A simple numerical simulation of current flowing through electronic devices was examined for a hybrid power supply system composed of a DMFC and a capacitor connected in parallel. The simulation was investigated by representing a combination of ohmic resistance, charge transfer reaction resistance, mass transfer resistance and double layer capacitance of a DMFC as a simple ideal resistor, based on measured data when DMFC was generating electricity. The simulation result was found to agree with experimental measured current flowing through the DMFC and the capacitor, although a slight disagreement was observed because of the presence of ohmic resistance between circuit components. The simulation of DMFC-capacitor hybrid power supply system indicated the importance of the inner resistance of the capacitor. The hybrid simulation was also applied to a system assumed to consist of μDMFC and micro electrochemical capacitor (MECC) system. The effect of applying a DC-DC converter to the system was indicated. The simulation allows to predict the degree of improvement required without performing actual fabrication of μDMFC and MECC.
The feasibility of a di-block copolymer, composed of a polyethylene oxide (PEO) chain and a polystyrene (PS) chain covalently bonded, as the gel electrolyte for lithium secondary batteries was investigated. The PEO-PS di-block copolymer gel electrolyte showed a high ionic conductivity of ∼1 mS/cm at room temperature. Moreover, it retained good mechanical strength within a co-continuous phase separated structure, and it suppressed the dendritic deposition of Li. Indications were that the interface between the electrolyte and the Li metal was chemically stable, as a result of the PEO phase fixed to PS by covalent bonding. In addition, it was indicated that the Li/PEOPS di-block copolymer gel electrolyte/LiFePO4 cell had a high charge-discharge efficiency of ∼99% during 30 cycles, while maintaining a discharge capacity of 124 mAh/g.
Switchable mirrors composing magnesium-nickel thin films with a palladium top layer are prepared by dc magnetron sputtering. Electrochromic properties of the switchable mirrors are investigated by means of various electrochemical methods. Electrochromic switching conditions influenced by the composition of the Mg–Ni alloy thin film and the thickness of palladium and Mg–Ni layers are investigated to obtain optimal switching behavior and transparent films using cyclic voltammetry and optical measurements. The values of the diffusion coefficients of hydrogen in Mg2Ni, Mg4Ni, and Mg6Ni films are estimated using a potential-step method.
Pressure effects on the water electrolysis performance of the cell using Nafion 117 for electrolyte were investigated. It was found that the internal resistance of the cell decreased with increasing the pressure, while it is expected that the chemical equilibrium shifts to the reactant side. Detail analysis of the internal resistance by a current interruption method suggests that decrease in the internal resistance results from the decreased IR loss, which is assigned to the increased conductivity of Nafion 117 film. On the other hand, the overpotential of cathode and anode slightly increases as the pressure increases. In particular, the concentration overpotential on both electrodes increased under an elevated pressure. Since the internal resistance decreased by elevating water pressure, water electrolysis efficiency was improved to a value of 65% at 20 MPa, 100 mA/cm2. Consequently, this study reveals that pressure shows the prospective effects on the water electrolysis performance of the cell using Nafion 117 electrolyte in an initial short period.
Lithium manganese oxide thick films were prepared on aluminum foils without any conductive agent or binder material by means of gas-deposition (GD) method. Charge/discharge performances were investigated on the coin-type cells consisting of the GD’ed cathode and the lithium metal anode, which were compared with the case using the cathode conventionally prepared with conductor and binder. In the case that LiMn2O4 powders with the particle size of 10 µm were employed as the cathode material, the GD’ed cathode showed smaller discharge capacities in early cycles in comparison with conventionally prepared cathode. However, by roughly milling the cathode powders to modify the particle size distribution, obvious enhancement of discharge capacity was observed only for GD’ed cathode. In terms of the cycle stability, the GD method was effective to prepare the cathode material having a good performance.