Surface Oxygen Vacancy Concentration Research Articles

Enhancing the Performance of 2D Ni-Fe Layered Double Hydroxides by Cabbage-Inspired Carbon Conjunction for Oxygen Evolution Reactions.

Layered double hydroxide (LDH) nanosheets as one type of two-dimensional materials have garnered increasing attention in the field of oxygen evolution reaction (OER) in recent decades. To address the challenges associated with poor conductivity and limited electron and charge transfer capability in LDH materials, we have developed a straightforward one-pot synthesis method to successfully fabricate a composite material with a microstructure resembling cabbage, which encompasses NiFe-LDH and nanocarbon (referred as NiFe-LDH@C). Atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM) revealed that the monolayer NiFe-LDH with a height of ~ 0.5-0.8 nm is uniformly distributed and closely bonded to the carbon support, leading to a significant enhancement in conductivity and facilitating faster electron and charge transfer. Moreover, the NiFe-LDH@C exhibits a substantial number of surface defect sites, which enhances the interaction with oxygen species. This dual enhancement in charge transfer and oxygen species-mediated transfer greatly improves the catalytic OER performance, which is further corroborated by theoretical calculations. Notably, the Ni10Fe6-LDH@C with the highest concentration of surface oxygen vacancies demonstrated superior water oxidation performance, surpassing commercially available RuO2 catalysts; an OER overpotential of 231 mV@10 mA cm-2 with a Tafel slope of 71 mV dec-1 was achieved.

Regulating concentration of surface oxygen vacancies in Bi2MoO6/Bi-MOF for boosting photocatalytic ammonia synthesis

Surface oxygen vacancies (OVs) engineering has been widely adopted as an effective strategy to enhance photocatalytic performance. At present, photocatalytic systems capable of precisely regulating surface OVs concentrations, which could help illuminate the effects of the surface OVs concentration on N2 fixation activity, are still scarce. Herein, bismuth-based metal organic framework (Bi-MOF) was loaded onto the surface of Bi2MoO6 (BMO) as an operable platform, and the OVs concentration in the Bi-MOF component of BMO/Bi-MOF could be regulated by reduction of bismuth ions therein. Experimental results confirm that optimum construction of OVs in the Bi-MOF promotes the photoelectrons transfer from BMO to Bi-MOF, facilitating the activation of N2 at OVs. Consequently, the optimized catalyst shows superior performance in NH3 production, which reaches 125.78 μmol h−1 g−1, 21.4 higher than that of BMO. This work underline the significance of regulating surface OVs concentration, providing inspiration for the development of efficient OVs-modified photocatalysts.

Photocatalytic N-formylation of amines with CO2 over Pt-Bi bimetallic decorated CeO2−x

N-formylation of amines with CO2 is a promising approach to high-efficient utilization of CO2 as C1 feedstock, while conventional thermocatalytic processes suffer from harsh reaction condition and intense energy consumption. In this work, photocatalytic N-formylation of amines with CO2 is achieved at room temperature over Pt-Bi/CeO2−x composite catalyst. The Pt-Bi bimetallic sites increase the concentration of surface oxygen vacancies. Furthermore, the synergistic effects of Pt and Bi improve the light absorption capacity, reduce the band gap energy of the photocatalyst and promote the separation of photoinduced charge carriers. Using PhSiH3 as the reducing agent, the conversion of N-methylaniline reaches 100 % after 3 h irradiation in N, N-dimethylformamide solvent with a N-methylformanilide selectivity of 90.8 %. The composite photocatalyst shows promising cycling stability and universality.

