Bucknell University Bucknell Digital Commons Other Faculty Research and Publications Faculty Scholarship 2016 Hybrid metal oxide cycle water splitting Richard B. Diver Jr Robert D. Palumbo Nathan P. Siegel Bucknell University James E. Miller Follow this and additional works at: https://digitalcommons.bucknell.edu/fac_pubs Part of the Energy Systems Commons, and the Thermodynamics Commons Recommended Citation Diver, Richard B. Jr; Palumbo, Robert D.; Siegel, Nathan P.; and Miller, James E., "Hybrid metal oxide cycle water splitting" (2016). Other Faculty Research and Publications. 137. https://digitalcommons.bucknell.edu/fac_pubs/137 This Other is brought to you for free and open access by the Faculty Scholarship at Bucknell Digital Commons. It has been accepted for inclusion in Other Faculty Research and Publications by an authorized administrator of Bucknell Digital Commons. For more information, please contact [email protected]. US009279188B2 (12) United States Patent (10) Patent No.: US 9.279,188 B2 Diver, Jr. et al. (45) Date of Patent: Mar. 8, 2016 (54) HYBRD METAL OXDE CYCLE WATER (58) Field of Classification Search SPLITTING CPC ......................................................... C25B 1/04 USPC .......................................................... 205/637 (75) Inventors: Richard B. Diver, Jr., Albuquerque, NM See application file for complete search history. (US); Robert D. Palumbo, Valparaiso, IN (US); Nathan P. Siegel, Lewisburg, (56) References Cited PA (US); James E. Miller, Albuquerque, NM (US) U.S. PATENT DOCUMENTS 3,807,090 A 4, 1974 Moss (73) Assignee: Sandia Corporation, Albuquerque, NM 4,192,726 A 3/1980 Pangbornet al. (US) 4,202,744. A * 5/1980 Pan et al. ...................... 205/339 4,256,549 A * 3/1981 Divisek et al. ................ 2O5,354 (*) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 (Continued) U.S.C. 154(b) by 99 days. FOREIGN PATENT DOCUMENTS (21) Appl. No.: 14/115,095 WO WO 2013,019 167 A1 3, 2013 (22) PCT Filed: Jul. 29, 2011 OTHER PUBLICATIONS PCT NO.: PCT/US2O11AOO1340 PCT/US2011/001340 International Search Report mailed Dec. 14, (86) 2011, 2 pages. S371 (c)(1), (2), (4) Date: Oct. 31, 2013 Primary Examiner — Nicholas A Smith (74) Attorney, Agent, or Firm — Daniel J. Jenkins (87) PCT Pub. No.: WO2O13/O19167 PCT Pub. Date: Feb. 7, 2013 (57) ABSTRACT Hybrid thermochemical water splitting cycles are provided in (65) Prior Publication Data which thermally reduced metal oxides particles are used to displace Some but not all of the electrical requirements in a US 2014/O1 O29 12 A1 Apr. 17, 2014 water splitting electrolytic cell. In these hybrid cycles, the Related U.S. Application Data thermal reduction temperature is significantly reduced com pared to two-step metal-oxide thermochemical cycles in (60) Provisional application No. 61/368,756, filed on Jul. which only thermal energy is required to produce hydrogen 29, 2010. from water. Also, unlike the conventional higher temperature cycles where the reduction step must be carried out under (51) Int. C. reduced oxygen pressure, the reduction step in the proposed C25B I/04 (2006.01) hybrid cycles can be carried out in air, allowing for thermal COIB 3/06 (2006.01) input by a solar power tower with a windowless, cavity (52) U.S. C. receiver. CPC, C25B I/04 (2013.01); COIB3/063 (2013.01); Y02E 60/36 (2013.01) 6 Claims, 2 Drawing Sheets s al US 9.279,188 B2 Page 2 (56) References Cited 2006, O1884.33 A1 8, 2006 Weimer et al. 2007/004.5.125 A1 3, 2007 Hartvigsen et al. U.S. PATENT DOCUMENTS 2008, OO19903 A1 1, 2008 Wegner 2009, O120802 A1 5/2009 Ciampi et al. 4,608,137 A * 8/1986 Vaughan et al. .............. 205,637 2012/0175268 A1* T/2012 Joshi et al. .................... 205/412 5.492.777 A * 2/1996 Isenberg ................. CO1B 3.061 429,221 * cited by examiner U.S. Patent Mar. 8, 2016 Sheet 1 of 2 US 9.279,188 B2 U.S. Patent Mar. 8, 2016 Sheet 2 of 2 US 9.279,188 B2 von 8 Inert 44 ReceiverReactive Part N Concentrated Solar Flux w & a a Aa A & a a as sala sa a A a Hot Particle Storage Particle To Electric Lift Power Cycle Heat Exchanger Electrolyzer H Electricity HO eCC 'O F.G. 2 US 9,279,188 B2 1. 2 HYBRD METAL OXDE CYCLE WATER Thermochemical cycles are an attractive alternative to SPLITTING electrolysis as they have the potential for higher energy effi ciency due to the fact that they avoid the need to first convert CROSS REFERENCE TO RELATED thermal energy into electrical energy. There are many pro APPLICATION posed metal oxide thermochemical cycles for water splitting. For example, the Iron Oxide cycle is one that has been inter This application claims priority to U.S. provisional appli esting to the research community because the reduced iron cation Ser. No. 61/368,756, filed on Jul. 29, 2010, which is oxide is capable of reacting with water to produce hydrogen. hereby incorporated by reference in its entirety. However, in this cycle very high temperatures are needed to 10 thermally reduce magnetite, Fe-O, to the reduced oxide, BACKGROUND OF THE DISCLOSURE wustite. FeC). Complicating matters is the fact that the recov ery of Fe0 is dependent on the reduction step being con The present disclosure relates generally to methods and ducted under reduced oxygen partial pressure, e.g. in a apparatus associated with hybrid metal oxide cycle water vacuum or in the presence of an inert Sweep gas. Also, the splitting. 