Search

To cite some of his research activities, it should be mentioned that Roberto Marassi was a pioneer in the field of electrochemical energy storage for more than 40 years, pursuing research in such areas as molten salts or ionic liquids, Na-S batteries, Li-ion batteries, low-temperature fuel cells, and vanadium redox flow batteries, in addition to his interests in electroanalytical chemistry. But Roberto is remembered mainly for his availability to interact with other people, especially the young scientists, as well as for his sincere enthusiasm for the progress in electrochemical science and technology. Roberto Marassi was one of the scientists who, by developing new or by extending existing methods or materials, significantly advanced the understanding of electrochemical energy conversion processes as well as of the fundamentals of electrocatalysis and electroanalysis. [Extracted from the article]

Abstract: 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. WO3, MoO3, TiO2, ZrO2, V2O5, and CeO2) 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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: A novel Pd electrocatalyst is developed by self-assembly of Pd nanopartilces on phosphomolybdic acid (HPMo)-poly(diallyldimethylammonium chloride) (PDDA)-functionalized multiwalled carbon nanotubes supports (Pd/HPMo-PDDA-MWCNTs). The as-synthesized Pd/HPMo-PDDA-MWCNTs were characterized by TEM, EDS mapping, Raman spectra, X-ray photoelectron spectroscopy, electrochmeical CO stripping and cyclic voltammetry techniques. Pd nnaoparticles deposited on HPMo-PDDA-MWCNTs are in the range of 3.1 nm with uniform distributon. Pd/HPMo-PDDA-MWCNT catalysts have lower overpotential for COad oxidation manifested as lower peak and onset potentials as compared to acid-treated MWCNTs supported Pd (Pd/AO-MWCNTs) and carbon supported Pd catalysts (Pd/C). Pd/HPMo-PDDA-MWCNTs catalysts also exhibit a much higher electrocatalytic activity and stability for formic acid oxidation reaction as compared to that on Pd/AO-MWCNTs and Pd/C. The high electrocatalytic activities of Pd/HPMo-PDDA-MWCNTs catalysts are most likely related to highly dispersed and fine Pd nanoparticles as well as synergistic effects between Pd and HPMo immobilized on PDDA-functionalized MWCNTs. [Copyright &y& Elsevier]

Abstract: RuSe x electrocatalytic nanoparticles were deposited onto hybrid carriers composed of Black Pearl carbon-supported tungsten oxide; and the resulting system''s electrochemical activity was investigated during oxygen reduction reaction. The tungsten oxide-utilizing and RuSe x nanoparticle-containing materials were characterized using transmission electron microscopy, X-ray diffraction and electrochemical diagnostic techniques such as cyclic voltammetry and rotating ring-disk voltammetry. Application of Black Pearl carbon carriers modified with ultra-thin films of WO3 as matrices (supports) for RuSe x catalytic centers results during electroreduction of oxygen in 0.5moldm−3 H2SO4 (under rotating disk voltammetric conditions) in the potential shift of ca. 70mV towards more positive values relative to the behavior of the analogous WO3-free system. Also the percent formation (at ring in the rotating ring-disk voltammetry) of the undesirable hydrogen peroxide has been decreased approximately twice by utilizing WO3-modified carbon carriers. The results are consistent with the bifunctional mechanism in which oxygen reduction is initiated at RuSe x centers and the hydrogen peroxide intermediate is reductively decomposed at reactive WO3-modified Black Pearl supports. The electrocatalytic activity of the system utilizing WO3-modified Black Pearl supports has been basically unchanged upon addition of acetic acid, formic acid or methyl formate to the sulfuric acid supporting electrolyte. [Copyright &y& Elsevier]

Abstract: We investigate oxygen permeation through Nafion 117 membrane in a direct ethanol fuel cell and elucidate how it affects the fuel cell efficiency. An obvious symptom of oxygen permeation is the presence of significant amounts of acetaldehyde and acetic acid in the mixture leaving anode when no current was drawn from the fuel cell (i.e. under the open circuit conditions). This parasitic process severely lowers efficiency of the fuel cell because ethanol is found to be directly oxidized on the surface of catalyst by oxygen coming through membrane from cathode in the absence of electric current flowing in the external circuit. Three commonly used carbon-supported anode catalysts are investigated, Pt, Pt/Ru and Pt/Sn. Products of ethanol oxidation are determined qualitatively and quantitatively at open circuit as a function of temperature and pressure, and we aim at determining whether the oxygen permeation or the catalyst''s activity limits the parasitic ethanol oxidation. Our results strongly imply the need to develop more selective membranes that would be less oxygen permeable. [Copyright &y& Elsevier]

Abstract: We propose a novel composite (hybrid) organic/inorganic system that can be prepared as a coating (on 1μm level) on glassy carbon and metal electrode substrates. Poly(3,4-ethylenedioxythiophene) or PEDOT based composite coatings were electrodeposited using cyclic voltammetry on glassy carbon and stainless steel substrates in the presence of 4-(pyrrole-1-yl) benzoic acid (PyBA) and phosphododecamolybdic acid (PMo12). The coating growth was facilitated by the addition of polyoxyethylene-10-laurylether (BRIJ10) neutral surfactant at the level of 0.04moldm−1 to improve solubility of the 3,4-ethylenedioxythiophene monomer and to form an aqueous micellear solution in the reaction medium. The fact that carboxylate-containing PyBA units link positively charged PEDOT structures tends to improve overall stability and adherence of composite coatings to stainless steel. The PEDOT/PyBA composite serves as a stable host matrix for large negatively charged polymolybdate inorganic species. Consequently, due to the formation of denser polymeric structures and to the existence of electrostatic repulsion effects, the polyanion-containing composite coatings are capable of largely blocking the access of pitting-causing anions (chlorides) to the surface of stainless steel. Interaction of phosphomolybdate with metal ions, namely with chromium(III) or even iron(III) or iron(II) that exist at the stainless steel–composite coating interface, may lead to the formation of insoluble deposits and exhibit overall passivating effect. [Copyright &y& Elsevier]

