Reactivity of Doped Ceria-Based Mixed Oxides for Solar Thermochemical Hydrogen Generation via Two-Step Water-Splitting Cycles

Abstract

Ceria-type materials were investigated as reactive chemical intermediates in view of solar thermochemical hydrogen production via two-step water-splitting. Ceria/zirconia mixed oxides and ceria doped with yttrium, lanthanum, praseodymium, or gadolinium were studied using a thermobalance to evaluate their thermal reduction capacity in inert atmosphere and their subsequent reactivity with water steam to generate hydrogen. Ceria/zirconia materials present the highest reduction yields with a noticeable linear increase as a function of the zirconium content (in the range 0-54% Zr), while the gravimetric amount of O 2 released during reduction tends to level off for Zr atomic contents above 25%. Temperatureprogrammed reduction experiments demonstrate that the zirconium insertion favours the bulk reduction. The addition of different dopants (among Y, La, Pr, and Gd) did not affect the global materials reducibility although it should favour the material thermal stability during repeated cycles. The marked effect of the synthesis method of the material and of the temperature of the reduction reaction on the reactivity of ceria/zirconia was highlighted. In addition, the beneficial influence of decreasing the system total pressure for improving the thermal reduction of ceria/zirconia was experimentally evidenced, offering new prospects for operating a solar thermochemical reactor.

Insights into the Redox Performance of Non–stoichiometric Lanthanum Manganite Perovskites for Solar Thermochemical CO2 Splitting

“…This demonstrates that addition of inert MgO as sintering inhibitor stabilizes the perovskite material and promotes the CO 2 ‐splitting activity. The gravimetric fuel production yields for lanthanum manganite perovskites are also significantly higher than the ones measured for both ceria and Zr‐substituted ceria in the same conditions (Figure S4) …”

A review and perspective of efficient hydrogen generation via solar thermal water splitting

“…Many elements have been doped into ceria in an attempt to increase the H 2 production and lower the required reduction temperature. Divalent (Li, Mg, Cu, Zn, Sr) and trivalent (Al, Sc, Cr, Mn, Fe, Co, Ni, Y, La, Pr, Sm, Gd, Ta) dopants have not achieved these goals. The divalent and trivalent elements decrease the oxygen vacancy formation enthalpy to such an extent that the oxygen vacancies no longer possess the energy required to split water.…”

Effective Macroporous Core–Shell Structure of Alumina‐Supported Spinel Ferrite for Carbon Dioxide Splitting Based on Chemical Looping

“…Then onuniform outer distribution of the Ni and Fe also verifiest hat the form of the NiFe 2 O 4 is large particles rathert han as hell, indicated by the significant differentc on- tent of Ni and Fe at both ends of the scanning line (Figure 4i). Interestingly,t he NiFe 2 O 4 particles on Al 2 O 3 -1200 are no longer evident after TGA.I na ccordance with previouss tudies, [42,44] we speculated that the NiFe 2 O 4 particles are incorporated into the framework of the Al 2 O 3 -1200 to form as olid solution.T hen the shell and macropores formed throught his interaction at the extremely high temperature.T he XRD patterns show that the three samples are composed of Ni-FeAlO 4…”

“…The CD‐S step proceeds at a lower temperature (typically below 1100 °C), and the metal oxide is oxidized by CO 2 to generate CO. The redox‐active metal oxide materials used as chemical intermediates exhibit a low thermal reduction temperature and a high reactivity with CO 2 in the oxygen‐deficient form and are nontoxic, abundant, and inexpensive . Although thermochemical cycles that use a variety of oxide systems are known, such as ZnO/Zn, SnO 2 /Sn, Fe 3 O 4 /FeO, ceria, ferrites, and perovskites, ferrites have been investigated thoroughly.…”

“…TheC D-S step proceedsa talower temperature (typically below 1100 8C), and the metal oxide is oxidized by CO 2 to generate CO.T he redox-active metal oxide materials used as chemical intermediates exhibit al ow thermal reduction temperature and ah igh reactivity with CO 2 in the oxygen-deficient form and are nontoxic, abundant, and inexpensive. [4] Although thermochemical cyclest hat use av arietyo fo xide systems are known, such as ZnO/Zn, [5] SnO 2 /Sn, [6,7] Fe 3 O 4 /FeO, [8,9] ceria, [10][11][12][13][14][15][16] ferrites, [17,18] and perovskites, [19][20][21][22] ferrites have been investigatedt horoughly.T hey can be reduced deeply withouth eating beyond their meltingp oints and thus remain in the condensed phase during the cyclic reaction. This makes ferrites easy to implement in ac oncentrateds olar energy process.…”