Full length articleCombustion synthesized A0.5Sr0.5MnO3-δ perovskites (where, A = La, Nd, Sm, Gd, Tb, Pr, Dy, and Y) as redox materials for thermochemical splitting of CO2
Introduction
Conversion of thermodynamically stable H2O and CO2 into synthetic liquid fuels via a renewable and environmentally sustainable process, such as metal oxide (MO) based solar thermochemical cycle, is essential to fulfill the forthcoming energy demand of the civilization [1]. The employment of the above-mentioned process can also aid to reduce the consumption of fossil fuels and emission of CO2, which ultimately results into a drop in the risk associated with the global warming. Several non-volatile MOs have been considered for this process including iron oxide [2,3], Ni-ferrite [4,5], Zn-ferrite [6,7], Co-ferrite [8,9], Mn-ferrite [10], Sn-ferrite [11], Ni-Zn-ferrite [12], Ni-Mn-ferrite [13], CeO2 [14,15], ceria-zirconia solid solution [16,17], and other doped ceria materials [18,19]. Among these MOs, the ceria based redox materials are increasingly more attractive because of their elevated oxygen storage capacity (OSC), faster reaction kinetics, and exceptional material stability during multiple thermochemical cycles.
As the thermal reduction (TR) temperatures required for the perovskite oxides (ABO3) are lower than the other MOs investigated so far, in recent years, ABO3 have been examined as an alternative for the ceria based redox materials [20]. The two-step TR and H2O (WS) and CO2 splitting (CS) reactions associated with the perovskite oxides are shown below:
Following is the list of key perovskites scrutnized until now for the thermochemical splitting of H2O and CO2: (LaSr)MnO3-δ [[21], [22], [23], [24], [25], [26]], (YSr)MnO3-δ [26,27], (LaSr)FeO3-δ [26], (LaSr)CoO3-δ [26], (LaCa)MnO3-δ [26,27], (BaSr)FeO3-δ [26], (BaSr)(FeCo)O3-δ [26], (LaSr)(CoFe)O3-δ [26], (LaSr)(FeMn)O3-δ [27], (LaBa)(Mn)O3-δ [27], (LaSr)(MnAl)O3-δ [27,28], and (LaSr)(CrCo)O3-δ [29].
The above mentioned list clearly indicate that most of the studies were directed towards varying the dopants associated with the B-site by keeping the A-site mainly stable at Lanthanum (La). According to us, the exploration of the influence of variation in the metal cations associated with the A-site of the perovskite is also essential. Furthermore, in most of the previous examinations, the redox reactivity of the perovskite oxides was investigated by performing only one thermochemical cycle. The solar thermochemical community is largely interested towards identifying the best MOs based on their ability towards stable amounts of O2 released (nO2) and H2 (nH2) or CO produced (nCO) in multiple thermochemical cycles. Thus, in this study, the TR and CS aptitude of A0.5Sr0.5MnO3-δ (where, A = La, Nd, Sm, Gd, Tb, Pr, Dy, and Y) was estimated by performing 10 thermochemical CS cycles. The A0.5Sr0.5MnO3-δ perovskites were synthesized by using a solution combustion synthesis (SCS) method. Physical properties of the derived perovskites were estimated by using multiple analytical techniques and the nO2 and nCO by each material was assessed by performing numerous thermogravimetric experiments.
Section snippets
Solution combustion synthesis of A0.5Sr0.5MnO3-δ
The A0.5Sr0.5MnO3-δ perovskites were synthesized by employing a solution combustion synthesis (SCS) approach (Fig. 1). The abbreviations provided to all the A0.5Sr0.5MnO3-δ perovskites are listed in Table 1. Measured quantities of metal nitrates (obtained from Sigma Aldrich) with stoichiometric glycine were dissolved into 50 ml of deionized water. This mixture was continuously agitated at room temperature to achieve a uniform solution. The prepared solution was preheated by placing it on the
Characterization of A0.5Sr0.5MnO3-δ perovskites
The phase composition of the annealed A0.5Sr0.5MnO3-δ perovskite powders was characterized by using a PANalytical XPert MPD/DY636 powder X-ray diffractometer (PXRD). The PXRD patterns reported in Fig. 3a specify phase pure composition of each A0.5Sr0.5MnO3-δ perovskite with absence of any metal or metal oxide impurities. As the crystal ionic radii of metal cation dopants decreases i.e., La (117.2 pm) > Pr (113.0 pm) > Nd (112.3 pm) > Sm (109.8 pm) > Gd (107.8 pm) > Tb (106.3 pm) > Dy
Summary and conclusions
The La, Nd, Sm, Gd, Tb, Pr, Dy, and Y doped strontium‑manganese perovskites were successfully prepared by using solution combustion synthesis method. The powders obtained after combustion were further calcined up to 1000 °C in air. The physico-chemical analysis of the calcined powders was conducted by utilizing the various analytical techniques. The PXRD and EDS analysis confirms phase pure composition of each A0.5Sr0.5MnO3-δ perovskite. Moreover, the SEM analysis indicate agglomerated larger
Acknowledgements
This publication was made possible by the NPRP grant (NPRP8-370-2-154) from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of author(s).
References (31)
- et al.
Two-step water splitting thermochemical cycle based on iron oxide redox pair for solar hydrogen production
Energy
(2007) - et al.
Solar hydrogen production via thermochemical iron oxide-iron sulfate water splitting cycle
Int. J. Hydrog. Energy
(2015) - et al.
Effectiveness of Ni incorporation in iron oxide crystal structure towards thermochemical CO2splitting reaction
Ceram. Int.
(2017) - et al.
Thermochemical water-splitting for H2 generation using sol-gel derived Mn-ferrite in a packed bed reactor
Int. J. Hydrog. Energy
(2012) - et al.
Opportunities and challenges for a sustainable energy future
Nature
(2012) - et al.
Hydrogen production via solar-aided water splitting thermochemical cycles with nickel ferrite: experiments and modeling
AICHE J.
(2013) - et al.
Kinetic investigations of the hydrogen production step of a thermochemical cycle using mixed iron oxides coated on ceramic substrates
Int. J. Energy Res.
(2010) - et al.
Propylene oxide assisted sol-gel synthesis of zinc ferrite nanoparticles for solar fuel production
Ceram. Int.
(2016) - et al.
Cobalt ferrite in YSZ for use as reactive material in solar thermochemical water and carbon dioxide splitting, part I: material characterization
JOM
(2013) - et al.
Kinetics and mechanism of solar-thermochemical H2 production by oxidation of a cobalt ferrite-zirconia composite
Energy Environ. Sci.
(2013)