Electrocatalysis of Cyclic Voltammetrically Prepared Co‐MnO2 Composite towards Oxygen Reduction Reaction (ORR)

For the first time, cobalt particles were electrodeposited on the surface of manganese oxides by cyclic voltammetry (CV) from an aqueous solution of 0.1 M Na₂SO₄ containing 5 mM CoSO₄, and then the samples obtained were characterized by scanning electron microscopy (SEM) and energy dispersive X‐ray analysis (EDAX), respectively. And then, the as‐prepared Co/MnO₂‐coated graphite electrode was employed to the oxygen reduction reaction (ORR). Interestingly, the reduction peak potential of ORR on a Co/MnO₂‐modified graphite electrode was positively shifted for about 100 mV as compared with that on a MnO₂‐modified graphite electrode, indicating that the electrocatalysis of Co/MnO₂ composite towards ORR is superior to that of pure MnO₂.     

Direct Preparation of Metal Ions‐Doped Manganese Oxide by Cyclic Voltammetry

In this work, for the first time, copper ions(II) and cobalt ions(II) were successfully electrodepositioned into manganese oxide by cyclic voltammetry (CV), respectively. The results obtained from energy dispersive X‐ray analysis (EDX) testified that copper ions and cobalt ions were doped into manganese oxide, and the images, taken from scan electron spectroscopy (SEM) also proved that the morphology of the resultant MnO₂ was altered by the doped metal ions to some extent. Interestingly, specific capacitance, obtained by cyclic voltammograms (CVs), for the metal ions‐doped MnO₂ exhibited a higher value compared to the non‐doped MnO₂. Developing a novel and simple method to generate the metal ions‐doped MnO₂ to improve the characteristics of MnO₂ is the main contribution of this work.     

Synthesis and high electrochemical performance of polyaniline/MnO2-coated multi-walled carbon nanotube-based hybrid electrodes

Multi-layered electrodes which consist of polyaniline (PANI)/manganese dioxide (MnO₂)-multi-walled carbon nanotubes (MWNTs) are prepared as the electrode materials for supercapacitors. MnO₂-MWNTs are made by the in situ direct coating method to deposit MnO₂ onto MWNTs; the core/shell structure of multi-layered fibrous electrodes can also be obtained by PANI coating onto the MnO₂-MWNTs. The effect of PANI coating on the electrochemical performance and cyclic stability of MnO₂-MWNTs is investigated. From the cyclic voltammograms, the PANI/MnO₂-MWNTs show remarkably enhanced specific capacitance and cycle stability compared to MnO₂-MWNTs, where the highest specific capacitance (350 F/g) is obtained at a current density of 0.2 A/g for the PANI/MnO₂-MWNTs as compared to 92 F/g for pristine MWNTs and 306 F/g for MnO₂-MWNTs. This indicates that the improved electrochemical performance of PANI/MnO₂-MWNTs is due to the enhanced electrical properties by nano-scale-coated MnO₂ onto MWNTs and the PANI coating that leads to the increased cycle stability by delaying the dissolution of MnO₂ during charge/discharge tests.     

Preparation and characterization of MnO<Subscript>2</Subscript>/MWCNTs-modified graphite electrode and its catalysis for oxygen reduction reaction (ORR)

Manganese dioxides were prepared onto multi-walled carbon nanotubes (MWCNTs) by cyclic voltammetry (CV). The obtained manganese oxide-MWCNTs (MnO₂/MWCNTs) samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR) and thermogravimetry (TG), respectively. The MnO₂/MWCNTs-modified graphite electrode was utilized in the electrochemical oxygen reduction reaction (ORR) and the enhanced oxygen reduction peak current strongly suggested that MnO₂/MWCNTs has catalysis for ORR when compared to the pure MnO₂ or MWCNTs. The catalysis mechanism of MnO₂/MWCNTs for ORR was also-discussed.     

