WATER SPLITTING SYSTEM FOR HYDROGEN AND OXYGEN SEPARATION IN THE ABSENCE OF AN ION EXCHANGE MEMBRANE

Abstract

Systems and processes for the production of hydrogen (H2) gas and oxygen (O2) gas from an aqueous electrolyte solution are described. A water-splitting system can include a reactor that includes H2 and O2 generating chambers that can be separate chambers but are not separated by a H2 and/or O2 gas permeable material. The H2 generating chamber can include a cathode and at least a first fluid inlet. The O2 generating chamber can include an anode in electrical communication with the cathode and at least a first fluid inlet. The first and second fluid inlets can each be configured to receive a purged electrolyte solution, a purge gas, or a mixture thereof.

Claims

1. A water-splitting system for the production of hydrogen (H.sub.2) gas and oxygen (O.sub.2) gas from an aqueous electrolyte solution, the system comprising: a reactor comprising: a H.sub.2 generating chamber comprising a cathode and at least a first fluid inlet fluidly coupled to a purged electrolyte source, a purge gas source, or a combination thereof; an O.sub.2 generating chamber comprising an anode in electrical communication with the cathode and at least a first fluid inlet fluidly coupled to the purged electrolyte source, the purge gas source, or a combination thereof, and a fluid mover for moving degassed electrolyte solution to the H.sub.2 generating chamber electrolyte inlet and the O.sub.2 generating chamber inlet via degassed electrolyte solution outlet and piping; wherein the piping fluidly couples the H.sub.2 generating chamber with the O.sub.2 generating chamber, and wherein the H.sub.2 and O.sub.2 generating chambers are coupled by one or more apertures.

2. The water-splitting system of claim 1, wherein the H.sub.2 or O.sub.2 gas permeable material is a membrane.

3. The water-splitting system of claim 1, further comprising a H.sub.2 reservoir fluidly coupled to the H.sub.2 generating chamber, the purged electrolyte source and an H.sub.2 product outlet.

4. The water-splitting system of claim 3, further comprising a H.sub.2 purification system, fluidly coupled to the H.sub.2 product outlet.

5. The water-splitting system claim 1, further comprising an O.sub.2 reservoir fluidly coupled to the O.sub.2 generating chamber, the purged electrolyte source, and an O.sub.2 product outlet.

6. The water-splitting system of claim 5, further comprising an O.sub.2 purification system, fluidly coupled to the O.sub.2 product outlet.

7. The water-splitting system of claim 1, wherein purged electrolyte source is fluidly coupled to the purge gas source.

8. The water-splitting system of claim 1, wherein the first fluid inlets are fluidly coupled to the purged electrolyte source, and wherein the H.sub.2 generating chamber further comprises a second inlet and/or the O.sub.2 generating chamber further comprises a second inlet, each second inlet fluidly coupled to the purge gas source.

9. (canceled)

10. The water-splitting system of claim 1, further comprising a conduit coupled to the H.sub.2 generating chamber and the O.sub.2 generating chamber, the conduit comprising a first aperture coupled to the H.sub.2 generating chamber and a second aperture coupled to the O.sub.2 generating chamber.

11. The water-splitting system of claim 1, wherein the anode and the cathode are comprised in a H.sub.2 and/or O.sub.2 gas impermeable material positioned at least partially between the H.sub.2 generating chamber and the O.sub.2 generating chamber.

12-15. (canceled)

16. A water-splitting process for the production of hydrogen (H.sub.2) gas and oxygen (O.sub.2) gas, the process comprising: (a) providing an electrolyte solution to each of the H.sub.2 generating chamber and the O.sub.2 generating chamber of the water-splitting system of claims 1 to 8 and 10 to 11, the electrolyte solution comprising water, a purge gas, and an electrolyte; (b) subjecting the electrolyte solution in the H.sub.2 generating chamber and the electrolyte solution in the O.sub.2 generating chamber to conditions sufficient to produce a H.sub.2 containing electrolyte solution in the H.sub.2 generating chamber and an O.sub.2 containing electrolyte solution in the O.sub.2 generating chamber, wherein at least a portion of the generated H.sub.2 is dissolved in the H.sub.2 containing aqueous electrolyte solution, and at least a portion of the generated O.sub.2 is dissolved in the O.sub.2 containing electrolyte solution; and (c) subjecting the H.sub.2 containing electrolyte solution and/or the O.sub.2 containing electrolyte solution to conditions suitable to produce a purge gas containing electrolyte solution, a gaseous H.sub.2 stream, a gaseous O.sub.2 stream, or combinations thereof.

17. The process of claim 16, further comprising: providing the purge gas containing electrolyte solution to the H.sub.2 generating chamber of the water-splitting system, the O.sub.2 generating chamber of the water-splitting system, or both, wherein the purge gas containing electrolyte solution comprises H.sub.2 and O.sub.2 in a molar H.sub.2/O.sub.2 ratio under the explosion limit; and/or providing a purge gas to the H.sub.2 generating chamber, the O.sub.2 generating chamber, or both; and providing the purged electrolyte solution to the H.sub.2 generating chamber and the O.sub.2 generating chamber.

18. The process of claim 16, wherein the water-splitting conditions comprise a pressure of 0.010 MPa to 2.1 MPa, a temperature of 5 C. to 100 C., a pH of 0 to 14, or a combination thereof.

19. The process of claim 16, wherein the purge gas reduces contamination of H.sub.2 into the O.sub.2 containing aqueous electrolyte stream, O.sub.2 into the H.sub.2 containing aqueous electrolyte stream, or both.

20. The process of claim 16, wherein: step (c) comprises: (i) compressing the H.sub.2 containing aqueous electrolyte solution stream to produce a gaseous H.sub.2 stream and the electrolyte solution comprising the purge gas, or (i) collecting the H.sub.2 containing aqueous electrolyte solution stream in the H.sub.2 reservoir, the O.sub.2 containing aqueous electrolyte solution stream in the O.sub.2 reservoir or both; (ii) separating the H.sub.2 gaseous stream from the H.sub.2 containing aqueous electrolyte solution and the O.sub.2 gaseous stream from the O.sub.2 containing aqueous electrolyte solution, or both; (iii) forming an aqueous electrolyte solution comprising residual H.sub.2, O.sub.2, or both; and (iv) purging the step (iii) aqueous electrolyte solution with the purge gas to form the purge gas containing aqueous electrolyte solution; and/or step (b) further comprises flowing the a portion of the electrolyte solution between the H.sub.2 generating chamber and the O.sub.2 generating chamber through at least one of the apertures of claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0026] FIG. 1 depicts a schematic of the water-splitting system of the present invention.

