Oxidative Electropolymerization Research Articles

Laminated Cell Properties of Lithium Sulfur Battery Using Polypyrrole Modified High Sulfur Loading Cathode with Comparing Al Foil and 3D Foam Current Collectors

In order to solve the problem of polysulfide dissolution into the electrolyte on sulfur-based cathodes, we have proposed a novel method to coat a sulfur cathode with Li+ permselective polypyrrole (PPy) by oxidative electropolymerization. The PPy coated S/KB (PPy-S/KB) cathode demonstrated relatively high specific capacity for 300 cycles stably with coulomb efficiency more than 97% in a coin cell [PPy-S/KB(S loading = 0.5 mg cm2) // 1.0 M LiTFSI DME/DOL (1:1 vol.) // Li] [1,2]. However, to increase energy density further, it is essential to increase sulfur-loading in the cathode. As increasing of sulfur-loading, lower PPy resistance is required to respond high current density.In this study, sulfur cathodes with sulfur-loadings of 1 mg cm-2, 2.5 mg cm-2, 5 mg cm-2 with Al foil current collectors and sulfur-loadings of 5 mg cm-2, 10 mg cm-2 and 15 mg cm-2 with 3D Al foam current collectors were prepared. The S/KB composite slurry was prepared by mixing 96.5 wt. of the S/KB composite (S/KB=6/4 by wt.) and 3.5 wt. of CMC/SBR. The slurry was applied to Al foil or Al foam to have an arbitrary sulfur-loading. PPy was coated on the cathode by using lithium-glyme equimolar ratio complex (LiTFSI: triglyme (1: 1, mol) + LiTFSI: monoglyme (1: 2, mol) (1: 1, vol.)) as a polymerization bath and the same technique as in our previous report [1,2]. Stacked laminated cells consist of 20*20 mm2 S/KB cathode with/without PPy, 1M LiTFSI DME/DOL (1/1 vol.) as electrolyte and Li foil as anode were prepared (E/S was 5-35).Fig. 1 shows the relationship between the sulfur-loading and the discharge capacity density using Al foil or 3D Al foam. Although the discharge capacity density decreased when sulfur-loading was increased to 5 mg cm-2 with Al foil (E/S=7), a high discharge capacity density of 1190 mAh/g-sulfur was maintained even when S loading was increased to 15 mg cm-2 with 3D Al foam (E/S=5). In the case of Al foil current collector, the discharge capacity density decreased with an increase in the sulfur loading would be caused by decreased sulfur utilization with longer paths of Li ions. On the other hand, since 3D Al foam has a better path for Li ions and electrons than a normal coated electrode, a high sulfur utilization was maintained even with a high sulfur-loading. Fig. 2 shows a charge/discharge curve of sulfur-loading of 10 mg cm2 with PPy coating at 0.01 C. Overcharging due to polysulfide dissolution was not observed even in DME/DOL electrolyte by the PPy coating, and a high discharge capacity of 1248 mAh/g-sulfur was achieved (E/S=9), while without PPy coationg, polysulfide dissolution and less discharge capacity were observed. It was confirmed that the PPy coating suppressed the dissolution of sulfur into the electrolyte and increased the utilization of sulfur, thereby slightly increasing the discharge capacity as compared to that without PPy coating. We will report the rate characteristics and cycle characteristics of laminated cells with various sulfur-loadings, PPy film thicknesses, and conductive additives.

Synthesis and characterization of terthiophene bearing stable radicals

The synthesis and characterization of a new terthiophene bearing stable radical II is described. Through a cross coupling reaction between 2-tributylstannylthiophene and 6-(2,5-dibromo-thiophene-3-yl)pyridine-2-carboxaldehyde (2), 6-[2,2′:5′,2″]terthiophen-3′-ylpyridine-2-carboxaldehyde (3) was prepared. The condensation of 3 with 2, 4-diisopropylcarbonohydrazide bis-hydrochloride affords the heterocyclic tetrazane (4), which was oxidized with 1,4-benzoquinone to form the stable radical II. II characterized by IR, ESR, and cyclic voltammetry. Oxidative electropolymerization of II and its precursor 4 at oxidation peak potential of the terthiophene using cyclic voltammetric scans produces radical functionalized polyterthiophene on a platinum electrode (poly(II)-Pt).

Spin-Dependent Enantioselective Electropolymerization

The electro-oxidative polymerization of an enantiopure chiral 3,4-ethylenedioxythiophene monomer, performed using spin-polarized currents, is shown to depend on the electron spin orientation. The spin-polarized current is shown to influence the initial nucleation rate of the polymerization reaction. This observation is rationalized in the framework of the chiral-induced spin selectivity effect.

