Ceria-based Materials Research Articles

Recent Advances on Fine-Tuning Engineering Strategies of CeO2-Based Nanostructured Catalysts Exemplified by CO2 Hydrogenation Processes

Ceria-based oxides have been extensively involved in a wide range of catalytic applications due to their intriguing properties, related mostly to their superior redox features in conjunction with peculiar metal-support interaction phenomena. Most importantly, the fine-tuning of key interrelated factors, such as the size, morphology and electronic state of the catalyst’s counterparts, can exert a profound influence on the intrinsic characteristics and interfacial reactivity with pronounced implications in catalysis. The present review, while also elaborating our recent efforts in the field, aims to provide key fundamental and practical aspects in relation to the rational design and functionalization strategies of ceria-based catalysts, exemplified by the CO2 hydrogenation processes, namely, CO2 methanation and reverse water–gas shift (rWGS) reactions. Firstly, a description of the most prominent catalytically relevant features of cerium oxide is provided, focusing on reducibility and metal-support interaction phenomena, followed by a brief overview of the current status of ceria-based catalysts for various energy and environmental applications. Then, the main implications of fine-tuning engineering via either appropriate synthesis routes or aliovalent doping on key activity descriptors are thoroughly discussed and exemplified by state-of-the-art ceria-based catalysts for CO2 hydrogenation. It is clearly revealed that highly active and cost-efficient ceria-based catalytic materials can be obtained on the grounds of the proposed functionalization strategy, with comparable or even superior reactivity to that of noble metal catalysts for both the studied reactions. In a nutshell, it can be postulated that the dedicated fabrication of CeO2-based systems with augmented redox capabilities and, thus, oxygen vacancies abundance can greatly enhance the activation of gas-phase CO2 towards CO or CH4. Besides, the morphology-engineering of CeO2-based catalysts can notably affect the CO2 hydrogenation performance, by means of an optimum metal-ceria interphase based on the exposed facets, whereas doping and promotion strategies can effectively shift the reaction pathway towards the selective production of either CO or CH4. The conclusions derived from the present work can provide design and fine-tuning principles for cost-efficient, highly active and earth-abundant metal oxide systems, not only for the CO2 hydrogenation process but for various other energy and environmental applications.

Alumina, Silica, and Ceria-Based Multifunctional Materials & Applications: A Review

Alumina, Silica, and Ceria-Based Multifunctional Materials & Applications: A Review

Ceria-based coatings on magnesium alloys for biomedical applications: a literature review.

Magnesium alloys are being studied for use in temporary orthopedic implants because of their mechanical properties, which are similar to those of human bone, and their good biocompatibility. However, their application is limited due to their rapid degradation, and early loss of their mechanical properties, decreasing the stability of the implant and its proper synchronization with tissue regeneration. In this regard, various surface coatings have been used to improve their biological, physico-chemical and biodegradation properties. Currently, one of the most explored strategies is using smart coatings because of their self-healing properties that can slow down the corrosion process of Mg and its alloys. Ceria-based materials show promise as coatings for these alloys. Their unique redox capacity not only provides Mg alloys with good self-healing properties but also interesting biological properties, which are described in this paper. Despite this, some problems and challenges related to the biocompatibility and application of these materials in coatings remain unsolved. In this article, a critical review is presented summarizing the most representative literature on ceria-based coatings on Mg alloys for their potential use as biomaterials. The results show that ceria is a versatile material that may be used in industrial and biomedical applications.

Investigation of CO2 Splitting on Ceria-Based Redox Materials for Low-Temperature Solar Thermochemical Cycling with Oxygen Isotope Exchange Experiments

