Oxygen Carriers For Chemical Looping Research Articles

Use of a high-entropy oxide as an oxygen carrier for chemical looping

One mixed oxide with 5 cations in equimolar proportions in the sublattice, to fulfil high-entropy oxide (HEO) criteria, has been developed and investigated as oxygen carrier for chemical looping combustion processes. As far as we know, nobody has explored this class of material for chemical looping combustion. Material is prepared by direct mixing of five metal oxides (CuO, Mn2O3, Fe2O3, TiO2, MgO), followed by calcination at 1000, 1100 and 1200 °C for 6 h in air. XRD characterization provides strong evidence that the synthesized oxygen carriers possess the hallmark properties of HEO, and SEM-EDX analysis shows an overall homogeneous metal distribution. Materials have one main cubic phase with the empirical formula MnCuMgFeTiO7, dominating under all conditions. One of the key objectives of this study is achieved, reduce chemical stress during redox cycles. Oxygen transfer capability is investigated by thermogravimetric analysis and batch fluidized bed reactor experiments for different fuels and atmospheres. Mass-based oxygen transport capacities for lattice oxygen and oxygen uncoupling are around 5.5 wt% and 1.1 wt%, respectively. This work opens up a new dimension for the future preparation of oxygen carriers for chemical looping processes, since the vast compositional space of HEO provides opportunities to tune both chemical and physical characteristics.

Solution Combustion Synthesis of Ce‐based Composite Oxygen Carriers for Chemical Looping Reforming of Methane

AbstractEfficient activation and the conversion of methane to value‐added products have long attracted interest. Chemical looping reforming has become a competitive technology to transform methane into syngas that can act as raw material for various chemicals. In this paper, the methane chemical looping reforming reactivity of the Ce−Co composite oxygen carriers fabricated with different preparation methods, including solution combustion, ball‐milling, hydrothermal, and co‐precipitation method, are investigated on a fixed‐bed. Various bulk/surface characterizations (TEM, XRD, BET, XPS, Raman, etc.) were applied to reveal the effect of preparation methods on the properties of these oxygen carriers. The results indicate that the oxygen carrier prepared by the solution combustion method exhibits excellent methane conversion, high syngas yield, and desirable H2/CO ratio, as well as stable regenerability because of its relatively small crystal size, large specific surface area, high oxygen vacancy concentration and Ce3+/Ce4+ ratio. This work may be helpful in the preparation of highly active and stable oxygen carriers for chemical looping reforming reaction of methane.

Effect of low-loading of Ni on the activity of La0.9Sr0.1FeO3 perovskites for chemical looping dry reforming of methane

Methane dry reforming (MDR) is a very appealing process to bring back waste CO2 into the chemical production chain. Operating in chemical looping (CL) conditions allows to reduce deactivation by coke deposition and facilitates the use of concentrating solar energy to power this reaction. Perovskites have successfully applied as oxygen carriers for chemical looping, and those of the family La1−xSrxFeO3 having lower Sr content have showed high activity and cycling stability for MDR. To further enhance the performance of these oxygen carriers, in this work we evaluate the impact of dispersing Ni in low concentration (<1 mol %) on the performance of La0.9Sr0.1FeO3 for CL-MDR. Simple impregnation allows to distribute evenly the metal, which according to XPS is present as Ni2+ in the fresh material. CH4-TPR reveal that NiOx species are firstly reduced at around 650 ºC and they shift the onset of methane partial oxidation to lower temperatures with regards to the unmodified perovskite. However, during isothermal CL tests at 850 ºC, the presence of Ni does not modify much the syngas production during the methane reforming stage, although the H2/CO ratio increases with the presence of this metal. This indicates an increment in the contribution of methane cracking. In contrast, when feeding CO2, the generation of CO is greatly enhanced by the incorporation of Ni, particularly at a loading of 0.4 mol %, while higher metal concentration are slightly less effective. Higher CO generation is attributed to the promotion of reverse Boudouard reaction, which can remove the coke previously deposited in the methane reforming stage. Accordingly, the Ni/ La0.9Sr0.1FeO3 presents stable activity during several consecutive cycles.

