Structural and electrochemical properties of lithium manganese spinels at 4 V and 5 V ranges were reviewed. To improve the cycle performance of spinel LiMn2O4 as the cathode of 4 V class lithium secondary batteries, the quaternary spinel solid solution phases LiMyMn2-yO4 (M = Co,Cr,Ni,Al, y = 1/12,1/9,1/6,1/3)(Fd3m) were prepared and studied extensively. The partially substituted spinels showed better cycle performance than the parent LiMn2O4. The improvement in cycling seems to be attributed to the stabilization in the spinel structure by the doped metal cations. In order to make the existing issues clear, local structural studies of LiMyMn2-yO4 were carried out by molecular dynamics (MD) and extended to the measurement of Extended X-ray Absorption Fine Structure (EXAFS). From the analysis of the site potential around the octahedral cation site from the MD simulation, it became clear that the substitution by selected metal ion M3+ or M2+ strengthens the bond between octahedral M and O atoms. As a possible candidate of 5 V class, stoichiometric LiNi0.5Nn1.5O4 (ordered-type P4332) and nonstoichiometric LiNi0.5Mn1.5O4-δ (disordered type Fd3m) were examined. The disordered-type phases showed higher rate properties than the ordered-type. From the Coulomb potential calculation of both structures, it was suggested that the diffusion of lithium in the disordered-type occurs more easily compared with that in the ordered-type. These results supported the observed charge-discharge behavior of the resulting cells.
Composite electrode material of crystalline β-FeOOH with a (2×2) tunnel-type structure and carbon was prepared by hydrolyzing of 0.1 mol dm-3 FeCl3 aqueous solution in which carbon powder was dispersed. The composite electrode material of fineβ-FeOOH particles and Ketjen black (KB: specific surface area 1270 m2 g-1) of high specific surface area exhibited the high capacity of more than 250 mAh g-1 per β-FeOOH weight and good cycle performance at rapid charge-discharge current density of 5.0 mA cm-2 (4.5 A g-1 per β-FeOOH weight) in nonaqueous electrolytes including lithium ions. Composite electrode with KB powder exhibited high capacities compared to that with acetylene black (AB) powder. Composite electrode materials of crystalline β-FeOOH and carbon are one of the promising candidates as electrode materials for energy storage devices such as hybrid capacitors that high-power operations are required.
Severe localized corrosion of buried steel pipes, called macro-cell corrosion in concrete/soil systems, is induced by cathodic reactions on steel surfaces in concrete accompanied by anodic reactions (i.e., corrosion) on those in soil. The addition of cathodic inhibitors to concrete is believed to be one of the effective means of suppressing this phenomenon. In order to evaluate the role of uric acid as an inhibitor for macro-cell corrosion, the inhibitory effects of uric acid on cathodic reaction of steels were investigated in saturated Ca(OH)2 solution to simulate the environment in pores in concrete. Polarization measurements showed that uric acid effectively inhibited these cathodic reactions, indicating that uric acid worked as an cathodic inhibitor for macro-cell corrosion. The relation between the inhibition ratio and the concentration indicated that uric acid was adsorbed on the steel with a Langmuir adsorption isotherm. Uric acid was suggested to be adsorbed onto cathodic areas of the steel through coordination of nitrogen atoms at positions 7 and 9, and oxygen in the carbonyl group at position 8 to the iron cations on the steel.
This work studied the design, fabrication, and performance evaluation of a novel micro direct methanol fuel cell (µ-DMFC). A µ-DMFC of 0.018 cm2 active area was prepared using a series of fabrication steps from micromachined silicon wafer including photolithography, deep reactive ion etching, and electron beam deposition. The novelty of this structure is that we have integrated the anodic and cathodic micro-channels arranged in plane onto a single silicon substrate. This architecture eliminates the need for the membrane electrode assembly (MEA) used in traditional polymer electrolyte-based fuel cells. Another original aspect is the successful electroplating of Pt and Pt-Ru catalysts in the microchannels. In addition, quasi-reference electrodes could be built in the prototype cell. The experimental trials were to verify the feasibility of this novel structure on basis of MEMS technology. The fuel and oxidant were supplied to the unit cell at a rate of 10 µL/min. Preliminary test results were able to confirm that this new concept of µ-DMFC generates electricity. At ambient temperature under atmospheric pressure, the maximum power density was 0.44 mW/cm2 at 3 mA/cm2 with Pt anode catalyst, while the maximum power density reached 0.78 mW/cm2 at 3.6 mA/cm2 for cell with Pt-Ru anode catalyst.
In this paper, we discussed the fabrication of micro-channel electrodes for very small DMFC (direct methanol fuel cell), i.e., µ-DMFC, where the channels composed of a current collector and a catalyst layer. The micro-channel electrodes were fabricated on a silicon wafer with a combination of photolithography, chemical etching with potassium hydroxide, spray coating, and electrodeposition method. The catalyst layer formation of Pt and PtRu was achieved by combining pulse electrodeposition with direct current electrodeposition. From these new processes, the µ-DMFC single unit cell was able to be operated for longer time operation compared with that of prototype test cell which was already reported in the previous paper.