Electrochemical Quartz Crystal Microbalance Technique Research Articles

Electrodeposition of copper from spent Li-ion batteries by electrochemical quartz crystal microbalance and impedance spectroscopy techniques

Information about the copper electrodeposition mechanism at different pH values was obtained using an electrochemical quartz crystal microbalance (EQCM) technique, as well as potentiodynamic, potentiostatic, and electrochemical impedance spectroscopy (EIS) techniques. In agreement with the measurements obtained from the EQCM and potentiostatic experiments, an intermediate Cu+ species and a CuO layer are formed. Simultaneous mechanism of direct reduction of Cu2+ and copper oxide (CuO) reduction at pH 2.0 and 4.5 occur. The EIS experiment shows a diffusion-controlled process by the presence of a Warburg element, a CPE related to the irregular metallic copper electrodeposition, and a resistance of the electrodeposit.

An EQCM Study of the Corrosion of Synthetic Aluminium Alloys

Thin film aluminum electrodes were sputter-deposited onto quartz resonators for the electrochemical quartz crystal microbalance technique. The aluminum electrodes were then photolithographically patterned and decorated with arrays of Cu islands or Al-Cu-Mg islands mimicking cathodic and anodic phases in commercial Al alloys. Open circuit exposure to 0.5 M NaCl of different pH was performed, and the resonance frequency of the quartz measured in parallel. In the beginning of the experiments a frequency increase due to loss of Al by corrosion was observed. Later on the deposition of corrosion products with a large roughness caused the frequency to decrease.

Synthesis and characterization of polypyrrole–magnetite–vitamin B12 hybrid composite electrodes

In this study vitamin B12 covered magnetite nanoparticles have been incorporated into a conducting polypyrrole. This polymer was electrochemically synthesized in the presence of the B12-coated magnetite. The adsorption of B12 was demonstrated by the decrease in absorbance of the vitamin in the supernatant liquid after B12 has been in contact with magnetite sol overnight. The composition of the layers was studied by the electrochemical quartz crystal microbalance technique during the polymerization. The slope of the mass change–charge curves indicate the incorporation of 27 m/m% magnetite and 15 m/m% B12. The redox transformation of the film in monomer- and nanoparticle-free solutions was also investigated by this method and the difference in the virtual molar masses of the moving species was evidenced. The morphology and the composition of the layers were characterized by scanning electron microscopy combined with energy dispersive X-ray microanalysis measurements, which latter proved the successful incorporation of the magnetic and bio-active components. The electrochemical behavior of the films unambiguously showed the complex redox activity of the composites and the current surplus were quantified by the redox capacity of the layers. These data show the doubling of the redox capacity in case of the hybrid material compared to the neat polymer. The successful enrichment of B12 can be exploited in the recently evidenced redox mediation process performed by a PPy/B12 film.

Sonoelectrochemical Deposition of Functional Composite Layers

Ultrasound was applied for the electrodeposition of metal/ceramic and metal/metal composites. Ni/ceria composites were deposited from Watts and sulfamate based electrolytes containing dispersed ceria using ultrasonic irradiation for the deagglomeration of oxide particles. The electrochemical deposition of silver at the tip of an ultrasonic horn probe using pulsed ultrasound was explored for its potential to electrodeposit Ni/Ag composites. First results are presented. Sonoelectrochemical processes were in part monitored in-situ by the electrochemical quartz crystal microbalance technique. Compositions of the electrodeposits were analyzed by energy dispersive spectroscopy and in part by electron probe microanalysis.

Electrochemical Quartz Crystal Microbalance Technique to Monitor External Polymeric Pipeline Coatings

Abstract Electrochemical Quartz Crystal Microbalance (EQCM) can be used to monitor changes in several material properties, including mass, electrochemical, viscosity, adsorption, and deposition. In this paper, EQCM was evaluated to determine if it can monitor changes to the metal-coating interface well before any visible/physical changes to the coating. Modified cathodic disbondment (CD) experiments were carried out over a period of 14 months on 13 coatings used to protect the external surfaces of oil and gas pipelines. During the experiments, EQCM measurements were recorded by placing the quartz crystal at the coating-steel interface. After the experiments, the CD area was measured and compared with the EQCM measurements. Of the 117 panels of 13 different pipeline coatings tested, for 67 % of coatings EQCM correctly predicted the coating performance. Twenty-five percent of coatings performed better than that predicted from EQCM data. Only for 8 % of coatings EQCM measurements predicted better performance but the coatings disbonded during CD area measurement. Based on these observations it was concluded that microscopic changes to the metal-coating interface could be assessed from oscillation frequency of the EQCM crystal placed at the metal-coating interface. However, in order to obtain useful information, extreme care should be exercised in placing the fragile EQCM crystal at the metal-coating interface.

