Stable Electroactivity Research Articles

CNTs Bridged Basal-Plane-Active 2H-MoS2 Nanosheets for Efficient Robust Electrocatalysis.

2D 2H-phase MoS2 is promising for electrocatalytic applications because of its stable phase, rich edge sites, and large surface area. However, the pristine low-conductive 2H-MoS2 suffers from limited electron transfer and surface activity, which become worse after their highly likely aggregation/stacking and self-curling during applications. In this work, these issues are overcome by conformally attaching the intercalation-detonation-exfoliated, surface S-vacancy-rich 2H-MoS2 onto robust conductive carbon nanotubes (CNTs), which electrically bridge bulk electrode and local MoS2 catalysts. The optimized MoS2 /CNTs nanojunctions exhibit outstanding stable electroactivity (close to commercial Pt/C): a polarization overpotential of 79mV at the current density of 10mAcm-2 and the Tafel slope of 33.5mVdec-1 . Theoretical calculations unveil the metalized interfacial electronic structure of MoS2 /CNTs nanojunctions, enhancing defective-MoS2 surface activity and local conductivity. This work provides guidance on rational design for advanced multifaceted 2D catalysts combined with robust bridging conductors to accelerate energy technology development.

Highly hydroresponsive nacre-like oligo proanthocyanidin-intercalated Ca–Al-Layered double hydroxides/graphene oxide/polyvinyl alcohol as a potential neural implant material

Neural implantation with a microscale electrode permits a real-time neuromoduration to enhance the treatment of neural disorders. However, the penetration of a neural microprobe into soft brain tissues always resulted in the invasive tissue damage and mechanical tissue-device friction, which further induced the extensive chronic inflammation that limited the device lifetime. To develop a biocompatible and biocompliant neural implant, this study presented a smart substrate with bioinspired nacre-like structure that can exhibit ultra-hydroresponsive mechanical strength transition, sustained anti-inflammatory drug delivery, and anti-biofouling ability. An organic-inorganic composite, called LOG-P, was synthesized with oligo proanthocyanidin (OPC)-intercalated Ca–Al layered double hydroxide (Ca–Al-LDH) and graphene oxide (GO), followed by crosslinked with linear structural polyvinyl alcohol (PVA) to form a brick-and-mortar architecture. LOG-P exhibited strong mechanical strength of ~ 5 GPa in Young's modulus at dehydrated state, while showing ~99% decrease of Young's modulus when getting hydrated. In addition, the intercalation of OPC in LDH led to zero-order release with duration up to 80 days. LOG-P with negatively charged surfaces inhibited the adhesion of astrocytes, while the released OPC led to robust neuronal cell viability. Finally, integrated with Ag circuits by aerosol jet printing, the fabricated LOG-P-based microelectrode arrays showed stable electroactivity, also permitting a complete penetration into brain-tissue phantoms without bending. Such organic-inorganic nanocomposite-based neural interface with physical, chemical, and biological compatibility was expected to be a revolutionary platform for development of next-generation neural implants.

Layer‐by‐layer assembly and electrically controlled disassembly of water‐soluble Poly(3,4‐ethylenedioxythiophene) derivatives for bioelectronic interface

AbstractPoly(3,4‐ethylenedioxythiophene (PEDOT) derivatives display a multitude of attractive properties such as high conductivity, biocompatibility, ease of functionalization, and high thermal stability. As a result, they show promise for applications in materials and biomedical engineering. In order to increase their applications in the practical domain, trivial fabrication techniques are required. Here, we present a simple layer‐by‐layer dip methodology to assemble water‐soluble PEDOT derivatives that can then be disassembled via electrical stimulation. As a result, a dynamic PEDOT layered system is fabricated and could be applied as responsive materials for bioengineering. PEDOT‐SO3 and PEDOT‐NMe3 are synthesized via direct C‐H arylation polymerization and chemical polymerization, respectively. The electrostatic interactions between oppositely charged SO3− and NMe3+ enabled the stacking of PEDOT derivatives. The layer‐by‐layer assemblies are confirmed by ultraviolet–visible spectroscopy and profilometer. Morphological analyses are performed using scanning electron microscopy and atomic force microscopy, which revealed that the polymer coatings are uniform without any cracks. In situ material assembly is studied using quartz crystal microbalance, and we also demonstrate that these PEDOT‐derivative assemblies can be disintegrated by electrical stimulation. Cyclic voltammetry shows a proportional increase in stored charge density with the increase in bilayer thickness, confirming stable electroactivity of these assemblies. Using this approach, we can assemble conductive bio interface on both conductive and nonconductive surfaces, expanding the capability to fabricate bioelectronic electrodes.

