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Abstract: Tungsten trioxide, unhydrated with hexagonal structure (h-WO3), has been prepared by hydrothermal method at a temperature of 180°C in acidified sodium tungstate solution. Thus prepared h-WO3 has been characterized by X-ray diffraction (XRD) method and using electrochemical techniques. The morphology has been examined by scanning and transmission electron microscopies (SEM and TEM) and it is consistent with existence of nanorods of 50–70nm diameter and up to 5μm length. Cyclic voltammetric characterization of thin films of h-WO3 nanorods has revealed reversible redox behaviour with charge–discharge cycling corresponding to the reversible lithium intercalation/deintercalation into the crystal lattice of the h-WO3 nanorods. In propylene carbonate containing LiClO4, two successive redox processes of hexagonal WO3 nanorods are observed at the scan rate of 50mV/s. Such behaviour shall be attributed to the presence of at least two W atoms of different surroundings in the lattice structure of h-WO3 nanorods. On the other hand, in aqueous LiClO4 solution, only one redox process is observed at the scan rate of 10mV/s. The above observations can be explained in terms of differences in the diffusion of ions inside two types of channel cavities existing in the structure of the h-WO3 nanorods. Moreover, the material can be applied as active support for the catalytic bi-metallic Pt–Ru nanoparticles during electrooxidation of ethanol in acid medium (0.5moldm−3 H2SO4). [Copyright &y& Elsevier]

Abstract: A comparative study describing immobilization of the Dawson type mixed addenda heteropolyanion, [P2W17VO62]8− into conducting polymer films of poly(3,4-ethylenedioxythiophene), PEDOT, and poly(2,2′-bithiophene), PBT, is reported. Electrosynthesis of these hybrid films was performed using a micellar aqueous solution of the nonionic surfactant, polyethylene glycol tert-octylphenyl ether (Triton X-100). Deposited composite films were characterised electrochemically and, on the whole, they exhibited fast electron transfer (ET) properties and relatively high stability towards continuous potential cycling in acidic media. In particular, PEDOT composite showed relatively faster ET properties in comparison to PBT composite. Their permeability was investigated in the presence of cationic and anionic redox probes. Our results implied good mediating capabilities of the [P2W17V4+O62]8− anion (within the [P2W17V4+O62]8−–PEDOT hybrid film) towards the iron (III) reduction. The specific electrocatalytic (reductive) capabilities of hybrid films were also studied by probing the reduction of bromate. The films were further characterised by X-ray photoelectron spectroscopy to establish their interfacial elemental composition. Moreover, their surface morphology was imaged by atomic force microscopy and scanning electron microscopy. Results have shown that physicochemical properties of the investigated hybrid films were affected by polymer hydrophobicity. [Copyright &y& Elsevier]

Abstract: The activity of Vulcan-supported Pt nanoparticles (Pt40%/Vulcan XC-72) towards oxidation of methanol and ethanol is increased by admixing them with zeolite-type cesium salts of heteropolymolybdic and heteropolytungstic acids: Cs2.5H0.5PMo12O40, Cs2.5H1.5SiMo12O40, Cs2.5H0.5PW12O40, and Cs2.5H1.5SiW12O40. It is apparent from IR measurements that these salts remain the Keggin-type structure. They are electroactive and undergo reversible redox transitions, as well as they are hydrated and contain mobile protons. As evidenced from cyclic voltammetric, stair-case voltammetric and chronoamperometric diagnostic experiments, the electrocatalytic enhancement effect has been most pronounced upon application of phosphododecamolybdate and phosphododecatungstate salts. The overall activation effect may also reflect the micro and mesoporous (zeolite-type) high surface area morphology of polyoxometallate cesium salts. The presence of well-defined polyoxometallate clusters in the vicinity of Pt is expected increase population of reactive oxo groups at the electrocatalytic interface. [Copyright &y& Elsevier]

Abstract: Se/Ru nanoparticles – a potent non-platinum catalyst towards oxygen reduction reaction – were modified by hydrated WO3 and investigated using the rotating disk/ring electrode methods and by synchrotron X-ray photoelectron spectroscopy. The modification resulted in an enhanced catalytic activity towards oxygen reduction reaction (ORR). Our data indicate that the oxygen reduction current starts ca. 70mV more positive and formation of undesirable hydrogen peroxide has significantly decreased following the modification of Se/Ru with WO3. X-ray photoelectron spectroscopy reveals that WO3 interacts electronically with Se/Ru as the W 4f and Se 3d line-shapes change. We therefore conclude that the electronic interactions between Se/Ru and WO3 are primarily responsible for the increase in activity and selectivity of the WO3-modified Se/Ru towards ORR. [ABSTRACT FROM AUTHOR]

Abstract: This study has focused on the synthesis of novel oxygen reduction reaction (ORR) chalcogenide catalysts, with Ru partially replaced by Fe in a cluster-type Ru x Se y . The catalysts were obtained by thermal decomposition of Ru3(CO)12 and Fe(CO)5 in the presence of Se. As indicated by the XPS data, the composition of catalyst nanoparticles depends on the solvent used (either p-xylene or dichlorobenzene). The presence of iron in synthesized catalysts has been confirmed by both EDAX and XPS. Voltammetric activation of the catalysts results in a partial removal of iron and unreacted selenium from the surface. The ORR performance of electrochemically pre-treated catalysts was evaluated using rotating disk and ring-disk electrodes in a sulfuric acid solution. No major change in the ORR mechanism relative to the Se/Ru catalyst has been observed with Fe-containing catalysts. [ABSTRACT FROM AUTHOR]

Abstract: As evidenced from the increase of electrocatalytic currents measured under voltammetric and chronoamperometric conditions, the activity of bimetallic Pt–Ru and Pt–Sn nanoparticles towards oxidation of ethanol is increased by modification of their surfaces with ultra-thin films of phosphododecamolybdic acid (H3PMo12O40). The enhancement effect has been most pronounced in a case of heteropolymolybdate-modified carbon-supported Pt–Sn catalysts. Independent high-resolution XPS measurements indicate the ability of heteropolymolybdates to stabilize tin (in bimetallic Pt–Sn particles) at higher oxidation states (presumably as tin oxo species). The overall activation effect may also be ascribed to changes in the morphology of catalytic films following modification with heteropolymolybdates. Presence of the polyoxometallate is also likely to increase of the interfacial population of reactive oxo groups in the vicinity of platinum centers. [Copyright &y& Elsevier]

