查看更多>>摘要：Here, we report on computational oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) efficiencies of a series of heteroatom-doped fullerene C-70 (X(Cn), with B, N, O or Si as dopant X, replacing five different types of carbon atoms (Cn, n = 1-5) on C-70). It is clarified that the X(Cn) is thermodynamically stable. delta G*OH shows a good linear relationship with delta G(*OOH) and delta G(*O). It is worth noting that the ORR overpotential values of N(C1), N(C2), N(C3) and N(C4) are 0.87 V, 0.75 V, 0.67 V and 0.73 V, respectively, which are all greater than Pt (eta(ORR) = 0.45 V), but it shows that ORR can still be catalyzed. Compared with the pristine C-70, both B and N doping can reduce OER overpotential value and improve OER performance. In particular, N(C4) (eta(OER) = 0.55 V) has the closest overpotential to traditional noble metal OER catalysts such as RuO2 (eta(OER) = 0.42 V), indicating that it can be used as a potential candidate for OER catalysts. According to the volcano plots, the best ORR and OER activities of X(Cn) appear at delta G(*OH) = 0.56 eV and delta G(*O) -delta G(*OH) = 1.78 eV, respectively. This work can provide some clues for the design and discovery of new non-metal carbon-based electrocatalysts.
查看更多>>摘要：A series of nickel cobalt bimetallic sulfide doped graphite carbon (NCBS/C) nanohybrids were fabricated by cross linking reaction, vacuum freeze-drying, heat treatment and hydrothermal method using sodium alginate (SA) as carbon source, nickel nitrate hexahydrate (Ni(NO3)(2).6H(2)O) and cobalt nitrate hexahydrate (Co(NO3)(2).6H(2)O) as transition metal ions source, thiourea as sulfur source. The electrochemical properties of the NCBS/C nano-hybrids as electrode materials could be tuned by adjusting the composition. The results show that the NCBS/C nano-hybrid fabricated at the molar ratio of Ni(NO3)(2).6H(2)O to Co(NO3)(2).6H(2)O of 1:1, and the thiourea amount of 0.1 g had the optimal electrochemical properties, the specific capacity was 742.9C g(-1) at 1 A g(-1), when the current density increased from 0.5 A g(-1) to 5 A g(-1), the specific capacity could remain 98.2%. The asymmetric supercapacitor assembled by the NCBS/C nanohybrid as the positive electrode, activated carbon as the negative electrode delivered energy density of 53.00 Wh kg(-1) at power density of 850 W kg(-1), and still maintained 43.57 Wh kg(-1) at 4.24 kW kg(-1). Moreover, the device had 83.78% capacitance retention after 5000 charge-discharge cycles at 5 A g(-1). The nanohybrids with high electrochemical properties could be attributed that the transition metal ions as cross-linking agents were well dispersed in the SA hydrogels as carbon source, resulting in that the in-situ formed nickel cobalt bimetallic sulfide nanoparticles were uniformly doped in graphite carbon materials. The strategy could be applied to fabricate other transition metals compounds doped carbon materials for the development of other high-performance electrode materials.
查看更多>>摘要：Classical molecular dynamics simulations have been performed to investigate five mechanical properties of defective penta-graphene under uniaxial tension, namely Young's modulus, Poisson's ratio, ultimate tensile stress, ultimate strain, and toughness. The reliable Erhart-Albe formulation of the Tersoff potential has been used in the simulations and monovacancies are the only kind of structural defect studied. The effects of defect density, chirality, and temperature on the mechanical properties are reported and thoroughly discussed. The results show that by incorporating defects up to 20%, Young's modulus is decreased by more than one order of magnitude and the sign of the mean Poisson's ratio changes to positive, which indicates the possibility of tuning this ratio. Furthermore, the anisotropic behavior of the material is not strong in terms of Young's modulus, ultimate stress, and ultimate strain and at higher temperatures, the ultimate stress, ultimate strain, and toughness almost converge for pristine and defective penta-graphene. It can be concluded that PG is an auxetic material while it can be tuned by defect engineering to behave as classic material. It should be noted that the results of current study can be used as benchmark for design and fabrication of novel potential industrial materials with both negative and positive Poisson's ratios.
NSTL
Elsevier