JP2012530845A - Bismuth metal oxide pyrochlore as electrode material - Google Patents

Abstract

A novel bismuth-based mixed metal oxide material having a pyrochlore structure as an anode for the electrolysis of ozone and perchlorate is disclosed. These materials have high conductivity and excellent stability in acidic electrolytes. These materials are more environmentally friendly than lead dioxide and are less expensive than platinum.

Description

(Cross-reference of related applications)
This application claims the priority of US Provisional Patent Application No. 61 / 218,554 “Bismuth Metal Oxide Pyrochlore as Electrode Ozone and Perchlorate Generation” filed June 19, 2009. The entire disclosure of which is incorporated herein by reference.

  The present invention relates to a Bi-based mixed metal oxide anode material having a pyrochlore structure that has been shown to be active as an anode electrocatalyst material for generating ozone and perchlorate. The invention further relates to an ozone or perchlorate generator for producing ozone or perchlorate by electrolysis of water or oxidation of chloride.

  Ozone water can be effectively used as an antibacterial detergent, as an oxidant and as an insecticide in the medical, food, beverage and agriculture (MFBA) industries. In recent years, the use of ozone has expanded to the semiconductor industry to clean electronic components. C. Gottschalk, A.M. Saupe, and J.M. A. Libra, “Ozonation of water and waste water: a practical guide to understand application,” Wiley-VCH, New York (2000). Ozone is mainly generated from air by discharge or exposure to ultraviolet light. However, since air contains 80% nitrogen, nitrogen oxidation also occurs and nitrogen oxides are also produced. When ozone generated in this way is dissolved in water to generate ozone water, nitrogen oxides are also dissolved, which makes the water acidic. Also, due to the low partial pressure of ozone in the gas phase and the limited solubility of ozone in water, the concentration of ozone in water will be low using this method.

  Alternatively, ozone can be obtained from water as shown in the anodic reaction shown in reaction formula (1) below and G. Fischer, “Electrical ozone production for super-pure water indication,” Pharma International, 2, 1997.

  The ozone thus produced is present at high concentrations in water and there are no problems with acidity or solubility. The disadvantage of this process is the high voltage response that increases power consumption. In addition, as shown in the following reaction formula (2), since oxygen generation competes with ozone generation, the efficiency of the process is low. Hydrogen evolution (Scheme 3) is a cathodic reaction.

  Hydrogen evolution occurs at the cathode according to the following reaction equation (3).

The use of lead dioxide (PbO ₂ ) as an anode material for generating ozone is described in the literature. P. C. Foller and C.I. W. Tobias, “The anodical evolution of Ozone”, “J. Electrochem. Soc. , 129 (3), 506 (1982). Electrolytic ozone generators based on PbO ₂ are commercially available. S. Stucki, et al. , “In Situ production of Ozone in water using a Membrel electrolyzer”, J. et al. Electrochem. Soc. 132 (2), 367 (1985).

In a typical process using PbO _{2, O 3} is generated in the water flow from the back surface of the porous PbO ₂ anode in contact with the Nafion membrane electrolyte. However, the lead dioxide anode is not completely stable at the high current density (> 1 A / cm ² ) required for ozone generation. PbO ₂ decomposes and enters ozone water as lead acid ions, contaminates the water, making it unusable directly for many cleaning and MFBA applications. In order to produce lead-free ozone water, ozone gas must first be recovered from lead-containing ozone water and then redissolved in fresh water before ozone is decomposed into oxygen. These additional steps make the process impractical. Therefore, it is preferable to produce lead-free ozone water so that it can be used directly for cleaning or MFBA applications.

  Platinum is one of the few other candidate anode materials for the electrolysis of ozone that is being considered for use in commercial ozone generators. See U.S. Pat. No. 4,541,989. The use of Pt as an anode to replace harmful heavy metals such as lead enables the generation of ozone water for MFBA and semiconductor industry applications. However, Pt is not currently used in commercial ozone generators because of its high cost and low long-term performance, i.e., the ozone generation efficiency decreases quickly compared to lead dioxide. During long-term ozone generation, the Pt anode has its Loses activity. Even Pt is known to dissolve at high anode current densities and enter the electrolyte.

