Structure-performance Relationship Research Articles

Block‐Copolymer‐Architected Materials in Electrochemical Energy Storage

The multiscale architecture of electrochemical energy storage (EES) materials critically impacts device performance, including energy, power, and durability. The pore space of nano‐ to macrostructured electrodes determines mass transport within the electrolyte and defines the effective energy density. The dimensions of the active charge‐storing materials can increase stability during cycling by accommodating strains from electrochemical–mechanical coupling while also defining surface area that increases capacitive charge storage, decreases charge‐transfer resistance, but also leads to low efficiency and degradation from interfacial reactions. Thus, elucidating and developing a fundamental understanding of these correlations requires materials with precisely tunable nanoscale architectures. Herein, approaches that take advantage of the nanoscale control offered by block copolymer (BCP) self‐assembly are reviewed and insights gained from associated nanoscale phenomena observed in EES are highlighted. Systematic studies that use custom‐tailored BCPs to reveal fundamental nanostructure–property–performance relationships are emphasized. Importantly, most reports of nanostructured materials utilize low loadings and thin electrodes and results represent mass transfer limitations at the particle scale. However, as cell‐level performance involves mass transport over 10–100s of micrometers, recently emerging BCP‐based processes are further highlighted, leading to hierarchical meso/macroporous materials needed for creating multiscale structure–performance relationships and next‐generation energy storage material architectures.

Deep core level hard X‐ray photoelectron spectroscopy for catalyst characterization

AbstractHeterogeneous catalysts are the crucial element for many catalytic processes. In most of the cases, the pivotal structure consists of catalytic metals/alloy particles supported by oxides. Knowledge of the interaction between metal and oxide is central to understand the structure–performance relationship of such systems. X‐ray photoelectron spectroscopy provides access to the chemical–physical properties of metal and oxide interface as well as polarization effects. The results are usually derived from changes of the measured binding energies based on initial state analysis. We propose to extend the analysis using photoelectron as well as Auger transition to include final state effects (Wagner/Hohlneichner plots). This gives additional information on the specific chemical neighborhood of the excited atom. Three archetypal systems are investigated by hard X‐ray photoelectron spectroscopy (HAXPES) to introduce two approaches to this analysis for the most common support elements Al and Si.

Effect of framework structure of ZSM-11 and ZSM-5 zeolites on their catalytic performance in the conversion of methanol to olefins

The catalytic performance of zeolites is closely related to their framework structure and a clear understanding of such a structure-performance relationship is of great significance in revealing catalytic reaction mechanism as well as in developing efficient zeolite catalysts. Herein, ZSM-11 and ZSM-5 zeolites with similar morphology, crystal size, textural properties and acidity were hydrothermally synthesized; the effects of their differences in the 10-ring channels on the catalytic performance in the conversion of methanol to olefins (MTO) were investigated by using various characterization techniques. The results indicate that in comparison with the straight channel of ZSM-11, the sinusoidal channel of ZSM-5 has stronger diffusion resistance, which promotes the hydrogen-transfer in higher olefins, leads to forming more polymethylbenzene species and then raises the contribution of aromatic-based cycle. In contrast, ZSM-11 with straight channel can reduce the formation of polymethylbenzene species and enhance the alkene-based cycle. As a result, compared with ZSM-5-60 with similar morphology and acidity, ZSM-11-60 as a catalyst in MTO exhibits longer lifetime (98.3 h vs. 65.4 h) and higher selectivity to propene (34.6% vs. 27.4%). The insight shown in this work helps to have a better understanding of the relation between zeolite structure and catalytic performance in MTO and is then beneficial to the development of better catalysts and processes for MTO.

Construction of intramolecular donor–acceptor type carbon nitride for photocatalytic hydrogen production

High-efficiency photocatalysts based on organic polymeric semiconductor are often limited by slow charge separation kinetics and sluggish redox reaction dynamics. Herein, the donor–acceptor conjugated polymeric carbon nitride (D/A-CN) was synthesized by grafting benzene ring and pyridine moiety into the backbone of CN through a flexible pyrolysis strategy. The D/A-CN shows a high photocatalytic H2 evolution rate of 4795 µmol·h−1·g−1, which is ≈6.08 times higher than that of pristine CN (787.5 µmol·h−1·g−1). Both experimental and theoretical results confirm that the robust internal electric field is established in the D/A-CN framework due to the enhanced molecular dipole, which apply a kinetic force to facilitate the separation and mobility of photogenerated carriers. Meanwhile, the deeper conduction band potential caused by the elevated orbital energy level of D/A-CN contributes to the enhanced reduction ability of photoinduced electron. Consequently, the faster carrier transfer kinetics and the stronger thermodynamic reduction driving force synergistically lead to efficient photocatalytic H2 production of D/A-CN. This work reinforces the comprehension of the structure-performance relationship of donor–acceptor structural photocatalysts and provides an insight for enhancing the photocatalytic activity of polymeric photocatalysts at the molecular level.

