Splitting of CO2 by Manganite Perovskites to Generate CO by Solar

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Splitting of CO by Manganite Perovskites to Generate CO by Solar Isothermal Redox Cycling Sunita Dey, and Chintamani Nagesa Ramachandra Rao ACS Energy Lett., Just Accepted Manuscript • DOI: 10.1021/acsenergylett.6b00122 • Publication Date (Web): 07 Jun 2016 Downloaded from http://pubs.acs.org on June 9, 2016

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Splitting of CO2 by Manganite Perovskites to Generate CO by Solar Isothermal Redox Cycling Sunita Dey and C. N. R. Rao* Chemistry and Physics of Materials Unit, Sheikh Saqr Laboratory, International Centre for Materials Science (ICMS), and CSIR Centre of Excellence in Chemistry. Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Jakkur P.O., Bangalore 560 064, India. *[email protected]

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ABSTRACT: Solar isothermal thermochemical splitting of CO2 to generate CO has been reported by oxides such as CeO2 in the literature. With CeO2, isothermal CO2 splitting occurs at 1773K but the results are not satisfactory in terms of fuel yield. The limited reducibility and sublimation prevent the use of CeO2. La1-xSrxMnO3 (LSM) based perovskites are recently being identified as a potential candidate of two-step process in view of the greater oxygen release at reduced temperature and greater fuel yield than CeO2. Considering the extraordinary properties of perovskites manganites in the two-step process, we have employed La1-xSrxMnO3 (x=0.3, 0.4 and 0.5) for solar isothermal CO production and obtained CO yields of 133.9 µmol/g by La0.5Sr0.5MnO3 as a temperature low as 1673K under the reduction and oxidation conditions of 10-5 atm O2 and 1 atm CO2 respectively. The global CO production rate by La0.5Sr0.5MnO3 (601.8 µmol/g/hr) is far superior (~3 times higher) than CeO2 at 1773K. Further improvement in performance is achieved by using Y0.5Sr0.5MnO3, containing a very small rare earth ion. This perovskite produces 1.8 times more CO than La0.5Sr0.5MnO3 at a record low temperature of 1573K. These results are noteworthy and show the potential for practical application.

TOC GRAPHICS

Ln1-xSrxMnO3-n Toxd

Tred

O2

Ln1-xSrxMnO3-n-δ Tred=Toxd


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Solar thermochemical cycles which operate by the utilization of renewable resources like solar radiation, CO2 and H2O provide alternative routes for the production of fuels and are of great relevance to present day concerns related to energy and climate change.1, 2 For the purpose of beneficiation of CO2, many strategies are being examined to reduce it to CO. One of the strategies is the solar thermochemical splitting of CO2 (TSCS). The basic reactions here are endothermal reduction (equation 1) and exothermal oxidation (equation 2) of the metal oxide (MOn): Endothermal Step: MOn → MOn−δ + δ⁄2 O2 − − − − − −(1) Exothermal step: MOn−δ + δCO2 → MOn + δCO − − − − − (2) Thermodynamic considerations demand Tred> Toxd as the condition to split CO2 in the above two steps. TSCS involving a temperature swing between Tred and Toxd, has been studied with various oxides wherein large changes in stoichiometry are favored at higher Tred (low oxygen partial pressure) while reoxidation occurs at a lower Toxd.3-14 Such cyclic rotation between Tred and Toxd is accompanied by irreversible heat losses causing reduction in thermodynamic efficiency. Furthermore, time loss to shuttle between Tred and Toxd is also an adverse factor. The efficiency penalty becomes more prominent in the case of metal oxides with a high specific heat,3 continuous swing over a large temperature window creating thermal stress on the reactive substrate as well as on system components.15-17 In this context, it is found desirable to employ isothermal splitting of CO2 (ITCS) which allows the two processes in the redox cycle to occur at the same temperature, since it depends on the large pressure swing in the gas composition between reduction and oxidation to produce nonstoichiometry. The major efficiency parameters solid state heat recovery in TSCS and fluid phase heat recovery in ITCS.16, 18, 19