Abstract: A novel electrocatalytic system for oxidation of ethanol, in which carbon-supported PtSn nanoparticles were modified with ultra-thin films/deposits of tungsten oxide, was proposed, fabricated and characterized here using electrochemical as well as spectroscopic (X-ray diffraction) and microscopic (transmission electron) techniques. The enhancement effect was evident from comparative diagnostic electrochemical experiments utilizing WO3-modified and bare (unmodified) PtSn nanoparticles in acid medium (0.5moldm−3 H2SO4) at room temperature in the presence of ethanol. It is noteworthy that, the chronoamperometric electrocatalytic currents measured at potentials as low as 0.3V (vs. RHE) were significantly larger for WO3-modified PtSn/C relative to bare PtSn/C. In another diagnostic “stripping” experiment, it was found that oxidation of CO-adsorbate occurred in the presence of WO3 at potentials almost 100mV lower in comparison to the unmodified system. The overall activation effect may have origin in interactions of tungsten oxide with tin (from PtSn alloy nanoparticles) leading to stabilization of the catalytic tin oxo species. WO3 may also provide large population of reactive oxo groups at the Pt/Sn-based electrocatalytic interface. [Copyright &y& Elsevier]

Abstract: Scanning electrochemical microscopy (SECM) in the feedback mode was utilized for monitoring the surface reactivity and the localized corrosion processes occurring on the Nd13.5Fe79.5Si1B6 permanent magnet (intrinsically comprising iron inclusions). SECM imaging experiments, performed with the application of ferrocenecarboxylic acid as the mediator, revealed distinctly reactive areas at the magnet surface during early stages of its immersion in 0.1moldm−3 phosphate buffer (pH=7). It was demonstrated that the iron inclusions were responsible for the existence of these reactive areas whereas the bulk material surface was practically unreactive (insulating). It was observed that the surface reactivity of the iron inclusions gradually decreased with time and after 7h immersion the whole magnet surface became uniformly unreactive (insulating). The results were explained in terms of differences in the dynamics of the passive film formation on the iron inclusions and on the bulk material. Another factor that might be responsible for the observed non-uniform surface reactivity was also considered, namely, the differences in abilities to charge propagation through passive films existing on the iron inclusions and on the bulk material. The role of the iron inclusions as pitting precursor sites in the presence of chlorides in the phosphate buffer solution was also examined. [Copyright &y& Elsevier]

Abstract: Combination of multi-walled carbon nanotubes, cobalt porphyrin and tungsten oxide in the film (deposited onto glassy carbon electrode substrate) produces an electrocatalytic system capable of effective reduction of oxygen in such acid medium as 0.5moldm−3 H2SO4. Co-existence of cobalt porphyrin and tungsten oxide, together with dispersed carbon nanotubes, leads to the enhancement effect evident from some positive shift in the oxygen reduction voltammetric potential and the significant increase of voltammetric currents (relative to those characteristic of the system free of carbon nanotubes and WO3). The multi-component 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 the cobalt porphyrin redox centers, and the undesirable hydrogen peroxide intermediate is further reduced at the tungsten oxide support. An important function of carbon nanotubes is to improve transport of electrons within the electrocatalytic multi-component film. [Copyright &y& Elsevier]

Abstract: Electrocatalytic properties (towards reduction of bromate in 0.5moldm−3 H2SO4) of multi-walled carbon nanotubes (CNTs) modified with phosphododecamolybdate (PMo12) monolayers have been diagnosed using cyclic voltammetry and amperometry. The ability of negatively charged PMo12-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 PMo12-modified CNTs inks. The latter system is characterized by good stability and relatively the highest sensitivities with respect to bromate concentration. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: Modification of carbon-supported RuSe x nanoparticles with ultra-thin WO3 films results in the enhancement of their electrocatalytic properties towards electroreduction of dioxygen in acid medium (0.5moldm−3 H2SO4) as evidenced from the positive shift of the O2 reduction potential (ca. 150mV) and the higher heterogeneous rate constant (ca. 3 times). An important issue is that the mixed-valent tungsten(VI,V) oxide support is characterized by good electronic and protonic conductivities. Further, not only RuSe x is catalytic but tungsten oxide itself is also capable of promoting the reduction of hydrogen peroxide. This bifunctional activity of the WO3-modified system has been the most pronounced at rather low loadings (e.g. 80μgcm−2) of RuSe x nanoparticles. To facilitate attachment of catalytic particles to glassy carbon substrate, they have been over-coated with Nafion. [Copyright &y& Elsevier]

