The refractory organic pollutant (phenol) was electro-catalytic-oxidized on the Sb-doped SnO2 anode prepared by coating pyrolysis method. The effect of electrolysis potential on phenol degradation has been studied. It is proved that the degradation rate has a parabola shape relationship with applied electrolysis potential, and 2 V is the most optimistic potential in our research. In situ cyclic voltammogram and Ultraviolet–visible spectrum were carried out to track the process of phenol oxidation and speculate the intermediate reaction process. All the results implied that phenol was oxidized through different pathways under different electrolysis potentials. The phenomena confirm the conclusion that when degradation voltage was 2 V, phenol was directly oxidized rather than through the process of benzoquinone intermediate, which happened under other potentials, and the direct oxidation pathway was more efficient. Based on experimental results and the previous reports by other researchers, reaction pathways proposed in our research are given.
A non-precious metal catalyst (CoMe/C) for oxygen reduction reaction was prepared by a simple procedure using acetylene black, melamine and cobalt chloride as raw materials. The relationship between catalytic activity and C-N structures of CoMe/C was investigated by X-ray photoelectron spectroscopy. Results show that the nitrogen atom exists as Co-N, pyrrolic C-N and pyridinic C-N structures in the CoMe/C catalyst. The Co-N structure has no activity to oxygen reduction reaction. Both pyrrolic and pyridinic C-N structures are the active sites of CoMe/C. The pyrrolic C-N structure is unstable than the pyridinic C-N structure in H2SO4 solution. In heat treating process, the Co(II) ion is reduced to metallic β-cobalt which facilitates the formation of pyrrolic and pyridinic C-N structures to ensure the better activity of CoMe/C catalyst.
In bioelectrochemical systems where the oxidative current is mediated by microorganisms, it remains unexplored as to whether low-potential substrates (e.g. formate) enable the anode to work at lower potentials. Due to implications to relevant engineering and natural systems, this study evaluated such possibility and underlying causes. The investigation compared voltammograms of the model exoelectrogen (to exclude the interfering factors in undefined cultures) Geobacter sulfurreducens grown with acetate and formate. G. sulfurreducens had an EM (half-saturation potential) of −0.138 ± 0.004 V vs. SHE when consuming acetate; an EM of −0.160 ± 0.002 V when utilizing formate. Such variation usually requires alternation in electrode reductase expressed by bacteria, according to the existing Nernst-Monod model with a single species of electron conduit. For both acetate- and formate-grown biofilm, non-catalytic voltammetries found multiple redox couples with distinct formal potentials. No clear evidence could support a hypothesis that the bacteria synthesized any different electron conduits when the substrate was changed. Significant changes in the relative abundance of high-potential and low-potential electrocatalytically active conduits were not observed as well. However, low-potential conduits showed elevated electrocatalytic activities in the formate-grown biofilm, which might induce the shift in apparent EM.
A Ge-bridged methylviologen derivative (GMV2+2I−) was synthesized by dimethylation of dipyridinogermole (DPyG). Viologen GMV2+2I− showed a UV absorption band at 270 nm, similar to DPyG and longer than the corresponding bridge-free methylviologen (MV2+2I−). Electrochemical properties of GMV2+2I− were investigated with respect to cyclic voltammograms, showing highly reversible two step reduction, like MV2+2I−. Interestingly, GMV2+2I− exhibited enhanced electron-affinity with higher 1st reduction potential by approximately 0.08 V than that of MV2+2I−, likely due to the effects Ge-bridge lowering the LUMO energy level. However, the 2nd potential was little affected by the bridge. Clear electrochromic colour changes based on the reversible electrochemical interconversion among GMV2+/GMV+/GMV were observed in acetonitrile. Monomethylated DPyG (GMV′+I−) was also prepared, whose properties are discussed in comparison with those of DPyG and GMV2+2I−.
Degradation mechanism of electrochemical double layer capacitors on high-voltage exposure is examined. Capacitance loss for positive electrodes is significantly accelerated above 4.5 V (vs. Li/Li+) whereas that of negative electrodes occurs on the electrochemical cycles down to 1.2 V. The surface of positive electrodes is covered with decomposition products of propylene carbonate used as electrolyte solution, and therefore high-voltage exposure increases impedance of electrodes. In contrast, the degradation of negative electrodes is triggered by the decomposition reaction of electrolyte salts, resulting in the formation of radical species. It is proposed that the radical species attack fluorinated polymer used as a binder, leading to the defluorination of binders and thus increase in polarization on electrochemical cycles.
Fe3O4/graphene composites have been prepared through a facile solvothermal process. Influence of PVP on the structure, morphologies, and electrochemical properties of composites were detected by means of X-ray diffraction, FT-IR spectra, Raman spectroscopy, scanning electron microscope, transmission electron microscopy, and electrochemical measurements. The results showed that Fe3O4 microspheres were dispersed and anchored on graphene nanosheets. The Fe3O4 microspheres are composed of nanoparticles and exhibit the interstitial cluster structure. The average size of Fe3O4 microspheres with introduction of PVP is smaller than that without PVP. As anodes materials for lithium-ion batteries, Fe3O4/G-PVP electrode exhibits better rate performance and higher capacities compared with Fe3O4/G electrode. Fe3O4/G-PVP can deliver an initial discharge capacity of 850.4 mA h g−1 and a high capacity of 400 mA h g−1 after 300 cycles at a current density of 1300 mA g−1.
To improve the wear resistance of Ni/Cu multilayer films, Ni and Cu layers were electrochemically formed by applying multi-constant current pulse. The wear resistance of Ni/Cu multilayers was improved with the increase in the number of pulses which can cause thin Cu layer formation during Ni deposition. The cross-sectional observation of the Ni/Cu multilayer samples with SEM and TEM, and XRD measurement indicated that the reason for the improvement of the wear resistance of Ni/Cu multilayer films prepared with multi-constant current pulse is because smaller Ni/Cu multilayer structure was formed in Ni layer of the Ni/Cu multilayer and because Ni layer was constructed with smaller crystals with increasing in the number of pulse.
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