Towards electron-transfer-driven peracetic acid oxidation: Catalytic performance adaptation of reduced graphene oxide to explosive thermal exfoliation

Direct electron transfer (DET)-mediated carbon/peracetic acid (PAA) oxidation systems are gaining momentum in water treatment owing to high selectivity and robustness in complex water matrices. However, the development of reaction-oriented and high-performance carbon catalysts for PAA oxidation is hindered by a limited understanding of the fundamental relationship between carbon structure and PAA activation performance. In this work, we focused on exploring the influence cascade of thermal annealing, especially explosive thermal exfoliation, on the catalytic performance adaptation of reduced graphene oxide (rGO) in PAA oxidation. By performing structure-performance relationship studies and Pearson correlation analyses, the improved catalytic efficacy of rGO is attributed to the induced high specific surface area (SSA) and pore volume of rGO in explosive thermal exfoliation. Large SSA and pore volume of rGO reinforce the DET pathway via the elevated PAA adsorption quantity and subsequent enhanced oxidative potential of the rGO-PAA complex, which are critical premises in initiating DET. Furthermore, increased annealing temperatures can tailor the graphitization level and functional group content of rGO, leading to the improved electrical conductivity of rGO, another crucial factor in DET-mediated rGO/PAA oxidation. This study emphasizes the key role of carbon physicochemical properties in PAA activation, providing insights into the rational design of DET-oriented carbon/PAA oxidation systems for fast water decontamination.

Progress on Noble-Metal-Free Organic–Inorganic Hybrids for Electrochemical Water Oxidation

Emerging as a new class of advanced functional materials with hierarchical architectures and redox characters, organic–inorganic hybrid materials (OIHs) have been well developed and widely applied in various energy conversion reactions recently. In this review, we focus on the applications and structure–performance relationship of OIHs for electrochemical water oxidation. The general principles of water oxidation will be presented first, followed by the progresses on the applications of OIHs that are classified as metal organic frameworks (MOFs) and their derivates, covalent organic framework (COF)-based hybrids and other OIHs. The roles of organic counterparts on catalytic active centers will be fully discussed and highlighted with typical examples. Finally, the challenges and perspectives assessing this promising hybrid material as an electrocatalyst will be provided.

Fundamental insights into structure-performance relationship for proton conductivity enhancement through polymer electrolyte membrane in Proton Exchange Membrane Fuel Cell

The efficiency of a polymer electrolyte membrane fuel cell (PEMFC) is limited by the proton conductivity of polymer electrolyte membrane (PEM). Local structural variation with hydrophobic-hydrophilic zone segregation in PEM affects proton conductivity profoundly. There is a lack of elemental theoretical model to predict proton transport in novel PEMs with a wide range of compositions and structures. In this work, the first-principle based meso-scale modelling has been attempted to address localised structural variations. The membrane is divided into repetitive lattice of uniform structure. The segregated domains follow periodic or random arrangements. The applicable governing equations are solved numerically under appropriate boundary conditions. The system parameters are recognized and their effects are thoroughly investigated. For the futuristic PEMs, the effect of variation in zone arrangement, its size and its gradual change was investigated. The model was validated with reported data of Nafion membranes with successful prediction of conductivity at different operating temperature and humidity. A phase-space plot was generated for use as a straight-forward tool for prediction of proton conductivity at different operating environment for varying segregation level. The developed model can enlighten the transport mechanism through any existing and futuristic PEMs, scale-up and design them according to the application requirement.

Ongoing Progress on Pervaporation Membranes for Ethanol Separation.