The surface exchange and bulk transport of oxygen are highly relevant to ceria-based redox materials, which are envisaged for the solar thermochemical splitting of carbon dioxide in the future. Experimental investigations of oxygen isotope exchange on CeO2-δ, Ce0.9M3+0.1O1.95-δ (with M3+ = Y, Sm) and Ce0.9M4+0.1O2-δ (with M4+ = Zr) samples were carried out for the first time utilizing oxygen-isotope-enriched C18O2 gas atmospheres as the tracer source, followed by Secondary Ion Mass Spectrometry (SIMS), at the temperature range 300 ≤ T ≤ 800 °C. The experimental K˜O and D˜O data reveal promising results in terms of CO2 splitting when trivalent (especially Sm)-doped ceria is employed. The reaction temperatures are lower than previously proposed/reported due to the weak temperature dependency of the parameters K˜O and D˜O. The majority of isotope exchange experiments show higher values of K˜O and D˜O for Sm-doped cerium dioxide in comparison to Y-doped and Zr-doped ceria, as well as nominally undoped ceria. The apparent activation energies for both K˜O and D˜O are lowest for Sm-doped ceria. Using Zr-doped cerium oxide exhibits various negative aspects. The Zr-doping of ceria enhances the reducibility, but the possible Zr-based surface alteration effects and dopant-induced migration barrier enhancement in Zr-doped ceria are detrimental to surface exchange and oxygen diffusion at lower temperatures of T ≤ 800 °C.

Effects of Hydrothermal Treatment on Mesopore Structure and Connectivity in Doped Ceria-Zirconia Mixed Oxides.

Pore size and pore connectivity control diffusion-based transport in mesopores, a crucial property governing the performance of heterogeneous catalysts. In many cases, transition-metal oxide catalyst materials are prepared from molecular precursors involving hydrothermal treatment followed by heat treatment. Here, we investigate the effects of such a hydrothermal aftertreatment step, using an aqueous ammonia solution, on the disordered mesopore network of CexZr1-x-y-zYyLazO2-δ mixed oxides. This procedure is a common synthesis step in the preparation of such ceria-based oxygen storage materials applied in three-way catalysis, employed to improve the materials' thermal stability. We perform state-of-the-art Ar-physisorption analysis, especially advanced hysteresis scanning, to paint a detailed picture of the alterations in mesopore space caused by the hydrothermal aftertreatment and subsequent aging at 1050 °C. Furthermore, we investigate the network characteristics by electron tomography in combination with suitable statistical analysis, enabling a consistent interpretation of the desorption scans (physisorption). The results indicate that the hydrothermal aftertreatment enhances the mesopore connectivity of the continuous 3D network by widening pores and especially necks, hence facilitating accessibility to the particles' internal surface area and the ability to better withstand high temperatures.

Sublimation and condensed phase thermodynamics of tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)cerium(IV) as a volatile precursor for ceria-based materials

Sublimation and condensed phase thermodynamics of tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)cerium(IV) as a volatile precursor for ceria-based materials

Novel Ceria and Ceria-based Nanocomposites as Potential Catalysts for Methanol Decomposition and Total Oxidation of Ethyl Acetate

The focus of our study is the development of novel ceria-based materials that can be successfully used as catalysts in various environmentally friendly processes due to a significant improvement of ceria intrinsic characteristics. In particular, the combination of ceria with low-dimensional carbon materials such as graphene oxide (GO) and nanodiamond (ND) appears as a very promising approach. Actually, the decrease of ceria crystallite sizes deep in the nanoscale have been found to convert them into highly effective destructive adsorbent materials owing to their high surface area, strong adsorbability, and large number of highly reactive sites. Besides, the addition of a nanostructured carbon containing component (nanodiamond or graphene oxide) contributes to both mechanical and catalytic properties of the obtained nanocomposite hybrids. The results show that the novel ceria and ceria-based composite materials significantly outperform the hydrothermally obtained ceria catalyst used for comparison in both activity and selectivity to CO and hydrogen in the methanol decomposition reaction, and in the process of total oxidation of ethyl acetate due to their significantly improved redox behaviour and textural characteristics.

The effect of sintering aids on BaCe0·7Zr0·1Y0.1Yb0.1O3-δ as the electrolyte of proton-conducting solid oxide electrolysis cells