Electropolymerization Triggered in Situ Surface Modification of Electrode Interphases: Alleviating First-Cycle Lithium Loss in Silicon Anode Lithium-Ion Batteries

We report on interphase modification by in situ generated protons (H+) via electropolymerization. The protons are released from oxidative electropolymerization of indole-3-carboxylic acid (InAc) us...

Flexible Energy Storage Device Based on Poly(N-phenylglycine), an Incentive-Energy Pseudocapacitive Conducting Polymer, and Electrochemically Exfoliated Graphite Sheets

Poly(N-phenylglycine) (PNPG), an original pseudocapacitive conjugative conducting polymer (CP), was synthesized by the electro-oxidative polymerization method. The synthesis process involves in sit...

Asymmetric reactions induced by electron spin polarization.

Essential aspects of the chiral induced spin selectivity (CISS) effect and their implications for spin-controlled chemistry and asymmetric electrochemical reactions are described. The generation of oxygen through electrolysis is discussed as an example in which chirality-based spin-filtering and spin selection rules can be used to improve the reaction's efficiency and selectivity. Next the discussion shifts to illustrate how the spin selectivity of chiral molecules (CISS properties) allows one to use the electron spin as a chiral bias for inducing asymmetric reactions and promoting enantiospecific processes. Two enantioselective electrochemical reactions that have used polarized electron spins as a chiral reagent are described; enantioselective electroreduction to resolve an enantiomer from a racemic mixture and an oxidative electropolymerization to generate a chiral polymer from achiral monomers. A complementary approach that has used spin-polarized, but otherwise achiral, molecular films to enantiospecifically associate with one enantiomer from a racemic mixture is also discussed. Each of these reaction types use magnetized films to generate the spin polarized electrons and the enantiospecificity can be selected by choice of the magnetization direction, North pole versus South pole. Possible paths for future research in this area and its compatibility with existing methods based on chiral electrodes are discussed.

Electropolymerizable N-heterocyclic carbene complexes of Rh and Ir with enantiotropic polymorphic phases.

New Rh (1) and Ir (2) complexes of an N-heterocyclic carbene (NHC) featuring a terthiophene backbone were synthesized. Single crystal X-ray diffraction studies of 1 and 2 at 100 K and 298 K respectively, revealed two enantiotropic polymorphic phases with similar lattice parameters for each compound. The transition temperature between two crystalline forms for each compound was determined by measuring the percentage of reflections with a different space group ranging from 100 K to 298 K. Both 1 and 2 were also found to catalyze the hydrogen transfer reaction. The conducting metallopolymers poly-1 and poly-2 were synthesized from oxidative electropolymerization of 1 and 2, respectively, in CH2Cl2 electrolyte solution on indium tin oxide-(ITO) coated glass. The electrochromic properties of synthesized conducting metallopolymers were studied by UV-vis-NIR spectroelectrochemistry.

Selenophene-containing heterotriacenes by a C-Se coupling/cyclization reaction.

A new novel family of tricyclic sulfur and/or selenium-containing heterotriacenes 2–4 with an increasing number of selenium (Se) atoms is presented. The heterotriacene derivatives were synthesized in multistep synthetic routes and the crucial cyclization steps to the stable and soluble fused systems were achieved by copper-catalyzed C–S and C–Se coupling/cyclization reactions. Structures and packing motifs in the solid state were elucidated by single crystal X-ray analysis and XRD powder measurements. Comparison of the optoelectronic properties provides interesting structure–property relationships and gives valuable insights into the role of heteroatoms within the series of the heterotriacenes. Electrooxidative polymerization led to the corresponding poly(heterotriacene)s P2–P4.

Cascade‐Type Prelithiation Approach for Li‐Ion Capacitors

AbstractAn industry‐relevant method for pre‐lithiation of lithium‐ion capacitors to balance the first charge irreversibility is demonstrated, which addresses the prime bottleneck for their market integration. Based on a composite positive electrode that integrates pyrene monomers and an insoluble lithiated base, Li3PO4, a “cascade‐type” process involving two consecutive irreversible reactions is proposed: i) oxidative electropolymerization of the pyrene moieties releases electrons and protons; ii) protons are captured by Li3PO4 and exchanged for a stoichiometric amount of Li+ into the electrolyte. (1H, 19F, and 31P) NMR spectroscopy, operando X‐ray diffraction, and Raman spectroscopy support this mechanism. By decoupling the irreversible source of lithium ions from electrons, the cascade‐type pre‐lithiation allows the simultaneous enhancement of the capacity of the positive electrode, thanks to p‐doping of the resulting polymer. Remarkably, the proton scavenging properties of Li3PO4 also boost the polymerization process, which enables a 16% increase in capacity without detrimental effect on power properties and cyclability. Full cells integrating a cheap carbon black based negative electrode, show much‐improved capacity of 17 mAh g‐1electrodes (44 F g‐1electrodes, 3–4.4 V) and excellent stability over 2200 cycles at 1 A g‐1. Thanks to its versatile chemistry and flexibility this approach in principle can be applied to any kind of ion‐battery.