A DFT-based microkinetic theory for Fe2O3 reduction by CO in chemical looping

Redox kinetics of oxygen carrier in chemical looping is an important component for material preparation, reactor design and process demonstration. How to bridge the gap between the microscale density functional theory (DFT) and the macroscale redox kinetics and develop a first-principle-based theoretical model is still a challenge in the field of chemical looping. This study addresses this challenge and proposes a DFT-based microkinetic rate equation theory to calculate the heterogeneous kinetics of Fe2O3 reduction by CO in chemical looping. Firstly, the DFT calculation is adopted to search the reaction pathways and to obtain the energy barriers of elementary reactions. Secondly, the DFT results are introduced into the transition state theory (TST) to calculate the reaction rate constants and build the rate equations of elementary surface reactions. Finally, by considering the bulk diffusion, a rate equation is developed to bridge the gap between the elementary surface reactions and the grain conversion. In the theory, the reaction mechanism obtained from DFT and kinetic rate constants obtained from TST are directly implemented into the rate equation to predict the reduction kinetics of oxygen carriers without fitting experimental data. The accuracy of the developed theory is validated by experimental data of two Fe2O3 oxygen carriers obtained from the thermogravimetric analyzer (TGA). The microkinetic rate equation theory is based on the first principles calculation and can predict directly the redox kinetics of oxygen carriers without depending on the experimental kinetic data, therefore, it provides a powerful theoretical tool to screen the oxygen carrier materials and optimize the microstructure of oxygen carriers.

Multi-scale kinetic study of the oxygen uncoupling of CuO oxygen carrier in chemical looping

As the kinetic influencing factors were not considered properly in the previous studies, the obtained oxygen uncoupling kinetics of CuO oxygen carrier varies greatly. In this paper, a multi-scale methodology is proposed to explore the oxygen uncoupling kinetics of CuO oxygen carrier through well-designed thermogravimetric experiments and multi-scale modelling. In order to minimize the effects of gas diffusion, a self-made thermogravimetric analyzer (TGA) is built firstly to measure the oxygen uncoupling rates of CuO samples. A multi-scale kinetic analysis model in which many influencing factors are considered is then established to analyze the experimental results. The kinetic parameters are thus extracted. Finally, based on the obtained intrinsic reaction kinetics, the effects of the physical structure of CuO oxygen carrier particle on its oxygen uncoupling rate are analyzed. It is found from this study that under typical CLOU conditions, neutral and singly charged copper vacancies are the dominant point defects in the product layer of CuO, and the chemical diffusions of these defects are NOT the rate limiting step. The gas diffusion in TGA crucible, the gas diffusion in sample layer, the polydispersity of the samples and the sintering of the samples are all important to describe the conversion process of the CuO samples. Among these, the effect of gas diffusion in the sample layer is less significant than that in the crucible. It is found that there is an optimal grain size (that is, 245 nm) of CuO oxygen carrier particle to maximize the averaged conversion rate of the particle, and the intrinsic activation energy and the pre-exponential factor of the oxygen uncoupling of CuO are determined to be 281.23 kJ/mol and 5.679 × 1016 mol/(m2s), respectively.