Abstract: The electrocatalytic reduction of oxygen at electropolymerized films of a number of different manganese, iron and cobalt porphyrins supported on multi-walled carbon nanotubes (MW-CNTs) which have been pre-stabilized with ultra-thin layers of organic 4-(pyrrole-1-yl) benzoic acid (PyBA) is reported. Special emphasis has been on the multiple oxidation states of manganese as central metal ion and its potential advantages for the electron transfer process during the reduction of molecular oxygen in a 0.1M phosphate buffer solution. Electropolymerization of metal porphyrins leads to catalytically active films on the electrode. The incorporation of MW-CNTs in the film leads to a significant decrease in the hydrogen peroxide produced during the oxygen reduction reaction (ORR) and a significant positive shift of the oxygen reduction potential. Of the complexes studied, manganese tetratolyl porphyrin (MnTTP) has shown the best activity and stability towards oxygen reduction. [Copyright &y& Elsevier]

The ability of such a common redox mediator as 2,2'azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) to undergo sorption on carbon surfaces is explored here to convert multiwalled carbon nanotubes (CNTs) into a stable colloidal solution of ARTS-modified carbon nanostructures, the diameters of which are ∼10 nm (as determined by transmission electron microscopy). Subsequently, inks composed of fungal laccase (Cerrena unicolor) mixed with the dispersion of ABTS-modifled CNTs and stabilized with Naflon, were deposited on glassy carbon and successfully employed to the reduction of oxygen in Mcllvain buffer at pH 5.2. For comparison, the systems utilizing only ABTS-free CNTs and laccase as well as ARTS-modified CNTs did not show appreciable activity toward the oxygen reduction. The three-dimensionally distributed ABTS-modified CNTs are expected to improve the film's overall conductivity and to facilate electrical connection between the electrode and the enzyme. The network film of ABTS-modified CNTs is rigid, and it is characterized by charge propagation capabilities comparable to the conventional redox polymers. The whole concept of utilization of CNTs modified with ultrathin films of redox mediators in the preparation of efficient bioelectrocatalytic films seems to be of general importance to electroanalytical chemistry and to the development of biosensors. [ABSTRACT FROM AUTHOR]

Abstract: The ability of Keggin-type phosphododecamolybdate (PMo12O40 3−, PMo12) to undergo chemisorption on solid surfaces (including gold) is explored here to convert (by ligand place-exchange and phase transfer to aqueous solution) the alkanothiolate-modified Au nanoparticles of controlled size (prepared in toluene) into a stable colloidal solution of PMo12-protected gold nanoparticles, PMo12–AuNPs, the sizes of which are ca. 4–5nm as determined by transmission electron microscopy. By dip-coating, PMo12–AuNPs were assembled on carbon electrode substrates. The step-by-step assembly, by which alternate exposures to the solutions of PMo12–AuNPs and either anilinium cations or pyrrole monomers, was utilized to grow in controlled manner hybrid network films in which the negatively charged PMo12–AuNP deposits were linked, or electrostatically attracted, by ultra-thin, positively charged conducting polymer (polyaniline or polypyrrole) structures. The three-dimensionally distributed PMo12–AuNPs immobilized within the polypyrrole-based composite film exhibited some electrocatalytic reactivity towards reduction of hydrogen peroxide. [Copyright &y& Elsevier]

Abstract: By modification of surfaces of multi-walled carbon nanotubes with ultra-thin monolayer-type films of phosphododecamolybdic acid, H3PMo12O40, an electrode material with improved capacitance properties is produced. It is apparent from three distinct test experiments (based on cyclic voltammetry, galavanostatic charging–discharging and AC impedance) that capacitors utilizing H3PMo12O40-modified carbon nanotubes are characterized by specific capacitances and energy densities on the levels of 40Fg−1 and 1.3Whkg−1, whereas the respective values for the systems built from bare carbon nanotubes are lower, 22Fg−1 and 0.7Whkg−1. It is reasonable to expect that fast and reversible multi-electron transfers of the Keggin-type H3PMo12O40 account for the pseudocapacitance effect and significantly contribute to the observed overall capacitance. [Copyright &y& Elsevier]

Abstract: Combination of multi-walled carbon nanotubes, cobalt porphyrin, and peroxidase (horseradish, cabbage) enzyme in the film (deposited onto glassy carbon electrode substrate) produces a bio-electrocatalytic system capable of effective reduction of oxygen in such neutral media as 0.1moldm−3 KCl and 0.1moldm−3 KCl+0.01 citrate buffer (pH 6). Carbon nanotubes have been modified with ultra-thin layers of 4-(pyrrole-1-yl) benzoic acid, or phosphododecamolybdate, to form stable colloidal suspensions of carbon nanostructures. The resulting inks have been utilized during sequential deposition of components. Co-existence of cobalt porphyrin, peroxidase enzyme together with dispersed carbon nanotubes leads to synergistic effect that is evident from some positive shift of the oxygen reduction voltammetric potentials (more than 50mV in citrate buffer) and significant (ca. twice) increase of voltammetric currents (relative to those of the enzyme-free system). The multi-component bio-electrocatalytic film has also exhibited relatively higher activity towards reduction of hydrogen peroxide. It is reasonable to expect that the reduction of oxygen is initiated at cobalt porphyrin redox centers, and the undesirable hydrogen peroxide intermediate is further reduced at the horseradish or cabbage peroxidase enzymatic sites. An important function of carbon nanotubes is to improve transport of electrons within the bio-electrocatalytic multi-component film. [Copyright &y& Elsevier]

Abstract: The ability of 4-(pyrrole-1-yl) benzoic acid (PyBA) to form monolayer-type carboxylate-derivatized ultra-thin organic films on solid electrode surfaces was explored here to attract coordinatively and immobilize Ni2+ ions at the electrode/electrolyte interface. In the next step, the system was exposed to Fe(CN)6 3− or Fe(CN)6 4− solution to form a robust nickel hexacyanoferrate (NiHCF) layer. By repeated and alternate treatments in solutions of PyBA, Ni2+ cations, and Fe(CN)6 3− or Fe(CN)6 4− anions, the amount of the material could be increased systematically in a controlled fashion to form three-dimensional multilayered NiHCF-based assemblies. The layer-by-layer method was also extended to the growth of hybrid conducting polymer stabilized NiHCF films in which the initial PyBA-anchored NiHCF layer (formed on glassy carbon) was subsequently exposed (a desired number of times) through alternate immersions to the monomer (3,4-ethylenedioxythiophene), Fe(CN)6 3− and Ni2+ solutions. During voltammetric potential cycling (electropolymerization) in the external supporting electrolyte solution, poly(3,4-ethylenedioxythiophene) or PEDOT linked NiHCF-based multilayered films were produced. They were characterized by good stability and high dynamics of charge transport. [Copyright &y& Elsevier]

