Jiuhui Han

Multifunctional Porous Graphene for High‐Efficiency Steam Generation by Heat Localization

Multifunctional nanoporous graphene is realized as a heat generator to convert solar illumination into high-energy steam. The novel 3D nanoporous graphene demonstrates a highly energy-effective steam generation with an energy conversation of 80%.

3D Nanoporous Nitrogen-Doped Graphene with Encapsulated RuO2 Nanoparticles for Li–O2 Batteries

Freestanding nanoporous N-doped graphene with encapsulated RuO2 nanoparticles is developed as a cathode for rechargeable Li-O2 batteries. The stabilized metal oxide catalyst reduces charge overpotentials enabling high-efficiency rechargeable Li-O2 batteries with a long cycling lifetime. This has important implications for the development of highly stable and catalytically active graphene-based cathodes for rechargeable Li-O2 batteries.

Atomic-Sized Pores Enhanced Electrocatalysis of TaS2 Nanosheets for Hydrogen Evolution

A plasma oxidation method is developed to fabricate atomic-scale pores in the basal planes of electrochemically inert TaS2 nanosheets to functionalize the 2D crystals with high electrocatalysis for hydrogen evolution reaction. Quantitative measurements of under-coordinated atoms at edges of the pores by aberration-corrected transmission electron microscopy reveal the intrinsic correlation between the defective atomic sites and electrocatalytic activities of 2D TaS2 .

On-Chip Micro-Pseudocapacitors for Ultrahigh Energy and Power Delivery

Microscale supercapapcitors based on hierarchical nanoporous hybrid electrodes consisting of 3D bicontinuous nanoporous gold and pseudocapacitive manganese oxide deliver an excellent stack capacitance of 99.1 F cm−3 and a high energy density of 12.7 mW h cm−3 with a retained high power density of 46.6 W cm−3.

Nanoporous metal/oxide hybrid materials for rechargeable lithium–oxygen batteries

Lithium–oxygen batteries have attracted considerable attention due to their expected specific energy being far higher than that of lithium-ion batteries. The high charge overpotentials of the cathodic oxygen evolution reaction of insulator lithium peroxide is one of the critical challenges for practical implementation of lithium–oxygen batteries, which results in low energy efficiency and poor stability of cathodes and electrolytes. Transition metal oxides are known to be the most active electrocatalysts that can dramatically decrease the charging overpotentials of rechargeable lithium–air batteries. However, the poor electrical conductivity of these oxide electrocatalysts, such as RuO2, MnO2 and Co3O4, limits the charge transport of cathodic reactions and the full utilization of their catalytic activities. Herein, we exploit the high oxygen evolution reaction activities of oxides by incorporating insulator oxides into the pore channels of highly conductive nanoporous gold to form three-dimensional nanoporous core–shell composites. The hybrid catalysts as the cathodes of rechargeable lithium–oxygen batteries show highly reversible cathodic reactions at extremely lower overpotentials for high efficiency lithium–air batteries, arising from the synergistic effect of high conductive nanoporous gold (NPG) and catalytically active metal oxides.

Hierarchical nanoporosity enhanced reversible capacity of bicontinuous nanoporous metal based Li-O 2 battery

High-energy-density rechargeable Li-O2 batteries are one of few candidates that can meet the demands of electric drive vehicles and other high-energy applications because of the ultra-high theoretical specific energy. However, the practical realization of the high rechargeable capacity is usually limited by the conflicted requirements for porous cathodes in high porosity to store the solid reaction products Li2O2 and large accessible surface area for easy formation and decomposition of Li2O2. Here we designed a hierarchical and bicontinuous nanoporous structure by introducing secondary nanopores into the ligaments of coarsened nanoporous gold by two-step dealloying. The hierarchical and bicontinuous nanoporous gold cathode provides high porosity, large accessible surface area and sufficient mass transport path for high capacity and long cycling lifetime of Li-O2 batteries.

