Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/13—Ozone
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material

Definitions

• the present invention pertains to Bi-based mixed metal oxide anode materials with pyrochlore structure which are shown to be active as anode electrocatalyst materials for generating ozone and perchlorate.
• the invention further relates to an ozone or perchlorate generator for producing ozone through the electrolytic decomposition of water or oxidation of chloride salts.
• Ozonized water can be effectively used in the Medical, Food, Beverage and Agricultural (MFBA) industries as an antibacterial cleaning agent, as an oxidant and as pesticide.
• Ozone usage has recently been extended over to the semi-conductor industry for cleaning electronic components.
• Ozone is primarily produced from air by either electrical discharge or by exposure to UV radiation. However, since air contains 80% of nitrogen, oxidation of nitrogen to nitrogen oxides also occurs.
• Platinum is one of the few other candidate anode materials for electrolytic generation of ozone that has been considered for usage in commercial ozonators. See, U.S. Pat. No. 4,541,989.
• Use of Pt as the anode instead of a detrimental heavy metal, such as lead, allows production of ozonized water for MFBA and semi-conductor industry applications.
• Pt is not presently used in commercial ozonators because of its high cost and poor long term performance, i.e., ozone generation efficiency drops quickly compared to lead dioxide.
• the Pt anode loses its activity due to: (1) degradation of Pt anode surface due to formation of either catalytically inactive or non- conductive surface coating and (2) degradation of the interface between Pt anode and the Nafion electrolyte. Even Pt is known to dissolve at high anodic current densities and enter the electrolyte.
• BDD Boron-doped diamond
• boron/carbon ratios of 100, 1000 and 5000 ppm are also potential anode materials for electrolytic ozone generation. See, U.S. Pat. No. 6,235,186.
• the overpotential for oxygen evolution was found to be > 2.0 V, which is significantly larger, compared to PbO 2 anodes.
• Increasing the Boron doping lowers the oxygen evolution overpotential.
• current efficiencies for ozone generation were approximately one third of those obtained with PbO 2 electrodes.
• a sharp increase in voltage is observed for all the three doped materials but the higher B-doped material lasted longer.
• Sodium chlorate may be produced from sodium chloride according to the following reaction:
• the present invention provides bismuth mixed metal oxide pyrochlore materials suitable as high current density electrodes for electrolytic ozone and perchlorate generation.
• the bismuth mixed metal oxide pyrochlore materials disclosed herein provide safe and effective replacement where lead dioxide electrodes are currently used for ozone and perchlorate generation.
• the high current density electrodes used in connection with the invention comprise bismuth mixed metal oxide pyrochlore materials having the general formula A 2 B 2 O 7 - X , where A is Bi and B is Ru, Ir, Rh, Sn, Ti, or Pt and 0 ⁇ x ⁇ 1.
• B is Ru and the pyrochlore material has the general formula Bi 2 Ru 2 O 7 - X , where 0 ⁇ x ⁇ 1.
• the electrode may be fabricated of a composite of the bismuth mixed metal oxide pyrochlore material and one or more noble metals selected from Pt, Ag, Au, Ru, Re, or Pd.
• Electrolyic cells and electrolytic methods within the scope of the present invention have an anode which comprises a bismuth mixed metal oxide pyrochlore material as described above.
• the cathode may optionally comprise a bismuth mixed metal oxide pyrochlore material.
• the cathode material may be the same or different material as the anode.
• the invention includes an electrolytic method of generating ozone using an electrolytic cell having an anode comprising a bismuth mixed metal oxide pyrochlore material as described above.
• the electrolytic cell anode is operated at a current density sufficient to generate ozone.
• the ozone is generated according to the reaction:
• This reaction requires high current density, typically greater than 1 A/cm 2 .
• the current density is greater than 1.2 A/cm 2 .
• the current density greater than about 1.4 A/cm 2 .
