A facile and effective self-crosslink assisted strategy is developed to fabricate 3D porous branch-like Fe3O4/C hybrids as high-performance anode materials for lithium ion batteries (LIBs) and sodium ion batteries (NIBs). Trivalent iron ions (Fe3+) are used to directly crosslink with biopolymer alginate to form nanoscale branch-like Fe-alginate hybrid nanostructures, which are converted to porous Fe3O4/C hybrids via a simple carbonization process. The resulting hybrids feature ultrafine active nanoparticles (∼5 nm), wrapping by thin graphitic layers, hierarchically nanoscale porous channels, and interconnected robust graphitic frameworks. Applying these in the anodes of LIBs, these structural features enable the hybrids to deliver high capacities of 974 and 570 mA h g−1 at 0.1 and 2 A g−1, respectively, and excellent cyclic stability with capacity retention of 98% after 200 cycles at 0.1 A g−1. In NIBs, reasonable capacities of 339 and 138 mA h g−1 are obtained at 0.05 and 5 A g−1, respectively. The high performance demonstrates the promising potential of the hybrids in next generation anodes for LIBs and NIBs.

A hybrid electrode material with ultrafine Co3O4 nanoparticles embedded throughout a hierarchically nanoporous graphitic carbon matrix has been obtained via a facile self-cross-linking route. Sodium alginate, a biopolymer with an ability of cross-linking with multivalent cobalt cations to form ordered microcrystalline zones, is used as a carbon source to produce nanoporous carbon frameworks of the hybrids. Ultrafine Co3O4 nanoparticles with tunable particle size (3–30 nm) are in situ grown within the nanoporous graphitic carbon frameworks by a simple carbonization of Co-cross-linked alginate. The obtained hybrid electrodes exhibit high specific capacitance of 645, 548, 486, and 347 F/g at scan rates of 5, 10, 20, and 50 mV/s, respectively, and excellent cycle performance with only 1% fading in capacitance after 10 000 cycles at a high current density of 20 A/g. Such excellent capacitive performance is ascribed to the collaborative contributions of well-dispersed ultrafine Co3O4 nanoparticles and conductive nanoporous carbon frameworks.

MnO/C hybrid with ultra-small MnO nanoparticles (5.2 nm) embedded in porous carbon is fabricated and applied as the anode material for lithium ion batteries. The MnO/C hybrid electrode exhibits excellent specific capacity of 820 mAh g−1 at a current density of 100 mA g−1 and also outstanding rate performance with specific capacity of 483 mAh g−1 at a current density of 5000 mA g−1. After cycling for 1000 times at 1000 mA g−1, the specific capacity increases to 1625 mAh g−1. The TEM photos show that the particles are broken into 2 nm particles after cycling. We also apply XAFS to detect the final state of the Mn in the hybrid electrodes and find that smaller MnO particles are oxidized to a mixture of Mn2O3 and MnO2.

This paper reports a versatile method to fabricate robust carbon/metal hybrids with ultrasmall particle and highly developed porous structure through a scalable and facile way. Alginate is used as the precursor for it could perform cross-linking reaction with different polyvalent metal ions to form gels. After simple freeze-drying and carbonization of the alginate-derived gels, we obtained the carbon/metal hybrids with fine nanostructure. Eleven kinds of metal ions were introduced to form gels and five kinds of the gels were carbonized to produce the carbon/metal hybrids. By adjusting the reaction condition, we could tune the size of the nanoparticles in the obtained hybrids. The obtained SnO2/C hybrid shows outstanding specific capacity, rate performance, and long cycle life when it is used as the anode materials of lithium ion batteries. The ultrasmall active nanoparticles were uniformly dispersed within an interconnected pore framework. It ensured a short diffusion and transportation distance of electrolyte ions to the surfaces of active nanoparticles. In addition, the robust carbon framework comprises of quasigraphitic carbon layers. It contributed to the high rate performance by providing excellent conductive pathways for electrons within the electrodes. This work provides a general method for fabrication of carbon/metal (oxide) hybrids with fine nanostructure for application in energy storage.Keywords: cross-linking; energy storage; long cycle life; nanohybrid; ultrasmall nanoparticles;

A novel approach is reported to synthesize carbon foams with designable hierarchical porous structures for energy storage. The obtained carbons have an interconnected macroporous channel structure with narrow mesopores (3–5 nm in diameter) embedded throughout the carbon walls, providing low-resistance pathways for ion transportation to internal carbon surfaces. The obtained carbon electrodes can offer a capacitance up to 270 F g−1 at a current density of 0.1 A g−1 and especially an excellent high-rate performance with 222 F g−1 as the current density increases to 10 A g−1. Additionally, the electrodes exhibit a long cycling life at a high current density up to 10 A g−1.