Abstract: The ability of a Keggin-type polyoxometallate, phosphododecamolybdate (PMo12O40 3−), to form stable anionic monolayers on carbon nanoparticles and multi-wall nanotubes is explored here to produce stable colloidal solutions of polyoxometallate covered carbon nanostructures and to disperse them within conducting polymer, poly(3,4-ethylenedioxythiophene), i.e. PEDOT, or polyaniline multilayer films. By repeated alternate treatments in the colloidal suspension of PMo12O40 3−-protected carbon nanoparticles or nanotubes, and in the acid solution of a monomer (3,4-ethylenedioxythiophene or aniline), the amount of the material can be increased systematically (layer-by-layer) to form stable three-dimensional organized arrangements (networks) of interconnected organic and inorganic layers on electrode (e.g. glassy carbon) surfaces. In hybrid films, the negatively charged polyoxometallate-covered carbon nanostructures interact electrostatically with positively charged conducting polymer ultra-thin layers. Consequently, the attractive electrochemical charging properties of conducting polymers, reversible redox behavior of polyoxometallate, as well as the mechanical and electrical properties of carbon nanoparticles or nanotubes can be combined. The films are characterized by fast dynamics of charge transport, and they are of potential importance to electrocatalysis and charge storage in redox capacitors. [Copyright &y& Elsevier]

Abstract: To fabricate electrocatalytic network films containing Pt nanoparticles, the ability of a Keggin-type polyoxometallate, phosphododecatungstate (PW12O40 3−), to form stable anionic monolayers on solid surfaces is explored. Three-dimensional assemblies on electrode (glassy carbon or platinum) surfaces are grown using the layer-by-layer method involving repeated alternate treatments in the solution of PW12O40 3− (or in the colloidal suspension of polyoxometallate-protected Pt-nanoparticles) and in the solution of monomer (e.g., anilinium) cations. In the resulting structured (organic–inorganic) films, the layers of negatively charged polyoxometallate, or polyoxometallate-protected (stabilized) Pt-nanoparticles, interact electrostatically with the ultra-thin layers of such a positively charged conducting polymer as polyaniline. Consequently, physicochemical properties of organic conducting polymers, and reactivities of inorganic polyoxometallate and/or noble metal particles can be combined. The modification of Pt nanoparticles by adsorbing monolayers of phosphododecatungstate tends to activate them towards efficient electrocatalytic reduction of oxygen in acid medium. [Copyright &y& Elsevier]

The dynamics of charge propagation in nickel hexacyanoferrate, a model metal-substituted analogue of Prussian Blue-type cyanide-bridged systems, was considered in electrolytes containing potassium and other alkali metal cations. The apparent (effective) diffusion coefficients for charge transport were determined using a large-amplitude potential-step chronocoulometry and small-amplitude potential-step chronocoulometric potentiostatic intermittent titration. The dependence of diffusion coefficient on the potential applied is consistent with the intercalation like model of the counter-cation sorption/desorption during redox processes of nickel hexacyanoferrate. Some differences in diffusion coefficients may originate from distinct charge densities (membrane properties) of the oxidized and reduced metal hexacyanoferrate structures. The existence of strong attractive interactions between an alkali metal cation and the cyanometallate matrix is also expected. The overall dynamics of charge propagation seems to be controlled by transport of electrolyte cations within the film rather than by electron self-exchange (hopping) between the mixed-valence hexacyanoferrate(III,II) ionic sites. [Copyright &y& Elsevier]

The ability of a polyoxometallate (dodecamolybdophosphate) to form negatively charged monolayers on solid electrode surfaces is explored here to perform immobilization of monomeric (anilinium) units followed by electropolymerization within the monolayer. Consequently, hybrid films containing ultrathin conducting polymer (polyaniline) layers can be formed. By repeated and alternate treatments in solutions of dodecamolybdophosphate anions and anilinium cations, the amount of the material can be increased systematically in a controlled fashion leading to stable three-dimensional multilayer hybrid assemblies. The fact, that formal potentials of the dodecamolybdophosphate redox processes appear in the potential range where polyaniline is conductive, allows the system to operate reversibly and reproducibly in acid electrolyte. [Copyright &y& Elsevier]

Proposes an electroanalytical approach for the quantitative and qualitative characterization of silicotungstic acid single crystals using ultramicroelectrodes. Model of mass transport; Determination of the effective diffusion coefficient and population of redox sites; Estimation of heterogeneous rate constants for electron transfer.

Investigates the interfacial oxidation and reduction of Prussian Blue powder when probed in situ with Fourier transform infrared attenuated total reflection spectroscopy. Cyanide stretching frequency range; Potential difference; Internal reflectance.

An electrochemical cell comprising a silica sol-gel solid electrolyte, a working electrode that protrudes into a gas phase, and reference and counter electrodes that contact the solid electrolyte comprises an amperometric detector for gas chromatography. Under potentiostatic conditions, a current related to the concentration of an analyte in the gas phase is produced by its oxidation at the three-phase boundary among the sol-gel, working electrode, and the gas phase. The sol-gel is processed to contain an electrolyte that also serves as a humidistat to maintain a constant water activity even in the presence the gas chromatographic mobile phase. Response was demonstrated toward a diverse set of analytes, namely hydrogen, 1,2-ethandithiol, phenol, p-cresol, and thioanisole. Using flow injection amperometry of hydrogen with He as the carrier gas, 90% of the steady-state current was achieved in < 1 s at a flow rate of 20 mL min −1 . A separation of 1,2-ethandithiol, phenol, p-cresol, and thioanisole at a 2.2 mL min −1 flow rate was achieved with respective detection limits (k = 3 criterion) of 4, 1, 3, and 70 ppmv when the working electrode potential was 800 mV. [ABSTRACT FROM AUTHOR]

