Electrochemically activated MnO as a cathode material for sodium-ion batteries

Besides classical electrode materials pertaining to Li-ion batteries, recent interest has been devoted to pairs of active redox composites having a redox center and an intercalant source. Taking advantage of the NaPF₆ salt decomposition above 4.2 V, we extrapolate this concept to the electrochemical in situ preparation of F-based MnO composite electrodes for Na-ion batteries. Such electrodes exhibit a reversible discharge capacity of 145 mAh g^− 1 at room temperature. The amorphization of pristine MnO electrode after activation is attributed to the electrochemical grinding effect caused by substantial atomic migration and lattice strain build-up upon cycling.     

Electropolymerization of Metallophthalocyanines Carrying Redox Active Metal Centers and their Electrochemical Pesticide Sensing Application

In this study, modified electrodes were constructed with the electropolymerization of metallophthalocyanines (MPcs) carrying redox active metal cations and electropolymerizable substituents. Then these electrodes were tested as selective and sensitive electrochemical pesticide sensors. Incorporation of the redox active Co(II) (CoPc(MOR‐NAF)), Cl–Mn(III) (MnPc(MOR‐NAF)), and Ti(IV)O (TiOPc(MOR‐NAF)) metal cations into Pc cavity increased the redox activity of Pc ring. Moreover, redox active and electropolymerizable 5‐{[(1E)‐(4‐morpholin‐4‐ylphenyl)methylene]amino}‐1‐naphthoxy substituents (MOR‐NAF) on the Pc ring triggered coating of the complexes on the electrode surface with the electropolymerization reactions. Therefore, modified electrodes GCE/MPc(MOR‐NAF) were constructed with the electropolymerizations of MPcs. These electrodes illustrated reasonable redox activity and conductivity for the potential applications in different fields of the electrochemical technologies. Pesticide sensing measurements indicated that changing the metal center of the complexes significantly altered their sensing activities. Among the complexes, GCE/CoPc(MOR‐NAF) electrode behaved as the most sensitive and selective electrode and it sensed the parathion with good selectivity and sensitivity. GCE/CoPc(MOR‐NAF) electrode showed a wider linear range (0.075‐5.75 μmoldm⁻³) and smaller LOD (0.025 μmoldm⁻³) and higher sensitivity (3.46 Acm⁻²M⁻¹) for the parathion sensing. Although GCE/TiOPc(MOR‐NAF) electrode also sensed the parathion with a high sensitivity, its selectivity was poor and the linear range of this sensing was very narrow. Differently GCE/Cl–MnPc(MOR‐NAF) electrode only sensed eserine with reasonably sensitivity.     

The study of redox reactions of bisarenechromium complexes by the rotating disk electrode technique: I. Oxidation of bisarenechromium(O) complexes and reduction of bisarenechromium(I) cations

The redox properties of twenty bisarenechromium complexes have been studied by the rotating disk electrode technique in an aprotic solvent (DMSO). The half-wave potentials, E_1/2, have been found to correlate well with the meta-substituent constants. The conclusion is drawn that the electronic effects of substituents are mainly transferred to the reaction centre (the metal atom) by the inductive mechanism. The conjugation of substituents with the coordinated ring is weaker in bisarenechromium complexes than in ferrocene derivatives.     

Voltammetric studies of the activity of an electrode made of a graphite-epoxy composite in redox reactions of ascorbic acid and hydroquinone

The potentials of the anodic peak of ascorbic acid oxidation and the potential differences of anodic and cathodic peaks (ΔE _p) of the hydroquinone/benzoquinone redox system at an electrode made of a graphite-epoxy composite are determined in weakly acidic and neutral supporting electrolytes by direct and cyclic voltammetry. The results obtained are compared with thermodynamic values and with the available values of these parameters at different solid electrodes for the above-mentioned redox systems. The effect of aging of the surface of electrodes made of graphite-epoxy composites on the potentials and peak currents of the anodic oxidation of ascorbic acid are studied. It is demonstrated that the regeneration of the electrode surface by mechanically cutting thin layers is important for reducing the δE _p value of the hydroquinone/benzoquinone redox system down to 28–30 mV in supporting electrolytes with pH 2.0 and 7.0. This value is typical of thermodynamically reversible electrode reactions involving two-electron transfer at 20–25°C.     