• the electrolytic cell anode is operated at a current density of approximately 1.5 A/cm 2 . It will be appreciated by those of skill in the art that other reactions may be used to produce ozone under certain conditions.
• One such non-limiting reaction may include:
• the invention includes an electrolytic cell for generating ozone.
• the electrolytic cell has an anode comprising a bismuth mixed metal oxide pyrochlore material as described above.
• the electrolytic cell further includes a cathode, electrolyzable water in contact with the anode and the cathode, and a source of electric potential and current electrically coupled to the anode and the cathode to produce an operating current density sufficient to generate ozone.
• the ozone is generated at the anode according to the reaction.
• 3H 2 O ⁇ O 3 + 6H + + 6e ⁇ E 0 + 1.49 V (1)
• the electrolytic cell may be operated at the current densities described above.
• the anode and cathode may be configured as described above. It will be appreciated by those of skill in the art that other reactions may be used to produce ozone under certain conditions.
• One such non-limiting reaction may include:
• the invention includes an electrolytic method of generating a perchlorate salt using an electrolytic cell having an anode comprising a bismuth mixed metal oxide pyrochlore material as described above.
• the electrolytic cell anode is operated at a current density sufficient to oxidize a chlorate salt in aqueous solution to form a perchlorate salt in aqueous solution according to the reaction:
• the chlorate and perchlorate salt is a sodium chlorate and perchlorate salt.
• This reaction requires high current density, typically greater than about 0.5 A/cm 2 , preferably greater than about 1.0 A/cm 2 , and more preferably in the range from 0.5 A/cm 2 and 1.3 A/cm 2 .
• the invention includes an electrolytic cell for generating a perchlorate salt.
• the electrolytic cell has an anode comprising a bismuth mixed metal oxide pyrochlore material as described above.
• the electrolytic cell further includes a cathode, a chlorate salt in aqueous solution in contact with the anode, and a source of electric potential and current electrically coupled to the anode and the cathode to produce an operating current density sufficient to oxidize a chlorate salt in aqueous solution to form a perchlorate salt in aqueous solution at the anode according to the reaction.
• the electrolytic cell may be operated at the current densities described above.
• the anode and cathode may be configured as described above.
• Figure 1 is an X-ray diffraction pattern of a synthesized bismuth ruthenium oxide
• Figure 2 shows a Rotating Ring Disk Electrode (RRDE) to study ozone generation
• Figure 3 is an X-ray diffraction pattern of sintered bismuth ruthenium oxide
• Figure 4 is a scanning electron micrograph (SEM) of a sintered bismuth ruthenium oxide disk
• Figure 5 is an energy dispersive X-ray spectroscopy (EDS) pattern of the bismuth ruthenium oxide sintered disk of Fig. 4;
• Figure 6 is a cyclic voltammogram of the Bi 2 Ru 2 O 7 disk in 5M phosphoric acid showing significant anodic current
• Figure 7 is a graph of Bi 2 Ru 2 O 7 disk electrolysis with ozone collection on a Pt ring in 5M phosphoric acid at 10 mV/s in oxygen;
• Figure 8 is a SEM image of the bismuth ruthenium oxide disk after electrolysis
• Figure 9 is an EDS of the bismuth ruthenium oxide disk after electrolysis
• Figure 10 is a schematic representation of an ozonator experimental setup
• Figure 11 is a graph showing detection of O 3 (sparged from a corona discharge ozonator) using Au disk in 5M H 2 SO 4 ;
• Figure 12 is a graph showing the operating performance parameters of voltage, temperature, and ozone current for an ozonator using a Bi 2 Ru 2 O 7 coated Pt current collector.
• Figure 13 is a graph showing the operating performance parameters of voltage, temperature, and ozone current for an ozonator using a Bi 2 Ru 2 O 7 coated Pt current collector.
• Bismuth mixed metal oxide pyrochlore materials are disclosed herein as high current density electrodes for electrolytic ozone and perchlorate generation.