Nanostructured mixed metal (W, Zr) oxide matrices (in a form of layered intercalated films of WO 3 and ZrO 2 ) are considered here for supporting and activating catalytic platinum nanoparticles toward electrooxidation of ethanol. Remarkable increases of electrocatalytic (voltammetric, chronoamperometric) currents measured in 0.5 mol dm −3 H 2 SO 4 (containing 0.5 mol dm −3 ethanol) have been observed. Comparison has been made to the behavior of methanol and acetaldehyde under analogous conditions. The enhancement effects are interpreted in terms of specific interactions between platinum nanoparticles and the metal oxide species, high acidity of the mixed oxide sites, as well as high population of surface hydroxyl groups and high mobility of protons existing in close vicinity of Pt catalytic sites. The metal oxide nanostructures are expected to interact competitively (via the surface hydroxyl groups) with adsorbates of the undesirable reaction intermediates, including CO, facilitating their desorption (“third body effect”), or even oxidative removal (e.g., of CO to CO 2 ). The fact that the partially reduced tungsten oxide (H x WO 3 ) component is characterized by fast electron transfers coupled to proton displacements tends to improve the overall charge propagation at the electrocatalytic interface. [ABSTRACT FROM AUTHOR]

Mixed-valent tungsten(VI,V) oxide and zirconium(IV) oxide have been sequentially deposited and integrated through voltammetric potential cycling to form robust sub-microstructured mixed metal oxide (WO 3 /ZrO 2 ) films on glassy carbon electrode. Attractive interactions between anionic tungstate units (of the inner WO 3 layer) and cationic oxo-zirconium surface species (existing in acid media on ZrO 2 nanostructures in the outer layer) tend to stabilize the mixed oxide system. By dispersing bimetallic platinum-ruthenium (PtRu) nanoparticles over such active WO 3 /ZrO 2 supports, the activity of PtRu toward the oxidation of ethanol has been enhanced in terms of both increasing the electrocatalytic currents and lowering the onset potential of this reaction. The catalytic effect is more pronounced relative to the performance of PtRu nanoparticles deposited at the same loading of 100 μg cm −2 onto single-component metal oxide films, WO 3 or ZrO 2 . Immobilization of rhodium nanoparticles onto WO 3 inner layer (before over-coating with outer ZrO 2 layer and deposition of PtRu) has led to further remarkable increases of electrocatalytic (voltammetric, chronoamperometric) currents recorded at the room temperature (22 °C) in 0.5 mol dm −3 H 2 SO 4 containing 0.5 mol dm −3 ethanol. Among important issues is the initial activation of ethanol molecule (presumably by inducing the C C bond breaking) before catalytic electrooxidation at PtRu. Furthermore, the mixed WO 3 /ZrO 2 film (support) is characterized by high acidity and fast charge (electron, proton) propagation during the system’s redox transitions. High population of OH reactive groups and good mobility of protons (particularly at zirconia sites) is expected to increase activity of PtRu sites toward the oxidative removal of poisoning (CO) intermediates. [ABSTRACT FROM AUTHOR]

The role Keggin-type phosphomolybdate (PMo 12 O 40 3− ) ions (adsorbed on carbon-supported PtRu, PtRu/C) on electrooxidation of ethanol is addressed here. The combined results obtained using Differential Electrochemical Mass Spectrometry, X-ray Photoelectron Spectroscopy and Cyclic Voltammetry are consistent with the view that presence of the Keggin-type polyoxometallate, phosphomolybdate, ions (adsorbates) leads to enlargement of the current densities associated with electrooxidation of ethanol at potentials greater than 700 mV vs. RHE. This increase of the anodic currents is correlated with the higher acetaldehyde yield which is likely to reflect changes in the reaction kinetics (e.g. more dynamic dehydrogenation of ethanol leading to acetaldehyde) or in the reaction mechanism defined by the preferential surface modification resulting not only in faster kinetics but also in higher selectivity with respect to acetaldehyde production. It is apparent from the spectroscopic data that modification of PtRu/C nanoparticles with phosphomolybdate ions leads to suppression of the formation of Ru surface oxides. [ABSTRACT FROM AUTHOR]

Benchmark carbon/Vulcan-supported Pt nanoparticles have been subjected to interfacial modification with defective ceria (CeO x , 1.5 < x≤2) nanostructures to clarify the influence of the metal oxide additive on the activity, selectivity, and stability of the low-Pt-content (Pt loading, 15 µg cm−2) electrocatalysts during the oxygen reduction reaction (ORR) in acidic medium. The prepared three-component (Pt, C, CeO x) hybrid catalytic materials have been rigorously characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), while the electrocatalytic and general electrochemical properties have been diagnosed using rotating ring-disk electrode (RRDE) voltammetry, chronocoulometry, and gas diffusion electrode methods. The NAP-XPS and Raman data have revealed that, among the distinct ceria additives studied, fine nanoparticles of cerium oxide deposited in situ on Vulcan XC-72 support are characterized by the most considerably defective structure with a noticeable amount of Ce(III). The results of electrochemical and NAP-XPS experiments imply the existence of strong mutual interactions between the defective ceria, platinum, and carbon components. The substoichiometric features of the ceria additive have been correlated with the ability of the low-Pt-content hybrid catalyst to minimize the formation of the undesirable hydrogen peroxide intermediate and promote the 4-electron ORR. On the whole, the addition of CeO x /C to Vulcan-supported Pt catalyst leads to their improved durability during prolonged potential cycling under RRDE voltammetric conditions. In the presence of ceria, the desorptive oxidation of poisoning CO-type adsorbates (that may originate from corrosion of carbon carriers) is largely enhanced. [Display omitted] • Three-component catalytic system of carbon-supported Pt and CeO x additive is considered. • CeO x additive enhances activity of low-Pt-content catalysts during O 2 -reduction. • CeO x /carbon additive synthesized by microwave-assisted hydrothermal method has effectively promoted 4-electron O 2 -reduction. • Application of substoichiometric CeOx structures affects the stability and selectivity of the catalytic system. • Both carbon – CeO x interactions and electron transfers from CeO x to Pt are evident from near-ambient pressure XPS. [ABSTRACT FROM AUTHOR]

