Solar hydrogen from a manganese oxide based thermochemical cycle

Sturzenegger, M.; Ganz, J.; Nuesch, P

doi:10.1051/jp4:1999351

Cited by 15 publications

(11 citation statements)

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“…The volatility of NaOH at >800°C and incomplete Na þ extraction by water to recover NaOH poses challenges to its implementation (17). Based upon the work of Tamaura et al, Sturzenegger et al first pointed out the possibility of creating a Mn-based cycle that utilizes Na 2 CO 3 rather than NaOH (23). Here, we have shown that a closed cycle of this type can be created.…”

Section: Resultsmentioning

confidence: 92%

“…However, their cycle was not closed due to the use of sacrificial Fe 2 O 3 to extract Na þ from sodium manganese iron oxide produced in the hydrogen evolution step (22). Sodium sources other than Na 2 CO 3 , such as NaOH, have also been employed to facilitate the oxidation of Mn 2þ to Mn 3þ in the water splitting step (23). The volatility of NaOH at >800°C and incomplete Na þ extraction by water to recover NaOH poses challenges to its implementation (17).…”

Section: Resultsmentioning

confidence: 99%

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Low-temperature, manganese oxide-based, thermochemical water splitting cycle

Bhawe

Davis

2012

Proc. Natl. Acad. Sci. U.S.A.

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Thermochemical cycles that split water into stoichiometric amounts of hydrogen and oxygen below 1,000°C, and do not involve toxic or corrosive intermediates, are highly desirable because they can convert heat into chemical energy in the form of hydrogen. We report a manganese-based thermochemical cycle with a highest operating temperature of 850°C that is completely recyclable and does not involve toxic or corrosive components. The thermochemical cycle utilizes redox reactions of Mn(II)/Mn(III) oxides. The shuttling of Na þ into and out of the manganese oxides in the hydrogen and oxygen evolution steps, respectively, provides the key thermodynamic driving forces and allows for the cycle to be closed at temperatures below 1,000°C. The production of hydrogen and oxygen is fully reproducible for at least five cycles.hydrogen production | Na + extraction | multistep cycle T hermochemical production of hydrogen and oxygen from water involves a series of chemical reactions that convert water into stoichiometric amounts of hydrogen and oxygen using heat as the only energy source. Thermochemical water splitting is of interest because it directly converts thermal energy into stored chemical energy (hydrogen and oxygen). Research on thermochemical water splitting cycles largely began in the 1960s and 1970s and involved nuclear reactors (1, 2) and solar collectors (3) as the energy sources. Numerous reviews of the thermochemical cycles proposed and experimentally investigated are available, e.g., (4). A large number of thermochemical cycles for splitting water has been proposed, and generally can be grouped into two broad categories: high-temperature two-step processes (5, 6) and lowtemperature multistep processes (7,8). One of us (M.E.D.) has conducted previous research on low-temperature multistep processes in the 1970s (9).Low-temperature multistep processes, typically with the a highest operating temperature below 1,000°C, allow for the use of a broader spectrum of heat sources, such as heat from nuclear power plants, and hence have attracted considerable attention. The majority of existing low-temperature processes produces intermediates that can be complex, corrosive halide mixtures. One of these processes, the sulfur-iodine cycle, has been studied extensively, and even piloted for implementation (8). This process produces strongly acidic mixtures of sulfuric and iodic acids that create significant corrosion issues, but requires only one high-temperature step at ca. 850°C. Two-step processes typically involve simpler reactions and intermediates, e.g., solid metal oxides, than the low-temperature multistep cycles. However, the temperatures required to close these types of cycles are well above 1,000°C. Because of the requirement of high-temperature heat sources, these types of cycles have been investigated for use with solar concentrators (10, 11). These cycles typically consist of one step that involves the oxidation of a metal [such as zinc (12)] or a metal oxide [such as iron (II) oxide (6, 13)] by water to produce...

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Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 99%

Low-temperature, manganese oxide-based, thermochemical water splitting cycle

Bhawe

Davis

2012

Proc. Natl. Acad. Sci. U.S.A.

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“…However, there are currently no studies reporting the direct use of manganese oxide for thermochemical water or CO 2 splitting, due to thermodynamic limitations. An indirect threestep cycle for H 2 generation was demonstrated by utilizing MnO and NaOH, subsequent hydrolysis of the birnessite mineral phase to generate Mn 2 O 3 and regenerate NaOH, followed by high-temperature reduction of Mn 2 O 3 to MnO [27][28][29][30][31]. The latter approach suffers from energy losses due to the significant temperature swings (ca.…”

Section: Introductionmentioning

confidence: 99%

Earth-abundant transition metal oxides with extraordinary reversible oxygen exchange capacity for efficient thermochemical synthesis of solar fuels

et al. 2018

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Efficient storage of solar and wind power is one of the most challenging tasks still limiting the utilization of the prime but intermittent renewable energy sources. The direct storage of concentrated solar power in renewable fuels via thermochemical splitting of water and carbon dioxide on a redox material is a scalable approach with up to 54% solar-to-fuel conversion efficiency. Despite progress, the search for earth-abundant materials that can provide and maintain high H 2 and CO production rates over long period of high-temperature cycles continues. Here, we report a strategy to unlock the use of manganese, the 12th most abundant element in the Earth's crust, for thermochemical synthesis of solar fuels, achieving superior thermochemical stability, oxygen exchange capacity, and up to seven times higher mass-specific H 2 and CO yield than cerium dioxide. We observe that incorporation of a small fraction of cerium ions in the manganese (II,III) oxide crystal lattice drastically increases its oxygen ion mobility, allowing its reduction from oxide to carbide during methane partial oxidation with simultaneous Ce exsolution. High CO 2 and H 2 O splitting rates are achieved by re-oxidation of the carbide to manganese (II) oxide with simultaneous reincorporation of the cerium ions. We demonstrate that the oxide to carbide reaction is highly reversible achieving remarkable CO 2 splitting rates over 100 thermochemical cycles of methane partial oxidation and CO 2 splitting, and preserving the initial oxygen exchange capacity of 0.65 mol O − mol Mn 1 and 89% of the fuel production rates. Due to this extraordinarily high reversible oxygen exchange capacity, the 3% Ce-doped manganese oxide achieves an average mass-specific CO yield for CO 2 splitting of 17.72 mmol CO g −1 , which is significantly higher than that previously achieved in thermochemical redox cycles. More generally, these findings suggest that incorporation of small soluble amounts of cerium in earth-abundant transition metal oxides like manganese oxide is a powerful approach to enable solar thermochemical fuel synthesis.

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“…Fe O Nakamura, 1977;Tofighi and Sibieude, 1984 . Sturzenegger and Nuesch, 1999 . Thermally induced reduction of these oxides occurs at temperatures above 2,000 K and ensures conversion of radiant energy into chemical en-Ž ergy with exergy efficiencies up to 70% Sizmann, 1991;Ste-.…”

Section: Introductionmentioning

confidence: 99%