Polypyrrole Carbon Research Articles

Carbon-nitrogen/graphene composite as metal-free electrocatalyst for the oxygen reduction reaction

Sheet-like carbon-nitrogen (CNx)/graphene composites with a high content of nitrogen (x ⩽ 0.15) was prepared by the carbonization of polypyrrole (PPy)/reduced-graphene-oxide (rGO) composite at 600–800°C. We used rGO instead of graphene oxide (GO) sheets as a template and a substrate to immobilize PPy since the PPy/GO composite agglomerates easily because of the dehydration of excess oxygen-containing groups on the GO sheets during the drying process. The dried PPy/rGO intermediate and its derived CNx/graphene products retain their high dispersion and loose-powder features. The as-prepared CNx/graphene composites have a total nitrogen content of about 10 at% and their nitrogen state is mainly of pyridinic and graphitic type. CNx/graphene composites exhibit excellent performance for the oxygen reduction reaction (ORR) in terms of electrocatalytic activity, stability and immunity towards methanol crossover and CO poisoning, suggesting their potential as metal-free electrocatalysts for the ORR.

Effect of 5-sulfosalicylic acid and poly[2,5-bis(3-sulfonatopropoxy)-1,4-ethynylphenylene-alt-1,4-ethynylphenylene] on electrodeposition of polypyrrole–carbon nanotube films on stainless steel

Polypyrrole (PPY) films were obtained on stainless steel substrates by anodic electropolymerization using sulfosalicylic acid (SSA) as an anionic dopant. SSA adsorption prevented anodic oxidation of stainless steel during electropolymerization, provided efficient charge transfer and enabled the formation of adherent films. It was shown that poly[2,5-bis(3-sulfonatopropoxy)-1,4-ethynylphenylene-alt-1,4-ethynylphenylene] sodium salt provided efficient dispersion of single-walled carbon nanotubes (SWNTs) and allowed the formation of composite PPY–SWNT films. The PPY–SWNT films showed improved capacitive behavior compared to PPY films due to lower resistance and higher porosity. The highest specific capacitance of 295 Fg−1 was obtained at a scan rate of 2mVs−1. The composite films are promising materials for application in electrochemical supercapacitors.

Polypyrrole-modified graphitized carbon black as a catalyst support for methanol oxidation

Surface-modified graphitized carbon black (GCB) was produced through carbonization of polypyrrole (Ppy) on the GCB surface to be used as a catalyst support for Pt nanoparticles in electro-oxidation of methanol. The Ppy modification led to the enhancement of the catalytic activity for the Pt catalysts. The improvement is largely attributed to uniform dispersion of the Pt nanoparticles as the Ppy modification appears to reduce the agglomeration of the Pt nanoparticles. The chronoamperometry and the accelerated cycling tests indicated that the Ppy modification did not improve the long-term stability of the GCB support for Pt.

Cobalt–polypyrrole–carbon black (Co–PPY–CB) electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells: Composition and kinetic activity

Electrocatalysts consisting of polypyrrole (PPY) and Co deposited on carbon black (CB) at several compositions were prepared and tested for the oxygen reduction reaction (ORR) in a HClO4 buffer (pH=1) using a rotating ring-disk electrode (RRDE). It was determined that the most favorable catalyst composition (prior to calcination) had a CB:PPY weight ratio of 2 and a pyrrole:Co (i.e., PY:Co) molar ratio of 4. This catalyst had an onset potential of 0.785V (vs. RHE) and a mass activity of ca. 1A/gcata at the fuel cell relevant voltage of 0.65V. Furthermore, it was found that the number of electrons exchanged during the ORR with the catalyst was ca. 3.5 and resulted in 28% yield of H2O2 at 0.65V, which hints to an indirect 4e− reduction of O2 to H2O, with H2O2 as an intermediate. From energy dispersive spectroscopy (EDS) and extended X-ray absorption fine structure (EXAFS) analysis, it is proposed that a PY:Co ratio of 4 favors the formation, prior to calcination, in the catalyst precursor of Co–N complexes in which Co is coordinated to 3 or 4 N atoms, resulting in strong Co–N interactions that limit the formation upon calcination of low ORR activity Co nanoparticles. These Co–N complexes give rise upon calcination to CoNx−2 sites in which the coordination of Co could favor the adsorption on them of O2, which would make those sites particularly active and selective. At the same mass activity of 1A/gcata, the voltage yielded by the catalyst was 200mV lower than that for a state-of-the-art Pt (10wt.%) catalyst, whose H2O2 output at 0.85V was 39% and involves the exchange of 3.2e−, overall making our material an attractive substitute to noble metal ORR electrocatalysts.

