Electroanalytical Study of Methanol Oxidation and Oxygen Reduction at Carbon Nanohorns‐Pt Nanostructured Electrodes

This work reports a comprehensive electroanalytical study of carbon nanohorns (CNHs) in electrochemical applications. Compared to other types of carbons, the bare CNHs electrode exhibited higher peak current densities and lowest anodic peak‐to‐cathodic peak separation of less than 50 mV for the [Fe(CN)^4?]₆/[Fe(CN)^3?]₆ redox couple. Furthermore, CNHs exhibited excellent electrocatalyst supporting properties for porous Pt film towards methanol oxidation reaction reaching a peak current density of 127 mA cm^?2 or peak current mass activity 184 mA mg_Pt^?1. Regarding oxygen reduction reaction, an onset potential as positive as 0. 77 V vs. Ag/AgCl was achieved with CNHs/porous Pt film.     

Electroconductive Hydrogels: Electrical and Electrochemical Properties of Polypyrrole‐Poly(HEMA) Composites

Composites of inherently conductive polypyrrole (PPy) within highly hydrophilic poly(2‐hydroxyethyl methacrylate)‐based hydrogels (p(HEMA)) have been fabricated and their electrochemical properties investigated. The electrochemical characteristics observed by cyclic voltammetry suggest less facile reduction of PPy within the composite hydrogel compared to electropolymerized PPy, as shown by the shift in the reduction peak potential from ?472 mV for electropolymerized polypyrrole to ?636 mV for the electroconductive composite gel. The network impedance magnitude for the electroconductive hydrogel remains quite low, ca. 100 Ω, even upon approach to DC, over all frequencies and at all offset potentials suggesting retained electronic (bipolaronic) conductivity within the composite. In contrast, sustained application of +0.7 V (vs. Ag/AgCl, 3 M Cl^?) for typically 100 min. (conditioning) to reduce the background amperometric current to <1.0 μA, resulted in complete loss of electroactivity. Nyquist plots suggest that sustained application of such a modest potential to the composite hydrogel results in impedance characteristics that resembles p(HEMA) without evidence of the conducting polymer component. PPy composite gels supported a larger ferrocene monocarboxylate diffusivity (D_appt=7.97×10^?5 cm² s^?1) compared to electropolymerized PPy (D_appt=5.56×10^?5 cm² s^?1), however a marked reduction in diffusivity (D_appt=1.01×10^?5 cm² s^?1) was observed with the conditioned hydrogel composite. Cyclic voltammograms in buffer containing H₂O₂ showed an absence of redox peaks for electrodes coated with PPy‐containing membranes, suggesting possible chemical oxidation of polypyrrole by the oxidant     

Relationship between Carbon Nanotube Structure and Electrochemical Behavior: Heterogeneous Electron Transfer at Electrochemically Activated Carbon Nanotubes

The electrochemical activation of multiwalled carbon nanotubes (MWCNTs) (at potentials of 1.5–2.0 V vs Ag/AgCl for 60–360 s) results in significantly increased rate constants ( ) for heterogeneous electron‐transfer with [Fe(CN)₆]^3?/4? (from 8.34×10^?5 cm s^?1 for as‐received MWCNTs to 3.67×10^?3 cm s^?1 for MWCNTs that were electrochemically activated at 2.0 V for 180 s). The increase in the value of arises from the introduction of wall defects exposing edge planes of the MWCNTs, as observed by high‐resolution TEM. The density of the edge plane defects increases from almost zero (for as‐received MWCNTs) to 3.7 % (for MWCNTs electrochemically activated at 2.0 V for 180 s). High‐resolution X‐ray photoelectron spectroscopy (HR‐XPS), Raman spectroscopy, and electrochemical impedance spectroscopy were used to gain a better understanding of the phenomena. HR‐XPS revealed that the increase in electrochemical activation potential increases the number of oxygen‐containing groups on the surface of carbon nanotubes.     

