Large Amount Of Oxygen Vacancies Research Articles

Insight into the Growth Mechanism and Photocatalytic Behavior of Tubular Hierarchical ZnO Structures: An Integrated Experimental and Theoretical Approach.

The hydrothermal synthesis of zinc oxide (ZnO) particles from zinc acetylacetonate monohydrate in "pure" aqueous solution and in aqueous NaOH solution at 90 °C is reported. The structural and morphological properties of ZnO particles were investigated by powder X-ray diffraction, X-ray absorption spectroscopy (XAS), field emission scanning electron microscopy, and transmission electron microscopy. The effect of NaOH on the growth mechanism and photocatalytic performance of hierarchical ZnO structures was investigated. The experimental findings, supported by results of quantum chemical calculations at the level of density functional theory, were used to propose the mechanism of nucleation and preferential growth of finely tuned hollow and nonhollow ZnO structures and their effects on the photocatalytic activity. The calculations indicate that the process of ZnO nucleation in "pure" aqueous solution mainly proceeds by the reaction of small monomers, while tetramers play a crucial role in aqueous NaOH solution. Both the preferred ZnO nanostructure and microstructure growth processes are driven by O-H···O hydrogen bonds as controlling elements. The calculated values of the EO···H interaction indicate a stronger interaction via O-H···O hydrogen bonds in "pure" aqueous media (EO···H = -11.73 kcal mol-1) compared to those obtained in aqueous NaOH solution (EO···H = -8.41 kcal mol-1). The specific structural motif of the (ZnO-H2O)12 dodecamers with calculated negative ΔG*INT free release energy indicates that the formation of anisotropic nanocrystalline ZnO with the c-axis as the primary growth direction is spontaneous and accelerated exclusively in "pure" aqueous solution, whereas it is an unfavorable endergonic process in aqueous NaOH solution (ΔG*INT > 0). Efforts have been made to determine the photocatalytic efficiency of the ZnO samples based on the XAS measurements. ZnO particles obtained in "pure" aqueous solution show the highest photocatalytic activity due to the presence of a larger amount of oxygen vacancies.

CdS@Polydopamine@SnO2-x sandwich structure with electrostatic repulsion effect and oxygen deficiency: enhanced photocatalytic hydrogen evolution activity and inhibited photo-corrosion

The activity and stability of photocatalysts are usually restricted to photo-corrosion issues. Here, an efficient electrostatic repulsion and anchor strategy via constructing a CdS@Polydopamine@SnO2-x sandwich structure with numerous oxygen vacancies through a simple chemical bath deposition approach. During the formation process, the CdS nanorods are wrapped by the catechol fragments from polydopamine (PDA) and display an electronegative surface. This strong electrostatic repulsion can effectively repel S2-, thereby effectively preventing S2- from being separated from CdS and being oxidized by holes or oxygen. Furthermore, the PDA employed as an interlayer of the heterojunction sandwich structure can fix the multivalent metal ions, such as Cd2+ and Sn4+ ions on CdS and SnO2-x, which can be used as a bridge for electronic transmission. More importantly, the as-prepared SnO2-x nanocrystals are found to possess a large amount of oxygen vacancies, which can effectively control the electronic structure of the catalyst, enhance the electron enrichment effect, promote the absorption of visible light and change the charge transfer ability. More importantly, the accumulation of CdS@PDA@SnO2-x (411.37 mmol) photocatalytic hydrogen evolution is 34.3 times than pristine CdS (12.0 mmol) within 5 h, and the catalytic activity remains stable after 10 cycles. Photoelectrochemical characterization, Scanning Kelvin Probe (SKP), Finite Difference Time Domain (FDTD) simulations verified the mechanism of enhanced photocatalytic activity. Herein, this work displays a novel structure and mechanism to enhance the stability of sulfide semiconductors, which may further open a new path in the structural control strategy of photocatalysts.