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CeO2, which operates solely based on oxygen nonstoichiometry (eqns. 1 and 2), is thermodynamically predicted to have conversion efficiencies of 18% during the isothermal splitting of CO2 at 1773K.13 Venstrom et. al20 have shown the rate of ITCS to be comparable to that of TSCS. The CO production rate by CeO2 of 284 µmol/g/hr is not very satisfactory considering the high temperature involved (1773K). The efficiency of CeO2 based isothermal cycle is predicted to increase with increasing temperature,15 but the oxide sublimes at high temperatures (>1773K)6, 21. In addition, CeO2 has negligible reducibility at lower temperatures (TLSM40>LSM30, but the values are very close to zero indicates stable weight changes when the equilibrium were deemed to be reached. In addition the δeq varies as LSM50>LSM40>LSM30 (Table S3), indicating that with increasing Sr2+ content greater amount of CO2 is required to stabilize the equilibrium (oxidation) during


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ITCS. The δeq values of LSMs are higher than CeO2, but more importantly CO production is considerably higher than CeO2 by ITCS. Thus with LSM50, the CO yield is ~3.5 times and ~2.8 times higher than CeO2 at 1773K and 1673K respectively. Entering CO2 during first oxidation shows sudden gain in weight which immediately decreases with reaching equilibrium. As the oxidation is kinetically more favored at high temperatures, the entrance of CO2 results in a sudden weight gain, but the oxygen activity of CO2 is not sufficient to maintain the equilibrium at that initial stoichiometry and the reduction continues until equilibrium is established. In separate experiments (Figure S13) we have heated LSM40 at 1673 K under CO2 flow (pCO2=1 atm). LSM40 establishes equilibrium in the presence of CO2 (Figure S13) and the δeq (~0.07) is found similar as observed in Figure 2a (~0.067). Further replacement of CO2 flow with sweep gas and followed by CO2 continues the regular isothermal process. The product gases of oxidation were collected in a metal collector attached to pressure a gauge and analyzed by a gas chromatograph equipped with a TCD detector (GC-TCD). The CO peak was detected at 0.9 min while CO2 appears after that (Figure S14). Gas chromatograph results indicate an increasing amount of CO with the increasing Sr substitution in LSM materials. The amount of CO detected by GC-TCD is in close agreement (variation of 10%-15%) with the values measured by TGA. The CO yield increases monotonically with Sr2+ content of LSM and the yields are higher at 1773K than 1673K, agreeing with the trends predicted by calculations (Figure S15). The experimentally obtained yields of CO are around ~32% and ~45% of the theoretically predicted yields at 1673K and 1773K respectively (Table S4). The theoretical estimated values represent the maximum possible yield under thermodynamically preferred conditions, where in the content of oxidative CO2 is assumed as infinite. During experiments the gas flow rates and the total cycle


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period were limited. Incomplete reduction can be one of the possible reasons for this discrepancy which is limited by slow gas phase mass transport and surface reaction kinetics.15,

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Microstructural evolution (as observed in FESEM images) with cycling also limits the reaction rates. Slower oxidation kinetics (which increases δeq) can also cause lower CO yields. In view of the difference between the experimental and theoretical CO productivity, the effect of reduction time and gas flow rates were investigated over in the case of LSM50 at 1773K (details of experiments are in supporting information). By increasing the reduction time (tred) from 15 min to 25 min enhances O2 production from 111.6 µmol/g to 140.6 µmol/g (Figure S16). Notably LSM50 reoxidizes completely during 5 min of CO2 exposure (toxd = 5 min) even for the tred of 25 min, yields upto 274.5 µmol/g of CO. Notably, 56% of theoretically predicted CO is achieved experimentally for tred of 25 min (Table S5). Further increase in CO (O2) yield could be achieved by increasing tred as evidenced by linear dependence of CO yield over tred (Figure S17). Increasing tred also increases the total cycle period (ttotal = tred+ toxd), altering the time averaged rate of CO production. Increasing the total cycle period from 20 min (tred=15 min) to 30 min (tred=25 min) increases the CO yield from 227.7 µmol/g to 274.5 µmol/g but estimated to reduce the time averaged rate of CO production from 683 µmol/g/hr to 549 µmol/g/hr (Figure S17, blue curve). The influence of sweep gas (10-5 atm O2) flow rate over the average rate of O2 production of LSM50 is shown in Figure S18 (experimental details are in supporting information). Although the total reduction time (tred) was 15 mins, more than 75% of expected O2 evolved within the initial 10 mins. As shown in Figure S18b, the average rate of O2 production (time averaged over 9.9 mins) increases monotonically with increasing sweep gas flow rate upto 1000 ml/min/g and remains nearly constant with further increase in flow rate. Hence the maximum rate of O2


