Solar Thermochemical Splitting Of CO2 Research Articles

High-entropy perovskite oxides for direct solar-driven thermochemical CO2 splitting

The global energy crisis and climate change have fueled interest in solar-driven thermochemical CO2 splitting as a potential solution. However, conventional materials like CeO2 encounter limitations attributable to their low solar absorptivity and CO yield (even at high reduction temperatures), exerting a detrimental influence on both solar energy utilization and process efficiency. This study proposes high-entropy A-site doped perovskites as a potential solution for efficient solar thermochemical CO2 splitting. The increased configurational entropy enhances the solar thermal CO2 splitting cycles by decreasing oxygen vacancy formation energy and lattice oxygen migration energy barrier. This is supported by experimental results, where Sm0.25Sr0.25Ca0.25La0.25MnO3 achieved a maximum CO yield of 764.76 μmol g−1 with low temperature difference between the reduction and oxidation steps, marking an important progress in solar thermal CO2 splitting cycles. The study demonstrates the potential of high-entropy perovskites for direct solar energy harvesting with high spectrum absorption coefficients and sustainable CO2 utilization.

Remarkable solar thermochemical CO2 splitting performances based on Ce- and Al-doped SrMnO3 perovskites

In the solar thermochemical CO2 splitting process, a remarkable CO yield (799.34 μmol g−1) at 1350/1100 °C is reported based on proposed Sr0.6Ce0.4Mn0.8Al0.2O3.

Solar Thermochemical CO2 Splitting Integrated with Supercritical CO2 Cycle for Efficient Fuel and Power Generation

Converting CO2 into fuels via solar-driven thermochemical cycles of metal oxides is promising to address global climate change and energy crisis challenges simultaneously. However, it suffers from low energy conversion efficiency (ηen) due to high sensible heat losses when swinging between reduction and oxidation cycles, and a single product of fuels can hardly meet multiple kinds of energy demands. Here, we propose an alternative way to upsurge energy conversion efficiency by integrating solar thermochemical CO2 splitting with a supercritical CO2 thermodynamic cycle. When gas phase heat recovery (εgg) is equal to 0.9, the highest energy conversion efficiency of 20.4% is obtained at the optimal cycle high pressure of 260 bar. In stark contrast, the highest energy conversion efficiency is only 9.8% for conventional solar thermochemical CO2 splitting without including a supercritical CO2 cycle. The superior performance is attributed to efficient harvesting of waste heat and synergy of CO2 splitting cycles with supercritical CO2 cycles. This work provides alternative routes for promoting the development and deployment of solar thermochemical CO2 splitting techniques.

Direct solar thermochemical CO2 splitting based on Ca- and Al- doped SmMnO3 perovskites: Ultrahigh CO yield within small temperature swing

Solar thermochemical CO2 splitting is a promising route to reduce environment pollution and mitigate energy crisis. However, traditional redox materials are limited by low CO production, slow reaction kinetics, and poor cycling stability, which results in low solar-to-fuel efficiency. Here, Ca- and Al- doped SmMnO3 perovskites are proposed for high-performance solar thermochemical CO2 splitting. The average CO yield of Sm0.6Ca0.4Mn0.8Al0.2O3 reaches a record-high value of 595.56 μmol g−1 when swinging between 1350 °C and 1100 °C. The CO yield is about 4.22 times as high as that of undoped SmMnO3 (140.97 μmol g−1) under the same conditions, and remains stable over multiple cycling. The ultrahigh CO yield can be attributed to the transformation of reaction mechanism from solid-state surface reaction (F2) to bulk diffusion model (D2). Besides, Ca- and Al- doped SmMnO3 perovskites possess high solar absorptance over 86.5% (in stark contrast to 12.1% of CeO2), so that only solar concentration ratio of 898 (Sm0.6Ca0.4Mn0.8Al0.2O3) is required to drive thermochemical reactions while benchmark CeO2 needs 1936. This work provides novel approaches for high-performance solar thermochemical CO2 splitting with high CO yield, good cycle stability, small temperature swing, and low solar concentration required.