Interfacial carbon quantum dot thin film impacts on morphological and chemical structures of fluorine-doped tin oxide films

Morphology and chemical bonding states, including surface roughness, film density, F-doping, and oxygen vacancy (VO) concentration directly affect the electrical and optical properties of fluorine-doped tin oxide (FTO) films. In this study, morphology and chemical bonding states of FTO films are engineered simultaneously by introducing a carbon quantum dot (CQD) thin film as an interface layer during ultrasonic spray pyrolysis deposition. The abundant oxygen-containing surface functional groups and large surface free energy of the CQD thin film promoted (200) oriented crystal growth and accelerated nucleation of FTO, resulting in smooth and dense FTO film morphology. The abundant carboxyl surface functional groups on the CQDs generate active F− species that are effectively doped into SnO2. Formic acid, formed by dissociation of the carboxyl group, can serve as a strong reducing agent for extracting oxygen atoms from the SnO2 lattice, thereby increasing the VO concentration. The accelerated F-doping and VO concentration result in the generation of additional free electrons. The effects of the optimized CQD on the morphological and chemical structures of FTO films are demonstrated by their superior electrical (sheet resistance of ∼5.7 Ω/□) and optical properties (visible transmittance of ∼85.9 %) compared with bare FTO. Moreover, CQD/FTO used as transparent conducting electrodes in electrochromic (EC) application exhibited improved EC performances, including fast switching speeds (5.3 s and 2.3 s for bleaching and coloration, respectively) and high coloration efficiency (81.1 cm2/C) compared to that of bare FTO.

Photoexcitation assisted oxygen vacancy for enhancing nitrogen fixation with Fe-CeO2

Photoexcitation assisted oxygen vacancy for enhancing N2 fixation was investigated with Fe-CeO2 as photocatalysts. Fe substituted doping of CeO2 promoted the formation of oxygen vacancies (Vo). 5 % Fe-CeO2 exhibited the highest Vo concentration with photocatalytic nitrogen fixation efficiency of 176 μmol·g−1·h−1. The oxygen vacancy could induce the formation of the oxygen vacancy level, which could reduce the band gap energy, attract electrons, and hinder the electron hole recombination. More importantly, the oxygen vacancy level could be used as a springboard to reduce the energy required for N2 activation. In addition, calcination and acid-wash were used to regulate the concentration of surface oxygen vacancies (Vo-s) and bulk oxygen vacancies (Vo-b), respectively. The results showed that acid-wash only reduced the Vo-s concentration, while calcination reduced both the Vo-s and the Vo-b concentration, and the high concentration of Vo and Vo-s was beneficial for photocatalytic nitrogen fixation. The regulation strategy of Vo had guiding significance for improving the photocatalytic performance of metal oxide photocatalysts.

β-Ga2O3 Schottky barrier height improvement using Ar/O2 plasma and HF surface treatments

In this report, we show that Ar/O2 plasma exposure followed by HF treatment improves the Schottky barrier height (SBH) in β-Ga2O3 Schottky barrier diodes (SBDs) by nearly 0.3 eV, resulting in a breakdown voltage (VBR) gain of over 100 V on 2 × 1016 cm−3 doped substrates, without compromising the specific on-resistance. The SBH and VBR enhancement is observed on (2¯01) as well as (001) surfaces. Through extensive surface characterization, the Ar/O2 plasma exposure is shown to amorphize and increase surface oxygen vacancy concentration. HF treatment cleans the surface damage and passivates the surface through fluorine adsorption, leading to Fermi-level de-pinning and SBH improvement. Remarkably, however, the Ar/O2 plasma exposure enhances fluorine adsorption when compared to fluorine treatment alone, resulting in a more substantial improvement in SBH and VBR. Surface clean/treatment plays a critical and fundamental role in determining the quality of the metal/β-Ga2O3 interface. The improved surface treatment process demonstrated in this work can be easily integrated with various field termination methods that can help further improve the β-Ga2O3 SBD performance.