Abstract: Fabrication of structured film (on glassy carbon substrate) composed of compact Prussian Blue (that has been prepared by alternate immersions and through assembling within ultra-thin layers of 4(pyrrole-1-yl)-benzoic acid, PPyBA) and poly(3,4-ethylendioxythiophene), PEDOT, is described. This functionalized film has been characterized by fast charge propagation, and it has served as a redox conducting template for permanent attachment of a model enzyme, horseradish peroxidase, HRP. The resulting organic–inorganic system acts as an effective hybrid bioelectrocatalyst for electroreduction of hydrogen peroxide, a model reactant for biosensors and biofuel cells. Among important issues are rigidity, permanence of enzyme attachment, morphology, hydrophilicity, and attractive mediating capabilities of the PEDOT-stabilized Prussian Blue based structured film. [Copyright &y& Elsevier]

Abstract: Optimisation of biocatalytic systems for the electroreduction of molecular O2 in biofuel cell cathodes implies screening of the catalytic activity of enzyme/redoxpolymer assemblies. Os-complex modified electrodeposition polymers are suggested for linking bilirubin oxidase catalysed O2 reduction via an electron hopping sequence along the redox polymer to the electrode. They can be non-manually precipitated on electrode surfaces by electrochemically induced pH modulation. Cyclic voltammetry provides a good estimation of the electrocatalytic activity of a redox polymer/enzyme modified electrode surface. In addition, scanning electrochemical microscopy operating in redox competition mode (RC-SECM) supplies images of the spatial distribution of the biocatalytic activity. [Copyright &y& Elsevier]

Abstract: Surfaces of bulk platinum and unsupported (Vulcan-free) Pt nanoparticles, that are modified and stabilized with such Keggin type heteropolyacids of molybdenum and tungsten as H3PMo12O40 and H3PW12O40, have been characterized using cyclic voltammetry, FTIR (by reflectance), as well as transmission and scanning electron microscopies. The presence of the polyoxometallate monolayer on platinum results in the partial suppression of the interfacial formation of PtOH/PtO oxides. Both molybdates and tungstates seem to interact with Pt surface via their corner oxygen atoms. The existence of spacious, largely hydrated, polyoxometallate monolayers on platinum does not block access of reactant (oxygen) to the catalytic Pt sites. The electrocatalytic properties of H3PMo12O40 and H3PW12O40 modified Pt nanoparticles towards reduction of oxygen in acid medium have been examined and compared using rotating ring–disk voltammetry. Reactivity of Pt-free H3PMo12O40 and H3PW12O40 with respect to reduction of hydrogen peroxide has also been considered. Our results clearly show that modification of Pt nanoparticles with PW12 (but not with PMo12) results in the enhancement of the electrocatalytic reduction of oxygen. [Copyright &y& Elsevier]

Abstract: Nafion stabilized inks of Vulcan XC-72 supported platinum (20wt.%) nanoparticles (Pt/XC-72) were utilized to produce electrocatalytic films on glassy carbon. The catalysts were modified (activated) with phosphododecatungstic acid H3PW12O40 (PW12). Comparison was made to bare (PW12-free) electrocatalytic films. Electroreduction of dioxygen was studied at 25°C in 0.5moldm−3 H2SO4 electrolyte using rotating disk voltammetry. For the same loading of platinum (≈95μgcm−2) and for the approximately identical distribution of the catalyst, the reduction of oxygen at a glassy carbon electrode modified with the ink containing PW12 proceeded at ca. 30–60mV more positive potential (depending on the PW12 content), and the system was characterized by a higher kinetic parameter (rate of heterogeneous electron transfer), when compared to the PW12-free electrocatalyst. Gas diffusion electrodes with Pt/XC-72 supported on carbon paper (Pt loading 1mgcm−2) were also tested. Under the same experimental conditions, while the exchange current density and the total resistance contribution to polarization components, computed from the galvanostatic polarization curves were found to be clearly higher and lower, respectively, for the ink modified with PW12 relative to the unmodified system. The results demonstrate that addition of heteropolytungstatic acid (together with Nafion) enhances the electrocatalytic activity of platinum towards reduction of oxygen. [Copyright &y& Elsevier]

Abstract: Platinum nanoparticles of ca. 8nm diameter (that had been first deposited on glassy carbon) were subsequently modified with ultra-thin films of polyoxometallates through their spontaneous adsorption on solid (platinum and carbon) surfaces. The following polyoxometallates (Keggin type heteropolyacids), H3SiW12O40, H3SiMo12O40, H3PW12O40 and H3PMo12O40, were considered as potential activating agents. Rotating disk voltammetry was used to probe the electroreduction of dioxygen in 0.5moldm−3 H2SO4 at 25°C. For the same loading and the approximately identical distribution of platinum nanoparticles on glassy carbon, the statistically higher (in comparison to bare Pt) electrocatalytic currents for the oxygen reduction were observed upon introduction of monolayers of heteropolyanions. Out of polyoxometallates considered, the system modified with heteropolytungstate (H3PW12O40) seemed to be the most effective in electrocatalysis. Although the possibility of structural changes cannot be excluded, the synergistic effect originated presumably from the bifunctional activity of the electrocatalyst. While Pt retained its usual reactivity towards the oxygen reduction, H3PW12O40 could act as both effective mediator (e.g. for the reduction of the hydrogen peroxide intermediate) and the source of mobile protons at the electrocatalytic interface. [Copyright &y& Elsevier]

Abstract: Two methods have been used for examination of transport of charge in gels soaked with DMF and containing dissolved polyoxometallates. The first method is based on the analysis of both Cottrellian and steady-state currents and therefore is capable of giving the concentration of the electroactive redox centres and their transport (diffusion-type) coefficient. The second method provides the real diffusion coefficients, i.e. transport coefficients free of migrational influence, for both the substrate and the product of the electrode reaction. Several gels based on poly(methyl methacrylate), with charged (addition of 1-acrylamido-2-methyl-2-propanesulphonic acid to the polymerization mixture) and uncharged chains, have been used in the investigation. The ratio obtained for the diffusion coefficient (second method) and transport coefficient (first method) was smaller for the gels containing charged polymer chains than for the gels with uncharged chains. In part these changes could be explained by the contribution of migration to the transport of polyoxomatallates in the gels. However, the impact of the changes in the polymer-channel capacity at the electrode surface while the electrode process proceeds was also considered. These structural changes should affect differently the methods based on different time domains. [Copyright &y& Elsevier]