Thermodynamic evaluation of solar assisted ZnO/Zn thermochemical CO2 splitting cycle

The solar thermochemical CO2 splitting (CDS) is scrutinized via a redox ZnO/Zn cycle. The second law efficiency analysis is carried out by acquiring the required thermodynamic data from HSC Chemistry software. The main focus of this study is to explore the influence of reduction temperature (Tred), molar flow rate of inert sweep gas (n˙inert), and energy required for the gas separation on the solar-to-fuel energy conversion efficiency (ηsolar−to−fuel) of the ZnO/Zn cycle. All the calculations are conducted at a constant gas-to-gas heat recovery effectiveness (εgg) equal to 0.5. n˙inert required is recorded to be too high (5050 mol/s) at Tred equal to 1500 K and moderately low (15 mol/s) for Tred equal to 2000 K. The amount of thermal energy required to heat the inert/O2 gas mixture (from CDS temperature to separator-1 temperature) and inert sweep gas (from separator-1 temperature to reduction temperature) has a significant impact on the total thermal energy requirement of the cycle (Q˙TC). The rise in Tred from 1500 K to 2000 K shows a considerable decline in Q˙TC from 77417.5 kW to 1161.8 kW, respectively. Consequently, the highest ηsolar−to−fuel (17.0%) is recorded for Tred equal to 2000 K.

Intensified solar thermochemical CO2 splitting over iron-based redox materials via perovskite-mediated dealloying-exsolution cycles

Solar thermochemical CO2-splitting (STCS) is a promising solution for solar energy harvesting and storage. However, practical solar fuel production by utilizing earth-abundant iron/iron oxides remains a great challenge because of the formation of passivation layers, resulting in slow reaction kinetics and limited CO2 conversion. Here, we report a novel material consisting of an iron-nickel alloy embedded in a perovskite substrate for intensified CO production via a two-step STCS process. The novel material achieved an unprecedented CO production rate of 381 mL g−1 min−1 with 99% CO2 conversion at 850 °C, outperforming state-of-the-art materials. In situ structural analyses and density functional theory calculations show that the alloy/substrate interface is the main active site for CO2 splitting. Preferential oxidation of the FeNi alloy at the interface (as opposed to forming an FeOx passivation shell encapsulating bare metallic iron) and rapid stabilization of the iron oxide species by the robust perovskite matrix significantly promoted the conversion of CO2 to CO. Facile regeneration of the alloy/perovskite interfaces was realized by isothermal methane reduction with simultaneous production of syngas (H2/CO = 2, syngas yield > 96%). Overall, the novel perovskite-mediated dealloying-exsolution redox system facilitates highly efficient solar fuel production, with a theoretical solar-to-fuel efficiency of up to 58%, in the absence of any heat integration.

Thermodynamic Discrimination between Energy Sources for Chemical Reactions

Summary Chemical transformations traverse large energy differences, yet the comparison of energy sources to drive a reaction is often done on a case-by-case basis; there is no fundamentally driven, universal framework with which to analyze and compare driving forces for chemical reactions. In this work, we present a reaction-independent expression for the equilibrium constant as a function of temperature, pressure, and voltage. With a specific set of axes, all reactions are represented by a single ( x , y ) point, and a quantitative divide between electrochemically and thermochemically driven reactions is visually evident. Additionally, we show that our expression has a strong physical basis in work and energy fluxes to the system, although specific data about operating conditions are necessary to provide a quantitative energy analysis. Overall, this universal equation and facile visualization of chemical reactions provides a consistent thermodynamic framework for comparing electrochemical versus thermochemical energy sources without knowledge of detailed process parameters.

Thermochemical splitting of CO2 using solution combustion synthesized lanthanum–strontium–manganese perovskites

Redox reactivity of La(1-x)SrxMnO3 (LSM) perovskites towards a solar thermochemical CO2 splitting (CS) cycle is investigated. The LSM perovskites are synthesized via a solution combustion synthesis (SCS) method using glycine as the reducing agent. Multiple analytical techniques are used for the structural characterization of the LSM perovskites. Thermogravimetric thermal reduction (TR) and CS cycles (in three sets: one, three and ten cycles) are conducted to estimate the amounts of O2 released (nO2) and CO produced (nCO) by each LSM perovskite. Higher nO2 by each LSM perovskite, as compared to the nCO during the first cycle. The nO2 is decreased, and the re-oxidation capacity of each LSM perovskite is improved from cycle one to three. In terms of the average nO2 and nCO from cycle 2 to cycle 10, the La0.60Sr0.41Mn0.99O2.993 (214.8 μmol of O2/g·cycle) and La0.30Sr0.70Mn0.99O2.982 perovskites (342.1 μmol of CO/g·cycle) are observed to have the uppermost redox reactivity. The redox reactivity of all the LSM perovskites (except for La0.88Sr0.11Mn1.00O2.980) is recorded to be higher than that of the widely studied CeO2 material.