Alkylation Effects on the Energy Transfer of Highly Vibrationally Excited Naphthalene

The energy transfer of highly vibrationally excited isomers of dimethylnaphthalene and 2‐ethylnaphthalene in collisions with krypton were investigated using crossed molecular beam/time‐of‐flight mass spectrometer/time‐sliced velocity map ion imaging techniques at a collision energy of approximately 300 cm^?1. Angular‐resolved energy‐transfer distribution functions were obtained directly from the images of inelastic scattering. The results show that alkyl‐substituted naphthalenes transfer more vibrational energy to translational energy than unsubstituted naphthalene. Alkylation enhances the V→T energy transfer in the range ?ΔE_d=?100～?1500 cm^?1 by approximately a factor of 2. However, the maximum values of V→T energy transfer for alkyl‐substituted naphthalenes are about 1500～2000 cm^?1, which is similar to that of naphthalene. The lack of rotation‐like wide‐angle motion of the aromatic ring and no enhancement in very large V→T energy transfer, like supercollisions, indicates that very large V→T energy transfer requires special vibrational motions. This transfer cannot be achieved by the low‐frequency vibrational motions of alkyl groups.     

Behavior of Palladium Nanoparticles in the Absence or Presence of Cobalt Tetraaminophthalocyanine for the Electrooxidation of Hydrazine

We report on the electrodeposition of palladium nanoparticles (PdNPs) on a glassy carbon electrode (GCE) and onto a poly‐CoTAPc‐GCE (CoTAPc=cobalt tetraamino phthalocyanine) surface. The electrodes are denoted as PdNPs‐GCE and PdNPs/poly‐CoTAPc‐GCE, respectively. PdNPs/poly‐CoTAPc‐GCE showed the best activity for the oxidation of hydrazine at the lowest potential of ?0.28 V and with the highest currents. The results were further supported by electrochemical impedance spectroscopy (EIS) which showed that there was less resistance to charge transfer for PdNPs/poly‐CoTAPc‐GCE compared to PdNPs‐GCE. The catalytic rate constant for hydrazine oxidation was 6.12×10⁸ cm³ mol^?1 s^?1 using PdNPs/poly‐CoTAPc‐GCE.     

Non-enzymatic analysis of glucose on printed films based on multi-walled carbon nanotubes

We report on the fabrication of an enzyme–free electrochemical sensor for glucose based on a printed film consisting of multi–walled carbon nanotubes (MWCNTs). The MWCNT–based film can be produced by means of a flexographic printing process on a polycarbonate (PC) substrate. The electrochemical response of the MWCNT–based film (referred to as MWCNT–PC) towards the oxidation of glucose at pH 7 was studied by means of cyclic voltammetry and electrochemical impedance spectroscopy. The MWCNT–PC film exhibits substantial electrocatalytic activity towards the oxidation of glucose at an anodic potential of 0.30?V (vs. Ag/AgCl). The findings reveal that the MWCNT–PC film enables non–enzymatic sensing of glucose with a detection limit as low as 2.16?μM and a sensitivity of 1045?μA?mM^?1?cm^?2.

Selective Detection of Dopamine in Presence of Ascorbic Acid by Use of Glassy‐Carbon Electrode Modified with Amino‐β‐Cyclodextrin and Carbon Nanotubes

A glassy carbon electrode modified with per‐6‐amino‐β‐cyclodextrin (β‐CDNH₂) and functionalized single‐walled carbon nanotubes (SWCNT‐COOH) was elaborated. This structure was investigated for the detection of dopamine acid (DA) in presence of ascorbic acid (AA). The sensor behavior was studied by cyclic voltammetry, square wave voltammetry and electrochemical impedance spectroscopy. The analysis results show that the electrode modification with CD derivative improves the sensitivity and selectivity of the DA recognition; the electrochemical response was further improved by introduction of SWCNT‐COOH. The sensor shows good and reversible linear response toward DA within the concentration range of 7×10^?7–10^?4 M with a detection limit of 5×10^?7 M.     

