Xinzhi Yu

Super long-life supercapacitors based on the construction of nanohoneycomb-like strongly coupled CoMoO4-3D graphene hybrid electrodes

Nanohoneycomb-like strongly coupled CoMoO4 -3D graphene hybird electrodes are synthesized for supercapacitors which exhibit excellent specific capacitance and superior long-term cycle stability. The supercapacitor device can power a 5 mm-diameter LED efficiently for more than 3 min with a charging time of only 2 s, and shows high energy densities and good cycle stability.

Facile synthesis and excellent electrochemical properties of CoMoO4 nanoplate arrays as supercapacitors

CoMoO4 nanoplate arrays (NPAs) were grown directly on Ni foam via a template-free hydrothermal route. The morphology of CoMoO4 NPAs was examined by scanning and transmission electron microscopy and the phase structure of nanoplates (NPs) was analyzed using X-ray diffraction spectroscopy. Based on a series of time-dependent experiments, a possible growth mechanism for this structure was proposed. The CoMoO4 NPAs supported on Ni foam could be directly used as integrated electrodes for electrochemical capacitors. Such unique array architectures exhibited remarkable electrochemical performance with a high specific capacitance of 1.26 F cm−2 at a charge and discharge current density of 4 mA cm−2 and 0.78 F cm−2 at 32 mA cm−2 with an excellent cycling ability (79.5% of the initial specific capacitance remained after 4000 cycles). The superior electrochemical performances could be attributed to the open network structure constituted of interconnected CoMoO4 NPAs directly grown on current collectors that could improve electron transport and enhance electrolyte diffusion efficiency.

A green and fast strategy for the scalable synthesis of Fe2O3/graphene with significantly enhanced Li-ion storage properties

In this study, we proposed and demonstrated an environmentally friendly and effective methodology to prepare Fe2O3/graphene composites. The essence of this method was that ferrous ions could serve as both reductant and the iron source for Fe2O3, which is greener and more facile than the preparation methods for other iron oxide/graphene composites. As anode materials for lithium ion batteries, Fe2O3/graphene composites achieved high reversible capacities of about 800 mA h g−1 after 100 cycles at a charge–discharge rate of 0.2 C. Moreover, they delivered rate capacities as high as 420 mA h g−1 at a rate of 5 C. Both the cycling performance and rate capacities of Fe2O3/graphene composites were better than those of commercial Fe2O3 and its graphene composites. The improved performance toward the storage of Li+ was ascribed to graphene sheets, which acted as volume buffers and electron conductors. We believe that the strategy of preparing Fe2O3/graphene composites proposed by us may open a new way for the synthesis of metal oxide/graphene for various potential purposes.

NiMoO4 nanowires supported on Ni foam as novel advanced electrodes for supercapacitors

NiMoO4 nanowires (NWs) supported on Ni foam were fabricated via a template-free hydrothermal route, and could be directly used as integrated electrodes for electrochemical capacitors (ECs). Such unique integrated architectures exhibited remarkable electrochemical performance with high capacitance, excellent rate capability and desirable cycle life at high rates.

Synthesis of bacteria promoted reduced graphene oxide-nickel sulfide networks for advanced supercapacitors.

Supercapacitors with potential high power are useful and have attracted much attention recently. Graphene-based composites have been demonstrated to be promising electrode materials for supercapacitors with enhanced properties. To improve the performance of graphene-based composites further and realize their synthesis with large scale, we report a green approach to synthesize bacteria-reduced graphene oxide-nickel sulfide (BGNS) networks. By using Bacillus subtilis as spacers, we deposited reduced graphene oxide/Ni3S2 nanoparticle composites with submillimeter pores directly onto substrate by a binder-free electrostatic spray approach to form BGNS networks. Their electrochemical capacitor performance was evaluated. Compared with stacked reduced graphene oxide-nickel sulfide (GNS) prepared without the aid of bacteria, BGNS with unique nm-μm structure exhibited a higher specific capacitance of about 1424 F g(-1) at a current density of 0.75 A g(-1). About 67.5% of the capacitance was retained as the current density increased from 0.75 to 15 A g(-1). At a current density of 75 A g(-1), a specific capacitance of 406 F g(-1) could still remain. The results indicate that the reduced graphene oxide-nickel sulfide network promoted by bacteria is a promising electrode material for supercapacitors.

Graphene Nanoribbons on Highly Porous 3D Graphene for High‐Capacity and Ultrastable Al‐Ion Batteries

Graphene nanoribbons on highly porous 3D graphene foam as the binder-free cathode for flexible Al-ion batteries exhibit low charge voltage, high capacity, excellent cycling ability (even after 10 000 cycles there is no capacity decay), and fast charging and slow discharging performance (the battery can be fully charged in 80 s and discharged in more than 3100 s).