PdCu alloy nanoparticles supported on reduced graphene oxide for electrocatalytic oxidation of methanol

PdCu nanoparticles supported on reduced graphene oxide nanosheets (PdCu/rGO) with uniform size distribution and dispersion are fabricated by a facile two-step reduction method. During the whole synthesis procedure, no capping agent or surfactant has been used. By varying the Pd/Cu molar ratio, electrocatalysts with different size distribution and dispersion of nanoparticles on graphene are prepared, and their electrocatalytic performance toward methanol oxidation reaction has been studied. It is concluded that the as-prepared electrocatalyst of Pd2Cu2/rGO, of which the Pd/Cu molar ratio is 1:1, exhibits the highest mass activity and most stable electroactivity. Compared to commercial Pd/C, the as-prepared Pd2Cu2/rGO also demonstrates 2.49 times higher mass activity and much more stable electroactivity. The excellent performance of the Pd2Cu2/rGO electrocatalyts is mainly due to the advantages of bimetallic synergistic effects and the supporting material of graphene. Owing to the advantages of high electroactivity, long stability, and cost-effectiveness, the as-prepared Pd2Cu2/rGO nanocomposites are promising anode electrocatalysts for direct methanol fuel cells.

Enhanced Electrochemical Activity of Polyaniline-Ferricyanide Films in Neutral Electrolyte

We have successfully developed a two-step chronopotentiometric routine for electropolymerizing a polyaniline-ferricyanide film with stable electroactivity in neutral pH electrolyte containing 1 M KCl. Here we present a spectroscopic, electrochemical, and gravimetric analysis of these films to determine the nature of doping and role of the ferricyanide ion. The experimental evidence currently supports the hypothesis that the presence of ferricyanide alters the electrochemical behavior of the films in 1 M KCl, specifically the films are found to be conducting in non-acidic media. The spectroscopic evidence suggests that the Fe(CN)6 interacts with the nitrogen atoms on the PANI chain, resulting in the increased presence of polarons (mostly localized) even while the film is in the emeraldine base form. Gravimetric measurements provide insight into the role of anion and proton exchange during voltammetric cycling.

Atomic Layer Deposition and Anodic Oxidation: A Good Tool Combination to Build Nanostructured Electrodes for Energy Applications

