Shuiyun Shen

Soft-Templated Self-Assembly of Mesoporous Anatase TiO2/Carbon Composite Nanospheres for High-Performance Lithium Ion Batteries

Mesoporous anatase TiO2/carbon composite nanospheres (designated as meso-ATCCNs) were successfully synthesized via a facile soft-templated self-assembly followed by thermal treatment. Structural and morphological analyses reveal that the as-synthesized meso-ATCCNs are composed of primary TiO2 nanoparticles (∼5 nm), combined with in situ deposited carbon either on the surface or between the primary TiO2 nanoparticles. When cycled in an extended voltage window from 0.01 to 3.0 V, meso-ATCCNs exhibit excellent rate capabilities (413.7, 289.7, and 206.8 mAh g(-1) at 200, 1000, and 3000 mA g(-1), respectively) as well as stable cyclability (90% capacity retention over 500 cycles at 1000 mA g(-1)). Compared with both mesoporous TiO2 nanospheres and bulk TiO2, the superior electrochemical performance of the meso-ATCCNs electrode could be ascribed to a synergetic effect induced by hierarchical structure that includes uniform TiO2 nanoparticles, the presence of hydrothermal carbon derived from phenolic resols, a high surface area, and open mesoporosity.

Soft-templated LiFePO4/mesoporous carbon nanosheets (LFP/meso-CNSs) nanocomposite as the cathode material of lithium ion batteries

A novel and facile in situ soft-templated method is proposed for synthesizing a LFP/mesoporous carbon nanosheets (LFP/meso-CNSs) nanocomposite, which involves solvent evaporation induced self-assembly of triblock copolymers, with resol and inorganic salts as co-precursors of CNSs and LFP, followed by a heat treatment. The LFP/meso-CNSs nanocomposite displays an excellent high-rate capability (122.1 mA h g−1 at 5 C and 102.1 mA h g−1 at 10 C) and stable cycling property as the cathode material of lithium ion batteries, benefitting from its high electronic conductivity, open mesoporosity, and the nano-size of its active material.

The respective effect of under-rib convection and pressure drop of flow fields on the performance of PEM fuel cells

The flow field configuration plays an important role on the performance of proton exchange membrane fuel cells (PEMFCs). For instance, channel/rib width and total channel cross-sectional area determine the under-rib convection and pressure drop respectively, both of which directly influence the water removal, in turn affecting the oxygen supply and cathodic oxygen reduction reaction. In this study, effects of under-rib convection and pressure drop on cell performance are investigated experimentally and numerically by adjusting the channel/rib width and channel cross-sectional area of flow fields. The results show that the performance differences with various flow field configurations mainly derive from the oxygen transport resistance which is determined by the water accumulation degree, and the cell performance would benefit from the narrower channels and smaller cross sections. It reveals that at low current densities when water starts to accumulate in GDL at under-rib regions, the under-rib convection plays a more important role in water removal than pressure drop does; in contrast, at high current densities when water starts to accumulate in channels, the pressure drop dominates the water removal to facilitate the oxygen transport to the catalyst layer.

Facile preparation of unique three-dimensional (3D) α-MnO2/MWCNTs macroporous hybrid as the high-performance cathode of rechargeable Li-O2 batteries

Undoubtedly, there remains an urgent prerequisite to achieve significant advances in both the specific capacity and cyclability of Li-O2 batteries for their practical application. In this work, a series of unique three-dimensional (3D) α-MnO2/MWCNTs hybrids are successfully prepared using a facile lyophilization method and investigated as the cathode of Li-O2 batteries. Thereinto, cross-linked α-MnO2/MWCNTs nanocomposites are first synthesized via a modified chemical route. Results demonstrate that MnO2 nanorods in the nanocomposites have a length of 100–400 nm and a diameter ranging from 5 to 10 nm, and more attractively, the as-lyophilized 3D MnO2/MWCNTs hybrids is uniquely constructed with large amounts of interconnected macroporous channels. The Li-O2 battery with the 3D macroporous hybrid cathode that has a mass percentage of 50% of α-MnO2 delivers a high discharge specific capacity of 8,643 mAh·g−1 at 100 mA·g−1, and maintains over 90 cycles before the discharge voltage drops to 2.0 V under a controlled specific capacity of 1,000 mAh·g−1. It is observed that when being recharged, the product of toroidal Li2O2 particles disappears and electrode surfaces are well recovered, thus confirming a good reversibility. The excellent performance of Li-O2 battery with the 3D α-MnO2/MWCNTs macroporous hybrid cathode is ascribed to a synergistic combination between the unique macroporous architecture and highly efficient bi-functional α-MnO2/MWCNTs electrocatalyst.

Icosahedral Pt-Ni Nanocrystalline Electrocatalyst: Growth Mechanism and Oxygen Reduction Activity

Engineering the structure of Pt alloy offers an effective way to the design of high performance electrocatalysts. Herein, we synthesize a sandwich-structured, icosahedral Pt2.1 Ni catalyst through a hot injection method. Its growth involves three steps: 1) burst nucleation of Pt atoms to form a Pt-enriched core, 2) heterogeneous nucleation of Ni atoms onto the Pt core to form a Ni-enriched interlayer, and 3) kinetic controlled growth of a Pt-enriched shell. The Pt-enriched core protects the nanostructure from collapse and mitigates the strain change caused by lattice mismatch, and thus enhances the stability of the structure. The Ni-enriched interlayer induces the electronic modification of the outermost Pt shell, and in turn tunes the activity. The Pt-enriched shell provides more active sites through the exposure of (1 1 1) facets and retards the dissolution of Ni atoms. As a result, this sandwich-structure enables impressive electrocatalytic activity (0.91 mA cm-2 and 0.32 AmgPt-1 @ 0.9 V) and duability.

An exploration of the use of Au submonolayer decorated Pd7Ir nanoparticles as a highly active electrocatalyst for the ethanol oxidation reaction in alkaline media

Although very promising in its stabilizing effect, an inevitable loss on activity mostly exists when combining gold (Au) with other noble metals. Contrary to this knowledge, in this research an unexpected promotion of the Au submonolayer on palladium-iridium/carbon (Pd7Ir/C) nanoparticles towards the ethanol oxidation reaction in alkaline media was explored and the corresponding mechanism was clarified.

The Experimental Measurement of Local and Bulk Oxygen Transport Resistances in the Catalyst Layer of Proton Exchange Membrane Fuel Cells

Remarkable progress has been made in reducing the cathodic Pt loading of PEMFCs; however, a huge performance loss appears at high current densities, indicating the existence of a large oxygen transport resistance associated with the ultralow Pt loading catalyst layer. To reduce the Pt loading without sacrificing cell performance, it is essential to illuminate the oxygen transport mechanism in the catalyst layer. Toward this goal, an experimental approach to measure the oxygen transport resistance in catalyst layers is proposed and realized for the first time in this study. The measuring approach involves a dual-layer catalyst layer design, which consists of a dummy catalyst layer and a practical catalyst layer, followed by changing the thickness of dummy layer to respectively quantify the local and bulk resistances via limiting current measurements combined with linear extrapolation. The experimental results clearly reveal that the local resistance dominates the total resistance in the catalyst layer.