CuO/ZrO2 modified by WO3 oxygen carriers for chemical looping with oxygen uncoupling

The use of mixed metal oxides as oxygen carriers for chemical looping with oxygen uncoupling (CLOU) applications has shown great potential compared to single metal oxide-based oxygen carriers. In this work, the effects of adding WO3 to CuO/ZrO2 oxygen carriers on the oxygen capacity and rate indices for CLOU applications are investigated using nitrogen gas environment. Two synthesis methods were used to prepare the CuO-WO3/ZrO2 oxygen carriers, namely the coimpregnation and sequential impregnation, to evaluate the role of the oxygen carriers’ preparation method. The resulting oxygen carriers were thoroughly characterized using XRD, ICP-OES, SEM-EDS and H2-TPR characterization techniques to evaluate the physicochemical properties of the mixed oxide oxygen carriers. The oxygen transport capacity was found to significantly increase for the WO3-modified oxygen carriers compared with the single metal oxide CuO/ZrO2 which was due to the formation of a Cu-W intermediate phases that was found to enhance the redox characteristics of the oxygen carriers. Moreover, the sample synthesized via coimpregnation method displayed higher oxygen release capacity than the sequentially impregnated sample. This was ascribed to the formation a Cu-rich intermediate phase (Cu3WO6) possessing higher Cu/W ratio on the coimpregnated sample compared with a CuWO4-x phase with lower Cu/W ratio and larger crystallite structure formed on the sequentially impregnated oxygen carrier. The mixed metal oxide oxygen carriers also showed a stable redox performance which highlights the potential of WO3 as a modifier to Cu-based oxygen carriers to enhance the oxygen capacity and subsequently decrease the solids inventory. The proposed WO3-based promotors offer significant trait to synthesize Cu-based oxygen carriers with excellent properties for CLOU applications.

First-principles-based microkinetic rate equation theory for oxygen carrier reduction in chemical looping

The reduction kinetics of oxygen carriers with reacting gases are typically modeled using shrinking-core-based models, in which, the elemental surface reaction mechanisms are simplified as only one global reaction, and the kinetic parameters are obtained by fitting with experimental data. In this study, a theoretical scheme is proposed to couple the elemental surface reaction mechanisms with the bulk diffusion of lattice oxygen, and a first-principle-based microkinetic rate equation theory is developed to model the reduction kinetics of oxygen carrier in chemical looping. The elemental surface reaction mechanisms are computed using quantum chemistry and are integrated into the mean-field microkinetic model, in which, oxygen bulk diffusion is also included. The elemental steps of gas adsorption, surface reaction, and surface species desorption are considered in the theory. The kinetic parameters used in the model are directly calculated by using transition state theory and density functional theory instead of fitting with experimental data. The developed theory is applied to predict the reduction kinetics of a CaMn0.775Ti0.125Mg0.1O2.9-δ perovskite oxygen carrier and validated to accurately predict the reduction kinetics by H2 and CO under a wide range of temperatures and gas concentrations. The effect of surface reaction and bulk diffusion on the overall reaction rate is analyzed and the rate-controlling step is discussed. When the bulk diffusion is considerably rapid, the interior oxygen concentration in the grain remains uniform throughout the reduction process and can be considered as a function of time only. Lumped parameter analysis is used to simplify the bulk diffusion of lattice oxygen without sacrificing accuracy. The developed microkinetic rate equation theory couples the surface reaction mechanism with the bulk diffusion, bridges the gap between atom-scale first-principles quantum chemistry calculations with particle-scale heterogeneous kinetics, and provides a theoretical framework for oxygen carrier reduction/oxidation kinetics, gas conversion mechanisms, and product selectivity in chemical looping.

Microstructured ZrO2 coating of iron oxide for enhanced CO2 conversion

This work provides a way to design oxygen carriers for chemical looping. Starting from Prussian blue microcubes, Zr-promoted Fe-based materials are developed for the conversion of CO2 into CO. Thermally induced oxidative decomposition of ZrO2-coated Prussian blue under the protection of the firstly formed ZrO2 shell leads to the formation of hollow structured materials.Detailed activity tests and in-situ characterization are used to investigate the relationship between material structure, stability and CO yield from CO2 conversion. Throughout one hundred H2-CO2 redox cycles, 10 %Fe2O3/ZrO2 exhibits a 27 times higher CO space-time yield (86mmol∙s-1∙kgFe2O3-1) than unpromoted, yet hollow structured Fe2O3. This superior performance derives from the dual role that ZrO2 plays: protecting the structure, thereby improving the iron oxide sintering resistance, and facilitating the reduction of iron oxide during redox cycles. The hollow structure and the interaction between Fe2O3 and ZrO2 are the main reasons for the enhanced redox activity.