Cyclic Voltammetrically‐Prepared MnO2 Coated on an ITO Glass Substrate

For the first time, nanostructured manganese dioxide was successfully electrodeposited onto an ITO (indium tin oxide) glass substrate by cyclic voltammetry (CV) method from an aqueous solution of 0.1 M Na₂SO₄ containing 5 × 10⁻³ M MnSO₄. The obtained manganese dioxide‐modified ITO glass substrates were characterized by energy dispersive spectrometry (EDS), Fourier transform infrared spectrometry (FTIR) and scanning electron microscopy (SEM), respectively. All results not only proved the existence of MnO₂ on an ITO glass substrate but also demonstrated that the morphology of the obtained MnO₂ was greatly affected by the electrodeposition conditions. Also, this MnO₂‐modified ITO electrode was systematically investigated by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS) in an aqueous electrolyte of 0.1 M Na₂SO₄. The results obtained from electrochemical measurement indicated that this developed MnO₂‐modified ITO electrode has a satisfied specific capacitance value of 264 F·g⁻¹ and exhibits excellent electrochemical stability and reversibility.     

Electrocatalytic Dioxygen Reduction at Glassy Carbon Electrode Modified with Polyaniline Grafted Multiwall Carbon Nanotube Film

The work details the electrocatalysis of oxygen reduction reaction (ORR) in 0.5 M H₂SO₄ medium on a modified electrode containing a film of polyaniline (PANI) grafted multi‐wall carbon nanotube (MWNT) over the surface of glassy carbon electrode. We have fabricated a novel modified electrode in which conducting polymer is present as connected unit to MWNT. The GC/PANI‐g‐MWNT modified electrode (ME) is fabricated by electrochemical polymerization of a mixture of amine functionalized MWNT and aniline with GC as working electrode. Cyclic voltammetry and amperometry are used to demonstrate the electrocatalytic activity of the GC/PANI‐g‐MWNT‐ME. The GC/PANI‐g‐MWNT‐ME exhibits remarkable electrocatalytic activity for ORR. A more positive onset potential and higher catalytic current for ORR are striking features of GC/PANI‐g‐MWNT‐ME. Rapid and high sensitivity of GC/PANI‐g‐MWNT‐ME to ORR are evident from the higher rate constant (7.92×10² M^?1 s^?1) value for the reduction process. Double potential chronoamperometry and rotating disk and rotating ring‐disk electrode (RRDE) experiments are employed to investigate the kinetic parameters of ORR at this electrode. Results from RDE and RRDE voltammetry demonstrate the involvement of two electron transfer in oxygen reduction to form hydrogen peroxide in acidic media.     

Electrodepositions and capacitive properties of hybrid films of polyaniline and manganese dioxide with fibrous morphologies

Electrocodepositions were conducted in solutions of aniline and MnSO₄ through potential cycling to afford hybrid films of polyaniline (PANI) and manganese dioxide (PANI/MnO₂). The films obtained displayed characteristic redox peaks of PANI on cyclic voltammograms in acidic aqueous solution. While in 1.0 M NaNO₃ at pH 1, the films showed pseudocapacitive behaviors from 0 to 0.65 V vs. SCE. MnO₂ was detected through XRD and XPS measurements on the films. The codeposition of PANI with MnO₂ had dramatic effects on morphologies of the obtained hybrid films that displayed fibrous morphologies instead of granular one of PANI. Hybrid film PM50 obtained in the presence of 50 mM Mn²⁺ displayed a specific capacitance of 532 F g⁻¹ at 2.4 mA cm⁻² discharging current, 26% higher than that of similarly prepared PANI. It showed a coulombic efficiency (η) of 97.5% over 1200 cycles with 76% specific capacitance maintained.     

