Zi Wen

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.

Al 13 @Pt 42 Core-Shell Cluster for Oxygen Reduction Reaction

To increase Pt utilization for oxygen reduction reaction (ORR) in fuel cells, reducing particle sizes of Pt is a valid way. However, poisoning or surface oxidation limits the smallest size of Pt particles at 2.6 nm with a low utility of 20%. Here, using density functional theory calculations, we develop a core-shell Al13@Pt42 cluster as a catalyst for ORR. Benefit from alloying with Al in this cluster, the covalent Pt-Al bonding effectively activates the Pt atoms at the edge sites, enabling its high utility up to 70%. Valuably, the adsorption energy of O is located at the optimal range with 0.0–0.4 eV weaker than Pt(111), while OH-poisoning does not observed. Moreover, ORR comes from O2 dissociation mechanism where the rate-limiting step is located at OH formation from O and H with a barrier of 0.59 eV, comparable with 0.50 eV of OH formation from O and H2O on Pt(111).

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.

Multi‐Field Effect on the Electronic Properties of Silicon Nanowires

The quantum confinement and electronic properties of silicon nanowires (SiNWs) under an external strain field ε and an electric field E-as well as both (ε plus E)-are systematically investigated using density functional theory. These two fields exist in working environments of integrated circuits. It is found that both ε and E lead to a drop of the band gap E(g)(ε,E) of the SiNWs. If both fields coexist, the interaction between ε and E causes that E(g)(ε,E) becomes orientation-dependent, which results from variations of both the conduction-band minimum and the valence-band maximum. The interaction is further illustrated by the density of states near the Fermi level and the eigenvalue of the highest occupied molecular orbital.

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.

Electronic structure of silicene: effects of the organic molecular adsorption and substrate

The potential of silicene-based integrated electronics originates from its extremely high carrier mobility, whereas the lack of a band gap impedes its application. Thus, opening a sizeable band gap without degrading its carrier mobility is a significant challenge for application in logic circuits. In this study, a sizable band gap is created in silicene by the dual effect of organic molecule adsorption and a substrate. As an electron donor molecule, tetrathiafulvalene (TTF) is found to non-covalently functionalize the silicene sheet. As a result, silicene with adsorbed TTF exhibits an open band gap. When silicane (hydrogenated silicene) substrate is applied, the band gap further widens. Moreover, the high carrier mobility is largely retained. These results provide effective and reversible routes for engineering the band gap of silicene.

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.

Design of Hydrogen Storage Alloys/Nanoporous Metals Hybrid Electrodes for Nickel-Metal Hydride Batteries

Nickel metal hydride (Ni-MH) batteries have demonstrated key technology advantages for applications in new-energy vehicles, which play an important role in reducing greenhouse gas emissions and the world’s dependence on fossil fuels. However, the poor high-rate dischargeability of the negative electrode materials—hydrogen storage alloys (HSAs) limits applications of Ni-MH batteries in high-power fields due to large polarization. Here we design a hybrid electrode by integrating HSAs with a current collector of three-dimensional bicontinuous nanoporous Ni. The electrode shows enhanced high-rate dischargeability with the capacity retention rate reaching 44.6% at a discharge current density of 3000 mA g−1, which is 2.4 times that of bare HSAs (18.8%). Such a unique hybrid architecture not only enhances charge transfer between nanoporous Ni and HSAs, but also facilitates rapid diffusion of hydrogen atoms in HSAs. The developed HSAs/nanoporous metals hybrid structures exhibit great potential to be candidates as electrodes in high-performance Ni-MH batteries towards applications in new-energy vehicles.