Abstract: A composite of silica sol–gel, generation-4 poly(amidoamine) dendrimer (PAMAM) and cobalt hexacyanoferrate (CoHCF) was synthesized as a potential electrochromic material. The solid-state voltammetry of the material had suggested that the two electroactive sites were present. To elucidate the redox properties, the electronic and the structure in the local atomic environment of Fe and Co was investigated by X-ray absorption spectroscopy (XAS). Although the nominal stoichiometries of the investigated CoHCFs were Co2 IIFeII(CN)6 (or K2CoIIFeII(CN)6) and KCoIIFeIII(CN)6, the spectral data demonstrated that CoIII was present in the composite. Among the supporting evidence for some metal-to-metal electronic transition of FeIII–CN–CoII to FeII–CN–CoIII was the shortening of the measured Co–N bond length in accord with the formation of CoIII. Further, IR measurements confirm the occurrence of charge transfer between Fe and Co sites in the silica–PAMAM composite. [Copyright &y& Elsevier]

Abstract: The solid-state electrochemistry and thermochromism of cobalt hexacyanoferrate (CoHCF) in a composite matrix comprising silica sol–gel and generation-4 poly(amidoamine) dendrimer was investigated and compared to analogous studies of CoHCF powders. The thermochromic behaviour over the range, 25–85°C, of the reduced form in the sol–gel matrix differed from that of the powder. The results suggested that even in the presence of KCl in this matrix, the dominate form of the reduced CoHCF was Co2 IIFeII(CN)6 rather than K2CoIIFeII(CN)6. In contrast, the thermochromic behaviour of the oxidized form of CoHCF was the same as that reported for the powders. The observed cyclic voltammetric behaviour of CoHCF in the sol–gel composite matrix was the same as that of powders in terms of the electrode processes, but the influence of scan rate on the current was dependent upon the cell configuration. With the CoHCF-doped composite contacted to a solution phase, this behaviour was consistent with anion intercalation/de-intercalation control, but in a solid-state cell, a transition from a surface-controlled to a mass-transport controlled current was observed. [Copyright &y& Elsevier]

Abstract: A novel polymetacrylate-based redox-conducting polymeric gel, into which Keggin-type polyoxometallate, phosphododecatungstic acid (H3PW12O40), had been incorporated, was electrochemically characterized in the absence of external liquid supporting electrolyte using an ultramicrodisk-working electrode. The phosphotungstate component (15wt.% of the gel block) was entrapped as the polar organic solvent solution within pores of the polymer matrix. H3PW12O40 plays bifunctional role: it provides well-behaved redox centers and serves as strong acid (source of mobile protons). The solid-state voltammetric properties of the system are defined by the reversible one-electron transfers between phosphotungstate redox centers. The following parameters have been determined from the combination of potential step experiments performed in two limiting (radial and linear) diffusional regimes: the concentration of heteropolytungstate redox centers, 6×10-2moldm-3, and the apparent diffusion coefficient, 5×10-7cm2s-1. The room temperature ionic (protonic) conductivity of the bulk gel was equal to 1.6×10-3Scm-1. The charge propagation mechanism was found to be primarily controlled by physical diffusion of heteropolytungstate units within the gel pores rather than by electron hopping (self-exchange) between mixed-valence sites. [Copyright &y& Elsevier]

Abstract: We develop a concept of fabrication of the multilayer network films on electrodes by exploring the ability of a Keggin-type polyoxometallate, phosphododecamolybdate (PMo12O40 3−), to form stable anionic monolayers (templates) on carbon and metals including platinum. By repeated alternate treatments in the solution of PMo12O40 3− (or in the colloidal suspension of polyoxometallate-protected Pt-nanoparticles) and in the solution of monomer (e.g. anilinium) cations, the amount of the material can be increased systematically (layer-by-layer) to form stable three-dimensional assemblies on electrode (e.g. glassy carbon) surfaces. In the resulting hybrid (organic–inorganic) films, the layers of negatively charged polyoxometallate, or polyoxometallate-protected (stabilized) Pt-nanoparticles, are linked or electrostatically attracted by ultra-thin layers of such positively charged conducting polymers as polyaniline (PANI), polypyrrole (PPy) or poly(3,4-ethylenedioxythiophene), PEDOT. Consequently, the attractive physicochemical properties of polymers and reactivity of polyoxometallate or noble metal particles are combined. The films are functionalized and show electrocatalytic properties towards reduction of nitrite, bromate, hydrogen peroxide or oxygen. They are of importance to the chemical and biochemical sensing as well as to the biochemical and medical applications. [Copyright &y& Elsevier]

A novel electroanalytical approach is proposed here, and it is demonstrated with the direct and simultaneous determination of two unknowns: the concentration of redox sites and the apparent diffusion coefficient for charge propagation in a single crystal of dodecatungstophosphoric acid. This Keggin-type polyoxometalate serves as a model bulk redox conducting inorganic material for solid-state voltammetry. The system has been investigated using an ultramicrodisk working electrode in the absence of external liquid supporting electrolyte. The analytical method requires numerical solution of the combination of two equations in which the first one describes current (or charge) in a well-defined (either spherical or linear) diffusional regime and the second general equation describes chronoamperometric (or normal pulse voltammetric current) under mixed (linear-spherical) conditions. The iterative approach is based on successive approximations through calculation and minimizing the least-squares error function. The method is fairly universal, and in principle, it can be extended to the investigation of other bulk systems including sol-gel processed materials, redox melts, and solutions on condition that they are electroactive and well behaved, they contain redox centers at sufficiently high level, and a number of electrons for the redox reaction considered is known. [ABSTRACT FROM AUTHOR]

Integration into a conducting polymer matrix to form a hybrid material is an effective way to harness the electrochemical activity of nanosized oxide clusters. By anchoring them into polyaniline, the reversible redox chemistry of the otherwise soluble polyoxometalate clusters can be combined with that of the conducting polymer and be put to work in energy storage applications. We present here preliminary results that show how the resulting hybrid polymer displays the combined activity of its organic and inorganic components to store and release charge in a solid state electrochemical capacitor device. [Copyright &y& Elsevier]

Focuses on the electronic conductivity properties of network polymer films of gold nanoparticles. Changes in electron hopping rates in dry films with ligand chainlength; Demonstration of electron tunneling in dry films; Response to vapor exposure; Response of network polymer films containing several different combinations of nonlinker and linker chain-length to saturated ethanol vapor.