Highly Sensitive Glucose Biosensor Based on One-Pot Biochemical Preoxidation and Electropolymerization of 2,5-Dimercapto-1,3,4-thiadiazole in Glucose Oxidase-Containing Aqueous Suspension

A novel and high-performance biosensing platform was prepared on the basis of one-pot biochemical preoxidation and electropolymerization of monomer (BPEM) for high-load and high-activity immobilization of enzymes. As representative materials here, 2,5-dimercapto-1,3,4-thiadiazole (DMcT) was used as the monomer, glucose oxidase (GOx) was used as the model enzyme, and enzymatically generated H2O2 (EG-H2O2) in the presence of glucose was used as the preoxidant. In the BPEM protocol, glucose was added to a pH 7.0 phosphate buffer suspension containing ultrasonically dispersed DMcT and GOx, in order to enzymatically generate H2O2, which preoxidized DMcT to DMcT oligomers/polymer (DMcTO) and thus led to the formation of DMcTO-GOx composites with a great deal of GOx entrapped; the composites were then co-electrodeposited with poly(DMcT) on a Au electrode. For comparison, the enzyme immobilization was also conducted by a preoxidation-free conventional electropolymerization protocol (CEP), as well as a chemical preoxidation and electropolymerization of monomer (CPEM) protocol with externally added H2O2 (EA-H2O2) as the preoxidant. The glucose biosensors constructed by the BPEM and CPEM protocols exhibited detection sensitivities enhanced by 119 and 88 times, respectively, compared to that constructed by the CEP protocol, as well as limits of detection lowered by ca. 2 orders of magnitude. The higher sensitivity of the enzyme electrode prepared by the BPEM protocol compared to that prepared by the CPEM protocol is probably due to the improved proximity of biochemical preoxidation around the enzyme molecules and thus a larger enzyme load. The electrochemical quartz crystal microbalance technique was used to investigate various electrode modification processes, which also revealed that poly(DMcT) could be cathodically detached from the electrode surface, favorably enabling the electrochemical regeneration of the electrode substrate. The proposed BPEM strategy is recommended for wide biosensing and biocatalysis applications based on many other polymers/enzymes.

Stability of Pd-Fe Alloy Catalysts

分别在酸性和碱性溶液中,结合旋转圆盘电极技术和电化学石英晶体微天平技术原位考察了钯铁合金催化剂对氧还原反应催化活性的稳定性.发现在酸性溶液中,钯铁合金催化剂对氧还原反应的催化活性不稳定,原因是钯铁合金催化剂在酸性溶液中发生电化学/化学溶解;在碱性溶液中,覆盖在电极表面的钯铁合金催化剂的质量及电化学活性面积在电化学扫描过程中不发生明显变化,保持对氧还原反应的催化活性,证明钯铁合金催化剂在碱性介质中非常稳定.

EQCM immunoassay for phosphorylated acetylcholinesterase as a biomarker for organophosphate exposures based on selective zirconia adsorption and enzyme-catalytic precipitation

A zirconia (ZrO2) adsorption-based immunoassay by electrochemical quartz crystal microbalance (EQCM) has been initially developed, aiming at the detection of phosphorylated acetylcholinesterase (Phospho-AChE) as a potential biomarker for bio-monitoring exposures to organophosphate (OP) pesticides and chemical warfare agents. Hydroxyl-derivatized monolayer was preferably chosen to modify the crystal serving as the template for directing the electro-deposition of ZrO2 film with uniform nanostructures. The resulting ZrO2 film was utilized to selectively capture Phospho-AChE from the sample media. Horseradish peroxidase (HRP)-labeled anti-AChE antibodies were further employed to recognize the captured phosphorylated proteins. Enzyme-catalytic oxidation of the benzidine substrate resulted in the accumulation of insoluble product on the functionalized crystal. Ultrasensitive EQCM quantification by mass-amplified frequency responses as well as rapid qualification by visual color changes of product could be thus, achieved. Moreover, 4-chloro-1-naphthol (CN) was studied as an ideal chromogenic substrate for the enzyme-catalytic precipitation. Experimental results show that the developed EQCM technique can allow for the detection of Phospho-AChE in human plasma with a detection limit of 0.020nM. Such an EQCM immunosensing format opens a new door towards the development of simple, sensitive, and field-applicable biosensor for biologically monitoring low-level OP exposures.