Revisiting the thermal and chemical expansion and stability of La0.6Sr0.4FeO3−δ

The thermal and chemical expansivity of La1-xSrxFeO3-δ (x ​= ​0.4) was measured using in situ powder neutron and synchrotron X-ray diffraction at temperatures between 932 ​K and 1170 ​K and oxygen partial pressures, PO2, between 10−19 ​bar and 0.1 ​bar, giving a wide range of oxygen non-stoichiometry from δ= 0.05 to 0.22. Changes in δ were measured independently using gas analysis. This PO2 and temperature range covers the material’s use as a chemical looping oxygen carrier, a sensor material and in solid oxide fuel cells. Thermal and chemical expansivities were found to be dependent on the oxygen non-stoichiometry, δ. For δ ​< ​0.2 and T ​= ​932–1050 ​K, the linear thermal expansivity was 5.72(4) ​× ​10−5 ​Å/K and the linear chemical expansivity was 0.144(9) Å per unit change in δ. For δ ​> ​0.2 and T ​= ​973–1173 ​K, the linear thermal expansivity increases to 6.18(8) ​× ​10−5 ​Å/K. For δ ​> ​0.2, the linear chemical expansivity varies with both δ and temperature.

Predictive screening and validation on chemical looping oxygen carrier activation by tuning electronic structures via transition metal dopants

Owing to its high fuel conversion efficiency and in-situ CO2 capture capability, chemical looping is a promising and versatile platform for fossil fuel utilization. Through the circulation of oxygen carriers (OCs), which are usually metal oxides, the carbonaceous fuels are oxidized into power/heat and/or value-added chemicals by lattice oxygen of OC in the fuel reactor. The reactivity of OC towards the carbonaceous fuels is crucial to the success of chemical looping processes. Incorporating low-percentage dopants into OC is a promising strategy to improve their reactivity while maintaining the recyclability. Consequently, a systematic screening strategy in dopant selection with a solid physical foundation is highly desired. Using hematite (α-Fe2O3) as the model OC material, density functional theory calculations were conducted herein to exemplify the impact of transition metal dopants on the surface reactivity with CO and CH4, the two most common C1 reducing agents in fossil fuels. We found that the amount of electrons accumulated on the lattice oxygen that bound with dopants is a key descriptor to evaluating the surface reactivity in the Mars-van Krevelen type reactions, which can be tailored by dopants with different electronegativities. Cu and Ni were predicted to be the most effective dopants, and such theoretical predictions were validated in temperature-programmed reduction and cyclic redox experiments, where a significant reactivity enhancement was observed using only 1% atomic ratio of effective dopants. The proposed screening strategy is expected to facilitate new OC designs and modifications in an energy and cost effective manner, thus significantly expedites the development of chemical looping technologies.

Cyclic reactivity of the sol–gel and graphite impregnation-derived Cu-based oxygen carriers for chemical looping with oxygen uncoupling

Chemical looping with oxygen uncoupling (CLOU) is a promising technology to be used in combination with the oxy-fuel combustion/gasification processes for carbon capture and sequestration in that it reduces the energy penalty for O2 generation; hence, much attention has been focused on the production of proper oxygen carriers. In this work, four oxygen carrier candidates for CLOU made of 90% CuO and 10% ZrO2 or Y2O3 are first prepared with the sol–gel and graphite impregnation methods. The reduction reactivity of the prepared oxygen carriers is investigated at 900, 950, and 1000 °C in the CO2 atmosphere, and the redox stability is evaluated through ten sequential cycles using the thermogravimetric analyzer. It is found that the Avrami–Erofeev random nucleation and subsequence growth model (A2) describes the reduction process very well. CuO/ZrO2 prepared by the graphite impregnation performs better reactivity and stability than the others. The agglomeration and sintering of the oxygen carriers at high temperatures are found to be the main cause of the low reactivity over the repeated cycles.

