detection and suppression of spurious singlet oxygen in Li-O batteries.

The rechargeable lithium air (oxygen) battery (Li-O) has very high energy density, comparable to that of fossil fuels (∼3600 W h kg). However, the parasitic reactions of the O reduction products with solvent and electrolyte lead to capacity fading and poor cyclability. During the oxygen reduction reaction (ORR) in aprotic solvents, the superoxide radical anion (O˙) is the main one-electron reaction product, which in the presence of Li ions undergoes disproportionation to yield LiO and O, a fraction of which results in singlet oxygen (O).

Direct Lithium Recovery from Aqueous Electrolytes with Electrochemical Ion Pumping and Lithium Intercalation.

In this mini-review, we provide an account of recent developments on electrochemical methods for the direct extraction of lithium (DEL) from natural brines, geothermal fluids, seawater, and battery recycling electrolytes by ion-pumping entropy cells. A critical discussion of selected examples with the LiMnO lithium intercalation battery cathode material is presented, with emphasis on the operation parameters, some experimental results and multiscale simulations, some limitations and challenges, and conditions for industrial scaleup.

Effect of porosity and active area on the assessment of catalytic activity of non-precious metal electrocatalyst for oxygen reduction.

We describe a method to study porous thin-films deposited onto rotating disc electrodes (RDE) applied to non-platinum group electrocatalyst obtained by pyrolysis of iron phthalocyanine and carbon, FePc/C. The electroactive area and porous properties of the thin film electrodes were obtained using electrochemical impedance spectroscopy under the framework of de Levie impedance model. The electrocatalytic activity of different electrodes was correlated to the total electroactive area () and the penetration ratio parameter through the film under ac current.

Electrochemical stability of glyme-based electrolytes for Li-O batteries studied by in situ infrared spectroscopy.

In situ subtractively normalized Fourier transform infrared spectroscopy (SNIFTIRS) experiments were performed simultaneously with electrochemical experiments relevant to Li-air battery operation on gold electrodes in two glyme-based electrolytes: diglyme (DG) and tetraglyme (TEGDME), tested under different operational conditions. The results show that TEGDME is intrinsically unstable and decomposes at potentials between 3.6 and 3.

Metal Nanoparticle Enhancement of Electron Transfer to Tethered Redox Centers through Self-Assembled Molecular Films.

Metal-nanoparticle-mediated electron transfer (ET) across an insulator thin film containing nanoparticles with attached redox centers was studied using electrochemical impedance spectroscopy. Specifically, a gold spherical microelectrode was modified with 16-amino-1-hexa-decanethiol, creating an insulator film. This was followed by the electrostatic adsorption of gold nanoparticles and the covalent attachment of Os redox centers.

Adsorption of 4,4'-Dithiodipyridine Axially Coordinated to Iron(II) Phthalocyanine on Au(111) as a New Strategy for Oxygen Reduction Electrocatalysis.

The coordination of PySSPy to FePc was monitored by UV/Vis spectroscopy while the adsobed FePc, anchored by PyS-Au(111), was examined by in situ STM in 0.1 M HClO and X-ray photoelectron spectroscopy (XPS). Rotating-disc-electrode (RDE) and linear-sweep-voltammetry (LSV) studies on the resulting FePc-modified Au(111) electrodes in an oxygen-saturated 0.

Surface Structure of 4-Mercaptopyridine on Au(111): A New Dense Phase.

4-Mercaptopyridine (4MPy) self-assembled on Au(111) has been studied by in situ electrochemical scanning tunneling microscopy (EC-STM) in HClO, cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). Samples prepared by varying the immersion time at constant concentration named short time (30 s) and long time (3 min) adsorption have been studied. Cyclic voltammetry and XPS showed that the chemistry of the adsorbed molecules does not depend on the adsorption time resulting in a well established chemisorbed thiol self-assembled monolayer on Au(111).

Palladium Nanoparticles Embedded in a Layer-by-Layer Nanoreactor Built with Poly(Acrylic Acid) Using "Electro-Click Chemistry".

