Creation Of Oxygen Vacancies Research Articles

High electrolysis performance of the SOEC cathode by creating oxygen vacancies to regulate the adsorption energy

The in situ surface modification of metal nanoparticles will significantly increase the oxygen vacancy concentration of the cathode material and reduce the adsorption energy, thus enhancing the catalytic activity of CO2RR.

Polyoxometalates tailoring of frustrated Lewis pairs on Ce-doped Bi2O3 for boosting photocatalytic CO2 reduction.

Constructing frustrated Lewis pairs (FLPs) on catalysts will provide catalytic sites to activate CO2 and boost photocatalytic CO2 reduction. Herein, a Ce-doped bismuth oxide (CeBiOX) with FLPs was designed by loading [(α-SbW9O33)2Cu3(H2O)3]12- (Cu3) via strong electrostatic interactions to create oxygen vacancies (OVs). Detailed experiments and measurements showed that Cu3 could regulate the FLPs and optimize the band structure of CeBiOX to boost photocatalytic CO2 reduction. In particular, the Cu3/CeBiOX composite exhibited the highest yields of CO (42.85 μmoL g-1) and CH4 (13.23 μmoL g-1), being 6.6 and 3.3 times, and 4.9 and 6.3 times higher than those of pristine Bi2O3 and CeBiOX, respectively. This work provides a significant and mild approach to obtaining advanced catalysts with tuneable FLPs for more fields.

Fast and Durable Lithium Storage Enabled By Tuning Entropy in Wadsley-Roth Phase Titanium Niobium Oxides

To date, Wadsley−Roth phase materials are one of the most promising intercalation-type hosts for fast lithium transport because of the unique crystalline diffusion channels. However, the volume expansion as well as sluggish ion/electron transport kinetics retards its application in grid scale. In recent years, various strategies have been suggested to further improve the overall performance of micro-sized Wadsley-Roth phase materials, such as oxygen vacancy creation or cation substitution.Lately, entropy tuning has received considerable interest due to the favorable entropy-dominated phase-stabilization and ionic conductivity boosting effects.[1,2] However, it has only been applied in a few materials and the understanding of its function is still limited. It has been suggested that entropy-stabilized Wadsley−Roth shear phases with a more ordered structure would be stable upon electrochemical lithium (de-)insertion without a phase transition, while a more disordered structure would compromise the stability of the active material.[3] Therefore, suitable entropy tuning in entropy-stabilized Wadsley−Roth phase materials remains challenging and detailed knowledge about its effect on crystal structure and lithium storage is still lacking.Here, we have successfully realized entropy-stabilized Wadsley-Roth phase Fe0.4Ti1.6Nb10O28.8 (FTNO) in which the increased entropy, due to iron substitution, leads to a reduced grain size, and therefore, a shortened Li+ diffusion channel length.[4] Secondly, the diffusion coefficient and the reaction rate constant are enhanced leading to a reduced overpotential and an improved rate performance. Benefiting from this, the micro-sized FTNO electrode exhibits an enhanced rate ability of 73.7 mAh·g-1 at 50 C as compared to 37.9 mAh·g-1 for its TNO counterpart. Thirdly, the increased entropy results in an extended cycling durability of FTNO electrode which can deliver a specific capacity of 130.0 mAh g-1 after 6000 cycles at high rate of 10 C. Operando XRD analysis demonstrates a suppression of the a-axis deformation during the first stage of the lithiation process. The mechanism is revealed by DFT calculations and found that Fe-O bond lengths undergo less changes than Ti-O during lithiation. Finally, the potential practical application of FTNO anodes has been demonstrated by successfully constructing fast charging and stable LiFePO4‖FTNO full cells.Our results demonstrate the effectiveness of tuning entropy by iron substitution to stabilize the Wadsley-Roth phase with fast charging ability, which can be extended to other intercalation electrodes for enhanced battery applications.[1] Y. Zeng et al., Science 2022, 378, 1320-1324.[2] R. Zhang et al., Nature 2022, 610, 67-73.[3] A. A. Voskanyan et al., Chem. Mater. 2020, 32, 5301-5308[4] J. Zheng et al., Small, smll.202301967R1, accepted.

