Ceria as a Thermochemical Reaction Medium for Selectively Generating Syngas or Methane from H₂O and CO₂

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.…”

“…5 Additionally, materials with high reduction enthalpies require high reduction temperatures and result in high H 2 O conversion; conversely, materials with low reduction enthalpies reduce at lower temperatures but require a larger temperature swing between the reduction and oxidation steps or result in low H 2 [12][13][14] and ceria (CeO 2 ). 15,16 Among these, ceria has become the benchmark material because of its rapid kinetics, and long term stability. 3,17,18 Some of these benecial effects stem from the redox mechanism of ceria.…”

“…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.…”

Solar fuel processing efficiency for ceria redox cycling using alternative oxygen partial pressure reduction methods

“…Particularly two-step, non-volatile metal oxidebased cycles show promise in avoiding gas separation issues, working at lower temperatures compared to direct thermolysis, enabling relatively simple design and operation, and theoretically achieving high solar-to-fuel efficiencies [10e14]. Ceria nonstoichiometric redox cycling has attracted interest due to its nonvolatile characteristics even at high operating temperature, fast kinetics causing high hydrogen generation rates [12,15,16], theoretical high solar-to-fuel efficiencies [13,14,17], and practical demonstration of reasonable efficiencies in working prototypes [18e21]. The two steps water and CO 2 …”

“…Riess et al [26] investigated the specific heat of ceria by an adiabatic temperature scanning calorimeter. Lapp et al [15] performed a parametric thermodynamic analysis of a ceriabased cycling scheme using an ideal mixing model and sweep gassing to maintain a low oxygen concentration atmosphere for the reduction step. They found that effective solid phase heat recovery was crucial in achieving solar-to-fuel efficiencies above 10%.…”