H2 Generation by Two-Step Water Splitting With CeO2-MOx Using Concentrated Solar Thermal Energy

Abstract

CeO2-MOx (M = Mn, Fe, Ni, Cu) reactive ceramics, having high melting points and high conductivities of O2−, were synthesized with the combustion method from their nitrates for solar hydrogen production. The prepared CeO2-MOx samples were solid solutions between CeO2 and MOx with the fluorite structure through XRD. Two-step water splitting reactions with CeO2-MOx reactive ceramics proceeded at 1573–1773K for the O2 releasing step and at 1273K for the H2 generation step by irradiation of infrared imaging furnace as a solar simulator. The amounts of O2 evolved in the O2 releasing reaction with CeO2-MOx and CeO2 systems increased with the increase of the reaction temperature. The amounts of H2 evolved in the H2 generation reaction with CeO2-MOx systems except for M = Cu were more than that of CeO2 system after the O2 releasing reaction at the temperatures of 1673 and 1773K. The largest amount of H2 was generated with CeO2-NiO after the O2 releasing reaction at 1573, 1673 and 1773K. The O2 releasing reaction at 1673K and H2 generation reaction at 1273K with CeO2-Fe2O3 were repeated four times with the evolving of O2 (1.3cm3/g-sample) and H2 (2.3cm3/g-sample) gases, respectively. The possibility of solar hydrogen production with CeO2-MOx (M = Mn, Fe, Ni) reactive ceramics system by using concentrated solar thermal energy was suggested.

Principles of doping ceria for the solar thermochemical redox splitting of H2O and CO2

“…Among the dopants, we rst discuss Zr and Hf tetravalent dopants which aid the redox performance, 24,30,[32][33][34] before discussing those dopants which do not, i.e. di-, tri-, Ti-, and pentavalent dopants, 16,20,[23][24][25][26][27][28][29][30][31] in that order. In each case, we investigated the elements from periodic table rows 4, 5, and 6, and detail the row 5 elements and then compare the row 4 and 6 elements to the exemplar.…”

“…However, ceria requires high temperatures (>1400 C) and low oxygen partial pressures (<10 À4 bar) in order to obtain a reasonable reduction extent (d). 3,[19][20][21][22] Because of this, the specic H 2 yield per unit mass of ceria is limited.…”

“…Di-, tri-and pentavalent dopants, including Li, Mg, Cu, Zn, Sr, Al, Sc, Cr, Mn, Fe, Co, Ni, Y, La, Pr, Sm, Gd, and Ta provide little, if any, improvement in the H 2 production capacity of ceria, although some prevent sintering and grain growth. 16,20,[23][24][25][26][27][28][29][30][31] Tetravalent Zr and Hf, however, have been shown to signicantly improve the redox capacity of ceria. 24,30,[32][33][34] To date the selection of dopants for STWS is mostly based on trial and error; therefore, we attempt to bring an understanding of ceria dopants to the STWS community.…”

Ceria‐Based Solid Catalysts for Organic Chemistry

“…[32,33] As mentioned above, it is generally accepted that one surface oxygen atom out of four is involved in the redox process shown in Equation (2), which represents a theoretical OSC value of 5.4 mmol O m À2 for a mean surface density of 13.1 mmol O m À2 . [22,33] Reduced ceria is able to dissociate water [34][35][36][37][38] or carbon dioxide [34,36] according to Equation (4) or the reverse of Equation (2) Ceria also possesses versatile acid-base properties, depending on the nature and temperature of the pretreatment. Ceria can chemisorb pyrrole, a proton donor, and CO 2 , an electron acceptor, which is characteristic of strong Lewis-base sites.…”

Unusual decrease in conductivity upon hydration in acceptor doped, microcrystalline ceria

“…These include heterogeneous catalysis, where they serve as active supports, 1 fuel cells, where they can serve as either electrolyte (due to fast oxygen-ion conduction) 2,3 or anode electrocatalyst (due to mixed conduction), [4][5][6] and, more recently, as oxygen storage materials for solar thermochemical dissociation of water 7,8 and carbon dioxide 7 to fuels. In all of these processes, water vapor is present at significant pressures and hence may plausibly impact overall device operation.…”