Photoelectrochemistry of oxygen in rechargeable Li-O2 batteries.

Rechargeable lithium-oxygen (Li-O2) batteries are promising energy storage devices due to their high theoretical energy density. However, the sluggish kinetics of the oxygen reduction and evolution reactions (ORR/OER) at the cathodes results in large polarization and low energy efficiency. Although advances have been achieved in electrode material designs and battery configurations, large discharge/charge voltage gaps remain. The introduction of light into Li-O2 batteries has been demonstrated to boost the reaction kinetics of the ORR/OER, leading to enhanced electrochemical performances, but the understanding of the photoelectrochemical process at oxygen cathodes is limited. This tutorial review focuses on the recent findings regarding photoinvolved oxygen cathodes, battery configurations, and the stability of Li-O2 batteries, aiming to provide a fundamental understanding of photoinvolved Li-O2 batteries. The challenges and perspectives are discussed in light of the interdisciplinary nature of photochemistry, materials chemistry, electrochemistry, computation, spectroscopy, and surface science.

Irradiation-induced reactions at the CeO2/SiO2/Si interface.

The influence of high-energy (1.6 MeV) Ar2+ irradiation on the interfacial interaction between cerium oxide thin films (∼15 nm) with a SiO2/Si substrate is investigated using transmission electron microscopy, ultrahigh vacuum x-ray photoelectron spectroscopy (XPS), and a carbon monoxide (CO) oxidation catalytic reaction using ambient pressure XPS. The combination of these methods allows probing the dynamics of vacancy generation and its relation to chemical interactions at the CeO2/SiO2/Si interface. The results suggest that irradiation causes amorphization of some portion of CeO2 at the CeO2/SiO2/Si interface and creates oxygen vacancies due to the formation of Ce2O3 at room temperature. The subsequent ultra-high-vacuum annealing of irradiated films increases the concentration of Ce2O3 with the simultaneous growth of the SiO2 layer. Interactions with CO molecules result in an additional reduction of cerium and promote the transition of Ce2O3 to a silicate compound. Thermal annealing of thin films exposed to oxygen or carbon monoxide shows that the silicate phase is highly stabile even at 450 °C.

Highly Selective Transport of Alkali Metal Ions by Nanochannels of Polyelectrolyte Threaded MIL-53 Metal Organic Framework.

Conventional ion-exchange polymeric membranes have limited selectivity due to their nonuniform and unstable structures. The rigid, regular, high porosity of metal organic framework (MOF) generally provides MOF membrane with exclusion/sieving effect but lack of electrostatic screening. Here we report for the first time a nonbiological highly selective MOF membrane with polyelectrolyte threaded in the nanochannel of metal organic framework (polyelectrolyte∼MOF) and its selective transport of alkali metal cations. Poly(sodium vinyl sulfonated-co-acrylic acid)∼MIL-53(Al) is prepared on anodic aluminum oxide substrate via steps of MOF MIL-53(Al) growth followed by in situ polymerization. The poly(VS-co-AA)∼MIL-53(Al) membrane demonstrates highly specific selectivity in transport of alkali metal cations. Rate of ion transport correlates inversely with the hydrated diameter of the ion reaching a low limiting rate near 0.7 nm hydrated diameter. Charge exclusion is demonstrated with blockage of anion transport under a concentration gradient. The highly uniform porous nanostructure of MOF and ionic function of polyelectrolyte offers the MOF membrane with synergistic selectivity based on exclusion forces of the framework and Coulomb forces from fixed charges of polyelectrolytes in nanochannels.

Poly(ethylene glycol) (PEG) in a Polyethylene (PE) Framework: A Simple Model for Simulation Studies of a Soluble Polymer in an Open Framework.