• the bismuth mixed metal oxide pyrochlore materials disclosed herein provide safe and effective lead-free electrode materials suitable for preparing ozonized water used in the medical, food, beverage and agricultural (MFBA) industries as an antibacterial cleaning agent, as an oxidant and as a pesticide. Such ozonized water may also be used in the semi-conductor industry for cleaning electronic components.
• the bismuth mixed metal oxide pyrochlore materials disclosed herein may also be used in an anode for the electrochemical preparation of perchlorate salts.
• the high current density electrodes used in connection with the invention comprise bismuth mixed metal oxide pyrochlore materials having the general formula A 2 B 2 Cv x , where A is Bi and B is Ru, Ir, Rh, Sn, Ti, or Pt and 0 ⁇ x ⁇ 1.
• the electrode may be fabricated of a composite of the bismuth mixed metal oxide pyrochlore material and one or more noble metals selected from Pt, Ag, Au, Ru, Re, or Pd.
• Electrolyic cells and electrolytic methods within the scope of the present invention have an anode which comprises a bismuth mixed metal oxide pyrochlore material as described above.
• the cathode may optionally comprise a bismuth mixed metal oxide pyrochlore material.
• the cathode material may be the same or different material as the anode.
• Bismuth ruthenium oxide (Bi 2 Ru 2 O 7 ) is a known conducting material that may be used as an alternative to lead dioxide and platinum as anodes for ozone and perchlorate salt generation.
• Bi 2 Ru 2 O 7 possesses the pyrochlore structure. It is known to exhibit stability in acidic as well as basic solutions under oxidizing conditions. J. M. Zen, R. Manoharan and J. B. Goodenough, /. Appl. Electrochem., 22 140 (1992). Extensive oxygen and chlorine evolution capability, high initial electrocatalytic activity for oxygen reduction and electrochemical oxidation of a number of organic compounds has been reported for this material. H. S. Horowitz, J. M. Longo and H. H.
• Jacobson et al. (U.S. Pat. No. 5,105,053) disclosed bismuth ruthenium oxide catalyst having the pyrochlore structure as an efficient catalyst for the conversion of hydrocarbons, and most preferably methane, to higher hydrocarbons and olefins.
• U.S. Pat. No. 4,163,706 discloses synthesis and characterization of high surface area bismuth rich pyrochlore-type compounds containing ruthenium, iridium and mixtures thereof for application in electrochemical processes, such as electrocatalysis.
• Preferred pyrochlore materials have high lead content and the formula Pb 2 [M 2 - X Pb x ]O 7 - Y , where M is Ru or Ir and where 0 ⁇ x ⁇ 1.2 and 0 ⁇ y ⁇ 1.0.
• Bismuth ruthenium oxide is within the scope of the broad disclosure. [0060] Applicants are not aware of reported studies on the use or performance of this material as an anode for electrolytic ozone and perchlorate evolution.
• FIG. 1 A Rotating Ring Disk Electrode (RRDE) method was used to demonstrate that bismuth ruthenate can indeed function as an anode in electrolytic ozonator.
• FIG. 2 A cross-sectional side view and bottom view of a typical RRDE device is shown in Figure 2.
• the theory behind the application of RRDE for in-situ generation/detection of ozone is briefly as follows.
• the RRDE 100 consists of a central disk electrode 102 surrounded by a concentric ring electrode 104 with a thin Teflon U-cup insulator 106 separating them.
• the potential or the current at each electrode can be controlled independently using a bipotentiostat (not-shown).
• a bipotentiostat controls the voltage and measures the current at two working electrodes immersed in an electrolyte, using only one reference electrode and one counter electrode.
• the RRDE shown in Figure 2 can be used to detect and measure O 3 that is generated at the disk of RRDE.
• the ring electrode can be swept in the potential region where the ozone can be reduced.
• the limiting ozone reduction current at the ring electrode 104 for each material could be determined.