• Pd0 is generated upon electroreduction of PdII ions in the supramolecular complex. • Pd° catalytic centers are stabilized and activated by ligand N,N coordination sites. • Thus generated Pd nanoparticles exhibit high activity during CO 2 -electroreduction. • CO and H 2 are the main reduction products in CO 2 -saturated aqueous KHCO 3. Tridentate Schiff base ligand L (L = C 14 H 12 N 2 O 3) reacts with palladium(II) chloride, to give a complex of formula [Pd(C 14 H 12 N 2 O 3)Cl 2 ] 2 ∙MeOH. The spectroscopic, microanalytical and X-ray crystallographic data are consistent with the view that palladium(II) ion is coordinated by two nitrogen donor atoms, with typical PdII-N distances and two chloride ligands, representing thus N,N instead of possible N,N,O coordination mode. The reduced Pd° catalytic sites are electrochemically generated (by voltammetric potential cycling) within the film of supramolecular network of tridentate Schiff base ligands. The IR and XPS data of the electroreduced material are consistent with the existence of interactions between the palladium catalytic centers and the network of supramolecular ligands with N,N coordination sites. In comparison to conventional Pd nanoparticles, the CO 2 -reduction current densities, which have been recorded in near-neutral KHCO 3 both under voltammetric and chronoamperometric conditions and normalized against electrochemically active surface area of palladium catalyst, are significantly higher at the supramolecular-ligand-supported Pd nanoparticles. [ABSTRACT FROM AUTHOR]

• Redox properties of anticancer drugs compared. • Electrochemistry of DNA-drug interactions and tests on cancer cells correlated. • Effect of Vitamin C on DNA-drug interactions tested. • Stability of DNA (plasmid)-covered glassy carbon electrode (GCE) tested. For the comparison of the DNA interactions with drugs, two newly synthesized prospective anticancer drugs, 6-(1 H -imidazo[4,5-b]phenasine-2-yl)benzene-1,3-diol (IPBD) and, its -Cl derivative (Cl-IPBD) have been compared with doxorubicin, a drug widely used in medicine, and with Vitamin C. These compounds were accumulated at a supercoiled scpUC19 plasmid layer formed on a glassy carbon electrode (GCE). Stability of the drug-plasmid/GCE layer was achieved by initial plasmid accumulation using prolonged potential cycling for ca. 200 min. from highly diluted scpUC19 solutions (8 pg/mL), followed by accumulation of the drugs from 1 µM − 50 µM. Electrochemical properties in terms of the redox potentials of the compounds and capacitative/resistive characteristics of the layers have been tested using, in sequence, four voltammetric methods: Square Wave (SWV), Differential Pulse (DPV) and Alternating Current (ACV) with phase detection 0° and 90 °. Importantly, with progressive drug accumulation in the plasmid, for Cl-IPBD, but not for IPBD, an increase in peak (I) at –0.42 V vs. SCE was observed, while biological tests revealed a higher cytotoxic activity for Cl-IPBD vs. IPBD. Moreover, an additional redox signal of Cl-IPBD was observed with the compound reductive accumulation at the plasmid layer in the presence of Vitamin C. [ABSTRACT FROM AUTHOR]

• Silicotungstic acid (H 4 SiW 12 O 40) is considered as electrolyte for supercapacitors. • The charge storage properties are evaluated vs. standard H 2 SO 4 electrolyte. • The porosity of carbon is of crucial importance for H 4 SiW 12 O 40 -based supercapacitor. • H 4 SiW 12 O 40 -based cell has higher discharge rate than its H 3 PW 12 O 40 counterpart. • The charge storage properties of H 4 SiW 12 O 40 system are well-preserved at −30 °C. The key factors influencing the application of Keggin-type silicotungstic acid electrolyte, H 4 SiW 12 O 40 (SiW 12), in electrochemical capacitors are considered here by means of electrochemical, N 2 adsorption, and Differential Scanning Calorimetry analysis. A series of activated carbons has been selected in order to match the porous structure of the electrode allowing to accommodate ca. 1.1 nm in diameter SiW 12 O 40 4− anions. It has been shown that for carbons with adequately wide pore size distribution, the electrical parameters of capacitor can be as high as for the standard acidic H 2 SO 4 electrolyte but the system is characterized by better discharge dynamics and, consequently, by higher specific power. The observation can be attributed to high population and mobility of protons in the Keggin structure and to a great ionic (molar) conductivity of SiW 12. It has been also shown that a water/methanol mixture can be used to permit application of the SiW 12 electrolyte at low temperatures with a performance exceeding the H 2 SO 4 counterpart. Additionally, the electrochemical behaviour of SiW 12 has been compared to the characteristics of phosphate-coordinated analogue, H 3 PW 12 O 40 , namely by exploring the influence of the POMs redox processes on the systems' charge storage properties and self-discharge rates. [ABSTRACT FROM AUTHOR]

The unique feature of Keggin-type dodecatungstosilicate (SiW 12 O 40 4−) to undergo adsorption on silver surfaces is explored here to fabricate, modify and stabilize silver nanoparticles in acid medium, as well as to link them to different reduced graphene oxide (rGO) substrates: SiO 2 -doted rGO, carboxylate-derivatized rGO, and conventional rGO (obtained through the chemical reduction method). Upon medium transfer to alkaline electrolyte, the inorganic polyoxometalate-capping-ligand disappears but silver nanostructures remain on rGO supports. The electrocatalytic activity of the resulting systems are probed during the oxygen reduction reaction (ORR). It is apparent from XRD data that silver is crystalline in nature and, particularly in a case of SiO 2 -doted rGO supports, metallic silver nanocrystals have face-centered-cubic structures enriched with high-index Ag(111) facets known to facilitate ORR. Functionalization of graphene with SiO 2 seems to provide an efficient way to keep the nanosheets of graphene exfoliated thus facilitating unimpeded flux of reactants and making the system easily accessible for intercalation with catalytic Ag. Silver nanoparticles supported onto SiO 2 -doted rGO are relatively the most active toward ORR when examined under rotating ring disk conditions in terms of the observed highest catalytic current density, the most positive ORR onset potential, and the lowest percent formation of the H 2 O 2 reaction intermediate. • Silicotungstates facilitate fabrication of Ag nanoparticles within rGO supports. • Functionalization with SiO 2 keeps graphene nanosheets exfoliated. • Ag dispersed over SiO 2 -doted rGO exhibits high catalytic activity (O 2 -reduction). • Formation of defect-rich highly-active Ag(111) surfaces is operative. [ABSTRACT FROM AUTHOR]

