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The metal sulfide-carbon nanocomposite is a new class of anode material for sodium ion batteries, but its development is restricted by its relative poor rate ability and cyclic stability. Herein, we report the use of double-helix structure of carrageenan-metal hydrogels for the synthesis of 3D metal sulfide (M S ) nanostructure/carbon aerogels (CAs) for high-performance sodium-ion storage. The method is unique, and can be used to make multiple M S /CAs (such as FeS/CA, Co S /CA, Ni S /CA, CuS/CA, ZnS/CA, and CdS/CA) with ultra-small nanoparticles and hierarchical porous structure by pyrolyzing the carrageenan-metal hydrogels. The as-prepared FeS/CA exhibits a high reversible capacity and excellent cycling stability (280 mA h at 0.5 A g over 200 cycles) and rate performance (222 mA h at 5 A g ) when used as the anode material for sodium-ion batteries. The work shows the value of biomass-derived metal sulfide-carbon heterostuctures in sodium-ion storage.

Novel single-crystalline-like CeO2 hollow nanocubes were synthesized through a solvothermal method using peroxyacetic acid (PAA) as the oxidant in the absence of any templates. The structure and morphology of CeO2 hollow nanocubes were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The hollow nanocubes have an average edge length of 120 nm and shell thickness of 30 nm. TEM analyses demonstrate the formation of CeO2 hollow nanocubes is ascribed to the combination of oriented attachment and Ostwald ripening. At the beginning, a well-defined cube-like geometrical structure is formed through oriented attachment of small nanocrystallites. Then, solid evacuation in the central part via Ostwald ripening leads to single-crystalline-like hollow nanocubes. It was found that both peroxide (CH3COOOH or H2O2) and solution acidity are critical factors in determining the final morphology of the products. Compared to bulky CeO2 powders, the prepared CeO2 hollow nanocubes exhibited a higher catalytic activity toward CO oxidation.

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Developing a composite electrode composed of a carbon-based material and a transition metal oxide is an effective way to address the problems such as poor conductivity and low porosity created by transitional metal oxide electrodes for supercapacitors. In this work, the activated carbon (AC) prepared from enteromorpha prolifera (ACEP) with typical hierarchically porous structure, was used as a substrate to grow MnO 2 nanostructures via wet chemical reaction process. The morphology and crystalline phase of the MnO 2 could be controlled by facilely adjusting reaction time. For instance, δ-MnO 2 nanosheets were anchored on the ACEP in the initial stage (1−6 h), but α-MnO 2 nanowires were obtained with the extension of reaction time (7− 12 h). The electrode prepared from ACEP@δ-MnO 2 nanosheets displays high specific capacitance (345.1 F g −1 at 0.5 A g −1 ) and excellent cycle stability (i.e., a capacitance retention of 92.8% after 5000 cycles). Moreover, an asymmetric supercapacitor was assembled by using as-prepared ACEP@δ-MnO 2 composite as positive electrode and AC as negative electrode. The assembled AC//δ-ACEP@MnO 2 supercapacitor is shown to work in a wide voltage range of 0−2.0 V and delivered a high energy density of 31.0 Wh kg −1 at a power density of 500.0 W kg −1 .