Proton-conducting solid oxide electrolysis cells (H-SOECs) are attracting attentions of researchers due to their unique advantages. The proton-conducting material BaCe0·7Zr0·1Y0.1Yb0.1O3-δ (BZCYYb) has both the advantages of barium ceria-based and barium zirconate-based materials. BZCYYb material usually is synthesized by solid-state reaction (SSR) method, hence the densification of this electrolyte material is the key to restrict the application of H-SOECs. In this paper, effects of adding 1 wt% of different sintering aids (NiO, CuO, ZnO) to BZCYYb on the grain size and the conductivity are investigated. After adding 1 wt% of NiO and CuO sintering aids, BZCYYb electrolyte achieves ideal density. The electrical conductivity of four samples (BZCYYb without adding sintering aid, BZCYYb with 1 wt% NiO, CuO, ZnO, respectively) is tested under different steam concentrations of air, nitrogen, hydrogen, and nitrogen-hydrogen mixture. The conductivity increased after the sintering aid is added. With the increase of steam concentration, the conductivity decreased slightly and then increased due to electron holes under oxygen atmosphere with steam at high temperature. In other atmospheres, the conductivity increases with the steam concentration. In the atmosphere of 20 vol% H2O-Air and H2, the conductivity of the BZCYYb samples with 1 wt% CuO is about 1.087 × 10−2 S cm−1 and 9.02 × 10−3 S cm−1 at 650 °C, and the conductivity of the BZCYYb samples with 1 wt% NiO is 1.277 × 10−2 S cm−1 and 8.24 × 10−3 S cm−1, respectively. However, compared with NiO, CuO has advantages in promoting hydration reaction and proton conduction of BZCYYb electrolyte.

Investigation of Triple-doped Ceria-Based Composite Materials for LT-SOFC Applications

Investigation of Triple-doped Ceria-Based Composite Materials for LT-SOFC Applications

New perspective of ceria nanodots for precise tumor therapy via oxidative stress pathway

Ceria-based nanomaterials have aroused major attentions among the biomedical application research field in recent years. Most of the researches have mainly focused on promoting the functional healing therapies of normal cells/organs with cerium oxide compounds, while the applications of ceria-based materials employed on cancer curing processes have been merely mentioned. To explore the possible capabilities of cerium oxide nanomaterials exterminating tumor cells, innovatively, we synthesized the eco-friendly pure cerium oxide nanodots (CNDs), proving the prominent ability of CNDs used in tumor chemotherapy (CDT) via Fenton reaction with the highly presence of H2O2 (acidic pH) in tumor tissues. CNDs reacted with the self-produced H2O2 of tumor cells, which generated piled up toxic hydroxyl radical (·OH). The accumulated virulent ·OH restrained the growth of cancer cells intensively. This peroxidase-like activity, provided a distinguished paradigm for effective cancer curing treatment. We also verified the biosafety of CNDs applied on normal cells. Notably, not only did CNDs be harmless to normal cells, but also it protected them from the damages of reactive oxygen species (ROS). In normal cells/tissues, under the microenvironment of neutral pH and low level of H2O2, the CNDs could effectively function as an annihilator inhibiting ROS. They reduced the damages caused by ROS, exhibiting catalase-like activity. The research we studied, which estimated CNDs thoroughly, has provided a new perspective to the future researches of the cerium oxide biomaterial applications.

Mechanistic Investigation of Enhanced Catalytic Selectivity toward Alcohol Oxidation with Ce Oxysulfate Clusters.

Ceria-based materials have been highly desired in photocatalytic reactions due to their redox properties and strong oxygen storage and transfer ability. Herein, we report the structures of one CeCe70 oxysulfate cluster and four MCe70 clusters (M = Cu, Ni, Co, and Fe) with the same Ce70 core. As noted, single-crystal X-ray diffraction confirmed the structures of CeCe70 and the MCe70 series, while Raman spectroscopy indicated an increase in oxygen defects upon the introduction of Cu and Fe ions. The clusters catalyzed the oxidation of 4-methoxybenzyl alcohol under ultraviolet light. CuCe70 and FeCe70 exhibited enhanced reactivity compared to CeCe70 and improved aldehyde selectivity compared to control experiments. In comparison with their homogeneous congeners, the CeCe70/MCe70 clusters altered the location of radical generation from the bulk solution to the clusters' surfaces. Mechanistic studies highlight the role of oxygen defects and specific transition metal introduction for efficient photocatalysis. The mechanistic pathway in this study provides insight into how to select or design a highly selective catalyst for photocatalysis.