[0027] FIG. 2 depicts a schematic of the water-splitting system of the present invention with a H.sub.2 reservoir and an O.sub.2 reservoir.

[0028] FIG. 3A depicts a schematic of the water-splitting system of the present invention of FIG. 1 with an aperture between the H.sub.2 generating chamber and the O.sub.2 generating chamber.

[0029] FIG. 3B depicts a schematic of the water-splitting system of the present invention of FIG. 2 with an aperture between the H.sub.2 generating chamber and the O.sub.2 generating chamber.

[0030] FIG. 4A depicts a schematic of the water-splitting system of the present invention with a H.sub.2 generating chamber and the O.sub.2 generating chamber and a H.sub.2 and O.sub.2 gas impermeable material positioned between the chambers.

[0031] FIG. 4B depicts a schematic of the water-splitting system of FIG. 4A with an aperture in the H.sub.2 and O.sub.2 gas impermeable material.

[0032] FIGS. 5A through 5D depict a (5A) front view of a stacked water-splitting reactor, (5B) back view of the stacked water-splitting reactor, (5C) gas impermeable material with anodic material, and (5D) gas impermeable material with cathodic material.

[0033] FIGS. 6A through 6D depict a (6A) front view of a stacked water-splitting reactor having a purge gas inlet, an electrolyte source inlet and a gas outlet, (6B) back view of the stacked water-splitting reactor, (6C) gas impermeable material with anodic material, (6D) gas impermeable material with cathodic material.

[0034] FIG. 7 depicts a schematic of a monolithically integrated photocatalyst catalyst configuration of the water-splitting system of the present invention.

[0035] FIGS. 8A and 8B depict schematics of photocatalyst catalyst configurations of the water-splitting system of the present invention.

[0036] FIGS. 9A and 9B are graphs of addition of H.sub.2 (FIG. 9A) and O.sub.2 (FIG. 9B) into a H.sub.2 reservoir and O.sub.2 reservoir of the system of the present invention.

[0037] FIGS. 10A and 10B are graphs of moles of H.sub.2 and O.sub.2 after injecting both separately to a H.sub.2 reservoir and O.sub.2 reservoir of the system of the present invention as a function of time.

[0038] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0039] A discovery has been made that provides a solution to the inefficiencies of water-splitting systems (e.g., PEC systems and/or an electrolysis systems). The discovery is premised on a reactor that does not require the use of a H.sub.2 and/or O.sub.2 gas permeable material such as a membrane or an ionic bridge. In lieu of such a membrane, a reactor of the present invention can provide purged electrolyte solution to a hydrogen generating chamber and an oxygen generating chamber with a minimal amount of H.sub.2 or O.sub.2 cross contamination in the respective chambers.

[0040] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to the FIGS. The systems and methods of described in FIGS. 1 to 6 can also include various equipment that is not shown and is known to one of skill in the art of chemical processing. For example, some controllers, piping, computers, valves, pumps, heaters, thermocouples, pressure indicators may not be shown.

A. Water-Splitting Systems

[0041] Referring to FIG. 1, a schematic of water-splitting system 100 of the present invention source. Water-splitting reactor 102 can include H.sub.2 generating chamber 106 and O.sub.2 generating chamber 108. In some embodiments, the chambers can receive electromagnetic radiation. In preferred instances, the electromagnetic radiation can be visible light (e.g., sunlight or artificially produced visible light) or ultraviolet radiation or a combination of the two. By way of example, reactor 102, H.sub.2 generating chamber 106, and O.sub.2 generation chamber 108 can include one or portions or sides that are transparent to light, either sunlight, or artificial light. Non-limiting examples of transparent materials include glass, quartz, organic polymers, silica-based polymers and the like. Alternatively, chamber 106 or 108 can be opaque and a light source can be placed within said chambers, affixed to the walls of said chambers, and/or built into the walls of said chambers (not shown). Reactor 102 can include a housing 110 (shown with dotted lines) that houses H.sub.2 generation chamber 106 and O.sub.2 generation chamber 108. Housing and chambers can include spacers and connectors suitable to position the chambers in the housing (See, for example FIGS. 4A-4D). In some embodiments, a portion or all of housing 110 can be transparent. In some embodiments, the chambers are aligned in a parallel configuration in the housing such that electromagnetic radiation passes through the housing, a chamber, and into the adjacent chamber. In some embodiments, a housing is not necessary and/or sides of the housing make up the sides of the chambers. As shown, H.sub.2 generating chamber 106 and O.sub.2 generating chamber 108 have four distinct sides. However, H.sub.2 generating chamber 106 and O.sub.2 generating chamber 108 can have a shared wall that is impermeable to H.sub.2 and O.sub.2 gases. In some embodiments, all or portions of the reactor 102, housing 110, H.sub.2 generating chamber 106, and O.sub.2 generation chamber 108 can be manufactured from a polymeric material (e.g., polymethylmethacrylate (PMMA)). H.sub.2 generating chamber 106 can include cathode 112 capable of reducing H.sup.+ ions in electrolyte solution 114. In some embodiments, cathode 112 is a photocatalyst capable of accepting electromagnetic radiation and catalyzing the generation of H.sub.2 from water and electrolyte solution 114. H.sub.2 generating chamber 106 can include H.sub.2 outlet 116 and electrolyte solution outlet 118. H.sub.2 outlet 116 can allow generated H.sub.2 to be removed from the H.sub.2 generating chamber and be in fluid communication with purification systems and/or collection systems (not shown). Electrolyte solution outlet 118 can be in fluid communication with electrolyte source 104 via piping 120 to allow H.sub.2 containing electrolyte solution to be removed from H.sub.2 generating chamber 106 and be provided to electrolyte source 104.

[0042] O.sub.2 generating chamber 108 can include anode 124 capable of oxidizing OH.sup. in electrolyte solution 114 to O.sub.2. In some embodiment anode 124 include a photocatalyst capable of catalyzing generation of O.sub.2 from water and electrolyte solution 114. Anode 124 and cathode 112 can be electrically coupled through circuit 126. Circuit 126 can be a wire (e.g., copper wire) that connects the two electrodes. In some embodiments, circuit 126 can include a power source to supply electricity to one or more electrons. It should be understood, that one of skill in the art can electrically connect the cathode and anode as needed depending on the chosen electrode or catalyst. O.sub.2 generating chamber 108 can include O.sub.2 outlet 128 and electrolyte solution outlet 130. O.sub.2 outlet 128 can allow generated O.sub.2 to be removed from the O.sub.2 generating chamber and be in fluid communication with purification systems and/or collection systems (not shown). Electrolyte solution outlet 130 can be in fluid communication with electrolyte source 104 via piping 132 to allow O.sub.2 containing electrolyte solution to be removed from O.sub.2 generating chamber 108 and be provided to electrolyte source 104.

