Yongfu Zhu

Integrated Solid/Nanoporous Copper/Oxide Hybrid Bulk Electrodes for High-performance Lithium-Ion Batteries

Nanoarchitectured electroactive materials can boost rates of Li insertion/extraction, showing genuine potential to increase power output of Li-ion batteries. However, electrodes assembled with low-dimensional nanostructured transition metal oxides by conventional approach suffer from dramatic reductions in energy capacities owing to sluggish ion and electron transport kinetics. Here we report that flexible bulk electrodes, made of three-dimensional bicontinuous nanoporous Cu/MnO2 hybrid and seamlessly integrated with Cu solid current collector, substantially optimizes Li storage behavior of the constituent MnO2. As a result of the unique integration of solid/nanoporous hybrid architecture that simultaneously enhances the electron transport of MnO2, facilitates fast ion diffusion and accommodates large volume changes on Li insertion/extraction of MnO2, the supported MnO2 exhibits a stable capacity of as high as ~1100 mA h g−1 for 1000 cycles, and ultrahigh charge/discharge rates. It makes the environmentally friendly and low-cost electrode as a promising anode for high-performance Li-ion battery applications.

Facile Synthesis of Non-Graphitizable Polypyrrole-Derived Carbon/Carbon Nanotubes for Lithium-ion Batteries

Graphite is usually used as an anode material in the commercial lithium ion batteries (LIBs). The relatively low lithium storage capacity of 372 mAh g–1 and the confined rate capability however limit its large-scale applications in electrical vehicles and hybrid electrical vehicles. As results, exploring novel carbon-based anode materials with improved reversible capacity for high-energy-density LIBs is urgent task. Herein we present TNGC/MWCNTs by synthesizing tubular polypyrrole (T-PPy) via a self-assembly process, then carbonizing T-PPy at 900 °C under an argon atmosphere (TNGC for short) and finally mixing TNGC with multi-walled carbon nanotubes (MWCNTs). As for TNGC/MWCNTs, the discharge capacity of 561 mAh g−1 is maintained after 100 cycles at a current density of 100 mA g−1. Electrochemical results demonstrate that TNGC/MWCNTs can be considered as promising anode materials for high-energy-density LIBs.

Single-crystalline Ni(OH)2 nanosheets vertically aligned on a three-dimensional nanoporous metal for high-performance asymmetric supercapacitors

Transition-metal hydroxides (TMHOs) or oxides (TMOs) with layered crystalline structures are attractive electrode materials for high-density charge storage in electrochemical supercapacitors. However, their randomly stacked nanostructures on conductive reinforcements, typically carbon materials, exhibit only modest enhancement of rate capability because of poor electron and ion transports that are limited by highly anisotropic conductivity, excessive grain boundaries and weak TMHO or TMO/C interfaces. Here we report a hybrid electrode design to tackle all three of these problems in layered Ni(OH)2 for high-performance asymmetric supercapacitors, wherein the single-crystalline Ni(OH)2 nanosheets are vertically aligned on a three-dimensional bicontinuous nanoporous gold skeleton with epitaxial Au/Ni(OH)2 interfaces (NP Au/VA Ni(OH)2). As a result of the unique nanoarchitecture, the pseudocapacitive behavior of Ni(OH)2 is dramatically enhanced for ensuring a volumetric capacitance as high as ∼2911 F cm−3 (∼2416 F g−1 for the constituent Ni(OH)2) in the NP Au/VA Ni(OH)2 electrode with excellent rate capability. Asymmetric supercapacitors assembled with this NP Au/VA Ni(OH)2 electrode and activated carbon have a high gravimetric energy of 31.4 W h kg−1 delivered at an exceptionally high power density of 100 kW kg−1 with excellent cycling stability.

Nanoporous Au/SnO/Ag heterogeneous films for ultrahigh and uniform surface-enhanced Raman scattering

There is a strong interest in plasmonic nanostructures that uniformly enhance Raman signals of chemical and biological molecules using surface-enhanced Raman spectroscopy (SERS) for trace detection. Although the resonant excitation of localized surface plasmons of single or assembled metallic nanoparticles can generate large electromagnetic fields, their SERS effects suffer from poor reproducibility and uniformity, limiting their highly reliable and stable applications. Here, we report self-supported large-scale nanoporous hybrid films with high density and uniform hot spots, produced by the implantation of SnO nanoparticles into nanoporous Au/Ag bimetallic films (NP Au/SnO/Ag) for the trace detections of both resonant and non-resonant molecules. The NP Au/SnO/Ag films exhibit extraordinary SERS enhancements, which increase with the increasing density of Au/SnO/Ag sandwich protrusions, as a result of the formation of abundant and uniform hot spots. The nanogaps in their wrinkled films further improve the capability to detect molecules at single molecular levels, making the hybrid films promising SERS-active substrates with superior reproducibility and reliability for applications in life science and environment protection.

