High-Flux Solar-Driven Thermochemical Dissociation of CO ₂ and H ₂ O Using Nonstoichiometric Ceria

Abstract

CeO 2 (Alfa Aesar 11328) was ball-milled with 16 wt% starch (Mallinckrodt 8188-2) for 19 to 24 h in anhydrous ethanol, and, after drying, mixed with 42 wt% graphite powders (-100 mesh, Alfa Aesar 14735). The composite powder was uniaxially pressed into quarter-circular-arc pieces. Subsequent heat-treatment at 1,500° C for 5 hr induced both thermal decomposition of the starch and graphite poreformers and sintering to yield suitably mechanically robust porous monoliths. The pieces measured approximately 40 mm in arc length, 8 mm in thickness, 9 mm in height. Porosity was determined by a simple measurement of the geometric dimensions and sample mass and comparing to the theoretical density of CeO 2 , 7.2 g cm-3 ; it was found to be 80 %. X-ray powder diffraction data were collected using a Philip X'Pert PRO diffractometer (Cu kα, 45 kV, 40mA). Scanning electron microscopy was performed on a Carl-Zeiss 1550 VP.

High-temperature isothermal chemical cycling for solar-driven fuel production

“…12, approximately 30 min, and that to achieve close-to-full hydrolysis at 800 1C is, on the basis of our previous studies, approximately 10 min. 6,7 The time required for ramping up and down between the two temperatures is a variable depending on the type of reactor utilized. In a tube reactor heated by an infrared image furnace, 6 the rate can be as high as 1000 1C min À1 , whereas in solar reactor average rates of about 50 1C min À1 have been achieved.…”

“…[1][2][3][4][5][6][7] The reaction scheme, as written out explicitly for the case of H 2 production from H 2 …”

“…To date, full demonstrations incorporating such a strategy have validated the technological viability of the approach, but efficiencies in the solar-to-fuel conversion process have been limited to a few per cent. 7,8 While such values are significant in light of the infancy of this technology, substantial advances are necessary for true commercial viability. To this end, considerable efforts are being directed towards the design of reactors that provide inherently higher efficiencies.…”

Splitting CO2 with a ceria‐based redox cycle in a solar‐driven thermogravimetric analyzer

“…This, in turn, led to an uncertainty in the weight change measurement of less than 7% of the absolute measured weight change for all samples at all times. Since the solar radiative input power and the solar radiative fluxes incident on the RPC are main design parameters of the solar reactor,13, 18 O 2 and CO evolutions are compared for samples exposed to the same incident radiative fluxes, i.e., 1280 suns during reduction and 440 suns during oxidation for all experimental runs. This way, the effect of the porous structure (porosity and pore size) on the overall kinetics can be assessed, including heat and mass transfer limitations during both redox steps, and the results can be directly applied to guide the design of these structures for solar reactors.…”

“…The difference δ red − δ ox determines the maximum molar amount of fuel capable of being produced per cycle and per mole of ceria. Various porous ceria structures have been investigated such as 3D ordered macroporous structures,11 electrospun fibers,12 monoliths,13 felts,14 and reticulated porous ceramics (RPC) 14. Although structures with submicron‐sized pores exhibited relatively fast oxidation rates, they lacked morphological stability as sintering occurred at elevated temperatures 11.…”