Ethanol, a versatile chemical extensively employed in several fields, including fuel production, food and beverage, pharmaceutical and healthcare industries, and chemical manufacturing, continues to witness expanding applications. Consequently, there is an ongoing need for cost-effective and environmentally friendly purification technologies for this organic compound in both diluted (ethanol-water-) and concentrated solutions (water-ethanol-). Pervaporation (PV), as a membrane technology, has emerged as a promising solution offering significant reductions in energy and resource consumption during the production of high-purity components. This review aims to provide a panorama of the recent advancements in materials adapted into PV membranes, encompassing polymeric membranes (and possible blending), inorganic membranes, mixed-matrix membranes, and emerging two-dimensional-material membranes. Among these membrane materials, we discuss the ones providing the most relevant performance in separating ethanol from the liquid systems of water-ethanol and ethanol-water, among others. Furthermore, this review identifies the challenges and future opportunities in material design and fabrication techniques, and the establishment of structure-performance relationships. These endeavors aim to propel the development of next-generation pervaporation membranes with an enhanced separation efficiency.

“Buckets effect” in the kinetics of electrocatalytic reactions

In this study, we systematically investigated the effect of proton concentration on the kinetics of the oxygen reduction reaction (ORR) on Pt(111) in acidic solutions. Experimental results demonstrate a rectangular hyperbolic relationship, i.e., the ORR current excluding the effect of other variables increases with proton concentration and then tends to a constant value. We consider that this is caused by the limitation of ORR kinetics by the trace oxygen concentration in the solution, which determines the upper limit of ORR kinetics. A model of effective concentration is further proposed for rectangular hyperbolic relationships: when the reactant concentration is high enough to reach a critical saturation concentration, the effective reactant concentration will become a constant value. This could be due to the limited concentration of a certain reactant for reactions involving more than one reactant or the limited number of active sites available on the catalyst. Our study provides new insights into the kinetics of electrocatalytic reactions, and it is important for the proper evaluation of catalyst activity and the study of structure-performance relationships.

Design of a novel anti-reflective coating with ultra-low reflectance based on resin-anchored hollow silica strategy

The strategy of resin-anchored hollow silica particles (HSPs) offers a tempting option for large-scale fabrication of anti-reflective functional surfaces on flexible plastic substrates. However, attempts to experimentally investigate the structure-performance relationship of such anti-reflective coatings and to further optimize the coating structure require long experimental cycles and significant labor costs. In view of this, the effectiveness of using COMSOL two-dimensional (2D) simulation to solve the problem is validated in conjunction with experimental results. Then three coating structure models are investigated. Finally, a coating with ultra-low reflectance in the entire visible wavelength band (380–780 nm) is designed. The coating has a novel structure consisting of resin-anchored double-layer unequal-size HSPs. It combines two anti-reflective principles, the moth-eye bionic structure and the refractive index adjustment of the film layer. The maximum reflectance of the coating is only 0.32 % over the entire visible wavelength range, and its average reflectance reaches an ultra-low level of 0.14 %. The coating has a wide angle anti-reflective performance. When the angle of incidence is <60°, the reflectance of the coating is <3 %. The results of this study are expected to provide direction for later experimental improvements.

Slow-release synthesis of Cu single-atom catalysts with the optimized geometric structure and density of state distribution for Fenton-like catalysis

Single-atom Fenton-like catalysis has attracted significant attention, yet the quest for controllable synthesis of single-atom catalysts (SACs) with modulation of electron configuration is driven by the current disadvantages of poor activity, low selectivity, narrow pH range, and ambiguous structure-performance relationship. Herein, we devised an innovative strategy, the slow-release synthesis, to fabricate superior Cu SACs by facilitating the dynamic equilibrium between metal precursor supply and anchoring site formation. In this strategy, the dynamics of anchoring site formation, metal precursor release, and their binding reaction kinetics were regulated. Bolstered by harmoniously aligned dynamics, the selective and specific monatomic binding reactions were ensured to refine controllable SACs synthesis with well-defined structure-reactivity relationship. A copious quantity of monatomic dispersed metal became deposited on the C3N4/montmorillonite (MMT) interface and surface with accessible exposure due to the convenient mass transfer within ordered MMT. The slow-release effect facilitated the generation of targeted high-quality sites by equilibrating the supply and demand of the metal precursor and anchoring site and improved the utilization ratio of metal precursors. An excellent Fenton-like reactivity for contaminant degradation was achieved by the Cu1/C3N4/MMT with diminished toxic Cu liberation. Also, the selective ·OH-mediated reaction mechanism was elucidated. Our findings provide a strategy for regulating the intractable anchoring events and optimizing the microenvironment of the monatomic metal center to synthesize superior SACs.