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production is 8.5 µmol/min/g achieved at 1000 ml/min/g of sweep gas flow rate. The total O2 yield (tred is 15 mins) is also increases with increasing sweep gas flow rate and a maximum yield of ~105 µmol/g is achieved with 1000ml/min/g of sweep gas flow rate (inset of Figure S18). LSM50 was oxidized reversibly (toxd ~ 5 mins) and maintaining the CO: O2 yield of 2:1 during each cycle (inset of Figure S18b). A constant CO yield of ~215 µmol/g is reached with sweep gas flow rate of 1000 ml/min/g. The influence of CO2 flow rates on the rate of CO production is shown in Figure S19 (experimental details are in supporting information). The impact of CO2 flow rate on the global CO production rate as well as on the production rate averaged over initial 3 mins of oxidation can be seen in Figures S19b and S19c respectively. The CO production rate increases with increasing CO2 flow rate upto 500 ml/min/g with a plateau occurring beyond this volume. Maximum CO production rate of 46 µmol/min/g (Figures S19c) is obtained. CO yield too increases with the CO2 flow rates upto 600 ml/min/g with a maximum yield of ~185 µmol/g. The CO: O2 ratio of 2:1 is maintained in each cycle (Figure S19d). As inferred from Figures S18 and S19, the maximum rate of O2 production and CO production are achieved with 1000 ml/min/g of sweep gas flow and 600 ml/min/g of CO2 flow respectively (TI is 1773K). Below these flow rates gas phase mass transport limits the production. The total yield of CO varies with the flow rates, reaching the limit with 1000ml/min/g sweep gas flow and 600ml/min/g CO2 flow.


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1773 K

tred= 10 min toxd= 5 min

O2 and CO produced (mol/g)

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O2

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Figure 3 Figure 3. Representative TGA of LSM50 shows the O2 and CO production rate during 13

consecutive ITCS cycles at 1773K. (b) Histogram represents the O2 and CO yield of LSM50 during 1st and at the end of 13th thermogravimetric cycles. Error bars indicate max/min values of multiple runs. Multiple cycling of LSM50 was carried out at 1773K, under the restriction of tred (𝑝O2 =10-5 atm, flow rate 1000 ml/min/g) and toxd (𝑝CO2 =1 atm, flow rate 400ml/min/g) of 10 min and 5 min per cycle respectively (Figure 3). The yield of CO was nearly the same even after 13th cycle (149.5 µmol/g) as found during 1st cycle (151.8 µmol/g). An average production of 150.4 µmol/g of CO (per cycle) was obtained, which leads to a time-averaged CO production rate of 601.8 µmol/g/hr. This is significantly higher than that found with CeO2 (200.9 µmol/g/hr). Our previous investigation of Ln0.5A0.5MnO3 (Ln= La, Nd, Sm, Gd, Dy and Y; A=Sr, Ca) family of perovskites has shown Y0.5Sr0.5MnO3 to be the best performing material for the twostep process.24, 34 Y0.5Sr0.5MnO3 not only enhances the O2 and CO production but it also lowers the reduction/oxidation temperature significantly. The performance of Y0.5Sr0.5MnO3 is much


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superior to all the other manganite perovskites due to its low tolerance factor and high size disorder. In the present study, we have investigated Y0.5Sr0.5MnO3 for isothermal CO2 splitting.