Boosting stability of spinel LiMn2O4 cathode materials by creating oxygen vacancies

Octahedral spinel lithium manganate dioxide (LiMn2O4, LMO) achieves remarkable electrochemical properties, but manganese dissolution during extended cycling process still cannot be well avoided. Herein, the oxygen vacancies within LiMn2O4 can be effectively modulated by extending the calcination duration. The density functional theory (DFT) calculation and experiments verified that appropriate oxygen vacancies not only promotes the structural stability, but also accelerates the charge transfer to improve the cycle performance under high C rate. Among them, the LMO sintered at 750 °C for 10 h (LMO-10) presented prominent electrochemical performance, delivering 114.58 mAh/g with the capacity retention rate of 95.90 % after 500 cycles at 5C, while the unmodified sample only exhibits 64.46 mAh/g with low retention of 63.75 %. This highly effective and facile approach to manipulate oxygen vacancies of spinel LiMn2O4 would facilitate to develop advanced cathode materials for lithium-ion batteries.

Porous Single-crystalline Centimeter-sized α-Al2 O3 Monoliths for Selective and Durable Non-oxidative Dehydrogenation of Ethane.

Alpha alumina (α-Al2 O3 ) are inert materials with outstanding thermal, chemical and mechanical stability. Herein, we fabricate porous single-crystalline (PSC) α-Al2 O3 monoliths at centimeter scale to endow them with high catalytic activity while maintaining their stability. We reduce PSC α-Al2 O3 monoliths to create oxygen vacancies in lattice and stabilize them by the ordered lattice to construct unsaturated Al-O coordination structures for enhancing the catalytic activity. The generation of oxygen vacancy at 18e wyckoff position contributes to the unsaturated Al-O coordination. As a case study, we demonstrate the outstanding performance with conversion (≈34 %) and selectivity (≈95 %) toward non-oxidative dehydrogenation of ethane to ethylene at 700 °C. We achieve the outstanding performance without obvious degradation even after a continuous operation over 1000 hours at 700 °C.

Porous Single‐crystalline Centimeter‐sized α‐Al2O3 Monoliths for Selective and Durable Non‐oxidative Dehydrogenation of Ethane

AbstractAlpha alumina (α‐Al2O3) are inert materials with outstanding thermal, chemical and mechanical stability. Herein, we fabricate porous single‐crystalline (PSC) α‐Al2O3 monoliths at centimeter scale to endow them with high catalytic activity while maintaining their stability. We reduce PSC α‐Al2O3 monoliths to create oxygen vacancies in lattice and stabilize them by the ordered lattice to construct unsaturated Al−O coordination structures for enhancing the catalytic activity. The generation of oxygen vacancy at 18e wyckoff position contributes to the unsaturated Al−O coordination. As a case study, we demonstrate the outstanding performance with conversion (≈34 %) and selectivity (≈95 %) toward non‐oxidative dehydrogenation of ethane to ethylene at 700 °C. We achieve the outstanding performance without obvious degradation even after a continuous operation over 1000 hours at 700 °C.

Oxygen-Bonding State and Oxygen-Reduction Reaction Mechanism of Pr0.7Ca0.3Mn1−xCoxO3−d (x = 0, 0.1, 0.2, 0.3)