The competition between direct gas–solid reduction and oxygen uncoupling of CuO oxygen carrier in chemical looping with oxygen uncoupling: A single particle simulation study

In chemical looping with oxygen uncoupling (CLOU), the oxygen carrier (e.g., CuO-based materials) can be reduced either by direct decomposition or by heterogeneous gas–solid reaction. In most cases, the above two reaction pathways take place in parallel and compete with each other, which therefore make it very difficult to quantify the exact proportion of their contributions to the oxygen carrier conversion. The failure to distinguish the individual significance of each reaction route hinders the acquisition of a convincing reaction kinetic model. In this work, the conversion processes of CuO oxygen carrier in free space and in thermogravimetric crucible were simulated by a single particle model, in which the heterogeneous/homogeneous reactions as well as the heat/mass transfer inside and outside a porous particle were incorporated. The competition between the direct gas–solid reduction (using H2 as fuel gas) and oxygen uncoupling of the CuO oxygen carrier was analyzed from the aspects of the relative significance of each reaction route and the interactions between them. The results showed that the significances of each reaction route varied with the temperature and H2 concentration conditions. To quantify the relative significance of each reaction route at different conditions, the controlling regime diagram of CuO conversion in free space was given. The CuO conversion was more likely to be dominated by the oxygen uncoupling process when the particle was in crucible. For the conversion of CuO in free space, the exothermic gas–solid reduction increased the particle temperature and further facilitated the oxygen uncoupling rate, which was considered as the predominant interactions. Differently, for the conversion of CuO in crucible, the key interactions were characterized as: the homogeneous reaction between H2 and O2 decreased the O2 concentration neighboring the CuO particle and thus increased its oxygen uncoupling rate.

Impact of fuel-derived chlorine on CuO-based oxygen carriers for chemical looping with oxygen uncoupling

During the chemical looping with oxygen uncoupling (CLOU) process for CO2 capture from solid fuels, CuO-based oxygen carriers are expected to efficiently transport oxygen from the air reactor and convert fuel in the fuel reactor by releasing gaseous oxygen. To maintain high fuel conversion and CO2 capture efficiency, it is important to understand the impact of the fuel-derived Cl, which is highly volatile and corrosive, on the CuO/Cu2O in a CLOU environment. In this work, thermodynamic modeling was carried out to predict the characteristics of Cu-Cl interaction and develop a Cu deactivation rate model. Combustion experiments were performed to examine the impact of the Cl-containing flue gas on the CuO-based oxygen carrier. The oxygen transport capacities of the oxygen carriers exposed to the Cl-containing flue gas were measured by TGA. XRD and SEM-EDS were employed to characterize the ashes and oxygen carrier particles, respectively. The modeling results suggest that Cu-Cl interaction leads to the formation of CuCl and Cu3Cl3, causing the loss of effective Cu. The fraction of HCl converted to CuCl/Cu3Cl3 (XHCl) was predicted to be almost linearly correlated with the Cl content, while H2O could hinder the Cu-Cl interaction. The Cu deactivation rate model was successfully developed. For the fuels containing 0.2–0.4 wt% Cl, the Cu loss rate was estimated to be 0.0025–0.01%/cycle with XHCl = 0.12–0.24. The results of combustion experiments and material characterization were consistent with the modeling predictions, clearly demonstrating the Cl-induced deactivation. Given the modeling predictions and experimental findings, potential countermeasures were proposed.