A dynamic surface prepared by electrochemical triggering of substituted methoxyphenol-terminated self-assembled monolayers for multi-functional purposes

We devised a methoxyphenol thiol derivative with an electron-withdrawing (–CHO) and an electron-donating (–CH₂OH) substituent for the preparation of a dynamic surface that can be used for multi-functional purposes. This molecule was electrochemically activated to an o-quinone form by the oxidative triggering through demethoxylation, followed by hydroxylation on para position upon potential cycling whose rate depended on the nature of substituents. An electron-withdrawing substituent facilitated nucleophilic addition of water, forming a 1,2,5-trihydroxy form, and only para-hydroquinone underwent a redox reaction. An electron-donating substituent, however, was not able to activate this process, leaving behind only an ortho form. The o-quinone showed catalytic activity toward ascorbic acid and NADH oxidation.     

Gold nanoparticle/alkanedithiol conductive films self-assembled onto gold electrode: Electrochemistry and electroanalytical application for voltammetric determination of trace amount of catechol

This paper describes novel electrochemical properties of gold nanoparticles/alkanedithiol conductive films and their electroanalytical applications for voltammetric determination of trace amount of one kind of environmental pollutants, catechol. The conductive films are prepared by closely packing 12-nm diameter gold nanoparticles (Au-NPs) onto Au electrodes modified with the self-assembled monolayers (SAMs) of alkanedithiols (i.e., HS(CH₂)_nSH, n = 3, 6, 9). The assembly of the Au-NPs onto the SAM-modified electrodes essentially restores the heterogeneous electron transfer between Au substrate and redox species in solution phase that is almost totally blocked by the SAMs and, as a result, the prepared Au-NP/SAM-modified electrodes possess a good electrode reactivity without a remarkable barrier toward the heterogeneous electron transfer. Moreover, the prepared Au-NP/SAM-modified electrodes are found to exhibit a largely reduced interfacial capacitance, compared with bare Au electrode. These electrochemical properties of the Au-NP/SAM-modified electrodes essentially make them very useful for electroanalytical applications, which is illustrated by voltammetric determination of trace amount detection of environmental pollutant, catechol.     

A ‘push-pull’ tropylium-fused aminoporphyrazine

Crossover Linstead macrocyclization of cycloheptatrienylmaleonitrile and (dimethylamino)-maleonitrile gave access to an unsymmetrical (A₃B) porphyrazine bearing six peripheral amino substituents and a fused cycloheptatrienyl ring. Subsequent hydride abstraction gave a tropylium-fused aminoporphyrazine, which contains both strongly electron-donating and withdrawing groups and thus can be labelled as a ‘push-pull’ macrocycle. Detailed structural studies of this novel porphyrazine are described.     

Palladium-catalysed tandem alkenyl- and aryl-C-N bond formation: a cascade N-annulation route to 1-functionalised 7-azaindoles

A series of 3-(2-haloalkenyl)-2-pyridyl-halides undergo consecutive palladium-catalysed inter- and intramolecular amination reactions to deliver a series of 1-functionalised 7-azaindoles. Anilines and amines can be readily employed as the N-nucleophile and incorporation of both electron-donating and electron withdrawing substituents on the pyridine core is possible.     

Effect of Substituents in Catechol Dye Sensitizers on Photovoltaic Performance of Type II Dye‐Sensitized Solar Cells

In order to provide a direction in molecular design of catechol (Cat) dyes for type II dye‐sensitized solar cells (DSSCs), the dye‐to‐TiO₂ charge‐transfer (DTCT) characteristics of Cat dyes with various substituents and their photovoltaic performance in DSSCs are investigated. The Cat dyes with electron‐donating or moderately electron‐withdrawing substituents exhibit a broad absorption band corresponding to DTCT upon binding to TiO₂ films, whereas those with strongly electron‐withdrawing substituents exhibit weak DTCT. This study indicates that the introduction of a moderately electron‐withdrawing substituent on the Cat moiety leads to not only an increase in the DTCT efficiency, but also the retardation of back electron transfer. This results in favorable conditions for the type II electron‐injection pathway from the ground state of the Cat dye to the conduction band of the TiO₂ electrode by the photoexcitation of DTCT bands.     

