Li Insertion into Li-Ti-O Spinels: Voltammetric and Electrochemical Impedance Spectroscopy Study

The insertion of Li into nanocrystalline Li-Ti-O spinel electrodes was studied using cyclic voltammetry combined with electrochemical quartz crystal microbalance, open circuit potential measurements, and electrochemical impedance spectroscopy studies. Insertion characteristics of spinel were compared with those of titania polymorphs. The insertion into spinel occurs at potential 300 mV more negative to that of insertion into anatase, and about 40 mV positive to that into rutile. The specific capacity (160 mAh/g) is comparable with that of TiO2 polymorphs. Due to the relatively negative potential of the insertion and significantly lower tendency to self-discharge, Li-Ti-O spinel is more convenient for use in a 2 V lithium-ion battery than are other active phases in the Li-Ti-O system. The behavior of the spinel electrodes in equilibrium can be described by the Frumkin insertion isotherm model. The value of interaction parameter, g, below -4 indicates that the insertion process leads to a first-order phase transition. Diffusion coefficient of Li in spinel ranges between 10-15 and 10-16 cm2 s-1; the charge transfer kinetics depends on the redox composition. Heterogeneous rate constant ranges between 1 × 10-8 and 4 × 10-10 cm s-1 that is ca. two orders of magnitude higher than that reported for anatase. © 2001 The Electrochemical Society. [DOI: 10.1149/1.1392321] All rights reserved

Lithium insertion into mesoscopic and single-crystal TiO2 (rutile) electrodes

Electrochemical behavior of single-crystal and mesoscopic TiO2 (rutile) was studied in propylene carbonate solutions at potentials negative to the flatband potential. In electrolytic solutions containing sodium or tetrabutylammonium (Bu4N+), the injected charge is compensated by protonization of the surface and/or by adsorption of cations in the double layer. In electrolytic solutions containing Li+, the insertion into the rutile lattice occurs at potentials below 1.5 V (Li/Li+). At higher potentials, the charge is compensated mainly by a nonfaradaic process. Lithium insertion into rutile proceeds at a potential ca. 0.4 V more negative than the insertion potential into anatase. The maximum insertion capacity of rutile is also lower than that of anatase. The insertion of lithium into rutile is accompanied by an increase of the electrode mass, while the mass/charge relations show hystereses between anodic and cathodic potential sweeps. This behavior is explained in terms of a free convection in the electrode vicinity

Lithium insertion into titanium dioxide (anatase) electrodes: Microstructure and electrolyte effects

Insertion characteristics of anatase electrodes were studied on single-crystal and polycrystalline electrodes of different microstructures. The lithium incorporation from propylene carbonate solution containing LiClO4 and Li(CF3SO2)2N was studied by means of cyclic voltammetry (CV), the quartz crystal microbalance (QCM) and the galvanostatic intermittent titration technique (GITT). The electrode microstructure affects both the accessible coefficient x and the reversibility of the process. The highest insertion activity was observed for electrodes composed of crystals with characteristic dimensions of ∼10-8 m. The insertion properties deteriorate for higher as well as for smaller crystal sizes. Enhanced insertion was observed in Li(CF3SO2)2N-containing solutions. Lithium insertion is satisfactorily reversible for mesoscopic electrodes; the reversibility in the case of compact polycrystalline and single-crystal electrodes is poor. The reversibility of the insertion improves with increasing electrolyte concentration. The lithium diffusion coefficient decreases with increasing x and ranges between 10-15 and 10-18 cm2 s-1. © Springer-Verlag 2001

Insertion of lithium into mesoscopic anatase electrodes - An electrochemical and in-situ EQCM study

The insertion of Li+ into mesoscopic TiO2 (anatase) electrodes was studied using cyclic voltammetry combined with the in situ gravimetric monitoring of the electrode mass in LiClO4 and Li(CF3SO2)2 N/propylene carbonate (PC)-based solutions. The insertion of Li+ takes place at potentials less than 2.0 V vs Li/Li+. The cathodic process is associated with a mass uptake; the subsequent oxidation process is associated with a mass decrease. The apparent molar mass of the inserted/extracted material is, however, remarkably different from that expected for the simple insertion/extraction of unsolvated Li+ ions. For a more accurate description of the behaviour of the mesoscopic anatase electrodes, we consider them as gold electrodes modified with a porous film. Thus, the mesoscopic anatase electrode behaves similarly to a polymer-modified electrode, i.e. the overall process includes coupled electron/ion transfer (insertion of Li+) and a transfer of neutral species. Analysing the EQCM (electrochemical quartz crystal microbalance) data, one can conclude that the controlling step of the insertion/extraction of Li+ into/from anatase electrodes is a coupled electron/ ion transfer or the transfer of neutral species in solutions containing ClO4 - and (CF3SO2)2N- respectively

Local structure and composition of PtRh nanoparticles produced through cathodic corrosion

Catalysis and Surface Chemistr

Reversible Voltage-Induced Assembly of Au Nanoparticles at Liquid|Liquid Interfaces