We investigated the effects of Co doping on Pr0.7Ca0.3MnO3−d in the perspective of an oxygen-bonding state change. In all compositions, Pr0.7Ca0.3Mn1−xCoxO3−d (PCMCx, x = 0, 0.1, 0.2, 0.3) showed an orthorhombic structure, and the lattice gradually contracted with increasing Co content. The doped Co was mostly present as 2+ and 3+, which decreased the average oxidation value of the B site and created oxygen vacancies for charge compensation. However, as the Co content increased, the proportion of Co3+ increased, and the content of oxygen vacancies gradually decreased. In addition, the ratio of adsorbed oxygen in PCMC0.1 was the highest, and the B-O covalency was enhanced. Accordingly, the electrochemical reaction of oxygen with the cathode material in PCMC0.1 could occur most easily, showing the smallest polarization resistance among the Co-doped Pr0.7Ca0.3MnO3−d. We can confirm the formation of oxygen vacancies via Co doping and the effect of B-O covalency on the oxygen-reduction reaction of Pr0.7Ca0.3MnO3−d.

Exploring the role of oxygen vacancies on the magnetic and electromagnetic absorption properties of La3+-modified M-type hexaferrite with Al3+ doping

The demand for effective microwave-absorbing materials has recently surged due to rapid advancements in electromagnetic (EM) devices. Recently, engineering oxygen vacancies has also become one of the effective ways to develop efficient microwave-absorbing materials. So, understanding the EM absorption mechanism of these materials has become crucial for better engineering of such materials. This article investigates the magnetic properties along with the EM absorption mechanism of M-type hexaferrite, with optimal incorporation of rare-earth element La3+ and doping of transition metal Al3+ cation. The presence of La3+ ions at an optimal level promotes the reduction of Fe3+ to Fe2+ cations and creating oxygen vacancies to offset the electrical charge imbalance. This phenomenon impacts both the magnetic and EM characteristics of the materials. The presence of Fe2+ cations enhanced the spin-orbital interaction, resulting in a strong magnetic anisotropy field along the c-axis. The lowest reflection loss of −36.37 dB at 14.19 GHz, is observed with a bandwidth of 3.61 GHz below −10 dB for x = 0.6. These microwave absorption properties can be attributed to the adequate compensation between dielectric and magnetic losses, which arise from phenomena like dielectric relaxation, magnetic resonance, and conduction loss due to electron hopping between Fe3+ and Fe2+ with proper incorporation of the attenuating constant and excellent impedance matching, along with microstructure of the materials. Furthermore, the material’s exceptional absorption properties are also influenced by the rapid movement of oxygen vacancies from its interior to its surface when exposed to high frequencies, thereby impacting its conductivity. Therefore, it is believed that the regulation of oxygen vacancies can serve as a versatile strategy for developing materials with efficient microwave-absorbing capabilities.

Alleviating Mn<sup>3+</sup> Dissolution in ZnMn<sub>2</sub>O<sub>4</sub> Cathode for the Extended Cyclability via Particle Size Increase

ZnMn<sub>2</sub>O<sub>4</sub> (ZMO) cathode possesses a high theoretical capacity of 224 mAh g<sup>-1</sup> and high operating voltage (1.9 V vs. Zn<sup>2+</sup>/Zn) for aqueous Zn–ion batteries. However, the disproportionation reaction of Mn<sup>3+</sup> leads to Mn dissolution in the ZMO cathode, deteriorating lifespan. In this study, we attempted to reduce Mn dissolution by enlarging the particle size, thereby diminishing the electrode/electrolyte interfacial area. The ZMO particle grew with increasing the calcination temperatures of 400℃, 500℃, and 600℃. Higher calcination temperature created oxygen vacancies within the lattice, thereby increasing the contents of Mn<sup>3+</sup> for charge neutrality. The rate capability decreased with the increase in particle size, which is presumed to be due to the lengthening of the diffusion path of Zn ions. After a long–cycle experiment of Zn–ion batteries assembled with ZMO cathode and Zn anode, the Mn deposit amount on the anode was measured to reveal the Mn dissolution from the ZMO cathode based on the disproportionation reaction. The ZMO particle synthesized at 600℃ with the largest particle size demonstrated the highest cyclability of 48.1% at 1.0 A g<sup>-1</sup> based on the lowest Mn deposit on the anode. Hence, the ZMO electrode with a larger particle size exhibited improved cycle stability by alleviating of the disproportionation reaction from the reduced electrode/electrolyte interfacial area.