Solar thermochemical conversion of CO2 via erbium oxide based redox cycle

AbstractInvestigation of the viability of the erbium oxide‐based solar thermochemical CO2 splitting cycle is reported. This study aimed to explore the effect of partial thermal reduction (TR) of Er2O3 on the thermodynamic process parameters desirable to design a solar reactor system for the erbium oxide‐based CO2 splitting (ErO‐CS) cycle. First, the percentage TR of Er2O3 is estimated as a function of the TR temperature (). Acquired results indicated that to achieve a percentage TR of Er2O3 in the range of 5–100%; the solar reactor has to be functioned in the temperature range of = 2327–2677 K. The solar energy required to drive the ErO‐CS cycle () was observed to be on the higher side due to the obligation of the elevated values of . This rise in the as a function of percentage TR of Er2O3 reflected in a decrease in the solar‐to‐fuel energy conversion efficiency (). The maximum = 4.04% is achieved for a percentage TR of Er2O3 = 25% ( = 2432 K). By employing 100% heat recuperation, the (for percentage TR of Er2O3 = 25%) increased up to 5.79%. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Experimental study on the high performance of Zr doped LaCoO3 for solar thermochemical CO production

Solar thermochemical CO production via CO2 splitting is an effective route to achieve carbon cycle and reduce carbon emissions. One of the most important issues for thermochemical fuel production technology is to find a material with high oxygen release capacity and fuel production as well as excellent thermal stability. Due to the excellent oxygen releasing capacity and limited fuel production and durability of LaCoO3, the feasibility of elemental doping for enhancing the redox capacity were studied in detail. Novel and high efficient redox materials, Zr doped LaCoO3 perovskites obtained were firstly used for solar thermochemical CO production. Zr doping is beneficial to improve CO yield and thermochemical redox stability. LaCo0.7Zr0.3O3, an optimum in doping for CO production, produced an average of 1066.6 μmol/g CO, which was an inspiring performance in the current perovskite based thermochemical field. The degree of reduction of LaCo0.7Zr0.3O3 was positively correlated with temperature and heating rate. Kinetics study shows that the activation energy of reduction reaction is 107.1 kJ/mol, which is much lower than that of CeO2, and the reduction process is a first order reaction. This material has better performances by comparison with CeO2 and other similar materials reported in literatures. The excellent CO production performance, pretty redox stability and kinetics manifested by LaCo0.7Zr0.3O3 provided a new approach for exploiting higher performing materials for solar thermochemical CO2 splitting.

Thermodynamic analysis of isothermal CO2 splitting and CO2-H2O co-splitting for solar fuel production

Isothermal solar thermochemistry is a promising approach for deriving solar fuels from concentrated solar energy with potential advantages in reactor design and heat recovery. Previous work has demonstrated the feasibility of isothermal water splitting with ceria, but the solar-to-fuel efficiency and operating temperature range are relatively undesirable. In this study, thermodynamic analysis is performed on the isothermal solar thermochemical splitting of CO2 as well as co-splitting of CO2 and H2O. The cycling reactions are found to exhibit considerably higher solar-to-fuel efficiencies than that of H2O due to the favorable Gibbs free energy change in the CO2 splitting reaction at elevated temperatures and the lower thermal energy requirement for gas heating due to the lack of phase change in CO2. Through the comparison of the conventional temperature-swing (T-swing) cycling strategy, the advantages and disadvantages of both methodologies, as well as indications on system and reactor design, are discussed. Strategies for controlling the composition of solar-syngas derived from isothermal co-splitting of CO2 and H2O mixtures are also proposed.

Experimental screening of perovskite oxides as efficient redox materials for solar thermochemical CO2 conversion

Perovskites and parent Ruddlesden–Popper structures were proved to be suitable redox materials for two-step solar thermochemical CO2 splitting.

