Fast Reduction Kinetics Research Articles

Nano-structuring metal organic frameworks on semiconductor nanowire arrays for highly sensitive and selective chemical sensing

Chemiresistive sensing of gas molecules has been widely investigated for application in medical diagnostics and environmental monitoring, showing high sensitivity and low limits of detection toward various volatile organic compounds. While metal oxide semiconductors offer numerous advantages, such as ease of fabrication, high sensitivity, and fast response times, they often suffer of high insufficient selectivity. Here, we report the engineering of a low-temperature sensing platform consisting of nanostructured zeolitic imidazolate framework (ZIF-8) metal organic frameworks (MOFs) over InP semiconducting nanowire (NW) arrays. These devices were fabricated via top-down etching of InP NW arrays, aerosol deposition of flame-made ZnO nanoparticles, and their chemical vapor conversion to ZIF-8. The presence of ZIF-8 significantly enhances the device sensitivity over that of the pristine InP NW arrays by providing a high density of adsorption sites and faster reduction kinetics. Our optimal sensors can detect NO2 in a large concentration range from 0.1 to 8 ppm, in addition to showing relatively higher responses toward various gas molecules, including CO2, methanol, ethanol, acetone, and propane, in comparison with pristine InP NW sensors. Given the large family of MOFs with controllable pore size and chemical composition, our findings provide a flexible approach for engineering the selectivity of highly sensitive and miniaturized gas sensors for integration in miniaturized devices.

Twin Proliferation and Prolongation under Kinetic Control: Pd-Au Janus Icosahedra versus Pd@Au Core-Shell Starfishes.

Heterogeneous bimetallic nanocrystals featuring explicit spatial configurations and abundant twin defects can simultaneously enable geometric and ligand effects to enhance catalytic and photonic applications. Herein, we report two growth patterns of Au atoms on penta-twinned Pd decahedra, involving twin proliferation to generate asymmetric Pd-Au Janus icosahedra and twin elongation to produce anisotropic Pd@Au core-shell starfishes, respectively. Mechanistic analysis indicates that the injection rate determines the lower-limit number (nlow) of Au(III) ions in the steady state and thus controls the growth pattern. When nlow ≤ 5.5, the kinetic rate is slow enough to initiate asymmetrical one-side growth but fast enough to outpace surface diffusion; Au tetrahedral subunits are successively proliferated along the axial ⟨110⟩ direction of Pd decahedra to form Pd-Au Janus icosahedra. Composed of five Pd and 15 Au tetrahedral subunits, such a heterogeneous icosahedron supports high (2.2 GPa) tensile strain and high strain difference up to +21.9%. In contrast, when nlow > 5.5, the fast reduction kinetics promotes symmetric growth with inadequate surface diffusion. As such, Au atoms are laterally deposited along five high-indexed ⟨211⟩ ridges of Pd decahedra to generate concave Pd@Au core-shell starfishes with tunable sizes (28-40 nm), twin elongation ratios (33.82-162.08%), and lattice expansion ratios (8.82-20.10%).

A 98.2% energy efficiency Li-O2 battery using a LaNi-0.5Co0.5O3 perovskite cathode with extremely fast oxygen reduction and evolution kinetics

Rechargeable lithium-oxygen (Li-O2) batteries have been regarded as a promising energy storage device, but its practical use is impeded by its low energy efficiency. Herein, a bi-functional catalytic perovskite LaNi0.5Co0.5O3 (LNCO) is employed as the cathode of an efficient Li-O2 battery with a molten nitrate salt electrolyte at 160 °C. It displays a stable low charge–discharge overpotential 50 mV with a high energy efficiency (EE) 98.2 % at 0.1 mA cm−2 for over 100 cycles. The excellent performance is attributed to the extremely fast oxygen reduction and evolution kinetics on the surface of LNCO. The discharge product is Li2O with a porous and fluffy morphology which facilitates the transfer of oxygen and other intermediate species. It is noted that Li2O as a discharge product enables a theoretical specific energy density of 5200 Wh kg−1, which is superior to the Li2O2 as product giving 3500 Wh kg−1 for those ambient temperature Li-O2 batteries.

