Gas-phase vs. material-kinetic limits on the redox response of nonstoichiometric oxides

Abstract

The rate of response of CeO2−δ to changes in gas composition can be systematically manipulated via changes to gas flow rate or material specific surface area.

Outstanding Properties and Performance of CaTi0.5Mn0.5O3–δ for Solar-Driven Thermochemical Hydrogen Production

“…On the other hand, in experiments in which gas flow rates are made so high that thermodynamic limitations can be fully ignored, it may be possible to determine kinetic parameters. 30,31 It has been shown that, under such conditions, the surface reaction rather than diffusion of oxygen through the material bulk is the rate-controlling material Article phenomenon. 27,28,32 It is of some note that both the model and experiment reveal that hydrogen production is possible from a non-stoichiometric oxide with an enthalpy of reduction that is smaller than the enthalpy of the steam thermolysis reaction, 11 albeit with a relatively small steam-to-hydrogen conversion ratio.…”

Perspective on high-temperature surface oxygen exchange in a porous mixed ionic-electronic conductor for solid oxide cells

“…The lower the particle size is, the higher the specific surface area and the higher the oxygen consumption rate. 1,24 Therefore, a different oxygen consumption rate may take place within porous materials when compared with dense materials. Finally, the porous electrode is characterized by inhomogeneous ORR kinetics, whereas the dense material is homogeneous.…”

“…The MATLAB code for the calculation of distributed characteristic time (DCT) from ECR data is available in our previous report. 1 To date, the ECR method has been used to characterize the k chem of some significant porous electrodes, including perovskite oxides (e.g., La x Sr 1Àx Co y Fe 1Ày O 3Àd (LSCF), 1,33,34 Ba 0.5 Sr 0.5 -Co 0.8 Fe 0.2 O 3Àd (BSCF) 30 ), Ruddlesden-Popper oxides (Nd 2 NiO 4+d ), 35 and fluorite solid solutions (CeO 2Àd , 24 Pr 0.1 Ce 0.9 O 2Àd…”

Simulation of two-step redox recycling of non-stoichiometric ceria with thermochemical dissociation of CO2/H2O in moving bed reactors – Part I: Model development with redox kinetics and sensitivity analysis

“…This also directly influences the yield from the oxidation step. Efficient oxygen exchange between redox cycles can be achieved by creating mesoporous or microporous forms of structures of ceria with shorter bulk diffusion lengths, higher surface area and increased porosity (as it helps in radiative heat transfer) (Davenport et al, 2017;Ji et al, 2017). It is reported that the rate determining in thermochemical redox cycle would either be gas-phase limited or surface kinetics (Davenport et al, 2016;Ji et al, 2016).…”