(Invited) Grain Boundary and Surface Atomic Structures and Diffusion in Li-Ion Battery Related Crystals

The properties of lithium ion battery cathodes strongly depend on the diffusion of lithium ions during charge/discharge process. Then, direct visualization of lithium site is required to understand the mechanism of the diffusion of lithium ions. In this study, aberration (Cs) corrected STEM were applied to directly observe the {010} surface, which corresponded to perpendicular to the 1-D diffusion orientation, of the olivine LixFePO4. The morphology of the interface between Li-rich and Li-poor phases of LixFePO4 after chemical delithiation were observed with atomic resolution at fit intervals during half a year. It was found that orientation of boundary layers at the FePO4/Li2/3FePO4 interface gradually changed from lower index planes to higher index planes. This indicates that intermediate phase plays an important role in healing crystal cracking by allowing the interface to remain coherent so that Li ions can diffuse back into regions depleted during delithiation. The mechanism of the lithiation/delithiation from and to the surface will be discussed based on the observation results.Lithium lanthanum titanate (LLTO) is expected to apply for an electrolyte in the all-solid-state Li-ion battery because of its high Li-ion conductivity in the bulk. However, it has been reported that Li-ion conductivity is strongly suppressed at the grain boundaries (GBs) in polycrystalline materials. It is therefore needed to understand the atomistic mechanism of the reduction of Li-ion conductivity at individual GBs in order to design suitable LLTO polycrystals. In this study, two different GBs, Σ5 and Σ13, were prepared by fabricating the bicrystals, and their structures were observed by Cs corrected STEM and atomic force microscopy (AFM). Then, the charge states, Li-ion conductivities, atomic and electronic structures at the respective Σ5 and Σ13 GBs of LLTO were systematically and quantitatively investigated. It was found that the Σ5 GB has no significant influence on Li-ion conductivity, but the Σ13 GB shows the significant reduction of the Li-ion conductivity. We further found that Σ13 GB is positively charged by the formation of large amount of oxygen vacancies at the GB. Li-ion depletion layers is considered to be formed at the Σ13 GB, which causes the significant reduction of Li-ion conductivity, to compensate such positive charge at the GB.References Kobayashi, C.A.J.Fisher, T.Kato,Y.Ukyo,T.Hirayama and Y.Ikuhara, Nano Lett. 16, 5409 (2016).Kobayashi, A. Kuwabara, C. A.J. Fisher, Y. Ukyo and Y. Ikuhara,Nat. Commun., 9, 2863 (2018)Sasano, R. Ishikawa, I. Sugiyama, T. Higashi, T. Kimura, Y. H. Ikuhara, N. Shibata and Y. Ikuhara, Applied Physics Express, 10, 061102 (2017)Sasano, R. Ishikawa, K. Kawahara, T. Kimura, Y. H. Ikuhara, N. Shibata and Y. Ikuhara, Applied Physics Letters, 116, 043901 (2020)

Catkin-derived mesoporous carbon-supported molybdenum disulfide and nickel hydroxyl oxide hybrid as a bifunctional electrocatalyst for driving overall water splitting

In this work, a two-dimensional heterostructure of molybdenum disulfide (MoS2) and nickelhydroxyloxide (NiOOH) nanosheets supported on catkin-derived mesoporous carbon (C-MC) was constructed and exploited as an efficient electrocatalyst for overall water splitting. The C-MC nanostructure was prepared by pyrolyzing biomass material of catkin at 600 °C in N2 atmosphere. The C-MC network exhibited hollow nanotube structure and had a large specific surface area, comprising trace nitrogen and a large amount of oxygen vacancies. It further served as the support for the growth of NiOOH nanosheets (NiOOH@C-MC), which was combined with MoS2 nanosheets by in situ growth, yielding a multicomponent electrocatalyst (MoS2@NiOOH@C-MC). By integrating the superior hydrogen evolution reaction (HER) performance of MoS2, oxygen evolution reaction (OER) performance of NiOOH, and the fast electron transfer capability of C-MC, the prepared MoS2@NiOOH@C-MC illustrated a low potential of − 250 mV for HER and 1.51 V for OER at the current density of 10 mV cm−2. Consequently, when applied as the working electrode for driving overall water splitting in a two-electrode system, the bifunctional MoS2@NiOOH@C-MC electrocatalyst displayed a low cell voltage of 1.62 V at the current density of 10 mA cm−2. The present work provides a new strategy that uses biomass material for developing bifunctional electrocatalyst for overall water splitting.

Greatly Facilitated Two-Electron Electroreduction of Oxygen into Hydrogen Peroxide over TiO2 by Mn Doping.