[0043] Electrolyte source 104 can include electrolyte solution inlet 134, purge gas (e.g., N.sub.2, argon, inert gas, or other gases) inlet 136, and electrolyte solution outlet 138. Electrolyte solution inlet 134 can be in fluid communication with piping 120 and/or other piping that allow gas containing (e.g., H.sub.2 and/or O.sub.2) electrolyte solutions and/or fresh electrolyte solution to enter electrolyte source 104. Purge gas inlet 136 can be in fluid communication with sparging system (not shown) capable of delivering a sufficient amount of purge gas to substantially or completely remove (degas) dissolved reactive gases (e.g., H.sub.2 and/or O.sub.2), forming degassed electrolyte solution 140. In certain instances, the purge gas can be any gas that does not react with the water-splitting materials or reagents (e.g., cathode material, anode material, intermediate reactants, products, or water). Non-limiting examples of purge gas include nitrogen (N.sub.2), helium (H.sub.2), argon (Ar), carbon dioxide (CO.sub.2), hydrocarbon gases (e.g., methane, ethane, propane and butane). In a preferred embodiment, N.sub.2 is used as the purge gas. System 100 can include fluid mover 146 (e.g., a pump). Degassed electrolyte solution 140 can be moved using fluid mover 146 to H.sub.2 generating chamber electrolyte inlet 142, O.sub.2 generating chamber inlet 144, via degassed electrolyte solution outlet 138 and piping 148, 150, and 152. Piping 148, 150, and 152 can fluidly couple the H.sub.2 generating chamber with the O.sub.2 generating chamber. In some embodiments, pressure from purge gas entering inlet 136 is sufficient to move the electrolyte solution to the various chambers. Removing the H.sub.2 and O.sub.2 from the electrolyte solution can minimize or inhibit cross-contamination of H.sub.2 into the O.sub.2 generating chamber and/or O.sub.2 into the H.sub.2 generating chamber. Such cross contamination can cause formation of water molecules from reactions of H.sup.+ and or OH.sup. with the generated O.sub.2, H.sub.2 respectively. The reactive gas mixture can be removed from the electrolyte source via reactive gas outlet 154. Reactive gas mixture can be a mixture of H.sub.2, O.sub.2 and purge gas and have a molar H.sub.2 to O.sub.2 ratio under the flammability limit. Reactive gas outlet 154 can be in fluid communication with a collection unit, purification unit, transportation line, or the like. In some embodiments, system 100 is an electrolysis system or a photoelectrochemical system.

[0044] In some embodiments, the water-splitting system includes a H.sub.2 reservoir and an O.sub.2 reservoir fluidly coupled to the electrolyte source and the H.sub.2 generating chamber and the O.sub.2 generating chamber. Inclusion of H.sub.2 and O.sub.2 reservoirs can allow for separation of the H.sub.2 gas and/or O.sub.2 gas from the H.sub.2 and O.sub.2 containing electrolyte solutions prior to the electrolyte solution entering electrolyte source 104. Referring to FIG. 2A a schematic of water-splitting system 200 of the present invention is depicted that includes H.sub.2 collection unit (reservoir) 202 and O.sub.2 collection unit (reservoir) 204. Although FIG. 2A depicts both reservoirs, it should be understood that one reservoir could be used (e.g., a H.sub.2 reservoir and no O.sub.2 reservoir or vice versa). System 200 shown in FIG. 2 includes water-splitting reactor 102, electrolyte source 104 and other components of FIG. 1. H.sub.2 reservoir 202 can be in fluid communication with H.sub.2 generating chamber 106 of reactor 102 via H.sub.2 outlet 116, piping 206, and reservoir H.sub.2 inlet 208. As H.sub.2 is generated in H.sub.2 generation chamber 106, a mixture of electrolyte solution with dissolved and free H.sub.2 can exit the H.sub.2 generation chamber and enter H.sub.2 reservoir. In H.sub.2 reservoir 202, aqueous electrolyte droplets can separate from the gaseous H.sub.2. In some embodiments, the purge gas can enter H.sub.2 generating chamber through inlet 142 or through a second inlet (not shown) and purge or sweep gaseous H.sub.2 from H.sub.2 generating chamber 106 into the H.sub.2 reservoir 202. Addition of the purge gas into H.sub.2 generating chamber 106 can saturate the cathode with purge gas and inhibit H.sup.+ ions present to combine with any OH.sup. present to form H.sub.2O. Gaseous H.sub.2 can exit H.sub.2 reservoir 202 via H.sub.2 outlet 210 and be in fluid communication with H.sub.2 permeable membrane 212 via piping 214. Membrane 212 can be a H.sub.2 permeable membrane capable of separating H.sub.2 from the purge gas and trace amounts of O.sub.2.

[0045] O.sub.2 reservoir 204 can be in fluid communication with O.sub.2 generating chamber 108 of reactor 102 via O.sub.2 outlet 128, piping 218, and reservoir O.sub.2 inlet 220. As O.sub.2 is generated in O.sub.2 generation chamber 108, a mixture of electrolyte solution with dissolved and free O.sub.2 can exit the O.sub.2 generation chamber and enter O.sub.2 reservoir. In O.sub.2 reservoir 204, aqueous electrolyte droplets separate from the gaseous O.sub.2. In some embodiments, the purge gas can enter O.sub.2 generating chamber 108 through inlet 144 or a second inlet (not shown) and purge or sweep gaseous O.sub.2 from O.sub.2 generating chamber 108 into O.sub.2 reservoir 204. Addition of the purge gas into O.sub.2 generating chamber 106 can saturate the anode with purge gas and inhibit OH-ions present to combine with any H.sup.+ present to form H.sub.2O. Gaseous O.sub.2 can exit O.sub.2 reservoir 204 via O.sub.2 outlet 222 and be in fluid communication with O.sub.2 permeable membrane 224 via piping 226. Membrane 224 can be an O.sub.2 permeable membrane capable of separating O.sub.2 from the purge gas and/or trace amounts of H.sub.2.

[0046] H.sub.2 reservoir 202 and O.sub.2 reservoir 204 can be in fluid communication with electrolyte source inlet 146 via piping 228 and 230, respectively. Electrolyte source 104 can receive electrolyte solution from H.sub.2 reservoir 202, O.sub.2 reservoir 204, or both. Such an electrolyte solution can have dissolved H.sub.2 and O.sub.2 in the solution. The dissolved H.sub.2 and O.sub.2 can be removed from the electrolyte solution to produce a degassed electrolyte solution that can be returned to H.sub.2 generating chamber and O.sub.2 generating chamber via piping 146, 148 and 150 as described for system 100.