MXene/In2S3 micro-nano composites for heighten the select specificity and rapid response to triethylamine

Molecular responsive materials with fast, stable, and specific selectivity are a key focus of chemical sensor technology research. In the field of triethylamine (TEA) sensor technology, developing TEA-selective responsive materials with superior performance is of great significance for promoting technological progress and industrialization of TEA sensor technology. In this study, MXene/In2S3 micro-nano powder was prepared by combining Ti3C2Tx-type MXene with nano-sized In2S3. The morphology, structure, and structure-performance relationship of the material were characterized and analyzed using SEM, TEM, XRD, HAADF, and XPS. Through experiments, it was confirmed that MXene/In2S3 exhibited outstanding specific selectivity to TEA. At a TEA concentration of 20 ppm and a temperature of 210 °C, the response value of the material to TEA was 8.74, while other typical gas molecules such as aldehydes, ketones, and aromatics showed almost no response, demonstrating excellent selectivity for TEA molecules. The response/recovery time was 19 s/42 s, and the response value was stable over 20 consecutive cycles, indicating excellent reliability of the material. In addition, in the concentration range of 1–500 ppm, the response value of the MXene/In2S3 material to TEA concentration followed an exponential fitting of the asymptotic model, with the formula y = a-b*cx and R2 of 0.99472. Furthermore, the selection and response process of MXene/In2S3 micro-nano materials and TEA molecules were analyzed from the molecular internal structure, and it was found that the selective response characteristics of the material to TEA were related to its microstructure, including shape adsorption.

Synchronous preparation and modification of LDH hollow polyhedra by polydopamine: Synthesis and application

Layered double hydroxides (LDH) have irreplaceable advantages in the field of polymer flame retardancy, but their thermal stability and compatibility with matrix still need to be improved. In this paper, the bottom-up method is adopted, and the phosphorus series flame retardant triphenyl phosphate (TPP) was first encapsulated inside ZIF-67. On this basis, ZIF-67 was etched to produce LDH while modified by polydopamine (PDA) concomitantly. An organic coated polydopamine hollow cage lamellar LDH microstructure loaded with TPP was constructed, and its structure-performance relationship was verified. When 2 wt% TPP@LDH@Co-PDA was added to the epoxy resin, the LOI value of the composite was increased to 29.4 %, the peak heat release was reduced by 43.1 %, and the smoke release was significantly reduced. The unique microstructure endows epoxy composites with good flame retardancy, improves mechanical properties, and provides a new solution to the migration problem of phosphorous based flame retardants.

Hierarchical Computational Screening of Quantum Metal-Organic Framework Database to Identify Metal-Organic Frameworks for Volatile Organic-Compound Capture from Air.

The design and discovery of novel porous materials that can efficiently capture volatile organic compounds (VOCs) from air are critical to address one of the most important challenges of our world, air pollution. In this work, we studied a recently introduced metal-organic framework (MOF) database, namely, quantum MOF (QMOF) database, to unlock the potential of both experimentally synthesized and hypothetically generated structures for adsorption-based n-butane (C4H10) capture from air. Configurational Bias Monte Carlo (CBMC) simulations were used to study the adsorption of a quaternary gas mixture of N2, O2, Ar, and C4H10 in QMOFs for two different processes, pressure swing adsorption (PSA) and vacuum-swing adsorption (VSA). Several adsorbent performance evaluation metrics, such as C4H10 selectivity, working capacity, the adsorbent performance score, and percent regenerability, were used to identify the best adsorbent candidates, which were then further studied by molecular simulations for C4H10 capture from a more realistic seven-component air mixture consisting of N2, O2, Ar, C4H10, C3H8, C3H6, and C2H6. Results showed that the top five QMOFs have C4H10 selectivities between 6.3 × 103 and 9 × 103 (3.8 × 103 and 5 × 103) at 1 bar (10 bar). Detailed analysis of the structure-performance relations showed that low/mediocre porosity (0.4-0.6) and narrow pore sizes (6-9 Å) of QMOFs lead to high C4H10 selectivities. Radial distribution function analyses of the top materials revealed that C4H10 molecules tend to confine close to the organic parts of MOFs. Our results provided the first information in the literature about the VOC capture potential of a large variety and number of MOFs, which will be useful to direct the experimental efforts to the most promising adsorbent materials for C4H10 capture from air.