• this method allows comparison of various anode materials for their ozone generation capacity.
• Cyclic voltammetry Cyclic voltammetry (CV) of the disk prepared in Example 3 was performed in 5M H 3 PO 4 in an oxygen atmosphere.
• the CV data reported in Figure 6 shows that oxygen evolution starts at anodic polarization potentials of > 1.5 V, and that large currents are obtained at higher potentials as in the case of Pt and Pb disks.
• the material was also fairly active towards hydrogen evolution when polarized cathodically.
• Constant potential electrolysis at 4 V showed that Bi 2 Ru 2 O 7 sustained a current density of 1.5 A/cm for up to an hour without decay.
• EDS analysis on the residue retrieved by filtering the electrolyte showed no Bi or Ru peaks. Longer-term electrolysis experiments are required to generate more soluble species for chemical analysis.
• the gaseous mixture 214 was then sparged into the Rotating Ring Disk Electrode (RRDE) cell 216 containing 5M phosphoric acid, where it was analyzed for ozone concentration in the ozonized water. The flow rate of generated gaseous mixture, the temperature and the voltage of the cell were monitored. All the components shown in Figure 10 were made of Teflon or titanium.
• the cell 206 where electrolysis of water takes place is divided into an anode compartment and a cathode compartment with a cation exchange membrane Nafionll7TM separating the two compartments.
• the anode and cathode were tightly pressed to either side of the ion exchange membrane forming a zero gap cell.
• a bismuth ruthenium oxide coated Ti mesh was used as the anode, Nafion 117 with Pt deposited on one surface as the electrolyte and a bare Ti mesh was used as cathode (the bare Ti mesh was in contact with the Pt deposited surface of the Nafion membrane).
• the RRDE method was utilized to determine the concentration of the ozone generated.
• the theory behind the application of RRDE for detection of ozone is briefly as follows.
• the RRDE consists of a gold disk electrode.
• the electrode is rotated at a very high speed. This rotational motion sets up a well-defined flow of solution towards the surface of the rotating disk electrode.
• the flow pattern is akin to a vortex that literally sucks the solution (containing dissolved ozone) towards the electrode.
• the potential of the disk is controlled by a potentiostat and is slowly swept back and forth across between oxygen and hydrogen evolution.
• the platinum anode current collector was used as a substrate for the bismuth ruthenium oxide coating in the above experiment. It is possible that ozone is being generated by the platinum anode current collector and not the bismuth ruthenium oxide material.
• the Bi 2 Ru 2 O 7 material was coated on a Ti mesh on top of the Pt anode current collector as the anode.
• the cell was assembled with bare titanium mesh on top of the Pt anode current collector. The cell could not be operated (3OA current could not be sustained) with this setup. Then the cell was assembled with Bi 2 Ru 2 O 7 material coated Ti mesh in the place of bare Ti mesh. This time the cell could be operated and the resulting data are shown in Figure 13.
• ozone may be generated by a Bi 2 Ru 2 O 7 pyrochlore anode in the ozonator. While the examples focus on Bi 2 Ru 2 O 7 as one suitable electrode material for the electrolytic ozone generation, the invention is not limited to Bi 2 Ru 2 O 7 .
• Other Bi based pyrochlores with Ir, Sn, Rh, Pt and Ti can also be potentially used and are within the scope of the disclosed invention. These bismuth pyrochlore materials are attractive electrode materials for electrolytic ozone or perchlorate generation.

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• 2010
  • 2010-06-16 JP JP2012516269A patent/JP2012530845A/ja not_active Withdrawn
  • 2010-06-16 US US12/816,537 patent/US20110226634A1/en not_active Abandoned
  • 2010-06-16 WO PCT/US2010/038850 patent/WO2010148107A2/en active Application Filing
  • 2010-06-16 EP EP10790131A patent/EP2443269A2/en not_active Withdrawn

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