Flow injection determination of catechol based on polypyrrole–carbon nanotube–tyrosinase biocomposite detector

A flow injection catechol biosensor based on tyrosinase entrapped in carbon nanotube modified polypyrrole biocomposite film on a glassy carbon surface has been developed. Amperometric response was measured as a function of concentration of catechol, at a fixed bias voltage of −50 mV at a flow rate of 1 mL/min. The proposed biosensor exhibited impressive analytical performance such as a linear range between 3 and 50 μM, a short response time (10 s), a detection limit of 0.671 μM and an excellent operational (with a relative standard deviation of 0.54%) and long-term stability (85% remained after 10th week). A comparison of the analytical parameters of the developed biosensor with polypyrrole/tyrosinase film electrode was performed in the study. CNT was shown to enhance the electron transfer between the electrode and enzyme and capable to carry higher bioactivity owing to its intensified surface area.

Study of Anode Catalysts and Fuel Concentration on Direct Hydrazine Alkaline Anion-Exchange Membrane Fuel Cells

A platinum-free fuel cell using liquid hydrazine hydrate as the fuel and comprised of a cobalt or nickel anode and a cobalt cathode exhibits high performance. In this study, the fuel cell performances using nickel, cobalt, and platinum as anode catalysts are evaluated and compared. It is found that fuel cell performance in the case of nickel and cobalt is higher than that in the case of platinum. Further, anodic reactions are discussed by comparing the hydrazine consumption and ammonia generation when cobalt and nickel are used as anode catalyst. Cobalt exhibits a higher rate of decomposition than nickel. Nickel is found to be the most suitable anode catalyst among the above mentioned anode catalysts for this fuel cell. The influence of hydrazine hydrate and KOH concentrations in the fuel on cell performance is also discussed. Cell performance is the highest at a hydrazine hydrate concentration of and a KOH concentration of . The maximum power density of the alkaline anion-exchange membrane fuel cell, comprised of a nickel anode and a Co–PPY–C (cobalt polypyrrole carbon) cathode, is .

A cobalt polypyrrole composite catalyzed cathode for the direct borohydride fuel cell

A cobalt polypyrrole carbon (Co-PPY-C) composite has been attempted for use as a cathode catalyst in a direct borohydride fuel cell (DBFC). A Co-PPY-C composite has been fabricated in laboratory and characterized by the field emission scanning electron microscopy, transmission electron microscopy, as well as X-ray photoemission spectroscopy. Fabricated Co-PPY-C catalyst demonstrates good short-term durability and activity which are comparable to those obtained from the Pt/C catalyst. A maximum power density of 65 mW cm −2 has been achieved at ambient conditions. This research concludes that metallo-organic coordination compounds would be potential candidates for use as cathode catalysts in the DBFC.

Polypyrrole-Based Nitrogen-Doped Carbon Replicas of SBA-15 and SBA-16 Containing Magnetic Nanoparticles

