Influence of Crystal Structure on the Electrochemical Performance of A-Site-Deficient Sr 1-xNb 0.1 Co 0.9 O 3-δ Perovskite Cathodes

The creation of A-site cation defects within a perovskite oxide can substantially alter the structure and properties of its stoichiometric analogue. In this work, we demonstrate that by vacating 2 and 5% of A-site cations from SrNb0.1Co0.9O3−δ (SNC1.00) perovskites (Sr1−sNb0.1Co0.9O3−δ, s = 0.02 and 0.05; denoted as SNC0.98 and SNC0.95, respectively), a Jahn–Teller (JT) distortion with varying extents takes place, leading to the formation of a modified crystal lattice within a the perovskite framework. Electrical conductivity, electrochemical performance, chemical compatibility and microstructure of Sr1−sNb0.1Co0.9O3−δ as cathodes for solid oxide fuel cells were evaluated. Among SNC1.00, SNC0.98 and SNC0.95, SNC0.95 (P4/mmm symmetry (#123)) which exhibits a large JT distortion in conjunction with charge-ordering of cobalt (Co) shows the best oxygen reduction reaction (ORR) activity at low temperature while SNC0.98 (P4mm symmetry (#99)), which displays a local JT distortion, shows the poorest performance

Influence of Crystal Structure on the Electrochemical Performance of A-Site-Deficient Sr\u3csub\u3e1-s\u3c/sub\u3eNb\u3csub\u3e0.1\u3c/sub\u3eCo\u3csub\u3e0.9\u3c/sub\u3eO\u3csub\u3e3-δ\u3c/sub\u3e Perovskite Cathodes

The creation of A-site cation defects within a perovskite oxide can substantially alter the structure and properties of its stoichiometric analogue. In this work, we demonstrate that by vacating 2 and 5% of Asite cations from SrNb0.1Co0.9O3-δ (SNC1.00) perovskites (Sr1-sNb0.1Co0.9O3-δ,s = 0.02 and 0.05; denoted as SNC0.98 and SNC0.95, respectively), a Jahn–Teller (JT) distortion with varying extents takes place, leading to the formation of a modified crystal lattice within a the perovskite framework. Electrical conductivity, electrochemical performance, chemical compatibility and microstructure of Sr1-sNb0.1Co0.9O3-δ as cathodes for solid oxide fuel cells were evaluated. Among SNC1.00, SNC0.98 and SNC0.95, SNC0.95 (P4/mmm symmetry (#123)) which exhibits a large JT distortion in conjunction with charge-ordering of cobalt (Co) shows the best oxygen reduction reaction (ORR) activity at low temperature while SNC0.98 (P4mm symmetry (#99)), which displays a local JT distortion, shows the poorest performance

Boosting oxygen evolution reaction by activation of lattice‐oxygen sites in layered Ruddlesden‐Popper oxide

Emerging anionic redox chemistry presents new opportunities for enhancing oxygen evolution reaction (OER) activity considering that lattice-oxygen oxidation mechanism (LOM) could bypass thermodynamic limitation of conventional metal-ion participation mechanism. Thus, finding an effective method to activate lattice-oxygen in metal oxides is highly attractive for designing efficient OER electrocatalysts. Here, we discover that the lattice-oxygen sites in Ruddlesden-Popper (RP) crystal structure can be activated, leading to a new class of extremely active OER catalyst. As a proof-of-concept, the RP Sr3(Co0.8Fe0.1Nb0.1)2O7-δ (RP-SCFN) oxide exhibits outstanding OER activity (eg, 334 mV at 10 mA cm−2 in 0.1 M KOH), which is significantly higher than that of the simple SrCo0.8Fe0.1Nb0.1O3-δ perovskite and benchmark RuO2. Combined density functional theory and X-ray absorption spectroscopy studies demonstrate that RP-SCFN follows the LOM under OER condition, and the activated lattice oxygen sites triggered by high covalency of metal-oxygen bonds are the origin of the high catalytic activity.This work was financially supported by the Australian Research Council (Discovery Early Career Researcher Award No. DE190100005)

Ex Situ Reconstruction-Shaped Ir/CoO/Perovskite Heterojunction for Boosted Water Oxidation Reaction