Optical and redox properties of ruthenium phthalocyanine complexes tuned with axial ligand substituents

The optical and electrochemical properties of the ruthenium phthalocyanine complexes [[(t-Bu)4Pc]Ru(4-Rpy)2], where R = NO2, Me, NH2, and NMe2, are reported. The electron density at the macrocycle may be adjusted using the axial ligand substituents, which have varying electron-donating/withdrawing strengths. Electrochemical data show that the axial pyridine ligand substituents exert significant influence over the phthalocyanine ring-based redox processes. The axial ligands also influence the electronic absorption properties of the complexes with influence also being observed in the electrogenerated oxidized and reduced species.     

Tuning the Photocatalytic Performance of Ruthenium(II) Polypyridine Complexes Via Ligand Modification for Visible-Light-Induced Phosphorylation of Tertiary Aliphatic Amines

Tuning the redox potential of commonly available photocatalyst to improve the catalytic performance or expand its scope for challenging synthetic conversions is an ongoing demand in synthetic chemistry. Herein, the excited state properties and redox potential of commercially available [Ru(bpy)₃]²⁺ photocatalyst were tuned by modifying the structure of the bipyridine ligands with electron-donating/withdrawing units. The visible-light-mediated photoredox phosphorylation of tertiary aliphatic amines was demonstrated under mild conditions. A series of cross-dehydrogenative coupling reactions were performed employing the Ru^II complexes as photocatalyst giving the corresponding α-aminophosphinoxides and α-aminophosphonates via carbon-phosphorus (C−P) bond formation.     

Nickel electrodes as a cheap and versatile platform for studying structure and function of immobilized redox proteins

Practical use of many bioelectronic and bioanalytical devices is limited by the need of expensive materials and time consuming fabrication. Here we demonstrate the use of nickel electrodes as a simple and cheap solid support material for bioelectronic applications. The naturally nanostructured electrodes showed a surprisingly high electromagnetic surface enhancement upon light illumination such that immobilization and electron transfer reactions of the model redox proteins cytochrome b₅ (Cyt b₅) and cytochrome c (Cyt c) could be followed via surface enhanced resonance Raman spectroscopy. It could be shown that the nickel surface, when used as received, promotes a very efficient binding of the proteins upon preservation of their native structure. The immobilized redox proteins could efficiently exchange electrons with the electrode and could even act as an electron relay between the electrode and solubilized myoglobin. Our results open up new possibility for nickel electrodes as an exceptional good support for bioelectronic devices and biosensors on the one hand and for surface enhanced spectroscopic investigations on the other hand.     

Effect of Poly(amine)s on the Redox Properties of Carboxymethylcellulose and Ferrocene‐modified Poly(amine) Layer‐by‐Layer Films

Multilayer films consisting of carboxymethylcellulose (CMC) and ferrocene‐modified poly(ethyleneimine) (Fc‐PEI) or poly(allylamine hydrochloride) (Fc‐PAH) were successfully prepared on a gold electrode to examine their redox properties. The redox current of (Fc‐PEI/CMC)_n film‐coated electrodes increased with the number of layers, while the (Fc‐PAH/CMC)_n film‐coated electrodes exhibited increased response only for the first eight bilayers. The (Fc‐PEI/CMC)_n and (Fc‐PAH/CMC)_n films deposited on the surface of Fc‐free multilayer film‐coated electrodes also showed a redox response. The (PEI/CMC)₅ film‐coated electrode showed redox responses in Fc‐PEI and Fc‐PAH solutions, confirming the uptake of the Fc‐polymers in the inner film. In contrast, the uptake of the Fc‐polymers in the (PAH/CMC)₅ film was severely suppressed, suggesting that different permeability of (PEI/CMC)₅ and (PAH/CMC)₅ films.     