Ambient electrochemical oxygen reduction into valuable hydrogen peroxide (H2O2) via a selective two-electron (2e-) pathway is regarded as a sustainable alternative to the industrial anthraquinone process, but it requires advanced electrocatalysts with high activity and selectivity. In this study, we report that Mn-doped TiO2 behaves as an efficient electrocatalyst toward highly selective H2O2 synthesis. This catalyst exhibits markedly enhanced 2e- oxygen reduction reaction performance with a low onset potential of 0.78 V and a high H2O2 selectivity of 92.7%, much superior to the pristine TiO2 (0.64 V, 62.2%). Additionally, it demonstrates a much improved H2O2 yield of up to 205 ppm h-1 with good stability during bulk electrolysis in an H-cell device. The significantly boosted catalytic performance is ascribed to the lattice distortion of Mn-doped TiO2 with a large amount of oxygen vacancies and Ti3+. Density functional theory calculations reveal that Mn dopant improves the electrical conductivity and reduces ΔG*OOH of pristine TiO2, thus giving rise to a highly efficient H2O2 production process.

Photocatalytic mineralization of indoor VOC mixtures over unique ternary TiO2/C/MnO2 with high adsorption selectivity

Formaldehyde (CH2O) and toluene (C7H8) are typical indoor air pollutants that have high harm to people’s health. Photocatalytic oxidation is a feasible approach, but still remains the problem of incomplete degradation to form refractory intermediates and uncertainty of interaction between multivariant components. This paper used natural proteins from waste shell as the carbon source and template to synthesize the ternary TiO2/C/MnO2 photocatalysts. It exhibited high adsorption selectivity and excellent photocatalytic performance for CH2O and C7H8 mixture mineralization under visible light irradiation. The optimal candidate achieved near completely mineralization within 60 min in the simulated indoor environment and exhibited remarkable stability after 5 cycles. Large amounts of oxygen vacancies, lattice distortions of TiO2, and tailored bandgap structure contributed to these excellent behaviors. Besides, carbon existence as an electron transfer channel dropped the interfacial charge-transfer resistance, thus prolonging the lifetime of charge carriers and making them rapidly go through the surface photo-oxidation reactions. In-situ DRIFTs results indicated that CH2O and C7H8 mixtures possessed the same reaction pathway and rate-determining step with single component. Above all, this paper offered a facile, sustainable, and green approach to synthesize efficient photocatalysts for treating indoor CH2O/C7H8 pollution with visible light irradiation.

Oxygen-vacancy engineering approach to bismuth basic nitrate/g-C3N4 heterostructure for efficiently photocatalytic hydrogen evolution

Formation of oxygen vacancy is emerging as one type of promising defect engineering in the preparation of inorganic functional composites. In this work, a novel composite upon the calcination of the nanosheets Bi6O6(OH)3(NO3)3·1.5H2O (BBN) and g-C3N4 was prepared. A large amount of oxygen vacancies was revealed by electron spin resonance (ESR) and Raman spectroscopy. These intriguing structural characters render the as-prepared composite with excellent interfacial charge transfer and photo-stimulated response as shown by electrochemical impedance spectroscopy (EIS) and photocurrent measurement. Upon visible-light activation, such composite enables photocatalyse H2 evolution with a rate of 181 μmol h−1 g−1 around the 4.2 times that of pure g-C3N4 as a reference. Such composite catalyst exhibits excellent recycling and reusable behaviors. The formation of BBN/CN heterojunction and the existence of oxygen vacancies are the main reasons for the distinctly improvement of its photocatalytic activity, which has been verified by theoretical calculations.

Correlation between Oxygen Vacancies and Oxygen Evolution Reaction Activity for a Model Electrode: PrBaCo2 O5+δ.

The role of the perovskite lattice oxygen in the oxygen evolution reaction (OER) is systematically studied in the PrBaCo2 O5+δ family. The reduced number of physical/chemical variables combined with in-depth characterizations such as neutron dif-fraction, O K-edge X-ray absorption spectroscopy (XAS), electron energy loss spectroscopy (EELS), magnetization and scanning transmission electron microscopy (STEM) studies, helps investigating the complex correlation between OER activity and a single perovskite property, such as the oxygen content. Larger amount of oxygen vacancies appears to facilitate the OER, possibly contributing to the mechanism involving the oxidation of lattice oxygen, i.e., the lattice oxygen evolution reaction (LOER). Furthermore, not only the number of vacancies but also their local arrangement in the perovskite lattice influences the OER activity, with a clear drop for the more stable, ordered stoichiometry.

