Electrochemical characterization of PANI-Nafion membranes and their electrocatalytic activity

PANI-Nafion^® membranes were prepared by a chemical method in which the faces of a commercial Nafion membrane were contacted with two acid solutions containing an oxidant (Fe³⁺) and aniline respectively. They were then characterized by a variety of electrochemical techniques (cyclic voltammetry, chronoamperometry, ac impedance). PANI was stored mostly in the vicinity of the Nafion face exposed to the oxidant. When this face was contacted with Hg and the other with electrolyte solutions, typical electrochemical responses of PANI were detected. Electrocatalytic reduction of O₂ and oxidation of N₂H₄ were achieved on PANI-Nafion electrodes and found to be only slightly slowed down with respect to ordinary PANI film electrodes, at variance with a fast process such as Fe³⁺ reduction, the rate of which was severely limited by diffusion through the membrane.     

Electrochemical storage properties of polyaniline-, poly(N-methylaniline)-, and poly(N-ethylaniline)-coated pencil graphite electrodes

Three types of conducting polymers, polyaniline (PANI), poly(N-methylaniline) (PNMA), poly(N-ethylaniline) (PNEA) were electrochemically deposited on pencil graphite electrode (PGE) surfaces characterized as electrode active materials for supercapacitor applications. The obtained films were electrochemically characterized using different electrochemical methods. Redox parameters, electro-active characteristics, and electrostability of the polymer films were investigated via cyclic voltammetry (CV). Doping types of the polymer films were determined by the Mott-Schottky method. Electrochemical capacitance properties of the polymer film coating PGE (PGE/PANI, PGE/PNMA, and PGE/PNEA) were investigated by the CV and potentiostatic electrochemical impedance spectroscopy (EIS) methods in a 0.1 M H₂SO₄ aqueous solution. Thus, capacitance values of the electrodes were calculated. Results show that PGE/PANI, PGE/PNMA, and PGE/PNEA exhibit maximum specific capacitances of 131.78 F g^?1 (≈ 436.50 mF cm^?2), 38.00 F g^?1 (≈ 130.70 mF cm^?2), and 16.50 F g^?1 (≈ 57.83 mF cm^?2), respectively. Moreover, charge-discharge capacities of the electrodes are reported and the specific power (SP) and specific energy (SE) values of the electrodes as supercapacitor materials were calculated using repeating chronopotentiometry.     

Conducting Polyaniline Nanowire Arrays Modified Electrode for High Performance Supercapacitor and Enhanced Catalysis of Nitrite Reduction

Vertically aligned conducting polymer nanowire arrays had great potential applications in supercapacitor electrode material and exhibited enhanced electrocatalytic behavior towards the reduction of nitrite. In this paper, a facial template‐free approach to synthesize large arrays of vertically aligned polyaniline (PANI) nanowires on electrochemically pretreated glassy carbon electrodes was reported by using a galvanostatic current method. The as‐prepared large arrays of PANI nanowires had very narrow diameters and were oriented perpendicular to the substrate, which was a benefit to the ion diffusion when being used as the supercapacitor electrode. The highest specific capacitance of PANI nanowire arrays was measured and kept high at a large charge‐discharge current density. Furthermore, it also can detect nitrite with ultrahigh sensitivity of 62.99 µA mM^?1 cm^?2 and a remarkable fast response time of less 1 s. The results indicated that the vertically aligned PANI nanowires could dramatically enhance the electrochemical performance.     

Impedance study of thiolated polyaniline

Covalent attachment of thiolated probes to conducting polymers such as polyaniline (PANI) is a promising approach towards the development of electrochemical sensors and biosensors. However, thiolation alters the conjugated polymer backbone and influences the electrochemical behavior of the conducting polymer. PANI studied in this work was electropolymerized on glassy carbon (GC) electrodes from a solution of 0.1 M aniline in 0.5 or 1.0 M H₂SO₄. The GC/PANI electrodes were then functionalized by covalent attachment of 2-mercaptoethanol to the PANI backbone. The progress of thiolation was studied by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Thiolation of PANI was found to cause an initial decrease in electroactivity at 0–0.25 V and an increase in electroactivity at 0.25–0.6 V. However, prolonged thiolation caused a loss of electroactivity of PANI, which could be seen from EIS measurements as a dramatic decrease in the bulk redox capacitance of PANI.     