EQCM study of redox properties of PEDOT/MnO<Subscript>2</Subscript> composite films in aqueous electrolytes

Electrochemical behavior of poly-3,4-ethylenedioxythiophene composites with manganese dioxide (PEDOT/MnO₂) has been investigated by cyclic voltammetry and electrochemical quartz crystal microbalance at various component ratios and in different electrolyte solutions. The electrochemical formation of PEDOT film on the electrode surface and PEDOT/MnO₂ composite film during the electrochemical deposition of manganese dioxide into the polymer matrix was gravimetrically monitored. The mass of manganese dioxide deposited into PEDOT at different time of electrodeposition and apparent molar mass values of species involved into mass transfer during redox cycling of PEDOT/MnO₂ composites were evaluated. It was found that during the redox cycling of PEDOT/MnO₂ composite films with various MnO₂ content, the oppositely directed fluxes of counterions (anions and cations) occur, resulting in a change of the slope of linear parts of the Δf–E plots with changing the mass fraction of MnO₂ in the composite film.Rectangular shape of cyclic voltammograms of PEDOT/MnO₂ composites with different loadings of manganese dioxide was observed, which is characteristic of the pseudocapacitive behavior of the composite material. Specific capacity values of PEDOT/MnO₂ composites obtained from cyclic voltammograms were about 169 F g^?1. The specific capacity, related to the contribution of manganese dioxide component, was about 240 F g^?1.     

Electrochemical Synthesis of Chitosan‐co‐polyaniline/WO3⋅nH2O Composite Electrode for Amperometric Detection of NO2 Gas

An electrode of hydrated tungsten oxide (WO₃?nH₂O) embedded chitosan‐co‐polyaniline (CHIT‐co‐PANI) composite was electrochemically prepared on an indium tin oxide (ITO) coated glass surface using mineral acid as a supporting electrolyte. The resulting CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode was characterized using ultraviolet‐visible spectroscopy (UV‐vis), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), and scanning electron microscopy (SEM). The composite electrode exhibited a three‐dimensional nanofibrous structure with the diameter of the nanofibers ranging from 20 to 100 nm. The CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode allowed for the low potential detection of NO₂ gas in acidic medium. The NO₂ gas sensing characteristics were studied by measuring change in the current with respect to concentration and time. Using the CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode, NO₂ gas was detected electrochemically without interference at pH 2.0 and 0.25 V vs. Ag/AgCl. The current of the electrochemical cell with the CHIT‐co‐PANI/WO₃?nH₂O/ITO electrode decreased linearly with an increase in NO₂ gas concentration in a range from 100 to 500 ppb with a response time of eight seconds.     

Nitrogen‐Rich Manganese Oxynitrides with Enhanced Catalytic Activity in the Oxygen Reduction Reaction

The catalytic activity of manganese oxynitrides in the oxygen reduction reaction (ORR) was investigated in alkaline solutions to clarify the effect of the incorporated nitrogen atoms on the ORR activity. These oxynitrides, with rock‐salt‐like structures with different nitrogen contents, were synthesized by reacting MnO, Mn₂O₃, or MnO₂ with molten NaNH₂ at 240–280 °C. The anion contents and the Mn valence states were determined by combustion analysis, powder X‐ray diffraction, and X‐ray absorption near‐edge structure analysis. An increase in the nitrogen content of rock‐salt‐based manganese oxynitrides increases the valence of the manganese ions and reinforces the catalytic activity for the ORR in 1 m KOH solution. Nearly single‐electron occupancy of the antibonding e_g states and highly covalent Mn?N bonding thus enhance the ORR activity of nitrogen‐rich manganese oxynitrides.     

Syntheses of conductive adhesives based on epoxy resin and polyanilines by using N‐tert‐butyl‐5‐methylisoxazolium perchlorate as a thermally latent curing reagent