[0047] In some embodiments, the H.sub.2 generating chamber and the O.sub.2 generating chamber can be in direct fluid communication with each other. By way of example, the two chambers can include an aperture that connects the two chambers. The aperture can be any size or shape (e.g., parabolic, circular, elliptical, trapezoid, parallelogram, square, rectangular, polygonal, or the like). The aperture can be sized to be sufficient to allow mass transport of ions (H.sup.+) and (OH.sup.) at a rate sufficient to sustain a water-splitting reaction. Such sizing can be determined by known engineering methods depending on the size of the reactor. FIG. 3A depicts system 300 that includes the water-splitting system of FIG. 1 having the H.sub.2 generating chamber directly coupled with O.sub.2 generating chamber via an aperture. FIG. 3B system 300 that includes the water-splitting system of FIG. 2 having the H.sub.2 generating chamber directly coupled with O.sub.2 generating chamber via an aperture. In FIGS. 3A and 3B, a first aperture 302 and a second aperture 304 are included in conduit 306. In some embodiments, first aperture 302 and second aperture 304 can be a single hole or a plurality of holes (e.g., a screen). Fluid can equilibrate between the two chambers so that the solutions remain pH neutral. As shown the aperture(s) are positioned at the lower portion of the chambers. Such a positioning can allow for minimal amount of cross-contamination of H.sub.2 and O.sub.2 in the respective chambers as H.sub.2 and O.sub.2 have low solubility in water and upward in the solution to H.sub.2 outlet/electrolyte solution 116 and O.sub.2 outlet/electrolyte solution 130. The exact positioning of aperture(s) within the lower portion of the chambers can be modified as desired and they can be placed in the lower half of the side walls of the chambers relative to the height of each chamber. In preferred instances, the apertures 302 and 303 and conduit 306 can be placed in the side walls of the chamber proximate to the bottom of the chambers. In some embodiments, apertures 302 and 304 can include covers (not shown) that can cover the apertures during use. By way of example, the apertures can be covered when cross-contamination of O.sub.2 is detected in the H.sub.2 generating chamber or cross-contamination of H.sub.2 is detected in the O.sub.2 generating chamber. In some embodiments, the covers can be electronically controlled. In system 100 of FIGS. 3A and 3B, circuit 126 can be connected through conduit 302 (not shown) instead of outside the reactor.

[0048] In some embodiments of the present invention, the water-splitting system includes a H.sub.2 and/or O.sub.2 impermeable material. Referring to FIGS. 4A and 4B, a schematic of water-splitting reactor 102 having H.sub.2 generating chamber 106, O.sub.2 generating chamber 108, and H.sub.2 and/or O.sub.2 impermeable material 402 positioned between the two chambers. Referring to FIG. 4B, impermeable material 402 includes aperture 404 that allows H.sub.2 generating chamber and O.sub.2 generating chamber to be fluidly coupled. As discussed for FIG. 3B, aperture can be a hole or a plurality of holes that allows transport of ions into each chamber. Reactor 102 of system 400 can be coupled to electrolyte source 104, H.sub.2 reservoir 202, O.sub.2 reservoir 204 as described in FIGS. 1, 2, 3A and 3B. FIGS. 4A and 4B H.sub.2 and/or O.sub.2 impermeable material 302 can be made of the same materials as H.sub.2 generating chamber 106, O.sub.2 generating chamber 108, and/or housing 110. In some embodiments, H.sub.2 or O.sub.2 impermeable material is an inner wall of both chambers. A portion of the surface of H.sub.2 or O.sub.2 impermeable material 302 in the H.sub.2 generating chamber can include the cathode and/or a photocatalyst capable of generating H.sub.2 from water. In some embodiments, the cathode material and/or the photocatalyst can be deposited on the surface or coated on the surface of the impermeable material. The opposite surface of H.sub.2 or O.sub.2 impermeable material 302 in the O.sub.2 generating chamber can be include the anode and/or photocatalyst capable of generating O.sub.2 from water. In some embodiments, the anode and/or photocatalyst can be deposited on the surface or coated on the surface of the impermeable material. In some embodiments, circuit 126 is not necessary. H.sub.2 and O.sub.2 generated in their respective chambers can be captured as previously described. The electrolyte solution from the chambers can be in fluid communication with the electrolyte source as previously described.

[0049] In some embodiments, the water-splitting system of the present invention can have a stacked configuration as shown in FIGS. 5A-5D. FIG. 5A is a front view of the stacked water-splitting reactor of the present invention that includes H.sub.2 generating chamber 106, electrolyte inlet 142, and H.sub.2/electrolyte solution outlet 116. FIG. 5B is a back view of a stacked water-splitting reactor that includes O.sub.2 generating chamber 108, electrolyte inlet 138, and O.sub.2/electrolyte solution outlet 128. Gas impermeable material 302 can be positioned between the two chambers and can include a cathode material and/or photocatalyst (e.g., 112) and an anode material and/or photocatalyst (e.g., 124) as shown in FIGS. 5C and 5D. Cathode material 112 can be in fluid communication with electrolyte solution flowing into inlet 142. Cathode material 124 can be in fluid communication with electrolyte solution flowing into inlet 138. Spacers 502 and 504 can be positioned between the gas impermeable material and the H.sub.2 generating chamber and the O.sub.2 generating chamber, respectively. As shown, reactor 102 includes transparent region 506 allows light to be transmitted through the cell to the photocatalysts. The reactor can be any suitable size for performing a water-splitting reaction. In one embodiment, the reactor can be 10 cm4.8 cm4.9 cm. The volume ratio of the H.sub.2 generating chamber 106 and the volume of O.sub.2 generating chamber 108 to the H.sub.2 and O.sub.2 reservoir 202 and 204, and the electrolyte reservoirs 104 can be 1:90:20 to 1:100:30, or 1:95:25, or any ratio there between.