Preparation of a Novel COOH Ion Implantation Sensor and Its Application

A novel ion implantation sensor (DNA/COOH/ITO) based on DNA immobilization in COOH/ITO probe was manufactured for the first time. The surface morphologies of the electrodes were characterized by X‐ray photoelectron spectroscopy (XPS), field‐emission‐scanning electron microscopy (FSEM) and electrochemical methods. In a 0.5 mol/L PBS solution, a sensitive oxidation peak of DNA on the COOH/ITO electrode was obtained by voltammetry. The electrochemical behavior of DNA was studied. And the oxidative peak potential of DNA was +0.400 V (vs. Ag/AgCl). Its peak current was proportional to the concentration of DNA over the range of 1.0×10^?8?1.0×10^?6 mol/L with a detection limit of 5.0×10^?9 mol/L (about 0.5 ng/mL). This sensor was applied to the direct detection of DNA samples.     

Fast Lithium Ion Conduction in Lithium Phosphidoaluminates

Solid electrolyte materials are crucial for the development of high‐energy‐density all‐solid‐state batteries (ASSB) using a nonflammable electrolyte. In order to retain a low lithium‐ion transfer resistance, fast lithium ion conducting solid electrolytes are required. We report on the novel superionic conductor Li₉AlP₄ which is easily synthesised from the elements via ball‐milling and subsequent annealing at moderate temperatures and which is characterized by single‐crystal and powder X‐ray diffraction. This representative of the novel compound class of lithium phosphidoaluminates has, as an undoped material, a remarkable fast ionic conductivity of 3 mS cm^?1 and a low activation energy of 29 kJ mol^?1 as determined by impedance spectroscopy. Temperature‐dependent ⁷Li NMR spectroscopy supports the fast lithium motion. In addition, Li₉AlP₄ combines a very high lithium content with a very low theoretical density of 1.703 g cm^?3. The distribution of the Li atoms over the diverse crystallographic positions between the [AlP₄]^9? tetrahedra is analyzed by means of DFT calculations.     

Spectroelectrochemical Study of N‐Substituted Phenoxazines as Electrochemical Labels of Biomolecules

The electrochemical conversion of N‐substituted phenoxazines (NSP's) bearing a CH₂CH₂? X substitute (where X?OH, COOH, CH₂NH₂, CH₂SO₃H, CH₂NHCOR) was investigated using cyclic voltammetry on a bulk gold electrode and a thin‐layer spectroelectrochemical cell. The electrochemical oxidation of NSP's on the gold electrode was quasi‐reversible and proceeded in a diffusion‐controlled regime. The formal redox potential of NSP's covered the range from 0.39 to 0.45 V vs. SCE. The electrochemical oxidation of NSP's in the thin‐layer spectroelectrochemical cell produced radical cations that showed absorbance at 385, 410 and 530 nm. Electrochemical conversion fitted the general voltammetric current‐potential equation of a reversible wave, whereas electrolysis at constant potential showed a typical Cottrell behavior. Combining of NSP's with a biologically‐relevant theophylline molecule did not change electrochemical and spectral properties of the phenoxazine core. Theophylline enlarged with NSP's demonstrated electrochemical and biocatalytic behavior similar to that of NSP's. The investigated NSP's possess electrochemical and spectral properties that are useful as biomolecular labels for electroanalysis.     

Enhancing effect of boron trifluoride diethyl etherate electrolytes on capacitance performance of electropolymerized poly[poly(<Emphasis Type="Italic">N</Emphasis>-vinyl-carbazole)] films