Palladium nanoparticles (Pd NPs) were formed by electrochemical reduction of Pd(NH3)4(3+) ions entrapped by ion exchange in poly(acrylic acid) (PAA) multilayer films grown by the Sharpless "click reaction." The alkyne (PAAalk) and azide (PAAaz) groups were covalently bound to the PAA, and the catalyzed buildup of the multilayer film was performed by electrochemical reduction of Cu(2+) to Cu(+). The size of the Pd NPs formed in Au/(PAAalk)3(PAAaz)2 multilayer films by the click reaction, that is, 50 nm, is larger than that of similar Pd NPs formed in electrostatically bound Au/(PAA)3(PAH)2 nanoreactors, that is, 6-9 nm, under similar conditions.

Revisiting direct electron transfer in nanostructured carbon laccase oxygen cathodes.

The biocatalytic electroreduction of oxygen has been studied on large surface area graphite and Vulcan® carbon electrodes with adsorbed Trametes trogii laccase. The electrokinetics of the O2 reduction reaction (ORR) was studied at different electrode potentials, O2 partial pressures and concentrations of hydrogen peroxide. Even though the overpotential at 0.

Molecular and electronic structure of osmium complexes confined to Au(111) surfaces using a self-assembled molecular bridge.

The molecular and electronic structure of Os(II) complexes covalently bonded to self-assembled monolayers (SAMs) on Au(111) surfaces was studied by means of polarization modulation infrared reflection absorption spectroscopy, photoelectron spectroscopies, scanning tunneling microscopy, scanning tunneling spectroscopy, and density functional theory calculations. Attachment of the Os complex to the SAM proceeds via an amide covalent bond with the SAM alkyl chain 40° tilted with respect to the surface normal and a total thickness of 26 Å. The highest occupied molecular orbital of the Os complex is mainly based on the Os(II) center located 2.

Lithium solvation in dimethyl sulfoxide-acetonitrile mixtures.

We present molecular dynamics simulation results pertaining to the solvation of Li(+) in dimethyl sulfoxide-acetonitrile binary mixtures. The results are potentially relevant in the design of Li-air batteries that rely on aprotic mixtures as solvent media. To analyze effects derived from differences in ionic size and charge sign, the solvation of Li(+) is compared to the ones observed for infinitely diluted K(+) and Cl(-) species, in similar solutions.

XPS analysis of enzyme and mediator at the surface of a layer-by-layer self-assembled wired enzyme electrode.

High potential purified Trametes trogii laccase has been deposited in mono- and multilayer thin films on gold surfaces by layer-by-layer electrostatic adsorption self-assembly. The osmium bipyridil redox relay sites on polycation poly(allylamine) backbone efficiently work as a molecular "wire" in oxygen cathodes for biofuel cells. X-ray photoelectron spectroscopy of Cu 2p3/2 and Os 4f signals provided chemical information on the enzyme and redox mediator surface concentrations after different adsorption steps.

AFM study of oxygen reduction products on HOPG in the LiPF6-DMSO electrolyte.

Ex situ atomic force microscopy (AFM) has been used to study the morphology of oxygen reduction products in the LiPF6-dimethyl sulfoxide (DMSO) electrolyte, i.e. Li2O2 on a highly oriented pyrolytic graphite (HOPG) surface.

O2 induced Cu surface segregation in Au-Cu alloys studied by angle resolved XPS and DFT modelling.

Surface segregation effects on polycrystalline Au-Cu alloys (Au(0.80)Cu(0.20), Au(0.

Some evidence for the formation of an azo bond during the electroreduction of diazonium salts on Au substrates.

Molecular films obtained by electrochemical reduction of diazoniuim tetrafluoroborate salts [4-carboxybenzene (PhCOOH) and 4-amino-(2,3,5,6-tetrafluoro)-carboxybenzene (PhF(4)COOH)] on Au substrates and post-functionalization with an osmium pyridil-bipyridine complex are studied by a combination of X-ray photoelectron (XPS) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS). The spectroscopic evidence suggests the formation of N=N bonds tethering the complexes to Au. The surface coverage of the azo-bonded osmium complexes strongly depends on the electrode potential.

