Electrochemical anion doping of poly[(tetraethyldisilanylene) oligot 2,5-thienylene)] derivatives and their p-type semiconducting properties

Chemically synthesized poly[(tetraethyldisilanylene)oligo(2,5-thienylene)] derivatives (DS/mT; m = 3 to 5) have been successfully anion-doped by electrochemical oxidation. Band-gap energies of 2.52, 2.65, 2.82 and 3.27 eV were evaluated for DS5T, DS4T, DS3T and DS2T respectively. The DS5T, DS4T and DS3T films exhibited electrical conductivities of the order of 10^?3 to 10^?4 S cm^?1 when doped with BF₄^?. The work functions of the films changed from 5.1 to ca. 5.5 eV with electrochemical anion doping. In cyclic voltammograms of the polymer films for anion doping and dedoping, an anodic peak potential and a cathodic one (E_pc.) shifted to the positive direction as the number m of thienylene units decreased. E_pcs at a sweep rate of 100 mV s^?1 were about 0.8, 0.9 and 1.0V for DS5T, DS4T and DS3T respectively. Reversible electrochemical doping and dedoping of the DS5T film were feasible when the potential was cycled between 0 and 1.2 V. At potentials more positive than 1.2 V, however, both overoxidation of the oligo(thienylene) unit and Si-Si bond cleavage took place, leading to decreases in conductivity and work function of the film.     

Voltammetric studies of the interaction of the lithium cation with reduced forms of the Dawson [S2Mo18O62]4− polyoxometalate anion

Multiple electron transfer steps observed in the reduction of [S₂Mo₁₈O₆₂]^4?, when LiClO₄ is used as electrolyte, are accounted for by assuming that Li⁺ acts as a moderately strong Lewis acid. For example, in the 95:5 CH₃CN+H₂O solvent mixture (0.1 M NBu₄ClO₄), the voltammetric behavior obtained on addition of Li⁺ can be simulated according a reaction scheme involving an extensive series of reversible potentials and equilibrium constants. Precipitation of highly reduced polyoxometalate salts occurring at the electrode surface complicates the voltammetry at very negative potentials when 0.1 M LiClO₄ is used as the electrolyte.     

Electrochemical synthesis and in situ spectroelectrochemical characterization of poly(3,4-ethylenedioxythiophene) (PEDOT) in room temperature ionic liquids

The electrochemical synthesis and the charging–discharging reactions of poly(3,4-ethylenedioxythiophene) (PEDOT) in two room-temperature ionic liquids, 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF₄) and 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIMPF₆) were studied with cyclic voltammetry, in situ attenuated total reflection Fourier transform infrared (ATR–FTIR) spectroscopy and by in situ UV–Vis spectroelectrochemistry. The structures of the films prepared in ionic liquids was compared to PEDOT films prepared in common organic media. The doping induced changes in absorption of the material both in the mid infrared and in the UV–Vis region were studied and interpreted according to spectra reported for PEDOT films prepared from common organic media.     

Interpretation of the ultra-fast electropolymerization of pyrrole in aqueous media on zinc in a one-step process: The specific role of the salicylate salt investigated by X-ray photoelectron spectroscopy (XPS) and by electrochemical quartz crystal microbalance (EQCM)

The use of sodium salicylate as an electrolyte makes it possible to deposit polypyrrole (PPy) films on oxidizable metals such as zinc by the electrochemical oxidation of pyrrole. In spite of the very large difference between the pyrrole and zinc oxidation potentials, which thermodynamically should lead to metal dissolution and not polymer formation, PPy films are formed as easily as on a platinum electrode. X-ray photoelectron spectroscopy (XPS) and in situ electrochemical quartz crystal microbalance (EQCM) experiments reveal that a very thin composite passivating zinc salicylate layer is formed prior to pyrrole electropolymerization and prevents zinc dissolution without inhibiting polymer formation. Ex situ XPS analysis of the surface at different potentials (?1 to 0.7 V) at a grazing and normal incidence of the photoelectrons shows that pyrrole is adsorbed on zinc at an early stage of the polarization and remains on the metal surface up to the beginning of electropolymerization. In situ EQCM measurements indicate that this passivation layer is very thin (about 5 nm), and does not desorb at the potential where pyrrole is oxidized. The rapid oxidation of pyrrole through this passivating layer is explained by the presence of conductive pyrrolic paths inside the salicylate layer which make this composite layer as active as a noble metal.     