The voltage-induced assembly of mercaptosuccinic acid-stabilized Au nanoparticles of 1.5 ± 0.4 nm diameter is investigated at the polarizable water|1,2-dichloroethane interface. Admittance measurements and quasi-elastic laser scattering (QELS) studies reveal that the surface concentration of the nanoparticle at the liquid|liquid boundary is reversibly controlled by the applied bias potential. The electrochemical and optical measurements provide no evidence of irreversible aggregation or deposition of the particles at the interface. Analysis of the electrocapillary curves constructed from the dependence of the frequency of the capillary waves on the applied potential and bulk particle concentration indicates that the maximum particle surface density is 3.8 × 1013cm-2, which corresponds to 67% of a square closed-pack arrangement. This system provides a unique example of reversible assembly of nanostructures at interfaces, in which the density can be effectively tuned by the applied potential bias

Engendering Unprecedented Activation of Oxygen Evolution via Rational Pinning of Ni Oxidation State in Prototypical Perovskite:Close Juxtaposition of Synthetic Approach and Theoretical Conception

Rational optimization of the OER activity of catalysts based on LaNiO3 oxide is achieved by maximizing the presence of trivalent Ni in the surface structure. DFT investigations of the LaNiO3 catalyst and surface structures related to it predict an improvement in the OER activity for these materials to levels comparable with the top of the OER volcano if the La content is minimized while the oxidation state of Ni is maintained. These theoretically predicted structures of high intrinsic OER activity can be prepared by a templated spray-freeze freeze-drying synthesis followed by a simple postsynthesis exfoliation-like treatment in acidic media. These nanocrystalline LaNiO3-related materials confirm the theoretical predictions, showing a dramatic improvement in OER activity. The exfoliated surfaces remain stable in OER catalysis, as shown by an in-operando ICP-OES study. The unprecedented OER activation of the synthesized LaNiO3-based materials is related to a close juxtaposition of the theoretical conception of ideal structural motifs and the ability to engender such motifs using a unique synthetic procedure, both principally related to stabilization and pinning of the Ni oxidation state within the local coordination environment of the perovskite structure. © 2021 American Chemical Society. All rights reserved

Dedifferentiation of Immortalized Human Podocytes in Response to Transforming Growth Factor-β: A Model for Diabetic Podocytopathy

OBJECTIVE: Diabetic nephropathy is associated with dedifferentiation of podocytes, losing the specialized features required for efficient glomerular function and acquiring a number of profibrotic, proinflammatory, and proliferative features. These result from tight junction and cytoskeletal rearrangement, augmented proliferation, and apoptosis. RESEARCH DESIGN AND METHODS: Experiments were performed in conditionally immortalized human podocytes developed by transfection with the temperature-sensitive SV40-T gene. Cells were then cultured in the presence of transforming growth factor (TGF)-β1 or angiotensin II in the presence or absence of a selective inhibitor of the TGF-β type I receptor kinase, SB-431542. Gene and protein expression were then examined by real-time RT-PCR and immunofluorescence, and correlated with changes observed in vivo in experimental diabetes. RESULTS: Treatment of cells with TGF-β1 resulted in dynamic changes in their morphology, starting with retraction and shortening of foot processes and finishing with the formation of broad and complex tight junctions between adjacent podocytes. This dedifferentiation was also associated with dose- and time-dependent reduction in the expression of glomerular epithelial markers (nephrin, p-cadherin, zonnula occludens-1) and increased expression of mesenchymal markers (α-smooth muscle actin, vimentin, nestin), matrix components (fibronectin, collagen I, and collagen IV α3), cellular proliferation, and apoptosis. The induction of diabetes in mice was also associated with similar changes in morphology, protein expression, and proliferation in glomerular podocytes. CONCLUSIONS: In response to TGF-β and other TGF-dependent stimuli, mature podocytes undergo dedifferentiation that leads to effacement of foot processes, morphologic flattening, and increased formation of intercellular tight junctions. This simplification of their phenotype to a more embryonic form is also associated with reentry of mature podocytes into the cell cycle, which results in enhanced proliferation and apoptosis. These "pathoadaptive" changes are seen early in the diabetic glomerulus and ultimately contribute to albuminuria, glomerulosclerosis, and podocytopenia

Orthorhombic distortion on Li intercalation in anatase

Published versio

Li Insertion into Li-Ti-O Spinels: Voltammetric and Electrochemical Impedance Spectroscopy Study

The insertion of Li into nanocrystalline Li-Ti-O spinel electrodes was studied using cyclic voltammetry combined with electrochemical quartz crystal microbalance, open circuit potential measurements, and electrochemical impedance spectroscopy studies. Insertion characteristics of spinel were compared with those of titania polymorphs. The insertion into spinel occurs at potential 300 mV more negative to that of insertion into anatase, and about 40 mV positive to that into rutile. The specific capacity (160 mAh/g) is comparable with that of TiO2 polymorphs. Due to the relatively negative potential of the insertion and significantly lower tendency to self-discharge, Li-Ti-O spinel is more convenient for use in a 2 V lithium-ion battery than are other active phases in the Li-Ti-O system. The behavior of the spinel electrodes in equilibrium can be described by the Frumkin insertion isotherm model. The value of interaction parameter, g, below -4 indicates that the insertion process leads to a first-order phase transition. Diffusion coefficient of Li in spinel ranges between 10-15 and 10-16 cm2 s-1; the charge transfer kinetics depends on the redox composition. Heterogeneous rate constant ranges between 1 × 10-8 and 4 × 10-10 cm s-1 that is ca. two orders of magnitude higher than that reported for anatase. © 2001 The Electrochemical Society. [DOI: 10.1149/1.1392321] All rights reserved