Nanostructured polyaniline-coated anode for improving microbial fuel cell power output

An approach for improving the power generation of a dual-chamber microbial fuel cell by using a nanostructured polyaniline (PANI)-modified glassy carbon anode was investigated. Modification of the glassy carbon anode was achieved by the electrochemical polymerisation of aniline in 1 M H₂SO₄ solution. The MFC reactor showed power densities of 0.082 mW cm^?2 and 0.031 mW cm^?2 for the nano- and microstructured PANI anode, respectively. The results from electron microscopy scanning confirmed formation of the nanostructured PANI film on the anode surface and the results from electrochemical experiments confirmed that the electrochemical activity of the anode was significantly enhanced after modification by nanostructured PANI. Electrochemical impedance spectroscopic results proved that the charge transfer would be facilitated after anode modification with nanostructured PANI.     

A completely spray-coated membrane electrode assembly

We present a proton exchange membrane fuel cell (PEMFC) manufacturing route, in which a thin layer of polymer electrolyte solution is spray-coated on top of gas diffusion electrodes (GDEs) to work as a proton exchange membrane. Without the need for a pre-made membrane foil, this allows inexpensive, fast, large-scale fabrication of membrane-electrode assemblies (MEAs), with a spray-coater comprising the sole manufacturing device. In this work, a catalyst layer and a membrane layer are consecutively sprayed onto a fibrous gas diffusion layer with applied microporous layer as substrate. A fuel cell is then assembled by stacking anode and cathode half-cells with the membrane layers facing each other. The resultant fuel cell with a low catalyst loading of 0.1 mg Pt/cm² on each anode and cathode side is tested with pure H₂ and O₂ supply at 80 °C cell temperature and 92% relative humidity at atmospheric pressure. The obtained peak power density is 1.29 W/cm² at a current density of 3.25 A/cm². By comparison, a lower peak power density of 0.93 W/cm² at 2.2 A/cm² is found for a Nafion NR211 catalyst coated membrane (CCM) reference, although equally thick membrane layers (approx. 25 μm), and identical catalyst layers and gas diffusion media were used. The superior performance of the fuel cell with spray-coated membrane can be explained by a decreased low frequency (mass transport) resistance, especially at high current densities, as determined by electrochemical impedance spectroscopy.     

Electrodeposition of polyaniline on high electroactive indium tin oxide nanoparticles-modified fluorine doped tin oxide electrode for fabrication of high-performance hybrid supercapacitor

In this study, hierarchical polyaniline (PANI) nanosheets were electrochemically deposited on indium tin oxide nanoparticles coated fluorine-doped tin oxide glass (ITONPs-FTO) substrate from an aqueous solution containing 0.5 M aniline and 1 M H₂SO₄. The ITONPs provide efficient support with high electroactive surface area in the electrochemical deposition of PANI and produce excellent PANI films. The developed PANI film deposited on the ITONPs-FTO electrode was characterized via field-emission scanning-electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. A hybrid supercapacitor (HSC) was fabricated using the developed PANI deposited ITONPs-FTO as a positrode and the jute sticks derived activated carbon nanosheets coated FTO (JAC-FTO) as a negatrode. Because of its high capacitive performance, unique structures of electrode materials, and optimum operating potential window, the fabricated PANI-ITONPs-FTO//JAC-FTO HSC performed excellently in 0.1 M HCl aqueous electrolyte, delivering a high areal capacitance of 318 mF/cm² at a 1.0 mA/cm² current density and exhibit a high energy density of 28 µWh/cm² at a high power density of 400 µW/cm². Moreover, the HSC exhibits excellent cyclic stability with ～ 87% Coulombic efficiency and ～ 91% capacitance retention after 1000 charge–discharge cycles.     