Boron doped diamond (BDD) with boron / carbon ratios of 100, 1000 and 5000 ppm is also a potential anode material for electrolytic ozone generation. See U.S. Patent No. 6,235,186. The oxygen generation overvoltage was found to be> 2.0 V, which is significantly higher compared to the PbO ₂ anode. Increasing boron doping decreases the oxygen generation overvoltage. However, the current efficiency of ozone generation was about one third that obtained with a PbO ₂ electrode. During the final stage of electrolysis, the voltage spike was seen for all three doped materials, but the higher B-doped material lasted longer. The failure is due to film peeling from the substrate caused by stress introduced during the film formation process at high temperatures. N. Katsuki et al. "Water electrolysis using Boron-doped diamond thin films", J. et al. Electrochem. Soc. , 145 (7), 2358 (1998).

From the foregoing, the PbO ₂ material used as the anode in current ozone generators cannot be used for MFBA and semiconductor cleaning applications. Although Pt and boron doped diamond (BDD) can potentially be used, they do not provide long cycle life. It would be an advance in the art to provide alternative lead-free electrode materials suitable for use in the electrolysis of ozone.

While the foregoing discussion focused on ozone generation, electrochemical synthesis of perchlorate from chloride or chlorate generally involves PbO ₂ , Pt or other electrodes with high oxygen overvoltage. Use. These are the same type of electrodes that are used to generate ozone. Chlorates can be oxidized in an electrochemical cell to produce perchlorates. One common starting material is sodium chlorate that can be oxidized at the anode according to the following reaction.

  Sodium chlorate can be generated from sodium chloride according to the following reaction.

  The energy efficiency of these reactors is as low as 20-40%. D. Pletcher and F.M. C. Walsh (1990), Industrial Electrochemistry, Chapman and Hill, New York. It would be an advance in the art to provide an anode material for the production of perchlorate that is lead free and can provide higher current efficiency and longer lifetime.

  The present invention provides a bismuth mixed metal oxide pyrochlore material suitable as a high current density electrode for electrolytic ozone and perchlorate generation. The bismuth mixed metal oxide pyrochlore material disclosed herein provides a safe and effective alternative to the lead dioxide electrode currently used for ozone and perchlorate generation.

Means for Solving the Invention

The high current density electrode used in connection with the present invention comprises a bismuth mixed metal oxide pyrochlore material having the general formula A ₂ B ₂ O _7-x , where A is Bi, B is Ru, Ir, Rh, Sn, Ti, or Pt, and 0 ≦ x ≦ 1. In one non-limiting embodiment within the scope of the present invention, B is Ru and the pyrochlore material has the general formula Bi ₂ Ru ₂ O _7-x , where 0 ≦ x ≦ 1. In another non-limiting embodiment, the electrode can be made of a composite of a bismuth mixed metal oxide pyrochlore material and one or more noble metals selected from Pt, Ag, Au, Ru, Re, or Pd. it can. An electrolysis cell and electrolysis method within the scope of the present invention has an anode comprising a bismuth mixed metal oxide pyrochlore material as described above. The cathode can optionally include a bismuth mixed metal oxide pyrochlore material. The cathode material may be the same or different material as the anode.

  The present invention includes an electrolysis method for generating ozone using an electrolysis cell having an anode containing a bismuth mixed metal oxide pyrochlore material as described above. The electrolysis cell anode is operated at a current density sufficient to generate ozone. In one embodiment, ozone is generated according to the following reaction.

This reaction requires a high current density, generally higher than 1 A / cm ² . In some non-limiting embodiments, the current density is higher than 1.2 A / cm ² . In other non-limiting embodiments, the current density is greater than about 1.4 A / cm ² . In yet another non-limiting embodiment, the electrolytic cell anode is operated at a current density of about 1.5 A / cm ² . One skilled in the art will appreciate that other reactions can be used to produce ozone under certain conditions. One such non-limiting reaction can include the following.

  The present invention includes an electrolysis cell for generating ozone. The electrolysis cell has an anode comprising a bismuth mixed metal oxide pyrochlore material as described above. The electrolysis cell further comprises a cathode, electrolyzed water in contact with the anode, and a source of electrical potential and current that is electrically coupled to the anode and the cathode and generates a working current density sufficient to generate ozone. In one embodiment, ozone is generated at the anode according to the following reaction.

  The electrolysis cell can be operated at the current density described above. The anode and cathode can be configured as described above. One skilled in the art will appreciate that other reactions can be used to produce ozone under certain conditions. One such non-limiting reaction can include the following.