Direct cytochrome c electrochemistry at boron-doped diamond electrodes

Highly boron-doped diamond electrodes are characterized voltammetrically employing Ru(NH₃)₆^3+/2+, Fe(CN)₆^3−/4−, benzoquinone/hydroquinone, and cytochrome c redox systems. The diamond electrodes, which are polished to nanometer finish, are initially `activated' electrochemically and then pretreated by oxidation, reduction, or polishing. All electrodes give reversible cyclic voltammetric responses for the reduction of Ru(NH₃)₆³⁺ in aqueous solution.Redox systems other than Ru(NH₃)₆^3+/2+ show characteristic electrochemical behavior as a function of diamond surface pretreatment. In particular, the horse heart cytochrome c redox system is shown to give reversible voltammetric responses at Al₂O₃ polished boron-doped diamond electrodes. No voltammetric response for cytochrome c is detected at anodically pretreated diamond electrodes. The observations are attributed to preferential interaction of the polished diamond surface with the reactive region of the cytochrome c molecule and low interference due to a lack of protein electrode fouling.     

Triaryl linked donor acceptor dyads for high-performance dye-sensitized solar cells

The effect of changing substituents of organic dyes for their performance on dye-sensitized solar cells (DSSCs) is examined. These dyes consist of an aromatic amine donor group, a cyanoacrylic acid acceptor group, and a triaryl spacer group, while they are linked together by consecutive palladium catalyzed coupling reactions. These materials exhibit strong charge transfer absorption bands in the UV/vis region. Their redox potential levels were estimated by cyclic voltammetry, and found to suit well to the charge flow in DSSCs. Adding electron-donating substituents on the phenyl groups of aromatic amines increased the electron density on the donor groups, therefore reduced the HOMO/LUMO band gap. These dyes were chemisorbed on the surface of nanocrystalline TiO₂, and fabricated into DSSCs through standard operations. For a typical device the maximal monochromatic incident photon-to-current conversion efficiency (IPCE) can reach to 80%, with a short-circuit photocurrent density (J_sc) 16.34 mA cm⁻², an open-circuit photovoltage (V_oc) 0.68 V, and fill factor (FF) 0.55, which corresponds to an overall conversion efficiency of 6.05%.     

Electrochemical,microscopic, and EQCM studies of cathodic electrodeposition of ZnO/FAD and anodic polymerization of FAD films modified electrodes and their electrocatalytic properties

Two kinds of chemically modified electrodes were prepared. In the first type of electrodes, zinc oxide (ZnO) and flavin adenine dinucleotide (FAD) molecules were deposited onto the glassy carbon-, gold-, and SnO₂-coated glass electrodes by using cyclic voltammetry from the bath solution containing aqueous 0.1 M zinc nitrate, 0.1 M sodium nitrate, and 1 × 10⁻⁴ M FAD. It was called as ZnO/FAD modified electrodes. The second type of modified electrode was prepared by the electropolymerization method. Electrochemical polymerization of FAD was carried out from the acidic solution containing 1 × 10⁻⁴ M FAD monomers onto electrode surfaces. This poly(FAD)-modified electrode yields a new redox couple in addition to the monomers redox couple. The influence of the concentrations, pH, and electrocatalytic properties of the ZnO/FAD- and poly(FAD)-modified electrodes are investigated by means of the in situ technique electrochemical quartz–crystal microgravimetry (EQCM) combined with cyclic voltammetry and the ex situ technique scanning electron microscopy. From these studies, it appears that the cathodic deposition of ZnO/FAD-modified electrodes gives only one redox couple, and the anodically polymerized FAD film-modified electrodes gives two reversible redox couples. The pH dependence of the redox responses were investigated and the kinetics of electron transfer was evaluated. In addition, the EQCM technique was employed to follow the deposition process of both kinds of modified electrodes in real time as well as the characteristics of the charge transfer associated with the surface-confined redox-active couples. The electrocatalytic activity of the poly(FAD)-modified electrode towards the reduction of hydrogen peroxide and the oxidation of dopamine and ascorbic acid was explored. The important electrocatalytic properties of poly(FAD)-modified electrode were observed for simultaneous separation of dopamine and ascorbic acid in neutral solution. This poly(FAD)-modified electrode has several advantages than the previously reported FAD-modified electrodes.     