EIS study of the redox reaction of Fe(CN)63−/4− at poly(3,4-ethylenedioxythiophene) electrodes: influence of dc potential and cOx:cRed ratio

The electron transfer between the ferri/ferrocyanide redox couple and poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes has been investigated by electrochemical impedance spectroscopy (EIS). Different thicknesses of the conducting polymer films were investigated (i) at a constant concentration of ferrocyanide in the solution at different applied dc potentials and (ii) at the open circuit potential with different ratios of Fe(CN)₆^3?:Fe(CN)₆^4? in the solution. PEDOT was prepared by galvanostatic electropolymerization on platinum electrodes from aqueous solutions containing 0.01 M 3,4-ethylenedioxythiophene (EDOT) and 0.1 M poly(sodium 4-styrenesulfonate) (NaPSS) as the supporting electrolyte. All impedance spectra were obtained in aqueous solutions with 0.1 M KCl as the supporting electrolyte at dc potentials, where the polymer is in the oxidized state. The EIS data were fitted to an equivalent electrical circuit resembling the Randles' circuit, where the double layer capacitance is replaced by the bulk redox capacitance and the associated transport impedance of the conducting polymer. The same potential and thickness dependence of the charge transfer resistance (R_ct) were obtained both (i) by varying the concentration ratio of the redox species in the solution and (ii) by applying different potentials at a constant concentration of ferrocyanide. The potential dependence of k₀ calculated from R_ct indicates that the conducting polymer influences the rate of electron transfer for the ferri/ferrocyanide redox couple.     

Electrochemistry of cis-diaquo ruthenium(II) complexes with substituted 2,2′-bipyridine ligands in a non-coordinating solvent. Application to the elaboration of corresponding functionalized polypyrrole films

New cis-diaquo ruthenium(II) complexes [Ru(L)₂(OH₂)2]²⁺ with L = 2,2′-bipyridine substituted by ramified or long chain alkyl groups have been prepared in order to study their electrochemical behaviour in a non-coordinating solvent like CH₂Cl₂. Slow mono and bis-aquo substitutions by counter anions (Y^?) from the electrolyte are observed leading to [Ru(L)₂(OH₂)(Y)]⁺ and [Ru(L)₂(Y)₂]. The kinetic of the process is time dependent on the electrolyte used (TBAP or TBATF). By using a 2,2′-bipyridine ligand functionalized by a pyrrole group (L₁), films of poly[Ru(L₁)₂(OH₂)₂]²⁺, poly[Ru(L₁)₂(OH₂(Y)]⁺ and poly[Ru(L₁)₂(Y)₂] are readily obtained by anodic polymerization. These modified electrodes were electrochemically and spectrochemically characterized and the electrocatalytical properties of the C/poly[Ru(L₁)₂(OH₂)₂]²⁺ modified electrode have been examined.     

Electrodeposition of Au from [EMIm][TFSA] room-temperature ionic liquid: An electrochemical and Surface-Enhanced Raman Spectroscopy study

In this paper we report in situ Surface-Enhanced Raman Scattering (SERS) experiments carried out during the electrochemical deposition of gold from Au(I) cyanocomplexes in the room-temperature ionic liquid (RTIL) 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl) amide ([EMIm][TFSA]). The obtained SERS spectra indicated the co-adsorption of CN⁻ and both anions and cations of the RTIL in the range from −1.8 to +0.3 V vs. an Au quasi-reference electrode (QRE). The surface CN⁻ peak exhibits a Stark tuning of ca. 28 cm⁻¹ V⁻¹. The oxidation of CN⁻ to OCN⁻ was observed at potentials more anodic than 0.3 V. The study was complemented by cyclic voltammetry, pinpointing RTIL reactivity at an Au electrode as well as CN⁻ adsorption effects and Au(I) reduction. SEM observations allowed to identify the conditions for the achievement of continuous Au films as well as the morphological peculiarities of Au electrodeposited from [EMIm][TFSA]. XPS measurements proved that no RTIL is incorporated into the Au film, under the investigated conditions.     

