Chuanwei Cheng

Three-Dimensional NiCo2O4@Polypyrrole Coaxial Nanowire Arrays on Carbon Textiles for High-Performance Flexible Asymmetric Solid-State Supercapacitor

In this article, we report a novel electrode of NiCo2O4 nanowire arrays (NWAs) on carbon textiles with a polypyrrole (PPy) nanosphere shell layer to enhance the pseudocapacitive performance. The merits of highly conductive PPy and short ion transport channels in ordered NiCo2O4 mesoporous nanowire arrays together with the synergistic effect between NiCo2O4 and PPy result in a high specific capacitance of 2244 F g(-1), excellent rate capability, and cycling stability in NiCo2O4/PPy electrode. Moreover, a lightweight and flexible asymmetric supercapacitor (ASC) device is successfully assembled using the hybrid NiCo2O4@PPy NWAs and activated carbon (AC) as electrodes, achieving high energy density (58.8 W h kg(-1) at 365 W kg(-1)), outstanding power density (10.2 kW kg(-1) at 28.4 W h kg(-1)) and excellent cycling stability (∼89.2% retention after 5000 cycles), as well as high flexibility. The three-dimensional coaxial architecture design opens up new opportunities to fabricate a high-performance flexible supercapacitor for future portable and wearable electronic devices.

Three-dimensional Co3O4@C@Ni3S2 sandwich-structured nanoneedle arrays: towards high-performance flexible all-solid-state asymmetric supercapacitors

In this paper, we report the design and fabrication of a novel hierarchical Co3O4@C@Ni3S2 sandwich-structured nanoneedle array (NNA) electrode for supercapacitor application. The supercapacitor performance based on Co3O4@C@Ni3S2 NNA electrodes is investigated in detail. A lightweight and flexible asymmetric supercapacitor (ASC) is successfully fabricated using Co3O4@C@Ni3S2 NNAs as the positive electrode and activated carbon (AC) as the negative electrode, which delivers an output voltage of 1.8 V and high energy/power density (1.52 mW h cm−3 at 6 W cm−3 and 0.920 mW h cm−3 at 60 W cm−3), as well as remarkable cycling stability (∼91.43% capacitance retention after 10u2006000 cycles), owing to the unique 3D porous sandwich-structured nanoneedle array architecture and a rational combination of the three electrochemically active materials. As a result, the ternary hybrid architectural design demonstrated in this study provides a new approach to fabricate high-performance metal oxide/sulfide composite nanostructure arrays for next-generation energy storage devices.

NiCo2O4 nanosheet supported hierarchical core–shell arrays for high-performance supercapacitors

Two types of homogeneous NiCo2O4 nanosheet@NiCo2O4 nanorod and heterogeneous NiCo2O4 nanosheet@NiO nanoflake hierarchical core–shell arrays are synthesized via facile solution methods in combination with a simple thermal treatment. In both cases, the NiCo2O4 nanosheets serve as the core backbone for anchoring the shell materials. The two as-prepared hierarchical nanoarrays are evaluated as supercapacitor electrodes and demonstrate excellent electrochemical performance with high specific capacitance (1925 and 2210 F g−1 for NiCo2O4@NiCo2O4 and NiCo2O4@NiO at 0.5 A g−1, respectively), good rate capability, and superior cycling stability. The superior capacitive performance is mainly due to the unique hierarchical core–shell architecture with faster ion/electron transfer, improved reactivity, and enhanced structural stability. Our work can allow for the fabrication of various NiCo2O4 nanosheet supported hierarchical nanostructures for applications in energy storage, catalysis, and sensing.