Canonical molecular dynamics simulations are performed to investigate the behavior of single-chain and multiple-chain poly(ethylene glycol) (PEG) contained within a cubic framework spanned by polyethylene (PE) chains. This simple model is the first of its kind to study the chemical physics of polymer-threaded organic frameworks, which are materials with potential applications in catalysis and separation processes. For a single-chain 9-mer, 14-mer, and 18-mer in a small framework, the PEG will interact strongly with the framework and assume a more linear geometry chain with an increased radius of gyration Rg compared to that of a large framework. The interaction between PEG and the framework decreases with increasing mesh size in both vacuum and water. In the limit of a framework with an infinitely large cavity (infinitely long linkers), PEG behavior approaches simulation results without a framework. The solvation of PEG is simulated by adding explicit TIP3P water molecules to a 6-chain PEG 14-mer aggregate confined in a framework. The 14-mer chains are readily solvated and leach out of a large 2.6 nm mesh framework. There are fewer water-PEG interactions in a small 1.0 nm mesh framework, as indicated by a smaller number of hydrogen bonds. The PEG aggregate, however, still partially dissolves but is retained within the 1.0 nm framework. The preliminary results illustrate the effectiveness of the simple model in studying polymer-threaded framework materials and in optimizing polymer or framework parameters for high performance.

Theoretical study on the mechanism of aqueous synthesis of formic acid catalyzed by [Ru3+]-EDTA complex.

Because formic acid can be effectively decomposed by catalysis into very pure hydrogen gas, the synthesis of formic acid, especially using CO and H2O as an intermediate of the water gas shift reaction (WGSR), bears important application significance in industrial hydrogen gas production. Here we report a theoretical study on the mechanism of efficient preparation of formic acid using CO and H2O catalyzed by a water-soluble [Ru(3+)]-EDTA complex. To determine the feasibility of using the [Ru(3+)]-EDTA catalyst to produce CO-free hydrogen gas in WGSR, two probable reaction paths have been examined: one synthesizes formic acid, while the other converts the reactants directly into CO2 and H2, the final products of WGSR. Our calculation results provide a detailed mechanistic rationalization for the experimentally observed selective synthesis of HCOOH by the [Ru(3+)]-EDTA catalyst. The results support the applicability of using the [Ru(3+)]-EDTA catalyst to efficiently synthesize formic acid for hydrogen production. Careful analyses of the electronic structure and interactions of different reaction complexes suggest that the selectivity of the reaction processes is achieved through the proper charge/valence state of the metal center of the [Ru(3+)]-EDTA complex. With the catalytic roles of the ruthenium center and the EDTA ligand being carefully understood, the detailed mechanistic information obtained in this study will help to design more efficient catalysts for the preparation of formic acid and further to produce CO-free H2 at ambient temperature.

Metal-organic framework threaded with aminated polymer formed in situ for fast and reversible ion exchange.

A porous metal-organic framework composite with flexible anion-exchange polymers threaded within the host cavity demonstrates very fast and reversible ion-exchange activity. Polyvinyl benzyl trimethylammonium hydroxide (PVBTAH) caged in ZIF-8 is synthesized in steps of chloro-monomer impregnation, in situ polymerization, amination, and alkaline ion exchange. The synthesized non-cross-linked PVBTAH∼ZIF-8 material exhibits superior ion-exchange kinetics compared to conventional ion-exchange resins.

Uniform dispersion of 1 : 1 PtRu nanoparticles in ordered mesoporous carbon for improved methanol oxidation.

PtRu nanoparticles dispersed in CMK3 mesoporous carbons have been prepared via a CPDM (carbonization over poly-furfuryl alcohol-protected dispersed mixed metals) method. The as-synthesized CMK3 supported PtRu nanoparticles are characterized using tomography and cross-sectional TEM analysis and are compared against those synthesized by the conventional ethylene glycol (EG) method. The atomic ratio of Pt : Ru, which has an essential role on methanol oxidation, is found to be consistent at the nanometer scale. The good dispersion and uniform composition of PtRu nanoparticles result in improved methanol oxidation performance including higher methanol oxidation current and long-term stability.

UiO66-Derived Catalyst for Low Temperature Catalytic Reduction of NO with NH3.