[0050] In some embodiments, the water-splitting system of the present invention can have a reactor having a stacked configuration that includes inlets for purge gas and electrolyte solution and outlets for H.sub.2 containing electrolyte solution and O.sub.2 containing electrolyte solution as shown in FIGS. 5A-5D. FIG. 5A is a front view of the stacked water-splitting reactor of the present invention that includes H.sub.2 generating chamber 106, electrolyte inlet 142, H.sub.2/electrolyte solution outlet 116, and purge gas inlet 502. FIG. 5B is a back view of a stacked water-splitting reactor O.sub.2 generating chamber 108, electrolyte inlet 138, and O.sub.2/electrolyte solution outlet 128. In some embodiments, H.sub.2 generating chamber 106 include electrolyte inlet 142 and H.sub.2/electrolyte solution outlet 116, and purge gas inlet 502 and O.sub.2 generating chamber 108 includes electrolyte inlet 138, O.sub.2/electrolyte solution outlet 128, and purge gas inlet 502. In another embodiment, both chambers include the purge gas inlet 602. Gas impermeable material 302 can be positioned between the two chambers and includes a cathode material and/or photocatalyst (e.g., catalyst 112) and an anode material and/or photocatalyst (e.g., catalyst 124) as shown in FIGS. 6C and 6D. Cathode material 112 can be in fluid communication with electrolyte solution flowing into inlet 142. Cathode material 124 can be in fluid communication with electrolyte solution flowing into inlet 138. Spacers 502 and 504 can be positioned between the gas impermeable material and the H.sub.2 generating chamber and the O.sub.2 generating chamber, respectively. As shown, reactor 102 includes transparent region 506 allows light to be transmitted through the cell to the photocatalysts.

B. Materials

[0051] 1. Polymeric Materials

[0052] As discussed above, the systems of the present invention can be made from transparent or opaque polymeric materials. Non-limiting examples of polymeric materials include thermoset and thermoplastic materials. The polymeric material can include a thermoplastic polymer, such as, for example, polyethylene terephthalate, polycarbonate (PC), polybutylene terephthalate (PBT), poly(1,4-cyclohexylidene cyclohexane-1,4-dicarboxylate) (PCCD), glycol-modified polycyclohexyl terephthalate (PCTG), poly(phenylene oxide) (PPO), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or polyetherimide (PEI) or a derivative thereof, a thermoplastic elastomer (TPE), a terephthalic acid (TPA) elastomer, poly(cyclohexanedimethylene terephthalate) (PCT), polyethylene naphthalate (PEN), a polyamide (PA), polystyrene sulfonate (PSS), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), acrylonitrile butyldiene styrene (ABS), polyphenylene sulfide (PPS), a copolymer thereof, or a blend thereof. The polymeric material can comprise a thermoset material, such as, for example, an unsaturated polyester resin, a polyurethane, bakelite, duroplast, urea-formaldehyde, diallyl-phthalate, epoxy resin, an epoxy vinylester, a polyimide, a cyanate ester of a polycyanurate, dicyclopentadiene, a phenolic, a benzoxazine, a co-polymer thereof, or a blend thereof. In a preferred embodiments, the entire or portions of the PEC system is made from PMMA.

[0053] Polycarbonate polymers suitable for use in the present disclosure can have any suitable structure. For example, such a polycarbonate polymer can include a linear polycarbonate polymer, a branched polycarbonate polymer, a polyester carbonate polymer, or a combination thereof. Such a polycarbonate polymer can include a polycarbonate-polyorganosiloxane copolymer, a polycarbonate-based urethane resin, a polycarbonate polyurethane resin, or a combination thereof.

[0054] Such a polycarbonate polymer can include an aromatic polycarbonate resin. For example, such aromatic polycarbonate resins can include the divalent residue of dihydric phenols bonded through a carbonate linkage and can be represented by the formula:

##STR00001##

where Ar is a divalent aromatic group. The divalent aromatic group can be represented by the formula: Ar.sub.1YAr.sub.2, where Ar.sub.1 and Ar.sub.2 each represent a divalent carbocyclic or heterocyclic aromatic group having from 5 to 30 carbon atoms (or a substituent therefor) and Y represents a divalent alkane group having from 1 to 30 carbon atoms. For example, in some embodiments, Ar.sub.1YAr.sub.2 is Ar.sub.1C(CH.sub.3)Ar.sub.2, where Ar.sub.1 and Ar.sub.2 are the same. As used herein, carbocyclic means having, relating to, or characterized by a ring composed of carbon atoms. As used herein, heterocyclic means having, relating to, or characterized by a ring of atoms of more than one kind, such as, for example, a ring of atoms including a carbon atom and at least one atom that is not a carbon atom. Heterocyclic aromatic groups are aromatic groups having one or more ring nitrogen, oxygen, or sulfur atoms.

[0055] In some embodiments, Ar.sub.1 and Ar.sub.2 can each be substituted with at least one substituent that does not affect the polymerization reaction. Such a substituent can include, for example, a halogen atom, an alkyl group having from 1 to 10 carbon atoms, an alkoxy group having from 1 to 10 carbon atoms, a phenyl group, a phenoxy group, a vinyl group, a cyano group, an ester group, an amide group, or a nitro group.

[0056] Aromatic polycarbonate resins suitable for use in the present disclosure can be commercially available, such as, for example, Lexan HF1110, available from SABIC Innovative Plastics (U.S.A.), or can be synthesized using any method known by those skilled in the art. Polycarbonate polymers for use in the present disclosure can have any suitable molecular weight; for example, an average molecular weight of such a polycarbonate polymer can be from approximately 5,000 to approximately 40,000 grams per mol (g/mol).

[0057] 2. Electrolyte Solution

[0058] The electrolyte solution can be an aqueous solution that has a pH of 0 to 14. In some embodiments, the electrolyte solution is a buffer solution have a pH of 6 to 7.5, or greater than, equal to, or between any two of 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7.0, 7.1, 7.2, 7.3, 7.4 and 7.5. The amount of electrolyte solution can be varied to fit the system. In some embodiments, an amount of electrolyte in the H.sub.2 and O.sub.2 reservoirs is minimal. By way of example, the amount of electrolyte is at least 5 vol % of the total volume of the reservoirs. In some embodiments, the amount of electrolyte solution in the reactor is 5 to 100% of the volume of the reactor. The electrolyte solution can be an aqueous solution of inorganic salts. The inorganic salts can have positive (K.sup.+, Na.sup.+, NH.sub.4.sup.+, Ca.sup.2+) and negative (NO.sub.3.sup., SO.sub.4.sup.2, PO.sub.4.sup.3, H.sub.2PO.sub.4.sup., HPO.sub.4.sup.2) ions that do not involve any kind of redox reaction under water oxidation condition in order to avoid possible redox reaction except pure water splitting reaction. Non-limiting examples of buffer solutions include phosphonium salts, sulfate salts, carbonate salts, and mixtures thereof.

