The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are the cornerstone of many renewable energy storage and conversion technologies such as metal-air batteries, fuel cells, and water electrolysis. [1][2][3] Both reactions, however, need highly active catalysts to achieve high efficiency since the oxygen electrode is a strongly irreversible system associated with high activation overpotential and sluggish kinetics. Noble metals (e.g., Pt) and their oxides (e.g., RuO 2 , IrO 2 ) have been found to be the most active catalysts for electrocatalytic reduction and evolution of molecular oxygen. However, their large-scale application is greatly prohibited by high cost, supply scarcity, and inferior durability. [4,5] On the other hand, as the universal choice of ORR catalyst, the OER activity of Pt is limited by the in situ formation of insulating platinum oxides in the process. IrO 2 and RuO 2 are unstable at high potentials due to the in situ transformation to higher-valent oxides, in spite of the highest activity towards OER. [6] To fulfill the demands in practical use, the development of lowcost yet durable bifunctional electrocatalysts with high activity toward both ORR and OER process is highly desired to reduce the cost and complexity of the renewable energy storage and conversion systems.Recent studies highlighted that transitional metal-N-doped carbon (NC) nanohybrids (MNC, MFe, Co, Ni, etc.) hold promise as substitutes of noble metal electrocatalysts in both acidic and alkaline medium. [7][8][9] In such catalysts, the presence of transitional metals helps to greatly improve the crystallinity and electrical conductivity of carbon matrix by catalytic graphitization upon preparation at high temperature, which in turn function to protect the metals from corrosion and aggregation during the electrochemical reactions. [10,11] More importantly, the interaction and synergy of metal species, the doped N species, and carbon lattice create sufficient localized reactive sites by modifying the charge distribution on carbon surface via the promoted electron transfer effect, which changes the local work function for O 2 adsorption and consequently facilitate the ORR or OER. [12,13] Very recently, the synergistic effect of metal@C nanoparticles and neighboring metal-N x coordination sites has been demonstrated to promote the O 2 adsorption The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are cornerstone reactions for many renewable energy technologies. Developing cheap yet durable substitutes of precious-metal catalysts, especially the bifunctional electrocatalysts with high activity for both ORR and OER reactions and their streamlined coupling process, are highly desirable to reduce the processing cost and complexity of renewable energy systems. Here, a facile strategy is reported for synthesizing double-shelled hybrid nanocages with outer shells of Co-N-doped graphitic carbon (Co-NGC) and inner shells of N-doped microporous carbon (NC) by templating against core-shell metal-orga...

Optimizing properties of phosphors for use in white-light-emitting diodes (WLEDs) is an important materials challenge. Most phosphors have a low level of lattice disorder due to mismatch between the host and activator cations. Here we show that deliberate introduction of high levels of cation disorder leads to significant improvements in quantum efficiency, stability to thermal quenching, and emission lifetime in Sr(CaBa)SiN:Eu (x = 0-1.5) phosphors. Replacing Sr by a (CaBa) mixture with the same average radius increases cation size variance, resulting in photoluminescence emission increases of 20-26% for the x = 1.5 sample relative to the x = 0 parent across the 25-200 °C range that spans WLED working temperatures. Cation disorder suppresses nonradiative processes through disruption of lattice vibrations and creates deep traps that release electrons to compensate for thermal quenching. Introduction of high levels of cation disorder may thus be a very useful general approach for improving the efficiency of luminescent materials.

A 3D hierarchical Mn3O4 nanoflake structure supported on nitrogenated reduced graphene oxide (NrGO), with excellent oxygen reduction in alkaline medium, was developed by electrodeposition. High performance is attributed to poor nanoflake crystallinity and strong nanoflake–NrGO coupling.

Combined temperature-dependent structural and electrical characterization of a series of "empty" ferroelectric tetragonal tungsten bronzes (TTBs) of composition Ba 4 (La 1-x Nd x ) 0.67 ! 1.33 Nb 10 O 30 are reported. The La-material exhibits a temperature dependent crossover from relaxor-ferroelectric to polar (but non-ferroelectric) to linear dielectric behavior. The loss of ferroelectric switching in the polar, non-ferroelectric phase is accompanied by disorder associated with structural relaxation due the significant vacancy concentration at the A1-perovskite-like site. In this disordered regime, large polarization can be re-established with application of sufficient electric field, however relaxation back into the disordered phase occurs on removal of the field as indicated by the loss of remenant polarization. The field against which "backswitching" (depolarization) occurs increases with temperature indicating increasing stability of the disordered regime. The disordered phase can be de-stabilized by substituting Nd for La at the A1-site and which reintroduces "normal" ferroelectric behavior. IntroductionThe field of polar dielectrics (piezo-, pyro-and ferro-electrics) is dominated by oxides with the perovskite structure.1, 2 The role of compositional tuning of perovskites and structural

By the use of atomic force microscopy (AFM), formation mechanism of nodular structure in cellulose acetate membranes was systematically investigated. Elementary factors affecting the nodule formation were delineated on the basis of both kinetic and thermodynamic considerations. It was shown that (1) the exact nature of nodular structure is thermodynamic equilibrium glassy state; nodular structure will vanish in the rubbery state; (2) the thermodynamic factor affecting nodule formation is the membrane formation temperature; with the membrane formation temperature decreasing, more chain segments are able to form nodular structures; (3) nodule formation is dependent on the segment rearrangement; variation of the solvent environment is the major kinetic factor affecting the segment rearrangement and nodule formation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1328–1335, 2003

Electrochemical CO2 reduction (ECR) is highly attractive to curb global warming. The knowledge on the evolution of catalysts and identification of active sites during the reaction is important, but still limited. Here, we report an efficient catalyst (Ag-D) with suitable defect concentration operando formed during ECR within several minutes. Utilizing the powerful fast operando X-ray absorption spectroscopy, the evolving electronic and crystal structures are unraveled under ECR condition. The catalyst exhibits a ~100% faradaic efficiency and negligible performance degradation over a 120-hour test at a moderate overpotential of 0.7 V in an H-cell reactor and a current density of ~180 mA cm−2 at −1.0 V vs. reversible hydrogen electrode in a flow-cell reactor. Density functional theory calculations indicate that the adsorption of intermediate COOH could be enhanced and the free energy of the reaction pathways could be optimized by an appropriate defect concentration, rationalizing the experimental observation.

The sodium oxygen battery is a promising metal-air battery; however, the discharge process is not well understood and the major discharge product is still under debate. The discharge products determined the theoretical specific energy and electrochemical performance of the battery. Now it is demonstrated that NaO spontaneously disproportionates to Na O , no matter whether it is dissolved in solution or stays on the surface. The behaviors of NaO in solution and on the surface are different. Solvents play a crucial effect on the disproportionation of dissolved NaO species, which is fast in low donor number (DN) solvents such as acetonitrile but sluggish in high DN solvents such as DMSO. In situ XRD results exhibited the different product growing processes in various solvents. Surface NaO would slowly disproportionate to Na O anyway, but this process is relatively slow compared to the time span of discharge process and it does not affect the major product on discharge.

An effective one-step method has been developed to synthesize CuPd bimetallic nanowire networks. Investigation of the growth process revealed that the nanowires were formed by attachment of spherical particles and strongly influenced by interactions between surface ligands and metals. The morphology of CuPd nanoparticles is tuned via changing the molecular weight of polyvinylpyrrolidone (PVP) and solvents. The versatility of this method was further demonstrated by preparation of AgPd nanowires. An electrochemical study of CuPd nanowire networks shows morphology dependent activity in oxygen reduction reaction (ORR), which is comparable to that of platinum.