  The present invention includes an electrolysis method for generating perchlorate using an electrolysis 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 the aqueous chlorate solution and form a perchlorate aqueous solution according to the following reaction.

In one non-limiting embodiment, the chloric acid and perchlorate are chloric acid and sodium perchlorate. This reaction is high, generally higher than about 0.5 A / cm ² , preferably higher than about 1.0 A / cm ² , more preferably 0.5 A / cm ^{2 to} 1.3 A / cm ² . Requires a current density in the range.

  The present invention includes an electrolysis cell for generating perchlorate. The electrolysis cell has an anode comprising a bismuth mixed metal oxide pyrochlore material as described above. The electrolysis cell is electrically coupled with the cathode, the chlorate aqueous solution in contact with the anode, and the anode and cathode, and oxidizes the chlorate aqueous solution at the anode to form a perchlorate aqueous solution according to the following reaction: It further comprises a source of potential and current that produces a sufficient operating current density.

  The electrolysis cell can be operated at the current density described above. The anode and cathode can be configured as described above.

  While the foregoing discussion has focused on the use of bismuth mixed metal oxide pyrochlore materials as anode materials for the electrolytic generation of ozone or perchlorate, those skilled in the art will disclose the disclosed bismuth mixed metal oxide pyrochlore materials. It will be appreciated that can be used for other electrochemical applications where a high current density electrode is required.

  These features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.

  For a better understanding of the method for obtaining the above listed and other features and advantages of the present invention, a more detailed description of the present invention, briefly described above, is presented in its specific form shown in the accompanying drawings. Provided by reference to the embodiments. The present invention will be described more specifically and in detail with reference to the accompanying drawings, since the drawings depict only typical embodiments of the present invention, and therefore should not be regarded as limiting the scope thereof. .

FIG. 1 is an X-ray diffraction pattern of a synthetic bismuth ruthenium oxide. FIG. 2 shows a rotating ring disk electrode (RRDE) for studying ozone generation. FIG. 3 is an X-ray diffraction pattern of sintered bismuth ruthenium oxide. FIG. 4 is a scanning electron micrograph (SEM) of a sintered bismuth ruthenium oxide disk. FIG. 5 is an energy dispersive X-ray spectroscopy (EDS) pattern of the bismuth ruthenium oxide sintered disk of FIG. FIG. 6 is a cyclic voltammogram of Bi ₂ Ru ₂ O ₇ disc in 5M phosphoric acid showing large anode current. FIG. 7 is a graph of Bi ₂ Ru ₂ O ₇ disc electrolysis resulting in ozone recovery on a Pt ring in 5M phosphoric acid at 10 mV / s in oxygen. FIG. 8 is an SEM image of the bismuth ruthenium oxide disk after electrolysis. FIG. 9 is an EDS of a bismuth ruthenium oxide disk after electrolysis. FIG. 10 is a schematic diagram of an ozone generator experimental configuration. FIG. 11 is a graph showing detection of O ₃ (diffused from a corona discharge ozone generator) using an Au disk in 5M H ₂ SO ₄ . FIG. 12 is a graph showing voltage, temperature, and ozone current operating performance parameters for an ozone generator using a Bi ₂ Ru ₂ O ₇ coated Pt current collector. FIG. 6 is a graph showing voltage, temperature, and ozone current operating performance parameters for an ozone generator using a Bi ₂ Ru ₂ O ₇ coated Pt current collector.

  Throughout this specification "an embodiment," "an embodiment," or similar word is included in at least one embodiment of the invention with the particular feature, structure, or characteristic described in connection with that embodiment. Means that Thus, throughout this specification, “in one embodiment”, “in one embodiment”, and similar phrases may, but need not be, all refer to the same embodiment.

  Furthermore, the described features, structures, or characteristics of the invention can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of suitable bismuth mixed metal oxide pyrochlore materials, to provide a thorough understanding of embodiments of the present invention. Those skilled in the relevant art will recognize, however, that the invention can be practiced without one or more specific details or with other methods, elements, materials, and the like. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

  The bismuth mixed metal oxide pyrochlore material is disclosed herein as a high current density electrode for electrolytic ozone and perchlorate generation. The bismuth mixed metal oxide pyrochlore material disclosed herein is suitable for producing ozone water for use as an antibacterial detergent, as an oxidant and as an insecticide in the medical, food, beverage and agriculture (MFBA) industries. A safe and effective lead-free electrode material is provided. Such ozone water can also be used in the semiconductor industry to clean electronic components. The bismuth mixed metal oxide pyrochlore materials disclosed herein can also be used in anodes for electrochemical production of perchlorate.

