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An ultrathin nickel hydroxide layer electrodeposited on a carbon-coated three-dimensional porous copper structure (3D-C/Cu) is suggested as an additive and binder-free conductive electrode with short electron path distances, large electrochemical active sites, and improved structural stability, for high performance supercapacitors. The 3D-porous copper structure (3D-Cu) provides high electrical conductivity and facilitates electron transport between the Ni(OH)2 active materials and the current collector of the Ni-plate. A carbon coating was applied to the 3D-Cu to prevent the oxidation of Cu, without degrading the electron transport behavior of the 3D-Cu. The 3D-Ni(OH)2/C/Cu exhibited a high specific capacitance of 1860 F g−1 at 1 A g−1, and good cycling performance, with an 86.5% capacitance retention after 10 000 cycles. When tested in a two-electrode system, an asymmetric supercapacitor exhibited an energy density of 147.9 W h kg−1 and a power density of 37.0 kW kg−1. These results open a new area of ultrahigh-performance supercapacitors, supported by 3D-Cu electrodes. [ABSTRACT FROM AUTHOR]

A microwave-assisted hydrothermal synthesis produces ZnFe2O4 containing Na residue as a precursor to a CO2 hydrogenation catalyst that displays high CO2 conversion and high selectivity to liquid hydrocarbon products in the gasoline and diesel range with high olefin-to-paraffin ratios. Compared to reference catalysts derived from Fe2O3 and a ZnO-Fe2O3 physical mixture, the ZnFe2O4-derived catalyst contains well-dispersed iron particles with Zn serving as a structural promoter. A profound effect of the residual Na as an electronic promoter is also observed, which improves the selectivity for C5+ hydrocarbons and olefins. The ZnFe2O4-derived catalyst exhibits excellent performance in the CO2 Fischer-Tropsch reaction as it forms the active Hägg iron carbide (χ-Fe5C2) phase readily through the in situ carburization of iron. [ABSTRACT FROM AUTHOR]

The rapidly developing electronics industry is producing miniaturized electronic devices with flexible, portable and wearable characteristics, requiring high-performance miniature energy storage devices with flexible and light weight properties. Herein, we have successfully fabricated highly porous, binder free three-dimensional flower-like NiCo2O4/Ni nanostructures on Ni-wire as a fiber electrode for high-performance flexible fiber supercapacitors. Such a unique structure exhibited remarkable electrochemical performance with high capacitance (29.7 F cm−3 at 2.5 mA), excellent rate capability (97.5% retention at 20 mA), and super cycling stability (80% retention, even after 5000 cycles). The remarkable electrochemical performance is attributed to the large active area in the 3D porous architecture and direct contact between the active materials and 3D-Ni current collectors, which facilitate easy ionic/electronic transport. The symmetric fiber supercapacitor showed a gravimetric energy density of 2.18 W h kg−1 (0.21 mW h cm−3) and a power density of 21.6 W kg−1 (2.1 mW cm−3) with good flexibility and cycling performance, signifying potential applications in high-performance flexible energy storage devices. Further, performance in a self-powered system was demonstrated by charging these wire type NiCo2O4/Ni supercapacitors by serially wound DSSCs to drive commercial LEDs. These results suggest that the fabricated device has excellent potential as a power source for flexible, portable and wearable applications as well as self-powered systems. [ABSTRACT FROM AUTHOR]

An efficient reduction method to obtain high-quality graphene sheets from mass-producible graphene oxide is highly desirable for practical applications. Here, we report an in situ deoxidation and graphitization mechanism for graphene oxide that allows for high-quality reduced graphene oxide sheets under the low temperature condition (<300 °C) by utilizing a well-known Fischer-Tropsch reaction catalyst (CuFeO 2 ). By applying modified FTR conditions, where graphene oxide was reduced on the catalyst surface under the hydrogen-poor condition, deoxidation with much suppressed carbon loss was possible, resulting in high-quality graphene sheets. Our experimental data and density functional theory calculations proved that reduction which occurred on the CuFeO 2 surface preferentially removed adsorbed oxygen atoms in graphene oxide sheets, leaving dissociated carbon structures to be restored to a near-perfect few-layer graphene sheet. TGA-mass data revealed that GO with catalysts released 92.8% less carbon-containing gases than GO without catalysts during the reduction process, which suggests that this process suppressed carbon loss in graphene oxide sheets, leading to near-perfect graphene. The amount of oxygen related to the epoxide group in the basal plane of GO significantly decreased to near zero (from 43.84 to 0.48 at. %) in catalyst-assisted reduced graphene oxide (CA-rGO). The average domain size and the density of defects of CA-rGO were 4 times larger and 0.1 times lower than those for thermally reduced graphene oxide (TrGO), respectively. As a result, CA-rGO had a 246 and 8 times lower electrical resistance than TrGO and CVD-graphene. With these performances, CA-rGO coated paper connected to a coin-cell battery successfully lit an LED bulb, and CA-rGO itself acted as an efficient catalyst for both the hydrogen evolution reaction and the oxygen evolution reaction.