No abstract

No abstract

In this study, we demonstrate that lignin, which constitutes 30-40 wt % of the terrestrial lignocellulosic biomass and is produced from second generation biofuel plants as a cheap byproduct, is an excellent precursor material for sodium-ion battery (NIB) anodes. Because it is rich in aromatic monomers that are highly cross-linked by ether and condensed bonds, the lignin material carbonized at 1300 °C (C-1300) in this study has small graphitic domains with well-developed graphene layers, a large interlayer spacing (0.403 nm), and a high micropore surface area (207.5 m g). When tested as an anode in an NIB, C-1300 exhibited an initial Coulombic efficiency of 68% and a high reversible capacity of 297 mA h g at 50 mA g after 50 cycles. The high capacity of 199 mA h g at less than 0.1 V with a flat voltage profile and an extremely low charge-discharge voltage hysteresis (<0.03 V) make C-1300 a promising energy-dense electrode material. In addition, C-1300 exhibited an excellent high-rate performance of 116 mA h g at 2.5 A g and showed stable cycling retention (0.2% capacity decay per cycle after 500 cycles). By comparing the properties of the lignin-derived carbon with oak sawdust-derived and sugar-derived carbons and a low-temperature carbonized sample (900 °C), the reasons for the excellent performance of C-1300 were determined to result from facilitated Na-ion transport to the graphitic layer and the microporous regions that penetrate through the less defective and enlarged interlayer spacings.

No abstract

No abstract

Hydrogen-enriched reduced graphene oxide (RGO) was achieved using double-oxidized graphene oxide (GO2) as an anode in high-performance lithium batteries is reported. GO2 exhibited a much lower carbon-to-oxygen ratio, lower crystallinity, higher Brunauer−Emmett−Teller surface area, higher pore volume, and higher porosity as compared to graphene oxides produced using the typical modified Hummer's method (GO1). The two forms of GO were reduced using two different reduction methods: supercritical isopropanol (scIPA) and heat treatment. The four types of RGOs synthesized using GO1/GO2 and scIPA/heat treatment exhibited significantly different chemical, morphological, and textural properties. The galvanostatic charge−discharge properties were highly dependent on the physicochemical properties of the RGOs. The scIPA-reduced GO2 exhibited superior electrochemical performance as compared to the thermally reduced GO1/GO2 and scIPA-reduced GO1. Highly reversible capacity (1331 mAh g −1 at 50 mA g −1 after 100 cycles), excellent rate-performance (328 mAh g −1 at 5 A g −1 ), and good cycling stability up to 1000 cycles even at a current density of 10 A g −1 were observed with the scIPA-reduced GO2 electrode. The characterization results suggested that a large amount of hydrogen-terminated groups, numerous defect sites, and large interlayer spacing have beneficial effects on the electrochemical performance of scIPA-reduced GO2.

Carbon-supported Mo 2 C nanoparticles were synthesized and used as catalysts for the deoxygenation of oleic acid and soybean oil to produce diesel-range hydrocarbons. Various carbon materials, such as reduced graphene oxide (RGO), glassy spherical carbon (SC), activated carbon (AC), and mesoporous carbon (MC), were used as supports to determine the effects of RGO in the deoxygenation reactions. The effects of the flow rate, Mo content of the catalyst, and the structure of the carbon support on the conversion and product selectivity were investigated. The morphology analysis revealed that Mo 2 C nanoparticles were well-dispersed onto the RGO (Mo 2 C/RGO). Under moderate reaction condition (T = 350 °C, P = 5.0 MPa, H 2 /oil ratio = 4.5, LHSV = 2 h −1 ), oleic acid was efficiently deoxygenated using the Mo 2 C/RGO catalyst, which produced hydrocarbons with ≥85% yield and ≥90% hydrocarbon selectivity. This value was much higher than those obtained using the Mo 2 C/SC, Mo 2 C/AC, and Mo 2 C/MC catalysts (yields = 18.5−50.3%) under identical conditions. The higher catalytic activity of the RGO-supported catalyst originated from its large pore size, which facilitated transport of the reactants, and uniform deposition of the Mo 2 C nanoparticles on the RGO surface. Even over a short contact time (LHSV = 8 h −1 ) and using natural triglyceride as a reactant, the Mo 2 C/RGO catalyst exhibited ≥40% yield of hydrocarbons, whereas a commercial CoMoS x /Al 2 O 3 catalyst produced ≤10% yield under identical conditions. The Mo 2 C/RGO catalyst was highly selective toward C−O bond scission in the hydroxyl group, which produced water and hydrocarbons without truncating the carbon skeleton of the starting material. Mo 2 C/RGO exhibited a prolonged catalyst lifetime for the deoxygenation of soybean oil (13% decrease in conversion after 6 h), compared with the commercial CoMoS/Al 2 O 3 catalyst (42% decrease).

No abstract