Fast electrochemical reduction behavior and kinetics of nanoflower-like MoS2-modified titanium plate cathode to oxidized mercury

Although mercury is a highly toxic environmental pollutant, it is also an important industrial resource. An attempt was made to use electrochemical method to reduce and collect mercury oxide in wastewater for resource utilization of mercury. In this study, nanoflower-like MoS2 powder and MoS2@Ti electrode were successfully prepared by one-step hydrothermal method. The successful preparation of MoS2@Ti electrodes and their better HER activity than Ti electrodes were confirmed using SEM, EDS and XRD characterisation methods, as well as exploring the reaction mechanism of the electroreduction system in conjunction with other characterisation methods. In the electrochemical system with MoS2@Ti electrode as cathode and IrO2/Ti as anode, the removal efficiency of Hg2+ can reach 92 % under optimal conditions. At the same time, the effects of reaction time, current, initial concentration of Hg2+, stirring rate and voltage on the reduction system were investigated. Compared with pure Ti plate system, the reaction time is shortened by 14 h while the reduction efficiency of Hg2+ is guaranteed, and the energy consumption is reduced. Moreover, by fitting the system kinetics, the reaction system conforms to the secondary kinetics.

The Role of Oxidation during the Synthesis of Silver-Glutathione Monolayer-Protected Clusters.

The synthesis of metal monolayer-protected clusters (MPCs) is still not well understood. It was recently shown that the mechanism of MPC formation involves sequential growth, wherein small MPCs form first and then grow into progressively larger sizes. The sequential growth model does not entirely explain all experimental observations, however. For example, the evolution of MPC product sizes is found to be a non-monotonic function of reaction kinetics, whereas the sequential growth model predicts monotonic behavior. Size evolution of MPCs is studied during synthetic reactions for a wide range of kinetics and it is found that all syntheses began with the sequential growth of MPCs but also found that growth transitioned to degradation if reduction kinetics are fast enough to give way to ambient oxidation. It is identified that MPCs can degrade via oxidation during syntheses and in a manner that is opposite to sequential growth, namely by forming smaller known MPC species from larger MPC species. This sequential degradation process therefore played an important role in determining final MPC products for reactions with fast reduction kinetics. Together, complementary oxidative and reductive processes provide a more complete description of MPC synthesis as well as new tools for controlling metal MPC synthesis.

Metal chalcogenide hollow polar bipyramid prisms as efficient sulfur hosts for Na-S batteries

Sodium sulfur batteries require efficient sulfur hosts that can capture soluble polysulfides and enable fast reduction kinetics. Herein, we design hollow, polar and catalytic bipyramid prisms of cobalt sulfide as efficient sulfur host for sodium sulfur batteries. Cobalt sulfide has interwoven surfaces with wide internal spaces that can accommodate sodium polysulfides and withstand volumetric expansion. Furthermore, results from in/ex-situ characterization techniques and density functional theory calculations support the significance of the polar and catalytic properties of cobalt sulfide as hosts for soluble sodium polysulfides that reduce the shuttle effect and display excellent electrochemical performance. The polar catalytic bipyramid prisms sulfur@cobalt sulfide composite exhibits a high capacity of 755 mAh g−1 in the second discharge and 675 mAh g−1 after 800 charge/discharge cycles, with an ultralow capacity decay rate of 0.0126 % at a high current density of 0.5 C. Additionally, at a high mass loading of 9.1 mg cm−2, sulfur@cobalt sulfide shows high capacity of 545 mAh g−1 at a current density of 0.5 C. This study demonstrates a hollow, polar, and catalytic sulfur host with a unique structure that can capture sodium polysulfides and speed up the reduction reaction of long chain sodium polysulfides to solid small chain polysulfides, which results in excellent electrochemical performance for sodium-sulfur batteries.

