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Design and synthesis of platinum catalysts within atomic level are of great significance for the practical application of fuel cells. We found that the ultrathin Co(OH)2 nanoparticles can be converted into Co3O4–Co core-shell nanostructures through a thermal annealing process in reducing atmosphere, which are uniformly distributed on the surface of 3D graphene (3DG). The Co3O4–Co core-shell nanoparticles have been successfully transformed into Co3O4–Pt core-shell nanoparticles via a controlled replacement reaction. The Co3O4–Pt @3DG contains only a few atomic layers of Pt shell, and presents a high Pt utilization nanostructure. Besides, the 3D graphene serves as a catalysts carrier with open structure, and offers a three-dimensional molecular accessibility and conducive to mass transfer. Significantly, the optimized mass activity and specific activity of 1.018 A/mgPt and 2.17 mA/cm2 have been achieved on Co3O4–Pt @3DG at 0.9 V vs RHE, which are 7.6- and 8.1- times higher than those of Pt/C (0.134 A/mgPt and 0.266 mA/cm2), respectively. The high activity is mainly attributed to the ultrathin core-shell structure with an ultrahigh Pt utilization, and the interaction between the near-surface Co3O4 and the surface Pt shell with a tensile strain to surface Pt shell, and the electrons transfer from Co to Pt.

A Au-doped SrTiO3 perovskite oxide catalyst (Sr0.995Au0.005TiO3−δ) has been designed and synthesized based on thermodynamic analysis and density functional theory calculations. During reduction, Au nanoparticles with an average diameter of 2 nm are in situ exsolved and evenly distributed on the surface of a SrTiO3 substrate. The as-prepared catalyst shows a high conversion of 95.0% and a high selectivity of 96.3% towards styrene epoxidation in CH3CN using H2O2 as the oxidant, and the conversion maintained at 78.2% after five cycles. Noteworthily, such performances surpass those of ex situ deposited Au nanoparticles on SrTiO3 with the same loading (88.5% initial conversion and 90.1% initial selectivity; 48.1% conversion after five cycles). The enhancement is attributed to the smaller particle size and stronger particle–substrate interaction, as revealed by XPS and TEM characterization. Mechanistic investigation confirms the strong support effect in the in situ exsolution system, where charge is transferred from SrTiO3 to Au, improving the reactivity and selectivity. The results demonstrate the unique advantages of the in situ exsolution approach, which may further be applied to develop heterogeneous catalysts with stable nanoparticles.

Atomically dispersed Fe–N–C catalysts with additional Fe-containing nanoparticles including metal, carbides or oxides have shown great potentials towards oxygen reduction reaction (ORR) catalysis. However, the formation of these synergistically active nanoparticles and the effect of the porous carbon structures remain unclear. In this work, a novel single-atom-involved electrochemical catalyst, i.e., Fe3O4 nanoparticles encapsulated in atomically dispersed Fe–N–C (Fe3O4@FeNC) was reported. The optimized Fe3O4@FeNC exhibits excellent ORR activity with a half-wave potential of 0.890 V and a Tafel slope of 58.8 mV dec−1, comparable with recently reported ORR catalysts and superior to these of commercial Pt/C. More importantly, the porous architectures not only affect the mass transfer and active sites, but casts huge influence on the nucleation of Fe3O4 nanoparticles, the graphitization degree of the carbon support, the chemical environments of the elements, and the ORR catalytic pathways. Density functional theory calculations show stronger O2 adsorption on Fe–N–C when supported on Fe3O4 moieties, which may increase the reactant concentration for ORR and promote the overall activity. These findings will provide important references for the future understanding and design of single-atom-involved catalysts with enhanced electrochemical properties.

We investigate the colored noise induced resonance at the 1/3 subharmonic frequency in the overdamped and the underdamped bistable systems by numerical simulations. We find that the resonance at the 1/3 subharmonic frequency may be stronger than the traditional stochastic resonance that occurring at the excitation frequency in some cases. Moreover, we study the effects of the correlation time of the colored noises on the response in detail. If the colored noise is generated by the Ornstein–Uhlenbeck process, there are two major results discovered. Firstly, the critical noise intensity which induces the strongest resonance will increase with the increase of the correlation time. Secondly, when the noise intensity is large enough, the response amplitude at the considered frequency will also increase with the increase of the correlation time. If the colored noise is generated by the power-limited process, the corresponding results are contrary to those in the system under the colored noise excitation that is generated by the Ornstein-Uhlenbeck process. The results in this paper indicate that the type of the colored noise has important effects on the responses of the system.

