Imaging Redox Activity at Bipolar Electrodes by Indirect Fluorescence Modulation

Bipolar electrochemistry (BPE) is nowadays well-known but relatively underexploited and still considered as unconventional. It has been used, among others, in the frame of materials science and most importantly has also found very promising applications in analytical chemistry. Here, we extend this emerging field of analytical applications to the development of a new sensing concept based on indirect BPE. This approach is based on the generation of local pH gradients which will allow detecting indirectly redox-active molecules due to a modulation of the fluorescence intensity in the vicinity of a bipolar electrode

Indirect Bipolar Electrodeposition

Based on the principles of bipolar electrochemistry, localized pH gradients are generated at the surface of conducting particles in solution. This allows the toposelective deposition of inorganic and organic polymer layers via a pH-triggered precipitation mechanism. Due to the intrinsic symmetry breaking of the process, the concept can be used to generate in a straightforward way Janus particles, with one section consisting of deposits obtained from non-electroactive precursors. These indirect electrodeposits, such as SiO₂, TiO₂, or electrophoretic paints, can be further used as an immobilization matrix for other species like dyes or nanoparticles, thus opening promising perspectives for the synthesis of a variety of bifunctional objects with a controlled shape

Mechanosynthesis of Solid Electrolytes: Preparation, Characterization, and Li Ion Transport Properties of Garnet-Type Al-Doped Li₇La₃Zr₂O₁₂ Crystallizing with Cubic Symmetry

Various polycrystalline samples of Al-doped garnet-like Li₇La₃Zr₂O₁₂ crystallizing with cubic symmetry were synthesized from the binary oxides Li₂O, ZrO₂, Al₂O₃, and La₂O₃. The synthesis of phase pure samples was carried out following a two-step preparation route. It consists of an activation step by high-energy ball milling and a subsequent annealing step at elevated temperatures. The synthesis route chosen allows the precise adjustment of the cationic ratios, leading to a garnet which is best described by the formula Li_{7–3<i>x</i>+<i>z</i>}Al_{<i>x</i>+<i>y</i>+<i>z</i>}La_3–<i>y</i>Zr_2–<i>z</i>O₁₂. As confirmed by X-ray powder diffraction and ²⁷Al magic angle spinning nuclear magnetic resonance (NMR), at low Al concentrations the incorporated Al³⁺ ions act as an aliovalent dopant by replacing three Li⁺ ions. However, with increasing Al content, La³⁺ and Zr⁴⁺ ions are progressively replaced by Al ions. It turned out that, in particular, the substitution of La³⁺ and Zr⁴⁺ with Al³⁺ ions stabilizes the cubic modification of the garnet and greatly affects the corresponding Li ion dynamics. The latter has been probed by both impedance and ⁷Li NMR spectroscopy. The high ion conductivity (10^–4 S cm^–1 at 293 K) found does not only depend on the stoichiometry and the annealing conditions chosen but also on the exact kind of Al distribution on the different sites in Li₇La₃Zr₂O₁₂

Electropolymerization of Polypyrrole by Bipolar Electrochemistry in an Ionic Liquid

Bipolar electrochemistry has been recently explored for the modification of conducting micro- and nanoobjects with various surface layers. So far, it has been assumed that such processes should be carried out in low-conductivity electrolytes in order to be efficient. We report here the first bipolar electrochemistry experiment carried out in an ionic liquid, which by definition shows a relatively high conductivity. Pyrrole has been electropolymerized on a bipolar electrode, either in ionic liquid or in acetonitrile. The resulting polymer films were characterized by scanning electron microscopy and by contact profilometry. We demonstrate that the films obtained in an ionic liquid are thinner and smoother than the films synthesized in acetonitrile. Furthermore, a well-defined band of polypyrrole can be obtained in ionic liquid, in contrast to acetonitrile for which the polypyrrole film is present on the whole anodic part of the bipolar electrode

Structural Stability Diagram of ALnP₂S₆ Compounds (A = Na, K, Rb, Cs; Ln = Lanthanide)