Platinum nanoparticles have been deposited onto hybrid carriers composed of iron hexacyanoferrate (Prussian Blue) pretreated or functionalized reduced graphene oxide (rGO), and the resulting system's electrocatalytic activity has been investigated during oxygen reduction reaction in acid solution. Physicochemical properties of the Pt nanoparticle-containing materials have been obtained using transmission electron microscopy, X-ray diffraction and various electrochemical diagnostic techniques including cyclic voltammetry and rotating ring-disk electrode (RRDE) voltammetry. Although functionalization of rGO carriers with Prussian Blue, followed by the system's thermal treatment at 300°C, does not change activity of Pt catalytic centers in terms of the electroreduction potential of oxygen in 0.5 mol dm−3 H 2 SO 4 (under rotating disk voltammetric conditions), the presence of cyanide-bridged iron ionic sites tends to decrease formation of the undesirable hydrogen peroxide intermediate, as demonstrated by monitoring ring currents during RRDE measurements. The results imply usefulness of PB-modified rGO supports for dispersed Pt nanoparticles at the low loading of 10 μg cm−2 in the oxygen reduction electrocatalysis. In addition to the possible metal-support activating interactions, the mechanism, in which oxygen reduction is initiated at Pt centers and the hydrogen peroxide intermediate is reductively decomposed at reactive PB-modified rGO supports, is feasible. • Modification of reduced graphene oxide with Prussian Blue produces active supports for Pt nanoparticles. • Oxygen reduction proceeds mostly to water in acid medium according to 4-electron mechanism. • Lower amounts of hydrogen peroxide intermediate are observed during ORR in acid medium. [ABSTRACT FROM AUTHOR]

Hybrid photocathode materials, which are composed of hierarchically deposited (onto the transparent fluorine-doped conducting glass electrode) copper(I) oxide (inner layer) and robust carbon structures, such as carbide derived carbons (CDC) or mixture of CDC with 70% (weight) tungsten carbide (WC-CDC), have been fabricated and examined using electrochemical methods, X-ray diffraction and various spectroscopic approaches including Raman technique. The resulting systems have been characterized by good stability and have exhibited high photoelectrochemical activity toward reduction of CO 2 upon illumination with sunlight in the Na 2 SO 4 neutral medium. While the semiconducting properties of Cu 2 O are not largely affected by the interfacial modification with CDC and WC-CDC, the photostability of the hybrid photocathode is significantly improved. The stabilization effect should reflect the capacitive properties of CDC and WC-CDC. The capability of CDC and WC-CDC over-layers to undergo efficient double-layer-type charging/discharging should facilitate collection and transport of photoelectrons and inhibit recombination of photogenerated electron-hole pairs. The relatively higher photoelectrochemical activity of the Cu 2 O system over-coated with WC-CDC, relative to the one containing CDC only, seems to reflect specific interactions between CO 2 and WC-CDC thus inducing reduction of CO 2 adsorbates. • Stabilization of Cu 2 O is achieved through over-coating with CDC and WC-CDC. • The carbon over-layers exhibit capacitive (charge storage) properties. • Addition of tungsten carbide induces electroreduction of CO 2 adsorbates. • Hybrid photocathodes are used for photoelectrochemical reduction of CO 2 to methanol. [ABSTRACT FROM AUTHOR]

Appropriate and rational management of the energy produced by renewable energy sources is one of the most urgent challenges for the global energy sector. This paper is devoted to the systematic experimental and theoretical studies of a modular solar charger based on silicon and dye-sensitized solar cells as an energy source, and supercapacitor as an energy bank. Using the MathCAD program, I-V characteristics were plotted for both a single cell and a photovoltaic module based on various series-to-parallel connections. To assess the surface quality of the modules, additional tests using a thermal imaging camera were carried out as well. The charging characteristics of the supercapacitor (two series-connected cells with a capacity of 300 F), were determined depending on the parameters of the photovoltaic module as well as considering the influence of the voltage balancing system and control system. The charge, discharge, and recharge characteristics were carefully analyzed to optimize the operating conditions, i.e. the number of photovoltaic cells. To evaluate the stability of parameters with operation time, and their temperature dependence (17-65 °C), solar modules were tested for ten days under Central European weather conditions. Importantly, a comparative analysis of solar chargers based on different configurations of photovoltaic cells showed an increase in electrical parameters for the proposed modular inorganic-organic concept compared to dye-sensitized solar cells produced alone on a rigid substrate. Finally, preliminary assumptions (requirements) were developed regarding the electrical and optical parameters for new dye-sensitized solar cells that could be used in the innovative solar charger instead of silicon cells along with a predicted role of artificial intelligence (AI) in these devices., (© 2024. The Author(s).)

A hybrid catalytic system composed of copper (I)-oxide-derived copper nanocenters immobilized within the network of tungsten oxide nanowires has exhibited electrocatalytic activity toward CO 2 reduction in an acid medium (0.5 mol dm -3 H 2 SO 4 ). The catalytic system facilitates conversion of CO 2 to methanol and is fairly selective with respect to the competing hydrogen evolution. The preparative procedure has involved voltammetric electroreduction of Cu 2 O toward the formation and immobilization of catalytic Cu sites within the hexagonal structures of WO 3 nanowires which are simultaneously partially reduced to mixed-valence hydrogen tungsten (VI, V) oxide bronzes, H x WO 3 , coexisting with sub-stoichiometric tungsten (VI, IV) oxides, WO 3- y . After the initial loss of Cu through its dissolution to Cu 2+ during positive potential scanning up to 1 V (vs RHE), the remaining copper is not electroactive and seems to be trapped within in the network of hexagonal WO 3 . Using the ultramicroelectrode-based probe, evidence has also been provided that partially reduced nonstoichiometric tungsten oxides induce reduction of CO 2 to the CO-type reaction intermediates. The chronocoulometric data are consistent with the view that existence of copper sites dispersed in WO 3 improves electron transfers and charge propagation within the hybrid catalytic layer. The enhanced tolerance of the catalyst to the competitive hydrogen evolution during CO 2 R should be explained in terms of the ability of H x WO 3 to consume protons and absorb hydrogen as well as to shift the proton discharge at Cu toward more negative potentials. However, the capacity of WO 3 to interact with catalytic copper and to adsorb CO-type reaction intermediates is expected to facilitate removal of the poisoning CO-type adsorbates from Cu sites., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

