To simultaneously synthesize carbon nanotubes and graphene on nickel foam without additional catalysts, one-step ambient pressure chemical vapor deposition (CVD) is used to grow them at different temperatures. Next, adding nitrogen-doped defects to the surface of the carbon nanotube/graphene composites, the carbon nanotube/graphene composites are modified by RF (radio frequency) nitrogen-plasma treatment at different power levels and time periods. Carbon nanotubes and graphene are simultaneously synthesized by CVD at 800°C. Furthermore, the specific capacity (618 mAh g−1) reaches a maximum at the nitrogen-plasma treatment conditions (power = 100 W and time = 15 min). Moreover, it also shows the nearly double improvement of the specific capacity and higher electrochemical stability after carbon nanotube/graphene composites are treated by nitrogen-plasma.
The development of SIB has attracted attention as a substitute for LIB. Low-temperature-fired soft carbon (LFSC) has been the target of study as SIB’s useful negative electrode material. We estimated Na chemical diffusion coefficient Dchem using the same approach and samples of previous report on LIB. The approach was potential step chronoamperometry (PSCA) method, and the samples were mesophase-pitch-based carbon fiber fired at four different low temperatures (600, 700, 800 and 950°C). The PSCA measurements by using a single LFSC fiber electrode were performed in an electrolyte of propylene carbonate (PC) containing 1 M NaClO4 at room temperature in a glove box filled with dried Ar. The largest Dchem value we obtained with four pristine LFSC was about 10−9 cm2/sec. The Dchem values depended not only on firing temperature of LFSC but also on the nature of LFSC’s surface. The effective surface treatment promoted Na insertion/extraction reaction rate on the carbon surface. The largest Na Dchem value we obtained after surface treatment was 10−8 cm2/sec. This Na Dchem value was close to the Li Dchem value (10−7.5 cm2/sec) by previous report, which suggests possibility of SIB’s practical use.
A sequential injection analysis (SIA) system with on-line preconcentration technique using a microfluidic chip with an embedded anionic surfactant ion-selective electrode (AS-ISE) as a detector, was developed for the determination of anionic surfactants. Under the SIA system with no on-line preconcentration technique, the AS-ISE in the SIA system showed a linear relationship between peak heights and logarithmic concentrations of AS ion such as dodecylbenzene sulfonate (DBS) ion with a Nernstian slope of 60.4 mV decade−1 in a concentration range from 3.0 × 10−6 to 1.0 × 10−3 mol dm−3. For the determination of trace levels of ASs, on-line preconcentration technique with solid-phase extraction process was incorporated into the SIA system. By using the on-line preconcentration technique in the SIA system, DBS ion in a concentration range from 1.0 × 10−7 to 3.0 × 10−6 mol dm−3 was successfully determined. The recovery for DBS ion added to river water samples was ca. 91–97% using on-line preconcentration technique in the SIA system. The result shows that the present SIA system with the on-line preconcentration technique can be applicable to the determination of the level of AS ion in river and tap water samples.
An electrochemical cell was developed for operando soft X-ray absorption spectroscopic (XAS) study of an all-solid-state lithium-ion battery. Operando XAS experiments were performed for a battery using LiMn2O4 as a cathode material and a NASICON-type lithium conductive glass ceramic sheet (LICGC) as a solid electrolyte. O K-edge, Mn L-edge and Ti L-edge XAS spectra were taken during the charging process up to 2.2 V. Detailed analysis of the XAS spectra revealed that the valence change from Mn3+ to Mn4+ occurred during charge with simultaneous change in the spectrum of O K-pre-edge region. Ti L-edge spectra revealed a partial change from Ti4+ to Ti3+ in the LICGC at the anode side, indicating a rather dispersed anode formation.
Herein, mixtures of water and propylene carbonate (PC) containing Ca(CF3SO3)2 were used as electrolytes to improve the electrochemical performance parameters of a Prussian blue analogue electrode, copper hexacyanoferrate, for use in calcium-ion batteries. The performance of the electrode was greatly influenced by the molar ratio of the two solvents (water and PC) in the electrolyte. The electrode exhibited a relatively high capacity when the molar ratio of calcium cations to water in the electrolyte was 1:6. In addition, the electrode exhibited a coulombic efficiency of ∼100% over 800 cycles, with ∼94% retention of the maximum capacity after 800 cycles in this electrolyte solution. Raman spectroscopy revealed that calcium cations were preferentially solvated by water molecules in the electrolyte, which is believed to be related to the improvement in electrode performance.
The behavior of the leak and reverse currents in a bipolar-type alkaline water electrolyzer has been investigated using a bipolar-type electrolyzer which consists of two cells. The electrodes were nickel mesh, which are the conventional electrodes for alkaline water electrolyzers. The leak circuit could be expressed by a simple equation and a simple equivalent circuit for the cell performance and ionic resistance of the manifolds. The electrolyte was replaced by a gas-free electrolyte after electrolysis to classify the influence of the reverse current into the gas reaction and electrode active material. As a result, the dominant driving force of the reverse current was the active nickel-based materials on the Ni electrode. The redox couples on the electrode surface during the reverse current were estimated based on the measured cell voltages and redox potentials on a nickel electrode. The final potentials of both sides on the bipolar plate for the replacement conditions were higher than those for the non-replacement condition, because the hydrogen of the reductant was removed from the cathode electrolyte, and the balance of the reductant and oxidant would change to the oxidation side.
The effect of carbon-coating on the electrochemical properties of LiCoPO4 was investigated by single particle measurement. For this analysis, micrometer-scale LiCoPO4 particles with and without carbon-coating were synthesized by hydrothermal method (LiCoPO4/C0 with 0.3 wt%, LiCoPO4/C1 with 0.8 wt%, LiCoPO4/C2 with 1.7 wt% carbon-coating and pristine LiCoPO4). In the electrochemical tests using the conventional composite electrodes, all the samples showed the similar electrochemical properties with potential plateaus at ∼4.7 V vs. Li/Li+. In contrast, single particle measurement showed clear differences in the charge and discharge curves. The pristine LiCoPO4 showed the potential plateau only in the discharge curve due to a large overpotential of charging. LiCoPO4/C0 also showed large overpotential. On the other hand, good electrochemical responses were obtained for the LiCoPO4/C1 and LiCoPO4/C2 particle electrodes even though their carbon-coating amounts were different. This result suggests that 0.8 wt% or higher carbon-coating enables to improve the electrochemical performance of one particle of LiCoPO4.