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Dawson-type 18-molybdodisulphate anion [S2Mo18O62](4-) has been immobilized within polypyrrole film by means of electrochemical polymerization. The polymer modified electrodes have been characteriz ...

Hierarchically structured materials (HSMs) are becoming increasingly important in catalysis, separation and energy applications due to their advantageous diffusion and flux properties. Here, we introduce a facile modular approach to fabricate HSMs with tailored functional conducting polypyrrole microparticles (PPyMP). The PPyMPs were fabricated with a calcium carbonate (CaCO3) template-assisted polymerization technique in aqueous media at room temperature, thus providing a new green chemistry for producing water-processable functional polymers. The sacrificial CaCO3 template guided the polymerization process to yield homogenous PPyMPs with a narrow size distribution. The porous nature of the CaCO3 further allows the incorporation of various organic and inorganic dopants such as an electrocatalyst and redox mediator for the fabrication of functional PPyMPs. Dawson-type polyoxometalate (POM) and methylene blue (MB) were chosen as the model electrocatalyst and electron mediator dopant, respectively. Hierarchically structured electrochemical interfaces were created simply by self-assembly of the functional PPyMPs. We demonstrate the versatility of this technique by creating two different hierarchical structured electrochemical interfaces: POM-PPyMPs for hydrogen peroxide electrocatalysis and MB-PPyMPs for mediated bioelectrocatalysis. We envision that the presented design concept could be extended to different conducting polymers doped with other functional organic and inorganic dopants to develop advanced electrochemical interfaces and to create high surface area electrodes for energy storage.

A functionalised Fe-substituted Keggin Na14[Fe4(C2O4)4(H2O)2(SbW9O33)2]·60H2O type POM termed “Fe4Ox4” has been successfully immobilised onto carbon electrode surfaces through the employment of conducting polypyrrole films and the layer-by-layer (LBL) technique. For the POM doped polypyrrole films the redox systems associated with the POM's tungsten-oxo framework was not apparent upon redox cycling, however a reversible redox couple associated with the FeIII/II redox system was clearly seen within the pH range 2–7. Organised multilayer assemblies were constructed by the employment of the layer by layer (LBL) technique through alternating anionic Fe4Ox4 layers and cationic RuII metallodendrimers with poly(diallyldimethylammonium chloride) (PDDA) employed as an initial base layer. Stable redox couples associated with both the FeIII/II and tungsten-oxo framework, for the Fe4Ox4 POM, and the RuIII/II for the metallodendrimer, were clearly observed upon layer construction and redox switching within the pH domain of 2–7. The resulting multilayer assembly showed good stability towards redox cycling. Further investigations into the multilayer assembly were undertaken by determining it is charge transfer resistance using AC-impedance voltammetry. The layer also showed catalytic ability towards the reduction of H2O2 at pH 6.5.

A series of transition metal (i.e. Cu2+ and Co2+) substituted Krebs type polyoxometalates (POMs), of the general formula [X2W20M2O70(H2O)6]n−, X = Sb or Bi, M = Co(II) or Cu(II), have been successfully immobilised onto carbon electrode surfaces through the employment of the layer-by-layer (LBL) technique. This involved the construction of alternating anionic POM, [X2W20M2O70(H2O)6]n−, layers and the cationic metallodendrimer, Ru(II)-metallodendrimer as the cationic layers, in addition to a [poly(diallyldimethylammonium chloride)] PDDA base layer. Stable multielectron redox couples associated with the W–O framework, for the Krebs type POMs, and the Ru(III/II) for the metallodendrimer, were clearly observed upon layer construction and redox switching within the pH domain of 2–6.5. The constructed multilayer assemblies exhibited pH dependent redox activity and thin layer behaviour up to 100 mV s−1. The porosity and permeability of the individual multilayer assemblies towards an anionic probe were determined by AC impedance and cyclic voltammetry. The surface morphology of each multilayer was also determined by Atomic Force Microscopy (AFM).

The conducting polymer, polypyrrole was successfully employed to surface immobilise the Krebs type polyoxometallate, K6NaH[Sb2W20Fe2O70(H2O)6]·29H2O, through cyclic voltammetry. The resulting K6NaH[Sb2W20Fe2O70(H2O)6]·29H2O doped polypyrrole films were found to exhibit the redox activity associated with both the Fe(III) and W–O redox centres within the POM. The former was found to be situated at potentials within the conducting part of the polymer whilst the latter redox process was in the insulating domain of the polypyrrole. The Fe(III/II) POM based redox process was found to be pH dependent. Upon redox switching of the polymer through this Fe(III/II) redox system, a process of cation insertion and expulsion into the polypyrrole matrix was observed with both the nature and concentration of the supporting electrolyte having a substantial effect upon the potential values at which this process occurred. This cation insertion–expulsion process was investigated through the application of the Electrochemical Quartz Crystal Microbalance (EQCM) technique. The result of which indicated that it was both the passage of alkali metal cations and protons from the background electrolyte into the polymer film which maintained electroneutrality within the POM polypyrrole films upon redox switching through the Fe(III/II) redox system. Finally the POM doped polypyrrole films exhibited a clear catalytic property towards the reduction of hydrogen peroxide (H2O2) with a sensitivity of 131.8 (±3.5) μA cm−2/mM with a LOD of 16.6 μM at neutral pH.