Performance and Kinetic Evaluation of Synthesized CuO/SBA‐15 Oxygen Carrier for Chemical Looping with Oxygen Uncoupling

Chemical looping oxygen uncoupling (CLOU), a variant of chemical looping combustion (CLC), is one of the most promising combustion technologies for inherent separation and feasible capture of carbon dioxide. Herein, synthesized SBA‐15, a highly ordered mesoporous silica support, is used to host CuO for developing a new variant of an oxygen‐carrier material. Based on thermoanalytical evaluations, a typical CuO/SBA‐15 composition with 36 mass% CuO loading is identified as highly suitable with an average oxygen transport capacity of 3.61%. In addition, extensive studies along with model‐dependent kinetic evaluations are carried out using isothermal thermogravimetric data for the reduction–reoxidation of CuO/SBA‐15. It is observed that the Avrami‐Erofeev random nucleation and subsequence growth model (A2) fitted well for the reduction reaction, while the 3D diffusion model (D3) described suitably the reoxidation reaction in the temperature range of 800–950 °C. Reduction–reoxidation rate data and kinetic information derived from corresponding isothermal conversion curves can contribute immensely to design and establish operational strategies for interconnected CLOU reactors.

Examining and Modeling Oxygen Uncoupling Kinetics of Cu-Based Oxygen Carriers for Chemical Looping with Oxygen Uncoupling (CLOU) in a Drop Tube Fluidized Bed Reactor

Chemical looping combustion with oxygen uncoupling (CLOU) is a promising carbon capture and storage (CCS) technology for conversion of gaseous and solid hydrocarbon fuels where the release of gaseo...

A Multiscale Model of Oxidation Kinetics for Cu-Based Oxygen Carrier in Chemical Looping with Oxygen Uncoupling.

Copper oxide is one of the promising oxygen carrier materials in chemical looping with oxygen uncoupling (CLOU) technology, cycling between Cu2O and CuO. In this study, a multiscale model was developed to describe the oxidation kinetics of the Cu-based oxygen carrier particle with oxygen, including surface, grain, and particle scale. It was considered that the solid product grows with the morphology of disperse islands on the grain surface, and O2 contacts with two different kinds of grain surfaces in the grain scale model, that is, Cu2O surface (solid reactant surface) and CuO surface (solid product surface). The two-stage behavior of the oxidation reaction of the Cu-based oxygen carrier was predicted successfully using the developed model, and the model results showed good agreement with experimental data in the literature. The effects of oxygen partial pressure, temperature, and particle structure on the oxidation performance were analyzed. The modeling results indicated that the transition of the conversion curve occurs when product islands cover most part of the grain surface. The oxygen partial pressure and particle structure have an obvious influence on the duration time of the fast reaction stage. Furthermore, the influence of the external mass transfer and the change of effectiveness factor during the oxidation reaction process were discussed to investigate the controlling step of the reaction. It was concluded that the external mass transfer step hardly affects the reaction performance under the particle sizes normally used in CLOU. The value of the effectiveness factor increases as the reaction goes by, which means the chemical reaction resistance at grain scale increases resulting from the growing number of product islands on the grain surface.

Predicting and alleviating coal ash-induced deactivation of CuO as an oxygen carrier for chemical looping with oxygen uncoupling