Assembly,electrochemical characterisation and electrocatalytic ability of multilayer films based on [Fe(bpy)3]2+, and the Dawson heteropolyanion, [P2W18O62]6−

Successive adsorption onto a glassy carbon electrode of the Dawson heteropolyanion, [P₂W₁₈O₆₂]^6?, and the multiply charged cation [Fe(bpy)₃]²⁺, resulted in the formation of stable multilayer assemblies on the electrode surface. Surface coverages were found to be typical of monolayer coverages for multilayer systems. Cyclic voltammetric studies of the assembly in aqueous 0.5 M NaHSO₄, gave a range of redox couples associated with the Fe^3+/2+ redox system, of the cationic [Fe(bpy)₃]²⁺ moiety and the tungsten-oxo framework of the Dawson parent heteropolyanion, [P₂W₁₈O₆₂]^6?. It was possible to immobilise up to thirty monolayers, with the system exhibiting well-behaved redox behaviour. The stability of the assembly towards redox switching was investigated, with it being found to be extremely stable once the outer layer is anionic in nature. The immobilised film was also tested for electrocatalytic activity for the reduction of nitrite, hydrogen peroxide and bromate, and was shown to be an efficient electrocatalyst.     

Electrochemical sensing of F− and Cl− with a boronic ester-functionalized polypyrrole

The anodic electropolymerization of pyrrole 3 substituted by a pinacolborane moiety 1 yielded anion-sensitive conjugated polymer films. The effect of different halides (F^?, Cl^? and Br^?) on the voltammetric response of poly(1) was examined in organic and hydro-organic media. Larger effects were observed in CH₂Cl₂ because of a weaker solvation of anions. In this solvent the system corresponding to the doping/undoping of poly(1) was shifted 450 and 175 mV towards less oxidizing potentials in the presence of F^? and Cl^?, respectively. In contrast, the polymer response was unchanged upon the addition of Br^?. These results were consistent with a greater affinity of the immobilized boronic ester groups for F^?, which could be explained by the hardness of the Lewis base.     

Electrocatalytic oxidation of hydrazine using glassy carbon electrode modified with carbon nanotube and terpyridine manganese(II) complex

Here, we report a simple and extremely effective method to modify a glassy carbon (GC) electrode with carbon nanotubes (CNTs) and [Mn(CH₃COO)(CH₃OH)₂(pyterpy)]ClO₄, (pyterpy = 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine) complex. The kinetics of the reaction between, the terpyridine manganese(II) complex, mediator and hydrazine has been characterized using cyclic voltammetry and rotating disk electrode voltammetry. The catalytic currents were proportional to the concentration of hydrazine giving rise to calibration curves characterized by two linear segments. The linear segment over the concentration range of 1.00 × 10⁻³–1.05 mM could be used with analytical purposes to determination of hydrazine with a detection limit of 0.50 μM and a sensitivity of 0.038 μA/μM. The heterogeneous rate constant, k′ for the oxidation of hydrazine at the surface of the modified electrode was determined by rotating disk electrode voltammetry using the Koutecky–Levich plot. The transfer coefficient (α) for electrocatalytic oxidation of hydrazine and the diffusion coefficient of this substance under the experimental conditions were also investigated. The resulting modified electrode retains its initial response for at least one month if stored dry in air.     

Electrochemical quartz crystal microbalance study of mass transport during electrochemical oxidation of [Os(bpy)3]2+ in clay-modified electrodes

Mass transport in clay films containing [Os(bpy)₃]²⁺ cations was investigated by EQCM and crystal impedance spectroscopy. Admittance measurements on 10 μg clay films exchanged with [Os(bpy)₃]²⁺ show no change in the width or height of the conductance peaks before and after potential scans or potential steps. The [Os(bpy)₃]²⁺ exchanged films could be considered to be rigid with no change in their viscoelastic properties, and the shifts in resonant frequency in the EQCM measurements interpreted as mass changes. In an electrode coated with a 8.5 μg clay film, oxidation of the adsorbed cations resulted in a large increase in frequency, corresponding to a decrease in mass. The mass per mole of electron transferred (MPE) was ?205 g/mol, or about one third of the weight of one [Os(bpy)₃]²⁺ ion. This was consistent with the ejection of one [Os(bpy)₃]³⁺ from the film for each three [Os(bpy)₃]²⁺ cations oxidized. The ratio of cathodic charge to anodic charge of 0.7 was also consistent with the loss of one third of the oxidized [Os(bpy)₃]³⁺ ions. The mechanism of charge neutralization was dependent of the weight of the clay films. Oxidation of [Os(bpy)₃]²⁺ in a 33 μg clay film resulted in a small decrease in frequency, corresponding to an increase in mass. The MPE, +50 g/mol, was consistent with charge neutralization by adsorption of sulfate anions from the electrolyte.     