The electrochemical characterisation of films formed by co-polymerisation of [Os(2,2′-bipyridine)2XCl] (Os–PMP) where X is 3-(pyrrole-1yl-methyl)pyridine with 3-methyl thiophene or 1,2-diaminobenzene was carried out. The use of the membrane template method, which allowed growth of tubules of redox co-polymer was employed in the case of 1,2-diaminobenzene. Cyclic voltammetry allowed formation of the most stable 3-methylthiophene/Os–PMP films while chronocoulometry was used to co-polymerise Os–PMP with 1,2-diaminobenzene, resulting in stable films of co-polymer micro-tubules with thin-film behaviour up to 0.5 V s−1 (r2 = 0.9997). Surface analysis was carried out using SEM.

The electrochemical behaviour of an Os (II) complex of the structurally well-defined conjugated polymer alternating regioregularly alkylated thiophene and 2,2’-bipyridine units (P4Os) has been elucidated in aqueous solution. In typical aqueous electrolyte systems the cyclic voltammogram of the resulting P4Os film exhibits a one electron reversible process corresponding to the Os3+/2+ redox system. However the observance of this reversible couple did depend upon the concentration of the supporting electrolyte. It was found that the Os3+ form did form ion-pairs with an anion from the electrolyte solution. Preliminary investigations into the homogeneous charge transport dynamics associated with this redox couple have been undertaken. The technique of cyclic voltammetry, and hence the Randles-Sevick expression, in conjunction with platinum microelectrodes have been employed to determine the DCT c value.

[Os(bpy)3]3[P2W18O62] has been synthesised and characterised by elemental analysis, spectroscopic (UV–vis, IR spectroscopy) and electrochemical techniques. In 0.1 M Bu4NPF6 DMSO the complex shows a series of redox couples associated with the Os3+/2+ and bipyridine ligands of the cationic [Os(bpy)3]2+ moiety and the tungsten-oxo framework of the associated Dawson parent heteropolyanion, [P2W18O62]6−. At this electrolyte concentration, the Os3+ redox form of the complex was seen to adsorb onto the electrode surface. When the electrolyte concentration is lowered to 0.01 M Bu4NPF6 in addition to the Os3+/2+ redox couple, the redox process associated with the [P2W18O62]8−/7− couple also exhibited properties indicating surface based processes were present. Electroactive films of the complex were formed on carbon macroelectrodes by the redox switching of the transition metal within the complex. Voltammetric investigations into the film's behaviour in a range of buffer solutions (pH 2.0, 4.5 and 7.0) were performed. The films were found to possess better stability in acidic pH and the same pH dependence for the tungsten-oxo framework of the heteropolyanions as in solution. Solid state electrochemical measurements on mechanically attached microparticles of the complex were performed, with the effect of both the nature and concentration of the aqueous electrolyte on this behaviour being investigated. Upon redox switching between the Os2+/3+ redox states, there is an associated insertion/expulsion of anions from/to the solution phase. Scanning electron micrographs of these solid state films were attained before and after redox cycling.

The charge transfer (CT) complexes between tetracyanoethylene (TCNE) and various pyrrole moieties (pyrrole, N-methylpyrrole and N-phenylpyrrole) have been characterised by UV-vis spectroscopy with values for their extinction coefficients (e), equilibrium constants (K), λ max values, heats of formation (ΔH), along with thermodynamic and kinetic information regarding their instability in solution being obtained. The tricyanovinylated products of the reaction between TCNE and the pyrrole moieties have been isolated and fully characterised. The three tri-cyanovinylated pyrrole species namely, 2-tricyanovinyl-pyrrole (C 4 H 4 N-C 5 N 3 ), 2-tricyanovinyl-N-methylpyrrole (C 5 H 6 N-C 5 N 3 ) and 2-tricyanovinyl-N-phenylpyrrole (C 10 H 8 N-C 5 N 3 ), have been characterised electrochemically by cyclic and normal pulse voltammetries. Each compound exhibits an irreversible anodic wave at more positive potentials than the unsubstituted monomer species along with a reversible reduction based one-electron redox couple. The calculated diffusion coefficients are similar to solution phase species, C 4 H 4 N-C 5 N 3 (3.77 × 10 -5 cm 2 s -1 ), C 5 H 6 N-C 5 N 3 (1.099 x 10 -5 cm 2 s -1 ) and C 10 H 8 N-C 5 N 3 (2.382 x 10 -5 cm 2 s -1 ). The reduction based redox processes for all synthesised compounds exhibited facile kinetics with heterogeneous rate constants, k°, of 2.65 × 10 -2 cm s-' (C 4 H 4 N-C 5 N 3 ), 1.35 × 10 -2 cm s -1 (C 5 H 6 N-C 5 N 3 ) and 7.85 × 10 -3 cm s -1 (C 10 H 8 N-C 5 N 3 ). Conducting polypyrrole and poly(N-methylpyrrole) films were grown electrochemically, by both chronocoulometry and cyclic voltammetry from reaction solutions of TCNE and the various pyrrole moieties. However, it was found that it was possible to form conducting polymer films from acetonitrile solutions containing the monomer species (0.1 M) in the absence of background electrolyte and TCNE. Upon electrochemical switching in various electrolyte solutions, between oxidised and reduced states the polypyrrole films exhibited cation movement as the predominant process that maintains charge neutrality. The latter films were unstable towards electrochemical cycling with a loss of global electroactivity after ten scans. On the other hand the poly(N-methylpyrrole) films exhibited anion movement as the predominant process upon redox switching with the films exhibiting a high level of stability towards electrochemical cycling.