(a)

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Figure 4. (a) Representative TGA and (b) corresponding histogram of ITCS of YSM50 (T I= 1573K and 1673K). Reduction (𝑝O2 =10-5 atm) and oxidation (𝑝CO2 = 1 atm) half cycle times are 15 min with flow rates of gases are 1000 ml/min/g of oxides. Error bars indicate max/min values of multiple runs. Y0.5Sr0.5MnO3 (YSM50) undergoes reduction at a much lower temperature (~1200K) in comparison with LSM50 (~1320K) during TSCS.24, 34 We have, therefore, carried out a ITCS study with YSM50. YSM50 shows remarkably good CO (O2) production of 183 µmol/g (96 µmol/g) and 196.4 µmol/g (108 µmol/g) at 1573K and 1673K respectively (Figure 4). In comparison with LSM50, the CO yield of YSM50 is ~1.25 times higher at 1673K and ~1.8 times higher even at 1573K (Figure 5). The average CO production rate of YSM50 was 61.2 µmol/min/g, significantly higher than LSM50 (34 µmol/min/g) at 1673K. It is noteworthy that the CO yield of YSM50 is about 3.8 times higher than CeO2 at 1673K. As YSM50 has a higher


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reducibility (δeqm) or lower enthalpy of reduction than LSM50 under similar T I, it encounters the need of more oxidant supply for reversible CO production. But, considering the system with heat recovery facilities from fluid might make YSM50 perovskite more applicable, in view of their higher fuel productivity, lower irradiance loss of solar reactor (ηabs = f(T, C))3,

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thermal stress related to significantly lower reaction temperature.

Figure 5. (a) TG plots of ITCS of YSM50 (solid line) in comparison with LSM50 (dotted line). Blue and red lines belong to measurements at TI of 1673K and 1573K respectively. Reaction conditions are same as in figure 4. (b) Histograms quantifies the CO production of YSM50 with respect to LSM50 (1573K and 1673K).15 Error bars indicate max/min values of multiple runs. Decreasing the rare earth ion sizes decreases the tolerance factor (τ) of manganites.35 Decrease in  indicates an increase in the lattice distortion, accompanied by increase in the tilting of the MnO6 octahedra which would favor O2 evolution.24, 35 Increase in τ decreases the Mn-OMn bond angles, which in turn reduces the spatial overlap of Mn eg and O 2p orbitals,35 which


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would ease oxide ions removal. Y0.5Sr0.5MnO3 with the smallest tolerance factor (τ= 0.965) and therefore shows the highest O2 yield and CO production. Y0.5Sr0.5MnO3 shows activity at a lower isotherm as expected from the large size variance factor (2) and the small tolerance factor (). The size variance factor, 2, arises from radii mismatch of Ln and A cations in Ln0.5A0.5MnO3 perovskites.36 It indicates greater displacement of the oxygens from the mean position which helps their easy removal.36 The 2 value of Y0.5Sr0.5MnO3 (15.610-3) is higher than that of La0.5Sr0.5MnO3 (1.610-3).24 After high temperature cycling, the structures of the perovskites were investigated by PXRD. LSM30, LSM40 and LSM50 remain chemically stable after isothermal cycles and no secondary phase was detected (Figure S20a). Sintering of the porus structure leads to the formation of larger crystallites (≥ 20 µm) besides smaller grains (~1-2 µm) as shown for LSM50 in Figure S20b. YSM50 shows structural stability for isothermal cycling at1673K (blue curve in Figure S21) and no impurity phase occurs. Hexagonal YMnO3 is formed as impurity phase due on heating at temperatures above 1673K as indicated by asterisk in the Figure S21 (black circle in the red curve of Figure S21). The weight gain of the nonstoichiometric oxide on passing CO2 can arise from carbonate formation instead of CO2 splitting alone.37 The CO2 splitting temperature is generally higher than 1573K in all the present experiments. Decomposition of Sr and La carbonates is reported around 1213K and 1073K respectively, which are well below 1273K.37, 38 Carbonate formation is therefore most unlikely in the present study. Galvez et. al37 has observed segregation of CaO or CaCO3 related phases during low temperature oxidation of La0.6Ca0.4MnO3 perovskites by high magnification FESEM images. We have recorded FESEM images (magnification 30000 x200000 x) over multiple places throughout the samples (Figure S22). Other than sintering of the