Anodic oxidation has been used for a longtime as a way to passivate metallic electrodes to prevent corrosion. It is the discovery of self-ordered nanoporous alumina membranes reported in 1995 [1] that has revealed its potential use for surface nanostructuring. Later, the anodic growth of TiO2 nanotubes (TiO2-nt) has considerably widened the field of applications of such approach since TiO2 exhibits many valuable properties [2]. It is now possible to use other metals or alloys to grow porous or tubular oxidized nanostructures. However to further improve the properties of such electrodes, it is necessary to functionalize their surface with other materials of interest. Among the various thin film deposition methods, Electrochemical Deposition (ED) and Atomic Layer Deposition (ALD) have shown a great ability to conformally coat porous structures exhibiting a high aspect ratio. The main advantages of ALD over ED is that it can be carried out onto non-conductive materials, it allows an accurate control of the thickness and it is usually more direct to grow oxides or nitrides. We report, here, three examples of nanostructured electrodes fabricated using anodic oxidation of Al and Ti in combination with ALD of active materials. The targeted applications are in the fields of electrocatalysis, Li-ion microbatteries and photoelectrochemical water splitting. Direct Ethanol Fuel Cells offer significant advantages due to ethanol non-toxicity and renewability and its high power density. TiO2 have been successfully used as replacement of C as catalyst support because it exhibits a good chemical stability and it can enhance the activity of the catalyst. After a brief reminding on the TiO2-nt fabrication and properties, the ALD of Pd nanoparticles into TiO2-nt array will be presented. The electrochemical activity toward ethanol oxidation has been tested in alkaline medium. Although a high and stable electroactivity has been measured further improvements such as annealing of the TiO2-nt and ALD of SnO2 onto the TiO2-nt have been proposed. As seen on Fig. 1a, the electrochemical response is at its highest when the tubes have been annealed and covered by SnO2. A 3D nano-architectured composite negative electrode has been fabricated in order to be used in microbatterie. It consists of TiO2-nt coated by a thin SnO2 film grown by ALD. TiO2-nt are known to exhibits very good insertion properties and the SnO2 coating that displays a high lithium insertion capability (max. theoretical capacity of 720 µAh/cm2·µm) is used to enlarge the capacity of the electrode. Such composite 3D structure increases therefore the active area, improves the kinetics of the system, facilitates the ion exchange at the electrode/electrolyte interface and, better accommodates the volume expansion induced by the Li insertion within the LixSn alloy. The ALD of SnO2 will be described in details. The influence of various parameters such as precursor nature, exposure sequence as well as reaction temperature on the deposit morphology, chemistry and crystalline structure will be presented. The electrochemical performances of such systems have been tested as function of the SnO2 film thickness and after thermal treatments that change the crystalline structure of the electrodes. The results show that TiO2/SnO2 delivers a promising capacity (~150 µAh/cm2) which is better than bare TiO2-nt (Fig. 1b). It demonstrated then that such 3D nano-architectured composite electrode opens valuable perspectives for microbatteries design. The last example consists of producing a nanostructured photocathode for water splitting in which the photogeneration and transport of the charge carriers do not occur in the same material. In order to create tailored 3D nanostructures, p-NiO and i-Sb2S3 thin films have been successively grown into nanoporous alumina by ALD (Fig. 1c). The photocathode composition, structure and geometry are well controlled. Then the optical and photoelectrochemical properties have been investigated and optimized using cyclic voltammetry in the dark and under illumination as well as UV-visible absorption spectroscopy. It has been sought to uncover trends in the photoelectrochemical activity of the system (photocurrent density and photovoltage) and rationalize them in terms of optical and electrical functions. [1] H. Masuda, K. Fukuda, Science, 268, 1466 (1995) [2] V. Zwilling, E. Darque-Ceretti, A. Boutry-Forveille, D. David, M. Y. Perrin, M. Aucouturier, Surf. Interface Anal., 27, 629 (1999) Figure 1

Functionalization of reduced graphene oxide by electroactive polymer for biosensing applications

A novel biosensing platform was designed by the functionalizing reduced graphene oxide sheets (rGO) with electroactive copolymer juglone. The composite film showed well-defined, stable electroactivity in a biocompatible buffer medium. Square wave voltammetry is used to record the redox signal for DNA hybridization. Current increase upon hybridization (signal-on) evidenced that short DNA target as well as polymerase chain reaction (PCR), so called ‘real sample’ products, related to different lineages of Mycobacterium tuberculosis strain. The signal-on reached ∼40% with 1 nM of short DNA (25 mer) target, while PCR product (Africanum, EAI and Beijing strains) produced a current change of ∼20%.

Amperometric sensing of nitrite based on electroactive ferricyanide–poly(diallyldimethylammonium)–alginate composite film

Poly(diallyldimethylammonium chloride) (PDDA) and sodium alginate (AlgNa) were mixed to obtain a water-insoluble interpenetrating polymer composite via electrostatic interaction and then cast on an Au electrode surface, followed by robust immobilization of K3Fe(CN)6 to yield a K3Fe(CN)6–PDDA–Alg/Au electrode of stable electroactivity. The interaction processes and electrode modification are studied by visual inspection and electrochemical methods. Under optimized conditions, the K3Fe(CN)6–PDDA–Alg/Au electrode can efficiently electrocatalyze the reduction of nitrite in acidic aqueous solution and give a linear nitrite-detection range of 5.0μM to 9.7mM with a sensitivity of 83.7μAcm−2mM−1, which is amongst the best results reported for nitrite sensing. The electrode was also used for nitrite electroanalysis in real sample matrices with satisfactory results.

Quinone-based polymers for label-free and reagentless electrochemical immunosensors: application to proteins, antibodies and pesticides detection.