Diesel exhaust emissions are major outdoor air pollutants. Reducing the emission of NOx by diesel commercial vehicles and related machineries is at present a great challenge. In this study, we synthesize a catalyst for low-temperature catalytic reduction of NO using calcinated UiO-66(Zr) as a host for the doping of cerium, manganese, and titanium by the incipient wetness impregnation, followed by the dispersion of 1.0 wt % platinum. A solid solution of Ce0.15Zr0.54Mn0.11Ti0.20O2/1.0Pt (CZMTO/Pt) is synthesized as evident by the structural characterizations. The catalyst demonstrates significant NO reduction in the laboratory due to the synergistic effect of various elements, with NO conversion above 80% at 160 °C.

Novel ice structures in carbon nanopores: pressure enhancement effect of confinement.

We report experimental results on the structure and melting behavior of ice confined in multi-walled carbon nanotubes and ordered mesoporous carbon CMK-3, which is the carbon replica of a SBA-15 silica template. The silica template has cylindrical mesopores with micropores connecting the walls of neighboring mesopores. The structure of the carbon replica material CMK-3 consists of carbon rods connected by smaller side-branches, with quasi-cylindrical mesopores of average pore size 4.9 nm and micropores of 0.6 nm. Neutron diffraction and differential scanning calorimetry have been used to determine the structure of the confined ice and the solid-liquid transition temperature. The results are compared with the behavior of water in multi-walled carbon nanotubes of inner diameters of 2.4 nm and 4 nm studied by the same methods. For D(2)O in CMK-3 we find evidence of the existence of nanocrystals of cubic ice and ice IX; the diffraction results also suggest the presence of ice VIII, although this is less conclusive. We find evidence of cubic ice in the case of the carbon nanotubes. For bulk water these crystal forms only occur at temperatures below 170 K in the case of cubic ice, and at pressures of hundreds or thousands of MPa in the case of ice VIII and IX. These phases appear to be stabilized by the confinement.

Catalytic Palladium Film Deposited by Scalable Low-Temperature Aqueous Combustion.

This article describes a novel method for depositing a dense, high quality palladium thin film via a one-step aqueous combustion process which can be easily scaled up. Film deposition of Pd from aqueous solutions by conventional chemical or electrochemical methods is inhibited by hydrogen embrittlement, thus resulting in a brittle palladium film. The method outlined in this work allows a direct aqueous solution deposition of a mirror-bright, durable Pd film on substrates including glass and glassy carbon. This simple procedure has many advantages including a very high deposition rate (>10 cm2 min-1) and a relatively low deposition temperature (250 °C), which makes it suitable for large-scale industrial applications. Although preparation of various high-quality oxide films has been successfully accomplished via solution combustion synthesis (SCS) before, this article presents the first report on direct SCS production of a metallic film. The mechanism of Pd film formation is discussed with the identification of a complex formed between palladium nitrate and glycine at low temperature. The catalytic properties and stability of films are successfully tested in alcohol electrooxidation and electrochemical oxygen reduction reaction. It was observed that combustion deposited Pd film on a glassy carbon electrode showed excellent catalytic activity in ethanol oxidation without using any binder or additive. We also report for the first time the concept of a reusable "catalytic flask" as illustrated by the Suzuki-Miyaura cross-coupling reaction. The Pd film uniformly covers the inner walls of the flask and eliminates the catalyst separation step. We believe the innovative concept of a reusable catalytic flask is very promising and has the required features to become a commercial product in the future.

Hierarchical NiCo2O4 Micro- and Nanostructures with Tunable Morphologies as Anode Materials for Lithium- and Sodium-Ion Batteries.

NiCo2O4 microrods with open structures are successfully synthesized using a solvothermal method. Compared with those of dense microspheres, the one-dimensional (1D) porous microrods show much higher capacities and stability for both Li- and Na-ion batteries due to the 1D open structure facilitating fast ion transport and buffering volumetric change during charge/discharge. This work demonstrates that the electrochemical performance of NiCo2O4 is highly dependent on morphologies of the active material.

Nafion-polyfurfuryl alcohol nanocomposite membranes with low methanol permeation.

