Shuhei Wakita

Bio: Shuhei Wakita is an academic researcher. The author has contributed to research in topics: Anode & Cathode. The author has an hindex of 12, co-authored 59 publications receiving 686 citations.

Water electrolysis using diamond thin-film electrodes

Abstract: Thin, boron-doped diamond films formed on a silicon substrate were evaluated during water electrolysis in acidic solution in order to determine their potential for industrial use. Though the electrode exhibited overvoltages in excess of 2 V in the industrial current range, ozone gas was produced at a current efficiency of a few percent at ambient temperature. It was confirmed that the consumption rate of the highly doped sample was small and comparable with a platinum-plated anode, indicating that the diamond is dimensionally stable under extreme conditions. The failure mechanism in the test is discussed on the basis of scanning electron microscopy, X-ray diffraction, and Raman analyses. The spalling of the film from the substrate, which was observed in the deteriorated sample after the electrolysis, is attributed to the residual stress that accumulated during the production process carried out under high temperature.

Electrode for electrolysis and electrolytic cell using the electrode

Abstract: An electrode for electrolysis comprising an electrode base material and an electrode substance having an electrically conductive diamond structure covering the surface of the electrode base material. The electrode substance having an electrically conductive diamond structure may be a diamond containing an impurity selected from boron, phosphorus and graphite. Alternatively, the electrode substance having an electrically conductive diamond structure may comprise a composite of a diamond and an electrically conductive material. In a preferred embodiment, the electrode further comprises an interlayer comprising at least one of the carbide of a valve metal and silicon carbide disposed between the electrode base material and the electrode substance having an electrically conductive diamond structure. Also disclosed is an electrolytic cell having two chambers including an anode chamber and a cathode chamber partitioned by an ion-exchange membrane. At least one of the anode placed in the anode chamber and a cathode placed in the cathode chamber is an electrode comprising an electrode base material and an electrode substance having an electrically conductive diamond structure covering the surface of the electrode base material. An electrolytic cell having three chambers is also disclosed, including an anode chamber, an intermediate chamber and a cathode chamber partitioned by ion-exchange membranes. At least one of an anode placed in the anode chamber and a cathode placed in the cathode chamber is an electrode comprising an electrode base material and an electrode substance having an electrically conductive diamond structure covering the surface of the electrode base material.

Electrochemical treating method and apparatus

Abstract: An electrochemical treating apparatus comprising an electrolytic cell comprising an anode and a cathode spaced apart from the anode, the anode including an electrode material made of diamond and the cathode including an electrode material made of diamond. Also disclosed is an electrochemical treating method for electrochemically decomposing a substance contained in a gas or solution, which comprises introducing a gas or solution containing a substance to be treated into the electrolytic cell, passing an electric current through the electrolytic cell, and recovering a treated gas or solution. In a preferred embodiment, the electrolytic cell comprises an anode including an electrode material made of diamond, a cathode including an electrode material made of diamond and an ion exchange resin or an ion exchange membrane as an electrolyte disposed between the anode and the cathode.

Electrolytic cell for hydrogen peroxide production and process for producing hydrogen peroxide

Abstract: An electrolytic cell and method of electrolysis for producing hydrogen peroxide at a moderate current density while preventing metal deposition on the cathode surface. A feed water from which multivalent metal ions have been removed and in which a salt of a univalent metal, e.g., sodium sulfate, has been dissolved in a given concentration is prepared with an apparatus for removing multivalent metal ions and dissolving a salt in low concentration. The feed water is supplied to an electrolytic cell. Even when electrolysis is continued, almost no deposition of a hydroxide or carbonate occurs on the cathode because multivalent metal ions are not present in the electrolytic solution. Due to the dissolved salt, a sufficient current density is secured to prevent an excessive load from being imposed on the electrodes, etc. Thus, stable production of hydrogen peroxide is possible over a long period of time.

Method and apparatus for water treatment

Abstract: A method and apparatus for water treatment. The method comprises supplying an oxygen-containing gas to cathode 6 to yield hydrogen peroxide, supplying an inorganic acid to anode 5 through an acid solution addition opening 4 to yield an oxidation product, e.g., hypochlorous acid, and using both the hydrogen peroxide and oxidation product thus generated to treat a liquid to be treated. The atmosphere around the cathode surface is kept neutral to acidic due to the acidity of the coexisting oxidation product to thereby inhibit the deposition of metal hydroxides.

Substrate Processing Apparatus

Abstract: Process gas discharged from a bypass pipe to a gas exhaust system can be prevented from diffusing back to the inside of a process chamber without having to install a dedicated vacuum pump at the downstream side of the bypass pipe. The substrate processing apparatus includes a process chamber accommodating a substrate, a gas supply system supplying process gas from a process gas source to the process chamber for processing the substrate, a gas exhaust system configured to exhaust the process chamber, two or more vacuum pumps installed in series at the gas exhaust system, and a bypass pipe connected between the gas supply system and the gas exhaust system. The most upstream one of the vacuum pumps is a mechanical booster pump, and the bypass pipe is connected between the mechanical booster pump and the rest vacuum pumps located at a downstream side of the mechanical booster pump.

The effect of the particle size on the kinetics of CO electrooxidation on high surface area Pt catalysts

Abstract: Using high-resolution transmission electron microscopy (TEM), infrared reflection−absorption spectroscopy (IRAS), and electrochemical (EC) measurements, platinum nanoparticles ranging in size from 1 to 30 nm are characterized and their catalytic activity for CO electrooxidation is evaluated TEM analysis reveals that Pt crystallites are not perfect cubooctahedrons, and that large particles have “rougher” surfaces than small particles, which have some fairly smooth (111) facets The importance of “defect” sites for the catalytic properties of nanoparticles is probed in IRAS experiments by monitoring how the vibrational frequencies of atop CO (νCO) as well as the concomitant development of dissolved CO2 are affected by the number of defects on the Pt nanoparticles It is found that defects play a significant role in CO “clustering” on nanoparticles, causing CO to decrease/increase in local coverage, which yields to anomalous redshift/blueshift νCO frequency deviations from the normal Stark-tuning behavior

Electrochemical synthesis of hydrogen peroxide from water and oxygen

Abstract: H2O2 is important in large-scale industrial processes and smaller on-site activities. The present industrial route to H2O2 involves hydrogenation of an anthraquinone and O2 oxidation of the resulting dihydroanthraquinone — a costly method and one that is impractical for routine on-site use. Electrosynthesis of H2O2 is cost-effective and applicable on both large and small scales. This Review describes methods to design and assess electrode materials for H2O2 electrosynthesis. H2O2 can be prepared by oxidizing H2O at efficient anodic catalysts such as those based on BiVO4. Alternatively, H2O2 forms by partially reducing O2 at cathodes featuring either noble metal alloys or doped carbon. In addition to the catalyst materials used, one must also consider the form and geometry of the electrodes and the type of reactor in order to strike a balance between properties such as mass transport and electroactive area, both of which substantially affect both the selectivity and rate of reaction. Research into catalyst materials and reactor designs is arguably quite mature, such that the future of H2O2 electrosynthesis will instead depend on the design of complete and efficient electrosynthesis systems, in which the complementary properties of the catalysts and the reactor lead to optimal selectivity and overall yield. Electrosynthesis is a practical and green route to hydrogen peroxide, and could reduce our dependence on less environmentally friendly oxidants. This Review describes catalyst and reactor designs for highly selective hydrogen peroxide electrosynthesis.