Polypyrrole-based ordered mesoporous carbons (OMCs) were synthesized via chemical vapor infiltration of pyrrole into pores of the SBA-15 and SBA-16 silica templates containing iron(III) chloride catalyst (FeCl3). After carbonization of polypyrrole at 800 °C and etching of the silica templates with hydrofluoric acid solution, nitrogen-doped and graphitic OMCs with incorporated magnetic nanoparticles were obtained. These materials were analyzed by CHNS elemental analysis, thermogravimetry (TG), nitrogen adsorption, small and wide angle powder X-ray diffraction (XRD), Raman spectroscopy, scanning, and transmission electron microscopy (TEM). The resulting carbon replicas retained the crystallographic symmetry of the silica templates: namely, P6mm in the case of the SBA-15 template, and Im3m in the case of the SBA-16 template. The uniformity, size, and volume of ordered mesopores in the carbon replicas were affected by structural properties of the templates used as shown by analysis of nitrogen adsorption isotherms and pore size distributions. A better infiltration of carbon precursor was achieved for the templates with larger pores, which resulted in the carbon replicas of improved adsorption and structural properties. Elemental analysis revealed the presence of nitrogen in the carbon replicas studied in the range of 3−8 wt %, whereas TG analysis of the replica samples in air gave about 2−5% residue, which was identified as hematite (Fe2O3). The presence of graphitic domains was confirmed by characteristic TG oxidation profile above 400 °C, the D and G bands on the Raman spectra, and the intense reflections on the wide angle XRD patterns. Powder XRD also showed the presence of extra-framework magnetic iron (α-Fe) and iron carbide (Fe3C) nanoparticles having crystallite size in the ranges of 40−80 and 20−40 nm, respectively. TEM images also revealed that these nanoparticles were larger than the carbon rods and pore widths of the SBA-15 carbon replica, which is in good agreement with the XRD-based estimation. The in situ EDS analysis of carbon rods and spheres showed that iron was present in the carbonaceous framework, which does not exclude the existence of much smaller nanoparticles, below 5 nm.

Synthesis and characterization of bimetallic Pt–Fe/polypyrrole–carbon catalyst as DMFC anode catalyst

A novel synthesis route, concerning in situ interfacial polymerization of pyrrole on carbon black and following co-deposition of Pt and Fe on polypyrrole–carbon support, is developed to prepare the bimetallic Pt–Fe/polypyrrole–carbon catalyst. In this synthesis process, ferrous precursor simultaneously functions as an oxidant for the polymerization of pyrrole. The Pt–Fe/polypyrrole–carbon catalyst shows improved catalytic activity towards methanol oxidation compared to commercial Pt/C catalyst, which may be of great potential in direct methanol fuel cells.

Nanostructured polypyrrole/carbon composite as Pt catalyst support for fuel cell applications

A novel catalyst support was synthesized by in situ chemical oxidative polymerization of pyrrole on Vulcan XC-72 carbon in naphthalene sulfonic acid (NSA) solution containing ammonium persulfate as oxidant at room temperature. Pt nanoparticles with 3–4 nm size were deposited on the prepared polypyrrole–carbon composites by chemical reduction method. Scanning electron microscopy and transmission electron microscopy measurements showed that Pt particles were homogeneously dispersed in polypyrrole–carbon composites. The Pt nanoparticles-dispersed catalyst composites were used as anodes of fuel cells for hydrogen and methanol oxidation. Cyclic voltammetry measurements of hydrogen and methanol oxidation showed that Pt nanoparticles deposited on polypyrrole–carbon with NSA as dopant exhibit better catalytic activity than those on plain carbon. This result might be due to the higher electrochemically available surface areas, electronic conductivity and easier charge-transfer at polymer/carbon particle interfaces allowing a high dispersion and utilization of deposited Pt nanoparticles.

Electrochemical quartz crystal impedance study on the overoxidation of polypyrrole–carbon nanotubes composite film for amperometric detection of dopamine