Nafion-polyfurfuryl alcohol nanocomposite membranes with low methanol permeability and high proton conductivity were synthesized by in-situ polymerisation of furfuryl alcohol inside commercial Nafion membranes.

Direct detection of cell surface interactive forces of sessile, fimbriated and non-fimbriated Actinomyces spp. using atomic force microscopy.

Actinomyces species are predominant early colonizers of the oral cavity and prime mediators of inter-bacterial adhesion and coaggregation. Previous workers have evaluated the adhesion of Actinomyces spp. by quantitative assessment of sessile, as opposed to planktonic cells attached to substrates, but did not quantify the cell surface interactive forces. Therefore we used atomic force microscopy to directly detect the interactive force between an approaching silicon tip and sessile Actinomyces spp. adhering to a substrate, at nanonewton (nN) range force levels. A total of eight strains each belonging to fimbriated and non-fimbriated Actinomyces species were employed, namely A. bovis, A. gerencseriae, A. israelii, A. meyeri, A. naeslundii genospecies 1 and 2, A. odontolyticus and A. viscosus. The sterile mica discs, used as the adhesion substrate, were immersed in mono-species bacterial suspensions for five days to obtain a thin bacterial biofilm. Interactive forces were measured using a silicon nitride cantilever attached to a Nanoscope IIIA atomic force microscope. The interactive forces between the approaching silicon nitride tip and bacterial biofilm surfaces were randomly quantified at three different locations on each cell; namely, the cell surface proper, the periphery of the cell and the substrate and, the interface between two cells. When the interactive forces at these locations of the same species were compared, significantly higher force levels at the cell-cell interface than the other two locations were noted with A. gerencseriae (P < 0.001), A. viscosus (P < 0.01) and A. israelii (P < 0.05). When the interactive forces of different Actinomyces spp. at an identical location were compared, fimbriated A. naeslundii genospecies 2 showed the greatest interactive force at the cell surface proper (-32.6 +/- 8.7 nN, P < 0.01). A. naeslundii genospecies 1, 2 and A. viscosus demonstrated greater interactive force at the cell-mica periphery than the other five species (P < 0.05); A. viscosus (-34.6 +/- 10.5 nN) displayed greater interactive force at the cell-cell interface than the others (P < 0.01), except for A. gerencseriae (P > 0.05). These data indicate that fimbriated Actinomyces spp., including A. naeslundii genospecies 1, 2 and A. viscosus exert higher cell surface interactive forces than those devoid of fimbriae and, such variable force levels may modulate their adhesion and coaggregation during biofilm formation.

Effects of toxic metals and chemicals on biofilm and biocorrosion.

Microbes in marine biofilms aggregated into clusters and increased the production of extracellular polymeric substances (EPS), by over 100% in some cases, when the seawater media containing toxic metals and chemicals, such as Cd(II), Cu(II), Pb(II), Zn(II), AI(III), Cr(III), glutaraldehyde, and phenol. The formation of microbial cluster and the increased production of EPS, which contained 84-92% proteins and 8-16% polysaccharides, accelerated the corrosion of the mild steel. However, there was no quantitative relationship between the degree of increased corrosion and the toxicity of metals/chemicals towards sulfate-reducing bacteria, or the increased EPS production.

Optimizing electron spin resonance detection of hydroxyl radical in water.

The parameters affecting the electron spin resonance (ESR) detection of hydroxyl free radical in water are studied and optimized. The hydroxyl radical is generated by the Fenton reaction with iron (II) ammonium sulfate and hydrogen peroxide reacting in a phosphate buffer using N-tert-butyl-alpha-phenylnitron as the spin trap. The concentrations of Fe(2+), H(2)O(2), and phosphate buffer are the parameters studied. The Taguchi method and the orthogonal experiment design were used to evaluate the effects of these parameters on the ESR signal intensity. By the analysis of the signal-to-noise ratio and the analysis of variance, the order of importance of the various parameters on the hydroxyl radical formation is determined for optimal ESR detection of hydroxyl radical. The results will help the development of water purification technologies using hydroxyl free radical as a green oxidant.