Electrocatalytic HER and magnetism performance of BiMnO3 modified BaTiO3 – A ultra high dielectric constant ceramic nanomaterial

High dielectric constant with green hydrogen gas productivity holds promising characteristics for futuristic advanced functional materials. Ultrahigh dielectric constant covering BiMnO3 modified BaTiO3 (0.5BaTiO3-0.5BiMnO3, abbreviated as BTBiM5) was chemically furnished through the precursor solution decomposition method. The spherical morphological nanocrystalline ceramics contain a tetragonal phase with 32 nm crystallite size. The cationic size alteration and temperature dealing creates oxygen vacancies which are reflected in powder X-ray diffraction (XRD) pattern shifting and the presence of lower oxidation states of Bi and Mn. The BTBiM5 sintered pellet demonstrates ultrahigh dielectric constant (108 order) at low frequencies (1 kHz). The relaxor-diffusive nature of BTBiM5 is identified with 1.37 diffusivity. The single semicircular Nyquist plot corresponds to non-Debye type characterizations with a grain conductivity nature. The room temperature magnetism performance finds saturation of magnetization of BTBiM5 after 200 Oe. The nanocrystalline BTBiM5 is functionalized as an electrocatalyst to produce green hydrogen gas under alkaline conditions. In this regard, 223 mV overpotential at 30 mA cm−2 current density is recorded with 152 mV dec−1 Tafel slope. The six-hour chronoamperometry test identifies the durability of the material during the electrocatalytic process that confers the probable grant massive footprint of such type of materials in the near future.

The Underlying Catalytic Role of Oxygen Vacancies in Fatty Acid Methyl Esters Ketonization over TiOx Catalysts.

Recently, interest in converting bio-derived fatty acid methyl esters (FAMEs) into added-value products has significantly increased. The selectivity of ketonization reaction in the conversion of the FAMEs has significantly hampered the efficiency of this process. Herein, this work reports the preparation of catalysts with different levels of oxygen vacancies while the crystal phase remained unchanged. The catalyst with the highest level of oxygen vacancy exhibited the maximum selectivity. The density functional theory (DFT) simulation showed an increase in interatomic distances leading to the formation of frustrated Lewis pairs (FLPs) upon the creation of oxygen vacancies. The surface measurements, type and density of acid sites of the catalysts, showed that the Lewis acid sites enhanced the selectivity for ketone production; while Bronsted acid sites increased the formation of by-products. Moreover, the ketone formation rate was directly proportional to acid density. The findings of this research provide a different approach for catalyst design, based on defects engineering and their effect on the surface activity, which could be used for enhancing the catalytic performance of novel metal oxides.

X-ray photoelectron spectroscopy of surface-treated TiO2 mesoporous film by 500 eV argon ion beam

The surface sensitivity profiling feature of x-ray photoelectron spectroscopy (XPS) regularly calls for sample surface treatment through irradiation with beam of argon ion. The beam potentially ensures surface cleanliness against contaminations under ultra-high vacuum conditions for elemental identification. This work systematically and elegantly employs an argon ion (Ar+) beam to create oxygen vacancies in TiO2 mesoporous film at different time of radiation exposure. Survey spectra acquired from XPS compositionally indicates the presence of oxygen (O 1s), titanium (Ti 2p) and carbon (C 1s). Three peaks were detected in the spectra of O 1s at high-resolution XPS which can be linked to oxygen vacancy, lattice oxygen and adsorbed oxygen while increase in radiation exposure time leads to increase in oxygen vacancy concentration. The presence of Ti3+ was observed in Ti 2p spectra analysis and indicates the creation of oxygen vacancies due to Ti4+ reduction. The potential of Ar+ to induce oxygen vacancies in TiO2 mesoporous film as demonstrated in this work would facilitate photocatalytic activity enhancement of TiO2 semiconductor films for different applications.

