Shulin Chen

Nanosized core–shell structured graphene–MnO2 nanosheet arrays as stable electrodes for superior supercapacitors

Directly fabricating vertically standing graphene–manganese dioxide (MnO2) nanoparticle hybrids as electrode materials remains a challenge, especially so without the use of organic binders. Such hybrids should exhibit high electrochemical performance and high stability. To address this challenge, we report a strategy for fabricating nanosized core–shell graphene–MnO2 nanosheet arrays (G–MnO2 NAs) for use as electrodes for supercapacitors. The as-grown MnO2 nanosheets are transformed into core–shell G–MnO2 nanoparticles by plasma-enhanced chemical vapor deposition. The in situ formed graphene layers act as binders and frameworks, and provide integrity and stability to the overall nanosheet. The resulting core–shell nanoparticles exhibit a high specific surface area and long-term cycling stability. The synergistic effect of the vertically standing intercalated architecture and in situ formed graphene provides a short ion diffusion pathway and a high conductivity. The G–MnO2 NAs exhibit a high specific capacitance of 1176 F g−1 at 2 mV s−1, and a long cycling lifetime with negligible capacitance loss after 10000 cycles. This process for the in situ formation of graphene may be useful for improving the electrochemical performance of other metal oxide-based electrodes.

In situ encapsulated Fe3O4 nanosheet arrays with graphene layers as an anode for high-performance asymmetric supercapacitors

Energy density of asymmetric supercapacitors (ASCs) is greatly limited by the electrochemical performance, especially low specific capacitance and poor cycling stability, of anode materials. To achieve high-performance ASCs, herein, we designed and synthesized a new anode material of Fe3O4 nanosheet arrays, which were encapsulated in situ by graphene layers (G@Fe3O4) through plasma enhanced chemical vapor deposition. Vertical-standing G@Fe3O4 nanosheet arrays directly on the conductive substrates can facilitate electrolyte diffusion and reduce the internal resistance. Furthermore, the highly conductive graphene layers in situ encapsulating the Fe3O4 nanosheets not only could provide fast ion and electron transport pathways, but could also maintain a stable structure for G@Fe3O4. When used as electrodes, G@Fe3O4 exhibited highest capacitance (up to 732 F g−1), better rate capability, and cycling stability as compared to pristine Fe3O4. Furthermore, an asymmetric supercapacitor device synthesized using G@Fe3O4 as an anode and CuCo2O4 as the cathode showed a high energy density of up to 82.8 W h kg−1 at a power density of 2047 W kg−1 and good cycling stability (88.3% capacitance after 10u2006000 cycles).

In Situ Synthesis of Vertical Standing Nanosized NiO Encapsulated in Graphene as Electrodes for High‐Performance Supercapacitors

Abstract NiO is a promising electrode material for supercapacitors. Herein, the novel vertically standing nanosized NiO encapsulated in graphene layers (G@NiO) are rationally designed and synthesized as nanosheet arrays. This unique vertical standing structure of G@NiO nanosheet arrays can enlarge the accessible surface area with electrolytes, and has the benefits of short ion diffusion path and good charge transport. Further, an interconnected graphene conductive network acts as binder to encapsulate the nanosized NiO particles as core–shell structure, which can promote the charge transport and maintain the structural stability. Consequently, the optimized G@NiO hybrid electrodes exhibit a remarkably enhanced specific capacity up to 1073 C g−1 and excellent cycling stability. This study provides a facial strategy to design and construct high‐performance metal oxides for energy storage.

Hierarchical CuCo2O4@NiMoO4 core–shell hybrid arrays as a battery-like electrode for supercapacitors

Herein, hierarchical CuCo2O4@NiMoO4 core–shell nanowire arrays were successfully synthesized on Ni foam via hydrothermal processes as a battery-like electrode. Owing to the unique core–shell structure and the synergetic effect from CuCo2O4 and NiMoO4, the resulting CuCo2O4@NiMoO4 core–shell arrays exhibit a high specific capacitance of 2207 F g−1 at 1.25 A g−1 and good rate capability with only about 4.4% capacitance loss after cycling tests. Furthermore, we assemble the corresponding asymmetric supercapacitor using CuCo2O4@NiMoO4 (positive electrode) and activated carbon (negative electrode), which delivers a high energy density (about 40 W h kg−1) and good cycle stability. Thereby, these electrochemical performances demonstrated that as-fabricated CuCo2O4@NiMoO4 core–shell arrays are promising candidates as electrodes for high-performance supercapacitors.