Study on the Catalytic Oxidation of Toluene Using CeO2@S-AZMB Prepared from Spent Zn-Mn Batteries

The recycling and utilization of waste alkaline zinc manganese batteries (S-AZMB) has always been a focus of attention in the fields of environment and energy. However, current research mostly focuses on the recycling of purified materials, while neglecting the direct reuse of waste batteries. Here, we propose a new concept of preparing thermal catalysts by combining unpurified S-AZMB with CeO2 by means of ball milling. A series of characterizations and experiments have confirmed that the combination with S-AZMB not only enhances the thermal catalytic activity of CeO2 but also significantly enhances the concentration of surface oxygen vacancies. In the toluene removal experiment, the temperature (T90) at 90% toluene conversions of CeO2@S-AZMB was 180 °C, lower than the 220 °C for CeO2. More noteworthy is that this S-AZMB-based thermal catalyst can maintain a good structure and thermal catalytic stability in cyclic catalysis.

Phyllantus acidus mediated combustion method synthesised yttria stabilized zirconia, its application as photocatalyst and antibacterial agent

The ceramic material combines different functionalities such as good thermal stability, selective bulk oxygen mobility and high surface oxygen vacancy concentration are the most attracted research to opt for the 8 yttria stabilized zirconia nanomaterial. Nanocomposite 8 yttria stabilized zirconia powder (8YSZ) by bio-mediated combustion synthesis utilizing Phyllanthus acidus fuel. Cubic 8YSZ powder were discovered to be photocatalytic for the deterioration of anionic dyes. The synthesised NP's structural characteristics were assessed with the use of PXRD, UV-Vis, SEM, FTIR and TGA and DTA analyses. Additionally, by monitoring the AO7 coloring change in absorbance under the UV spectroscopy, the photo catalytic action of the 8YSZ on NPs dye has been shown. By tracking the drop in dye concentration relative to the initial dye concentration, the photodegradation of the AO7 organic dye was determined. Investigations have also been conducted on the impacts of operating parameters like pH, catalyst dosage. The present work stated that 8YSZ NP’s have a greater capability for deterioration when exposed to Visible radiation and investigated the antibacterial properties of high-quality ceramic material 8YSZ for use in dentistry.

Dual mechanisms in hydrogen reduction of copper oxide: surface reaction and subsurface oxygen atom transfer.

The study of the reduction of copper oxide (CuO) by hydrogen (H2) is helpful in elucidating the reduction mechanism of oxygen carriers. In this study, the reduction mechanism of CuO by H2 and the process of oxygen atom transfer were investigated through the density functional theory (DFT) method and thermodynamic calculation. DFT calculation results showed that during the reaction between H2 and the surface of CuO, Cu underwent a Cu2+ → Cu1+ → Cu0 transformation, the Cu-O bond (-IpCOHP = 2.41) of the Cu2O phase was more stable than that (-IpCOHP = 1.94) of the CuO phase, and the reduction of Cu2O by H2 was more difficult than the reduction of CuO. As the surface oxygen vacancy concentration increased, it was more likely that the subsurface O atoms transfer to the surface at zero H2 coverage (no H2 molecule on the surface), allowing the surface to maintain a stable Cu2O phase. However, when the H2 coverage was 0.25 monolayer (ML) (one H2 molecule every four surface Cu atoms), the presence of H atoms on the surface made the upward transfer of O atoms from the subsurface more difficult. The rate of consuming surface O atoms in the reduction reaction was greater than the rate of subsurface O atom transfer induced by the reduction reaction and the surface Cu2O phase could not be maintained stably. Through thermodynamic analysis, at high H2 concentration, the reaction between H2 and CuO was more likely to generate Cu, while at low H2 concentration, it was more likely to generate Cu2O. In summary, the valence state of Cu in the reaction process between CuO and H2 depended on the concentration of H2.