Lithium-sulfur batteries have great potential as the next-generation clean energy storage systems due to their remarkable high-energy density and electrochemical capacity. Additionally, sulfur is used as a cathode material because of its characteristics of a low cost, environmental friendliness, and abundant nature. However, the polysulfide shuttle effect decreases the electrochemical performance of lithium-sulfur batteries. Here, a rational membrane/electrode design has been applied to lithium-sulfur batteries. A three-dimensional hierarchical nanoporous carbon material derived from cationic resins in a cost-effective process was synthesized at a high temperature and utilized as an intermediate layer to improve the rate capability and cycle stability of lithium-sulfur batteries. Furthermore, stereotaxically -constructed multiporous graphene with a high conductivity (1.6 × 103 S m−1), porosity and large specific surface area (824 m2 g−1) has been applied in the cathode to increase the conductivity of sulfur, improve the transport of lithium-ions and increase the contact with the electrolyte. In particular, stereotaxically-constructed multiporous graphene was used as the sulfur carrier (sulfur loading 70 wt %). The electrochemical results revealed an initial discharge capacity of the hierarchical nanoporous carbon material intermediate layer-coated membrane of 1008 mAh g−1 at 0.5C, and the reversible capacity was 532 mAh g−1 at 1C after 300 cycles. Based on the experimental evidence and analyses, we concluded that the enhanced performance is due to the confinement of lithium polysulfides by the micropores and mesoporous structure of the hierarchical porous carbon material and the increased transportation of lithium ions and the improved wettability of membrane by electrolyte.

Controllable synthesis of Pt-based materials at the nanoscale can efficiently tailor their electrocatalytic performance, enabling enhancement in both activity and durability. Herein, we report the synthesis of ultrathin PtCo nanorod assemblies (NRAs) terminated with high index facets through a grain-boundary corrosion approach. Atomic insight reveals that grain boundaries and other defects are formed in PtCo nanowire assemblies (NWAs) during the hydrothermal reaction. With a further increase in reaction time, selective dissolution at these sites generated PtCo NRAs composed of shorter nanorod assemblies with larger surface areas and high index facets termination. The carbon-supported catalyst of PtCo NRAs exhibits high mass activity of 0.914 A/mgPt at 0.9 V vs RHE for ORR, 2.4 times higher than those of the smooth PtCo NWAs (0.377 A/mgPt), 5.7 times higher than those of the commercial Pt/C (0.161 A/mgPt). Most significantly, the PtCo NRAs show high stability with about 25.6% loss of mass activity after 10,000 cycles, while only 22.3% loss of mass activity from 10,000 cycles to 50,000 cycles of accelerated durability test. The high durability is mainly attributed to the jagged surface resulted from the surface reconstruction of PtCo NRAs during the electrochemical process. This self-optimization phenomenon may lead to a new effective long-life electrocatalyst.

Knowledge of the decomposition process of the microstructure during the precipitation reaction is a requisite step in many cases for exploiting their unique properties. While the earlier work demonstrated that the formation of one-dimensional (1D) Guinier–Preston–Bagaryatsky (GPB) zones is critical for the initial- and peak-hardening of the Al-Cu-Mg alloys, the essential questions remain: what are the basic structural features and the precursors of GPB zones, and how do these precursors transform to the GPB zones? Here we employ atomic-resolution scanning transmission electron microscopy (STEM) and first-principles calculations to address these problems. In mostly GPB zones-strengthened alloys, we identify two atomistic building blocks of 1D GPB zones, which merge together maintaining a crystallographic orientation of [014]Al. These two particular structures are formed from initial copper double (Cu2) column-skeleton, associated with charge transfer between adjacent Cu and Mg as well as Cu and Al inside the structural units and at the interface between two building block units. Existence of initial and transitional phases is further suggested by ab initio calculations based on STEM observations and image simulations. These results demonstrate the atomistic mechanisms governing Cu2 columns-guided nucleation, growth, maturation and coarsening of the atomistic building blocks of GPB zones. Keywords: Al alloys, Precipitation, Atomic structure, Phase transformations, Transmission electron microscopy

Foam fractionation is a cost-effective method to separate laccase from its fermentation broth. However, the enzyme readily suffered a substantial activity loss in the separation process. To reduce the activity loss, we firstly analyzed the structure-function relationship of laccase to explain how laccase was denatured in the foam fractionation of laccase from fermentation broth of Trametes hirsuta 18 using cetyltrimethyl ammonium bromide (CTAB) as a collector. The results demonstrate that via electrostatic force, CTAB interacted with laccase molecules to cause their structural unfolding, so CTAB resulted in the denaturation of laccase. Increasing the molar ratio of CTAB vs laccase at the gas-liquid interface over that in the feed solution, foaming enhanced the CTAB-induced denaturation. On this ground, we attempted to use β-cyclodextrin and ultrasound to assist the refolding of laccase denatured jointly by CTAB and foaming in the foamate. Ultrasound effectively assisted the renaturation of denatured laccase after it was separated from CTAB by β-cyclodextrin in 40 min at 20 °C or lower. Furthermore, their renaturation performances highly depended on pH, volumetric airflow rate, CTAB concentration and molar ratio of β-cyclodextrin vs CTAB in the foamate. At pH 6.0, volumetric airflow rate 60 mL/min, CTAB concentration 0.4 g/L and molar ratio of β-cyclodextrin vs CTAB in the foamate of 1.6:1, the enrichment ratio and recovery yield of laccase activity and purification fold of laccase reached 73.4%, 11.9 and 3.5, respectively. They were 230% higher than those without β-cyclodextrin and ultrasound. Therefore, ultrasound and β-cyclodextrin effectively enhanced the CTAB-assisted foam fractionation of laccase from the fermentation broth of T. hirsuta 18. In addition, a SDS-PAGE analysis determined that laccase of 55 kDa in molecular weight was highly enriched by the foam fractionation.