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microstructural perovskites we have not observed any distinct phase separation related to SrO or SrCO3 segregation. The PXRD patterns of the perovskites before and after thermogravimetric measurements do not show the presence of carbonate peaks (Figures S20a and S21). Besides, the CO measured by GC-TCD is in good agreement with the CO expected from TGA measurements, ruling out the possibility of carbonate formation. The present study shows how manganite perovskites perform well in the isothermal thermochemical CO2 splitting process. What is especially noteworthy is that the CO production with LSM50 is around 2.8 times and 3.5 times higher than with CeO2 at 1673 and 1773K respectively. Increasing the reduction time increases CO production further, reaching about 56% of thermodynamically estimated CO2 conversion. What is more interesting is that one can lower the redox temperature to 1573K by using Y0.5Sr0.5MnO3 (YSM50). Even at 1573K, YSM50 produces ~1.8 times more CO than LSM50. The CO yield of YSM50 at 1673K is 3.8 times higher than CeO2. These results are significant for possible use in practical solution considering that solar thermal splitting of CO2 has been demonstrated with CeO2. Experimental Sections: Synthesis and Characterization: Reactive oxides were obtained by cutting porus monolith. Initially, La1-xSrxMnO3 (x=0.3-0.5), Y0.5Sr0.5MnO3 and CeO2 are prepared by modified Pecini route. Stoichiometric amounts of metal nitrate precursors were dissolved in water followed by slow addition of EDTA dissolved in NH4OH and citric acid (EDTA: citric acid: metal cations molar ratio= 1:1:2). Excess NH4OH was added to make the final solution become transparent (pH=10). The gel was formed at 80C, followed by 12 hrs drying at 200C. The product was heated at 800C (5 hrs) under air to remove the organics. To obtain the porous monolith these


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powder particles were mixed with isopropanol and the thick paste was mounted on a cylindrical alumina crucible (diameter~10mm) and further heated at 1500°C (1773K) for 2 hrs under air. PXRD analysis was performed with a Bruker D8 Advance diffractometer using Cu K radiation in the range of 20-120. Lebail fitting was performed using Fullprof software in order to obtain the cell parameters. FESEM images and Energy Dispersive X-Ray analysis (EDAX) was carried out by FEI Nova Nanosem 600. BET measurements were performed in Quantachrome Autosorb instrument at 77K from N2 absorption. Reactivity Tests: Isothermal CO2 splitting experiments were performed by thermo gravimetric measurement (TGA) using a Mettler Toledo TGA 1 instrument. About 100 mg of porus body (obtained by cutting the porus monolith) was placed in a platinum crucible and kept inside the furnace chamber. The sample was heated to the reduction temperature (Tred) at a ramping rate of 25C/min under continuous flow of 10-5 atm of O2 premixed with N2 (10 ppm of O2 premixed with N2, accuracy ± 2% , certified by Chemix gases pvt. ltd.) and maintained for 15 min. Gas switching was performed immediately by injecting 100% CO2 (𝑝CO2 =1 atm) inside the furnace chamber at the same temperature and maintained for 15 min. Gas flow rate was 1000 ml/min/g. Quantification of O2 and CO produced was done by calculating the change in mass (eqns. S5 and S6). Other special reactions conditions are mentioned in supporting information in detail. During oxidation, the product gas was collected in a metal collector attached with pressure gauge and analyzed by a Gas chromatograph (Agilent) equipped with a TCD detector. Concentration of CO was detected from calibration curve. ASSOCIATED CONTENT Supporting Information. Experimental details, Lebail fitted PXRD patterns, structural parameters, EDAX spectra, FESEM images, thermodynamic calculation details, plot of CO


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variation with 𝑝CO2 , TG calculation details, evaluation of δeq, TGA of CeO2, experimental vs theoretical CO yield comparison, CO yield as a function of reduction time, sweep gas and CO 2 flow rates, GC-TCD CO detection.