In this work, a multifunctional binder with self‐healing, flame retardant, high conductivity, and abundant polar groups is prepared by the free radical polymerization method and applied to lithium–sulfur (Li‐S) batteries to achieve high safety and exceptional electrochemical performance. The self‐healing characteristic of binder induced by intermolecular hydrogen bonds and SS dynamic covalent bonds can repair volume expansion cracks. The polar groups and excellent conductivity endue binder with strong chemisorption on polysulfides and fast charge transportation, which can effectively inhibit the shuttle effect and accelerate polysulfides redox kinetics. More important, the considerable flame retardant performance of binder can improve the safety of the LiS batteries. As a result, the LiS cells using FHCP binder deliver an outstanding cycle stability of a high‐capacity retention rate of 85% after 100 cycles at 0.2 C, and a high reversible area specific capacity of 5.25 mAh cm–2 at a sulfur loading of 4.72 mg cm–2 and a correspondingly lean electrolyte condition (E/S ratio = 6 µL mg–1). [ABSTRACT FROM AUTHOR]

Heteropolymolybdate (PMo 12 O 40 3− ) modified gold nanocarriers (diameters, ca. 30–40 nm) were integrated with ZrO 2 nanostructures (sizes, ca. 15–20 nm) to form hybrid supports (on glassy carbon electrodes) for bimetallic platinum-ruthenium (PtRu) electrocatalytic nanoparticles. The anionic heteropolymolybdate monolayers covering Au surfaces not only stabilized gold nanoclusters but also tended to attract electrostatically zirconium oxo cations that were expected to exist on zirconia surfaces in acid medium. By dispersing PtRu nanoparticles over such hybrid integrated supports, the electrocatalytic activity of PtRu toward the oxidation of ethanol was enhanced. When compared to the behavior of bare PtRu nanoparticles (deposited on glassy carbon at the same loading of 100 μg cm −2 ), the enhancement effect was demonstrated in terms of remarkable increases of electrocatalytic (voltammetric, chronoamperometric) currents recorded at room temperature (22 °C) in 0.5 mol dm −3 H 2 SO 4 containing 0.5 mol dm −3 ethanol. The effect was even more evident at low potentials, particularly below 0.35 V (vs. RHE). Introduction of the metal oxide (zirconia and heteropolymolybdate) nanostructures, and their integration with gold nanoparticles, led to formation of the hybrid electrocatalytic supports characterized by improved distribution of electrons as well as by the high population of reactive OH groups favoring mobility of protons and inducing the oxidative removal of poisoning (methanolic and, indirectly, CO-type intermediates) at ruthenium sites of the deposited bimetallic PtRu nanoparticles. [ABSTRACT FROM AUTHOR]

We report here the results of electrochemicalstudies on CO2electroreduction at multilayered catalystcomposed of themonatomic layer of copper covering palladium overlayers (0.8–10monolayers) deposited on the well-defined Au(111) surface. These multilayeredsystems were obtained by successive underpotential deposition steps:Pd on Au(111) as well as Cu on Pd/Au(111). Low index orientation ofAu substrate was chosen to compare Pd overlayers with bulk Pd(111),which is known to reduce CO2to CO adsorbates in acidicsolutions. The process of CO2electroreduction was studiedby using classical transient electrochemical methods. Catalytic activityof bare Pd layers was investigated in acidic and neutral solutions.In the latter case, much higher activity of Pd overlayers was observed.The results showed that the palladium layer thickness significantlychanged the catalytic activities of both bare Pd overlayers and theone Cu monolayer covered electrodes toward CO2electroreduction.Results show that catalytic activity can be finely tuned by usingthe multilayered near-surface-alloy approach. [ABSTRACT FROM AUTHOR]

We report on the discovery of the first two examples of cationic palladium(II)‐oxo clusters (POCs) containing f‐metal ions, [PdII6O12M8{(CH3)2AsO2}16(H2O)8]4+ (M=CeIV, ThIV), and their physicochemical characterization in the solid state, in solution and in the gas phase. The molecular structure of the two novel POCs comprises an octahedral {Pd6O12}12− core that is capped by eight MIV ions, resulting in a cationic, cubic assembly {Pd6O12MIV8}20+, which is coordinated by a total of 16 terminal dimethylarsinate and eight water ligands, resulting in the mixed PdII‐CeIV/ThIV oxo‐clusters [PdII6O12M8{(CH3)2AsO2}16(H2O)8]4+ (M=Ce, Pd6Ce8; Th, Pd6Th8). We have also studied the formation of host‐guest inclusion complexes of Pd6Ce8 and Pd6Th8 with anionic 4‐sulfocalix[n]arenes (n=4, 6, 8), resulting in the first examples of discrete, enthalpically‐driven supramolecular assemblies between large metal‐oxo clusters and calixarene‐based macrocycles. The POCs were also found to be useful as pre‐catalysts for electrocatalytic CO2‐reduction and HCOOH‐oxidation. [ABSTRACT FROM AUTHOR]