Conductive composites consisted of epoxy resin and polyanilines (PANIs) doped with dodecylbenzenesulfonic acid ( 1 ), dodecylsulfonic acid (2), di(2‐ethylhexyl)sulfosuccinic acid (3), and HCl were synthesized by use of N‐tert‐butyl‐5‐methylisoxazolium perchlorate (5) under various reaction conditions. It was found that the composites with PANI doped with acid 2 (PANI‐2) prepared by curing with 10 mol % of reagent 5 at 80 °C for 12 h showed high electroconductivity along with the low conducting percolation threshold (3 wt % of PANI‐2). Furthermore, the composite with even ?10 wt % of PANI‐2 exhibited ?10^?1 S/cm of electroconductivity. The UV–vis and IR measurements indicated that the conductive emeraldine salt form of PANI‐2 in the composite was maintained after the curing reaction. The thermal stability was studied by TGA and DSC measurements, and then, the T_d10 and T_g of the composite with 5 and 10 wt % of PANI‐2 were found to be similar to those with the cured epoxy resin itself. In addition, the similar investigation with an oxetane resin instead of the epoxy resin was also carried out. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 718–726, 2006     

Studies on UV‐stability of poly(MMA‐co‐M12‐co‐BPMA)/TiO2composite particles prepared by ultrasonically initiated emulsion polymerization

In this paper, poly(methyl methacrylate‐co‐sodium sulfopropyl lauryl maleate‐co‐2‐hydroxy‐4‐(3‐methacryloxy‐2‐hydroxylpropoxy) benzophenone)/TiO₂ (i.e., poly(MMA‐co‐M12‐co‐BPMA)/TiO₂) composite particles were prepared by ultrasonically initiated emulsion polymerization. To study the dispersion and UV‐stability of the composite particles, laser diffraction particle size analyzer (LDPSA), ultraviolet‐visible absorption spectroscopy (UV‐vis), UV‐vis diffuse reflectance spectroscopy (DRS), differential scanning calorimeter (DSC), and the weight loss measurement were used. The results indicate that the dispersion of the poly(MMA‐co‐M12‐co‐BPMA)/TiO₂ composite particles prepared by ultrasonically initiated emulsion polymerization is good. And the composite particles can absorb UV light; the ultraviolet absorption strength of poly(MMA‐co‐M12‐co‐BPMA) grafted onto the surface of TiO₂ has not changed after UV irradiation while that of PMMA changed significantly. The UV absorption strength, weight loss, and Tg changes are in the order PMMA> poly(MMA‐co‐M12‐co‐BPMA) >PMMA grafted onto TiO₂> poly(MMA‐co‐M12‐co‐BPMA) grafted onto TiO₂. These results show that the ultrasonically initiated emulsion polymerization will enhance the UV stability of composite particles, and the UV‐stability of PMMA can be enhanced by the introduction of the organic UV‐stabilizer BPMA and the inorganic UV‐stabilizer titanium dioxide into the PMMA chains by covalent bond, and the effect of the BPMA and the TiO₂ used together is better than that used, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and characterization of polyaniline/manganese dioxide composites via oxidative polymerization: Effect of acids

Polyaniline/manganese dioxide (PANI/MnO₂) composites have been chemically prepared by oxidative polymerization of aniline in acidic medium containing MnO₂ as an oxidant. The acids used were; H₂SO₄, HNO₃, HCl, and H₃PO₄ The prepared composites were characterized by SEM, elemental analysis, FT-IR, XRD, TGA, and magnetic susceptibility. XRD measurements of the composites revealed that the crystal structure of incorporated MnO₂ undergone a distortion and converted into amorphous. Thus, the XRD pattern of PANI was predominate. The degree of crystallinity of the prepared composites is depended on the type of compensated acid anions and has the order; . This order is agrees with the order of crystallographic radii and the shape of the corresponding acid anions. From the value of point zero charge of MnO₂ (pzc at pH ≈7.5) and FT-IR spectra, it was concluded that adsorbed acids anions on the oxide surface works as the charge compensator for positively charge PANI in the formation of PANI/MnO₂. The content of PANI in the composite was depended on the type of acid used. Thermogravimetric study exhibited that the composite with low content of PANI has a higher thermal stability. Magnetic susceptibility measurements revealed that the composites has a diamagnetic properties. A schematic composition of the composites has been suggested.     