Support induced influence on the reactivity and selectivity of nitrate reduction by Sn-Pd bimetallic catalysts

In this study, two different materials i.e., naturally occurring kaolinite (Al-Si containing structured clay) and industrially produced red mud (mixture of metal oxides) were used as support surfaces for Sn-Pd bimetallic catalysts to investigate the effects of support on catalytic nitrate (NO3−) reduction. Under the same experimental conditions, the Sn-Pd-kaolinite reduced NO3− at a higher rate (k = 15.46 × 10−2 min−1) and lower N2 (70 %) selectivity compared to that of Sn-Pd-red mud, which exhibited slower reduction kinetics (k = 9.16 × 10−2 min−1) but higher N2 selectivity (85 %). We found that support material with a relatively low surface area (i.e., red mud) provided optimal Sn-Pd proximity at relatively low Sn:Pd ratios, but suffered from metallic overlap at high Sn:Pd ratios. Temperature program reduction (TPR) analysis showed that the kaolinite interaction with the Sn-Pd ensembles maintained a higher H2 activation capacity, which resulted in fast reduction kinetics but low N2 selectivity. However, the red mud support exhibited a strong alloying effect toward the Sn-Pd ensembles and regulated the H2 capacity of the Pd to suppress the reduction kinetics and NH4+ selectivity. The NO3− removal and byproduct selectivity was sustainable over a wide range of CO2:H2 ratios. Sn-Pd-red mud showed a 100 % NO3− removal and ∼85 % N2 selectivity at CO2:H2 ≥ 0.6, while complete NO3− removal was obtained by Sn-Pd-kaolinite at CO2:H2 ≥ 1. A groundwater NO3− removal experiment showed that the reactivity of the Sn-Pd-red mud was stable toward fouling by impurities.

A Quantitative Analysis of the Reduction Kinetics Involved in the Synthesis of Au@Pd Concave Nanocubes.

Surface capping has been shown to play a pivotal role in controlling the evolution of metal nanocrystals into different shapes or morphologies. With the synthesis of Au@Pd concave nanocubes as an example, here we demonstrate that the capping agent can also impact the reduction kinetics of a precursor, and thereby its reduction pathway, for the formation of metal nanocrystals with distinct morphologies. A typical synthesis involves the reduction of a PdII precursor by ascorbic acid at room temperature in the presence of Au nanospheres as seeds, together with the use of hexadecyltrimethylammonium chloride (CTAC) or hexadecyltrimethylammonium bromide (CTAB) as the capping agent. In the case of CTAC, the PdII precursor prevails as PdCl4 2- , leading to the formation of Au@Pd concave nanocubes with a rough surface because of the fast reduction kinetics and thus the dominance of solution reduction pathway. When switched to CTAB, the PdII precursor changes to PdBr4 2- that features slow reduction kinetics and surface reduction pathway. Accordingly, the Au@Pd concave nanocubes take a smooth surface. This work demonstrates that both reduction kinetics and surface capping play important roles in controlling the morphology of metal nanocrystals and these two roles are often coupled to each other.

Stability of Sn-Pd-Kaolinite catalyst during heat treatment and nitrate reduction in continuous flow reaction.

In this study, a novel and highly reactive Sn-Pd catalyst supported by environmentally benign kaolinite (Sn-Pd-kaolinite) was developed and evaluated for stability for effective nitrate (NO3-) reduction in batch and continuous mode. Complete NO3- removal with fast reduction kinetics (k = 18.16 × 10-2 min-1) and 71% selectivity toward N2 were achieved by the Sn-Pd-kaolinite catalyst during batch reactions. During continuous tests, 100% NO3- removal and 80% N2 was achieved for 60 h. However, NO3- removal efficiency gradually decreased to 80% in170 h. The catalyst was then successfully regenerated in the system by increasing H2 flow which achieved a complete NO3- removal again. The metal leaching from catalyst surface was negligible (Sn 0.01% and Pd 0.006%) and the structure was stable during the continuous test, confirming that the Sn-Pd-Kaolinite catalyst had a superior reaction kinetics and operational durability.

