Huijun Yan

Graphene homogeneously anchored with Ni(OH)2 nanoparticles as advanced supercapacitor electrodes

A green and facile approach was demonstrated to prepare graphene nanosheet/Ni(OH)2 (GNS/Ni(OH)2) composites for supercapacitor materials. GNSs as a support material can offer moderate active sites for the nucleation of Ni(OH)2, as well as an excellent electron transfer path. Then, ultrafine Ni(OH)2 nanoparticles were homogeneously anchored onto the surface of GNSs as spacers to ensure the high electrochemical utilization of the graphene layers and supply the open nano-channels for shortening the ion diffusion pathway. The results show that the GNS/Ni(OH)2 composites exhibit a superior specific capacitance of 1985.1 F g−1 and excellent cycle life with a loss of specific capacitance of only 6.5% after 500 cycles. The improved high electrochemical performance is attributed to the increased electrode conductivity in the presence of the graphene network and the increased effective interfacial area caused by the well-dispersed Ni(OH)2 on the GNSs.

Optimizing the charge transfer process by designing Co3O4@PPy@MnO2 ternary core–shell composite

In this paper, the incorporation of a highly conductive material (polypyrrole) into a binary metal-oxide core–shell structured composite is adopted to optimize the charge transfer process to further improve electrochemical performance. Because of enhanced electron transfer capability, charge transfer resistances of the ternary core–shell structured composites are reduced and the electrochemical performances are improved. For example, the Co3O4@PPy@MnO2 ternary core–shell heterostructured composite exhibits high specific capacitance and excellent rate capability (53% of capacity retention rate at 40 A g−1 compared with 782 F g−1 at 0.5 A g−1). The composite shows good cycling stability with 97.6% capacity retention over 2000 cycles at 5 A g−1. These results demonstrate the potential of core–shell composites to further improve the performance in supercapacitor electrodes.

Fabrication of urchin-like NiCo2(CO3)1.5(OH)3@NiCo2S4 on Ni foam by an ion-exchange route and application to asymmetrical supercapacitors

Pseudocapacitor electrode materials, such as transition metal oxides/sulfides, have been extensively investigated and shown to have fast energy storage properties, but their low rate performance and poor cycle stability are serious problems in practical applications. We present here a design for the architecture of these electrode materials with the aim of improving the rate performance and cycle stability of pseudocapacitors by using an interface ion-exchange method. Precursor materials obtained by a hydrothermal reaction were soaked in aqueous NaHS solution to synthesize the urchin-like core–shell structure of NiCo2(CO3)1.5(OH)3@NiCo2S4. Such core–shell nanostructure electrode materials can make full use of both components with synergistic effects. Excellent results were obtained with a capacitance of 956.4 F g−1 at a current density of 4 A g−1 in the three-electrode system and an actual energy density of 32.3 W h kg−1 and power density of 1835 W kg−1 in the asymmetrical supercapacitor.

High U(VI) adsorption capacity by mesoporous Mg(OH)2 deriving from MgO hydrolysis

Hierarchical mesoporous–macroporous MgO (HMMM) is successfully synthesized by using a facile calcination method. Mesoporous Mg(OH)2 produced from HMMM hydrolysis in uranium solution was used to remove U(VI) from aqueous solutions. TEM confirms that mesoporous Mg(OH)2 partly retains interconnected porous structure of HMMM. Influence of U(VI) concentrations, adsorbent dosage, solution pH, salt concentration, contact time and temperatures on the adsorption properties were studied. The results indicate that mesoporous Mg(OH)2 exhibits excellent adsorption properties, particularly at high uranium concentration. The maximum adsorption capability of U(VI) is 3111 mg g−1 and the highest uranium removal efficiency is 99% at an initial uranium concentration of 500 mg L−1. We also demonstrate that HMMM hydrolysis process greatly improves adsorption capability of U(VI). The isotherm evaluations reveal that the Freundlich model attains a better fit to the experimental equilibrium data than the Langmuir model. The results of adsorption kinetics and adsorption mechanism for U(VI) indicate that chemical adsorption is the rate-limiting step. Furthermore, mesoporous Mg(OH)2 can be regenerated by using 1 M Na2CO3, which is reused with 9.3% loss of activity. Therefore, the mesoporous Mg(OH)2 is a potential absorbent in wastewater treatment because of its high uptake capability of U(VI).

Deft dipping combined with electrochemical reduction to obtain 3D electrochemical reduction graphene oxide and its applications in supercapacitors

In this paper, a combination of deft dipping and simple rapid electrochemical reduction were used to coat electrochemically reduced graphene oxide (ERGO) on Ni foam. After acid etching, a 3D ERGO with sufficient mechanical strength, low density and high electrical conductivity was obtained. As proof, a high mass loading of Co3O4 sheets has been grown on the 3D ERGO. The 3D ERGO/Co3O4 composite electrode exhibits a specific capacitance of 600 F g−1 and a power density of 2.5 kW kg−1.

Preparation of magnetic calcium silicate hydrate for the efficient removal of uranium from aqueous systems

To obtain an adsorbent for uranium with superb adsorption capacity, a rapid adsorption rate and quick magnetic separation, magnetic calcium silicate hydrate (MCSH) is fabricated through in situ growth of calcium silicate hydrate (CSH) onto the surface of the magnetic silica microspheres via a sonochemical method. The chemical components, and structural and morphological properties of MCSH are characterized by FTIR, XRD, TG, VSM, SEM, TEM and N2 adsorption–desorption methods. The results show that MCSH with a mesoporous structure is constructed by an agglomeration of CSH nanosheets. The BET specific surface area and saturation magnetization of MCSH are determined to be 196 m2 g−1 and 15.4 emu g−1, respectively. Based on the synthetic MSCH, adsorption isotherms, thermodynamics and kinetics are investigated. The adsorption mechanism fits the Langmuir isotherm model with a maximum adsorption capacity of 2500 mg g−1 at 298 K. The calculated thermodynamic parameters demonstrate that the adsorption process, which is in accordance with a pseudo-second-order model, is spontaneous and endothermic. MCSH exhibits a quick and highly efficient adsorption behavior, and more than 80% of uranium (1000 mg L−1) is adsorbed in the first 10 min. The superb adsorption capacity and rapid adsorption rate are likely attributed to the ultrahigh specific surface area and facile exchanges of uranium ions and calcium ions of CSH ultrathin nanosheets. These results demonstrate that MSCH is an excellent adsorbent for uranium removal from aqueous systems.