15 oxides melt and are somewhat Volatile at the required tem peratures. The thermodynamic high temperature require SUMMARY OF THE INVENTION ments and thermodynamic and kinetic requirements forcing the reaction to take place under an inert atmosphere as well as In one aspect of the disclosure, a hea hybrid thermochemi numerous materials challenges posed for these types of cal water splitting cycle includes thermally reducing a metal cycles compromise significantly the potential of engineering oxide with concentrated Solar energy and reoxidizing an oxy these cycles into an efficient and industrially economically gen-deficient metal oxide in an electrochemical cell, wherein realizable process. We are, therefore, interested in processes the chemical potential for the reactions is provided by the where the thermal reduction step can be done attemperatures metal oxide and electrical energy, and wherein the electrical below 1500° C. and even in air. energy required is significantly lower than needed for water 25 As an example, oxygen can be driven off from cobalt and or carbon dioxide electrolysis alone. manganese oxides (i.e. Co-O, MnO, and Mn2O) at signifi cantly lower temperatures than needed to thermally reduce BRIEF DESCRIPTION OF THE DRAWINGS magnetite. In addition, oxygen can also be produced from hematite, Fe2O, at much lower temperatures. FIG. 1 illustrates a schematic view of a hybrid metal oxide 30 cycle; and FIG. 2 shows one implementation strategy of the hybrid The factor previously eliminating the use of these attractive metal oxide cycle of FIG. 1. thermal reduction chemistries has been the other half of the two-step cycle. The Gibbs free energy, AG, of the oxidation DETAILED DESCRIPTION 35 FeO and the thermally reduced States of cobalt and manga nese oxides with water are positive at any temperature above Hybrid thermochemical water splitting cycles are pro and including room temperature. That is, they are thermody posed in which thermally reduced metal oxides particles are namically stable in the presence of water and steam, and will used to displace Some but not all of the electrical requirements not spontaneously oxidize to yield hydrogen. (Note: Because in a water splitting electrolytic cell. In these hybrid cycles, the 40 the reaction with water is not favorable, steam is essentially thermal reduction temperature is significantly reduced com inert in the system and could be employed gainfully as a pared to two-step metal-oxide thermochemical cycles in sweep to promote the reduction reaction if desired). which only thermal energy is required to produce hydrogen The factor previously eliminating the use of these attractive from water. Also, unlike the conventional higher temperature thermal reduction chemistries has been the other half of the cycles where the reduction step must be carried out under 45 two-step cycle. The Gibbs free energy, AG, of the oxidation reduced oxygen pressure, the reduction step in the proposed FeO and the thermally reduced States of cobalt and manga hybrid cycles can be (but are not required to be) carried out in nese oxides with water are positive at any temperature above air, allowing for thermal input by a solar power tower with a and including room temperature. That is, they are thermody windowless, cavity receiver. These proposed hybrid cycles namically stable in the presence of water and steam, and will could also potentially enable the use of heat from a nuclear 50 not spontaneously oxidize to yield hydrogen. (Note: Because reactor. Regardless of the energy input source, Solar or the reaction with water is not favorable, steam is essentially nuclear, in the hybrid scheme the products from thermal inert in the system and could be employed gainfully as a reduction are utilized as a chemically active anode material in sweep to promote the reduction reaction if desired). a water splitting electrolyzer. Because the anode is re-oxi dized during electrolysis, the electrical input required to split 55 water is reduced substantially below the electric input Employing a third reaction with sodium hydroxide or required to drive a conventional water splitting electrolyzer. potassium hydroxide has been proposed to make the oxida For example, the ideal decomposition Voltage can drop from tion thermodynamics favorable for metal oxide cycles in the 1.23 volts needed in a conventional cell to values as low as which the oxidation reaction is not favorable However, the 0.23 volts.