Influence of oxidizing and reducing pretreatment on the catalytic performance of CeO2 for CO oxidation

Cerium oxide (CeO2) and ceria-based materials have been extensively investigated as catalyst and support materials for various catalytic reactions, due to higher oxygen storage capacity and excellent redox properties. In the current work, we investigated the impact of pretreatment conditions (e.g., oxidation and reduction) on the physical properties of bulk CeO2 and catalytic activity for CO oxidation as a model reaction. To understand the physical properties of pretreated CeO2 catalysts, a suite of complementary characterization techniques, including X-ray diffraction (XRD), surface area analysis (BET), X-ray photoemission spectroscopy (XPS), and Raman spectroscopy, were applied. The results showed that a higher pretreatment temperature led to a decreased specific surface area (SSA), a decrease in oxygen vacancy/defect sites, and increased crystallite size, while surface Ce3+/Ce4+ ratio did not show a specific relationship to the treatment conditions. The 700 °C treated CeO2 samples under oxidizing and reducing conditions showed higher specific oxidation rate (μmolCO/s/m2) compared to other samples at 280 and 300 °C (or < 15% CO conversion). The CO conversion per total mass of catalysts, however, decreased with increasing temperatures, especially at 700 °C under reducing condition, indicating that the catalytic performance was affected by the physical properties (SSA, oxygen vacancy/defect sites, and crystallite size)..

Thermodynamic stability of niobium-doped ceria surfaces

Ceria (CeO2) displays a profound catalytic capacity even when utilized as a stand-alone material. Catalyzed reactions by ceria could be enhanced when it is decorated with a trace content of d or f-metals. This study addresses the stability and properties of niobium incorporated ceria surfaces. Doping a trace amount of metals often alter catalytic properties of the host metal oxide. Herein, we investigate mixed Ce-Nb-O oxides with a prime focus on the surface free energy, lattice constant, as well as atomic charges and density of states. It was found that the most stable Ce-Nb-O configuration is obtained when Nb atoms supersede top-layer O atoms at highest niobium occupancy where the surface energy decreases by 0.3 eV/Å2 compared to neat ceria surface. It was also shown that the changes in lattice constants in this configuration is in accord with data obtained from X-Ray Diffraction patterns. Results from this study could be useful in fine-tuning catalytic attributes of ceria-based materials.

Investigations of the Effect of H2 in CO Oxidation over Ceria Catalysts

The preferential CO oxidation (so-called CO-PROX) is the selective CO oxidation amid H2-rich atmospheres, a process where ceria-based materials are consolidated catalysts. This article aims to disentangle the potential CO–H2 synergism under CO-PROX conditions on the low-index ceria surfaces (111), (110) and (100). Polycrystalline ceria, nanorods and ceria nanocubes were prepared to assess the physicochemical features of the targeted surfaces. Diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFTS) shows that ceria surfaces are strongly carbonated even at room temperature by the effect of CO, with their depletion related to the CO oxidation onset. Conversely, formate species formed upon OH + CO interaction appear at temperatures around 60 °C and remain adsorbed regardless the reaction degree, indicating that these species do not take part in the CO oxidation. Density functional theory calculations (DFT) reveal that ceria facets exhibit high OH coverages all along the CO-PROX reaction, whilst CO is only chemisorbed on the (110) termination. A CO oxidation mechanism that explains the early formation of carbonates on ceria and the effect of the OH coverage in the overall catalytic cycle is proposed. In short, hydroxyl groups induce surface defects on ceria that increase the COx–catalyst interaction, revealed by the CO adsorption energies and the stabilization of intermediates and readsorbed products. In addition, high OH coverages are shown to facilitate the hydrogen transfer to form less stable HCOx products, which, in the case of the (110) and (100), is key to prevent surface poisoning. Altogether, this work sheds light on the yet unclear CO–H2 interactions on ceria surfaces during CO-PROX reaction, providing valuable insights to guide the design of more efficient reactors and catalysts for this process.

Current understanding of ceria surfaces for CO2 reduction in SOECs and future prospects – A review

Ceria-based materials form a very promising class of electrocatalysts for CO2 reduction in solid oxide electrolysis cells (SOECs). On the pathway towards the implementation of ceria into technological electrodes on a large scale, an in-depth atomistic understanding of the reaction mechanism over ceria surfaces is crucial in order to optimize its intrinsic electrocatalytic activity. In this review article, we offer a critical discussion of the phenomena governing the electrochemical reduction of CO2 over ceria surfaces. We focus on the steps that limit the reaction rate and on how these can be accelerated by appropriate tuning of ceria properties and defect chemistry, via the introduction of tensile or compressive isotropic strain in the lattice, the promotion of a specific surface orientation and the control of the amount of acceptor or donor dopants incorporated in the fluorite structure. Our review aims to gather and examine the evidence of the role that these levers play in altering the energy landscape of the reaction, along with their influence on the capability of ceria to suppress carbon deposition during cell operation. Ultimately, we identify the areas that need further investigation and propose new lines of work towards the performance optimization of ceria as highly efficient catalyst for CO2 reduction in SOECs.