Creating oxygen vacancies on porous tungsten oxide nanospheres via one-step muffle calcination for ultra-fast detection of ppb-level hydrogen sulfide sensors

Exploring the relationship between tungsten oxides with a controlled amount of oxygen vacancies and their gas-sensing properties with respect to hydrogen sulfide is interesting for developing excellent comprehensive gas-sensing performance materials with fast and accurate response. In this work, the WO3 nanoparticles with oxygen defective structure were synthesized by a straightforward one-step muffle calcining method. The WO3 nanoparticles prepared at the calcination temperature of 600 ℃ (Ov-WO3-600) display the high response value (2777) and ultra-fast response time (2 s) to 5 ppm hydrogen sulfide (H2S) at 100 ℃. Moreover, it also exhibits low practical detection limit (100 ppb), long-term stability, as well as remarkable admirable selectivity. The gas sensing mechanism can be explained by the fact that oxygen vacancies, as donor energy levels provide more electrons, increase the carrier mobility and narrow the band gap. This makes it easier for oxygen to capture electrons to form more adsorbed oxygen, which improves the gas sensing performance of WO3-based sensors. Hence, our study can offer guidance for the construction of fast and accurate sensing materials based on WO3.

Encapsulation of few-layered MoS2 on electrochemical-treated BiVO4 nanoarray photoanode: Simultaneously improved charge separation and hole extraction towards efficient photoelectrochemical water splitting

Bismuth vanadate (BiVO4) photoanode shows great potential for photoelectrochemical (PEC) water splitting but still suffers from the sluggish surface reaction kinetic and high charge loss. Further strengthening the intrinsic charge transport for the improvement of solar-to-hydrogen conversion becomes the top priority. Herein, an innovative highly-oriented E-BiVO4/MoS2 heterojunction photoanode is rationally designed and fabricated via directly encapsulating few-layered MoS2 nanosheets on electrochemical-treated BiVO4 (E-BiVO4) nanopyramid arrays. Systematic studies reveal that the electrochemical reduction process can create oxygen vacancies on BiVO4 lattice, thereby increasing the overall carrier concentration, and boosting the bulk and surface charge separation efficiencies. Meanwhile, the introduction of MoS2 as a heterojunction helps build the unidirectional charge transfer channels for further facilitated surface hole extraction and oxidation kinetics, synergistically devoting to the significantly enhanced PEC activity and photostability. As a result, the optimized E-BiVO4/MoS2 photoanode exhibits the highest photocurrent density of 2.11 mA/cm2 at 1.23VRHE and incident photon-to-electron conversion efficiency (IPCE) of 40.6 %, which are approximately 4.6 and 4.9 times higher than the pristine BiVO4. The present work demonstrates a feasible collaborative strategy to develop photoanodes with simultaneously improved charge separation and hole transport for efficient PEC water splitting application.

Creation of robust oxygen vacancies in 2D ultrathin BiOBr nanosheets by irradiation through photocatalytic memory effect for enhanced CO2 reduction

An interesting photocatalytic memory effect was found in 2D ultrathin BiOBr nanosheets, which endowed them the capability to trap photogenerated electrons on Bi3+ and Br- in this material system for an extended period of time and resulted in the creation of stable oxygen vacancies (Ov) by just visible light irradiation due to the charge balance requirement. Thus, a broader visible light absorption, more negative conduction band minimum, stronger piezoelectric response, better charge carrier separation and transfer, and enhanced CO2 adsorption and activation were occurred in these BiOBr nanosheets with prior visible light irradiation, all of which were beneficial for their enhanced CO2 reduction performances in photocatalysis, piezocatalysis, and photopiezocatalysis, respectively, than their counterparts without it. This work demonstrated a novel approach to create oxygen vacancies by light irradiation through the photocatalytic memory effect, which could be readily applied to similar photocatalyst systems to boost their performances and generate novel functionalities.