An EQCM study of ultrasonically assisted electrodeposition of Co/CeO2and Ni/CeO2composites for fuel cell applications

The electrodeposition of Co/CeO2 and Ni/CeO2 composites from electrolytes containing suspended nanoparticles of gadolinia doped ceria under the influence of power ultrasound was studied using the electrochemical quartz crystal microbalance technique (EQCM). The amount of oxide incorporation into the layers was determined by electron probe microanalysis. From 0.1 M cobalt electrolytes rough Co layers with ceria contents of up to 8% were deposited, and a strong increase in the damping of the quartz was observed. In the case of Ni deposition an increase of the deposition rate enhanced the current efficiency and lead to larger ceria contents. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Electropolymerized tyrosine-based thin films: Selective cell binding via peptide recognition to novel electropolymerized biomimetic tyrosine RGDY films

We have created thin films by cyclic voltammetry (CV) electropolymerizations of the following phenolic functional group-based monomers: phenol; tyrosineamide; the tetrapeptide RGDY-containing the integrin membrane adhesion protein recognition tripeptide RGD; RDGY, a nonsense control tetrapeptide; and 1:3 mixtures of tyrosineamide with the two tetrapeptide monomers. The film formation process and description of the film properties were obtained by repetitive CV cycling using the oscillating quartz frequency shift, Δ f, and motional resistance shift, Δ R, parameters obtained with the electrochemical quartz crystal microbalance technique. Only the poly(phenol) film exhibited close chain packing-based self-limiting behavior, where all film synthesis ceased after approximately 7 CV cycles. All other films continued to form by electropolymerization with successive CV cycles out to the maximum cycle number (30 cycles) we measured. All of the films exhibited little energy dissipation behavior. Using the quartz crystal microbalance, we next compared the time course of cell attachment with the washed films and demonstrated that cells bound best to films in the following order: RGDY sense peptide:tyrosineamide films > RDGY nonsense peptide:tyrosineamide films = tyrosineamide films > phenol films. Cell enumeration after washing and trypsinization revealed firm protein-based cell attachment to the underlying extracellular matrix for the RGDY-containing films. These sense peptide films bound and retained two- to fivefold as many cells as the other films, with cells exhibiting a normal morphology. These results suggest the operation of specific cell attachment to the electropolymerized films via the RGD binding site for cellular integrin membrane proteins. The electropolymerization method we studied here forms a cassette system for creating electropolymerized films tailored to specific attachment of different cell types by varying the electropolymerized Y(tyrosine)-containing recognition peptide.

Trace analysis of cefotaxime at carbon paste electrode modified with novel Schiff base Zn(II) complex

Cefotaxime a third generation cephalosporin drug estimation in nanomolar concentration range is demonstrated for the first time in aqueous and human blood samples using novel Schiff base octahedral Zn(II) complex. The cefotaxime electrochemistry is studied over graphite paste and Zn(II) complex modified graphite paste capillary electrodes in H 2SO 4 (pH 2.3) using cyclic voltammetry and differential pulse voltammetry. Cefotaxime enrichment is observed over Zn(II) complex modified graphite paste electrode probably due to interaction of functional groups of cefotaxime with Zn(II) complex. Possible interactions between metal complex and cefotaxime drug is examined by UV–vis and electrochemical quartz crystal microbalance (EQCM) techniques and further supported by voltammetric analysis. Differential pulse voltammetry (DPV) with modified electrode is applied for the determination of cefotaxime in acidified aqueous and blood samples. Cefotaxime estimation is successfully demonstrated in the range of 1–500 nM for aqueous samples and 0.1–100 μM in human blood samples. Reproducibility, accuracy and repeatability of the method are checked by triplicate reading for large number of samples. The variation in the measurements is obtained less than 10% without any interference of electrolyte or blood constituents.