In this paper, poly[poly(N-vinyl-carbazole)] (PPVK) films electrodeposited in tetrahydrofuran (THF) containing 12 % boron trifluoride diethyl etherate (BFEE) were studied as electrode active material for supercapacitors. The morphology and thermal property were characterized by SEM, atomic force microscopy (AFM), and thermogravimetry (TG), respectively. The electrochemical capacitive behaviors of the PPVK films were also investigated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The electrochemical results showed that the specific capacitance of PPVK films in CH₃CN solution was about 126 mF cm^?2 at 1.5 mA cm^?2 and the capacitance retention was only 14.4 % after 1000 cycles. It was exciting to improve the specific capacitance up to 169.3 mF cm^?2 at 1.5 mA cm^?2 and to make the cyclic stability increase to 81.8 % capacitance retention after 5000 cycles when the equivalent BFEE was added into the CH₃CN solution containing 0.05 M Bu₄NBF₄ electrolyte. These results clearly demonstrated that BFEE was an efficient promoter for the enhancement of the capacitance performance of PPVK films. Therefore, with the help of BFEE electrolyte, the PPVK films have potential application as capacitive materials in high-performance energy storage devices.     

An Unusual Stable Mononuclear MnIII Bis‐terpyridine Complex Exhibiting Jahn–Teller Compression: Electrochemical Synthesis,Physical Characterisation and Theoretical Study

The mononuclear manganese bis‐terpyridine complex [Mn(tolyl‐terpy)₂](X)₃ ( 1 (X)₃; X=BF₄, ClO₄, PF₆; tolyl‐terpy=4′‐(4‐methylphenyl)‐2,2′:6′,2“‐terpyridine), containing Mn in the unusual +III oxidation state, has been isolated and characterised. The 1 ³⁺ ion is a rare example of a mononuclear Mn^III complex stabilised solely by neutral N ligands. Complex 1 ³⁺ is obtained by electrochemical oxidation of the corresponding Mn^II compound 1 ²⁺ in anhydrous acetonitrile. Under these conditions the cyclic voltammogram of 1 ²⁺ exhibits not only the well‐known Mn^II/Mn^III oxidation at E_1/2=+0.91 V versus Ag/Ag⁺ (+1.21 V vs. SCE) but also a second metal‐based oxidation process corresponding to Mn^III/Mn^IV at E_1/2=+1.63 V (+1.93 V vs. SCE). Single crystals of 1 (PF₆)₃?2 CH₃CN were obtained by an electrocrystallisation procedure. X‐ray analysis unambiguously revealed its tetragonally compressed octahedral geometry and high‐spin character. The electronic properties of 1 ³⁺ were investigated in detail by magnetic measurements and theoretical calculations, from which a D value of +4.82 cm^?1 was precisely determined. Density functional and complete active space self consistent field ab initio calculations both correctly predict a positive sign of D, in agreement with the compressed tetragonal distortion observed in the X‐ray structure of 1 (PF₆)₃?2 CH₃CN. The different contributions to D were calculated, and the results show that 1) the spin–orbit coupling part (+2.593 cm^?1) is predominant compared to the spin–spin interaction (+1.075 cm^?1) and 2) the excited triplet states make the dominant contribution to the total D value.     

Electrochemical Treatment for Effectively Tuning Thermoelectric Properties of Free‐Standing Poly(3‐methylthiophene) Films

The degree of oxidation of conducting polymers has great influence on their thermoelectric properties. Free‐standing poly(3‐methylthiophene) (P3MeT) films were prepared by electrochemical polymerization in boron trifluoride diethyl etherate, and the fresh films were treated electrochemically with a solution of propylene carbonate/lithium perchlorate as mediator. The conductivity of the resultant P3MeT films depends on the doping level, which is controlled by a constant potential from ?0.5 to 1.4 V. The optimum electrical conductivity (78.9 S cm^?1 at 0.5 V) and a significant increase in the Seebeck coefficient (64.3 μV K^?1 at ?0.5 V) are important for achieving an optimum power factor at an optimal potential. The power factor of electrochemically treated P3MeT films reached its maximum value of 4.03 μW m^?1 K^?2 at 0.5 V. Moreover, after two months, it still exhibited a value of 3.75 μW m^?1 K^?2, and thus was more stable than pristine P3MeT due to exchange of doping ions in films under ambient conditions. This electrochemical treatment is a significant alternative method for optimizing the thermoelectric power factor of conducting polymer films.     

Magnesium Cyanide or Isocyanide?