The electrochemical quartz crystal impedance (EQCI) method was used to study the overoxidation of polypyrrole (PPy)–multiwalled carbon nanotubes (MWCNT) nanocomposite film in neutral and alkaline solutions. The values of molar mass per electron transferred (M/n) obtained during the overoxidation of PPy in 0.10molL−1 Na2SO4 and 0.20molL−1 NaOH aqueous solutions were estimated to be ca. 17 and 22gmol−1, respectively, suggesting the nucleophilic attack of solution OH− to the pyrrole units during the overoxidation, and the possible partial formation of carboxylic groups after the overoxidation in the NaOH solution. Also, the overoxidized PPy–MWCNT composite film prepared in the NaOH solution showed a notably larger affinity to dopamine (DA) dissolved in a neutral phosphate buffer than that prepared in the Na2SO4 solution. The modification of the overoxidized nanocomposite film improved substantially the sensitivity for DA assay in a neutral phosphate buffer, as compared with the modification of overoxidized PPy or MWCNT alone. At a −6kHz (201-nm thickness) nanocomposite film prepared in a polymerization bath containing 1.0mgmL−1 MWCNT and overoxidized in 0.20molL−1 aqueous NaOH, the peak current response from differential pulse voltammetric assay of DA was linear with DA concentration from 4.0×10−8 to 1.4×10−6molL−1, with a lower limit of detection of 1.7nmolL−1, good anti-interferent ability, as well as good stability and reproducibility.

MEMS sensor material based on polypyrrole–carbon nanotube nanocomposite: film deposition and characterization

Conductive polymer-based nanocomposite has been utilized as a MEMS sensing material via a one-step, selective on-chip deposition process at room temperature. A doped polypyrrole (PPy) variant synthesized by incorporating multi-walled carbon nanotube (MWCNT) into electropolymerized PPy has been shown to improve the sensing performance utilizing a two-terminal, micro-gap chemiresistor architecture. The dodecylbenzenesulfonate (DBS)-doped PPy–MWCNT nanocomposites are found to be responsive to oxidants, such as hydrogen peroxide (H2O2), and this effect can be extended to glucose detection using H2O2 as a proxy material. The oxidant sensing effect is demonstrated by subjecting a glucose oxidase (GOx)-laden PPy–MWCNT nanocomposite film to various concentrations of glucose solution. Such PPy–MWCNT nanocomposite, when applied in a chemiresistor configuration, obviates the need for reference electrode and electron mediators, by measuring the direct and reversible, oxidation–reduction induced conductivity change. Experimentally, GOx-laden, doped PPy–MWCNT is tested to be sensitive to glucose concentration up to 20 mM, which covers the physiologically important range for diabetics of 0–20 mM.

Mesoporous carbons with graphitic structures fabricated by using porous silica materials as templates and iron-impregnated polypyrrole as precursor

Templated mesoporous carbons containing graphitic structures and a well-developed porosity were synthesised by using mesoporous silica materials (i.e. SBA-15 and silica xerogel) as templates and polypyrrole as carbon precursor. The polypyrrole was synthesised by in situ polymerization of pyrrole which was infiltrated into the silica pores containing FeCl3. The carbonization of polypyrrole in presence of iron allows carbon structures with some degree of graphitic order to be formed. The samples were characterised by XRD, nitrogen sorption, TEM, Raman and elemental analysis. The results show that the templated carbons have BET surface areas >1000 m2 g−1 and a porosity built up by two pore systems with sizes centred at ∼3–4 nm and at 10–14 nm. In addition, they have a good electrical conductivity due to the presence of graphitic structures in the carbon framework.

Studies of deposition of and charge storage in polypyrrole?chloride and polypyrrole?carbon nanotube composites with an electrochemical quartz crystal microbalance

Carbon nanotubes and their composites with conducting polymers are of interest for supercapacitor and other electrode applications. This paper reports the use of the electrochemical quartz crystal microbalance to investigate the deposition and intercalation behaviour of polypyrrole–carbon nanotube and polypyrrole–chloride thin layers. The standard plots of mass versus potential were converted to “massograms” by differentiating the mass with respect to time. As dm/dt is proportional to I, the plot is directly comparable to the voltammogram. Using these data, deposition potentials of 0.7 and 0.8 V were selected for polypyrrole–chloride and polypyrrole–carbon nanotube films, respectively. In polypyrrole–chloride deposits, anion uptake upon oxidation was observed. In the polypyrrole–nanotube layers, a mix of cation expulsion and anion uptake upon oxidation is observed when using 0.1 M KCl (aq) as the electrolyte. However, using 0.1 M tetrabutylammonium bromide, only uptake of bromide is observed, due to the bulkiness of the cation. In addition to this complex charge neutralisation behaviour, a redox pseudocapacitance was confirmed directly using the massogram data.