We report on the discovery of the first two examples of cationic palladium(II)‐oxo clusters (POCs) containing f‐metal ions, [PdII6O12M8{(CH3)2AsO2}16(H2O)8]4+ (M=CeIV, ThIV), and their physicochemical characterization in the solid state, in solution and in the gas phase. The molecular structure of the two novel POCs comprises an octahedral {Pd6O12}12− core that is capped by eight MIV ions, resulting in a cationic, cubic assembly {Pd6O12MIV8}20+, which is coordinated by a total of 16 terminal dimethylarsinate and eight water ligands, resulting in the mixed PdII‐CeIV/ThIV oxo‐clusters [PdII6O12M8{(CH3)2AsO2}16(H2O)8]4+ (M=Ce, Pd6Ce8; Th, Pd6Th8). We have also studied the formation of host‐guest inclusion complexes of Pd6Ce8 and Pd6Th8 with anionic 4‐sulfocalix[n]arenes (n=4, 6, 8), resulting in the first examples of discrete, enthalpically‐driven supramolecular assemblies between large metal‐oxo clusters and calixarene‐based macrocycles. The POCs were also found to be useful as pre‐catalysts for electrocatalytic CO2‐reduction and HCOOH‐oxidation. [ABSTRACT FROM AUTHOR]

Abstract: A solid-state photo-rechargeable capacitor (photocapacitor) is obtained here by coupling a dye-sensitized solar cell and a ruthenium oxide based electrochemical capacitor. This integrated system permits direct storage of energy generated by sunlight within a single optoelectronic microelectrochemical device. It utilizes three planar electrodes arranged sequentially to include a polymer hole conductor (poly-(3-hexylthiophene-2,5-diyl)), between the titanium oxide photoanode modified with dye (E)-3-(5-(4-(Bis(20,40-dibutoxybiphenyl-4-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic acid (D35) and the intermediate silver electrode as well as two hydrous ruthenium oxide layers (separated by protonically conducting Nafion™ membrane) between the intermediate (silver) and the external (counter) electrode. Upon integration of the capacitor and dye-sensitized solar cell into a single photocapacitor hybrid device, the following parameters were obtained under simulated 100 mW cm−2 solar illumination: specific capacitance, 407 F g−1 (3.26 F cm−2); energy and power densities, 0.17 mWh cm−2 and 0.34 mW cm−2 and coulombic efficiency, 88%. These data together with results of experiments performed at different light intensities (10–100 mW cm−2) are consistent with very good performance of the optoelectronic device under various light conditions. [Copyright &y& Elsevier]

Abstract: A new concept of utilization of titanium dioxide matrix in electrocatalysis by admixing it with polyoxometallate modified gold nanoparticles is described here. The approach utilizes Keggin-type phosphododecamolybdate (PMo12O40 3−) adsorbates capable of modifying, activating and stabilizing Au nanoparticles of the sizes of 30–40nm. Ultra-thin films of phosphomolybdates on nanostructured gold are characterized by well-defined fast (reversible) multi-electron electrochemical reactions. By dispersing platinum black over the Au-containing TiO2, the electrocatalytic activity of Pt nanoparticles towards oxidation of ethanol has been enhanced. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account improvement of overall conductivity (due to the presence of nanostructured gold) at the electrocatalytic interface (including TiO2-support), as well as and possibility of specific Pt–TiO2 or Pt–Au electronic interactions and existence of active hydroxyl groups (on titanium dioxide or polyoxometallate surfaces) in the vicinity of catalytic Pt sites. [Copyright &y& Elsevier]

• Vulcan-supported PtSn are decorated with Ru-black or bimetallic PtRu nanoparticles. • Thus prepared hybrid catalysts exhibit high activity toward dimethyl ether oxidation. • Ru supports activity of Sn in oxidative removal of poisoning adsorbates on Pt sites. • PtRu-decorated Vulcan-supported PtSn shows high activity for methanol oxidation. Electrocatalytic activity of Vulcan-supported PtSn (PtSn/C) nanostructured alloys toward electrooxidation of dimethyl ether (DME), a potential small-organic-molecule fuel, has been significantly enhanced in acid medium (0.5 mol dm−3 H 2 SO 4) by decorating PtSn/C with ruthenium black or bimetallic PtRu nanoparticles. The enhancement effect concerns both shifting the onset potential for the DME-oxidation toward less positive values and increase of the DME electrocatalytic current densities recorded under both cyclic voltammetric and chronoamperometric conditions. The activating capabilities of ruthenium nanostructures seem to originate from the existence of reactive ruthenium oxo/hydroxo groups (even below 0.45 V vs. RHE) on their surfaces capable of inducing the oxidative removal of poisoning (CO-type) adsorbates from the neighboring platinum catalytic sites. In that respect, the Ru-oxo species originating from Ru or PtRu additives seem to support activity of Sn cocatalytic sites interacting with Pt within the PtSn heterogenous alloy. The Ru-decorated PtSn/C and, in particular, PtSn/C admixed with PtRu exhibit very high activity toward the oxidation of methanol which is also an important DME-oxidation intermediate. On the whole, the hybrid materials composed of Vulcan-supported PtSn decorated with Ru or PtRu nanoparticles seem to act as multifunctional nanoreactors inducing not only oxidative stripping of poisoning adsorbates but also catalyzing oxidation of the DME-reaction intermediates (methanol). [ABSTRACT FROM AUTHOR]