Polyquinone derivatives are widely recognized in the literature for their remarkable properties, their biocompatibility, simple synthesis, and easy bio-functionalization. We have shown that polyquinones present very stable electroactivity in neutral aqueous medium within the cathodic potential domain avoiding side oxidation of interfering species. Besides, they can act as immobilized redox transducers for probing biomolecular interactions in sensors. Our group has been working on devices based on such modified electrodes with a view to applications for proteins, antibodies and organic pollutants using a reagentless label-free electrochemical immunosensor format. Herein, these developments are briefly reviewed and put into perspective.

Chemical and Electrochemical Synthesis of Highly Conductive and Processable PolyProDOP-alkyl Derivatives

New monomers, possessing various alkyl substituents on propylene dioxypyrrole, were synthesized. The monomers could be easily polymerized to produce highly conductive and soluble polymers. The corresponding polymers showed excellent solubility, retaining electrochemical and optical properties of their parent polymer [poly(propylene dioxypyrrole)]. The conductivities of chemically prepared polymers were quite high in a range of 20 and <TEX>$60\;Scm^{-1}$</TEX>. Solubility of the polymer in a common organic solvent was as high as no polymer is deposited on an electrode. The redox potentials of the electrochemically prepared polymers revealed quite stable electro-activity during repeated redox switching up to 500 times. The optoelectrochemistry studies also showed distinct color changes of the polymers upon changing the doping state, indicating strong absorption peaks at 400~600 nm in reduced states and complete bleaching in fully oxidized states.

Design of a new electrogenerated polyquinone film substituted with glutathione. Towards direct electrochemical biosensors

We developed a method to graft a tripeptide (glutathione) onto 5-hydroxy-1,4-naphthoquinone, an electropolymerizable molecule. The resulting thin conducting polymer presents a well-defined and stable electroactivity in neutral buffered solution, due to the embedded quinone group, and is able to covalently graft amino-modified DNA probe strands. It is shown that the bioelectrode presents positive current change following DNA hybridization. This makes a “signal-on” direct electrochemical DNA sensor. The results were obtained with low target concentration (50 nM) and the selectivity is excellent as a single-mismatch sequence can be discriminated from the full-complementary target.

Poly(3,4-(2-methylene)propylenedioxythiophene) for Electrochemical Grafting of Polystyrene via Methylene Functionality

A monomer 3,4-(2-methylene)propylenedioxythiophene (MProDOT) was synthesized and electrochemically polymerized to yield PMProDOT with methylene groups that have the potential to be further functionalized. Electrochemical redox switching of PMProDOT between −0.6 and +1.5 V (vs ) caused the cross-linking reaction between methylene moieties at the anodic potential limit and resulted in the fast decrease of electroactivity due to destruction of π-conjugation. When PMProODT was subjected to +1.5 V in the presence of styrene (ST) monomers, the loss of electroactivity was not significant and the mass of the PMProDOT was rapidly increased. The mass increase was ascribed to polystyrene (PST) grafting onto PMProDOT. Simultaneous oxidation of methylene groups and ST at +1.5 V led to the coupling of ST to PMProDOT, which reduced cross-linkable free-methylene moieties. PST-grafted PMProDOT showed relatively stable electroactivity over repeated potential cycling. The infrared spectrum of PST-grafted PMProDOT also showed additional C–H stretching peaks possibly due to PST grafting.

Study of the DNA hybridization transduction behavior of a quinone-containing electroactive polymer by cyclic voltammetry and electrochemical impedance spectroscopy

We report the characterization of a new bifunctional electroactive polymer, poly(5-hydroxy-1,4-naphthoquinone (juglone)-co-5-hydroxy-3-thioacetic acid-1,4-naphthoquinone), which can be used for direct electrochemical detection of DNA hybridization. The polymer structure was characterized based on molecular orbital calculations and ex situ and in situ FT-IR spectroscopy. The quinone group integrated in the polymer presents very stable electroactivity in neutral aqueous medium and can act as a redox marker for hybridization. The carboxylic function allows the preparation of oligonucleotides (ODN) probe-modified films by covalent binding. The mechanism of hybridization detection was studied by cyclic voltammetry and electrochemical impedance spectroscopy. The “signal-on” upon hybridization could be attributed to a change in conformation from random ODN coils on the probe-modified film to helix double stranded ODNs upon hybridization.