Microstructural, electrical and thermal characterization of Dy3+, Sm3+, Er3+, Y3+ and Gd3+ multi-doped cerium dioxide as SOFCs solid electrolytes

The production of electrolytes with high ionic conductivity has been a key challenge in the progressive development of solid oxide fuel cells (SOFCs) for practical applications. Conventional approaches use ionic doping to develop electrolyte materials, such as yttria-stabilized zirconia (YSZ), but challenges remain. The doping systems discovered so far can confirm that co-doping/triple doping can introduce more oxygen vacancies to improve the electrical properties of ceria-based electrolytes compared to unitary doping. Therefore, In this work, we select the optimal dopant based on the criterion of optimal doping in cerium dioxide (effective average ionic radius close to 1.093 Å). And propose a novel multi-doped cerium-based Ce1−x(Dy1/5Sm1/5Er1/5Y1/5Gd1/5)xO2-δ (x = 0.10, 0.15, 0.20, 0.25, 0.30, abbreviated as DSEYG1, DSEYG2, DSEYG3, DSEYG4, DSEYG5) electrolytes to study its microstructure, electrical properties and thermal properties. Dy3+, Sm3+, Er3+, Y3+, and Gd3+ multi-doped electrolyte materials. Over 95% of the relative density values were obtained by sintering DSEYG series samples at 1400 °C. The single-phase cubic fluorite structure, high-density surface microstructure, elemental confirmation, and oxygen vacancy concentration were confirmed using X-ray diffraction, scanning electron microscope, energy dispersive spectrum, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electrical analysis by impedance spectroscopy confirmed the highest value of total ionic conductivity (σ800 °C= 4.04 ×10−2 S/cm) and the lowest value of activation energy (Ea= 0.834 eV) for the DSEYG3 composition. Thermal expansion analysis confirmed the moderate thermal expansion coefficient values for all compositions (TEC =11.12 ×10−6 K−1) in the range of RT-800 °C) and was found to be in good agreement with recently developed materials. The enhanced total ionic conductivity and moderate thermal expansion coefficient of DSEYG3 make it a potential electrolyte material for medium-temperature fuel cells.

Effect of annealing temperature on the formation of oxygen vacancies on the surface of flower-like SnSe/SnO2 heterostructure and visible light catalytic performance

The morphology, structure, and oxygen vacancies in principle determine the light absorption, charge transfer, and separation of photocatalysts, thereby determining their photocatalytic performance. In this study, flower-like SnSe obtained from hydrothermal reactions was oxidized to obtain heterojunctions with SnSe/SnO2. Flower-like SnSe/SnO2 heterojunctions with different concentrations of oxygen vacancies were prepared by annealing them in an argon atmosphere at different temperatures. The flower-like SnSe/SnO2 series with different oxygen vacancies were systematically characterized by TEM, XRD, XPS, PL, and EPR. The research results demonstrate the presence of oxygen vacancies in the flower-like SnSe/SnO2. As the annealing temperature increases, the surface oxygen vacancy concentration shows a trend of first increasing and then decreasing. When the annealing temperature reaches 600 °C, the oxygen vacancy concentration of flower-like SnSe/SnO2 is the highest. Meanwhile, research has shown that surface oxygen vacancies help expand the light absorption range, and the increased valence bandwidth leads to effective charge transfer and separation, thereby promoting visible light photoactivity. SnSe/SnO2-600 °C exhibited excellent visible light photocatalytic activity. The photodegradation of methylene blue (MB) at ≥ 400 nm can reach ∼70% within 120 min. This study verified the route for the introduction of oxygen vacancies via facile calcination and constructed SnSe/SnO2 with surface oxygen vacancies, providing a reference with deep insights for improving photocatalytic activity.

Effectively boosting hydration capacity and oxygen reduction activity of cobalt-free perovskite cathode by K+ doping strategy for protonic ceramic fuel cells