Highly sensitive and surface-renewable electrochemical quartz crystal microbalance assays of heparin and chondroitin sulfate based on their effects on the electrodeposition of neutral red

The electrochemical quartz crystal microbalance (EQCM) technique was used to investigate the electrochemistry of neutral red (NR) in phosphate buffer solution (PBS) and the effects of coexisting heparin (Hep) or chondroitin sulfate (CS) for the first time. The pH dependence of the electrochemistry of NR was examined, and a V-shaped frequency response (versus time) was observed during the cyclic voltammetric experiment of NR in a nearly neutral medium (pH ca. 6.10–7.00), being due to the electrodeposition and stripping of the poorly soluble reduced product of NR (NR Red) at these pH values. The effects of potential scan rate, the concentration of NR, and several supporting electrolytes were examined at pH 6.80. The V-shaped response to the redox switching of NR was weakened by the introduction of Hep or CS, being due to the increased inhibition of the NR Red electrodeposition probably via the electrostatic interaction of the NR and especially the NR Red with Hep or CS. The height of the V-shaped response decreases with the increase of Hep or CS concentration, with limits of detection down to 3 nmol L −1 for Hep and 2 nmol L −1 for CS, respectively. The novel and surface-regenerable EQCM assay protocol based on the electrochemically switchable deposition of a dye is highly recommended for wide biosensing applications.

Electrochemical Preparation of Bromo Thymol Blue-PEDOT Composite Electrode and Characterization

Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with bromo thymol blue (BTB) composite electrode was prepared electrochemically by using cyclic voltammetric (CV) technique. Hereafter, the above-modified electrode is termed the BTB-PEDOT composite electrode. The BTB-PEDOT composite electrode showed a well-defined reversible symmetric redox peak at around (vs ), with , and the BTB modified electrode showed an ill-defined peak in solution. The symmetric peak in BTB-PEDOT composite electrode might be due to the small electronic bandgap and the high conductivity of PEDOT. The modified electrode was characterized using CV, electrochemical quartz crystal microbalance (EQCM), Fourier transform infrared (FTIR) spectroscopy, and atomic force microscopy. FTIR spectroscopy helps to confirm presence of BTB on the composite electrode. The amount of composite deposited in the Au electrode was determined using the EQCM technique. The modified electrode displayed surface-confined and pH-dependent electrochemical properties. The BTB-PEDOT composite electrode was used for electrocatalytic reduction of Cr(VI). The composite electrode selectively detected Cr(VI) from its interference in the presence of a 10-fold excess of Cr(III) and humic acid. The sensitivity and detection limit of the electrode were and , respectively.

Electrochemically Active Dendritic−Linear Block Copolymers via RAFT Polymerization: Synthesis, Characterization, and Electrodeposition Properties

We describe a series of well-defined dendritic−linear block copolymer architectures via the reversible addition−fragmentation chain transfer (RAFT) polymerization technique. Using dendritic chain transfer agents (CTA)s possessing a single dithioester moiety at the focal point, RAFT polymerization was carried out to attach polystyrene (PS) and poly(methyl methacrylate) (PMMA) chains of controlled lengths by kinetic control. To provide electrochemical functionality, the dendritic CTAs were designed with carbazole moieties at the periphery of the structures. The results on the electrochemical polymerization of the carbazole moieties at the periphery of the dendritic component of the block copolymers reveal quantitative cyclic depositions with changes in viscoelastic properties of the deposited films as monitored by the electrochemical quartz crystal microbalance technique. The electroactive dendritic blocks proved to be an effective electrochemically active macromonomer for the electrodeposition of these str...