Preference for the binding mode of the CN^? ligand to Mg (Mg?CN vs. Mg?NC) is investigated. A monomeric Mg complex with a terminal CN ligand was prepared using the dipyrromethene ligand ^MesDPM which successfully blocks dimerization. While reaction of (^MesDPM)MgN(SiMe₃)₂ with Me₃SiCN gave the coordination complex (^MesDPM)MgN(SiMe₃)₂?NCSiMe₃, reaction with (^MesDPM)Mg(nBu) led to (^MesDPM)MgNC?(THF)₂. A Mg?NC/Mg?CN ratio of ≈95:5 was established by crystal‐structure determination and DFT calculations. IR studies show absorbances for CN stretching at 2085 cm^?1 (Mg?NC) and 2162 cm^?1 (Mg?CN) as confirmed by ¹³C labeling. In solution and in the solid state, the CN ligand rotates within the pocket. The calculated isomerization barrier is only 12.0 kcal mol^?1 and the ¹³C NMR signal for CN decoalesces at ?85 °C (Mg?NC: 175.9 ppm, Mg?CN: 144.3 ppm). Experiment and theory both indicate that Mg complexes with the CN^? ligand should not be named cyanides but are more properly defined as isocyanides.     

Electrochemical Study of Schiff Bases by Means of Self‐Assembled Monolayers

In this paper, Schiffbases were investigated using cyclic voltammetry (CV) and impedance electrochemical spectroscopy (EIS) techniques by means of self‐assembled monolayers for the first time, where a 0.1 M KCl solution and the redox couple of Fe(CN)₆^3?/Fe(CN)₆^4?were used as the electrolyte and probing‐pin, respectively. The monolayers formed by the employed Schiff base were proved to be relatively stable, and its electrochemical response in the studied system with different pH values was also de scribed clearly with CV and EIS plots. The results show that the monolayer of Schiff bases could exist in the solution with pH value from 2 to 10. In the EIS measurement in the concentration range from 10^?5 M to 5× 10^?4 M, a nearly linear relation ship between the charge transfer resistance (R_ct) and the logarithm concentration of Cu²+was observed, suggesting that Cu²+ could be titrated with the EIS method quasi‐quantitatively. The phenomenon agreed with the former report very well. Using the self‐assembled monolayers to study Schiff bases with the electrochemical method is the major contribution of our work.     

Host–Guest Chemistry between Perylene Diimide (PDI) Derivatives and 18‐Crown‐6: Enhancement in Luminescence Quantum Yield and Electrical Conductivity

Perylene diimide (PDI) derivatives exhibit a high propensity for aggregation, which causes the aggregation‐induced quenching of emission from the system. Host–guest chemistry is one of the best‐known methods for preventing aggregation through the encapsulation of guest molecules. Herein we report the use of 18‐crown‐6 (18‐C‐6) as a host system to disaggregate suitably substituted PDI derivatives in methanol. 18‐C‐6 formed complexes with amino‐substituted PDIs in methanol, which led to disaggregation and enhanced emission from the systems. Furthermore, the embedding of the PDI ? 18‐C‐6 complexes in poly(vinyl alcohol) (PVA) films generated remarkably high emission quantum yields (60–70 %) from the PDI derivatives. More importantly, the host–guest systems were tested for their ability to conduct electricity in PVA films. The electrical conductivities of the self‐assembled systems in PVA were measured by electrochemical impedance spectroscopy (EIS) and the highest conductivity observed was 2.42×10^?5 S cm^?1.     

