Weina Ren

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.

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.

Improvement of light extraction of LYSO scintillator by using a combination of self-assembly of nanospheres and atomic layer deposition

The self-assembled monolayer periodic array of polystyrene spheres conformally coated with TiO₂ layer using atomic layer deposition is designed to obtain a further enhancement of light extraction for LYSO scintillator. The maximum enhancement is 149% for the sample with polystyrene spheres conformally coated with TiO₂ layer, while the enhancement is only 76% for the sample with only polystyrene spheres. Such further enhancement could be contributed from the additional modes forming by TiO₂ layer due to its high refractive index, which can be approved by the simulation of electric field distribution. The experimental results are agreement with the simulated results. Furthermore, the prepared structured layer exhibits an excellent combination with the surface of scintillator, which is in favor of the practical application. Therefore, it is safely concluded that the combination of self-assembly method and atomic layer deposition is a promising approach to obtain a significant enhancement of light extraction for a large area. This method can be extended to many other luminescent materials and devices.

Metal–organic framework-derived integrated nanoarrays for overall water splitting

Earth-abundant electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in a wide pH range are highly desirable for sustainable energy conversion technologies, but challenging to develop. Herein, we report hollow CoP nanosphere-embedded carbon nanotube/nitrogen-doped carbon (NC-CNT/CoP) nanoarrays, in which a nanoscale Kirkendall effect generates few-layer graphene-coated hollow CoP nanospheres with abundant active sites. The integrated NC-CNT/CoP electrode behaves as an efficient pH-universal HER catalyst and, through in situ transformation, the derived materials show excellent OER performance. The NC-CNT/CoP-based electrolyzers achieve a current density of 10 mA cm−2 at low voltages of 1.63, 1.69, and 1.66 V in KOH, PBS, and H2SO4, respectively, which are similar to the values obtained using noble metal catalysts. Importantly, the integrated electrode exhibits superior stability than that of the benchmark noble metals in a wide pH range. This work presents a promising method for achieving nonprecious catalysts for efficient energy conversion.

Pt decorated 3D vertical graphene nanosheet arrays for efficient methanol oxidation and hydrogen evolution reactions

Highly active and durable electrocatalysts are highly desirable for electrochemical energy conversion devices. Herein, we report the design and fabrication of Pt nanoplate decorated 3D vertical graphene nanosheet arrays supported on carbon cloth (Pt-VGNSAs/CC) as an integrated binder-free catalyst for both methanol oxidation and hydrogen evolution reactions (HER). The vertically aligned graphene nanosheets with large surface area and excellent conductivity provide an ideal support for dispersing the Pt nanoplates. As a result, the as-obtained Pt-VGNSAs/CC with optimized Pt loading exhibits significantly improved methanol electro-oxidation performance in terms of a high mass activity of 1050 mA mg−1 and areal activity of 1.45 mA cm−2, superior CO tolerance and reliable stability in contrast to those of commercial Pt/C catalysts. In addition, the Pt-VGNSAs/CC catalyst also shows promising electrocatalytic activity with a small onset potential of −60 mV vs. the RHE at 10 mA cm−2, and a low Tafel slope of 28.5 mV dec−1 as well as excellent long-term stability for the HER. The significantly enhanced electrocatalytic performance could be attributed to the structural advantages and strong synergistic effects between graphene and Pt.