3 years ago

Doshisha University (Private)

Doshisha University (Private)

Prof. Masatsugu

Prof. Masatsugu MORIMITSU Environmental Systems Engineering Laboratory Major Research Topics Rechargeable metal hydride - air batteries Smart anodes for electrowinning, electroplating, water electrolysis, and waste water treatment water Highly sensitive and selective biosensors using intelligent electrodes Research Contents Rechargeable Metal Hydride - Air Batteries A zinc-air battery is well known as a commercially available metal-air battery, which is used for a power supply of hearing aid and has some attractive properties such as no limitation on the capacity of the positive electrode and a high theoretical energy density, since the active mass of the positive electrode is oxygen in air. However, commercially available metal-air batteries are limited to be a primary zinc-air battery, and no rechargeable metal-air battery has been developed, except mechanically rechargeable zinc-air batteries, although many efforts have been done to realize a secondary metal-air battery. One of the reasons is a difficulty to develop a bi-functional air electrode enabling oxygen reduction and evolution reversibly. For example, the air electrode of a zinc-air primary battery consists of catalyst/carbon mixed material, and carbon is consumed when the battery is recharged due to generation of carbon dioxide. On the other hand, we have developed a new bi-functional air electrode consisting of nickel, PTFE, and pyrochlore-type oxide, Bi2Ir2O7-Z, and have demonstrated that the air electrode has a good reversibility for oxygen reactions and a high durability for charge-discharge cycles up to 2000 cycles. We have been also trying to develop a new class of secondary air battery with the bi-functional air electrode and focusing on hydrogen storage alloys as the negative material in combination with an alkaline electrolyte, as shown in Fig. 1. This secondary air battery is expressed as an MH-air battery, which has a cell configuration analogue to Ni-MH battery where the nickel oxide electrode is replaced with the air electrode. The reactions of this battery are expressed as follows (→ discharge, ← charge); Positive electrode: O2 + 2 H2O + 4 e Negative electrode: 4 MH + 4 OH- 4 OH- 4 M + 4 H2O + 4e Total reaction: O2 + 4 MH 4 M + 2 H2O

The battery has a high theoretical energy density more than 1,000 Wh/kg, and the EMF is 1.22 V. Our recent studies have been demonstrating that the current efficiency and the utilization of MH are higher than 90% and the projected energy density is more than 400 Wh/L. A good cycling performance has also confirmed. The battery is expected as a promising candidate for use in electric and hybrid vehicles, solar and wind power storages, and power supply to mobile devices. Smart anodes for electrowinning, electroplating, water electrolysis, and waste water treatment Industrial electrolysis including electrowinning and electroplating of metals, water electrolysis, waste water treatment and etc. consumes a large amount of electric power, and the energy consumption depends on the voltage of the electrolytic cell, in which the electrolyte is usually an aqueous solution and the anode's reaction is oxygen or chlorine evolution. A low potential anode is much important for energy saving of industrial electrolysis, and our developing smart anode can promote the anode's reaction and reduce oxygen or chlorine evolution potentials. The anode consists of a mixture of IrO2 and Ta2O5 formed on a titanium substrate, which is prepared by thermal decomposition of a precursor solution. The anode is similar to those known as DSA, but is quite different from commercially available DSA, because IrO2 in the coating is amorphous. We have been revealing that amorphous IrO2-Ta2O5/Ti anodes has lower potential for oxygen or chlorine evolution than commercially available DSA or lead alloy anodes; for example, the amorphous oxide anode can reduce oxygen evolution potential by 0.55 V for zinc electrowinning compared to the lead alloy anode, which corresponds to 18% energy saving. In addition, the amorphous oxide anode prevent some unwanted side reaction simultaneously occurring oxygen or chlorine evolution such as MnOOH deposition in zinc or copper electrowinning, PbO2 deposition in zinc or copper electrowinning and in copper foil production, and CoOOH deposition in cobalt electrowinning. The prevention of such unwanted side reactions is valuable to prolong the anode's lifetime, eliminate the maintenance of the anode to remove the oxide deposits from the anode's surface, and suppress the contamination of minor components in the cathode's product. Therefore, our developing anode is a smart anode which can distinguish the wanted and unwanted reactions from each other. Highly sensitive and selective biosensors using intelligent electrodes Compositional analysis of blood and urine is critical to illness diagnosis and health management, and electrochemical biosensors are one of the tools that can be used for such analysis. These operate by quantifying components from electric current values when oxidizing or reducing the intended component with an electrode. Compared to other methods that use chemical reactions or optical absorption measurements, biosensors offer greater sensitivity and more compactness of equipment. Blood and urine, however, contain many components that resemble each other, which means that it is not so easy to detect just the intended component with an electrode. Even electrodes with a high sensitivity to a certain component do not function sufficiently as sensors unless there is a large gap between that sensitivity and the sensitivity to interfering components. Besides, to make a biosensor respond only to a certain component is important not only for sensitivity but also for controlling deterioration of the electrode over time. "Intelligent electrodes" with the function to distinguish responses have demonstrated the ability to meet these requirements of biosensors. Presently our laboratory is developing intelligent electrodes intended to be applied to various biosensors, including glucose sensors. Keywords Rechargeable MH-air batteries Smart Anodes Industrial electrolysis Biosensors Energy Saving

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