Progress of polymer chain structure regulation of alkaline anion-exchange membranes for fuel cells

Alkaline anion-exchange membrane fuel cells (AAEMFCs) have attracted worldwide interest due to their advantages including fast oxygen reduction kinetics, high compatibility with non-precious-metal catalyst and low cost. As one of the key components in AAEMFCs, the performance of alkaline anion exchange membranes (AAEMs) directly affects the power output and durability of the fuel cells. During fuel cell operating, AAEMs require high ionic conductivity, excellent dimensional and chemical stability to ensure high efficiency and outstanding durability. However, it is still difficult for any type of the AAEMs to meet all these requirements. This monograph summarizes recent development around the world for AAEMs, especially for the trade-off effect between ionic conductivity and stability of AAEMs as well as the proposed strategies for this issue. The charge carrier in AAEMs is OH-, and it has a lower transporting efficiency owing to its lower mobility, higher dependence on water molecular and the blocking of many hydrophobic domains in AAEMs. The improvement of ion-exchange capacity (IEC) by increasing the grafting degree (GD) of cationic functional groups can, to some extent, solve this issue. however, a high GD always bring the following negative issues: (1) Excessive swelling of AAEMs and significant reducing in the dimensional stability of membranes; (2) the increase of OH- concentration accelerates the kinetics of nucleophilic substitution and Hofmann elimination, leading to the degradation of cationic groups; (3) the enhanced polarization of the cationic groups and the hydrophilicity of the main chain enable the polymer backbone susceptible to nucleophilic attack by OH-, resulting in the degradation of the membrane, and even short-circuit of the fuel cells. In order to solve these issues, various of polymer chain architectures have been designed and regulated. To balance the ionic conductivity and the dimensional stability in AAEMs, double, triple and multi-cations are grafted on one site of polymer backbone to achieve a sufficiently high IEC at relatively low GD. Another realistic strategy is constructing 3D anion channels by the segregated hydrophilic/hydrophobic phase. The alkali stability of the cationic groups is affected by many factors including field effects, steric effects and conformation of substituent groups, and so on. The improvement of chemical stability of AAEMs has been another formidable scientific challenge. Researchers reduce the kinetics of the nucleophilic substitution and elimination reactions, and improve the basic stability of the cationic groups by modulating the structure of substituent groups such as the introduction of electron-donating groups, increased steric hindrance, and adequate hydration of OH-. Among various cationic groups, the piperidinium-based cations show high resistance against both nucleophilic substitution and elimination in alkaline conditions and at elevated temperature. Furthermore, the polymer backbones without ether band and electron-withdrawing groups have been synthesized and exabit highly resistant to alkali hydrolysis. Recently, new strategy for constructing ordered ion channels in AAEMs by novel porous materials such as metal-organic frameworks (MOF), Trogers base, and macrocyclic crown ether compounds, provide for efficient ionic transport. Additionally, highly stable metal complexes have been used as cationic group in AAEMs. These new trends will open up an exciting opportunity to design high-performance AAEMs. The appearance of highly stable AAEMs enables the AAEMFCs to be operated at 80°C, and the cell works stably in a period of study over 100 h. Although this progress is encouraging, there still remains work for improving the cell performance and stability. A 1000 h of stable operation at elevated temperatures will be the next mission for AAEMFCs. In addition, there are some fundamental issues necessary to explore, such as the transport mechanism of OH- in the membrane, the molecular interaction of polyelectrolytes and their self-assembly mechanism in solution and film formation, the mechanism of the influence of morphology on the chemical stability of AAEMs, and the factors affecting the long-term stability of AAEMFCs. These scientific issues will be the focus of future research. The development of AAEMFCs is on its way, and it calls for more efforts in fundamental study, polymer chain architectures and morphology designing, and fuel cell engineering to make it viable.