Development of triple-conducting cathode can extend the electrochemically active region to the entire cathode to more effectively promoting oxygen reduction reaction (ORR). Herein, a cobalt-free perovskite Sr1.75K0.25Fe1.5Mo0.5O6−δ (SKFM) was developed as a single-phase triple-conducting cathode material for protonic ceramic fuel cells (PCFCs). Introduction of K into Sr-site leads to a 21.54 % increase in the hydration capacity compared to the undoped Sr2Fe1.5Mo0.5O6−δ (SFM). The bulk diffusion coefficient and surface exchange coefficient of SKFM are 3.8 and 5.2 times higher than those of SFM at 550 °C, respectively. XAS and EPR results demonstrate that the average valence state of Fe and the concentration of surface oxygen vacancies in SKFM are higher than those in SFM. The polarization resistances (Rp) value of SKFM cathode in wet air is 0.06 Ω cm2 at 700 °C, while it is 0.11 Ω cm2 for SFM cathode, which is reduced by 45.5 %, indicating significantly improved ORR activity. The Rp is dominated by the adsorption and diffusion process of oxygen associated with low-frequency part in wet air. The single cell with a configuration of Ni-BZCY4/21-μm-thick BZCY4/SKFM delivers a power output of 1000.8 mW cm−2 in wet H2 at 700 °C and steady operation at 600 °C for a total of 100 h.

Coke formation pathway under various reaction conditions during the production of syngas in a dielectric barrier discharge plasma environment using CeO2 nanorods supported Ni catalysts

Plasma-assisted dry reforming of methane (DRM) was investigated using CeO2 nanorods (NR) supported Ni catalysts in a fixed-bed coaxial dielectric barrier discharge (DBD) reactor. This study individually examined the catalyst support, packing material, and 10 wt% Ni-CeO2 NR catalyst under pure thermal and plasma-assisted thermal DRM environments to explore the plasma-thermal synergy. Support and packing material displayed no discernible reactivity under thermal DRM within 450 °C; however, the catalyst exhibited reactivity beginning around 350 °C. Alternatively, plasma-assisted DRM experiments revealed a distinct reaction occurrence at significantly lower temperatures across all sample types. Introducing plasma demonstrated a significant enhancement in CH4 conversion compared to CO2 conversion. The 10 wt% Ni-CeO2 NR catalyst in plasma-assisted DRM testing showed increasing conversions of CH4 and CO2 with rising temperatures, peaking at 52.1 % and 46.1 %, respectively, at 450 °C. The catalyst’s improved performance in the plasma environment can be attributed to the enhanced metal-support interaction between NiO and the CeO2 NR support, a consequence of the rich surface oxygen vacancy concentration. However, this increase in conversion was accompanied by an escalation in carbon deposition. Considering contributions from the thermal DRM process, the optimal operating temperature was determined as 350 °C. Increasing plasma power at this temperature led to enhanced conversion. However, beyond a threshold of 23.8 W power, the reaction path altered, resulting in reduced syngas output. Increasing the CH4:CO2 feed gas flow ratio, while maintaining constant plasma power and temperature, elevated H2/CO generation. Moreover, increasing the total flow rate under identical conditions, with a constant feed gas flow ratio, reduced both conversions due to decreased chemical residence time. Consequently, under a constant feed gas ratio, a higher syngas yield is achievable with lower overall flow rates.

Modulating internal electric field by oxygen vacancy engineering and consequent forming quantum wells for boosted selective CO2 photoreduction

Although internal electric field of photocatalysts is considered as the potent driving force for efficient charge separation, modulating the internal electric field intensity remains a challenge. Herein, we considered that the internal electric field intensity of Sillén-structured bimetallic oxyhalide PbBiO2Cl could be modulated by tuning surface oxygen vacancy concentration, thereby influencing the corresponding charge transfer. In comparison to bulk PbBiO2Cl and PbBiO2Cl with deficient oxygen vacancies, the PbBiO2Cl with rich oxygen vacancies possessed enhanced internal electric field intensity due to its high oxygen vacancy concentrations, resulting in the primary charge separation spatially. Then the surface oxygen vacancies captured more dissociative electrons as quantum wells to promote the photocatalytic selective CO2-CO conversion. The mechanism was researched and verified by in-situ FTIR and DFT calculations. Using defect engineering to simultaneously modulate internal electric field and form quantum wells for promoting charge separation is an efficient strategy to rationally improve photocatalytic performances.