AUTHOR INFORMATION *[email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT SD would like to thank CSIR for SRF fellowship and the awarded Sheikh Saqr student fellowship. SD is thankful to Mr. Vasudeva for helping with TGA measurements. REFERENCES (1)

Kodama, T.; Gokon, N. Thermochemical Cycles for High-Temperature Solar Hydrogen

Production. Chem. Rev. 2007, 107, 4048-4077. (2)

Scheffe, J. R.; Steinfeld, A. Oxygen Exchange Materials for Solar Thermochemical

Splitting of H2O and CO2: A Review. Materials Today 2014, 17, 341-348. (3)

Scheffe, J. R.; Weibel, D.; Steinfeld, A. Lanthanum-Strontium-Manganese Perovskites as

Redox Materials for Solar Thermochemical Splitting of H2O and CO2. Energy Fuels 2013, 27, 4250-4257. (4)

Chueh, W. C.; Falter, C.; Abbott, M.; Scipio, D.; Furler, P.; Haile, S. M.; Steinfeld, A.

High-Flux

Solar-Driven

Thermochemical

Dissociation

of

CO2

and

H2O

Using

Nonstoichiometric Ceria. Science 2010, 330, 1797-1801.


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(5)

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Scheffe, J. R.; Jacot, R.; Patzke, G. R.; Steinfeld, A. Synthesis, Characterization, and

Thermochemical Redox Performance of Hf4+, Zr4+, and Sc3+ Doped Ceria for Splitting CO2. J. Phys. Chem. C 2013, 117, 24104-24114. (6)

Le Gal, A.; Abanades, S. Dopant Incorporation in Ceria for Enhanced Water-Splitting

Activity during Solar Thermochemical Hydrogen Generation. J. Phys. Chem. C 2012, 116, 13516-13523. (7)

McDaniel, A. H.; Miller, E. C.; Arifin, D.; Ambrosini, A.; Coker, E. N.; O'Hayre, R.;

Chueh, W. C.; Tong, J. Sr- and Mn-Doped LaAlO3-δ for Solar Thermochemical H2 and CO Production. Energy Environ. Sci. 2013, 6, 2424-2428. (8)

Deml, A. M.; Stevanovic, V.; Holder, A. M.; Sanders, M.; O'Hayre, R.; Musgrave, C. B.

Tunable Oxygen Vacancy Formation Energetics in the Complex Perovskite Oxide SrxLa1xMnyAl1-yO3.

(9)

Chem. Mater. 2014, 26, 6595-6602.

Singh, P.; Hegde, M. S. Ce0.67Cr0.33O2.11: A New Low-Temperature O2 Evolution

Material and H2 Generation Catalyst by Thermochemical Splitting of Water. Chem. Mater. 2010, 22, 762-768. (10)

Bulfin, B.; Lowe, A. J.; Keogh, K. A.; Murphy, B. E.; Lubben, O.; Krasnikov, S. A.;

Shvets, I. V. Analytical Model of CeO2 Oxidation and Reduction. J. Phys. Chem. C 2013, 117, 24129-24137. (11)

Chueh, W. C.; Haile, S. M. A Thermochemical Study of Ceria: Exploiting an Old

Material for New Modes of Energy Conversion and CO2 Mitigation. Phil. Trans. R. Soc. A 2010, 368, 3269-3294.