A Physical Model of Nanotwin Unit and Orientation Organization for Designing Mechanical Performance: Cases of InSb, GaAs, ZnS

AbstractFunctional unit and organization (FUO) paradigm starts with functional units and assembles these functional units into specific organizations to optimize material performance. An advantage of FUO paradigm is interpretation of physical essence of traditional structure–performance relationships. Experimental achievements based on FUO paradigm abound in recent years, demanding theoretical explanations for further quantitative material design. Following FUO paradigm, here a three‐step model (bond‐region‐structure) of nanotwin (NT) unit and orientation organization to optimize mechanical performance is established. First, anisotropic elasticities of representative bonds and assembled regional elastic constants are evaluated. Second, yield conditions of different regions, which are summarized as critical resolved shear stress (CRSS) criteria of NT structure, are quantified. Third, anisotropic yield strengths of NT structure from the regional elastic constants and CRSS criteria are derived. This FUO‐based model is implemented into InSb, GaAs, and ZnS, predicted elastic constants and yield strengths are validated with molecular dynamics (MD) simulations. The method is more efficient than MD with comparable accuracy, and is also flexible to combine with density function theory and experiment. This demonstration sets foundation of NT unit and orientation organization design for achieving optimum mechanical performance.

Ammonia Adsorption Performance of Zeolitic Imidazolate Frameworks for Cooling.

Promoting the cooling performance of adsorption chillers (ACs) greatly relies on the exploration of high-performance adsorbent/refrigerant working pairs. Ammonia is not only an environmentally friendly refrigerant but also favorable for heat and mass transfer in ACs owing to its large vapor pressure and enthalpy of evaporation. Zeolite imidazolate frameworks (ZIFs) with excellent ammonia stability are identified as a class of potential adsorbents for practical ammonia-based ACs. However, high-performing ZIF/ammonia working pairs with excellent AC performance are still to be developed. In this work, the cooling performance including the coefficient of performance for cooling (COPC) and the specific cooling effects (SCEs) of 26 ZIFs with the same composites but different topologies was evaluated by combining molecular simulation and mathematical modeling. Five high-performing ZIFs with COPC > 0.45 and SCE > 250 kJ/kg were identified, among which gis-ZIF with the highest COPC of 0.51 and lta-ZIF with the highest SCE of 354 kJ/kg both are promising to be synthesized and applied further. Besides, the quantitative structure-performance relationship (QSPR) was extracted that can help quickly identify and design high-performing ZIFs according to their ammonia adsorption isotherms and structural characteristics. Moreover, "S"-shaped adsorption isotherms with high saturation adsorption capacity (>0.2 g/g), suitable step position (0.2-0.4), and relatively low Henry's constant (<1 × 10-5 mol/(kg·Pa)) are more favorable for excellent COPC and SCE. From the perspective of structure characteristics, ZIFs possessing low crystal density (<0.9 g/cm3), high accessible surface area (>2000 m2/g), balanced largest cavity diameter (∼15 Å), and accessible pore volume (∼0.65 cm3/g) are beneficial for high-efficient cooling performance.

Predicting PEMFC performance from a volumetric image of catalyst layer structure using pore network modeling

A pore-scale model of a PEMFC cathode catalyst layer was developed using the pore network approach and used to predict polarization behavior. A volumetric image of a PEMFC catalyst layer was obtained using FIB-SEM with 4 nm resolution in all 3 directions. The original image only differentiated between solid and void, so a simple but effective algorithm was developed to insert tightly packed, but non-overlapping carbon spheres into the solid phase, which were then decorated with catalyst sites. The resultant image was a 4-phase image containing void, ionomer, carbon, and catalyst, each in proportion to the known Pt loading, carbon-to-ionomer ratio, and porosity. A multiphase pore network model was extracted from this image, and multiphysics simulations were conducted to predict the polarization behavior of an operating cell. It was shown that not only can beginning of life polarization performance be predicted with minimal fitting parameters, but degraded performance 30 k cycles was also well captured with no additional fitting. This latter result was accomplished by deleting catalyst sites from the network in proportion to the experimentally observed distribution of electrochemical surface area loss, obtained from TEM image of catalyst loading. The model included partitioning of oxygen into the ionomer phase, explicitly incorporating the oxygen transport resistance which dominates cell performance at higher current density. Although Knudsen diffusion is present at the scales present (<100nm), it represented a negligible fraction of the total transport resistance, which was dominated by the low solubility and slow diffusivity in the ionomer phase. This work showed that the performance of a typical PEMFC is highly dependent on the structural details of the catalyst layer, to the extent that polarization curves can be well predicted by direct inspection of an image of the catalyst layer. This work paves the way for a deeper understanding of the structure-performance relationship in these complex materials and the search for optimized catalyst layer designs.