Microheterogeneous dispersion electrolysis with nanoscale electrode-modified zeolites1

This study demonstrates the utility of supported nanoscale Pt or RuO₂ particles as ensembles of ultramicroelectrodes for controlled potential electrolyses, including implications for their use in practical electrosyntheses. Microheterogeneous dispersions of nanoelectrode-modified aluminosilicate zeolites (M-Z) increase the effective electrode area of conventional large surface electrodes in electrolytes of customary ionic strength (μ≥0.1 M). For [Fe(CN)₆]^3? solutions (in pH 6.86 phosphate buffer), the time for total reduction of the iron complex using a dilute 2.5 mg/ml suspension density of 1 wt.% Pt–NaY was 67% less than that for the same solution with no electrode-modified zeolite added. The use of Pt–NaY dispersed in solutions of low electrolyte content (650 μM) exploits the nanoelectrode nature of the Pt particles and enables effective electron transfer to be conducted at applied potentials similar to those applied in high ionic strength electrolyte. In the absence of dispersed nanoelectrodes, no electrolysis can be sustained under these conditions of high resistance. Divorcing the electrocatalyst from the reactor electrodes allows inexpensive large area feeder electrodes to be used while the dispersed nanoscale electrodes can be a small mass of a high cost electrocatalyst. These studies demonstrate that heterogeneous dispersion electrolyses using electrode-modified zeolites can overcome the difficulties normally associated with industrial applications of electrosynthetic schemes: slow reaction times, difficult electrolyte separations, and high electrode costs.     

Novel studies on the electrochemical oxidation of 2-[4-(N,N-dimethylamino)phenyl]-6-methyl benzothiazole (DPMB) in acetonitrile at platinum electrodes

The electrochemical oxidation mechanism of 2-[4-(N,N-dimethylamino)phenyl]-6-methyl benzothiazole (DPMB) is studied in a 0.1 M N(C₄H₉)₄ClO₄ + acetonitrile (ACN) reaction medium by cyclic (CV) and square wave voltammetries (SWV) as well as by controlled potential bulk electrolysis at platinum electrodes. The primary radical cation formed by the one electron oxidation of DPMB undergoes a deprotonation process, which is the rate-determining step, followed by a radical–radical coupling. On the other hand, an initial quasi-reversible monoelectronic charge transfer mechanism is inferred from cyclic and square wave voltammograms recorded at scan rates and frequencies higher than 0.4 V s^?1 and 40 Hz, respectively. Diffusion coefficients of DPMB at different temperatures were calculated from the quasi-reversible convoluted cyclic voltammograms. DigiSim® and COOL software were used to fit the quasi-reversible cyclic and square wave voltammetric responses, respectively. Formal potentials, formal rate constants and positive transfer coefficients at different temperatures were evaluated from the fitting of cyclic voltammograms. The experimental activation parameters were also determined. The effects of the analytical concentration of the reagent and the temperature, as well as the addition of trifluoracetic acid and a strong base such as lutidine on the electrochemical responses are discussed. A general reaction mechanism as well as probable structures for dimeric products are proposed.Besides, the presence of an acid–base equilibrium in DPMB solutions is also studied by employing UV–Vis spectroscopic measurements at different trifluoracetic acid concentrations. An apparent value of (1.5 ± 0.2) × 10³ M^?1 was estimated for the DPMB basic constant at 20.0 °C     

Electrochemical impedimetry of electrodeposited poly(propylene imine) dendrimer monolayer

Voltammetric and electrochemical impedance spectroscopic (EIS) studies of generation one poly(propylene imine) (G1 PPI) dendrimer as an electroactive and catalytic nanomaterials both in solution and as an electrode modifier based on a simple one step electrodeposition method is presented. The G1 PPI exhibited a reversible one electron redox behaviour at E^0′ ca 210 mV in phosphate buffer pH 7.2 with diffusion coefficient and Warburg coefficient of 7.5 × 10⁻¹⁰ cm² s⁻¹ and 8.87 × 10⁻⁴ Ω s^−1/2 respectively. Cyclic voltammetric electrodeposition of a monolayer of G1 PPI on glassy carbon electrode was carried out between −100 mV and 1100 mV for 10 cycles. The nanoelectrode was electroactive in PBS at E^0′ ca 220 mV. Kinetic profiles such as time constant (4.64 × 10⁻⁵ s rad⁻¹), exchange current (1.55 × 10⁻⁴ A) and heterogeneous rate constant (4.52 × 10⁻³ cm s⁻¹) obtained from EIS showed that the dendrimer layer catalysed the redox reaction of Fe^2+/3+ in [Fe(CN)₆]^3−/4− redox probe.     