High current density electrode used in connection with the present invention includes a bismuth mixed metal oxide pyrochlore materials having the general formula _{A 2 B 2 O 7-x} , wherein, A is Bi, B is Ru, Ir , Rh, Sn, Ti, or Pt, and 0 ≦ x ≦ 1. The electrode can be made of a composite of a bismuth mixed metal oxide pyrochlore material and one or more noble metals selected from Pt, Ag, Au, Ru, Re, or Pd. An electrolysis cell and electrolysis method within the scope of the present invention has an anode comprising a bismuth mixed metal oxide pyrochlore material as described above. The cathode can optionally include 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 conductive material that can be used as an alternative to lead dioxide and platinum as an anode for ozone and perchlorate generation. Bi ₂ Ru ₂ O ₇ has a pyrochlore structure. It is known to show stability in acidic and basic solutions under oxidizing conditions. J. et al. M.M. Zen, R.A. Monoharan and J.M. B. Goodenough, J.A. Appl. Electrochem. 22 140 (1992). A high oxygen and chlorine generation capacity, high initial electrocatalytic activity for oxygen reduction and electrochemical oxidation of a number of organic compounds have been reported for this material. H. S. Horowitz, J. et al. M.M. Longo and H.C. H. Horowitz, J. et al. Electrochem. Soc. , 130, 1851 (1983); Praksah, A.M. K. Shukla and E.I. Yeager, J .; Power Sources, 29, 413 (1990); M.M. Markovic and P.M. N. Ross, Jr. J. et al. Electrochem. Soc. 141 2590 (1994).

  Jacobson et al. (US Pat. No. 5,105,053) describe a bismuth ruthenium oxide catalyst having a pyrochlore structure as an efficient catalyst for the conversion of hydrocarbons, most preferably methane to higher hydrocarbons and olefins. Disclosed.

  US Pat. No. 4,163,706 describes the synthesis of pyrochlore type compounds rich in high surface area bismuth containing ruthenium, iridium and mixtures thereof for use in electrochemical processes such as electrocatalysis and Disclose characteristics. U.S. Pat. No. 4,129,525 discloses lead enriched and bismaspyrochlore compounds containing ruthenium and iridium that are useful in catalytic or electrocatalytic environments. Similar disclosures are included in US Pat. Nos. 4,203,871; 4,225,469; 4,434,031; and 4,440,670.

U.S. Pat. No. 4,146,458 discloses an electrochemical device having an oxygen electrode containing a pyrochlore type material. Suitable pyrochlore materials have a high lead content and the formula _{Pb 2 [M 2-x Pb} x] O 7-y, wherein, M is Ru or Ir, 0 ≦ x ≦ 1.2 and 0 ≦ y ≦ 1.0. Bismuth ruthenium oxide is within the broad disclosure.

  Applicants are unaware of reported studies of the use or performance of this material as an anode for electrolytic ozone and perchlorate generation.

  To better describe the bismuth mixed metal oxide pyrochlore material, several exemplary embodiments of suitable manufacturing methods and electrolysis applications are described with reference to FIGS. Although other perchlorates can be produced using the bismuth mixed metal oxide pyrochlore material described, for simplicity, the following examples discuss how to produce ozone using an electrode material.

  The following non-limiting examples are provided to illustrate various embodiments within the scope of the present invention. It is understood that this example is provided for purposes of illustration only, and that the following example is not an exhaustive or complete form of the many types of embodiments of the present invention that can be generated according to the present invention.