Single-Atom and Dual-Atom Electrocatalysts: Synthesis and Applications.

Distinguishing themselves from nanostructured catalysts, single-atom catalysts (SACs) typically consist of positively charged single metal and coordination atoms without any metal-metal bonds. Dual-atom catalysts (DACs) have emerged as extended family members of SACs in recent years. Both SACs and DACs possess characteristics that combine both homogeneous and heterogeneous catalysis, offering advantages such as uniform active sites and adjustable interactions with ligands, while also inheriting the high stability and recyclability associated with heterogeneous catalyst systems. They offer numerous advantages and are extensively utilized in the field of electrocatalysis, so they have emerged as one of the most prominent material research platforms in the direction of electrocatalysis. This review provides a comprehensive review of SACs and DACs in the field of electrocatalysis: encompassing economic production, elucidating electrocatalytic reaction pathways and associated mechanisms, uncovering structure-performance relationships, and addressing major challenges and opportunities within this domain. Our objective is to present novel ideas for developing advanced synthesis strategies, precisely controlling the microstructure of catalytic active sites, establishing accurate structure-activity relationships, unraveling potential mechanisms underlying electrocatalytic reactions, identifying more efficient reaction paths, and enhancing overall performance in electrocatalytic reactions.

Charge Dynamics Engineering Sparks Hetero-Interfacial Polarization for an Ultra-Efficient Microwave Absorber with Mechanical Robustness.

Microwave absorbers with high efficiency and mechanical robustness are urgently desired to cope with more complex and harsh application scenarios. However, manipulating the trade-off between microwave absorption performance and mechanical properties is seldom realized in microwave absorbers. Here, a chemistry-tailored charge dynamic engineering strategy is proposed for sparking hetero-interfacial polarization and thus coordinating microwave attenuation ability with the interfacial bonding, endowing polymer-based composites with microwave absorption efficiency and mechanical toughness. The absorber designed by this new conceptual approach exhibits remarkable Ku-band microwave absorption efficiency (-55.3dB at a thickness of 1.5mm) and satisfactory effective absorption bandwidth (5.0GHz) as well as desirable interfacial shear strength (97.5MPa). The calculated differential charge density depicts the uneven distribution of space charge and the intense hetero-interfacial polarization, clarifying the structure-performance relationship from a theoretical perspective. This work breaks through traditional single performance-oriented design methods and ushers a new direction for next-generation microwave absorbers.

Direct Evidence of Dynamic Metal Support Interactions in Co/TiO2 Catalysts by Near-Ambient Pressure X-ray Photoelectron Spectroscopy.

The interaction between metal particles and the oxide support, the so-called metal-support interaction, plays a critical role in the performance of heterogenous catalysts. Probing the dynamic evolution of these interactions under reactive gas atmospheres is crucial to comprehending the structure-performance relationship and eventually designing new catalysts with enhanced properties. Cobalt supported on TiO2 (Co/TiO2) is an industrially relevant catalyst applied in Fischer-Tropsch synthesis. Although it is widely acknowledged that Co/TiO2 is restructured during the reaction process, little is known about the impact of the specific gas phase environment at the material's surface. The combination of soft and hard X-ray photoemission spectroscopies are used to investigate in situ Co particles supported on pure and NaBH4-modified TiO2 under H2, O2, and CO2:H2 gas atmospheres. The combination of soft and hard X-ray photoemission methods, which allows for simultaneous probing of the chemical composition of surface and subsurface layers, is one of the study's unique features. It is shown that under H2, cobalt particles are encapsulated below a stoichiometric TiO2 layer. This arrangement is preserved under CO2 hydrogenation conditions (i.e., CO2:H2), but changes rapidly upon exposure to O2. The pretreatment of the TiO2 support with NaBH4 affects the surface mobility and prevents TiO2 spillover onto Co particles.