The oxygen evolution reaction (OER) is the performance-limiting step in the process of water splitting. In situ electrochemical conditioning could induce surface reconstruction of various OER electrocatalysts, forming reactive sites dynamically but at the expense of fast cation leaching. Therefore, achieving simultaneous improvement in catalytic activity and stability remains a significant challenge. Herein, we used a scalable cation deficiency-driven exsolution approach to ex situ reconstruct a homogeneous-doped cobaltate precursor into an Ir/CoO/perovskite heterojunction (SCI-350), which served as an active and stable OER electrode. The SCI-350 catalyst exhibited a low overpotential of 240 mV at 10 mA cm-2 in 1 M KOH and superior durability in practical electrolysis for over 150 h. The outstanding activity is preliminarily attributed to the exponentially enlarged electrochemical surface area for charge accumulation, increasing from 3.3 to 175.5 mF cm-2. Moreover, density functional theory calculations combined with advanced spectroscopy and 18O isotope-labeling experiments evidenced the tripled oxygen exchange kinetics, strengthened metal-oxygen hybridization, and engaged lattice oxygen oxidation for O-O coupling on SCI-350. This work presents a promising and feasible strategy for constructing highly active oxide OER electrocatalysts without sacrificing durability

Realizing ultrafast oxygen evolution by introducing proton acceptor into perovskites

The oxygen evolution reaction (OER) is of prime importance in multiple energy storage devices. Perovskite oxides involving lattice-oxygen oxidation are generally regarded as highly active OER catalysts, but the deprotonation of surface-bound intermediates limit the further activity improvement. Here, it is shown that this kinetic limitation can be removed by introducing Sr3B2O6 (SB) which activates a proton-acceptor functionality to boost OER activity. As a proof-of-concept example, an experimental validation is conducted on the extraordinary OER performance of a Sr(Co0.8Fe0.2)(0.7)B0.3O3-delta (SCFB-0.3) hybrid catalyst, made using Sr0.8Co0.8Fe0.2O3-delta as active component and SB as a proton acceptor. This smart hybrid exhibits an exceptionally ultrahigh OER activity with an extremely low overpotential of 340 mV in 0.1 m KOH and 240 mV in 1 m KOH required for 10 mA cm(-2) which is the top-level catalytic activity among metal oxides reported so far, while maintaining excellent durability. The correlation of pH and activity study reveals that this enhanced activity mainly originates from the improved interfacial proton transfer. Such a strategy further demonstrated to be universal, which can be applied to enhance the OER activity of other high covalent oxides with close O 2p-band centers relative to Fermi energy

Toward reducing the operation temperature of solid oxide fuel cells: our past 15 years of efforts in cathode development

The development of clean and efficient energy conversion and storage systems is becoming increasingly vital as a result of accelerated global energy consumption. Solid oxide fuel cells (SOFCs) as one key class of fuel cells have attracted much attention, owing to their high energy conversion efficiency and low emissions. However, some serious problems appeared because of the scorching operating temperatures of SOFCs (800–1000 °C), such as poor thermomechanical stability and difficult sealing, resulting in a short lifespan and high cost of SOFCs. Therefore, lowering the operating temperature of SOFCs to mid-range and even low range has become one of the main goals for SOFC development in the recent years. Looking for new cathode materials with high electrocatalytic activity and robust stability at relatively low temperatures is one of the essential requirements for intermediate-to-low-temperature SOFCs (ILT-SOFCs). During the past 15 years, we put considerable efforts into the development of alternative cathode materials for ILT-SOFCs. In this review, we give a summary of our progress from such efforts. We first summarize several strategies that have been adopted for developing cathode materials with high activity and durability toward reducing operating temperatures of SOFCs. Then, our new ideas and progress on cathode development with respect to activity and stability are provided. Both the cathodes of oxygen-ion-conducting SOFCs and protonic-conducting SOFCs are discussed. In the end, we outline the opportunities, challenges, and future approaches for the development of cathodes for ILT-SOFCs

Na_0.86Co_0.95Fe_0.05O₂ Layered Oxide As Highly Efficient Water Oxidation Electrocatalyst in Alkaline Media

Electrochemical energy storage and conversion technologies, such as water-splitting devices, rechargeable metal-air batteries, and regenerative fuel cells, are promising alternatives to traditional nonrenewable energy systems. Given the sluggish oxygen evolution reaction (OER) in the above renewable-energy technologies, the development of efficient OER electrocatalysts with high performance is of great importance. Here, we demonstrate a layer-structured oxide Na_0.86Co_0.95Fe_0.05O₂ (NCF0.05) as a novel electrocatalyst for efficient water oxidation in alkaline media. NCF0.05 shows enhanced performance, including lower overpotential, lower Tafel slope and better stability than the parent Na_0.86CoO₂ (NC). Especially, the OER performance of NCF0.05 is comparable to the state-of-the-art IrO₂ catalyst. This enhanced catalytic activity of NCF0.05 may be ascribed to the unusual synergistic interplay between Fe and Co. A possible dual-metal-site mechanism was also proposed for OER on NCF0.05

Chlorine-anion doping induced multi-factor optimization in perovskties for boosting intrinsic oxygen evolution