Efficient hydrogenolysis of lignin over CeO2/AC catalyst prepared by a simple impregnation method

There are limited renewable sources of aromatic chemicals, with lignin being one of the most prominent, accounting for approximately 30% of the planet's organic carbon. Due to its intricate and irregular structure, lignin is recalcitrant to chemical conversion, often resulting in low yields of mixtures of products when it is depolymerized. This study synthesized a CeO2/AC catalyst via an impregnation technique and then explored its ability to depolymerize lignin via an oxidation-reduction strategy. The CeO2/AC catalyst efficiently depolymerized lignin by an oxidation-reduction strategy. At 200 °C, an argon pressure of 1 MPa, and a reaction time of 4 h, the conversion of the lignin model compound reached 98.5%. When using lignin derived from poplar, birch, pine, and cotton stalk, the total yields of phenolic monomers were 36.2 wt.%, 31.2 wt.%, 17.4 wt.%, and 12.1 wt.%, respectively. The CeO2/AC catalyst exhibited a higher surface oxygen vacancy concentration than CeO2, which was crucial for facilitating the hydrogenolysis of lignin.

CeO2 nanorods supported CuOx-RuOx bimetallic catalysts for low temperature CO oxidation

Bimetallic catalysts often outperform monometallic catalysts due to changeable structural orientation, synergistic effects, and integration of two different metal or metal oxide properties. Here, a series of CeO2 nanorods (NR) supported bimetallic CuOx and RuOx catalysts (Cu: Ru ratios of 9:1, 7:3, and 5:5) were prepared using a wet impregnation method. In situ DRIFTS, H2 temperature programmed reduction (H2-TPR), CO temperature programmed desorption (CO-TPD), and other characterization techniques were used to investigate the effect of the Cu:Ru ratio on the activity of low-temperature CO oxidation. Among three catalysts, CeO2 NR supported 7 wt% Cu-3 wt% Ru catalyst after a reduction activation treatment showed the best performance with 100 % CO conversion at 166 °C and the lowest activation energy of 18.37 kJ mol−1. Raman and XPS profiles revealed that the origin of the superior performance is at least partially related to the high surface oxygen vacancy concentration and other distinct oxygen species (physi-/chemi-sorbed oxygen and bulk lattice oxygen), leading to outstanding adsorption and oxidation property of CO.

Studying Surface Chemistry of Mixed Conducting Perovskite Oxide Electrodes with Synchrotron-Based Soft X-rays.

A fundamental understanding of the electrochemical reactions and surface chemistry at the solid-gas interface in situ and operando is critical for electrode materials applied in electrochemical and catalytic applications. Here, the surface reactions and surface composition of a model of mixed ionic and electronic conducting (MIEC) perovskite oxide, (La0.8Sr0.2)0.95Cr0.5Fe0.5O3-δ (LSCrF8255), were investigated in situ using synchrotron-based near-ambient pressure (AP) X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure spectroscopy (NEXAFS). The measurements were conducted with a surface temperature of 500 °C under 1 mbar of dry oxygen and water vapor, to reflect the implementation of the materials for oxygen reduction/evolution and H2O electrolysis in the applications such as solid oxide fuel cell (SOFC) and electrolyzers. Our direct experimental results demonstrate that, rather than the transition metal (TM) cations, the surface lattice oxygen is the significant redox active species under both dry oxygen and water vapor environments. It was proven that the electron holes formed in dry oxygen have a strong oxygen character. Meanwhile, a relatively higher concentration of surface oxygen vacancies was observed on the sample measured in water vapor. We further showed that in water vapor, the adsorption and dissociation of H2O onto the perovskite surface were through forming hydroxyl groups. In addition, the concentration of Sr surface species was found to increase over time in dry oxygen due to Sr surface segregation, with the presence of oxygen holes on the surface serving as an additional driving force. Comparatively, less Sr contents were observed on the sample in water vapor, which could be due to the volatility of Sr(OH)2. A secondary phase was also observed, which exhibited an enrichment in B-site cations, particularly in Fe and relatively in Cr, and a deficiency in A-site cation, notably in La and relatively in Sr. The findings and methodology of this study allow for the quantification of surface defect chemistry and surface composition evolution, providing crucial understanding and design guidelines in the electrocatalytic activity and durability of electrodes for efficient conversions of energy and fuels.