Modifying the electrochemical performance of vertically-oriented few-layered graphene through rotary plasma processing

Vertically-oriented few-layered graphene (VFG) has a unique three-dimensional morphology and exposed ultrathin edges, and shows great promise for high-performance supercapacitor applications. However, VFG shows limited capacitance owing to poor wettability with electrolytes, which has been a bottleneck for further applications. Herein, we designed and developed an effective strategy, based on rotary plasma etching, to create defects on the side surfaces while simultaneously maintaining the structural integrity of VFG. Rotary plasma etching decreased the contact angle (CA) of VFG from 123° to 34°, compared with conventional vertical etching, which only reduced the CA to 71°. Electrochemical studies demonstrated that VFG samples with a high density of surface defects, introduced by rotary plasma etching, exhibited a high areal capacitance of 1367 μF cm−2 (a volumetric specific capacitance of 137 F cm−3), which was approximately 4 times as large as for pristine VFG-based materials. Our study offers feasible insight into the use of an industrially viable method, rotary plasma processing, for modifying and enhancing the properties of VFG. Our findings may help to accelerate the development of more effective energy storage devices.

Rational construction of core–shell Ni3S2@Ni(OH)2 nanostructures as battery-like electrodes for supercapacitors

Rationally constructing hybrid nanostructure electrodes is a promising approach for the development of high-performance supercapacitors. Here, we propose the fabrication of Ni3S2@Ni(OH)2 nanostructures directly on Ni foam by employing hydrothermal and chemical bath processes. In this core–shell nanostructure, the design of conductive Ni3S2 nanorods directly on Ni foam without organic binders could ensure intimate contact and fast electron transport. Meanwhile, porous Ni(OH)2 nanosheets coated on conductive Ni3S2 nanorods can effectively supply large surface areas with electrolyte and provide fast ion diffusion. Consequently, the as-fabricated Ni3S2@Ni(OH)2 nanostructures showed good electrochemical performance, such as high capacitance up to 3.55 F cm−2 and a good capacity retained after 10u2006000 cycles of about 85%. Furthermore, an asymmetric device, based on Ni3S2@Ni(OH)2 and activated carbon, was also fabricated and achieved a maximum energy density of 60.5 W h kg−1 at 1159 W kg−1. These results suggest that the as-designed core–shell Ni3S2@Ni(OH)2 nanostructures demonstrated in this research are promising electrode materials for energy storage.

Hierarchical NiCo-LDH/NiCoP@NiMn-LDH hybrid electrodes on carbon cloth for excellent supercapacitors

To realize high-performance and long life span supercapacitors, highly electrochemically active materials and rational design of structure are highly desirable. Herein, a hierarchical NiCo-LDH/NiCoP@NiMn-LDH hybrid electrode (NCLP@NiMn-LDH) was synthesized on carbon cloth via a hydrothermal reaction and phosphorization treatment. Owing to the introduction of NiCoP and design of the core–shell structure, the hybrid electrode showed significantly improved electrochemical performance. The as-fabricated hybrid electrode exhibited a high specific capacitance of 2318 F g−1 at 1 A g−1, with a superior cyclic stability. Additionally, an asymmetric supercapacitor (NCLP@NiMn-LDH//AC) was assembled with a voltage window of 1.5 V. The ASC device delivered a maximum energy density of 42.2 W h kg−1 at a power density of 750 W kg−1.

Confirming the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials by PECVD

In order to confirm the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials (NCMs), here we report a novel strategy to create different Ar+ ion states in situ in plasma enhanced chemical vapor deposition (PECVD) by separating catalyst film from the substrate. Different bombardment environments on either side of the catalyst film were created simultaneously to achieve multi-layered structural NCMs. Results showed that Ar+ ion bombardment is crucial and complex for the growth of NCMs. Firstly, Ar+ ion bombardment has both positive and negative effects on carbon nanotubes (CNTs). On one hand, Ar+ ions can break up the graphic structure of CNTs and suppress thin CNT nucleation and growth. On the other hand, Ar+ ion bombardment can remove redundant carbon layers on the surface of large catalyst particles which is essential for thick CNTs. As a result, the diameter of the CNTs depends on the Ar+ ion state. As for vertically oriented few-layer graphene (VFG), Ar+ ions are essential and can even convert the CNTs into VFG. Therefore, by combining with the catalyst separation method, specific or multi-layered structural NCMs can be obtained by PECVD only by changing the intensity of Ar+ ion bombardment, and these special NCMs are promising in many fields.