS is a promising negative electrode material.