Fabricating Conducting Polymer Electrochromic Devices Using Ionic Liquids

Electrolytes play an important role in determining the performance of conducting polymer electrochromic devices. Good electrolytes should have high conductivity, large electrochemical windows, excellent thermal and chemical stability, and negligible evaporation. Room-temperature ionic liquids are ideal electrolytes to satisfy these requirements. In the present work, we explored the applications of ionic liquids as electrolytes in electrochemical synthesis of conducting polymers, in electrochemical and electrochromic characterization of both electrochemically and chemically synthesized conducting polymers and in fabrication of conducting polymer electrochromic devices. In ionic liquids, highly stable electroactivity has been obtained for polyaniline in a wide potential range covering its entire redox process of for >1,000,000 cycles. During the fabrication of electrochromic devices, electrochemically synthesized polymers were employed for displays, while chemically synthesized polymers (via spin-coating) were preferable for large-area electrochromic windows. We have successfully fabricated the prototypes of alphanumeric displays and large-area electrochromic windows. High device performance of low operation voltages (<1.5 V), high coloration contrast (>50%), fast coloration speed (<100 ms), and high coulombic efficiency (>98%) has been realized. © 2004 The Electrochemical Society. All rights reserved.

Square Wave Voltammetric Determination of Trace Amounts of Europium(III) at Montmorillonite-Modified Carbon Paste Electrodes

A carbon paste electrode modified with montmorillonite for the determination of Eu(III) was developed. This chemically modified electrode exhibits strong and stable electroactivity for Eu(III). Square wave voltammetry (SWV) of Eu(III) was evaluated with respect to the quantity of modifier, pH of electrolyte solution, accumulation potential and time. The stripping peak currents increase linearly with concentrations of Eu(III) from 1.0 × 10-7 to 2.0 × 10-5 mol l-1. The detection limit is estimated to be 4 × 10-8 mol l-1 (S/N = 3). The recommended method has been applied to the quantitation of Eu(III) in stream sediment samples; the results obtained by the SWV approach are in good agreement with reference values.

Poly(Cyano-Substituted Diheteroareneethylene) as Active Electrode Material for Electrochemical Supercapacitors

A new class of low band gap thiophene polymers prepared from (E)-α-cyanoethylene thiophene derivatives were electrochemically and physically evaluated as active electrode material for electrochemical supercapacitors. The corresponding polymers were prepared by electrochemical polymerization of these monomers from a nonaqueous solution (acetonitrile) containing tetraethylammonium tetrafluoroborate. The electrochemical properties and the stability under cyclic voltammetry of the polymers were found to be strongly dependent on their electronic configuration, especially in the case where the monomer has two different aromatic heterocycles. The range of stable electroactivity of the polymers in organic media spans about 2 V. Since poor stability was observed by cyclic voltammetry for poly-(E)-α-[(2-thienyl)methylene]-2-(3-methylthiophene)acetonitrile and poly-(E)-α-(2-thienylmethylene)-2-furanacetonitrile, only poly-(E)-α-[(2-thienyl)methylene]-2-thiopheneacetonitrile, poly-(E)-α-[(3-methyl-2-thienyl)methylene...

Aniline electropolymerization on mild steel and zinc in a two-step process

Abstract A two-step process for aniline electropolymerization on mild steel and zinc from aqueous electrolytes has been developed. The first step is the electrodeposition of a thin polypyrrole film. It acts as a pretreatment of the surface and completely modifies its electrochemical response to usual acidic solutions suitable for aniline electropolymerization. It is much faster than any chemical pretreatment (less than 3 s) and can be performed with almost no metal dissolution. Pretreated mild steel or zinc substrates can then be used for the electrodeposition of a PANI film of controllable thickness. No or very little metal oxidation occurs in this second step. The films show stable electroactivity in acidic electrolytes, similar to that of PANI deposited on platinum, which indicates that the underlying oxidizable metal is fully protected. The overall system has a bilayer structure, indicating that the electrochemical interface during aniline electrodeposition might be situated at the polypyrrole ∣ solution interface. This suggests a new interpretation for the anticorrosion properties of conductive polymers based on the displacement of the electroactive interface from its usual location (metal ∣ solution) to the polymer ∣ solution interface.