Metal-ion responsive redox polyelectrolyte multilayers.

We present polyelectrolyte multilayer modified electrodes exhibiting novel chemically responsive redox behaviour due to the combination of both redox and metal-ion-ligand functionalities on the same sites.

Layer-by-layer self-assembled osmium polymer-mediated laccase oxygen cathodes for biofuel cells: the role of hydrogen peroxide.

High potential purified Trametes trogii laccase has been studied as a biocatalyst for oxygen cathodes composed of layer-by-layer self-assembled thin films by sequential immersion of mercaptopropane sulfonate-modified Au electrode surfaces in solutions containing laccase and osmium-complex bound to poly(allylamine), (PAH-Os). The polycation backbone carries the Os redox relay, and the polyanion is the enzyme adsorbed from a solution of a suitable pH so that the protein carries a net negative charge. Enzyme thin films were characterized by quartz crystal microbalance, ellipsometry, cyclic voltammetry, and oxygen reduction electrocatalysis under variable oxygen partial pressures with a rotating disk electrode.

Charge transport in redox polyelectrolyte multilayer films: the dramatic effects of outmost layer and solution ionic strength.

The redox switching kinetics, that is, charge transfer and transport in layer-by-layer-deposited electroactive polyelectrolyte multilayers is systematically studied with variable-scan-rate cyclic voltammetry. The experiments are performed with films finished in the redox polycation (an osmium pyridine-bipyridine derivatized polyallylamine, PAH-Os) and the polyanion (polyvinyl sulfonate, PVS), in solutions of different electrolyte concentrations. A modified diffusion model is developed to account for the experimentally observed dependence of the average peak potential with the scan rate.

Methylene blue incorporation into alkanethiol SAMs on Au(111): effect of hydrocarbon chain ordering.

A detailed polarization modulation infrared reflection absorption spectroscopy, scanning tunneling microscopy, and electrochemical study on methylene blue (MB) incorporation into alkanethiolate self-assembled monolayers (SAMs) on Au(111) is reported. Results show that the amount of MB incorporated in the SAMs reaches a maximum for intermediate hydrocarbon chain lengths (C10-C12). Well-ordered SAMs of long alkanethiols (C > C12) hinder the incorporation of the MB molecules into the SAM.

Electrochemical scanning tunneling spectroscopy of redox-active molecules bound by Au-C bonds.

A comparison of the electrochemical gating of molecular conduction by a redox [Os(bipyridine)(pyridine)Cl] complex tethered to Au(111) with two different metal-molecule junctions in a scanning tunneling microscope nanogap is presented. The same redox molecular structure was tethered by mercaptobenzoic acid or reduction of the aryldiazonium salt of p-aminobenzoic acid, resulting in a Au-S or Au-C bond, respectively. A two-step electron-transfer mechanism with vibrational relaxation of the redox molecule is apparent in each case.

Redox molecule based SERS sensors.

We describe a general framework to design nanobiosensors based on a wired enzyme coupled to a redox molecule and integrated with SERS Au core-shell nanoparticles and ordered nanocavities. The response of the proposed sensor is based on the different electronic resonant Raman behavior of the oxidized or reduced electronic states of the molecular wire, and on the surface plasmon amplification induced by the tailored metallic substrate. The nanobiosensors can be interrogated remotely through the resonant Raman scattering intensity recovery or spectral variation of the redox molecule, an Os-complex, when the latter varies its oxidation state.

Molecular orientation in self-assembled multilayers measured by second harmonic generation using femtosecond pulses.

We present measurements of the optical second-harmonic generation in self assembled multilayer films of PAZO/PAH polymers with the aim to investigate molecular order in the layer-by-layer architecture. The experiments are performed in transmission, using a femtosecond Ti:Sa pulsed laser, which allows a more accurate determination of the amplitude of the second harmonic signal, without interference fringes usually present in nanosecond experiments. We found that the first bilayer, in contact with the substrate, presents a broad distribution of the orientation of the molecules, while the addition of successive bilayers (up to 12) produces ordering of the molecules with a small tilt angle respect to the surface normal.