Catalytic Reduction of CO2 into Solar Fuels via Ferrite Based Thermochemical Redox Reactions

ABSTRACTIn this study, Ni based ferrite nanomaterials were synthesized using sol-gel method for solar thermochemical splitting of CO2 using a thermogravimetric analyzer. To synthesize the ferrite materials, the corresponding metal precursors were dissolved in ethanol (with required molar ratios). After achieving the dissolution, propylene oxide (PO) was added to achieve the gel formation. Freshly synthesized gels were aged, dried, and calcined by heating up to 600°C in air. Powder x-ray diffractometer (XRD), BET surface area, as well as scanning (SEM) and transmission (TEM) electron microscopy characterized the calcined powders. The sol-gel derived ferrites were further tested towards their thermal reduction and CO2 splitting ability using a high temperature thermogravimetric analyzer (TGA).

Assessment of CexZryHfzO2 based oxides as potential solar thermochemical CO2 splitting materials

In this paper, we report the synthesis, characterization, and assessment of CexZryHfzO2 (CZH) materials for solar thermochemical splitting of CO2 in up to 20 consecutive thermochemical cycles. CZH materials with different stoichiometries were synthesized by using the co-precipitation of hydroxides method. CZH materials acquired after calcination were characterized using powder X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and BET surface area. The thermochemical CO2 splitting ability of the derived CZH materials was assessed by performing multiple thermochemical cycles using a thermogravimetric analyzer. All CZH materials studied exhibit a higher activity than ceria modified with Hf or Zr alone. Thus a synergistic effect seems to be present. Among the different CZH materials examined, Ce0.895Zr0.046Hf0.053O1.988 (CZH5) was observed to be the most active exhibiting a sustained redox activity in terms of CO production/O2 release in the temperature range of 1000–1400°C. Moreover, CZH5 was subjected to 20 consecutive thermochemical cycles during which no degradation could be observed. The results obtained indicate that CZH5 is a promising candidate for solar thermochemical conversion of CO2 as it is capable of producing stable amounts of O2 and CO in multiple thermochemical cycles.

Design Principles for Metal Oxide Redox Materials for Solar-Driven Isothermal Fuel Production.

The performance of metal oxides as redox materials is limited by their oxygen conductivity and thermochemical stability. Predicting these properties from the electronic structure can support the screening of advanced metal oxides and accelerate their development for clean energy applications. Specifically, reducible metal oxide catalysts and potential redox materials for the solar-thermochemical splitting of CO2 and H2O via an isothermal redox cycle are examined. A volcano-type correlation is developed from available experimental data and density functional theory. It is found that the energy of the oxygen-vacancy formation at the most stable surfaces of TiO2, Ti2O3, Cu2O, ZnO, ZrO2, MoO3, Ag2O, CeO2, yttria-stabilized zirconia, and three perovskites scales with the Gibbs free energy of formation of the bulk oxides. Analogously, the experimental oxygen self-diffusion constants correlate with the transition-state energy of oxygen conduction. A simple descriptor is derived for rapid screening of oxygen-diffusion trends across a large set of metal oxide compositions. These general trends are rationalized with the electronic charge localized at the lattice oxygen and can be utilized to predict the surface activity, the free energy of complex bulk metal oxides, and their oxygen conductivity.

CO2 and H2O Splitting for Thermochemical Production of Solar Fuels Using Nonstoichiometric Ceria and Ceria/Zirconia Solid Solutions

The solar thermochemical splitting of CO2 and H2O with ceria and Zr-doped ceria for CO and H2 production is considered. The two-step process is composed of the thermal reduction of the ceria-based compound followed by the oxidation of the nonstoichiometric ceria with CO2/H2O to generate CO/H2, respectively. As a reference, the reactivity of pure undoped ceria was first characterized during successive thermochemical cycles using a thermobalance. Then, Zr0.25Ce0.75O2 was synthesized using different soft chemical synthesis routes to evaluate the influence of the powder morphology on the reactivity during the reduction and the oxidation steps. The reduction yield of ceria was significantly improved by doping with Zr as well as the CO/H2 production yields, but the kinetic rates of the oxidation step for doped ceria were lower than for pure ceria. CO and H2 production of 241 and 432 μmol/g, respectively, have been measured. A kinetic analysis of the CO2-splitting step allowed one to estimate the activation ener...