Example 1
Synthesis of Bi ₂ Ru ₂ O ₇ . Stoichiometric amounts of Bi ₂ O ₃ and RuO ₂ xH ₂ O (the concentrations of RuO ₂ and H ₂ O were determined to be 76% and 24% by thermogravimetric analysis (TGA), respectively) Was added to and mixed into a slurry by mixing with a mortar and pestle. After 15 minutes of mixing, a homogeneous slurry was formed. The slurry was then dried in a drying oven, mixed again with a pestle and then heated at 650 ° C. for 24 hours and then at 750 ° C. for 24 hours. X-ray diffraction (XRD) was performed at each stage to measure the phase purity of the product. The XRD result is shown in FIG. The XRD data after the 750 ° C. process was in good agreement with the Joint Committee (JCPDS) reference pattern for powder diffraction standards in Bi ₂ Ru ₂ O _7.3 except for two peaks. These peaks cannot be attributed to any of the starting materials Bi ₂ O ₃ and RuO ₂ . An additional 24 hours of heating at 750 ° C. did not change the intensity of the two peaks. It was therefore concluded that these peaks could be due to either some polymorph of the starting material or the different (non-pyrochlore) phases of bismuth and ruthenium. However, this second phase represents a relatively small percentage (<10%) and is not critical.

(Example 2)
Rotating ring disk electrode for ozone analysis. Using a rotating ring disk electrode (RRDE) method, it was shown that bismuth ruthenate can function reliably as an anode in an electrolytic ozone generator. A cross-sectional side view and a bottom view of a typical RRDE device are shown in FIG. The theory behind the use of RRDE for in situ generation / detection of ozone is briefly as follows. The RRDE 100 is comprised of a central disk electrode 102 surrounded by concentric ring electrodes 104 and a thin Teflon U-cup insulator 106 separating them. The potential or current at each electrode can be controlled independently using a bipotentiostat (not shown). A bipotentiostat is two working electrodes immersed in an electrolyte, using only one reference electrode and one counter electrode, controlling the voltage and measuring the current. The RRDE shown in FIG. 2 can be used to detect and measure O ₃ generated on the RRDE disk. When the central disk electrode 102 is subjected to anodic polarization, ozone generated at the central disk electrode 102 is quantitatively detected by the ring electrode 104 held at a potential (E ° = 2.07 V vs. NHE) at which ozone is reduced. be able to. Alternatively, the ring electrode can be placed in a potential region where ozone can be reduced. Therefore, the limit ozone reduction current at the ring electrode 104 can be measured for each material according to the amount of ozone generated at the disk electrode 102. This method thus allows a comparison of the various anode materials in terms of their ability to generate ozone.

  The associated electrode reaction that occurs in RRDE is shown below.

Central disk electrode reaction:

Ring electrode reaction:

(Example 3)
Manufacture of Bi ₂ Ru ₂ O ₇ RRDE discs. The synthetic Bi ₂ Ru ₂ O ₇ product from Example 1 was mixed with an aqueous suspension of polyvinyl alcohol binder and applied to the particles with the binder. Bi ₂ Ru ₂ O ₇ material and binder were compressed into pellets and fired in air at 1100 ° C. for 24 hours. The XRD pattern of the sintered material is shown in FIG. The XRD pattern shows that the crystal structure of the sintered material is quite different from the starting material. The identity of this material phase is currently unknown. The final diameter of the pellet was ~ 0.6 mm. The pellets were further ground to the size and shape of the RRDE disc used in the RRDE configuration. The surface of the disk was also polished to make the surface even smoother. A conductive silver paint was applied on the back side of the disk and cured at 700 ° C. This was done to ensure good electrical contact between the RRDE metal spring and the mixed metal oxide disk. Scanning electron micrographs (SEM) and energy dispersive X-ray spectroscopy (EDS) analyzes were performed on the disks. The SEM data recorded in FIG. 4 shows that the surface of the disk has significant porosity formed during the sintering process. The EDS data recorded in FIG. 5 shows no additional elements other than the expected Bi, Ru and O.

Example 4
Cyclic voltammetry. Cyclic voltammetry (CV) of the disk produced in Example 3 was performed in 5M H ₃ PO ₄ under an oxygen atmosphere. The CV data recorded in FIG. 6 shows that oxygen evolution starts with an anodic polarization potential of> 1.5 V, and a large current is obtained at a higher potential as in the case of Pt and Pb disks. The material was also quite active in terms of hydrogen evolution when cathodic polarized. Constant potential electrolysis at 4V showed that Bi ₂ Ru ₂ O ₇ maintained a current density of 1.5 A / cm ² for up to 1 hour without decay. EDS analysis on the residue removed by filtering the electrolyte showed no Bi or Ru peaks. Long-term electrolysis experiments are required to generate more soluble species for chemical analysis.