Complete Ca/Cu cycle for H2 production via CH4 sorption enhanced reforming in a Lab-Scale fixed bed reactor

The three main reaction stages of a H2 production process based on the combination of the CaO/CaCO3 and Cu/CuO loops have been experimentally studied in a lab scale fixed bed reactor. The solid bed contained the three functional materials required to run the process, namely a commercial Ni-based catalyst, a CaO-Ca12Al14O33 CO2 sorbent and a CuO-Al2O3 material in a proportion that resulted in a bed with 43.3% wt. CuO, 25.6% wt. CaO and 1.7% wt. Ni. The system was able to convert 13.5 kg CH4 h−1 kg Ni−1, at 675 °C producing a gas stream with a 93.5% vol. H2 at 10 bar. The Cu-based material presented high oxidation kinetics, being totally converted in a narrow reaction front with a highly diluted air stream at 10 bar. The Cu-based material presented also fast reduction kinetics and it was completely converted with a fuel gas with typical composition of a Steam Methane Reforming stage at high temperature. A Cu/Ca molar ratio of 2 allowed for calcination efficiencies over 85% molar basis at the CO and H2 break-through, and 95% of the CO2 from CaCO3 exited the reactor at CH4 break-through. The experimental results have been validated with an existing pseudo homogeneous reactor model that had been developed in previous works for the three reaction stages. The model was able to predict product gas compositions, bed breakthrough, and temperature profiles along bed.

Controlling Reduction Kinetics in the Galvanic Replacement Involving Metal Oxides Templates: Elucidating the Formation of Bimetallic Bowls, Rattles, and Dendrites from Cu2O Spheres

AbstractThis study demonstrates that the precursor reduction kinetics can be employed to control the morphology and composition of bimetallic metal/metal oxides systems obtained by galvanic replacement reaction using metal oxides as sacrificial templates. This work investigated Cu2O as a proof‐of‐concept example, in which the relative rates of Cu2O oxidation by O2 and by noble metal precursors determined the morphology and composition of the products. We focused on three metal precursors with fast, medium, and slow reduction kinetics in the presence of Cu2O under aerobic conditions: , , and Ru3+, respectively. It was found that metal‐oxide‐based bowls, rattles, or dendrites can be obtained by simply changing the precursor reduction kinetics. These results provide novel insights over the versatility and mechanistic understanding of galvanic replacement to the synthesis of metal/metal‐oxide bimetallic nanoparticles.

Termination of nanoscale zero-valent iron reactivity by addition of bromate as a reducing reactivity competitor

Remediation of contaminated groundwater by nanoscale zero-valent iron (nZVI) is widely becoming a leading environmentally friendly solution throughout the globe. Since a wide range of various nZVI-containing materials have been developed for effective remediation, it is necessary to determine an appropriate way to terminate the reactivity of any nZVI-containing material for a practical experimental procedure. In this study, bimetallic Ni/Fe-NPs were prepared to enhance overall reduction kinetics owing to the catalytic reactivity of nickel on the surface of nZVI. We have tested several chemical strategies in order to terminate nZVI reactivity without altering the concentration of volatile compounds in the solution. The strategies include surface passivation in alkaline conditions by addition of carbonate, and consumption of nZVI by a reaction competitor. Four halogenated chemicals, trichloroethylene, 1,1,1-trichloroethane, atrazine, and 4-chlorophenol, were selected and tested as model groundwater contaminants. Addition of carbonate to passivate the nZVI surface was not effective for trichloroethylene. Nitrate and then bromate were applied to competitively consume nZVI by their faster reduction kinetics. Bromate proved to be more effective than nitrate, subsequently terminating nZVI reactivity for all four of the tested halogenated compounds. Furthermore, the suggested termination method using bromate was successfully applied to obtain trichloroethylene reduction kinetics. Herein, we report the simple and effective method to terminate the reactivity of nZVI by addition of a reducing reactivity competitor.

Controlling the Deposition of Pd on Au Nanocages: Outer Surface Only versus Both Outer and Inner Surfaces.