3D hierarchical Co3O4@Co3S4 nanoarrays as cathode materials for asymmetric pseudocapacitors

Three-dimensional (3D) hierarchical Co3O4@Co3S4 nanoarrays (NAs) were synthesized via a stepwise hydrothermal method involving precipitation and in situ sulfurization of Co3O4 nanoneedle arrays (NNAs). By controlling both anion exchange and Ostwald ripening reactions during the sulfurization process, 3D hierarchical Co3O4@Co3S4 NAs with tailored Co3S4 nanostructures have been fabricated as electrode materials for electrochemical capacitor applications. Owing to an interconnected matrix within the 3D architecture, the as-prepared Co3O4@Co3S4 NAs exhibit excellent electrical conductivity, high specific capacity and high cycling stability. It can deliver a high capacitance of 1284.3 F g−1 at 2 mV s−1 and maintain a capacitance retention of 93.1% after 5000 cycles. Moreover, a flexible solid-state asymmetric supercapacitor (ASC) composed of Co3O4@Co3S4 NAs as the positive electrode and activated carbon (AC) as the negative electrode exhibited an energy density of 1.5 mW h cm−3 and a power density of 6.1 W cm−3 at a high operating voltage of 1.6 V. Our results not only present the 3D hierarchical nanostructure of Co3O4@Co3S4 NAs, but they also demonstrate the potential of electrodes for future generation supercapacitors.

ALD TiO2-Coated Flower-like MoS2 Nanosheets on Carbon Cloth as Sodium Ion Battery Anode with Enhanced Cycling Stability and Rate Capability

We report the fabrication of 3D flower-like MoS2 nanosheets arrays on carbon cloth as a binder-free anode for sodium ion battery. Ultrathin and conformal TiO2 layers are used to modify the surface of MoS2 by atomic layer deposition. The electrochemical performance measurements demonstrate that the ALD TiO2 layer can improve the cycling stability and rate capability of MoS2. The MoS2 nanosheets with 0.5-nm TiO2 coating electrode show the highest initial discharge capacity of 1392 mA h g-1 at 200 mA g-1, which is increased by 53% compared with that of bare MoS2. After 150 cycles, the capacity retention rate of the TiO2-coated MoS2 achieves 75.8% of its second cycles capacity at 200 mA h g-1 in contrast to that of 59% of pure MoS2. Furthermore, the mechanism behind the experimental results is revealed by ex situ scanning electron microscope (SEM), X-ray powder diffraction (XRD), and electrochemical impedance spectroscopy (EIS) characterizations, which confirms that the ultrathin TiO2 modifications can prevent the structural degradation and the formation of SEI film of MoS2 electrode.

Scalable synthesis of graphene-wrapped Li4Ti5O12 dandelion-like microspheres for lithium-ion batteries with excellent rate capability and long-cycle life

A three-dimensional dandelion-like Li4Ti5O12@graphene microsphere electrode is designed by using a simple and scalable solution fabrication process. The graphene nanosheets are incorporated into the porous dandelion-like Li4Ti5O12 microspheres homogenously, which provide a highly conductive network for electron transportation. When tested as an anode for Li-ion batteries, the dandelion-like Li4Ti5O12@graphene composite with 3 wt% graphene exhibits excellent rate capabilities and superior cycle life between 0.01 and 3.0 V. The capacities of Li4Ti5O12@graphene (3 wt%) reach 206 mA h g−1 after 500 cycles between 0.01 and 3.0 V and 166 mA h g−1 after 100 cycles between 0.7 and 3.0 V at a current density of 0.12 A g−1, respectively. In addition, Li4Ti5O12-based anode materials at lower voltage can offer a higher cell voltage and discharge capacity for lithium-ion batteries. Hence, it is significant to study the electrochemical behaviors of the Li4Ti5O12-based anode in a wide voltage range of 0.01–3.0 V. This facile and scalable method for Li4Ti5O12@graphene composites represents an effective strategy to develop advanced electrochemical energy storage systems with long cycle life and high rate performance.