Oxygen Vacancy Ordering and Molten Salt Corrosion Behavior of ZnO-Doped CeYSZ for Solid Oxide Membranes.

Although 4Ce4YSZ has high corrosion resistance, it faces challenges concerning its sinterability and ionic conductivity. Therefore, we studied destabilization behavior caused by corrosion and oxygen vacancy ordering according to ZnO doping. Powders of (4Ce4YSZ)1-x(ZnO)x (x = 0.5, 1, 2, 4 mol%) were synthesized using the sol-gel method. With the addition of ZnO, the cubic phase increased, and secondary phases were not observed. The (111) peak showed a higher angle shift in ZnO-doped 4Ce4YSZ compared to 4Ce4YSZ, and TEM-SAED revealed a reduction in the spacing of the (011)t plane, suggesting lattice contraction due to the substitution of the smaller Zn2+ (60 Å) for Zr4+ (84 Å) in the lattice. The local atomic structure analysis was conducted using EXAFS to investigate the oxygen vacancy ordering behavior. Zr K-edge Fourier transform data revealed a decrease in the Zr-O1 peak intensity with an increasing amount of ZnO doping, indicating an increase in oxygen vacancies. The Zr-O1 peak position shifted to the right, leading to an increase in the Zr-O1 interatomic distance. In the Y K-edge Fourier transform data, the Y-O1 peak intensity did not decrease, and there was little variation in the Y-O1 interatomic distance. These results suggest that the oxygen vacancies formed due to ZnO doping are located in the neighboring oxygen shell of Zn, rather than in the neighboring oxygen shells of Y and Zr. Impedance measurements were conducted to measure the conductivity, and as the amount of ZnO doping increased, the total conductivity increased, while the activation energy decreased. The increase in oxygen vacancies by ZnO doping contributed to the enhancement of conductivity, and it is considered that these created oxygen vacancies did not interact with Zn2+ and did not form defect associations. Fluoride-based molten salts were introduced to the specimens to assess the corrosion behavior in a molten salt environment. Yttrium depletion layers (YDLs) were formed on the surfaces of all specimens due to the leaching of yttrium. However, Ce remained relatively stable at the interface according to EDS line scans, suggesting a reduction in the phase transformation (cubic, tetragonal to monoclinic) typically associated with yttrium leaching in YSZ.

Nitrogen-doped porous carbon TiO2 produced by thermolysis of MIL-125-NH2 under an inert atmosphere for enhanced visible light photocatalytic activity

Metal-organic frameworks have gained significant attention as precursors for the synthesis of functional materials with tailored properties. In this study, we present the synthesis and characterization of nitrogen-doped porous carbon TiO2 (N-C/TiO2) by thermolysis of MIL-125-NH2. The effect of calcination temperature (ranging from 300 to 900°C) and atmospheric conditions on the phase transition, elemental composition and morphological structure is thoroughly investigated. Through X-ray diffraction (XRD) analysis, we identified the formation of the rutile phase in the N-C/TiO2 nanoporous structure, which leads to the creation of oxygen vacancies and metal defects. Interestingly, the orthorhombic shape of MIL-125-NH2 is retained in the final N-C/TiO2 product, indicating the robustness of the conversion process. The UV-Vis diffuse reflectance (UV-Vis) and photoluminescence (PL) analysis demonstrated that the phase transition results in a narrowed band gap energy and reduced recombination of photogenerated electron-hole pairs. The photocatalytic activity of the synthesized N-C/TiO2 is evaluated by the degradation of methylene blue (MB) dye under visible light irradiation. Our results revealed that superoxide radicals are the primary species responsible for the photocatalytic reaction. Furthermore, the N-C/TiO2 photocatalyst exhibits excellent stability and recyclability for five consecutive photocatalytic cycles. Overall, this study provides novel insights into the synthesis, characterization and photocatalytic activity of N-C/TiO2 material derived from MIL-125-NH2, emphasizing the significance of calcination temperature and atmospheric conditions. The developed N-C/TiO2 poses great potential for various environmental and energy applications where enhanced visible light photocatalytic activity is desired.

