Preparation and Application of CQDs/Ni(OH)20.75H2O as Electrodes in Supercapacitors

In this paper, a hydrothermal synthesis method for preparation Carbon Quantum Dots (CQDs)/Ni(OH)20.75H2O composite electrode material, and loaded on Nickel Foam(NF) by rolling method. The crystal phase, structure, morphology and the reaction process were characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the composite were measured by cyclic voltammetry impedance spectroscopy and couple method charge-discharge techniques. The results showed that the composites material was evenly adhered to nickel foam. When the current density is 1 A g−1, the specific capacity of CQDs/Ni (OH) 20.75H2O composite can reach 2115.4 Fg−1, which is close to 5 times of Ni (OH) 20.75 H2O electrode material.

Interdiffusion of major elements at 1 atmosphere between natural shoshonitic and rhyolitic melts

The diffusive mass exchange of eight major elements (Si, Ti, Al, Fe, Mg, Ca, Na, and K) between natural, nominally dry shoshonitic and rhyolitic melts was studied at atmospheric pressure and temperatures between 1230 and 1413 °C using the diffusion couple method. For six elements, effective binary diffusion coefficients were calculated by means of a concentration-dependent method to obtain an internally consistent data set. Among these components, the range in diffusivities is restricted, pointing to a coupling of their diffusive fluxes. We find that the calculated diffusivities fit well into the Arrhenius relation, with activation energies (Ea) ranging from 258 to 399 kJ/mol in rhyolitic (70 wt% SiO2) melt and from 294 to 426 kJ/mol in the latitic melt (58 wt% SiO2). Ti shows the lowest Ea, while Si, Fe, Mg, Ca, and K have a similar value. A strong linear correlation is observed between logD0 and Ea, confirming the validity of the compensation law for this system. Uphill diffusion is observed in Al in the form of a concentration minimum in the rhyolitic side of the couple, (at ca. 69 wt% SiO2), and in Na indicated by a maximum in the shoshonitic side (ca. 59 wt% SiO2). Fe shows weak signs of uphill diffusion, possibly due to the contribution of ferric iron. The data presented here extend the database of previously published diffusivities in the shoshonite-rhyolite system (González-García et al. 2017) toward the water-free end and allows us to better constrain the water-dependence of major element diffusion at very low water concentrations. Combining both data sets, we find that logD is proportional to the square root of water concentration for a range between 0 and 2 wt% H2O. These results are of particular interest in the study of mass transfer phenomena in alkaline volcanic systems.