Diamond-like carbon electrodes in electrochemical microgravimetry

Conducting diamond-like carbon films on quartz crystal electrodes were prepared by laser ablation of graphite. They were stable in many solvents including water, dichloromethane, and acetonitrile. Their potential window is much wider than those of the metal electrodes used usually in quartz oscillators and the electron transfer rate at the electrode surface is fast enough to perform electrochemistry. In dichloromethane with 0.1 M (n-Bu)₄NClO₄, DLC electrodes could scan the potential range between +2.0 and ?2.0 V to record cyclic voltammetric (CV) curves of [Ru(bpy)₃]^3+/2+. We also showed that the DLC works satisfactorily as a useful electrode material for electrochemical microgravimetry by examining the deposition–dissolution of [Ru(bpy)₃]³⁺ in dichloromethane solutions. It was found that the oxidized [Ru(bpy)₃]³⁺ have two different fates, that is, some of them make deposits on the DLC electrode and the rest diffuse out of the electrode surface instead of depositing. Based on the frequency data representing the amount of deposit only and the oxidation charge data reflecting the amount of oxidized species, deposits were found to have the average composition of [Ru(bpy)₃](ClO₄)₃?·?1.7(n-Bu)₄NClO₄.     

Ion-exchange voltammetry of tris(2,2′-bipyridyl) ruthenium(II), iron(II), osmium(II) and tris(2,2′-bipyrazyl) ruthenium(II) in acetonitrile solutions at poly(ester-sulphonate) coated electrodes

Glassy carbon electrodes modified with the poly(ester-sulphonate) ionomer Kodak AQ 55 D are used and characterized in acetonitrile solutions. The potential window accessible in acetonitrile + tetrabutylammonium hexafluorophosphate extends from ?1.750 V to +1.900 V vs. an aqueous KCl saturated Ag/vbAgCl reference electrode.The electrochemical behaviour of [Ru(bpy)₃]²⁺, [Fe(bpy)₃]²⁺, [Os(bpy)₃]²⁺ and [Ru(bpz)₃]²⁺ (where bpy = 2,2′bipyridyl and bpz = 2,2′bipyrazyl) is studied at the modified electrode. All the electroactive cations are preconcentrated efficiently in the polymeric coating. In the case of bpy complexes both a one-electron oxidation as well as two one-electron steps of the stepwise reduction of the starting complex are detected at the modified electrode.In the case of [Ru(bpz)₃]²⁺, three consecutive reduction steps can be observed, while no oxidation process is observed in the direct positive scan before reaching the upper limit of the potential range accessible at the modified electrode.The relative order in the ion-exchange selectivity coefficients in acetonitrile solutions for the cations studied is evaluated by comparison with the electrochemical behaviour observed at unmodified electrodes. The possibility of gaining information on preconcentration effects for ion-exchange voltammetry in non-aqueous solvents from the Gibbs energies of transfer from water to hydrophobic media is also discussed.     

Simultaneous electrochemical detection of uric acid and ascorbic acid at a poly(N,N-dimethylaniline) film-coated GC electrode