Silicon Contamination of the Praseodymium Doped Ceria Oxygen Surface Exchange Coefficient

Chemical oxygen surface exchange coefficients are used to quantify and rank the performance of oxygen exchange catalysts used in solid oxide fuel cell, solid oxide electrolysis cell, oxygen separation membrane, catalytic converter, and other oxygen-exchange-enabled devices. Unfortunately, during the manufacture and operation of these devices it is easy to introduce siliceous contaminants that degrade their oxygen exchange performance. Surprisingly, despite the well-known negative impact siliceous impurities have on the oxygen transport properties of ceria-based materials, quantitative measurements of how siliceous impurities impact the chemical oxygen surface exchange coefficient of praseodymium doped ceria are largely absent from the literature. In this work, the crystal structure, film thickness, surface composition, bulk composition, and chemical oxygen exchange coefficient of (100)-oriented PCO thin films with, and without, surface silica contaminants were evaluated via X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Secondary Ion Mass Spectroscopy (SIMS), and Curvature Relaxation (κR) experiments, respectively. The results show that siliceous surface phases only a few nanometers thick are capable of (1) reducing the PCO chemical oxygen surface exchange coefficient by approximately 3 orders of magnitude and (2) approximately doubling the activation energy for oxygen exchange.

Tuning structural, optical, and gas sensing properties of ceria-based materials by rare-earth doping

In this study, we investigate the influence of rare-earth dopants on the structural, optical, gas sensing properties of Ce1-(3/4)xRExO2 (RE = Eu, La; x = 0.0 and 0.08) nanoparticles synthesized using the microwave-assisted hydrothermal method. X-ray diffraction analysis confirmed the formation of CeO2 fluorite structure free of secondary phases. Raman spectroscopy indicates oxygen vacancies are the dominant defect in the samples. Additionally, doping with La and Eu decreased the bandgap energy of the pure sample. The different dopants changed the photoluminescence spectrum of pure ceria, leading to blue (La) and red (Eu) emissions with a higher number of electronic transitions for the Eu-doped nanoparticles, which consists of six bands between 550 and 750 nm. For the thick films fabricated using the as-prepared nanoparticles, a measurable response in terms of resistivity was observed during interactions with vacuum, dry air, and carbon monoxide atmospheres. The Eu-doped thick film reacted much faster (1 s) with carbon monoxide compared to La-doped (4.2 s) and pure ceria (6.6 s), corresponding to an improvement when compared with other studies reported in the literature. Doping the ceria structure proved to be beneficial to its carbon monoxide sensing properties and produced tunable photoluminescent emissions, which are promising for white LED applications.