Chemical looping with oxygen uncoupling (CLOU) using CuO oxygen carrier enables the release of gaseous oxygen in the fuel reactor for the efficient conversion of solid fuels, achieving inherent CO2 separation while avoiding the energy penalty associated with air separation units. In terms of the coal-fired CLOU, certain types of coal ash were found to interact with CuO and compromise the performance CuO, while some other types of coal ash seemed stable. To predict the interaction products based on ash composition and the major solid phase transformations of coal ash/CuO mixture, the phase diagrams of SiO2–Al2O3–CaO–Fe2O3–CuO system were developed through thermodynamic modeling. According to the phase diagrams, coal ash can be categorized into three types with different interaction products, and the Type 1 ash responsible for the deactivation of CuO can be described as Al2O3/CaO > 1.82 (mass ratio). CaO addition was proposed as an approach to alleviate the ash-induced CuO deactivation by forming the more thermodynamically favored CaAl2Si2O8 (anorthite) than CuAl2O4. The redox cycles of various CuO/coal ash/CaO mixtures were performed to test the modeling predictions and evaluate the effects of CaO addition. The experimental results validated the modeling predictions on the real coal ashes, and CaO addition proved to significantly curb the CuO deactivation in the presence of Type 1 ashes. XRD analysis verified the addition of CaO into the CuO/coal ash mixture inhibits the formation of CuAl2O4 by producing CaAl2Si2O8, but the decrease in the amount of Cu–Fe complex actually results from the formation of Ca2Fe9O13.

Sustainable iron-based oxygen carriers for Chemical Looping for Hydrogen Generation

We report a detailed reactor study of two sustainable Fe-based oxygen carriers (OC) prepared by spray drying. We compare Fe2O3 supported on Al2O3 and MgFeAlOx in isothermal Chemical Looping for Hydrogen Generation. In this process, CH4 is converted into syngas (H2 + CO) and H2O is used as the oxidant that reduces to pure H2. We noticed that the Al2O3 supported OC deactivates quickly while the MgFeAlOx supported OC withstands >60 cycles. We will show that the irreversible formation of an inactive FeAl2O4 phase is responsible for the deactivation of the alumina supported OC. We show detailed information on all the transient stages of the process and the different crystalline forms that are created, and combine this information into a full chemical looping cycle for both OC. Moreover, we evaluate the crushing strength of the oxygen carriers within a full chemical looping cycle and during long-term operation and we investigated the conversion of H2O and the selectivity to H2-production during long-term oxygen carrier regeneration. The MgFeAlOx support with an extra Fe-based active phase is a promising material to replace the typical Ni-based oxygen carriers, as it forms a sustainable non-toxic, stable and green alternative for hydrogen generation by chemical looping.

Effects of Coal Ash on CuO as an Oxygen Carrier for Chemical Looping with Oxygen Uncoupling

Chemical looping with oxygen uncoupling (CLOU) features the natural release of gaseous oxygen from oxygen carriers to efficiently burn solid fuels, producing a nearly nitrogen-free CO2 stream for c...

Atomic Layer Deposition of a Film of Al2O3 on Electrodeposited Copper Foams To Yield Highly Effective Oxygen Carriers for Chemical Looping Combustion-Based CO2 Capture.

A rapid electrochemical deposition protocol is reported to synthesize highly porous Cu foams serving as model oxygen carriers for chemical looping, a promising technology to reduce anthropogenic CO2 emission. To overcome the sintering-induced decay in the oxygen carrying capacity of unsupported Cu foams, Al2O3 films of different thicknesses (0.1-25 nm) are deposited onto the Cu foams via atomic layer deposition (ALD). An ALD-grown Al2O3 overcoat of 20 nm thickness (∼4 wt % Al2O3) is shown to be sufficient to ensure excellent redox cyclic stability. Al2O3-coated Cu foams exhibit a capacity retention of 96% over 10 redox cycles, outperforming their coprecipitated counterpart (equal Al2O3 content). The structural evolution of the stabilized foams is probed in detail and compared to benchmark materials to elucidate the stabilizing role of the Al2O3 overcoat. Upon heat treatment, the initially conformal Al2O3 overcoat induces a fragmentation of large Cu(O) branches into small particles. After multiple redox cycles, the Al2O3 overcoat transforms into sub-micrometer-sized grains of aluminum-containing phases (δ-Al2O3, CuAl2O4, and CuAlO2) that are dispersed homogeneously within the CuO matrix. Finally, the diffusion of Cu through an Al2O3 layer upon heat treatment in an oxidizing atmosphere is probed in model thin films.