The 48-Fe III -containing 96-tungsto-16-phosphate, [Fe III 48 (OH) 76 (H 2 O) 16 (HP 2 W 12 O 48 ) 8 ] 36- (Fe 48 ), has been synthesized and structurally characterized. This polyanion comprises eight equivalent {Fe III 6 P 2 W 12 } units that are linked in an end-on fashion forming a macrocyclic assembly that contains more iron centers than any other polyoxometalate (POM) known to date. The novel Fe 48 was synthesized by a simple one-pot reaction of an {Fe 22 } coordination complex with the hexalacunary {P 2 W 12 } POM precursor in water. The title polyanion was characterized by single-crystal XRD, FTIR, TGA, magnetic and electrochemical studies., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

The thin-layer-stacked dye-sensitized NiO photocathodes decorated with palladium nanoparticles (nPd) can be used for the visible-light-driven selective reduction of CO 2 , mostly to CO, at potentials starting as low as 0 V vs. RHE (compared to -0.6 V in the dark for electrocatalysis). The photosensitization of NiO by the organic dye P1, with a surface coverage of 1.5 × 10 -8 mol cm -2 , allows the hybrid material to absorb light in the 400-650 nm range. In addition, it improves the stability and the catalytic activity of the final material decorated with palladium nanoparticles (nPd). The resulting multi-layered-type photocathode operates according to the electron-transfer-cascade mechanism. On the one hand, the photosensitizer P1 plays a central role as it generates excited-state electrons and transfers them to nPd, thus producing the catalytically active hydride material PdH x . On the other hand, the dispersed nPd, absorb/adsorb hydrogen and accumulate electrons, thus easing the reductive electrocatalysis process by further driving the separation of charges at the photoelectrochemical interface. Surface analysis, morphology, and roughness have been assessed using SEM, EDS, and AFM imaging. Both conventional electrochemical and photoelectrochemical experiments have been performed to confirm the catalytic activity of hybrid photocathodes toward the CO 2 reduction. The recorded cathodic photocurrents have been found to be dependent on the loading of Pd nanoparticles. A sufficient amount of loaded catalyst facilitates the electron transfer cascade, making the amount of dye grafted at the surface of the electrode the limiting parameter in catalysis. The formation of CO as the main reaction product is postulated, though the formation of traces of other small organic molecules ( e.g. methanol) cannot be excluded., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The 15-copper(ii)-containing 36-tungsto-4-silicates [Cu15O2(OH)10X(A-α-SiW9O34)4]25- (X = Cl, 1; Br, 2) have been prepared in 70% yield by reaction of the trilacunary 9-tungstosilicate precursor [A-α-SiW9O34]10- with Cu2+ ions in aqueous pH 8 medium. Both polyanions 1 and 2 were isolated as hydrated mixed potassium/sodium salts and characterized in the solid state by FT-IR, TGA, single-crystal XRD, and elemental analysis. DC magnetic susceptibility measurements from 1.8-300 K established the ground state to be paramagnetic with a magnetic moment corresponding to 15 uncoupled Cu2+ (S = 1/2) ions. EPR measurements and simulations were consistent with this analysis. Electrochemical studies were performed for polyanions 1 and 2 dissolved in solution to elucidate the electroactivity of both copper and tungstate sites. Using 2 as a representative example, the electrocatalytic activity towards CO2 reduction upon deposition on a glassy carbon electrode surface, while retaining selectivity relative to hydrogen evolution, was demonstrated.

The ability of Pt nanostructures to induce the splitting of the II bond in iodine (triiodide) molecules is explored here to enhance electron transfer in the iodine/iodide redox couple. Following the dispersal of Pt nanoparticles at 2 % (weight) level, charge transport was accelerated in triiodide/iodide-containing 1,3-dialkylimidazolium room-temperature ionic liquid. If both Pt nanoparticles and multi-walled carbon nanotubes were introduced into the ionic-liquid-based system, a solid-type (nonfluid) electrolyte was obtained. By using solid-state voltammetric (both sandwich-type and microelectrode-based) methodology, the apparent diffusion coefficients for charge transport increased to approximately 1×10(-6)  cm(2)  s(-1) upon the incorporation of the carbon-nanotube-supported iodine-modified Pt nanostructures. A dye-sensitized solar cell comprising TiO2 covered with a heteroleptic Ru(II) -type sensitizer (dye) and the semisolid triiodide/iodide ionic liquid electrolyte admixed with carbon-nanotube-supported Pt nanostructures yielded somewhat higher power conversion efficiencies (up to 7.9 % under standard reporting conditions) than those of the analogous Pt-free system., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Different approaches to enhancement of electrocatalytic activity of noble metal nanoparticles during oxidation of small organic molecules (namely potential fuels for low-temperature fuel cells such as methanol, ethanol and formic acid) are described. A physical approach to the increase of activity of catalytic nanoparticles (e.g. platinum or palladium) involves nanostructuring to obtain highly dispersed systems of high surface area. Recently, the feasibility of enhancing activity of noble metal systems through the formation of bimetallic (e.g. PtRu, PtSn, and PdAu) or even more complex (e.g. PtRuW, PtRuSn) alloys has been demonstrated. In addition to possible changes in the electronic properties of alloys, specific interactions between metals as well as chemical reactivity of the added components have been postulated. We address and emphasize here the possibility of utilization of noble metal and alloyed nanoparticles supported on robust but reactive high surface area metal oxides (e.g. WO 3 , MoO 3 , TiO 2 , ZrO 2 , V 2 O 5 , and CeO 2 ) in oxidative electrocatalysis. This paper concerns the way in which certain inorganic oxides and oxo species can act effectively as supports for noble metal nanoparticles or their alloys during electrocatalytic oxidation of hydrogen and representative organic fuels. Among important issues are possible changes in the morphology and dispersion, as well as specific interactions leading to the improved chemisorptive and catalytic properties in addition to the feasibility of long time operation of the discussed systems.