Sacrificial template synthesis of ultrathin polyaniline nanosheets and their application in highly sensitive electrochemical dopamine detection

Unique functional nanomaterials as electroactive media for efficiently electrochemical biosensing have always been an ever-increasing topic in biotechnology and environmental fields. In this study, we report a simple sacrificial template-guided polymerization strategy to fabricate ultrathin two-dimensional (2D) polyaniline (PANI) nanosheets for electrochemical detection of dopamine (DA). By using vanadium pentoxide nanosheets as both sacrificial templates and oxidants, the resulting PANI nanosheets show an ultrathin thickness of ca. 4 nm with a favorable electrical conductivity of ca. 10 S cm^?1. Furthermore, PANI nanosheets have been modified on a glass carbon electrode for highly sensitive DA detection. The proposed DA sensor delivers a linear range of 0.5–300 μM with a low detection limit of 0.118 μM (S/N = 3). In addition, the as-fabricated electrochemical sensor exhibits an outstanding selectivity, stability, reproducibility, and repeatability, enabling its feasible application for DA detection in real samples. Therefore, the ultrathin PANI nanosheets reported here are good candidates as electrodes for the sensitive and selective DA detection.     

Surface redox polymerized SPEEK–MO2–PANI (M = Si, Zr and Ti) composite polyelectrolyte membranes impervious to methanol

We reported sulfonated poly(ether ether ketone) (SPEEK, 61% degree of sulfonation)–metal oxides (MO₂:SiO₂, TiO₂ and ZrO₂)–polyaniline composite membranes. Metal oxides were incorporated into the swelled SPEEK membrane by sol–gel method and cured by thermal treatment. SPEEK–metal oxide membranes surfaces were modified with polyaniline (PANI) by a redox polymerization process. It was observed that water retention capacity of membrane was increased and methanol permeability was reduced due to synergetic effect of metal oxides and surface modification with polyaniline. These composite membranes showed extremely low methanol permeability (1.9–1.3 × 10⁻⁷ cm² s⁻¹), which was lower than till reported values either for SPEEK–metal oxide or SPEEK/PANI membranes. Relatively high selectivity parameter (SP) values at 343 K of these membranes, especially S–SiO₂–PANI and S–TiO₂–PANI, indicated their great advantages over Nafion117 (N117) membrane for targeting on moderate temperature applications due to the synergetic effect of MO₂ and PANI in SPEEK matrix. S–TiO₂–PANI and N117 showed comparable cell performance in direct methanol fuel cell (DMFC).     

Electrochemical immunoassay of benzo[a]pyrene based on dual amplification strategy of electron-accelerated Fe3O4/polyaniline platform and multi-enzyme-functionalized carbon sphere label

An electrochemical immunosensor, basing on a dual amplification strategy by employing a biocompatible Fe₃O₄/polyaniline/Nafion (Fe₃O₄/PANI/Nafion) layer as sensor platform and multi-enzyme-antibody functionalized highly-carbonized spheres (multi-HRP-HCS-Ab₂) as label, was constructed for sensitive detection of benzo[a]pyrene (BaP). The stable film, Fe₃O₄/PANI/Nafion, can not only immobilize biomolecules, but also catalyze the reduction of hydrogen peroxide, indicating an accelerated electron transfer pathway of the platform. The experimental conditions, including the concentration of Nafion, concentration of Fe₃O₄/polyaniline (Fe₃O₄/PANI), pH of the detection solution and concentrations of biomolecules, were studied in detail. Basing on a competitive immunoassay, the current change was proportional to the logarithm of BaP concentration in the range of 8 pM and 2 nM with the detection limit of 4 pM. The proposed immunosensor exhibited acceptable reproducibility and stability. This new type of dual amplification strategy may provide potential applications for the detection of environmental pollutants.     