[0059] 3. Anode, Cathode, and Photocatalysts

[0060] Any anode or cathode material known for water-splitting reactions can be used. Non-limiting examples of anode material include metal oxides. Non-limiting examples of cathode material include metals or metal alloys. The metal oxide and metals can include platinum (Pt), cobalt (Co), molybdenum (Mo), nickel (Ni), iron (Fe, tungsten (W), tin (Sn), ruthenium (Ru), irdium (Ir), copper (Cu), manganese (Mn), chromium (Cr), zinc (Zn), cerium (Ce), lanthanum (La) or oxides, or alloys thereof. Non-limiting examples of oxygen evolution catalysts include Ir, Ru, Co, Co/phosphorus (P), CoFe, Cu, Fe, FeMn, Ni, NiCe, NiCo, NiCr, NiFe, NiCe, NiCeCoCe, NiLa, NiMoFe, NiSn, NiZn, or oxides thereof, or combinations thereof. Non-limiting examples of hydrogen evolution catalysts can include, Pt, Co, CoMo, CoNiFe, Fe, FeMo, Mo/sulfur (S), Ni, NiCo, NiFe, NiMo, NiMoC, NiMoFe, NiSn, NiW, or combinations thereof.

[0061] The photocatalysts useful in the present invention is suitable to generate H.sub.2 and O.sub.2 from water. By way of example, Z-scheme catalysts using two different semiconductor materials. In a preferred embodiment, the anodic catalyst can include metal oxides and the cathodic catalyst can include metal/metal alloy. Non-limiting examples semiconductor materials include strontium (Sr), titanium (Ti), Co, and thallium (Tl), and arsenic (As). Dopants such as phosphorous (P), sulfur (S) and barium (Ba) can be added. Non-limiting examples of semiconductor-type catalysts include SrTiO.sub.3, BaTiO.sub.3, GaN, CoPS, GaAs, GaAs/InGaP, NiMo/GaAs, InGaP/TiO.sub.2Ni, or combinations thereof. The photocatalysts can have layers of metals, metal oxides, and other materials of various thicknesses (e.g., 1 nm to 300 microns or any value there between. For example, a cathodic photocatalyst can include a bottom Ga layer, a InGaAs layer, a Tl layer, backsurface field layer (BSF), two InGaAs layers, an InGaP layer, a Tl layer, a BSF layer, two InGaP layers, an AlInP layer, and a top layer of InGaAs. In another example, an anodic photocatalyst can include be a p-n junction type catalyst that can include a GaAs layer on a support with InAlP layer, InGaP layer, a InGaP layer, a AlInGaP layer, a AlGaAs layer, an InGaP layer, an InAlP layer, a GaAs layer, a InGa P layer, a GaAs layer, and a Ni substrate layer as the top layer.

[0062] Systems 100, 200, 300 and 400 can have photocatalysts arranged as shown in FIGS. 4A, 4B, 7, 8A, and 8B. FIGS. 4A and 4B represent an electrolysis system with the electrodes being attached to a voltage source. In some embodiments, the photocatalyst can be attached to the impermeable material 402 as shown in FIG. 7. This type of catalyst can be a monolithically integrated system and the entire catalyst and any hydrogen and oxygen co-catalysts 702 integrated into a thin film. During use, where one side of the film generates H.sub.2 (cathode) and the other side generates O.sub.2 (anode) as shown in FIG. 7, when exposed to irradiation source 704. Non-limiting examples of these types of photocatalysts are monolithically integrated solar-driven water-splitting devices can be based on tandem, Z-scheme or multi-junction structures.

[0063] In some embodiments, photocatalysts can be are used either for generating H.sub.2 or O.sub.2 and they can separated from corresponding counter electrodes. The photocatalysts (e.g., 112 and/or 124) and corresponding electrodes (e.g., 112 and/or 124) can be connected through circuit 126 (e.g. a copper wire). The photocatalyst can be based on tandem, Z-scheme or multi-junction structures. In some embodiments, circuit 126 can be attached to impermeable material 402 or conduit 302. Referring to FIG. 8A, cathodic photocatalyst 802 is attached to support 804 and is positioned in hydrogen generating chamber 106. Cathodic photocatalyst 802 is separated from oxygen generating chamber 108 conduit 302 or impermeable material 402 (not shown). Cathodic photocatalyst 802 is connected to metal (e.g., Pt) anodic electrode 806 via circuit 126 (e.g., copper wire) through conduit 302. When cathodic catalyst 802 is irradiated with a light source H.sub.2 can be generated from H.sup.+ in hydrogen generating chamber 106, and O.sub.2 can be generated in O.sub.2 generating chamber from voltage applied to the anodic electrode.

[0064] Referring to FIG. 8B, anodic photocatalyst 808 is attached to support 804 and is positioned in oxygen generation chamber 108. Anodic photocatalyst 808 is separated from hydrogen generating chamber by conduit 302 or impermeable material 402 (not shown). Anodic photocatalyst 808 is connected to metal (e.g., Pt) cathodic electrode 810 via circuit 126 (e.g., copper wire) through conduit 302. When anodic catalyst 808 is irradiated with a light source, O.sub.2 and electrons can be generated in O.sub.2 generating chamber. The electrons can travel through circuit 126 to cathode 810, which can generate from H.sup.+ in hydrogen generating chamber 106.

[0065] 4. Gas Selective Membranes for Gas Phase Separation

[0066] Hydrogen selective and oxygen selective membranes used to purify the generated H.sub.2 and/or O.sub.2 can be manufactured or be obtained from commercial sources. Non-limiting examples of commercial membrane sources are Air Products (U.S.A.), Membrane Technology Research, Inc. (U.S.A.), Air Liquid (U.S.A.), UBE Industries, LTD. (JAPAN), or the like.

[0067] Non-limiting examples of materials that compose the hydrogen separation membrane include polymeric and carbon membranes. Polymeric membranes typically achieve hydrogen selective molecular separation via control of polymer free volume. Polymeric membranes may be comprised, for example, of glassy polymers, epoxies, polysulfones, polyimides (e.g., polyimide membrane from UBE, or Proteus membranes from Membrane Technology and Research, Inc., and other materials, and may include crosslinks and matrix fillers of non-permeable (e.g., dense clay) and permeable (e.g., zeolites) varieties to modify polymer properties. Carbon membranes are generally microporous and substantially graphitic layers of carbon prepared by pyrolysis of polymer membranes or hydrocarbon layers. Carbon membranes may include carbonaceous or inorganic fillers, and are generally applicable at both low and high temperature. The hydrogen separation membrane may be a dense membrane composed only of the above-mentioned materials, or may be a dense thin membrane composed of the above-mentioned materials supported on a porous body. In the case of the former, the thickness of the hydrogen separation membrane is preferably 0.1 m or more and more preferably 0.5 m to 5 m from the viewpoints of mechanical strength and hydrogen permeability. In the case of the latter, the thickness of the thin membrane is 0.1 to 25 m or more and more preferably 0.1 m to 2 m from the viewpoint of processability.