Correlation between Oxygen Vacancies and Oxygen Evolution Reaction Activity for a Model Electrode: PrBaCo2O5+δ

AbstractThe role of the perovskite lattice oxygen in the oxygen evolution reaction (OER) is systematically studied in the PrBaCo2O5+δ family. The reduced number of physical/chemical variables combined with in‐depth characterizations such as neutron dif‐fraction, O K‐edge X‐ray absorption spectroscopy (XAS), electron energy loss spectroscopy (EELS), magnetization and scanning transmission electron microscopy (STEM) studies, helps investigating the complex correlation between OER activity and a single perovskite property, such as the oxygen content. Larger amount of oxygen vacancies appears to facilitate the OER, possibly contributing to the mechanism involving the oxidation of lattice oxygen, i.e., the lattice oxygen evolution reaction (LOER). Furthermore, not only the number of vacancies but also their local arrangement in the perovskite lattice influences the OER activity, with a clear drop for the more stable, ordered stoichiometry.

Co3S4 Nanoplate Arrays Decorated with Oxygen-Deficient CeO2 Nanoparticles for Supercapacitor Applications

Cobalt sulfide is favorable for supercapacitors, but its application is inhibited by the inherent slow charge transfer kinetics and poor stability in alkaline solution. Herein, zeolitic imidazole framework (ZIF)-derived Co3S4 nanoplate arrays (NPAs) decorated with CeO2 nanoparticles (NPs) grown on Ni foam have been developed. The obtained Co3S4/CeO2-NPAs display a 2D leaf-like nanoplate morphology (average thickness of nearly 230 nm) with a large amount of oxygen vacancies and exhibits remarkably boosted specific capacity/capacitance, i.e., 1155.8 C/g (2408 F/g) at 0.5 A/g with a notable rate capability (76.5% at 10 A/g), compared to Co3S4-NPAs or CeO2 NPs. More importantly, a two-electrode cell comprising the Co3S4/CeO2-NPAs and an activated carbon electrode displays a high energy density of 45.4 Wh/kg (at a power density of 850 W/kg) with decent long-term durability. Furthermore, a red light-emitting diode can be lighted up for 10 min by two charged cells, showing great prospect of Co3S4/CeO2-NPAs. The outstanding electrochemical properties of the Co3S4/CeO2-NPAs are mainly attributed to the 2D nanoplate morphology with much accessible active sites and the introduction of CeO2 NPs. The Co3S4/CeO2-rich interfaces promote electron transfer between Co3S4 and CeO2. The abundant oxygen vacancies adhere to the surface of Co3S4 and can enhance the electronic conductivity and the capture of OH–. In addition, the CeO2 layer can protect the Co3S4-NPAs from corrosion by the KOH electrolyte during the electrochemical process. Therefore, the electrode developed by this work has great potential in electrochemical applications.

Effects of Ni2+ substitution on the structure and dielectric properties of Bi1.5MgNb1.5O7 cubic pyrochlores

The dielectric properties of bismuth-based cubic pyrochlores strongly depend on the environment of the A-site ions, e.g. the Ni2+ ions doped into Bi1.5MgNb1.5O7 (BMN) pyrochlores for tailoring dielectric properties. Both BMN and Bi1.5NiNb1.5O7 (BNN) ceramics exhibit a cubic pyrochlore structure with preferential (222) planes. However, {442} reflections are observed in BNN pyrochlores, revealing an off-center displacement of A and O' ions. The dielectric constant of BNN pyrochlores is lower than that of BMN pyrochlores, besides BNN pyrochlores have a larger dielectric loss (0.002) than BMN pyrochlores (0.0007). Ni-doping results in a loose and flexible structure contributing positively to the dielectric tunability, besides creating a large amount of oxygen vacancies. The higher amount of oxygen vacancies increases the dielectric loss of BNN pyrochlores. However, BNN pyrochlores exhibit enhanced temperature stability, with a temperature coefficient of –57 ppm/oC, which is significantly better than that of BMN pyrochlores (–362 ppm/oC).