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(12)

Dey, S.; Naidu, B. S.; Rao, C. N. R. Beneficial Effects of Substituting Trivalent ions in

the B-site of La0.5Sr0.5Mn1-xAxO3 (A= Al, Ga, Sc) on the Thermochemical Generation of CO and H2 from CO2 and H2O. Dalton Trans. 2016, 45, 2430-2435. (13)

Bader, R.; Venstrom, L. J.; Davidson, J. H.; Lipinski, W. Thermodynamic Analysis of

Isothermal Redox Cycling of Ceria for Solar Fuel Production. Energy Fuels 2013, 27, 55335544. (14)

Le Gal, A.; Abanades, S.; Bion, N.; Le Mercier, T.; Harle, V. Reactivity of Doped Ceria-

Based Mixed Oxides for Solar Thermochemical Hydrogen Generation via Two-Step WaterSplitting Cycles. Energy Fuels 2013, 27, 6068-6078. (15)

Hao, Y.; Yang, C. K.; Haile, S. M. High-Temperature Isothermal Chemical Cycling for

Solar-Driven Fuel Production. Phys. Chem. Chem. Phys. 2013, 15, 17084-17092. (16)

Muhich, C. L.; Evanko, B. W.; Weston, K. C.; Lichty, P.; Liang, X.; Martinek, J.;

Musgrave, C. B.; Weimer, A. W. Efficient Generation of H2 by Splitting Water with an Isothermal Redox Cycle. Science 2013, 341, 540-542. (17)

Diver, R. B.; Miller, J. E.; Siegel, N. P.; Moss, T. A. Testing of a CR5 Solar

Thermochemical Heat Engine Prototype, ASME 2010 4th International Conference on Energy Sustainability, 2010; 97-104. (18)

Michalsky, R.; Botu, V.; Hargus, C. M.; Peterson, A. A.; Steinfeld, A. C. Design

Principles for Metal Oxide Redox Materials for Solar-Driven Isothermal Fuel Production. Adv. Energy Mater. 2015, 5, 1401082(1-10). (19)

Ermanoski, I.; Miller, J. E.; Allendorf, M. D. Efficiency Maximization in Solar-

Thermochemical Fuel Production: Challenging the Concept of Isothermal Water Splitting. Phys. Chem. Chem. Phys. 2014, 16, 8418-8427.


21

ACS Energy Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(20)

Page 22 of 24

Venstrom, L. J.; De Smith, R. M.; Hao, Y.; Haile, S. M.; Davidson, J. H. Efficient

Splitting of CO2 in an Isothermal Redox Cycle Based on Ceria. Energy Fuels 2014, 28, 27322742. (21)

Furler, P.; Scheffe, J. R.; Steinfeld, A. Syngas Production by Simultaneous Splitting of

H2O and CO2 via Ceria Redox Reactions in a High-Temperature Solar Reactor. Energy Environ. Sci. 2011, 5, 6098-6103. (22)

Yang, C. K.; Yamazaki, Y.; Aydin, A.; Haile, S. M. Thermodynamic and Kinetic

Assessments

of

Strontium-Doped

Lanthanum

Manganite

Perovskites

for

Two-Step

Thermochemical Water Splitting. J. Mater. Chem. A 2014, 2, 13612-13623. (23)

Panlener, R. J.; Blumenthal, R. N.; Garnier, J. E. A Thermodynamic Study of

Nonstoichiometric Cerium Dioxide. J. Phys. Chem. Solids 1975, 36, 1213-1222. (24)

Dey, S.; Naidu, B. S.; Rao, C. N. R. Ln0.5A0.5MnO3 (Ln=Lanthanide, A= Ca, Sr)

Perovskites Exhibiting Remarkable Performance in the Thermochemical Generation of CO and H2 from CO2 and H2O. Chem. Eur. J. 2015, 21, 7077-7081. (25)

Dey, S.; Naidu, B. S.; Govindaraj, A.; Rao, C. N. R. Noteworthy Performance of La1-

xCaxMnO3

Perovskites in Generating H2 and CO by the Thermochemical Splitting of H2O and

CO2. Phys. Chem. Chem. Phys. 2015, 17, 122-125. (26)

Demont, A.; Abanades, S. High Redox Activity of Sr-Substituted Lanthanum Manganite

Perovskites for Two-Step Thermochemical Dissociation of CO2. RSC Adv. 2014, 4, 5488554891. (27)

Demont, A.; Abanades, S.; Beche, E. Investigation of Perovskite Structures as Oxygen-

Exchange Redox Materials for Hydrogen Production from Thermochemical Two-Step WaterSplitting Cycles. J. Phys. Chem. C 2014, 118, 12682-12692.