Graphene oxide oxidizes stannous ions to synthesize tin sulfide-graphene nanocomposites with small crystal size for high performance lithium ion batteries†

This study reports a novel strategy of preparing graphene composites by employing graphene oxide as precursor and oxidizer. It is demonstrated that graphene oxide can oxidize stannous ions to form SnS2 and is simultaneously reduced to graphene, directly resulting in the formation of SnSx–graphene (1 < x < 2) nanocomposites. The particle size of SnSx in the nanocomposites is tailored to be about 5 nm, which is much smaller than that obtained in a previous study. As anodic materials for lithium ion batteries, SnSx–graphene nanocomposites retain a discharge capacity of 860 mA h g−1 after 150 cycles at a charge–discharge rate of 0.2 C, higher than the theoretical capacities of SnS2 (645 mA h g−1) and SnS (782 mA h g−1) based on the traditional mechanism. A possible new mechanism, that Li2S arising from tin sulfide in the first discharge cycle could be reversibly decomposed at a low potential to storage lithium, is proposed based on experimental results to explain the excellent properties of SnSx–graphene nanocomposites.

Facile synthesis of well-ordered manganese oxide nanosheet arrays on carbon cloth for high-performance supercapacitors

Well-ordered manganese oxide (MnO2) nanosheet arrays (NSAs) were grown directly on carbon cloth via a simple in situ redox replacement reaction between potassium permanganate (KMnO4) and carbon cloth without any other oxidant or reductant addition. The morphology of MnO2 NSAs was examined by scanning and transmission electron microscopy and the phase structure of nanosheets (NSs) was analyzed by X-ray diffraction spectroscopy. Based on a series of time-dependent experiments, a possible growth process for this structure was proposed. The MnO2 NSAs supported on carbon cloth were directly used as integrated electrodes for electrochemical capacitors. The ordered MnO2 NSAs yielded high-capacitance performance with a high specific capacitance of 2.16 F cm−2 at a charge and discharge current density of 5 mA cm−2 and 1.01 F cm−2 at 20 mA cm−2 with a cycling ability (61.4% of the initial specific capacitance remains after 3000 cycles). The MnO2 nanosheet arrays with large surface area and high degree of ordering, combined with the flexible carbon cloth substrate can offer great promise for large-scale supercapacitor applications.

Large-scale production of silicon nanoparticles@graphene embedded in nanotubes as ultra-robust battery anodes

The nanosized silicon for lithium-ion batteries (LIBs) is mainly limited by cracking and pulverization caused by the large volume change during deep cycles. Here, we demonstrated a commercial viability (scalable synthesis) of Si nanoparticles@graphene encapsulated in titanium dioxide nanotubes (Si@G@TiO2NTs) or carbon nanotubes (Si@G@CNTs) for the next generation of high-energy battery anodes. The nanotubes can not only provide strong protection and sufficient void space to buffer the huge volume expansion of Si nanoparticles during the charge/discharge process, but also enforce a most solid-electrolyte interphase to form on the outer surface of the nanotube instead of on individual Si nanoparticles, leading to ultrahigh coulombic efficiency and excellent cycling stability. The obtained Si@G@TiO2NT and Si@G@CNT electrodes showed a high reversible capacity of 1919.2 mA h g−1 (1.02 mA h cm−2) after 800 cycles and 2242.2 mA h g−1 (1.19 mA h cm−2) after 1000 cycles (>1 year) at the constant current density of 500 mA g−1, respectively. Furthermore, both Si@G@TiO2NT and Si@G@CNT electrodes presented superior average coulombic efficiency more than 99.9% during the whole cycling process.

Semimetallic vanadium molybdenum sulfide for high-performance battery electrodes

The ultrathin thickness and lateral morphology of a two dimensional (2D) MoS2 nanosheet contribute to its high surface-to-volume ratio and short diffusion path, rendering it a brilliant electrode material for lithium-ion batteries (LIBs). However, the low conductivity and easy restacking character of the pure MoS2 nanosheet during extended cycling result in severe capacity fading and poor cycling performance. In this work, we developed an attractive strategy by using a metal-doping method to engineer chemical, physical and electronic properties of MoS2, achieving an outstanding performance in LIBs. The computational results show that V–Mo–S has semimetallic properties. Semimetallic vanadium molybdenum sulfide nanoarrays (V–Mo–S NAs) were prepared to overcome the low conductivity of semiconducting MoS2 and thus further optimize its performance in LIBs. A reversible capacity as high as 1047 mA h g−1 was achieved at 1000 mA g−1. It also displayed an excellent stability even after 700 cycles. This fascinating study may pave a way for utilizing semimetallic material-based nanomaterials for batteries.