(Example 5)
Constant potential. The constant potential electrolysis experiment was performed with the Bi ₂ Ru ₂ O ₇ disk electrode prepared in Example 3. The disk electrode was kept at 4 V (potential was predetermined so that the disk current was ~ 1.5 A / cm ² ), ozone was generated, and then recovered with a ring. The ring potential was placed in an ozone reduction potential window of 0.5-1.2V. FIG. 7 shows the CV of the ring during disk electrolysis. When the disk was electrolyzed, there was a large ring current for ozone reduction, indicating that ozone was generated in the disk. The CV of the ring before and after electrolysis did not show such cathode current due to ozone reduction. Since no cathodic current was seen on the ring after electrolysis, the ozone generated during electrolysis is believed to be due to the current rather than any soluble species formed by decomposition of the Bi ₂ Ru ₂ O ₇ disk.

Some amount of disk physical decomposition was confirmed during long-term gas evolution and could be recognized by a small amount of solids at the bottom of the cell. A scanning electron micrograph (SEM) image of the disc after electrolysis showed that only a small portion of the electrode was lost from the surface as shown in FIG. EDS analysis showed the presence of Ag on the surface as shown in FIG. This unexpected result may be due to the porosity of the sintered disk. It is possible that the electrolyte has penetrated the disk and has reached the silver applied on the back side. Based on these results, the Bi ₂ Ru ₂ O ₇ disc is considered suitable for ozone generation. RRDE experiments have confirmed that bismuth ruthenium oxide (Bi ₂ Ru ₂ O ₇ ) can be successfully used as an anode material for the electrolysis of ozone.

The generation of ozone by electrolysis of the constituent water of the ozone generator is well documented and several experimental configuration variations are known. A schematic diagram of the experimental setup 200 used in the tests reported herein is shown in FIG. The structure used the soft water produced | generated by letting a tap water pass through a commercially available soft water apparatus. The soft water source 202 continuously supplied the soft water 204 to the electrolysis cell 206. The flow rate of water 204 was changed as desired. A current of 30 A (1.5 A / cm ² ) was applied to the cell 206. Oxygen / ozone-containing water 208 exited the anode compartment and was separated in the gas-liquid separator 210. The water supply recovered from the gas-liquid separator was discharged 212. The gaseous mixture 214 was then diffused into a rotating ring disk electrode (RRDE) cell 216 containing 5M phosphoric acid and analyzed for ozone concentration in ozone water. The flow rate of the gaseous mixture generated, the cell temperature and the voltage were measured. All elements shown in FIG. 10 are made of Teflon or titanium.

  A cell 206 in which water is electrolyzed is divided into an anode compartment and a cathode compartment by a cation exchange membrane Nafion 117 (trademark), and the two compartments are separated. The anode and cathode were pressed tightly on both sides of the ion exchange membrane to form a zero gap cell. Bismuth ruthenium oxide coated Ti mesh was used as anode, Nafion 117 with Pt deposited on one surface as electrolyte, and bare Ti mesh as cathode (bare Ti mesh was in contact with Pt deposition surface of Nafion film) Was).

  The concentration of generated ozone was measured using the RRDE method. The theory behind the use of RRDE for the detection of ozone is briefly as follows. RRDE is composed of gold disk electrodes. The electrode is rotated at an ultra high speed. This rotational motion creates a clear flow of solution to the surface of the rotating disk electrode. The flow pattern is literally like a vortex that entrains a solution (containing dissolved ozone) towards the electrode. The potential of the disk is controlled by a potentiostat and is slowly reciprocated between oxygen and hydrogen generation. When cathodic polarization of the disk, ozone present in the solution can be quantitatively detected with a disk electrode held at a potential at which ozone is reduced. Alternatively, the disc is placed in a potential region where ozone can be reduced. Therefore, the limit ozone reduction current can be measured according to the amount of ozone present in the electrolyte. Thus, this method allows a comparison of different ozone generators for their ozone generation capacity.

(Example 6)
Effectiveness of the RRDE method. To demonstrate the effectiveness of the RRDE analysis method, we saturated the solution with ozone using an external ozone generating device (corona discharge ozone generator), and performed cyclic voltammetry (CV) of the Au disk after ozonization. . FIG. 11 shows that ozone is 1.0 V vs.. It shows that the cathode potential is reduced by gold RRDE from SCE. FIG. 11 shows that oxygen reduction at the ring is about 0.6 V vs. room temperature. Indicates start with SCE. The presence of ozone causes a reduction current at a cathode potential from 1.3 V, and a limit current region of 0.2 V to 1.0 V can be measured. Simultaneous reduction of ozone and oxygen occurs at cathodic potentials from 0.2V. The main conclusion from FIG. 11 is that ozone can be clearly detected at a potential between 0.2V and 1.0V and the ozone reduction limit current can be observed within these ranges. These results are consistent with other RRDE studies. The critical ozone reduction current is a direct indicator of the amount of ozone present in the solution.