Abstract: Immobilization of carbon-supported Pt/Pd nanoparticles (that have been modified with ruthenium oxo species) within the tungsten oxide film containing Pt/Ru nanoparticles results in the enhancement of the catalytic properties towards electrooxidation of methyl formate in 0.5moldm−3 H2SO4. The over-coating of Pt/Pd nanoparticles with cationic Ru-oxo species facilitates their attachment to tungsten oxide matrix. Because oxidation of the ester is mechanistically complex and it is expected to occur most rapidly on the formate component, the comparative measurements have been done with formic acid. In spite of modification of Pt/Pd with Ru-oxo species, the system retains high electrocatalytic activity during oxidation of formic acid. It is rationalized that not only Pt/Ru is catalytic towards oxidation of methyl formate (or products of its hydrolysis) but also oxoruthenium modified Pt/Pd is capable of promoting effectively the oxidation of formic acid or formate component of the ester. The multifunctional activity of co-deposited Pt/Ru and Pt/Pd centers is supported by good electronic and protonic conductivities of hydrated tungsten oxide matrix. [Copyright &y& Elsevier]

Abstract: The electrochromic and voltammetric features of electrocrystallized tungsten oxide films in aqueous medium are compared in two potential regions corresponding to partial W(VI/V) reduction and deep reduction with formation of W(IV). Assignment of certain features to the crystalline components of different structures is presented. [Copyright &y& Elsevier]

Abstract: The protective properties of polypyrrole coatings containing hexacyanoferrate anions are presented. The composite coatings were electrodeposited galvanostatically on stainless steel from the aqueous solutions containing pyrrole monomer and potassium hexacyanoferrate(II) together with traces (10 μmoldm−3) of free CN− ions. The protective properties of the resulting coatings were investigated in the highly aggressive medium of 0.1 moldm−3 HCl and 0.4 moldm−3 NaCl. Diagnostic experiments included measurements of open circuit potential with time of exposure, chronoamperometric (current–time) examination of the steel samples at a selected constant potential of 0.5 V and potentiodynamic measurements. To get insight into the dynamics of the steel dissolution at open circuit potential and at the selected anodic potential, changes of concentrations of iron and chromium in the test solution as a function of exposure time were determined using atomic absorption spectrometry. Morphology of the composite film was examined using scanning electron microscopy. [Copyright &y& Elsevier]

The catalytic activity of commercial carbon-supported PtFe (PtFe/C) nanoparticles admixed with mesoporous polyoxometalate Cs3H3PMo9V3O40, (POM3-3–9), has been evaluated towards oxygen reduction reaction (ORR) in acid medium. The polyoxometalate cesium salt co-catalyst/co-support has been prepared by titration using the aqueous solution of phosphovanadomolibdic acid. The synthesized material has been characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results confirm formation of the polyoxometalate salt with the characteristic Keggin-type structure. The composite catalyst has been prepared by mixing the POM3-3–9 sample with the commercial PtFe/C by sonication. The diagnostic rotating ring-disk voltammetric studies are consistent with good performance of the system with low Pt loading during ORR. The fuel cell membrane electrode assembly (MEA) utilizing the PtFe/POM-based cathode has exhibited comparable or better performance (at relative humidity on the level of 100, 62, and 17%), in comparison to the commercial MEA with higher Pt loading at the cathode. Furthermore, based on the cell potential and power density polarization curves, noticeable improvements in the fuel cell behavior have been observed at the low relative humidity (17%). Finally, the accelerated stress test, which uses the potential square wave between 0.4 V and 0.8 V, has been performed to evaluate MEA stability for at least 100 h. It has been demonstrated that, after initial losses, the proposed catalytic system seems to retain stable performance and good morphological rigidity. [ABSTRACT FROM AUTHOR]

Electrochemical properties of thin films and microcrystalline precipitates of nickel(II) hexacyanoferrate(II, III), NiHCNFe, are strongly dependent on the method of their preparation and experimental conditions of their investigation. The films have been generated on both inert (gold) and parent metal (nickel) substrates. Interpretation of voltammetric responses of nickel hexacyanoferrate microstructures on electrodes is supported with the data of elemental analysis estimations obtained using atomic absorption and surface examination based on X-ray energy dispersive spectroscopy. Both electrodeposited films and mechanically-attached precipitates of nickel hexacyanoferrate constitute mixed structures in which the relative ratios of K and Ni to Fe reflect composition of a solution for modification, choice of the deposition potential and time, and the time and potential limits of exposure of the system to voltammetric potential cycling in potassium salt supporting electrolyte. We demonstrate here that the more positive set of peaks of nickel hexacyanoferrate is related to the electroactivity of the form containing relatively larger amount of potassium and smaller of nickel. On the other hand, the more negative set of the system’s peaks shall be attributed to the form that is largely potassium depleted and containing more nickel relative to iron. In this context, the use of the previously proposed approximate formulas, K2Ni[FeII(CN)6] and KNi1.5[FeII(CN)6], for the predominant nickel hexacyanoferrate (reduced) forms is justified. [Copyright &y& Elsevier]