Two-phase bipolar electrografting

Bipolar electrochemistry is a wireless technique by which surface modifications at the extremities of a conducting object can be accomplished. In this study a new methodology for doing simultaneous electrografting of two different organic films at each end of a gold substrate is reported. A two-phase system consisting of an aqueous and an organic phase is developed to separate the two grafting agents that otherwise would react to form a non-grafting species. The surface modifications are achieved by the simultaneous electrografting of an aryldiazonium salt and a primary alkylamine, which are grafted by reduction and oxidation, respectively. The breadth and thicknesses of the grafted films depend on i.a. the electrical field in the solution, which easily is altered by changing the applied voltage between the feeder electrodes. To demonstrate that the system is not limited to electrografting, the oxidative electropolymerization of thiophene at the anodic end of the electrode was carried out as well. Finally, bipolar experiments using a diazonium salt and thiophene in the same phase were conducted.

Enhanced Bio-Electrochemical Reduction of Carbon Dioxide by Using Neutral Red as a Redox Mediator.

Microbial electrosynthetic cells containing Methylobacterium extorquens were studied for the reduction of CO2 to formate by direct electron injection and redox mediator‐assisted approaches, with CO2 as the sole carbon source. The formation of a biofilm on a carbon felt (CF) electrode was achieved while applying a constant potential of −0.75 V versus Ag/AgCl under CO2‐saturated conditions. During the biofilm growth period, continuous H2 evolution was observed. The long‐term performance for CO2 reduction of the biofilm with and without neutral red as a redox mediator was studied by an applied potential of −0.75 V versus Ag/AgCl. The neutral red was introduced into the systems in two different ways: homogeneous (dissolved in solution) and heterogeneous (electropolymerized onto the working electrode). The heterogeneous approach was investigated in the microbial system, for the first time, where the CF working electrode was coated with poly(neutral red) by the oxidative electropolymerization thereof. The formation of poly(neutral red) was characterized by spectroscopic techniques. During long‐term electrolysis up to 17 weeks, the formation of formate was observed continuously with an average Faradaic efficiency of 4 %. With the contribution of neutral red, higher formate accumulation was observed. Moreover, the microbial electrosynthetic cell was characterized by means of electrochemical impedance spectroscopy to obtain more information on the CO2 reduction mechanism.

Electrochromism in Electropolymerized Films of Pyrene-Triphenylamine Derivatives.

Two star-shaped multi-triphenylamine derivatives 1 and 2 were prepared, where 2 has an additional phenyl unit between a pyrene core and surrounding triphenylamine units. The oxidative electropolymerization of 1 and 2 occurred smoothly to give thin films of polymers P1 and P2. The electrochemistry and spectroelectrochemistry of P1 and P2 were examined, showing two-step absorption spectral changes in the near-infrared region. The electrochromic properties, including contrast ratio, response time, and cyclic stability of P1 and P2 were investigated and compared. Thin film of P2 displays slightly better electrochromic performance than P1, with a contrast ratio of 45% at 1475 nm being achieved.

Efficiency of Pyrrole Electropolymerization under Various Conditions

The electrooxidative polymerization of pyrrole on the surface of a glassy carbon electrode was studied, while varying the solvent, the type and concentration of supporting electrolyte, redox mediator addition to the polymerization medium, and hydrodynamic conditions. The efficiency of polymerization was determined as the ratio of the charge of the redox response of the polymer film under the standard conditions to the total charge of film formation in the monomer solution. The above factors were varied to determine the conditions that allow minimization of the ratio in order to obtain the highest yield of the polymer product. This was achieved by using a combination of a redox mediator addition with active stirring of solution.