(Example 7)
Manufacture of anodes for ozone generators. This was done by first producing the ink with a synthetic Bi ₂ Ru ₂ O ₇ material produced according to Example 1. An equal amount (by weight) of Bi ₂ Ru ₂ O ₇ material and 5 wt% Nafion solution (Aldrich) were mixed thoroughly to form an ink. Ink was applied to the Pt anode current collector using a brush. The coating was dried in an oven for 1 hour at 130 ° C. to remove all organics from the Nafion solution. Multiple coatings were applied by this method to produce a uniform coating of Bi ₂ Ru ₂ O ₇ material on the Pt substrate. The coated anode was rehydrated by soaking in distilled water overnight.

(Example 8)
Operation of an ozone generator with a bismuth ruthenium oxide anode. A Bi ₂ Ru ₂ O ₇ coated Pt anode current collector prepared according to Example 7 was used as the anode in an ozone generator instead of Pt or PbO ₂ . The performance of the Bi ₂ Ru ₂ O ₇ cell is shown in FIG. The initial ozone current is 70 μA (compared to 80 μA recorded with a similarly constructed and operated PbO ₂ cell). However, the ozone current decreased to about 30 μA in about 2 hours. The cause of this sudden drop in ozone current may be due to (1) loss of Bi ₂ Ru ₂ O ₇ material, (2) clogging of the Nafion film or (3) loss of contact between the coating and the current collector.

A platinum anode current collector was used as the substrate for the bismuth ruthenium oxide coating in the above experiment. Ozone can be generated by a platinum anode current collector rather than a bismuth ruthenium oxide material. To prove that this was not the case, Bi ₂ Ru ₂ O ₇ material was applied as an anode onto a Ti mesh over a Pt anode current collector. First, a cell was made with a bare titanium mesh over a Pt anode current collector. The cell could not be operated in this configuration (the 30 A current could not be maintained). Cells were then made with Bi ₂ Ru ₂ O ₇ material coated Ti mesh instead of bare Ti mesh. The cell can now be activated and the data obtained is shown in FIG. It was recorded that the initial ozone current of 13 μA reached 23 μA after about 1 hour of operation and gradually decreased to 17 μA after about 4.5 hours of operation. The fact that ozone was generated in this experiment indicates that it involves Bi ₂ Ru ₂ O ₇ material rather than a Pt anode current collector. The cell voltage and temperature were stable at 13.5 V and 33 ° C., respectively. These values are higher than those recorded for experiments using a Bi ₂ Ru ₂ O ₇ material coated Pt anode current collector as the anode. This may be due to an increase in interfacial resistance when using a Ti mesh.

The foregoing experiment shows that ozone can be generated by a Bi ₂ Ru ₂ O ₇ pyrochlore anode in an ozone generator. While the examples focused on Bi ₂ Ru ₂ O ₇ as one electrode material suitable for electrolytic ozone generation, the present invention is not limited to Bi ₂ Ru ₂ O ₇ . Other Bi-based pyrochlores including Ir, Sn, Rh, Pt and Ti can also potentially be used and are within the scope of the disclosed invention. These bismuth spirochlore materials are attractive electrode materials for electrolytic ozone or perchlorate generation.

  While specific embodiments and examples of the invention have been shown and described, many modifications can be made without significantly departing from the spirit of the invention, and the scope of protection is limited only by the appended claims. .