Oligoorganogermanes: Interplay between Aryl and Trimethylsilyl Substituents

Derivatives of main group elements containing element–element bonds are characterized by unique properties due to σ-conjugation, which is an attractive subject for investigation. A novel series of digermanes, Ar₃Ge-Ge(SiMe₃)₃, containing aryl (Ar = p-C₆H₄Me (1), p-C₆H₄F (2), C₆F₅ (3)) and trimethylsilyl substituents, was synthesized by the reaction of germyl potassium salt, [(Me₃Si)₃GeK*THF], with triarylchlorogermanes, Ar₃GeCl. The optical and electronic properties of such substituted oligoorganogermanes were investigated spectroscopically by UV/vis absorption spectroscopy and theoretically by DFT calculations. The molecular structures of compounds 1 and 2 were studied by XRD analysis. Conjugation between all structural fragments (Ge-Ge, Ge-Si, Ge-Ar, where Ar is an electron-donating or withdrawing group) was found to affect the properties.     

Effect of Fluoride Atoms on the Electrochemical Performance of Tetracyanoquinodimethane(TCNQ) Electrodes in Zinc-ion Batteries

Tetracyanoquinodimethane (TCNQ) electrode material has achieved excellent performance in aqueous zinc-ion batteries (AZIBs). However, fundamental understanding about effect of substitutes on electrochemical performance of TCNQ remain unknown. In this work, the effects of fluorine (F) as an electron-absorbing group on the structure, morphology and electrochemical performance of TCNQ and storage mechanism of TCNQ in AZIBs are discussed. Theoretical calculation proves that the introduction of fluorine atoms decreases lowest unoccupied molecular orbital (LUMO) energy of TCNQ thus affect the redox potential. Electrochemical performance of TCNQ/Fluoro-7,7,8,8-tetracyanoquinodimethane (FTCNQ)/2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F₄TCNQ) is evaluated from 25 °C to −20 °C in AZIBs. Results tend out that with the increasing substituents of F on TCNQ molecular, their stability in AZIBs decrease. Dipole moment calculation further shows that the introduction of fluorine atoms is inconducive to the stability of the electrode material in aqueous solution. Ex-situ characterization demonstrate that electron withdrawing groups do not change the REDOX center of TCNQ electrode materials. Our work provides a new thought for the selection of the electrode material in AZIBs.     

Synthesis and Luminescent Properties of s-Tetrazine Derivatives Conjugated with the 4H-1,2,4-Triazole Ring

New derivatives obtained by the combination of unique 1,2,4,5-tetrazine and 4H-1,2,4-triazole rings have great application potential in many fields. Therefore, two synthetic few-step methodologies, which make use of commercially available 4-cyanobenzoic acid (method A) and ethyl diazoacetate (method B), were applied to produce two groups of the aforementioned heterocyclic conjugates. In both cases, the target compounds were obtained in various combinations, by introducing electron-donating or electron-withdrawing substituents into the terminal rings, together with aromatic or aliphatic substituents on the triazole nitrogen atom. Synthesis of such designed systems made it possible to analyze the influence of individual elements of the structure on the reaction course, as well as the absorption and emission properties. The structure of all products was confirmed by conventional spectroscopic methods, and their luminescent properties were also determined.     

Standard rate constants of charge transfer of Nb(V)/Nb(IV) redox pair in equimolar NaCl-KCl melt

Standard rate constants of charge transfer (k _s) on platinum and glassy carbon electrodes for Nb(V)/Nb(IV) redox pair in the NaCl-KCl-K₂NbF₇ melt are determined using the method of cyclic voltammetry in the temperature range of 973 to 1123 K. It is found that k _s increases with increasing temperature and when we pass from glassy carbon to platinum electrode. The “apparent” activation energies of charge transfer are determined; it is shown that the charge transfer between the Nb(V) and Nb(IV) complexes is quasi-reversible and is controlled predominantly by the diffusion.