The oxygen evolution reaction (OER) plays a crucial role in many electrochemical energy technologies, and creating multiple beneficial factors for OER catalysis is desirable for achieving high catalytic efficiency. Here, we highlight a new halogen-chlorine (Cl)-anion doping strategy to boost the OER activity of perovskite oxides. As a proof-of-concept, proper Cl doping at the oxygen site of LaFeO3 (LFO) perovskite can induce multiple favorable characteristics for catalyzing the OER, including rich oxygen vacancies, increased electrical conductivity and enhanced Fe-O covalency. Benefiting from these factors, the LaFeO2.9-δCl0.1 (LFOCl) perovskite displays significant intrinsic activity enhancement by a factor of around three relative to its parent LFO. This work uncovers the effect of Cl-anion doping in perovskites on promoting OER performance and paves a new way to design highly efficient electrocatalysts.</p

Distribution Characteristics and Main Control Measures of Spartina alterniflora in Mainland China

The rapid invasion and spread of Spartina alterniflora will cause great damage to the ecological environment of the invasive areas. Spartina alterniflora is widely distributed in coastal areas from north to south of China, which seriously reduces the biodiversity and ecological barrier function of the coastal zone. The main control methods of Spartina alterniflora invasion in China include physical, chemical and biological control. At present, the single control methods, such as mowing, crushing and burying, and cofferdam flooding, can effectively control the invasion of Spartina alterniflora in small areas, but the control effect of large areas or patches is not good. Based on the analysis and comparison of the existing control methods, combined with the practical experience of scientific research, this paper put forward a comprehensive control method of Spartina alterniflora suitable for different areas of China, which combined the physical control method, chemical control method and biological control method

Development of Novel PET Ligands for Imaging Orexin 2 Receptor

Purpose/Background:The orexin 2 receptor (OX2R) is a G-protein coupled receptor expressed in brain that binds orexin neuropeptides A and B. OX2R is involved in motivation, feeding behaviour, and sleep-wake regulation. Modulation of OX2R with agonists has been found to be a potential treatment towards sleep related disorders. Herein we report [11C]1 and [11C]2 as novel and potential PET ligands for imaging orexin 2 receptor and explore their applications in small animals.Methods:Compounds 1 and 2 were prepared according to a published patent.1 The phenolic precursors were synthesized via demethylation of compounds 1 and 2. The radiosynthesis of [11C]1 and [11C]2 were performed by 11C-methylation of phenolic precursors with [11C]CH3I and Cs2CO3 as the base in DMF at 80 oC for 5 min. The in vitro autoradiography was performed with [11C]1 and [11C]2 on Sprague Dawley rat brain slices. Dynamic PET imaging studies with [11C]1 and [11C]2 were carried out on Sprague Dawley rats with 60 min scans.Results:Compounds 1 (OX2: IC50 = 4 nM, OX1: IC50 > 4000 nM) and 2 (OX2: IC50 = 4 nM, OX1: IC50 > 5000 nM) are selective antagonists at the OX2.1 Compounds 1 and 2 were prepared in 2% and 20% overall yields over four steps, respectively. The phenolic precursors were synthesized via demethylation of compounds 1 and 2 in 41% and 45% yields, respectively. The radiosynthesis of PET ligands [11C]1 and [11C]2 were via 11C-methylation of phenolic precursors with [11C]CH3I and both [11C]1 and [11C]2 were obtained in more than 10% radiochemical yields (decay corrected). Both [11C]1 and [11C]2 had radiochemical purities greater than 99%, and no obvious decompositions of [11C]1 and [11C]2 were found in saline in 90 min. In in vitro autoradiography studies with [11C]1 and [11C]2, high radioactivity accumulation was observed in the hippocampus and cortex. In blocking studies of autoradiography, EMPA (10 μM) rendered diminished radioactivity in OX2R-rich brain regions. In dynamic PET imaging studies with [11C]1, the standard uptake value (SUV) of [11C]1 in hippocampus and cerebellum reached the max value of 0.2 at 2 min and washed out rapidly, and finally reduced to 0.1 at 60 min. PET imaging with [11C]2 showed a similar result. In blocking studies of PET imaging, no significant difference in uptake in the hippocampus and cerebellum was observed for both [11C]1 and [11C]2. Pretreatment with elacridar (3 mg/kg) led to a significant increase of uptake in hippocampus and cerebellum for both [11C]1 and [11C]2.Conclusion:We have developed two novel PET ligand [11C]1 and [11C]2 for imaging OX2R. The PET ligands [11C]1 and [11C]2 were both prepared in more than 10% radiochemical yield (decay corrected). In autoradiography studies, both [11C]1 and [11C]2 showed high binding specificities in hippocampus and cortex in vitro. While in vivo PET imaging with [11C]1 and [11C]2 demonstrated moderate binding affinities towards OX2R, their poor blood-brain barrier permeabilities and rapid clearance from the brain prevent further evaluation.SNMMI202