22

Page 23 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Energy Letters

(28)

Cooper, T.; Scheffe, J. R.; Galvez, M. E.; Jacot, R.; Patzke, G.; Steinfeld, A. Lanthanum

Manganite Perovskites with Ca/Sr A-site and Al B-site Doping as Effective Oxygen Exchange Materials for Solar Thermochemical Fuel Production. Energy Technology 2015, 3, 1130-1142. (29)

Bork, A. H.; Kubicek, M.; Struzik, M.; Rupp, J. L. M. Perovskite La0.6Sr0.4Cr1-xCoxO3-δ

Solid Solutions for Solar-Thermochemical Fuel Production: Strategies to Lower the Operation Temperature. J. Mater. Chem. A 2015, 3, 15546-15557. (30)

Takacs, M.; Hoes, M.; Caduff, M.; Cooper, T.; Scheffe, J. R.; Steinfeld, A. Oxygen

Nonstoichiometry, Defect Equilibria, and Thermodynamic Characterization of LaMnO3 Perovskites with Ca/Sr A-Site and Al B-Site doping. Acta Materialia 2016, 103, 700-710. (31)

Mizusaki, J.; Mori, N.; Takai, H.; Yonemura, Y.; Minamiue, H.; Tagawa, H.; Dokiya,

M.; Inaba, H.; Naraya, K.; Sasamoto, T. Oxygen Nonstoichiometry and Defect Equilibrium in the Perovskite-type Oxides La1−xSrxMnO3+d. Solid state ionics 2000, 129, 163-177. (32)

Tagawa, H.; Mori, N.; Takai, H.; Yonemura, Y.; Minamiue, H.; Inaba, H.; Mizusaki, J.;

Hashimoto, T. Oxygen Nonstoichiometry in Perovskite-type Oxide, Undoped and Sr-Doped LaMnO3, Proceedings of the 5th International Symposium on Solid Oxide Fuel Cells (SOFC-V), 1997; 785-794. (33)

Hao, Y.; Yang, C.-K.; Haile, S. M. Ceria-Zirconia Solid Solutions (Ce1–xZrxO2−δ, x ≤ 0.2)

for Solar Thermochemical Water Splitting: A Thermodynamic Study. Chem. Mater. 2014, 26, 6073-6082. (34)

Rao, C. N. R.; Dey, S. Generation of H2 and CO by Solar Thermochemical Splitting of

H2O

and

CO2

by

Employing

Metal

Oxides.

J.

Solid

State

Chem.

2015,

DOI.org/10.1016/j.jssc.2015.12.018.


23

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(35)

Page 24 of 24

Woodward, P. M.; Vogt, T.; Cox, D. E.; Arulraj, A.; Rao, C. N. R.; Karen, P.; Cheetham,

A. K. Influence of Cation Size on the Structural Features of Ln1/2A1/2MnO3 Perovskites at Room Temperature. Chem. Mater. 1998, 10, 3652-3665. (36)

Attfield, J. P. A Simple Approach to Lattice Effects in Conducting Perovskite-Type

Oxides. Chem. Mater. 1998, 10, 3239-3248. (37)

Galvez, M. E.; Jacot, R.; Scheffe, J.; Cooper, T.; Patzke, G.; Steinfeld, A. Physico-

Chemical Changes in Ca, Sr and Al-Doped La-Mn-O Perovskites upon Thermochemical Splitting of CO2 via Redox Cycling. Phys. Chem. Chem. Phys. 2015, 17, 6629-6634. (38)

Sarbajna, R.; Devi, A. S.; Purandhar, K.; Suryanarayana, M. V. Thermogravimetric

Method Validation and Study of Lanthanium Carbonate Octahydrate and its Degradants. Int. J. of ChemTech Research 2013, 5, 2810-2820.


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Splitting of CO2 by Manganite Perovskites to Generate CO by Solar

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