Thiophosphate compounds have been studied extensively in the past for their rich structural variations and for a large variety of interesting properties. Here, we report 11 new phases with the composition ALnP₂S₆ (A = Na, K, Rb, Cs; Ln = lanthanide). These new thiophosphates crystallize in four different structure types, with the space groups <i>Fdd</i>2, <i>P</i>1̅, <i>P</i>2₁, and <i>P</i>2₁/<i>c</i>, respectively. All phases are insulating and the calculated band gaps range between 3 eV and 3.5 eV. Magnetic measurements on the compounds with open f-shells show paramagnetic behavior and magnetic moments that match the expected free ion values of the respective lanthanide cations. We present a structural stability phase diagram for the ALnP₂S₆ family of compounds, which reveals a clear relationship between ionic radii and the preferred crystal structure, as well as stability regions to form ALnP₂S₆-type phases

Additional file 1: Table S1. of Multiscale positive feedbacks contribute to unidirectional gastric disease progression induced by helicobacter pylori infection

Model equations and parameters. (DOCX 32 kb

Wireless Synthesis and Activation of Electrochemiluminescent Thermoresponsive Janus Objects Using Bipolar Electrochemistry

In this work, bipolar electrochemistry (BPE) is used as a dual wireless tool to generate and to activate a thermoresponsive electrochemiluminescent (ECL) Janus object. For the first time, BPE allows regioselective growth of a poly­(<i>N</i>-isopropylacrylamide) (pNIPAM) hydrogel film on one side of a carbon fiber. It is achieved thanks to the local reduction of persulfate ions, which initiate radical polymerization of NIPAM. By controlling the electric field and the time of the bipolar electrochemical reactions, we are able to control the length and the thickness of the deposit. The resulting pNIPAM film is found to be swollen in water at room temperature and collapsed when heated above 32 °C. We further incorporated a covalently attached ruthenium complex luminophore, Ru­(bpy)₃²⁺, in the hydrogel film. In the second time, BPE is used to activate remotely the electrogenerated chemiluminescence (ECL) of the Ru­(bpy)₃²⁺ moieties in the film. We take advantage of the film responsiveness to amplify the ECL signal. Upon collapse of the film, the ECL signal, which is sensitive to the distance between adjacent Ru­(bpy)₃²⁺ centers, is strongly amplified. It is therefore shown that BPE is a versatile tool to generate highly sophisticated materials based on responsive polymers, which could lead to sensitive sensors

Electrokinetic Assembly of One-Dimensional Nanoparticle Chains with Cucurbit[7]uril Controlled Subnanometer Junctions

One-dimensional (1D) nanoparticle chains with defined nanojunctions are of strong interest due to their plasmonic and electronic properties. A strategy is presented for the assembly of 1D gold-nanoparticle chains with fixed and rigid cucurbit­[<i>n</i>]­uril-nanojunctions of 9 Å. The process is electrokinetically accomplished using a nanoporous polycarbonate membrane and controlled by the applied voltage, the nanoparticle/CB­[<i>n</i>] concentration ratio, time and temperature. The spatial structure and time-resolved analysis of chain plasmonics confirm a growth mechanism at the membrane nanopores

Copper Selenidophosphates Cu₄P₂Se₆, Cu₄P₃Se₄, Cu₄P₄Se₃, and CuP₂Se, Featuring Zero‑, One‑, and Two-Dimensional Anions

Five new compounds in the Cu/P/Se phase diagram have been synthesized, and their crystal structures have been determined. The crystal structures of these compounds comprise four previously unreported zero-, one-, and two-dimensional selenidophosphate anions containing low-valent phosphorus. In addition to two new modifications of Cu₄P₂Se₆ featuring the well-known hexa­selenido­hypodiphosphate­(IV) ion, there are three copper selenidophosphates with low-valent P: Cu₄P₃Se₄ contains two different new anions, (i) a monomeric (zero-dimensional) selenidophosphate anion [P₂Se₄]^4– and (ii) a one-dimensional selenidophosphate anion [P(−Se)]−∞1, which is related to the well-known gray-Se-like [P]−∞1 Zintl anion. Cu₄P₄Se₃ contains one-dimensional [P4(−Se)2]2−∞1 polyanions, whereas CuP₂Se contains the 2D selenidophosphate [P2(−Se)]−∞2 polyanion. It consists of charge-neutral CuP₂Se layers separated by a van der Waals gap which is very rare for a Zintl-type phase. Hence, besides black P, CuP₂Se constitutes a new possible source of 2D oxidized phosphorus containing layers for intercalation or exfoliation experiments. Additionally, the electronic structures and some fundamental physical properties of the new compounds are reported. All compounds are semiconducting with indirect band gaps of the orders of around 1 eV. The phases reported here add to the structural diversity of chalcogenido phosphates. The structural variety of this family of compounds may translate into a variety of tunable physical properties