When a metal precursor is reduced in the presence of Au nanocages with a hollow interior and porous walls, in principle the resultant metal atoms can be deposited onto both the outer and inner surfaces or just the outer surface. Here we demonstrate that these two different scenarios of metal deposition can be deterministically achieved by controlling the reduction kinetics of the precursor. Specifically, if PdCl42- is employed as the precursor, its fast reduction kinetics favors the solution reduction pathway, in which the resultant Pd atoms are deposited only onto the outer surface for the generation of Au@Pd double-shelled nanocages. When the precursor is switched to PdBr42- to slow down the reduction, the precursor can readily diffuse into the interior of the Au nanocages prior to its reduction to elemental Pd. As such, both the outer and inner surfaces of the nanocages become coated with Pd for the generation of Pd@Au@Pd triple-shelled nanocages. This study not only offers a new synthetic approach to metal nanocages with diverse compositions and structures but also demonstrates the necessity of controlling the relative rates of reduction and bulk diffusion of a metal precursor when nanostructures with a hollow interior and porous walls are used for seed-mediated growth.

Rational one-step synthesis of porous PtPdRu nanodendrites for ethanol oxidation reaction with a superior tolerance for CO-poisoning.

Precise fabrication of porous ternary Pt-based nanodendrites is very important for electrochemical energy conversion owing to high surface area and great molecular accessibility of these nanodendrites. Herein, PtPdRu porous nanodendrites (PNDs) were prepared via a facile one-step ultrasonic irradiation approach at room temperature. Intriguingly, the ultrasonic irradiation drove the formation of PtPdRu PNDs with spatially interconnected porous structures, whereas magnetic stirring produced PtPdRu nanoflowers (NFs) with less porosity. The formation mechanism was ascribed to the acoustic cavitation effect and fast-reduction kinetics under sonication. The as-made PtPdRu PNDs displayed a superior catalytic performance towards ethanol oxidation reaction with a high tolerance for CO-poisoning as compared to PtPdRu NFs, PtPd NDs, and commercial Pt/C catalyst.

Effects of the Incorporation of Sc2O3 into CeO2–ZrO2 Solid Solution: Structural Characterization and in Situ XANES/TPR Study under H2 Atmosphere

Nanostructured CeO2-rich samples cosubstituted with ZrO2 and Sc2O3 are studied. The effects of the combined additions of both oxides on structural, morphological, and, especially, redox properties of the substituted lattice are assessed. In situ near edge X-ray absorption (XANES) experiments with synchrotron light were performed to study oxygen exchange capacity in a reducing environment for these ternary oxides. Structural characterization revealed that up to 8 at. % Sc was successfully incorporated into the CeO2–ZrO2 lattice without phase segregation. Increased scandia solubility was achieved through a soft chemical route synthesis involving citrate complexation which gave rise to porous powders with crystallite sizes in the nanometer range. In situ XANES experiments in 5 mol % H2/He atmosphere demonstrated that adding Sc3+ to the CeO2–ZrO2 mixed oxide leads to a ternary system (Ce0.9ScxZr0.1–xO2−δ) with faster reduction kinetics and enhanced reducibility in the whole temperature range analyzed (25–800 °C) compared to both binary materials: Ce0.9Zr0.1O2 and Ce0.9Sc0.1O1.95.

Enhanced photocatalytic reduction of concentrated bromate in the presence of alcohols

Membrane separation of bromate can continuously treat bromate-containing water; however concentrated bromate solutions would be an inevitable waste which requires proper treatments before discharge. In addition to hydrogenation of bromate using transitional metallic catalysts and hydrogen gas, chemical reduction of bromate can be also achieved by photo-catalysis. While chemically-doped photocatalysts are extensively studied to improve photocatalytic reduction of bromate, another strategy for enhancing photocatalytic efficiency of bromate reduction by adding hole-scavengers (e.g., alcohols) has not been investigated. Thus, in this study, we aim to evaluate photocatalytic reduction of bromate in the presence of alcohols. As TiO2+UV was selected as a model photocatalytical process, TiO2+UV+alcohol exhibited remarkably higher reduction efficiency and faster reduction kinetics than TiO2+UV, possibly owing to suppressed recombination of electron-hole pair as alcohols act sacrificial reagents. A higher fraction of methanol (MeOH) also increased the reduction kinetics. The elevated temperature improved the reduction kinetics, whereas lowering pH of bromate solution substantially accelerated bromate reduction. TiO2+UV+MeOH remained effective to reduce bromate in the presence of other anions; it exhibited a significantly high selectivity toward the bromate reduction over the nitrate reduction. TiO2+UV+MeOH can be re-used for multiple cycles without loss of conversion efficiency even though no MeOH was refilled and bromide was accumulated within the reactor. These features reveal that TiO2+UV+MeOH is a highly effective and promising approach to treat concentrated bromate in water.