Insights into influence of CeO2 crystal structure effects on hydrothermal hydrogenation for palmitic acid over Ni/CeO2 catalysts

In recent years, upgrading renewable bio–oil to hydrocarbon fuels has received increasing attention. It is crucial to develop a catalyst with high activity, low cost, and high hydrothermal stability for bio–oil upgrading. In this work, the non-noble metal Ni/CeO2 is proved to be a potential catalyst for hydrothermal hydrogenation of palmitic acid (model compound of microalgae based bio–oil). The effect of the crystal structure of the support on the hydrothermal hydrogenation activity of palmitic acid is investigated for the first time. The research results indicate that the catalytic activity of catalysts with different support crystal structures is in the following order: Ni/CeO2–r (nanorods) > Ni/CeO2–c (nanocubes) > Ni/CeO2–p (nanoparticles). The excellent activity of Ni/CeO2–r is attributed to its larger specific surface area, higher defect and oxygen vacancy concentration, and the formation of more Ni0 due to strong metal − support interaction (SMSI). After optimization of conditions at 300 °C, 98.9 % conversion and 92.4 % alkanes yield are obtained over the Ni/CeO2–r. In addition, the coating structure formed by the SMSI provides good hydrothermal stability for the catalyst.

Elucidating the effect of Ce with abundant surface oxygen vacancies on MgAl2O4-supported Ru-based catalysts for ammonia decomposition

Ammonia is a promising COx-free hydrogen (H2) carrier because of its high volumetric H2 density. However, developing highly active/stable ammonia decomposition catalysts for H2 production remains challenging. In this study, the role of ceria (CeO2) as a promoter for Ru-based catalysts was investigated. Ru/Cex/MgAl(y00) catalysts were prepared by the incipient wetness impregnation (IWP) and deposition–precipitation (DP) methods. The surface oxygen vacancy (OV) concentration was controlled by the Ce loading and calcination temperature. By evaluating the surface reaction behavior of the ammonia decomposition catalysts, this study proposes that CeO2 effectively improves the recombination/desorption of N and H atoms. The optimal catalyst Ru/Ce5/MgAl(600) achieved a high H2 formation rate (27.4 mmolH2·gcat−1∙min−1 at 30,000 mL·gcat−1·h−1, 450 °C) and stable performance after exposure at 650 °C for 20 h. This study provides insight into the effect of abundant surface OVs in CeO2 on the physicochemical properties and ammonia decomposition performance of the catalysts.

Exploring the influence of rare earth ions at A-site on the properties of LnBaCo2O5+δ cathode for solid oxide fuel cells

The influence of rare earth ions on layered perovskite (AA'B2O5+δ) is the key to the development of highly active layered perovskite cathode. Herein, we make a systematic explanation through experiment and first-principles calculation. The lattice constant decreases with the decrease of Ln3+ ionic radius, resulting in a smaller space of interstitial oxygen position and increasing oxygen Frenkel energy. The electrochemical activity of LnBaCo2O5+δ (Ln = Pr, Nd and Sm) electrodes decreases with the decrease of Ln3+ ionic radius, which is mainly attributed to a lower oxygen Frenkel energy. Electrochemical impedance spectra tests show that there are significant differences in the surface exchange process of oxygen because of different surface oxygen vacancy concentration for LnBaCo2O5+δ. For Ln = Pr, Nd, and Sm cathodes, the maximum power densities of the anode-supported Ni-YSZ/YSZ/GDC/LnBaCo2O5+δ single cells reach 1.48, 1.36 and 1.06 W/cm2 at 800 °C, respectively, indicating that PrBaCo2O5+δ with the maximum rare earth ion radius exhibits better oxygen reduction reaction. These findings provide guidance for the design and fabrication of highly active layered perovskite electrode materials.