Here we report a method to fabricate porous carbon with small mesopores around 2–4 nm by simple activation of charcoals derived from carbonization of seaweed consisting of microcrystalline domains formed by the “egg-box” model. The existence of mesopores in charcoals leads to a high specific surface area up to 3270 m2 g–1, with 95% surface area provided by small mesopores. This special pore structure shows high adaptability when used as electrode materials for an electric double layer capacitor, especially at high charge–discharge rate. The gravimetric capacitance values of the porous carbon are 425 and 210 F g–1 and volumetric capacitance values are 242 and 120 F cm–3 in 1 M H2SO4 and 1 M TEA BF4/AN, respectively. The capacitances even remain at 280 F g–1 (160 F cm–3) at 100 A g–1 and 156 F g–1 (90 F cm–3) at 50 A g–1 in the aqueous and organic electrolytes, demonstrating excellent high-rate capacitive performance.Keywords: egg-box; high-rate performance; porous carbon; small mesopores;

Novel carbonaceous hybrid materials are fabricated through the in situ growth of open-tipped mesoporous carbon nanotubes (CNTs) on low-cost activated carbon (AC) substrates with cobalt (Co) nanoparticles as the growing seeds via a chemical vapor deposition process. The CNTs are strongly bonded with the surface of the AC supports using the fine Co nanoparticles (<10 nm) as the joints. The unique three-dimensional hybrid architectures enable the resultant materials to exhibit a considerable specific capacitance of up to 440 F g−1 at 1 A g−1 as well as an excellent rate performance (97% retention ratio at 5 A g−1 compared to 1 A g−1). In addition, the hybrid materials have an impressive cycling stability with an initial capacitance retention of 98.4% after 3000 cycles at 5 A g−1. Besides the high specific surface area, such an excellent capacitive performance is mainly attributed to the combination of (i) the well-dispersed open-tipped CNTs (5–12 nm) that could provide more effective ion channels, (ii) the interconnected CNT conducting networks facilitating the transport of electrons, and (iii) superfine Co nanoparticles (3–9 nm) offering pseudocapacitance, indicating the synergistic effect of both the electrical double layer capacitance and pseudocapacitive reactions.

Three dimensional hybrid carbon materials have been prepared using different biomass-derived porous carbons as catalyst supports for growing multi-walled carbon nanotubes (MWCNTs) via a chemical vapor deposition method. The nickel catalyst-loaded supports before and after growing MWCNTs were characterized by scanning and transmission electron microscopy, Fourier transform infrared spectroscopy spectra, and mercury porosimetry. The results show that the grown MWCNTs microstructures are closely related to the porous structures and surface conditions of the carbon supports. By using bamboo as template, a porous carbon support with a large total pore volume, appropriate pore size, and abundant favorable surface functional groups is obtained, which is found to be an ideal support for growing the MWCNTs. Investigation of growth mechanism demonstrated that the combination of appropriate porous structures and surface conditions plays an essential role in catalyst distribution and MWCNTs growth.

Ultrathin graphitic nanostructures are grown inside solid activated carbon particles by catalytic graphitization method with the aid of Ni. The graphitic nanostructures consist of 3–8 graphitic layers, forming a highly conductive network on the surface of disordered carbon frameworks. Owing to the ultrathin characteristic of the produced graphitic nanostructures, the resulted porous graphitic carbons show a high specific surface area up to 1622 m2/g. A detailed investigation reveals that the features of the growing graphitic nanostructures are strongly associated with the catalytic temperature as well as the state of Ni nanoparticles. Some well-dispersed fine Ni particles with diameter below 15 nm are found to be the key to form the ultrathin graphitic nanostructures at appropriate catalytic temperature. Also, a novel mechanism is proposed for the catalytic formation of the ultrathin graphitic nanostructures. As the electrode material of electrochemical capacitors, the porous graphitic carbon exhibits much higher high-rate capacitive performance compared to its activated carbon precursor.

Hierarchical porous carbon fabricated from biomass provides an effective support for catalysts. Nitrogen doped TiO2 particles (50 nm in size) synthesized from titanium tetraethoxide were loaded uniformly on the porous carbons carbonized from Zizania latifolia leaves by a sol–gel method. X-Ray diffraction and Auger Electronic Spectrometer analysis indicated that nitrogen atoms were doped into anatase TiO2 lattices. The bandgap of the nitrogen doped TiO2 derived from the light absorption spectrum was about 3.05 eV. The nitrogen doped TiO2 on the hierarchical porous carbon hybrid photocatalysts showed a high degradation rate of 2-propanol in water with visible light irradiation.

A novel approach is reported to synthesize carbon foams with designable hierarchical porous structures for energy storage. The obtained carbons have an interconnected macroporous channel structure with narrow mesopores (3–5 nm in diameter) embedded throughout the carbon walls, providing low-resistance pathways for ion transportation to internal carbon surfaces. The obtained carbon electrodes can offer a capacitance up to 270 F g−1 at a current density of 0.1 A g−1 and especially an excellent high-rate performance with 222 F g−1 as the current density increases to 10 A g−1. Additionally, the electrodes exhibit a long cycling life at a high current density up to 10 A g−1.

Novel carbonaceous hybrid materials are fabricated through the in situ growth of open-tipped mesoporous carbon nanotubes (CNTs) on low-cost activated carbon (AC) substrates with cobalt (Co) nanoparticles as the growing seeds via a chemical vapor deposition process. The CNTs are strongly bonded with the surface of the AC supports using the fine Co nanoparticles (<10 nm) as the joints. The unique three-dimensional hybrid architectures enable the resultant materials to exhibit a considerable specific capacitance of up to 440 F g−1 at 1 A g−1 as well as an excellent rate performance (97% retention ratio at 5 A g−1 compared to 1 A g−1). In addition, the hybrid materials have an impressive cycling stability with an initial capacitance retention of 98.4% after 3000 cycles at 5 A g−1. Besides the high specific surface area, such an excellent capacitive performance is mainly attributed to the combination of (i) the well-dispersed open-tipped CNTs (5–12 nm) that could provide more effective ion channels, (ii) the interconnected CNT conducting networks facilitating the transport of electrons, and (iii) superfine Co nanoparticles (3–9 nm) offering pseudocapacitance, indicating the synergistic effect of both the electrical double layer capacitance and pseudocapacitive reactions.