Sensitive and Simple Electrochemical Detection of Lead(II) with Carbon Ionic Liquid Electrode

In this paper a carbon ionic liquid electrode (CILE) was fabricated by using ionic liquid 1‐ethyl‐3‐methylimidazolium ethylsulphate ([EMIM]EtOSO₃) as the modifier and further used as the working electrode for the sensitive anodic stripping voltammetric detection of Pb²⁺. The characteristics of the CILE were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In pH 4.5 NaAc‐HAc buffer Pb²⁺ was accumulated on the surface of CILE due to the extraction effect of IL and reduced at a negative potential (‐1.20 V). Then the reduced Pb was oxidized by differential pulse anodic stripping voltammetry with an obvious stripping peak appeared at ?0.67 V. Under the optimal conditions Pb²⁺ could be detected in the concentration range from 1.0 × 10^?8 mol/L to 1.0 × 10^?6 mol/L with the linear regression equation as I_p(μA) = ?0.103 C (μmol/L) + 0.0376 (γ = 0.999) and the detection limit as 3.0 × l0^?9 mol/L (3σ). Interferences from other metal ions were investigated and Cd²⁺ could be simultaneously detected in the mixture solution. The proposed method was further applied to the trace levels of Pb²⁺ detection in water samples with satisfactory results.     

Extraordinary Supercapacitor Performance of a Multicomponent and Mixed‐Valence Oxyhydroxide

We report a novel multicomponent mixed‐valence oxyhydroxide‐based electrode synthesized by electrochemical polarization of a de‐alloyed nanoporous NiCuMn alloy. The multicomponent oxyhydroxide has a high specific capacitance larger than 627 F cm^?3 (1097±95 F g^?1) at a current density of 0.25 A cm^?3, originating from multiple redox reactions. More importantly, the oxyhydroxide electrode possesses an extraordinarily wide working‐potential window of 1.8 V in an aqueous electrolyte, which far exceeds the theoretically stable window of water. The realization of both high specific capacitance and high working‐potential windows gives rise to a high energy density, 51 mWh cm^?3, of the multicomponent oxyhydroxide‐based supercapacitor for high‐energy and high‐power applications.     

Synthesis and Properties of Alkoxy‐ and Alkenyl‐Substituted Peralkylated Imidazolium Ionic Liquids

Novel peralkylated imidazolium ionic liquids bearing alkoxy and/or alkenyl side chains have been synthesized and studied. Different synthetic routes towards the imidazoles and the ionic liquids comprising bromide, iodide, methanesulfonate, bis(trifluoromethylsulfonyl)imide ([NTf₂]^?), and dicyanamide {[N(CN)₂]^?} as the anion were evaluated, and this led to a library of analogues, for which the melting points, viscosities, and electrochemical windows were determined. Incorporation of alkenyl moieties hindered solidification, except for cations with high symmetry. The alkoxy‐derivatized ionic liquids are often crystalline; however, room‐temperature ionic liquids (RTILs) were obtained with the weakly coordinating anions [NTf₂]^? and [N(CN)₂]^?. For the viscosities of the peralkylated RTILs, an opposite trend was found, that is, the alkoxy derivatives are less viscous than their alkenyl‐substituted analogues. Of the crystalline compounds, X‐ray diffraction data were recorded and related to their molecular properties. Upon alkoxy substitution, the electrochemical cathodic limit potential was found to be more positive, whereas the complete electrochemical window of the alkenyl‐substituted imidazolium salts was shifted to somewhat more positive potentials.     

Reversible adsorption change of 2‐amino‐4,5‐imidazoledicarbonitrile on Ag electrode surfaces by potential‐dependent surface‐enhanced Raman scattering

The potential‐induced adsorption change of 2‐amino‐4,5‐imidazoledicarbonitrile (AIDCN) on Ag electrode surfaces has been examined by surface‐enhanced Raman scattering (SERS) in an applied potential range between ?1.0 and 0.2 V. Upon adsorption, AIDCN has a substantial interaction with the Ag metal surfaces via its two nitrile groups. The CN stretching peaks at ～2200 cm^?1 appeared to be more intensified and redshifted at a negative potential. The deconvolution peak analysis of the CN bands at various voltages suggests that there should be a change in binding modes of AIDCN on Ag surfaces. This potential‐dependent orientation change appeared to be reversible. The density functional theory (DFT) calculation of AIDCN on Ag cluster atoms is used to explain its potential‐dependent adsorption. Copyright © 2010 John Wiley & Sons, Ltd.