(Invited) Dissimilar Interfaces As a Driver to Oxygen Reduction on Perovskite Oxide Surfaces

Interfaces between dissimilar oxides are attracting significant interest for their potential role in accelerating charge transport and surface reaction kinetics. If well understood and controlled, they can provide a new way to enable high-performance solid-oxide fuel cells, separation membranes as well as fast switching memristors. For example, recent studies have demonstrated that cobaltite hetero-interfaces exhibit orders of magnitude faster oxygen reduction kinetics compared with either single phase. The interfacial strain fields, anisotropy, electronic and chemical interactions between the two phases are the likely mediators behind such an unprecedented enhancement. The underlying mechanisms must be understood quantitatively, so that we can go beyond isolated and empirically found interface structures to rationally designing dissimilar oxide interfaces with superior properties. Towards this goal, we have investigated the local electronic structure at nanometer resolution in model multilayer superlattices and vertical nanostructures that are made of dissimilar cobaltites. To accomplish this, we used a novel combination of in-situ scanning tunneling spectroscopy and focused ion beam milling. We found that the wide band-gap cobaltite is electronically activated at elevated temperatures through an interfacial coupling with a reducible cobaltite. Such electronic activation is expected to facilitate charge transfer to oxygen, and accelerate the reduction kinetics at the surface. Furthermore, based on our computational and experimental work, we have put forth elastic strain to be an important driver of the kinetics of surface reactions and diffusion in functional oxides, and demonstrated these concepts on fluorite, perovskite and Ruddlesden Popper structures. There remains still a large amount of open questions on how dissimilar oxide interfaces impact oxygen diffusion and oxygen exchange on the surfaces. However, these recent results are encouraging for an improved understanding of oxide hetero-interfaces at elevated temperatures and could enable new interfaces with fast oxygen transport and oxygen reduction kinetics.

One-pot synthesis of noble metal nanoparticles with a core–shell construction

Noble metal nanoparticles with a core-shell construction not only have great potential in diverse applications, but also can serve as starting templates for the fabrication of noble metal nanomaterials with controllable structures. Herein, we present a one-pot route with remarkable simplicity and universality for the synthesis of noble metal nanoparticles with a core-shell construction. This strategy rationally makes use of the difference in reduction kinetics of various noble metal precursors in oleylamine, whereby one metal precursor with fast reduction kinetics is reduced first to form seed particles for the subsequent nucleation and growth of other metals, resulting in an overall one-step formation of core-shell structured noble metal nanoparticles with single or multiple shells. Core-shell noble metal nanoparticles with Ag or Au residing in the core regions or core-shell-shell noble metal nanoparticles with Au and Ag residing in the core and inner shell regions are prepared in this way. This facile one-pot approach may provide a promising method with ease of control for creating heterogeneously structured nanomaterials.

Electrochemical properties of B-site Ni doped layered perovskite cathodes for IT-SOFCs

Offering fast oxygen reduction kinetics and high electrical conductivities relative to those of ABO3-type perovskite oxides, layered perovskite cathode materials have received considerable attention for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this study, we have investigated the effects of Ni substitution for the Co site in SmBa0.5Sr0.5Co2O5+δ in terms of structural characteristics, electrical properties, and electrochemical performance of SmBa0.5Sr0.5Co2−xNixO5+δ (x = 0, 0.1, and 0.2) in relation to its application as an IT-SOFC cathode material. At the given temperature, the electrical conductivities of SmBa0.5Sr0.5Co2−xNixO5+δ (x = 0, 0.1, and 0.2) decrease with increasing Ni content. For x = 0.1, the lowest ASR value, 0.125 Ω cm2, and the highest single cell performance, 1.78 W cm−2 at 600 °C, are obtained.