Synthesis and characterization of polyaniline/silicon dioxide composites and preparation of conductive films

The focus of this study was to synthesize the inherently conductive polymer polyaniline using an optimized process to prepare polyaniline/silicon dioxide (PANI/SiO₂) composites by in situ polymerization and ex situ solution mixing. PANI and PANI/SiO₂ composite films were prepared by drop‐by‐drop and spin coating methods. The electrical conductivities of HCl doped PANI film and PANI/SiO₂ composite films were measured according to the standard four‐point‐probe technique. The composite films exhibited an increase in electrical conductivity over neat PANI. PANI and PANI/SiO₂ composites were also investigated by spectroscopic methods including UV‐Vis, FT‐IR, and Photoluminescence. UV‐Vis and FT‐IR studies showed that SiO₂ particles affect the quinoid units along the polymer backbone and indicate strong interactions between the SiO₂ particles and the quinoidal sites of PANI (doping effect). The photoluminescence properties of PANI and PANI/SiO₂ composites were studied and the PANI/SiO₂ composites showed increased intensity as compared to neat PANI. The increase of conductivity of PANI/SiO₂ composite may be partially due to the doping or impurity effect of SiO₂ where the silicon dioxides compete with chloride ions. The morphology of particles and films were examined by a scanning electron microscope (SEM). SEM measurements indicated that the SiO₂ were well dispersed and isolated in composite films. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and characterization of PVC/PANI conductive composite with extremely low percolation threshold

Aniline was polymerized in the presence of poly(vinyl chloride) (PVC) powders in hydrochloric acid to in situ prepare poly(vinyl chloride)/polyaniline (PVC/PANI) composite particles. UV‐vis spectra and FT‐IR spectra indicate PANI in PVC/PANI composite particles possessed a higher oxidation state with decreased aniline content in reactants. Both conductivity and impact strength of the dodecylbenzenesulfonic acid (DBSA) doped PANI composites (PVC/PANI‐DBSA), which were compression molded from the in situ prepared PVC/PANI particles, increase with the pressing temperature and decrease with the increase of DBSA doped PANI (PANI‐DBSA) loading. An excellent electric conductivity of 5.06 × 10^?2 S/cm and impact strength of 0.518 KJ/m² could be achieved for the in situ synthesized and subsequently compression molded composite. Copyright © 2004 John Wiley & Sons, Ltd.     

Electrochemical Properties of a Conducting Film Derived from Iron(II) Tris(diaminopolypyridyl) Complex in the S(IV) Oxoanions Reduction

A new conducting film derived from the complex [Fe (diaphen)₃]²⁺, (diaphen=5,6‐diamino‐1,10‐phenanthroline) was electropolymerized by cyclic voltammetry onto a glassy carbon electrode. Poly‐[Fe^II (diaphen)₃] was studied by cyclic voltammetry, SEM, UV‐vis and micro‐Raman spectroscopy. Poly‐[Fe^II (diaphen)₃] shows electrocatalytic activity in HSO₃^? reduction in an ethanol/water solution. Electrocatalysis is centered at the π ring of phenanthroline. Rotating disk electrode studies showed a 0.117 V/dec Tafel slope, suggesting an EC process where the electrochemical process is the determining step. The chemical step was studied by UV‐vis spectroelectrochemistry. Amperometric behavior showed a linear range between 47.5 µM to 417 µM and the LOD was 19.5 µM.     

The Hybrid of Gold Nanoparticles and 3D Flower‐like MnO2 Nanostructure with Enhanced Activity for Detection of Hydrogen Peroxide