Immobilization of Enzymes through One-Pot Chemical Preoxidation and Electropolymerization of Dithiols in Enzyme-Containing Aqueous Suspensions To Develop Biosensors with Improved Performance

A protocol of one-pot chemical preoxidation and electropolymerization of monomers (CPEM) in enzyme-containing aqueous suspensions (or solutions) was proposed as a universal strategy for high-activity and high-load immobilization of enzymes to construct amperometric biosensors, which was proven to be effective for the monomer of 1,4-benzenedithiol (BDT), 1,6-hexanedithiol, o-phenylenediamine, o-aminophenol or pyrrole, the preoxidant of K3Fe(CN)6 or p-benzoquinone, and the enzyme of glucose oxidase (GOx) or alkaline phosphatase (AP) to develop GOx-based glucose biosensors or AP-based disodium phenyl phosphate biosensors. As a case examined in detail, a well-dispersed aqueous suspension of the poorly soluble BDT was obtained through its dispersion assisted by ultrasonication and coexisting GOx, which was then subject to chemical preoxidation through adding K3Fe(CN)6, yielding many composites of insoluble BDT oligomers with lots of high-activity enzyme molecules entrapped. Some insoluble composites were then electrochemically codeposited with poly(1,4-benzenedithiol) on an Au electrode, yielding an enzyme film with high-load and high-activity enzyme immobilized. The glucose biosensor prepared here from the CPEM protocol showed much better performance than that from the preoxidant-free conventional electropolymerization (CEP) protocol, with a detection sensitivity increase by a factor of 32 in this case. The GOx-based and AP-based first-generation biosensors developed from the present CPEM protocol all exhibited notably improved performance compared with the analogues from the preoxidant-free CEP protocol. The electrochemical quartz crystal microbalance (EQCM) technique was used to investigate various electrode modification processes. The values of quantity and enzymatic specific activity (ESA) of the immobilized enzymes were evaluated through the EQCM and the conventional UV-vis spectrophotometric method, given that the CPEM protocol notably improved the quantity and the ESA of immobilized enzymes as compared with the preoxidant-free CEP protocol. The proposed CPEM protocol may be interesting in a number of fields, including biosensing, biocatalysis, biofuel cells, bioaffinity chromatography, and biomaterials, and the successful electropolymerization of dithiols in aqueous suspensions (two-phase electropolymerization) may open a new avenue for many monomers that are poorly soluble in neutral aqueous solutions to in situ immobilize biomolecules for bioapplications.

Capacitance effect on Co-layer dissolution during pulse potentiostatic deposition of Co–Cu/Cu multilayers

Electrodepositon of Co–Cu/Cu multilayer was carried out employing two-pulse potentiostatic method from a sulphate based single solution electrolyte. Dissolution characteristics of thin Co-layer preceding a Cu-layer, were investigated using chronoamperometry, chronocolumetry and electrochemical quartz crystal microbalance (EQCM) techniques. Both galvanic displacement due to Cu 2+ ions and cell capacitance effect were found to be responsible for the dissolution of Co-layer during pulse switchover from Co to Cu-discharge. Competitive effect of these two factors on Co-dissolution was found to depend solely on the choice of discharge potential pair of Cu and Co. Co-layer dissolution could be prevented on application of Cu-discharge potential very close to the point of onset of Co-reduction potential. An effort has been made to understand the thickness loss due to capacitance effect by adopting a double layer model. It was also seen that the Cu-layer formed due to galvanic displacement reaction was porous in nature, and allows the Co-layer underneath to corrode for several nanometers upon allowance.

Correlation between conductance and mass changes during p-doping of 2-methoxynaphthalene films

The redox response of 2-methoxynaphthalene films electrosynthesized in two different organic solvents, acetonitrile (ACN) and nitrobenzene (NB) has been studied by different in situ electrochemical techniques: the in situ conductance technique, electrochemical quartz crystal microbalance (EQCM) and electrochemical voltage spectroscopy (EVS). In situ measurements of conductance as a function of the potential during p-doping of 2-methoxynaphthalene films, electrosynthesized in TBAPF 6-ACN and TBAPF 6-NB, show that the conductance properties are strongly dependent on the solvent used during electrosynthesis, resulting in higher conductance values for films electrosynthesized in NB solutions. The EQCM technique has been used to correlate the frequency changes (mass changes) at the electrode surface with conductance changes during p-doping of the different films. The molar mass of the species involved in the charging–discharging reactions has been estimated from the EQCM results. For the determination of the electrochemical bandgap of the two different films, cyclic voltammetry (CV) and EVS were applied. Films electrosynthesized in NB solutions have a lower value of the bandgap (1.34 eV) than films electrosynthesized in ACN solutions (2.00 eV).