Mesoporous ferromagnetic manganese ferrite nanoparticles for enhanced visible light mineralization of azoic dye into nontoxic by-products

In this study, a one pot facile synthesis of ferromagnetic manganese ferrite nanoparticles (MnFe2O4) was carried out using chemical co-precipitation method for mineralization of azo dye (Congo red (CR)) in aqueous solution under visible light irradiation. The synthesized MnFe2O4 nanoparticles were highly crystalline and showed face-centred cubic (FCC) structure with average particle size of 58 ± 4 nm. The BET analysis of the MnFe2O4 nanoparticles revealed the mesoporous distribution of material with high surface area can provide large electro active sites and short diffusion paths for the transport of ions which plays a vital role in the photocatalytic degradation of CR. The point of zero charge (pHPZC) was observed to be 6.7 indicating favourable condition for material-anionic dye interaction. The XPS studies revealed that the large amounts of oxygen vacancies were produced due to the defects in the lattice oxygen. The MnFe2O4 nanoparticles mineralised 98.3 ± 0.2% of 50 mg/L CR within 30 min when tested in photocatalytic reactor under 565 nm. The particles were recoverable under the influence of an external magnet after the photocatalytic reaction and were reusable. The recovered nanoparticles showed 96% of CR degradation efficiency even after five cycles of reuse. The by-product analysis with GC–MS indicated mineralization of CR into simple alcohols and acids. The aqueous solution containing mineralised CR was nontoxic to Trigonella foenumgraecum and Vigna mungo seeds and favoured increased germination, plumule and radicle length when compared to untreated CR.

Cu-Promoted Iron Catalysts Supported on Nanorod-Structured Mn-Ce Mixed Oxides for Higher Alcohol Synthesis from Syngas

A series of supports were prepared through the method of hydrothermal synthesis, and copper–iron catalysts supported on ceria nanorods modified by different amounts of manganese were prepared by the liquid phase co-reduction method. The effect of the catalytic performance after Mn addition mainly on higher alcohols synthesis (HAS) was evaluated. Different techniques, such as BET, ICP-AES, XRD, H2-TPR, CO-TPD, TEM, FESEM, XPS and MES, were performed for catalyst characterization. The results indicated that the abilities of CO chemical desorption and carbon chain growth were promoted with appropriate Mn addition, and higher ratio of Cu0/Cu+ species facilitated the methanol homologous reaction and the C2+OH formation. The Ce4+ species were reduced into Ce3+ species during HAS process, providing a large amount of oxygen vacancies. Proper Mn content promoted the formation of χ-Fe5C2 and leaded to the Fe 2p binding energy shift, causing the electron transformation between Fe and Mn species. The largest weight selectivity of C2+OH appeared in the reaction over CuFe/3.6MnCe catalyst with CO conversion 41.43%, and weight fraction of C2+OH 84.41 wt% in the alcohols distribution.

High Oxygen Evolution Activity of Tungsten Bronze Oxides Boosted by Anchoring of Co2+ at Nb5+ Sites Accompanied by Substantial Oxygen Vacancy.

The participation of lattice oxygen in the oxygen evolution reaction (OER) process has been proved to be faster in kinetics than the mechanisms where only metal is involved, although activating the lattice oxygen in the traditional rigid structures remains a big challenge. In this work, efforts are devoted to exploring a new flexible structure that is competent in providing large amounts of oxygen vacancies as well as offering the freedom to manipulate the electronic structure of metal cations. This is demonstrated by anchoring low valence state Co at high valence state Nb sites in the tetragonal tungsten bronze (TTB)‐structured Sr0.5Ba0.5Nb2‐ xCoxO6‐δ, with different ratios of Co to Nb to optimize the Co substitution proportion. It is found that the occupation of Co in the Nb5+ sites gives rise to the generation of massive surface oxygen vacancies (Ovac), while Co itself is stabilized in Co2+ by adjacent Ovac. The coexistence of Ovac and LS Co2+ enables an oxygen intercalation mechanism in the optimal SBNC45 with specific activity at 1.7 V versus reversible hydrogen electrode that is 20 times higher than for the commercial IrO2. This work illuminates an entirely new avenue to rationally design OER electrocatalysts with ultrafast kinetics.