Structural and Chemical Properties of NiOx Thin Films: Oxygen Vacancy Formation in O2 Atmosphere.

NiOx films on Si(111) were put in contact with oxygen at elevated temperatures. During heating and cooling in oxygen atmosphere Near Ambient Pressure (NAP)-XPS and -XAS and work function (WF) measurements reveal the creation and replenishing of oxygen vacancies in dependence of temperature. Oxygen vacancies manifest themselves as a distinct O1s feature at 528.9 eV on the low binding energy side of the main NiO peak as well as by a distinct deviation of the Ni2p3/2 spectral features from the typical NiO spectra. DFT calculations reveal that the presence of oxygen vacancies leads to a charge redistribution and altered bond lengths of the atoms surrounding the vacancies causing the observed spectral changes. Furthermore, we observed that a broadening of the lowest energy peak in the O K-edge spectra can be attributed to oxygen vacancies. In the presence of oxygen vacancies, the WF is lowered by 0.1 eV.

Atomistic Insights into Medium-Entropy Perovskites for Efficient and Robust CO2 Electrolysis.

Solid oxide electrolysis cells (SOECs) show great promise in converting CO2 to valuable products. However, their practicality for the CO2 reduction reaction (CO2RR) is restricted by sluggish kinetics and limited durability. Herein, we propose a novel medium-entropy perovskite, Sr2(Fe1.0Ti0.25Cr0.25Mn0.25Mo0.25)O6-δ (SFTCMM), as a potential electrode material for symmetrical SOEC toward CO2RR. Experimental and theoretical results unveil that the configuration entropy of SFTCMM perovskites contributes to the strengthened metal 3d-O 2p hybridization and the reduced O 2p bond center. This variation of electronic structure benefits oxygen vacancy creation and diffusion as well as CO2 adsorption and activation and ultimately accelerates CO2RR and oxygen electrocatalysis kinetics. Notably, the SFTCMM-based symmetrical SOEC delivers an excellent current density of 1.50 A cm-2 at 800 °C and 1.5 V, surpassing the prototype Sr2Fe1.5Mo0.5O6-δ (SFM, 1.04 A cm-2) and most of the state-of-the-art electrodes for symmetrical SOECs. Moreover, the SFTCMM-based symmetrical SOEC demonstrates stable CO2RR operation for 160 h.

Tuning Oxygen Vacancies in Oxides by Configurational Entropy.

Tuning surface oxygen vacancies is important for oxide catalysts. Doping elements with different chemical valence states or different atomic radii into host oxides is a common method to create oxygen vacancies. However, the concentration of oxygen vacancies in oxide catalysts is still limited to the amount of foreign dopants that can be tolerated (generally less than 10% atoms). Herein, a principle of engineering the configurational entropy to tune oxygen vacancies was proposed. First, the positive relationship between the configuration entropy and the formation energy of oxygen vacancies (Eov) in 16 model oxides was estimated by a DFT calculation. To verify this, single binary oxides and high-entropy quinary oxides (HEOs) were prepared. Indeed, the concentration of oxygen vacancies in HEOs (Oβ/α = 3.66) was higher compared to those of single or binary oxides (Oβ/α = 0.22-0.75) by O1s XPS, O2-TPD, and EPR. Interestingly, the reduction temperatures of transition metal ions in HEOs were generally lower than that in single-metal oxides by H2-TPR. The lower Eov of HEOs may contribute to this feature, which was confirmed by in situ XPS and in situ XRD. Moreover, with catalytic CO/C3H6 oxidation as a model, the high-entropy (MnCuCo3NiFe)xOy catalyst showed higher catalytic activity than single and binary oxides, which experimentally verified the hypothesis of the DFT calculation. This work may inspire more oxide catalysts with preferred oxygen vacancies.