De veloping transition metal oxides/carbon substrate hybrids as highly promising non-precious metal oxygen reduction reaction(ORR) electrocatalysts is crucial to replace the scarce platinum and solve the world-wide energy predicament. In this work, γ-Fe2O3/N-carbon nanotubes(N-CNTs) and α-Fe2O3/N-CNTs nanocatalysts were successfully synthesized by simultaneous formation of crystal configuration of Fe2O3 and the doping of nitrogen on CNTs. α-Fe2O3/N-CNTs catalysts exhibited superior ORR electrocatalytic activity with lower onset and peak potential of-0.21 and-0.27 V, and possessed a more efficient four-electron-dominant ORR process compared with γ-Fe2O3/N-CNTs, N-CNTs and CNTs. The crystal distortions on octahedral α-Fe2O3 held great potential for displacement of either iron or other ions, serving as the active sites and contributing to its better ORR catalytic ability than the vacancies integrated in γ-Fe2O3/N-CNTs. Both the two nanocatalysts possessed superior methanol tolerance and long-term stabili ty of ORR compared with Pt/C, indicating great potential for their practical utilization in fuel cells.
Optical properties of metallic edge-like structures known as knife-edges are a topic of interest and possess potential applications in enhanced Raman scattering, optical trapping, etc. In this work, we investigate the near-field optical polar- ization response at the edge of a triangular gold nanosheet, which is synthesized by a wet chemical method. A homemade scanning near-field optical microscope （SNOM） in collection mode is adopted, which is able to accurately locate its probe at the edge during experiments. An uncoated straight fiber probe is used in the SNOM, because it s611 preserves the prop- erty of light polarization though it has the depolarization to some extent. By comparing near-field intensities at the edge and glass substrate, detected in different polarization directions of incident light, the edge-induced depolarization is found, which is supported by the finite differential time domain （FDTD） simulated results. The depolarized phenomenon in the near-field is similar to that in the far-field.
SnO2 hollow nanospheres were successfully synthesized via a facile one-step solvothermal method.Characterizations show that the as-prepared SnO2 spheres are of hollow structure with a diameter at around 50 nm,and especially,the shell of the spheres is assembled by single layer SnO2 nanocrystals.The surface area of the material reaches up to 202.5 m^2/g.As an anode material for Li ion batteries,the sample exhibited improved electrochemical performance compared with commercial SnO2 particles.After cycled at high current rate of 0.5 C,1 C and 0.5 C for 20 cycles,respectively,the electrode can maintain a capacity of 509 mAh/g.The suitable shell thickness/diameter ratio endows the good structural stability of the material during cycling,which promises the excellent cycling performance of the electrode.The large surface area and the ultra thin shell ensure the high rate performance of the material.
Microbial fuel cells(MFCs) are environmentally friendly technology capable of converting chemical energy stored in wastewaters directly into electrical energy by using microorganisms as biocatalysts. However, the overall low power density of the MFC and the high cost of its components are two major barriers for its commercialization. Among all the factors, the electrodes(cathode and anode) materials play the significant role in affecting the performance of MFCs. Recently, the performance of MFCs has been improved by using graphene-based electrodes that are more conductive and mechanically stable with larger surface area and higher electrocatalytic activity compared to the conventional carbon materials. This paper provides an overview of recent research progress in graphene-based materials as electrodes for MFCs, which will be the promising candidates for developing MFCs and other bioelectrochemical systems to achieve sustainable water/wastewater treatment and bioenergy production.