Highly sensitive sensor based on ordered porous ZnO nanosheets for ethanol detecting application

Ethanol sensors with high sensitivity are demanded for healthcare and environmental monitoring applications, especially in drunk driving detection. In this work, we present a high-performance gas sensor based on ordered porous ZnO (PZnO) nanosheets with a low cost. Gas sensing tests show that PZnO exhibits the highest ethanol sensing responsiveness at 307 °C to some toxic organic volatiles. The response of our PZnO based sensor is 212.0 toward 200 ppm ethanol vapor, the response and recovery time are only 8 s and 7 s, respectively. Compared with other ZnO based sensors shown in recent literatures, our PZnO based sensor exhibits faster response/recovery speed and higher sensitivity, which can be ascribed to the single-crystalline feature, more (002) facets exposure, ordered porous structure and a large amount of oxygen vacancy on the sensitive surface according to the sensing mechanism and density functional theory simulation study. The response also shows good linear relationship with the ethanol concentration in logarithm. Besides, the PZnO sensor is immune to high relative humidity. These characteristics enable PZnO based sensors for ethanol detecting applications.

Oxygen Evolution Reaction in Ba0.5Sr0.5Co0.8Fe0.2O3-δ Aided by Intrinsic Co/Fe Spinel-Like Surface.

Among the perovskites used to catalyze the oxygen evolution reaction (OER), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) exhibits excellent activity which is thought to be related to dynamic reconstruction at the flexible perovskite surface due to accommodation of large amount of oxygen vacancies. By studying the local structure and chemistry of BSCF surfaces, in detail, via a range of transmission electron microscopy (TEM) methods, we show that the surfaces of the as-synthesized BSCF particles are Co/Fe rich, and remarkably, adopt a spinel-like structure with a reduced valence of Co ions. Post-mortem and identical location TEM analyses reveal that the Co/Fe spinel-like surface retains a stable chemical environment of the Co/Fe ions, although its structure weakens after electrochemical processing. Further, it is verified that prior to the onset of OER, the Co/Fe spinel-like surface promotes the formation of the highly active Co(Fe)OOH phase, which enhances the OER electrocatalytic properties of the underlying conductive BSCF perovskite. This study provides a detailed understanding of the fundamental transformations that oxide catalysts undergo during electrochemical processes and can aid in the development of novel oxide catalysts with enhanced activity.

Visible photocatalysis of Cr(VI) at g/L level in Si/N-TiO2 nanocrystals synthesized by one-step co-hydrolysis method

This paper focuses on a novel one-step co-hydrolysis synthesis strategy of silicon modified N-doped titanium dioxide nanocrystals and its application in the visible light photocatalysis of chromium at g L−1 level in wastewater. Titanium(IV) bis(ammonium lactato)dihydroxide (TALH) has been adopted firstly as both Ti and N sources for synthesis of N-doped TiO2 microspheres (N-TiO2). Si modified N-TiO2 was fabricated by adding γ-(2,3-epoxypropoxy) propyltrimethoxysilane (KH560) before hydrolysis of TALH. The adsorption and co-hydrolysis of silane molecules significantly inhibit the growth of N-TiO2 crystals, and further promote appropriate cross-linking of particles through silanol (hydrolysate) intermolecular force or potential Si-O-Si bond by the polycondensation reaction to form nano-sized Si/N-TiO2. Interestingly, the introduction of silicon turns the negative charge surface of N-TiO2 into positive charge one through the Si-O-N-Ti/Si-N-O-Ti bond, and improves the adsorption of Cr(VI). Systematic characterization and photocatalytic test documented that abundant adsorption pores, large amount of oxygen vacancies and transport channels jointly accelerate the reduction of Cr(VI) on Si/N-TiO2 nanocrystals surface. Up to 98.7% (30 min for 0.2 g L−1) and 53.2% (120 min for 1.0 g L−1) removal efficiency, importantly, confirmed that the Si/N-TiO2 nanocrystals was competitive for the treatment of highly [Cr(VI)] containing wastewater.