Potentiometric evaluation of antioxidant capacity using polyoxometalate-immobilized electrodes

The voltammetric behaviour of polyoxometalates (POMs) is greatly affected by acid and solvent conditions. POMs can be immobilized on an electrode surface by various cationic conducting polymers prepared via in situ electro-oxidative polymerization. In the present study, the effects of acid and organic solvent concentrations on POM immobilization on the surface of a glassy carbon electrode (GCE) were investigated with cyclic voltammetry. Several Keggin-type POMs, such as [PMo12O40]3−, [PVMo11O40]4−, [PVW11O40]4− and [SVMo11O40]3−, were examined with three types of conducting polymers, polypyrrole (PPy), poly(3,4‑ethylenedioxythiophene) (PEDOT) and polyaniline (PAni). In addition, the voltammetric behaviour of the POM-immobilized electrodes was investigated under various conditions. Finally, the most appropriate POM-immobilized electrode was selected as a redox probe to potentiometrically evaluate antioxidant activity. The antioxidant activities of several typical antioxidants contained in food and beverages were evaluated using an appropriate PMo12O40-immobilized electrode under the optimized conditions, and the results were compared with those obtained from two well-known spectroscopic methods: the oxygen radical absorbance capacity (ORAC) and 2,2‑diphenyl‑1‑picrylhydrazyl (DPPH) radical assays.

Electrochemical Atomic Force Microscopy and First-Principles Calculations of Ferriprotoporphyrin Adsorption and Polymerization.

The adsorption and subsequent electrooxidative polymerization of ferriprotoporphyrin IX chloride (hemin; FePPCl) was investigated on highly ordered pyrolytic graphite, glassy carbon, and polycrystalline Pt electrodes using electrochemical atomic force microscopy, first-principles calculations, and cyclic voltammetry. Hemin was shown to readily adsorb to all three surfaces; however, it was more continuous over the carbon surfaces compared to the Pt surface. This disparity in adsorption appears to be a major contributing factor to differences observed between the electrodes following hemin electropolymerization. Despite differences in roughness and morphology, hemin polymerized as a continuous layer over each electrode surface. Periodic density functional theory calculations were used to model FePP (without Cl) on both the Pt(111) and graphite surfaces using the vdW-DF-optPBE functional to account for the dispersion interactions. Our calculations suggest that the FePP molecule chemisorbs to the Pt surface while at the same time exhibiting intramolecular hydrogen bonding between the carboxylic acid groups, which are extended away from the surface. In contrast to FePP-Pt chemisorption, FePP was found to physisorb to graphite. The preferred spin state upon adsorption was found to be S = 2 on Pt(111), whereas on graphite, the high and intermediate spin states were nearly isoenergetic. Additionally, gas-phase calculations suggest that much of the surface roughness observed microscopically for the polymerized porphyrin layer may originate from the nonparallel stacking of porphyrin molecules, which interact with each other by forming four intermolecular hydrogen bonds and through dispersion interactions between the stacked porphyrin rings. Regardless of polymer thickness, the underlying electrode appears to be able to participate in at least some redox processes. This was observed for the hemin-polymerized Pt electrode using the 2H+/H2 redox couple and was suspected to be due to some Pt surface atoms not being specifically coordinated to the hemin molecules and therefore available to react with H+ that was small enough to diffuse through the polymer layer.

O-Carborane, Ferrocene, and Phthalocyanine Triad for High-Mobility Organic Field-Effect Transistors.

An unsymmetrical zinc phthalocyanine with ferrocenylcarborane linked to the phthalocyanine ring through a phenylethynyl spacer was designed for organic field-effect transistor (OFET). The unsymmetrical phthalocyanine derivatives were characterized using a wide range of spectroscopic and electrochemical methods. In particular, the ferrocenylcarborane structure was unambiguously revealed based on the single-crystal X-ray diffraction analysis. In-depth investigations of the electrochemical properties demonstrated that the ferrocenylcarborane insertion extended the electrochemical character of ferrocenylcarborane-substituted phthalocyanine (7). Moreover, in the anodic potential scans, the oxidative electropolymerization of etynylphthalocyanine (6) and 7 was recorded. To clarify the effect of the insertion of ferrocenylcarborane (2) on the field-effect mobility, solution-processed films of 2, 6, and 7 were used as an active layer to fabricate the bottom-gate top-contact OFET devices. An analysis of the output and transfer characteristics of the fabricated devices indicated that the phthalocyanine derivative functionalized with ferrocenylcarborane moiety has great potential in the production of high-mobility OFET.