Comparison of Residual Stress Measurement Methods in Solid Oxide Fuel Cell

SOFCs need to be able to operate for long periods of time without significant degradation in performance, and mechanical reliability and durability are problems that need to be addressed.Since SOFC operate at high temperatures and in oxidizing and reducing atmospheres, it is difficult to measure residual stress in-situ under actual operating conditions. Therefore, evaluation methods during operation have not been fully developed. Current methods for measuring residual stress in SOFC include curvature method, X-ray stress measurement method, and Raman scattering spectroscopy.In the curvature method, the stress is obtained by combining curvature, anode substrate thickness, and elastic modulus. Therefore, it is not suitable for residual stress measurement during reduction and re-oxidation of anodes, where physical properties such as elastic modulus change with time.In the X-ray stress measurement method, the change in lattice strain is measured, and the stress is obtained by multiplying the strain by an elastic constant. Typical methods of X-ray stress measurement are sin2ψ method and cosα method. The characteristics of the sin2ψ method are as follows;(1)By using several measuring points to determine the stress value, the variation of the measured value can be suppressed, resulting in high measurement accuracy. Furthermore, the reliability limit of the measured value can be quickly evaluated from the linearity.(2)A goniometer mechanism is used to measure the diffraction profile, which requires a large device.(3)Measurement time is long because several points are measured by moving the angle of incidence.Thus, although the sin2ψ method has high measurement accuracy, it is not very suitable for in-situ measurements.The method devised to solve these problems is cosα method. The characteristics of the cosα method are as follows;(1) Since it is single-incidence, the optical system is simple and does not require goniometric scanning, making it possible to reduce the size and weight of the measurement system. It is also possible to measure in a short time.(2) From the slope of the cosα and sinα diagrams, vertical stress and shear stress can be measured simultaneously. In addition, the reliability of the stress values can be evaluated from the linearity of the diagram.(3) In the case of coarse grains or strongly aggregated structure, only continuous rings can be obtained, or the strength may be significantly non-uniform, making stress measurement difficult.It has been demonstrated that the measurement accuracy of the cosα method for vertical stress is comparable to that of the sin2ψ method, and moreover, it is suitable for in-situ residual stress measurement because of its rapidity and simplicity.In Raman scattering spectroscopy, the change in lattice volume, i.e., the change in stress conditions, can be obtained by measuring the Raman shift. The characteristics of the Raman scattering spectroscopy are as follows;(1) Since the measurement can be performed under atmospheric pressure and through glass, it is suitable for in-situ measurement in the SOFC operating environment where atmosphere control is usual.(2)High spatial resolution (up to ~1µm resolution is possible with micro-Raman spectrometers) enables measurement of small areas.(3) Since Raman peaks with sufficiently strong intensity need to appear in the Raman spectrum, there is a limit to the number of materials that can be measured. Among the SOFC constituent materials, ceria-based materials are the most suitable for observation.As mentioned in (3), Raman scattering spectroscopy is used to calculate the stress value of the interlayer (ceria-based material). Therefore, the stress in the electrolyte is calculated by assuming that the electrolyte and the interlayer are rigid bodies under the operating conditions. In this study, we performed in-situ measurement of residual stress in the anode-supported cell using sin2ψ method, cosα method and Raman scattering spectroscopy. And then we compared the results and summarized the advantages and disadvantages of each method. We used a commercially available general cell and a cell fabricated at Tsinghua University. In order to reproduce the actual operating conditions, the measurements were carried out under elevated temperature and under reduced temperature. Since the anode may be re-oxidized when the fuel runs out or during an emergency shutdown, the measurements were also conducted under re-oxidation. Furthermore, we proposed suitable conditions for each measurement method and conducted experiments under those conditions.

Ceria-Based Materials for Thermocatalytic and Photocatalytic Organic Synthesis

Ceria-Based Materials for Thermocatalytic and Photocatalytic Organic Synthesis

Synthesis and thermochemical redox cycling of porous ceria microspheres for renewable fuels production from solar-aided water-splitting and CO2 utilization

Porous ceria-based architected materials offer high potential for solar fuels production via thermochemical H2O and CO2-splitting cycles. Novel porous morphologies and micro-scale architectures of redox materials are desired to provide suitable thermochemical activities and long-term stability. Considering particle-based solar reactors, porous ceria microspheres are promising because of their excellent flowability and large surface area. In this work, such porous microspheres with perfect spherical shape, high density, and interconnected pore network were fabricated by a chemical route involving ion-exchange resins. The method involved the cationic loading of the resin in an aqueous medium followed by thermal treatment for oxide formation and porous microstructure stabilization. The utilization of these microspheres (∼150–350 μm in size) as redox materials for solar fuel production was investigated in packed-bed solar reactors (directly and indirectly irradiated). Superior redox performance was obtained for the pure ceria microspheres in comparison with other morphologies (powders and reticulated foams). Low pO2 values thermodynamically favored the reduction extent and associated fuel yield, whereas high pCO2 kinetically promoted the oxidation rate. The highest fuel production rate reached 1.8 mL/min/g with reduction step at 1400 °C, low total pressure (∼0.1 bar), and oxidation step below 1050 °C under pure CO2. Low pressure during reduction both improved reduction extent (oxygen under-stoichiometry δ up to 0.052) and associated fuel production yield (331 μmol/g CO). After 19 redox cycles (∼32 h under high-flux solar irradiation), the porous microspheres maintained their individual integrity (no agglomeration), spherical shape, and internal porosity, with great potential for stable fuel production capacity in particle-based solar reactors.