Europium-Doped Ceria Nanowires as Anode for Solid Oxide Fuel Cells

CeO2-based materials have been studied intensively as anodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this work, pristine and europium (Eu)-doped CeO2 nanowires were comprehensively investigated as anode materials for IT-SOFCs, by a combination of theoretical predictions and experimental characterizations. The results demonstrate: (1) Oxygen vacancies can be energetically favorably introduced into the CeO2 lattice by Eu doping; (2) The lattice parameter of the ceria increases linearly with the Eu content when it varies from 0 to 35 mol.%, simultaneously resulting in a significant increase in oxygen vacancies. The concentration of oxygen vacancies reaches its maximum at a ca. 10 mol.% Eu doping level and decreases thereafter; (3) The highest oxygen ion conductivity is achieved at a Eu content of 15 mol.%; while the 10 mol.% Eu-doped CeO2 sample displays the highest catalytic activity for H2-TPR and CO oxidization reactions. The conducting and catalytic properties benefit from the expanded lattice, the large amount of oxygen vacancies, the enhanced reactivity of surface oxygen and the promoted mobility of bulk oxygen ions. These results provide an avenue toward designing and optimizing CeO2 as a promising anode for SOFCs.

PLD-fabricated perovskite oxide nanofilm as efficient electrocatalyst with highly enhanced water oxidation performance

The practical application of perovskite oxides as electrocatalysts for oxygen evolution reaction (OER) has been greatly hindered by their limited catalytically active sites and poor electrical conductivity. Herein, we report the use of a perovskite-oxide nanofilm as highly improved electrocatalyst for OER. A facile fabrication method, pulsed laser deposition (PLD), is employed for the first time to fabricate the SrCo0.85Fe0.1P0.05O3−δ nanofilm on nickel foam (SCFP-NF) with abundant active sites and enhanced electrical conductivity. We find that the SCFP-NF fabricated by PLD exhibits excellent OER activity and durability in alkaline solutions. Especially, the PLD method can create a large amount of oxygen vacancies on the surface of the perovskite nanofilm, leading to a high concentration of highly oxidative oxygen O22−/O−. This O22−/O− species is generally recognized to be active for OER. As a result, the SCFP-NF catalyst with low mass loading (≈30 μg cm-2) demonstrates a remarkable OER activity with a low overpotential of 290 mV and a superb stability up to 200 h at 10 mA cm−2 in alkaline media. The catalytic performance of this perovskite nanofilm is superior to most of the reported metal-oxide-based catalysts and benchmark RuO2. Our findings show that the catalytic performance of oxide-based electrocatalysts can be greatly improved by defect-engineering, and the PLD and other film fabrication methods may help us to realize practical application.

Electrochemical characterization of PrBa2−xSrxCu3O6+δ layered oxides as innovative and efficient oxygen electrode for IT-SOFCs

PrBa2Cu3O6+δ (P) and PrBa1.5Sr0.5Cu3O6+δ (PS) layered perovskite-type oxides are synthesized and characterized as oxygen electrodes in IT-SOFCs. The layered structure of P and PS compounds is constituted by the regular alternation along the crystallographic c axis of PrO planes, Cu2+ chains (CN = 4) and Cu3+ pyramidal (CN = 5) layers. Interesting features of the PrBa2Cu3O6+δ structure are the absence of cobalt, the presence of aliovalent cations and large amounts of oxygen vacancies. The substitution of 25% Ba with Sr is evaluated in order to improve the electronic conductivity of the undoped material. The compounds are synthesized via Citrate-Nitrate procedure and characterized by XRPD, 4-probe conductivity tests (100–800 °C) and EIS measurements on symmetric cells in air varying the temperature (450–850 °C). SEM images of post mortem cells are collected to evaluate the adhesion between components, layers thickness and particle morphology. Sr doping does not significantly improve the electrical conductivity but prompts a considerable hysteresis in the P sample between the cooling and the heating ramps. Conductivity values are lower than 100 S cm−1, but no electrical limitations are observed in EIS results. The introduction of a thin PrDC interlayer greatly reduces the Area Specific Resistances for both the compounds and the 0.15 Ω cm2 target is almost fulfilled at 600 °C (0.17 Ω cm2 for PS + PrDC sample).