[0068] In cases where the hydrogen separation membrane includes the dense thin membrane composed of the above-described materials and the porous body supporting the membrane thereon, the replacement of gaseous species tends to be inhibited on the side of the porous body and, thus, it is preferable for a dense thin membrane to be the side contacted with a mixed gas, and a porous body to be the side contacted with permeated hydrogen.

[0069] Oxygen selective membranes can include a perfluorocarbon material, a polysiloxane material, a fluorinated polysiloxane material, a perfluorinated polyethers material, and an alkyl methacrylate-based copolymeric material. Oxygen selective membranes are available from commercial sources. For example, Sepuran membranes from Evonik Industries (Austria) can be used. In some embodiments, oxygen can be released to the environment.

C. Method of Producing H.sub.2 and O.sub.2 from Water

[0070] The water-splitting systems of the present invention can be used to produce H.sub.2 and O.sub.2 from water. With reference to FIGS. 1-6, an electrolyte solution (e.g., electrolyte solution 114) can be provided to H.sub.2 generating chamber 106 and O.sub.2 generating chamber 108 of reactor 102. Purge gas can enter electrolyte solution 140 and the solution can be purged until no or substantially no H.sub.2 and O.sub.2 are present in the electrolyte solution. For example, the solution can include 1 vol. % or less, 0.05 vol. % or less, or 0.005 vol. % or less or undetectable amounts of H.sub.2 and/or O.sub.2. The degassed electrolyte solution 114 can be moved (e.g., pumped or pressurized) from electrolyte source 104 to the H.sub.2 and O.sub.2 generating chambers. The degassed electrolyte solution 114 can include purge gas, but H.sub.2 and O.sub.2 are preferably removed from solution 114 prior to entering the H.sub.2 and O.sub.2 generating chambers. In some embodiments, degassed electrolyte solution 114 is added to the reservoirs independently. By way of example, purge gas can enter H.sub.2 generating chamber through inlet 502 of FIG. 5A. Purge gas can be provided to H.sub.2 generating chamber or the H.sub.2 and O.sub.2 generating chambers continuously or intermittently. By way of example, prior to starting the water-splitting reaction, the electrolyte solution can be added to the chambers and purge gas can be provided to the chambers until the electrolyte solution includes little to no O.sub.2 present as measured using known analytical techniques (e.g., gas detectors). The purge gas can be slowed or discontinued in the H.sub.2 and O.sub.2 generating chambers and/or the electrolyte source for a desired amount of time. Purging can be resumed when detectable amounts of O.sub.2 and/or H.sub.2 are found in the electrolyte solutions exiting the H.sub.2 and O.sub.2 generating chambers, respectively. Such monitoring and addition of purge gas can inhibit and/or prevent H.sub.2 or O.sub.2 cross-contamination in the H.sub.2 and O.sub.2 generating chambers during the water-splitting reaction.

[0071] In reactor 102, current and/or electromagnetic radiation can be applied to anode 124 to generated electrons, which travel through circuit 126 to cathode 112 to generate H.sub.2. In some embodiments, both anode and cathode photocatalysts can receive electromagnetic radiation. In other embodiments, voltage and light are applied. When electromagnetic radiation is used, the source of the electromagnetic radiation can be natural (e.g., sunlight) or artificial (e.g., a lamp). A non-limiting example of an artificial source is a UV lamp that provides light at 300 to 400 nm. Excitation of the photocatalyst 112 in the presence of water can generate hydrogen ion (H.sup.+). Conditions for the water-splitting can include temperature and pressure. The reaction temperature can be greater than, equal to, or between any two of 5 C., 10 C., 20 C., 30 C., 40 C., 50 C., 60 C., 70 C., 80 C., 90 C. and 100 C. The reaction pressure can be greater than, equal to, or between any two of 0.01 MPa, 0.1 MPa, 0.5 MPa, 1 MPa, 1.1 MPa, 1.2 MPa, 1.3 MPa, 1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa, 2.0 MPa and 2.1 MPa.

[0072] As H.sub.2 and O.sub.2 are generated, electrolyte solution 114 having H.sub.2 and O.sub.2 dissolved therein exits chambers 104 and 106 and enters H.sub.2 reservoir 202 and O.sub.2 reservoir 204, respectively. In some embodiments, electrolyte solution 114 exiting H.sub.2 generating chamber 106 passes through a compressor and gaseous H.sub.2 is separated from the electrolyte solution and enters purification unit 212. In some embodiments, a compressor is not used. In H.sub.2 reservoir 202, dissolved H.sub.2 is released from the electrolyte solution producing an electrolyte solution that can have less than 0.2 ppm or 0 to 0.2 ppm dissolved H.sub.2 remaining. Released H.sub.2 can exit H.sub.2 reservoir 202 and enter purification and/or collection unit 212. In some embodiments, released H.sub.2 can be provided directly to other units or used as a fuel. In O.sub.2 reservoir 204, dissolved O.sub.2 is released from the electrolyte solution producing an electrolyte solution that can have 0.2 ppm to 0.4 ppm or greater than, equal to, or between any two of 0.2 ppm, 0.25 ppm, 0.3 ppm, 0.35 ppm and 4 ppm of O.sub.2 remaining. Released O.sub.2 can exit O.sub.2 reservoir 202 and enter purification and/or collection unit 214. In some embodiments, released O.sub.2 can be provided directly to other units for use as an oxidant. Release of H.sub.2 and O.sub.2 can be facilitated by purging, compression, heating or any known techniques to degas an aqueous solution.

[0073] The electrolyte solutions can exit reservoirs 202, 204, and enter electrolyte source 104. As shown in the FIGS. 2 and 3B, the solutions are combined prior to entering electrolyte source 104. However, the solutions can each independently enter electrolyte source 104. As the electrolyte solutions are combined the concentration of the H.sub.2 and O.sub.2 can remain under the flammability limit. Combining the electrolyte solutions can restore the pH gradient of the electrolyte solution used in the H.sub.2 and O.sub.2 generating chambers. In electrolyte source 104, the residual or low amounts of H.sub.2 and O.sub.2 are removed from the electrolyte solution and exit electrolyte source 104 via outlet 154. Removal of H.sub.2 and O.sub.2 can be facilitated by purging, compression, heating or any known techniques to degas an aqueous solution. In a preferred embodiment, the remaining H.sub.2 and O.sub.2 are removed by purging with nitrogen gas. The exiting gases can be sent to a collection unit, purification unit or transported to other processing units. The purged electrolyte solution exits electrolyte source (e.g., reservoir) via outlet 138 and enters H.sub.2 generating chamber 106 via inlet 142 and O.sub.2 generating chamber 108 via inlet 144. In some embodiments, the process is conducted in a continuous manner with electrolyte solution being added to the chambers while H.sub.2 and O.sub.2 are being removed. In some embodiments reservoirs 202 and 204 are not used and the H.sub.2 and O.sub.2 are removed from the electrolyte solution in electrolyte source 104.