A functionalized MIL-101(Cr) metal-organic framework for enhanced hydrogen release from ammonia borane at low temperature.

Hydrogen released from ammonia borane in MIL-101(Cr) can be significantly improved by the attached amino and amide groups. The release with minimum impurities starts at 68 °C, reaching 1.6 equivalent of ammonia borane at 85 °C for the amino modified MOFs (NH2-MIL-101).

Effects of shear and charge on the microphase formation of P123 polymer in the SBA-15 synthesis investigated by mesoscale simulations.

Mesoscale simulation was performed to investigate the dynamical structural behavior of the pluronic P123 block copolymer in the synthesis of mesoporous SBA-15. Shear is introduced to represent stirring in the actual experiment, and a weak charge is included to simulate the acidic conditions in the synthesis. Under shear, with the increase in weak charge in the PEO [poly(ethylene oxide)] block, the template forms more ordered hexagonal phases, and the pore sizes of the cylindrical hydrophobic PPO [poly(propylene oxide)] blocks decrease. The structural factor shows three types of water molecules in the mesoscale aggregates, including bulk water in the solution, bound water around the hydrophilic PEO corona, and trapped water in the hydrophobic PPO core. When 1,3,5-trimethyl-benzene (TMB) is added to the system as a swelling agent, expanded hexagonal phases are formed, and the density mapping of TMB shows that the TMB molecules are mainly located in the hydrophobic PPO cores. In configurations with spherical micelles, although bimodally dispersed spheres are observed, the face-centered cubic (fcc) packing of the micelles hardly changes with the addition of TMB. In agreement with experimental results, the simulations show that the shear and the weak charge are essential to the formation of hexagonal templates in the copolymer. Mesoscopic simulations complement experimental investigations on the morphology changes of amphiphilic polymer in template syntheses and can provide important guidance for further experiments.

Low activation energy dehydrogenation of aqueous formic acid on platinum-ruthenium-bismuth oxide at near ambient temperature and pressure.

Highly selective dehydrogenation of formic acid in water was observed at near ambient temperature on a metal/metal oxide catalyst composed of platinum ruthenium and bismuth with a low activation energy of 37.3 kJ mol(-1).

Highly thermal stable and highly crystalline anatase TiO2 for photocatalysis.

In the absence of any doping and modification, the anatase-to-rutile phase transformation was inhibited at high temperatures giving rise to highly thermal stable and highly crystalline anatase TiO2 fibers. The initial formation of the TiO2(B) phase is found to be key in inhibiting this transformation. The intermediate structure of the TiO2 fiber comprises an inner anatase core with an outer TiO2(B) shell, which has a specific crystallographic orientation with respect to the anatase structure. During the calcination process from 300 to 800 degrees C, both the TiO2(B) shell and the bulk anatase crystal structure was preserved. At temperatures of 800-900 degrees C the TiO2(B)-to-anatase transformation was finished and a near-pure and thermally stable anatase fiber was obtained. This final product shows the same activity as a standard commercial photocatalyst Degussa P-25 when measured against unit mass, and 5 times the activity when measured with respect to the unit surface area. The anatase TiO2 fibers presented here have considerable interest as practical photocatalysts for water purification, as they can be easily recycled without a decrease in their photocatalytic activity and can be prepared at large scale and at low cost.

Preparation of amino-functionalized mesostructured cellular foams and application as hosts for large biomolecules.

Large mesopores cellular foam (LMCFs) materials were synthesized using microemulsion templating in acidic solutions. The amine functional groups were attached to channels of LMCFs materials via post-synthesis grafting. The structural and chemical properties of these prepared materials were characterized by TEM, XRD, FTIR and nitrogen adsorption. These resulting materials had disordered mesopores with well-defined large mesopore. The bovine serum albumin (BSA) and glucose oxidase (GOx) were used for adsorption experiment. The biomolecule was immobilized by covalently couple to the interior surface of amino-functionalized mesostructured cellular foams (AF-MCFs). The results showed that AF-MCFs had high-capacity bioimmobilization ability.