Impact of enhanced oxide reducibility on rates of solar-driven thermochemical fuel production

Abstract

Abstract

Modifying La0.6Sr0.4MnO3 Perovskites with Cr Incorporation for Fast Isothermal CO2‐Splitting Kinetics in Solar‐Driven Thermochemical Cycles

“…The thermolysis contribution to CO production was subtracted from the total CO generated in order to analyze the performance of La 0.6 Sr 0.4 Cr x Mn 1−x O 3 perovskites under isothermal CO 2 splitting. [11] It can be seen in Figure 5b that La 0.6 Sr 0.4 MnO 3 exhibits a threefold higher oxygen exchange capacity than La 0.6 Sr 0.4 Cr 0.85 Mn 0.15 O 3 . The highest fuel production was observed for x = 0.1, with 3.3 mL g −1 of CO, although x = 0.3-0.75 exhibited close performance with CO production around 2.9 mL g −1 .…”

“…This effect has been reported for isothermal H 2 and CO production with ceria [31,33] and hercynite, [56] however, this is the first observation of this kind for isothermal cycling of perovskites, since previous studies rely on thermogravimetric analysis (TGA) [34,57] that cannot monitor catalytic processes unrelated to weight changes. [10,11] Because of the shorter oxidation time, the total CO production and CO/O 2 molar ratios for La 0.6 Sr 0.4 MnO 3 are generally lower when compared to literature. Figure 5a depicts the total CO produced isothermally at 1400 °C, differentiating both sources, thermolysis and CO 2 splitting.…”

“…In addition, the oxide should show favorable thermodynamics toward splitting of CO 2 and H 2 O. [10,11] High CO yields were obtained for La 1−x Sr x MnO 3 perovskites (x = 0.4), but the decrease in enthalpy of reduction with increasing Sr content [12] also leads to a lower thermodynamic driving force for fuel production resulting in slower splitting kinetics. Recently, ceria was reported to attain solar-to-fuel efficiencies as high as 5.25%.…”

“…Currently, the state-of-the-art material is ceria due to its suitable thermodynamic properties and fast kinetics for syngas production. [10,11] Based on the amount of fuel produced per cycle, the La 0.6 Sr 0.4 MnO 3 perovskite is still an attractive option for thermochemical syngas production, [10,11,[13][14][15][16][17][18][19][20] provided the kinetics and/or thermodynamics are improved. [6] Exploring alternative materials that provide a higher oxygen release and better splitting kinetics (when compared to that of ceria) is of scientific and technological interest.…”

“…[10,11] High CO yields were obtained for La 1−x Sr x MnO 3 perovskites (x = 0.4), but the decrease in enthalpy of reduction with increasing Sr content [12] also leads to a lower thermodynamic driving force for fuel production resulting in slower splitting kinetics. In addition, under practical solar-to-fuel conditions, the kinetics of the oxidation in perovskites are governed by their thermodynamic properties rather than material kinetic properties as shown in our previous work on the perovskite La 1−x Sr x MnO 3 , [11] and we expect that Cr doping will result in faster fuel production rates based on thermodynamic considerations depicted in Figure 1. This fact motivated the present work, in which we have explored the partial substitution of Mn by Cr with the purpose of studying its effect on the CO 2 -splitting capabilities.…”