Seed-assisted growth of α-Fe2O3 nanorod arrays on reduced graphene oxide: a superior anode for high-performance Li-ion and Na-ion batteries

α-Fe2O3 nanorod/reduced graphene oxide nanosheet composites (denoted as α-Fe2O3@r-GO NRAs) are fabricated by using a facile and scalable seed-assisted hydrothermal growth route, in which the α-Fe2O3 nanorods are assembled onto the side surfaces of r-GO nanosheets. Such α-Fe2O3@r-GO hybrid nanostructures are tested as anodes for both Li-ion and Na-ion batteries (LIBs and SIBs), which exhibit excellent performance with high capacity and long-cycling stability. When used for LIBs, the hybrid α-Fe2O3@r-GO NRAs electrode exhibits a highly stable Li+ storage capacity of 1200 mA h g−1 after 500 cycles at 0.2C and excellent rate capability. Moreover, the hybrid α-Fe2O3@r-GO NRAs also display their versatility as an anode for SIBs, which delivers high reversible Na+ storage capacity of 332 mA h g−1 at 0.2C over 300 cycles with long-term cycling stability. The excellent electrochemical performance of the hybrid α-Fe2O3@r-GO NRAs anodes could be ascribed to the synergistic effect between the α-Fe2O3 nanorod arrays and reduced graphene oxide nanosheets, which could availably promote the charge transport and accommodate the volume change upon the long-term charge–discharge process for reversible Li+ or Na+ storage.

Fe3O4 quantum dot decorated MoS2 nanosheet arrays on graphite paper as free-standing sodium-ion battery anodes

A novel composite consisting of vertical ultrathin MoS2 nanosheet arrays and Fe3O4 quantum dots (QDs) grown on graphite paper (GP) as a high-performance anode material for sodium-ion batteries (SIBs) has been synthesized via a facile two-step hydrothermal method. Owing to the high reversible capacity provided by the MoS2 nanosheets and the superior high rate performance offered by Fe3O4 QDs, superior cycling and rate performances are achieved by Fe3O4@MoS2-GP anodes during the subsequent electrochemical tests, delivering 468 and 231 mA h g−1 at current densities of 100 and 3200 mA g−1, respectively, as well as retaining ∼72.5% of their original capacitance at a current density of 100 mA g−1 after 300 cycles. The excellent electrochemical performance resulted from the interconnected nanosheets of MoS2 providing flexible substrates for the nanoparticle decoration and accommodating the volume changes of uniformly distributed Fe3O4 QDs during the cycling process. Moreover, Fe3O4 QDs primarily act as spacers to stabilize the composite structure, making the active surfaces of MoS2 nanosheets accessible for electrolyte penetration during charge–discharge processes, which maximally utilized electrochemically active MoS2 nanosheets and Fe3O4 QDs for sodium-ion batteries.

Seed-assisted synthesis of Co3O4@α-Fe2O3 core–shell nanoneedle arrays for lithium-ion battery anode with high capacity

A novel hierarchical Co3O4@α-Fe2O3 core–shell nanoneedle array (Co3O4@α-Fe2O3 NAs) on nickel foam substrate is synthesized successfully by a stepwise, seed-assisted, hydrothermal approach. This composite nanostructure serving as an anode material for lithium-ion batteries (LIBs) is advantageous in providing large interfacial area for lithium insertion/extraction and short diffusion pathways for electronic and ionic transport. The results show that a high initial discharge capacity of 1963 mA h g−1 at 120 mA g−1 was obtained by using these hierarchical Co3O4@α-Fe2O3 NAs heterostructures as an anode, and is retained at 1045 mA h g−1 after 100 cycles, better than that of pure Co3O4 nanoneedle arrays (Co3O4 NAs) and α-Fe2O3 film grown under similar conditions, indicating a positive synergistic effect of the material and structural hybridization on the enhancement of the electrochemical properties. The fabrication strategy presented here is facile, cost-effective, and scalable, which opens new avenues for the design of optimal composite electrode materials with improved performance.

3D WO3/BiVO4/Cobalt Phosphate Composites Inverse Opal Photoanode for Efficient Photoelectrochemical Water Splitting

A novel 3D WO3 /BiVO4 /cobalt phosphate composite inverse opal is designed for photoeletrochemical (PEC) water splitting, yielding a significantly improved PEC performance.