Self-grown Ni(OH)(2) layer on bimodal nanoporous AuNi alloys for enhanced electrocatalytic activity and stability.

Au nanostructures as catalysts toward electrooxidation of small molecules generally suffer from ultralow surface adsorption capability and stability. Here, we report Ni(OH)2 layer decorated nanoporous (NP) AuNi alloys with a three-dimensional and bimodal porous architecture, which are facilely fabricated by a combination of chemical dealloying and in situ surface segregation, for the enhanced electrocatalytic performance in biosensors. As a result of the self-grown Ni(OH)2 on the AuNi alloys with a coherent interface, which not only enhances adsorption energy of Au and electron transfer of AuNi/Ni(OH)2 but also prohibits the surface diffusion of Au atoms, the NP composites are enlisted to exhibit significant enhancement in both electrocatalytic activity and stability toward glucose electrooxidation. The highly reliable glucose biosensing with exceptional reproducibility and selectivity as well as quick response makes it a promising candidate as electrode materials for the application in nonenzymatic glucose biosensors.

SnO2 nanoparticles embedded in 3D nanoporous/solid copper current collectors for high-performance reversible lithium storage

Nanostructured SnO2 is an attractive anode material for high-energy-density lithium-ion batteries because of the fourfold higher theoretical charge capacity than commercially used graphite. However, the poor capacity retention at high rates and long-term cycling have intrinsically limited applications of nanostructured SnO2 anodes due to large polarization and ∼300% volume change upon lithium insertion/extraction. Here we report the design of a SnO2-based anode, which is constructed by embedding SnO2 nanoparticles into a seamlessly integrated 3D nanoporous/solid copper current collector (S/NP Cu/SnO2), with an aim at tackling both problems for the high-performance reversible lithium storage. As a result of the unique hybrid architecture that enhances electron transfer and rapid access of the lithium ion into the particle bulk, the S/NP Cu/SnO2 anode can store charge with a capacity density as high as ∼3695 mA h cm−3 and an exceptional rate capability. Even when the discharge rate is increased by a factor of 160 (12 A g−1), it still retains ∼1178 mA h cm−3, one order of magnitude higher than that of a traditional SnO2-based electrode (∼111.6 mA h cm−3), which is assembled by mixing SnO2 nanoparticles with conductive carbon black and a polymeric binder and coating on flat Cu foil. In addition, not only do the rigid Cu skeleton and the stable Cu/SnO2 interface improve the microstructural stability, but also the pore channels accommodate the large SnO2 volume changes, enlisting the S/NP Cu/SnO2 anode to exhibit high specific capacity over 1000 cycles at a high rate.

Eu and F co-doped ZnO-based transparent electrodes for organic and quantum dot light-emitting diodes

A novel Eu and F co-doped zinc oxide (EFZO) thin film has been prepared by ion-assisted electron beam evaporation. The effects of different atomic contents of Eu and F on the structural, optical, and electrical properties of EFZO films were investigated. Eu3+ and F− ions are successfully incorporated into the ZnO lattice by the substitution of Zn2+ and O2− sites, respectively. Simultaneously, F− ions also play an important role of filling oxygen vacancy defects. Eu3+ and F− ions serve cooperatively as charge donor centers and compensate for the deformation in the ZnO crystal structure produced by either Eu or F individual ions, thus resulting in improving crystalline quality and electrical properties as compared with single element doping. Complementarity of Eu3+ and F− doping is assumed to be conducive to the F− filling oxygen vacancy effect in consideration of the changes in lattice constant and electrical parameters with varying dopant contents in EFZO films. An optimized EFZO film shows an average visible optical transmittance of 82.9% and a resistivity of 5.7 × 10−4 Ω cm corresponding to a carrier density of 1.86 × 1020 cm−3 and a mobility of 58.8 cm2 V−1 s−1. Conventional organic light-emitting diodes based on the EFZO anode and inverted structural quantum dot light-emitting diodes based on the EFZO cathode have been designed and fabricated, both of which show equivalent or a little higher electroluminescence performance in comparison to the reference ITO-based devices. Our results indicate that Eu and F are effective co-doping elements for ZnO transparent conducting oxide films, and EFZO transparent electrodes have efficient hole and electron injection abilities. As a promising candidate for low cost and high-performance transparent conducting oxide (TCO) films, EFZO can be used for a variety of optoelectronic devices.

Modeling of the Atomic Diffusion Coefficient in Nanostructured Materials

A formula has been established, which is based on the size-dependence of a metal’s melting point, to elucidate the atomic diffusion coefficient of nanostructured materials by considering the role of grain-boundary energy. When grain size is decreased, a decrease in the atomic diffusion activation energy and an increase in the corresponding diffusion coefficient can be observed. Interestingly, variations in the atomic diffusion activation energy of nanostructured materials are small relative to nanoparticles, depending on the size of the grain boundary energy. Our theoretical prediction is in accord with the computer simulation and experimental results of the metals described.