A polymer film of N,N-dimethylaniline (PDMA) having a positive charge on the quarternary ammonium group in its backbone was electrochemically deposited on a glassy carbon (GC) electrode surface. The resulting film-coated GC electrode was used to detect uric acid (UA) electrochemically in the presence of ascorbic acid (AA). Both UA and AA are anionic in a solution of pH 7 and thus were attracted to the film, which lowered their oxidation potentials and increased their oxidation currents. In cyclic voltammetric measurements, the negative shift of the oxidation potential of UA (by 0.28 V) compared with that at the bare electrode was larger than that of AA (by 0.2 V). Also the increase in the oxidation current of UA at the PDMA film-coated electrode was larger than that of AA. In square wave voltammetric measurements, the PDMA film-coated electrode could separate the oxidation peak potentials of UA and AA present in the same solution by about 200 mV though the bare electrode gave a single broad response. A successful elimination of the fouling effect by the oxidized product of AA on the response of UA has been achieved at the PDMA film-coated electrode. The detection limit of UA in the presence of 160-fold excess of AA was found as 1.25 μM and the current response for UA increased linearly with increase of its concentration from 1.25 to 68.75 μM in the presence of AA with a correlation coefficient of 0.999 and a sensitivity of 0.0276 μA μM⁻¹. In flow injection analysis, a good linear relationship between the oxidation current and the concentration from 2 to 21 μM of UA was found. The sensitivity of the PDMA film-coated electrode towards UA was calculated as 0.0285 μA μM⁻¹ with a correlation coefficient of 0.997. The stable and reproducible response for both AA and UA at the PDMA film-coated electrode was verified by flow injection experiments. As the response of UA was reproducible in the presence of AA, it was expected that the oxidized product of AA would not affect the electrode response of UA. Moreover, the physiologically common interferents (i.e., glucose, purine, urea and citrate) negligibly affected the response of UA. The PDMA film-coated electrode exhibited a stable and sensitive response to UA in the presence of interferents.     

Electrochemical characteristics of a cobalt pentacyanonitrosylferrate film on a modified glassy carbon electrode and its catalytic effect on the electrooxidation of hydrazine

Electrochemically prepared thin films of cobalt pentacyanonitrosylferrate (CoPCNF) were used as surface modifiers for glassy carbon electrodes. The electrochemical behavior of a CoPCNF-modified glassy carbon electrode was studied by cyclic voltammetry; the modified electrode shows one pair of peaks with a surface-confined characteristic in 0.5 M KNO₃ as supporting electrolyte. The effect of different alkali metal cations in the supporting electrolyte on the behavior of the modified electrode was studied and the transfer coefficient (α) and charge transfer rate constant (k_s) for the electron transfer between the electrode and modifier layer were calculated. The experimental results show that the peak potential and peak current vary with different alkali metal cations, but anions such as Cl^?, NO₃^?, CH₃COO^?, H₂PO₄^?/HPO₄^2? and SO₄^2? at 0.5 M concentration have no effect on the peak potential and peak current. An extensive study showed that the response of the modified electrode is not affected within a pH range of 2–8. The CoPCNF films on glassy carbon electrodes show excellent electrocatalytic activity toward the oxidation of hydrazine in 0.5 M KNO₃. The kinetics of the catalytic reaction were investigated by using cyclic voltammetry, rotating disk electrode (RDE) voltammetry and chronoamperometry. The average value of the rate constant for the catalytic reaction and the diffusion coefficient were evaluated by different approaches for hydrazine.     

Analysis of the impedance spectra of Pt|poly(o-phenylenediamine) electrodes – hydrogen adsorption and the brush model of the polymer films

Electrochemical impedance spectra obtained for poly(o-phenylenediamine) films on platinum in contact with 0.5 M H₂SO₄ solution were analyzed on the basis of the brush model elaborated for conducting polymer films on electrodes. It is assumed that the polymer film consists of short and long polymer chains forming bundles in such a way that only a small part of the metal substrate is covered by the polymeric material. The analysis of the impedance spectra taken at several potentials in the region of hydrogen adsorption on platinum supports the validity of the model. The model has been tested also by varying the film thickness and the roughness of the platinum substrate.     

Enhanced electron transfer for hemoglobin in poly (ester sulfonic acid) films on pyrolytic graphite electrodes

Stable films made from the ionomer poly (ester sulfonic acid) Eastman AQ55 on pyrolytic graphite (PG) electrodes gave reversible voltammetry for the incorporated protein hemoglobin (Hb). Cyclic voltammetry of Hb-AQ films showed a pair of well-defined, reversible peaks at about ?0.04 V versus SHE at pH 5.5. Compared to solutions, electron transfer between Hb and PG electrodes was greatly facilitated in the AQ films. Soret absorption band positions suggest that Hb retains a near native conformation in AQ films in the medium pH range. The formal potential of the Hb heme Fe(III)/Fe(II) couple in AQ films shifted linearly between pH 4 and 11 with a slope of ?52 mV pH^?1, suggesting that one proton transfer is coupled to each electron transfer in the electrochemical reaction. Square wave voltammograms of Hb-AQ films were fit by nonlinear regression analysis using a model featuring dispersion of formal potentials. Hb can act as an enzyme-like catalyst in these films as demonstrated by catalytic reduction of trichloroacetic acid with significant decreases in the electrode potential required.