Macroporous mesh of nanoporous gold in electrochemical monitoring of superoxide release from skeletal muscle cells

Real-time monitoring of metabolically relevant biochemicals released in minuscule amounts is of utmost diagnostic importance. Superoxide anion as a primary member of reactive oxygen species, has physiological and pathological effects that depend on its concentration and release rate. Here we present fabrication and successfully testing of a highly sensitive electrochemical biosensor featuring a three-dimensional macroporous mesh of nanoporous gold tailored to measure the dynamics of extracellular superoxide concentration. Wide and accessible surface of the mesh combined with high porosity of the thin nanoporous gold coating enables capturing the analyte in pico- to nano-molar ranges. The mesh is functionalized with cytochrome-c (cyt-c) and incorporated as a working electrode to measure the release rate of drug-induced superoxides from C2C12 cells through a porous membrane. The device displays a considerably improved superoxide sensitivity of 7.29nAnM-1cm-2 and a low level of detection of 70pM. Such sensitivity is orders of magnitude higher than any similar enzyme-based electrochemical superoxide sensor and is attributed to the facile diffusion of the analyte through the well-spread nanofeatured gold skin. Superoxide generation rates captured from monolayer myoblast cultures containing about 4×104 cells, varied from 1.0 to 9.0nMmin-1 in a quasi-linear fashion as a function of drug concentration. This work provides a platform for the development of highly sensitive molecular electrochemical biosensors.

Correlation between Local Structure Order and Spatial Heterogeneity in a Metallic Glass

Although nanoscale spatial heterogeneity of metallic glasses has been demonstrated by extensive experimental and theoretical investigations, the nature of spatial heterogeneity remains poorly known owing to the absence of a structural depiction of the inhomogeneity from experimental insight. Here we report the experimental characterization of the spatial heterogeneity of a metallic glass by utilizing state-of-the-art angstrom-beam electron diffraction and scanning transmission electron microscopy. The subnanoscale electron diffraction reveals that the nanoscale spatial heterogeneity and corresponding density fluctuation have a close correlation with the local structure variation from icosahedronlike to tetragonal crystal-like order. The structural insights of spatial heterogeneity have important implications in understanding the properties and dynamics of metallic glasses.

Direct Observations of the Formation and Redox-Mediator-Assisted Decomposition of Li2O2 in a Liquid-Cell Li–O2 Microbattery by Scanning Transmission Electron Microscopy

Operando scanning transmission electron microscopy observations of cathodic reactions in a liquid-cell Li-O2 microbattery in the presence of the redox mediator tetrathiafulvalene (TTF) in 1.0 m LiClO4 dissolved dimethyl sulfoxide electrolyte are reported. It is found that the TTF addition does not obviously affect the discharge reaction for the formation of a solid Li2 O2 phase. The coarsening of Li2 O2 nanoparticles occurs via both conventional Ostwald ripening and nonclassical crystallization by particle attachment. During charging, the oxidation reaction at significantly reduced charge potentials mainly takes place at Li2 O2 /electrolyte interfaces and has obvious correspondence with the oxidized TTF+ distributions in the electric fields of the charged electrode. This study provides direct evidence that TTF truly plays a role in promoting the decomposition of Li2 O2 as a soluble charge-transfer agent between the electrode and the Li2 O2 .

Engineering the internal surfaces of three-dimensional nanoporous catalysts by surfactant-modified dealloying

Tuning surface structures by bottom-up synthesis has been demonstrated as an effective strategy to improve the catalytic performances of nanoparticle catalysts. Nevertheless, the surface modification of three-dimensional nanoporous metals, fabricated by a top-down dealloying approach, has not been achieved despite great efforts devoted to improving the catalytic performance of three-dimensional nanoporous catalysts. Here we report a surfactant-modified dealloying method to tailor the surface structure of nanoporous gold for amplified electrocatalysis toward methanol oxidation and oxygen reduction reactions. With the assistance of surfactants, {111} or {100} faceted internal surfaces of nanoporous gold can be realized in a controllable manner by optimizing dealloying conditions. The surface modified nanoporous gold exhibits significantly enhanced electrocatalytic activities in comparison with conventional nanoporous gold. This study paves the way to develop high-performance three-dimensional nanoporous catalysts with a tunable surface structure by top-down dealloying for efficient chemical and electrochemical reactions.Tuning the ratio of facets in materials can affect catalytic activity but methods to achieve this can be difficult to control. Here, using surfactants during dealloying, the authors prepare nanoporous gold with controlled facet ratios and show how it can significantly improve electrocatalytic activity.