3D Flower‐like manganese dioxide (MnO₂) nanostructure with the ability of catalysis for hydrogen peroxide (H₂O₂) and super large area that can support gold nanoparticles (AuNPs) with enhanced activity of electron transfer have been developed. The nanostructure of hybrids was prepared by directly mixing citric‐capped AuNPs and 3‐aminopropyltriethoxysilane (3‐APTES)‐capped nano‐MnO₂ using an electrostatic adsorption strategy. The Au‐MnO₂ composite was extensively characterized by scanning electron microscope (SEM), X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), the Brunauer‐Emmett‐Teller (BET) method and X‐ray photoemission spectroscopy (XPS). Electrochemical properties were evaluated through cyclic voltammetry (CV) and amperometric method. The prepared sensor showed excellent electrochemical properties towards H₂O₂ with a wide linear range from 2.5×10⁻³∼1.39 mM and 3.89∼13.89 mM. The detection limit is 0.34 μM (S/N=3) with the sensitivities of 169.43 μA mM⁻¹ cm⁻² and 55.72 μA mM⁻¹ cm⁻². The detection of real samples was also studied. The result exhibited that the prepared sensor can be used for H₂O₂ detection in real samples.     

Electrochemical Surface Structuring with Polyaniline Wrapped Hb for Hydrogen Peroxide Biosensing

Through the electrodeposition of aniline with hemoglobin (Hb) on zincoxide‐gold colloidal sols (ZnO‐AuNPs) modified indium oxide electrode, a hydrogen peroxide (H₂O₂) biosensor was constructed. Polyaniline (PANI) form a nano‐cage wrapped Hb, which provided a comfortable and stable site for the immobization of Hb. UV‐vis spectrum was employed to characterize Hb retained original structure in the resulting Hb‐PANI/ZnO‐AuNPs membrane. Electrochemical investigation of the biosensor showed a pair of well‐defined, quasi‐reversible redox peaks with E_pa= ‐0.139 V and E_pc = ‐0.238 V (vs. SCE) in 0.1 M pH 7.0 phosphate buffer solution at the scan rate of 100 mV/s. The biosensor displayed a fast response time (<3 s) and broad linear response to H₂O₂ in the range from 1.5 μM to 1.7 mM with a detection limit of 0.8 μM (S/N = 3).     

A Third‐Generation Hydrogen Peroxide Biosensor Based on Horseradish Peroxidase Immobilized in Carbon Nanotubes/ SBA‐15 Film

A new third‐generation biosensor for H₂O₂ assay was developed on the basis of the immobilization of horseradish peroxidase (HRP) in a nanocomposite film of carbon nanotubes (CNTs)‐SBA‐15 modified gold electrode. The biological activity of HRP immobilizing in the composite film was characterized by UV‐vis spectra. The HRP immobilized in the nanocomposite matrix displayed excellent electrocatalytic activity to the reduction of H₂O₂. The effects of the experimental variables such as solution pH and working potential were investigated using steady‐state amperometry. Under the optimal conditions, the resulting biosensor showed a linear range from 1 µM to 7 mM and a detection limit of 0.5 µM (S/N=3). Moreover, the stability and reproducibility of this biosensor were evaluated with satisfactory results.     

Preparation of 3D MnO2/Polyaniline/Graphene Hybrid Material via Interfacial Polymerization as High‐Performance Supercapacitor Electrode

MnO₂/polyaniline/graphene composite as a supercapacitor electrode material was synthesized through an interfacial polymerization approach in the interface of oil/water phase. The as‐synthesized MPG is characterized by infrared spectroscopy, XRD, XPS, SEM and TEM, and its electrochemical performance is measured by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. The 3D nanostructure of MPG and loose nanorod structure of polyaniline (PANI) coated with round MnO₂ pellets could be clearly observed. The maximum energy density of MPG is 45.4 Wh/kg (at a power density of 67.8 kW/kg) and the highest power density is 229.2 kW/kg (at an energy density of 25.7 Wh/kg). The capacitance retentions after 500 cycles at the scan rate of 5 mV/s for MGP composite and PANI/graphene are 70.4% and 59.1%, respectively, and the capacitance values after 500 cycles are 158.4 F/g and 114.8 F/g, respectively. The improved performance of MPG is due to the 3D nanostructure, loose nanorod structure of PANI and stable support of graphene, which prevent the mechanical deformation effectively during the fast charge/discharge process and facilitate the diffusion of the electrolyte ions into the inner region of active materials. The composite material is very promising for the next generation of high‐performance supercapacitors electrode.