Influence of Analyte Flow Rate on Signal and Response Time of the Amperometric Gas Sensor with Nafion Membrane

This paper presents results of an investigation on influence of volumetric flow rate on the signal and response time of a prototype of sulfur dioxide gas sensor with Nafion membrane. The sensors differing in type of working electrode and composition of internal electrolyte were compared. We used Au and Pt working electrodes obtained via vacuum sublimation deposition on a Nafion membrane surface. The electrolytes were aqueous solutions of sulfuric acid of the summary concentration 5 mol dm^?3 (electrolyte A). The electrolyte B contained an addition of dimethylsulfoxide (DMSO); the water/DMSO molar ratio was 2 : 1. Based on a proposed equation, which takes diffusion resistance into account, the obtained sensor signals were analyzed for the flow rate within a range of 0–100 cm³ min^?1. The sensor response time was also determined for the above flow rate range.     

Synergistical assembly of multiwalled carbon nanotubes/polyaniline network for dye‐sensitized solar cells

In this study, an aniline (ANI) solution containing well‐dispersed multiwall carbon nanotubes (CNTs) has been prepared. With an aim of improving the dispersability of CNTs in ANI monomer, we synthesize CNTs/ANI complexes using a reflux technique which can be electrochemically polymerized to form well‐dispersed CNTs/polyaniline (PANI) films. The refluxed CNTs/ANI solution can be used to prepare high porous CNTs/PANI network via an electrochemical polymerization for applying as counter electrodes in dye‐sensitized solar cells. Compared with the pristine PANI, the multiwalled CNTs/PANI network shows more porous morphology and higher electrocatalytic activity, resulting in the acceleration of the reaction (triiodide (I^3?) to iodide (I^?)) of the redox electrolyte. The enhancement of the electrocatalytic activity is attributed to the interactions between multiwalled CNTs and PANI, promoting the quinoid ring structure and thus enhancing the conductivity of the polymer chains. The device, assembled with multiwalled CNTs/PANI network as counter electrodes, delivers 7.67% power conversion efficiency, which is comparable to 7.43% of that with Pt. Copyright © 2014 John Wiley & Sons, Ltd.     

Electrodeposition of Three‐Dimensional Porous Platinum Film on Removable Polyaniline Template for High‐Performance Electroanalysis

Three‐dimensional porous platinum (Pt_por) films are prepared based on Pt electrodeposition on polyaniline (PANI) modified electrodes followed by selective dissolution of PANI with HNO₃. Electrochemical quartz crystal microbalance data suggest that the PANI‐H₂PtCl₆ interaction involves redox and coordination reactions, depending on the working potential. The Pt_por shows better electrocatalytic performance than the Pt/PANI and conventionally electrodeposited Pt. The Pt_por modified glassy carbon electrode (GCE) can electrocatalyze the oxidation of H₂O₂ with a sensitivity of 414 µA cm^?2 mM^?1 and a detection limit of 9 nM, and the chitosan‐glucose oxidase/Pt_por/GCE can sense glucose with a sensitivity of 93.4 µA cm^?2 mM^?1.     

A Polyaniline-Deposited Nonplatinum Metal as a Potentiometric Sensor—An Inexpensive Alternate to Conventional Platinum for Some Potentiometric Redox Reactions

For the purpose of employing an inexpensive alternative to conventional platinum for use by upper-division as well as graduate students, polyaniline (PANI)-deposited stainless steel (SS) and mild steel (MS) electrodes are described as indicator electrodes for potentiometry and potentiometric titrations of some redox reactions. PANI is deposited on the nonplatinum metal by electrochemical polymerization of aniline using cyclic voltammetric technique. Alternate methods to produce the PANI electrodes are also suggested. The electrodes respond to concentration changes of hydroquinone (H₂O), Fe²⁺/Fe³⁺, and [Fe(CN)₆]^4–/[Fe(CN)₆]^3– in HCL electrolytes, and the potential variation with concentration follows the Nernst relationship. Under identical experimental conditions, the response time of the PANI/SS, PANI/MS, and Pt electrodes for a change in concentration of Fe³⁺ in a mixed electrolyte of Fe²⁺ and Fe³⁺ is found to be about 20 s. Neutralization reaction of HC1 versus NaOH, redox reaction of Fe²⁺ and Ce⁴⁺, and redox reaction of Fe²⁺ and KMnO₄ in several concentrations in the range from 1 mM to 100 mM are carried out using the PANI/SS, PANI/MS, and Pt indicator electrodes. The performance of the PANI/SS and PANI/MS electrodes is as good as that of the Pt at all concentration levels of the titrations. The electrodes can be reused for several titrations by storing them in an acid electrolyte for a long period of time. Thus, the conventional inert Pt or Au can be substituted for by using a PANI-deposited nonplatinum reactive metal as a potentiometric sensor for redox titrations.     