Prevention of redox shuttle using electropolymerized polypyrrole film in a lithium–oxygen battery

Among the recent advancements in lithium–oxygen (Li–O2) chemistries, redox mediators (RMs) have been revealed to play a significant role in decreasing overpotential on charging and in improving cycling performance. However, an intrinsic problem is redox shuttle of RMs, which leads to degraded RM utilization and induces the accumulation of discharge products on the cathode surface; this remains a significant issue in the current battery cell configuration (Li anode/separator/cathode). To address this detrimental problem, herein we propose a novel Li–O2 cell incorporating a freestanding electropolymerized polypyrrole (PPy) film for the restriction of the redox-shuttle phenomenon of lithium iodide (Li anode/separator/PPy film/cathode). In this study, a PPy film, which is prepared through oxidative electropolymerization using an ionic liquid of 1-methyl-1-butylpyrrolidinium mixed with pyrrole and lithium bis(trifluoromethanesulfonyl)imide, is introduced between the cathode and the separator. From the charge–discharge voltage profile, it is confirmed that the PPy film suppresses the diffusion of the oxidized I3− to the Li anode, while allowing Li ion transport. Secondary scanning electron microscope measurements confirm that the chemical reactions between I3− and Li2O2 are facilitated by the presence of the PPy film because I3− remains near the cathode surface during the charging process. As a result, the cycling performance in the Li–O2 cells with PPy film exhibits a cycling life four times as long as that of the Li–O2 cells without PPy film.

Azulene-ethylenediaminetetraacetic acid: A versatile molecule for colorimetric and electrochemical sensors for metal ions

A new synthesized molecular receptor, 2,2'-(ethane-1,2-diylbis((2-(azulen-2-ylamino)-2-oxoethyl)azanediyl))diacetic acid (L) has been used as building block for the development of new colorimetric and electrochemical sensors for metal ions complexation. The monomer L shows a high selectivity towards mercury ions among other cations, as highlighted by naked eye and UV–Vis spectra. The oxidative electropolymerization of L on glassy carbon electrodes lead to complexing polyL coated electrodes. They have been characterized by electrochemical techniques, their surface morphology and topography being evaluated by scanning electron microscopy and atomic force microscopy. These new modified electrodes show the ability to complex metal ions using chemical preconcentration-anodic stripping voltammetry technique.

Near-IR electrochromism of the electropolymerization film prepared from a cyclometalated dinuclear Pt(II) complex

The cyclometalated dinuclear platinum acetylide with a 9,9-dioctylfluorene spacer and two terminal triphenylamine groups has been successfully synthesized and characterized by 1H NMR, 13C NMR and MALDI-TOF MS. The active triphenylamine groups efficiently trigger the oxidative electropolymerization process to form a reddish-orange film on the working Pt and ITO electrodes by cyclic voltammetry. The compact film shows a polyaniline-like AC impedance behavior and an inverse dependence of AC impedance on its thickness. As a result of switching of the MLCT/ICT and dication absorption transitions between 0 and +1.8 V, this metallopolymer film exhibits the near-IR electrochromism with significant optical contrast ratio (ΔT%=78.3% at λ=775nm), comparative response time (3.8s for the coloration step and 11.0s for the bleaching step) and high anodic coloration efficiency (CE=208.3C−1·cm2).

Synthesis and electropolymerization properties of new axially substituted subphthalocyanines bearing polymerizable 2-[4-({(1E)-[4-(dimethylamino,diethylamino)phenyl]methylene}amino)phenyl]ethoxy groups

New subphthalocyanines were synthesized by threatening 2-[4-({(1E)-[4-(dimethylamino)phenyl]methylene}amino)phenyl]ethanol 2 and 2-[4-({(1E)-[4-(diethylamino)phenyl]methylene}amino)phenyl]ethanol 3 with excess of boron subphthalocyanine chloride in toluene. The subphthalocyanines containing 2-[4-({(1E)-[4-(dimethylamino)phenyl]methylene}amino)phenyl]ethoxy and 2-[4-({(1E)-[4-(diethylamino)phenyl]methylene}amino)phenyl]ethoxy substituents located at the axial positions of macrocycle. The novel subphthalocyanines were characterized by standard spectroscopy methods. Subphthalocyanines were decorated with electropolymerizable 2-[4-({(1E)-[4-(dimethylamino)phenyl]methylene}amino)phenyl]ethoxy and 2-[4-({(1E)-[4-(diethylamino)phenyl]methylene}amino)phenyl]ethoxy substituents. Synthesized subphthalocyanines were electrochemically characterized with voltammetry techniques. Voltammetric analyses indicated that subphthalocyanines gave ring based reduction processes. During oxidation reaction, subphthalocyanines were coated on the platinum electrode surface with oxidative electropolymerization reactions.