Claims (27)

Providing an electrolytic cell having an anode comprising a bismuth mixed metal oxide pyrochlore material having the general formula A ₂ B ₂ O _7-x , wherein A is Bi and B is Ru, Ir, Rh, An electrolysis method for generating ozone, comprising: Sn, Ti, or Pt, wherein 0 ≦ x ≦ 1, and operating the electrolysis cell anode at a current density sufficient to generate ozone. The process according to claim 1, wherein the generation of ozone is achieved according to the reaction: 3H ₂ O → O ₃ + 6H ⁺ + 6e ⁻ . The method of claim 1, wherein the electrolysis cell anode is operated at a current density greater than about 1 A / cm ² . The method of claim 1, wherein the electrolysis cell anode is operated at a current density greater than about 1.2 A / cm ² . The method of claim 1, wherein the electrolysis cell anode is operated at a current density greater than about 1.4 A / cm ² . The method of claim 1, wherein the electrolysis cell anode is operated at a current density greater than about 1.5 A / cm ² .   The method of claim 1, wherein B is Ru.   The method of claim 1, wherein the electrolysis cell has a cathode comprising a bismuth mixed metal oxide pyrochlore material.   The method of claim 1, wherein the anode comprises a composite of a bismuth mixed metal oxide pyrochlore material and one or more noble metals selected from Pt, Ag, Au, Ru, Re, and Pd. An anode comprising a bismuth mixed metal oxide pyrochlore material having the general formula A ₂ B ₂ O _7-x , wherein A is Bi and B is Ru, Ir, Rh, Sn, Ti, or Pt Yes, 0 ≦ x ≦ 1, anode;
Cathode;
Electrolyzed water in contact with the anode and the cathode; and a source of potential and current that is electrically coupled to the anode and the cathode and generates a working current density sufficient to generate ozone at the anode; Electrolytic cell for generating ozone. The electrolysis cell according to claim 10, wherein the generation of ozone is achieved according to the reaction: 3H ₂ O → O ₃ + 6H ⁺ + 6e ⁻ . The electrolysis cell of claim 10, wherein the electrolysis cell anode is operated at a current density greater than about 1 A / cm ² . The electrolysis cell of claim 10, wherein the electrolysis cell anode is operated at a current density greater than about 1.2 A / cm ² . The electrolysis cell of claim 10, wherein the electrolysis cell anode is operated at a current density greater than about 1.4 A / cm ² . The electrolysis cell of claim 10, wherein the electrolysis cell anode is operated at a current density greater than about 1.5 A / cm ² .   The electrolysis cell according to claim 10, wherein B is Ru.   The electrolysis cell of claim 10, wherein the electrolysis cell has a cathode comprising a bismuth mixed metal oxide pyrochlore material.   The electrolysis cell of claim 10, wherein the anode comprises a composite of a bismuth mixed metal oxide pyrochlore material and one or more noble metals selected from Pt, Ag, Au, Ru, Re, and Pd. Providing an electrolytic cell having an anode comprising a bismuth mixed metal oxide pyrochlore material having the general formula A ₂ B ₂ O _7-x , wherein A is Bi and B is Ru, Ir, Rh, Sn, Ti, or Pt, where 0 ≦ x ≦ 1, and the electrolytic cell anode is operated at a current density sufficient to oxidize the aqueous chlorate solution and form the aqueous perchlorate solution And an electrolysis method for generating perchlorate. The method of claim 19, wherein the electrolysis cell anode is operated at a current density greater than about 1 A / cm ² .   20. A method according to claim 19, wherein B is Ru.   The method of claim 19, wherein the electrolysis cell has a cathode comprising a bismuth mixed metal oxide pyrochlore material.   20. The method of claim 19, wherein the anode comprises a composite of a bismuth mixed metal oxide pyrochlore material and one or more noble metals selected from Pt, Ag, Au, Ru, Re, and Pd. An anode comprising a bismuth mixed metal oxide pyrochlore material having the general formula A ₂ B ₂ O _7-x , wherein A is Bi and B is Ru, Ir, Rh, Sn, Ti, or Pt Yes, 0 ≦ x ≦ 1, anode;
Cathode;
An aqueous chlorate solution in contact with the anode; and an electrical coupling with the anode and the cathode to oxidize the aqueous chlorate solution at the anode to produce a working current density sufficient to form an aqueous perchloric acid solution An electrolysis cell for generating perchlorate, comprising a source of electrical potential and current.   The electrolysis cell according to claim 24, wherein B is Ru.   25. The electrolysis cell of claim 24, wherein the electrolysis cell has a cathode comprising a bismuth mixed metal oxide pyrochlore material.   25. The electrolysis cell of claim 24, wherein the anode comprises a composite of a bismuth mixed metal oxide pyrochlore material and one or more noble metals selected from Pt, Ag, Au, Ru, Re, and Pd.

Images