Interlaced polyaniline/carbon nanotube nanocomposite co-electrodeposited on TiO<Subscript>2</Subscript> nanotubes/Ti for high-performance supercapacitors

A series of PANI-CNTs/TiO₂ nanotubes/Ti electrodes were fabricated via pulse current co-electrodeposition of polyaniline and functionalized carbon nanotubes onto TiO₂ nanotubes/Ti electrodes. FT-IR spectrometry, X-ray photoelectron spectroscopy, and scanning electron microscopy were applied in order to characterize the modified TiO₂ nanotubes/Ti electrodes. The morphology studies showed that the PANI-CNTs/TiO₂ nanotubes/Ti nanocomposite electrode has many interlaced PANI-CNTs nanorods on the surface of TiO₂ nanotubes. The electrochemical measurements of the modified electrodes confirmed that the CNTs in the composite can significantly improve the capacitive behavior as well which have been compared with that of PANI/TiO₂ nanotubes/Ti electrodes. The modified electrode exhibited much higher specific capacitance (190 mF cm^?2 with 90% retention after 1000 cycles) compared to the PANI/TiO₂ nanotubes/Ti (70 mF cm^?2 with 77% retention after 1000 cycles) at a current density of 0.85 mA cm^?2, indicating its great potential for supercapacitor applications.

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Graphical abstract Interlaced polyaniline/carbon nanotube nanocomposite electrodeposited on TiO₂ nanotubes/Ti

     

PANI/La2O3复合纳米材料的合成及其电化学降解的抑制作用

作为离子型表面活性剂, 对-甲基苯磺酸可用于氧化镧的预超声分散处理, 同时还可作为质子酸对聚苯胺(PANI)进行掺杂, 从而赋予聚苯胺导电性. 采用化学法合成了聚苯胺/氧化镧复合纳米材料, 用四探针法测定了材料的电导率, 用扫描电镜、电子能谱、X射线衍射、红外光谱等检测分析手段对材料进行了表征. 结果表明, 聚苯胺及聚苯胺/氧化镧复合纳米材料的电导率分别为1.0•和1.9 S•cm^－1, 粒子直径分别约为200和50 nm. 氧化镧的掺杂未降低聚苯胺的电导率, 并使粒径减小. 循环伏安实验结果说明, 氧化镧的掺杂可提高氧化还原峰的电流密度, 并能有效抑制聚苯胺在0.25～2.0 mol•L^－1的H₂SO₄及H₃PO₄水溶液中的电化学降解.     

Improvements in the electrochemical generation of arsine at gold electrodes as a sample introduction strategy for arsenic determination in well-water samples by atomic absorption spectrometry

The development and evaluation of a cathode consisting of a gold electrode covered by a polyaniline film, PANI/Au modified electrode, for electrochemical generation of arsine is described. The efficiency of arsine production using the new electrode was ascertained by comparison with corresponding hydride generation atomic absorption spectroscopy determinations of arsenic (As) in aqueous standards. The PANI/Au modified electrodes provide better sensitivity, accuracy and precision than the pure Au cathodes. The PANI/Au cathodes were prepared by controlled electrodeposition cycles of polyaniline films on top of Au electrodes. Cathodes obtained after 10 electrodeposition cycles showed the best performance, while the ones obtained after five voltammetry cycles produced films too thin and those obtained after 20 voltammetry cycles produced films too thick for the purpose of this work. Under optimised conditions, the As limit of detection in aqueous solutions, according to the (3σ) criterion, was 2.48 µg L^?1. For accuracy determination, the modified electrode was applied to quantification of As(III) in acidified aqueous solutions of the certified standard reference material, NIST SRM 1643d, and in well-water samples containing possible interfering ions. Application of the Student’s t-test showed no significant difference between the expected and obtained results of the NIST SRM standard analysis at the 95% confidence level. Values for six replicate determinations of As(III) in the well-water samples showed close agreement with values obtained by analyses using hydride generation atomic absorption. Recoveries were in the range of 95–105% at test for acceptable accuracy in the analysis of real samples.     