In Situ Electrochemical Quartz Crystal Microbalance Measurement of Au Deposition and Dissolution in Room-Temperature Ionic Liquid Containing Chloride Ion

Abstract In-site gold electro-deposition and electro-dissolution have been examined using polycrystalline gold-coated quartz crystal electrode in a room-temperature ionic liquid of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4). In EMIBF4 media containing 1-ethyl-3-methylimidazolium chloride, the species of AuI (probably [AuICl2]−) resulting from the electrochemical oxidation of the Au surface was very stable and a reversible voltammetric response of the AuI/Au0 couple was observed at 0.25 V vs. Ag wire quasi-reference electrode (Ag(QRE)). In situ electrochemical quartz crystal microbalance (EQCM) technique combined with cyclic voltammetry, double potential-step chronoamperometry and double potential-step chronocoulometry has been successfully applied to investigate the cathodic deposition of AuI ion to Au metal and the anodic dissolution of Au from the Au electrode surface. It was found that the frequency change of quartz crystal electrode during the electrolysis can be interpreted in terms of rigid mass changes based on the Sauerbrey equation. The EQCM analysis of the electro-dissolution and electro-deposition of Au in the potential range of −0.60 to 0.50 V vs. Ag(QRE) gave the molecular mass equivalent of Au (197 g mol−1) corresponding to a one-electron reduction and oxidation of the AuI/Au0 redox couple.

Electrochemical Quartz Crystal Microbalance Studies on the Codeposition of Dextran Sodium Sulfate with the Charge‐Transfer Complexes Generated During Electrooxidation of Benzidine Derivatives

AbstractThe electrochemical quartz crystal microbalance (EQCM) technique was used to investigate the electrochemistry of three benzidine derivatives, o‐tolidine (o‐TD), 3,3′,5,5′‐tetramethyl‐benzidine (TMB) and o‐dianisidine (o‐DA), in Britton‐Robinson (B‐R) buffer solutions with and without coexisting dextran sodium sulfate (DSS), respectively. During the anodic potential sweep from 0.1 to 0.7 V vs. SCE in pH 5.0 B‐R buffer solution containing o‐TD, the EQCM frequency was decreased during the first‐step oxidation of o‐TD and then increased to some extent during its second‐step oxidation, implying that a poorly soluble charge‐transfer complex (CTC) was produced here as an oxidation intermediate, and its precipitation and then dissolution at the EQCM Au electrode decreased and then increased the frequency. The depth of the V‐shaped time‐dependent frequency response (−Δf0V) to the redox switching of the CTC/o‐TD couple (0.1–0.37 V vs. SCE) was notably enhanced in the presence of DSS, being due to the formation of a mass‐enhanced CTC‐DSS adduct via electrostatic affinity. Similar phenomena were evident in the TMB system, but the CTC behavior was not observed during o‐DA oxidation in the absence of DSS, namely, the EQCM frequency kept decreasing all the time, due probably to the too high lability of the CTC from o‐DA oxidation, and the coexistence of DSS could well stabilize this CTC and turn on its CTC behavior. The o‐TD system showed the highest sensitivity to DSS and was thus examined in detail. The mechanism for the CTC‐DSS interaction is discussed from EQCM, FT‐IR and UV‐vis data. The CTC‐based EQCM determination of DSS, which is featured by a dynamically renewed surface of the detection electrode, was thus proposed, with a linear range from 0.002 to 1.6 μmol L−1 and a detection limit down to 0.7 nmol L−1 (o‐TD system).

Immobilisation of the polyoxometallate cluster, K 6NaH[Sb 2W 20Fe 2O 70(H 2O) 6]·29H 2O, in a polypyrrole film

The conducting polymer, polypyrrole was successfully employed to surface immobilise the Krebs type polyoxometallate, K 6NaH[Sb 2W 20Fe 2O 70(H 2O) 6]·29H 2O, through cyclic voltammetry. The resulting K 6NaH[Sb 2W 20Fe 2O 70(H 2O) 6]·29H 2O 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 (H 2O 2) with a sensitivity of 131.8 (±3.5) μA cm −2/mM with a LOD of 16.6 μM at neutral pH.