Modification of electrodes with nm-scale organically modified silica films with pores diameters controlled at 10- and 50-nm is described. An oxidation catalyst, mixed-valence ruthenium oxide with cyano crosslinks or gold nanoparticles protected by dirhodium-substituted phosophomolybdate (AuNP-Rh 2 PMo 11 ), was immobilized in the pores. These systems comprise size-exclusion films at which the biological compounds, phosphatidylcholine and cardiolipin, were electrocatalytically oxidized without interference from surface-active concomitants such as bovine serum albumin. 10-nm pores were obtained by adding generation-4 poly(amidoamine) dendrimer, G4-PAMAM, to a (CH 3 ) 3 SiOCH 3 sol. 50-nm pores were obtained by modifying a glassy carbon electrode (GC) with a sub-monolayer film of aminopropyltriethoxylsilane, attaching 50-nm diameter poly(styrene sulfonate), PSS, spheres to the protonated amine, transferring this electrode to a (CH 3 ) 3 SiOCH 3 sol, and electrochemically generating hydronium at uncoated GC sites, which catalyzed ormosil growth around the PSS. Voltammetry of Fe(CN) 6 3- and Ru(NH 3 ) 6 3+ demonstrated the absence of residual charge after removal of the templating agents. With the 50-nm system, the pore structure was sufficiently defined to use layer-by-layer electrostatic assembly of AuNP-Rh 2 PMo 11 therein. Flow injection amperometry of phosphatidylcholine and cardiolipin demonstrated analytical utility of these electrodes.

The integrated, structured, and multifunctional bioelectrocatalytic system for effective oxidation of ethanol is developed here. The concept is based on the layer-by-layer (LbL) assembly through electrostatic attraction of positively charged, multiwalled carbon nanotubes and the controlled combination of dehydrogenase enzymes. More specifically, the LbL technique was employed for sequential immobilization of two dehydrogenase enzymes and poly(diallyldimethylammonium chloride)-covered multiwalled carbon nanotubes onto a glassy carbon electrode substrate. Both monoenzymatic [utilizing a single enzyme, alcohol dehydrogenase (ADH)] and bienzymatic (anchoring sequentially both ADH and aldehyde dehydrogenase) systems were tested. Multilayers were characterized using scanning electron microscopy, infrared spectroscopy, and cyclic voltammetry. The results are consistent with the view that our approach enables good control of distribution and efficient utilization of both enzymes within the biocomposite film and leads to sizable enhancement of the oxidation of ethanol through significant (more than 2-fold) increase of bioelectrocatalytic currents and by shifting the ethanol oxidation potential to 0.1 V (vs Ag/AgCl) or decreasing the overvoltage by ca. 200 mV in comparison with the monoenzymatic electrode system. This simple biocomposite (enzyme-cascade) system permits fabrication of highly sensitive ethanol biosensors based on nicotinamide adenine dinucleotide coenzyme-dependent dehydrogenases. Our ethanol biosensor exhibited a good linearity ranging from 50 to 300 μM, and it was characterized by a high sensitivity of 118.8 μA mM(-1) cm(-2) as well as a low detection limit of 24 μM.

Both Keggin-type phosphotungstic acid (HPW) and Pd are not prominent catalysts towards the oxygen reduction (ORR), but their composite Pd-HPW catalyst produces a significantly higher electrochemical activity for the ORR in acidic media. The novel composite catalyst was synthesized by self-assembly of HPW on multi-walled carbon nanotubes (MWCNTs) via the electrostatic attraction between negatively charged HPW and positively charged poly(diallyldimethylammonium (PDDA)-wrapped MWCNTs, followed by dispersion of Pd nanoparticles onto the HPW-PDDA-MWCNT assembly. The as-prepared catalyst was characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). TEM images show that Pd nanoparticles were uniformly dispersed on the surface of MWCNTs even when the Pd loading was increased to 60 wt%. Electrochemical activity of the catalysts for the ORR was evaluated by steady state polarization measurements using a rotating disk electrode. Compared with the acid treated MWCNTs, Pd nanoparticles supported on the HPW-assembled MWCNTs show a much higher ORR activity that is comparable to conventional Pt/C catalysts. The high electrocatalytic activities could be related to high dispersion of Pd nanoparticles as well as synergistic effects originating from the high proton conductivity of HPW. The Pd/HPW-PDDA-MWCNTs system as the cathode catalyst in proton exchange membrane fuel cells is demonstrated.

Electrocatalytic properties (towards reduction of bromate in 0.5moldm(-3) H(2)SO(4)) of multi-walled carbon nanotubes (CNTs) modified with phosphododecamolybdate (PMo(12)) monolayers have been diagnosed using cyclic voltammetry and amperometry. The ability of negatively charged PMo(12)-modified CNTs to attract electrostatically ultra-thin, positively charged conducting polymer (PEDOT or polypyrrole) structures is explored to grow in controlled manner hybrid organic-inorganic network electrocatalytic films. Due to the presence of three-dimensionally distributed CNTs, the films' conductivity and porosity are improved. The hybrid systems utilizing polypyrrole, rather than PEDOT, have produced fairly higher bromate electroreduction catalytic currents. Comparison is also made to Nafion-stabilized dispersion of PMo(12)-modified CNTs inks. The latter system is characterized by good stability and relatively the highest sensitivities with respect to bromate concentration.

Scanning electrochemical microscopy (SECM) in feedback mode was applied to monitor changes in the electronic conductivity of a passive layer existing on a nanocrystalline Nd-Fe-B-type permanent magnet of the following composition, Nd13.5Fe79.5Si1B6 (where subscripts denote at. %). This model magnet being a complex multimetallic-phase material (fabricated according to the hydrogenation-disproportionation-desorption-recombination route) contained intrinsic iron inclusions, as evident from SEM and EDX mapping. SECM measurements performed in feedback mode using ferrocenecarboxylic acid as a mediator (in phosphate buffer at pH 7) in the presence and absence of chloride anions permitted evaluation of the local surface (passive layer) conductivity changes during pitting corrosion caused by Cl- anions. The spots of high conductivity (electronic or redox) act as precursor sites for initiation of pits. It can be rationalized that iron inclusions are responsible for the high susceptibility of Nd-Fe-B magnets to pitting corrosion. The approach is fairly general and allows localization of pitting precursor sites under different corrosion environments that include a wide range of concentrations of anions causing the passive layer breakdown.