Tungsten oxide nanowires and polyaniline hybrid film-based electrochromic device with multicolor display and enhanced capacitance

Electrochromic devices (ECDs) have exhibited promising applications in the fields of energy-saving intelligent buildings and next-generation displays because of their simple structure, low power consumption, and multicolor displays. W₁₈O₄₉/polyaniline (PANI) hybrid films are prepared and assembled to ECDs. Compared with pure PANI and W₁₈O₄₉ films, the hybrid film exhibits superior electrochemical and electrochromic performance, including high optical modulation (70.2%), large areal capacity (79.6 mF/cm²), and good capacitance retention. The excellent electrochemical and electrochromic performance is ascribed to the formation of the donor (PANI)-acceptor (W₁₈O₄₉) pair, the porous structure in the nanowires, and the large surface area, which enhance electron delocalization of the W₁₈O₄₉/PANI, improve the ion diffusion rate, and increase the charge storage sites. Furthermore, benefitting from the outstanding optical, electrical, and multifunctional properties, the W₁₈O₄₉/PANI hybrid film-based ECD platform is expected to play an important role in electrochromism and energy storage.     

RECTIFYING EFFECT OF POLYANILINE(PANI)/N-TYPE POROUS SILICONE HETEROJUNCTION*

Heterojunctions between polyaniline (PANI) and n-type porous silicon (PS), Al/PS-PANI/Au cell,were fabricated, and the rectifying parameters of this heterojunction diode were measured as a function of thepreparation conditions of PANI and PS, the electronic structure of PANI as well as cell structure. Therectifying parameters of Al/PS-PANI/Au cell were determined to be γ= 1 .8×10~1～ 1 .0×10~5 for the rectifyingratio at 3V, n = 3 ～12 for the ideal factor,j_0 = 8.0×10~(-5)～5.6×10~(-2) mA/cm~2 for the reversed saturated currentdensity, and φ_b = 0.67～ 0.83 V for the barrier height, respectively. The best rectifying heterojunction diodemade between PANI and n-type PS with higher rectifying factor (γ= 1 .0×10~5 at 3V ), output current (>1500mA/cm~2 at 3V) and lower ideal factor (n = 3.3) was obtained by preventing the oxidation of PS beforeevaporating Al electrode.     

Synthesis of PANI and Study of Morphology in the Process of Polymerization

The polyaniline micro/nanostructure was prepared by a self‐assembly process with molybdic acid as dopants in the presence of ammonium persulfate as the oxidant. It was found that the morphology of PANI micro/nanostructure was affected by the concentration of the dopant, that is, the morphology of PANI changed from nanofibers to co‐existence of nanofibers and microspheres as the molar ratio of molybdic acid to aniline varied from 0.01 to 1.5. Under the same condition it was also found that the conductivity value of PANI enhanced from 4.58×10^?3 S·cm^?1 to 3.8×10^?1 S·cm^?1. The structure of PANI was characterized by FTIR and XRD which confirmed the presence of the molybdic acid in the PANI. The electrochemical characteristics of the PANI nanofibers were investigated by means of cyclic voltammetry. The morphology of PANI in the process of polymerization was characterized by SEM. It was found that when the molar ratio of molybdic acid to aniline was 0.3, the morphology of PANI was co‐existence of nanofibers and microspheres and the formation of microspheres was ahead of the nanofibers.