EXAMPLES

[0074] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

Generation of H.SUB.2 .and O.SUB.2 .from an Aqueous Electrolyte Solution in the Absence of a Purge Gas

[0075] A water-splitting system included a reactor having electrolyte (200 mL, 0.1 M Na.sub.2SO.sub.4), an anode (Pt coated-Ni mesh) in an O.sub.2 generating chamber, a cathode (GaAs based triple junction solar cell) in an H.sub.2 generating chamber. The H.sub.2 generating chamber connected to a H.sub.2 reservoir and the O.sub.2 generating chamber were connected to an O.sub.2 reservoir. The reactor and the H.sub.2 and O.sub.2 reservoirs were connected to an electrolyte reservoir. The reactor was irradiated with a solar simulator at the intensity of 1 Sun (100 mW/cm.sup.2). The light intensity reaching the reactor was maintained at 100 mW/cm.sup.2 by adjusting the distance between the lamp and the reactor cell. The distance range was typically between is between 20 cm to 50 cm depending on the desired light flux. The rate of pumping of the electrolyte solution through the system was about 100 mL/min. No nitrogen purge was used. In the absence of a nitrogen purge, 75% H.sub.2/O.sub.2 separation was achieved (Table 1). Solar To Hydrogen (STH) was 7.5% at pH=7 under one sun. Table 1 lists the total water splitting results with multi-junction system using the membrane-less reactor without the N.sub.2 purging during the water-splitting reaction. From the data, it was determined that the dissolved H.sub.2 gas was transferred from the H.sub.2 reservoir (Compartment 1) to the O.sub.2 reservoir (Compartment 2) via the O.sub.2 chamber (See, FIG. 2) and then released to the gas phase until equilibrium was released.

TABLE-US-00001 TABLE 1 Compart- Compart- Compartment 1 plus Results ment 1 ment 2 Compartment 2 H.sub.2 (mmol/s) 6 10.sup.6 2 10.sup.6 8 10.sup.6 Exposed Area (cm.sup.2) 0.25 0.25 0.25 G (J/mol at 25 C.) 237000 237000 237000 Flux (mW/cm.sup.2) 100 100 100 320-1000 nm STH (%) 5.688 1.896 7.584

Example 2

Cross-Contamination of H.SUB.2 .and O.SUB.2 .from an Aqueous Electrolyte Solution as a Function of Flow

[0076] Using the experimental reactor system of Example, 1 the cross-over of H.sub.2 to the O.sub.2 chamber was studied as a function of nitrogen flow. In this study, H.sub.2 was injected into the H.sub.2 reservoir (C1 in FIGS. 9A & 9B, e.g., H.sub.2 reservoir 202 in FIG. 2) and the amount of H.sub.2 was measured in both reservoirs (C1 and C2 in FIGS. 9A & 9B, e.g., H.sub.2 reservoir 202 and O.sub.2 reservoir 204 in FIG. 2) with gas chromatography as a function of time while circulating water with a flow rate of about 80 mL/min and a N.sub.2 purge rate of about 1 mL/s during the experiment. Injection of H.sub.2 and O.sub.2 simulated the production of H.sub.2 and O.sub.2 from H.sub.2O in larger amounts using the catalytic system of Example 1. At the end of the H.sub.2 injection experiment the whole system was purged with N.sub.2 to remove all the H.sub.2 from the H.sub.2 and O.sub.2 reservoirs. Subsequently, O.sub.2 was injected into the O.sub.2 reservoir (C2) and the O.sub.2 content in the H.sub.2 and O.sub.2 reservoirs was monitored as a function of time. FIGS. 9A and 9B are graphs of addition of H.sub.2 (FIG. 9A) and O.sub.2 (FIG. 9B) into their respective reservoir. In FIG. 9A, the data line 900 the changes of H.sub.2 concentration with time in the H.sub.2-injected reservoir (C1) and data line 902 shows the changes of H.sub.2 concentration in the O.sub.2 reservoir (C2). In FIG. 9B, data line 904 shows the changes of O.sub.2 concentration with time in the O.sub.2-injected reservoir (C2) and data line 906 shows the changes of O.sub.2 concentration in the H.sub.2 reservoir (C1). The results of these experiments showed that after 90 min, around 0.3 vol. % of total H.sub.2 was transferred from the H.sub.2-injected reservoir (C1) to the O.sub.2 reservoir (C2) under the applied experimental conditions as shown in FIG. 9A (i.e., line 902 increases and line 900 decreases). Furthermore, no O.sub.2 crossing was observed (within experimental error) after 180 min as shown in FIG. 9B.

Example 3

Cross-Contamination of H.SUB.2 .and O.SUB.2 .from an Aqueous Electrolyte Solution as a Function of Time

[0077] Using the experimental design of Example, 3, the performance/efficiency of the separation of H.sub.2 and O.sub.2 of the reactor system in the presence of both gases was evaluated. H.sub.2 and O.sub.2 were injected into H.sub.2 reservoir (C1, FIGS. 10A and 10B) and O.sub.2 reservoir (C2, FIGS. 8A and 8B), respectively, and the amounts of gases were measured in both reservoirs with gas chromatography as a function of time. In FIG. 10A, data line 1000 shows the changes of H.sub.2 concentration with time in the H.sub.2-injected reservoir (C1) and data line 1002 shows the changes of O.sub.2 concentration in the same reservoir (C1). In FIG. 10B, data line 1004 shows the changes of O.sub.2 concentration with time in the O.sub.2-injected reservoir (C2) and data line 1006 shows the changes of H.sub.2 concentration in the same reservoir (C2). From these results, it was determined that after 170 min, a small amount (around 0.5 vol. %) of H.sub.2 gas was transferred from the injected reservoir (C1) to the other one (C2) (See, FIG. 10A), whereas after 140 min about 3 mol. % of O.sub.2 gas was transferred from the C2 to the C1 (See, FIG. 10B).

[0078] Based on the data, the low amount of H.sub.2 and O.sub.2 crossing resulted in a H.sub.2/O.sub.2 oxygen mixture with low H.sub.2 and O.sub.2 ratios, which was under the explosion limit (5%). As a result, the H.sub.2 rich gas mixture of H.sub.2, O.sub.2 and N.sub.2 can be further separated by conventional gas separation membrane to obtain high purity H.sub.2 when needed.