Studies of deposition of and charge storage in polypyrrole–chloride and polypyrrole–carbon nanotube composites with an electrochemical quartz crystal microbalance

Carbon nanotubes and their composites with conducting polymers are of interest for supercapacitor and other electrode applications. This paper reports the use of the electrochemical quartz crystal microbalance to investigate the deposition and intercalation behaviour of polypyrrole–carbon nanotube and polypyrrole–chloride thin layers. The standard plots of mass versus potential were converted to “massograms” by differentiating the mass with respect to time. As d m/d t is proportional to I, the plot is directly comparable to the voltammogram. Using these data, deposition potentials of 0.7 and 0.8 V were selected for polypyrrole–chloride and polypyrrole–carbon nanotube films, respectively. In polypyrrole–chloride deposits, anion uptake upon oxidation was observed. In the polypyrrole–nanotube layers, a mix of cation expulsion and anion uptake upon oxidation is observed when using 0.1 M KCl (aq) as the electrolyte. However, using 0.1 M tetrabutylammonium bromide, only uptake of bromide is observed, due to the bulkiness of the cation. In addition to this complex charge neutralisation behaviour, a redox pseudocapacitance was confirmed directly using the massogram data.

Control of surface structure of graphite fibres for improved composite interfacial properties

The properties of carbon fibres modified by aqueous electrochemical synthesis of pyrrole have been determined by using a dynamic contact angle analyser, scanning electron microscopy, and Fourier transform infrared spectroscopy (FTIR). Electrochemical process parameters such as initial pyrrole concentration, electrolyte concentration, applied voltage, electrolyte type, and reaction time were systematically varied and their impacts on the polypyrrole–carbon fibre interphase surface free energy and morphology ascertained. The surface free energies of the polypyrrole–carbon fibre interphases were obtained using single fibre filaments. SEM analysis of the interphases revealed several distinct surface structures, including smooth, porous, granular, microspheroidal, and plateletlike morphologies. Non-coated, commercially surface oxidised carbon fibres have smooth surface morphology with occasional longitudinal striations. FTIR analysis of the polypyrrole interphases confirmed that the counterions derived from the electrolytes were incorporated into the film. The surface free energies of the electrochemically formed polypyrrole–carbon fibre interphases (0·06–0·075 J m-2) were determined to be up to 40% higher than those of surface oxidised but unsized carbon fibres (0·05 J m-2). This improvement in the surface free energies of the polypyrrole–carbon fibre interphases suggests easy wettability by polymer matrices such as epoxy resin and polyimide (surface free energies around 0·047 and 0·045 J m-2 respectively).

Physical and chemical properties of polypyrrole-carbon fiber interphases formed by aqueous electrosynthesis

The properties of carbon fibers modified by aqueous electrochemical synthesis of pyrrole has been determined by using the dynamic contact angle analyzer (DCA), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). Electrochemical process parameters such as the initial pyrrole concentration, electrolyte concentration, applied voltage, electrolyte type, and reaction time were systematically varied, and their impact on the polypyrrole–carbon fiber interphases surface free energy and morphology was ascertained. The surface free energies of the polypyrrole–carbon fiber interphases were obtained by using single fiber filaments. SEM analysis of the interphases revealed several distinct surface structures, including smooth, porous, granular, microspheroidal, and leafoidal morphologies. The noncoated but commercially surface oxidized carbon fibers have smooth surface morphology with occasional longitudinal striations. FTIR analysis of the polypyrrole interphases confirmed that the counterions derived from the electrolytes were incorporated into the film. The surface free energies of the electrochemically formed polypyrrole–carbon fiber interphases equivalent to 60–75 dynes/cm, was determined to be up to 40% higher than that for the surface oxidized but unsized carbon fibers equivalent to 50 dynes/cm. This improvement in the surface free energies of the polypyrrole–carbon fiber interphases suggests easy wettability by polymer matrices such as epoxy resin, γ ˜ 47 dynes/cm and, polyimide matrix, γ ˜ 45 dynes/cm. © 1996 John Wiley & Sons, Inc.