Split ring disk gold electrode was fabricated on quartz crystal by photolithography, vacuum plating and sputtering. Using this quartz crystal, a wall jet split ring disk electrode (WJSRDE) was combined with electrochemical quartz crystal microbalance (EQCM). This combination was applied to the investigation of copper dissolution in acidic chloride solution. The average valence of dissolved ions n was estimated from the changes of resonant frequency when a constant anodic current was imposed on the copper electrode. Furthermore, it was compared with the n determined by the ring electrode currents.
Adding 5 wt% of K2CO3 to a 52/ 48 mol% Li/Na carbonate melt increased the oxygen reduction current in Steady State Voltammograms (SSV) measured in half cell set-up's with a factor of 3 at 650°C. A gas atmosphere with a P (O2) and P (CO2) of 5% with balance Nitrogen was used. Adding more K2CO3 proved not to be more beneficial. This increase varied with temperature between 600 and 750°C, but was never lower than a factor of two. The NiO solubility increased from 0.35 to 0.6 and even 0.8µmol cm−3 at 650°C by adding 5 and 8 wt% of K2CO3 respectively.
These results indicate that adding 5 wt% of K2CO3 to the Li/Na electrolyte will increase MCFC performance, using the important cathode gasses lean in oxygen and/ or CO2, but lower MCFC cathode endurance due to NiO solubility substantially. However despite the large increase of NiO solubility this work in half cell set-up's shows that it is worthwhile trying to optimize MCFC cathode polarization versus endurance by adding small amounts of K2CO3 to the 52/48 mol% Li/Na electrolyte.
A novel method to modify the surfaces of SnO2-based CO gas sensors in order to improve their temperature and humidity dependence has been developed. This surface modification is accomplished by dipping the sensor element in a dilute aqueous solution containing platinum and/or iridium for only a few seconds, then heating it at 600℃ for 5 min. This simple method effectively suppresses variations in sensor resistance to temperature and humidity in a specific concentration of CO; a decrease in sensor resistance with lowering temperature and humidity is prevented by the surface modifications with platinum and/or iridium. This effect is more enhanced by using both platinum and iridium than by using either metal individually. Moreover, preliminary surface treatments with sulfuric acid and thiourea further reduce the temperature and humidity dependence of sensor resistance in CO. It has been also proven that the modification of the SnO2-based CO gas sensor's surface using mixed elements results in its excellent long-term stability.
The solvent extraction of Co(II) was investigated by electrochemical methods. It was found in the measurement of i-E curves that the extraction rate was in proportion to the Co(II) concentration in aqueous phase and 8-hydroxyquinoline (HQ) concentration in organic phase and that the Co(II) formed a 1:1 complex with HQ. Furthermore, the electrochemical impedance spectroscopy (EIS) was applied to the kinetic investigation. The capacitive semicircle due to the time constant of charge transfer resistance and the interfacial capacitance was described in the electrochemical impedance on the Nyquist plane at low extraction rate. The apparent Warburg impedance was shown on the Nyquist plane at high extraction rate, indicating that the diffusion process contributes to the total extraction rate. On the basis of experimental results by the electrochemical methods and the numerical simulation, the solvent extraction mechanism of Co(II) was discussed.
The properties of the oxide film formed on the surface of the aluminum as a chemical potential barrier separating the melt and the oxidizing atmosphere were investigated from the electrochemical point of view. The emf generated across the film was measured under various potential conditions and analyzed theoretically considering that the oxide film works as the solid electrolyte having a certain amount of proton and oxide ion conductivity. The emf was found to coincide with the value expected for pure proton conductor but considerably lower than that estimated for pure oxide ion conductor. This phenomenon is explained by the fact that the high hydrogen potential in the molten metal is sustained by the "chemical polarization" mechanism induced by the extremely large potential difference of oxygen between the inside and the outside of the film.
In order to optimize the preparation condition of electrodes for phosphoric acid fuel cell (PAFC), we studied effects of dispersion and flocculation of particles (catalyst and PTFE) on the performance of electrodes. The average diameter and ζ potential of particles in pure water, anionic or nonionic surfactant solution were measured. Structures (poresize distribution, specific surface areas, FE-SEM images and wettability with phosphoric acid) and performances (1-V characteristic and endurance test) of electrodes prepared from these dispersions were evaluated. It was found that particles of catalyst and PTFE flocculate selectively each other (heteroflocculation) under the condition of flocculation (pH˂3) because of the opposite polarity of ζ potentials, when particles were dispersed in pure water or anionic surfactant solution. Both of electrodes prepared from dispersions in pure water and anionic surfactant solution have high output and long life as a PAFC cathode owing to a large effective reaction area (three phase boundary) because particles of catalyst and PTFE were distributed homogeneous in these electrodes. We succeeded in preparing high performance PAFC cathode from concentrated dispersion with particles with the system of anionic surfactant solution. This technology is industrially useful, because both the size of equipment and the time for filtration can be reduced.