Chronoamperometry and cyclic voltammetry (CV) were used to address the platinum deposition kinetics on glassy carbon and polycrystalline Pt supports from H2PtCl6-containing solutions with and without additives of different Keggin-type heteropoly acids (HPAs) of tungsten. The effect of addition of these polyoxometallates manifested itself in the pronounced disturbance of instantaneous nucleation and it can be interpreted in terms of strong HPA adsorption on certain nucleation centers followed by the modification of their activity. HPA additives decreased the current efficiency for Pt deposition despite the fact that the reduction of HPA additives was thermodynamically forbidden at the potentials chosen for electrodeposition. The latter fact can be explained as selective inhibition of the intermediate PtII reduction by tungstates. CV of Pt deposits in sulfuric acid solutions indicated a noticeable increase in the deposit roughness if P- and Si-containing HPA were added in the course of platinization. More complex behavior was found for B-dodecatungstate that most likely originated from its tendency to undergo codeposition with Pt. Ex situ scanning tunneling microscopy (STM) images demonstrate more pronounced globular structure and smaller crystal sizes for HPA-affected deposits as compared with usual platinized platinum. These features can be explained by HPA effects on deposition kinetics assumed on the basis of electrochemical data and demonstrate that HPA can act in template-like manner. [Copyright &y& Elsevier]

We describe the electrochemical behavior of solid copper hexacyanoferrate (powder) investigated in the absence of contact with a liquid external supporting electrolyte. In addition to a typical hexacyanoferrate(III,II) redox transition, the system is characterized by a second electrode process which appears at more negative potentials. Diagnostic experiments, which include spectrochemical and solid-state voltammetric characterization, support our view that the latter redox reaction most likely originates from reduction of the system''s lattice copper(II) ions. The overall dynamics of charge transport in the material, when discussed in terms of effective diffusion, is moderately high (on the level of 10−8 cm2 s−1). Comparison has been also made to the electrochemical behavior of solid Prussian blue and to the voltammetric characteristics of conventional electrodes modified with thin films of copper hexacyanoferrate. [Copyright &y& Elsevier]

The 48‐FeIII‐containing 96‐tungsto‐16‐phosphate, [FeIII48(OH)76(H2O)16(HP2W12O48)8]36− (Fe48), has been synthesized and structurally characterized. This polyanion comprises eight equivalent {FeIII6P2W12} 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 Fe48 was synthesized by a simple one‐pot reaction of an {Fe22} coordination complex with the hexalacunary {P2W12} POM precursor in water. The title polyanion was characterized by single‐crystal XRD, FTIR, TGA, magnetic and electrochemical studies. [ABSTRACT FROM AUTHOR]

Electrocatalytic activity of Pt and bimetallic PtRu nanoparticles (both Vulcan supported and unsupported) toward electrooxidation of dimethyl ether (DME), a potential small organic molecule fuel, in an acid medium (0.5 mol dm−3 H2SO4) has been significantly enhanced by dispersing them over a thin film of zirconia (ZrO2). The enhancement effects concern increases of the DME electrocatalytic current densities recorded under both cyclic voltammetric and chronoamperometric conditions. Similar effects have been observed for the oxidation of methanol. Regarding the dissimilar DME electrooxidation mechanisms at Pt and PtRu catalytic centers, the activating capabilities of zirconia seem to originate from the high population of reactive –OH groups favoring mobility of protons and the capability of inducing the oxidative removal of poisoning (CO-type) intermediates both at platinum and ruthenium catalytic sites. In the presence of the zirconia matrix, the onset potential for the oxidation of DME (particularly at PtRu) is shifted more than 50 mV toward less positive potentials. Mutual metal-support interactions are also postulated. [ABSTRACT FROM AUTHOR]

• Fe 2 P catalyst induces electrochemical reduction of N 2 to NH 3 in alkaline medium. • Combination of Fe0 and P sites form active centers at the electrocatalytic interface. • Fe 2 P is characterized by reasonable selectivity with respect to hydrogen evolution. • Fe 2 P also exhibits catalytic properties toward electroreduction of O 2 , NO 3 − and NO 2 −. • The NH 3 product can be detected by voltammetric oxidation at Pt nanoparticles. A catalytic system based on iron phosphide (Fe 2 P) has exhibited electrocatalytic activity toward N 2 -reduction reaction in alkaline medium (0.5 mol dm−3 NaOH). Based on voltammetric stripping-type electroanalytical measurements, Raman spectroscopic and spectrophotometric data, it can be stated that the Fe 2 P catalyst facilitates conversion of N 2 to NH 3 , and the process is fairly selective with respect to the competing hydrogen evolution. A series of diagnostic electrocatalytic experiments (utilizing platinum nanoparticles and HKUST-1) have been proposed and performed to control purity of nitrogen gas and to probe presence of potential contaminants such as ammonia, nitrogen oxo-species and oxygen. On the whole, the results are consistent with the view that the interfacial reduced-iron (Fe0) centers, while existing within the network of P sites, induce activation and reduction of nitrogen, parallel to the water splitting (reduction) to hydrogen. It is apparent from Tafel plots and impedance measurements that mechanism and dynamics of nitrogen reduction depends on the applied electroreduction potential. The catalytic system exhibits certain tolerance with respect to the competitive hydrogen evolution and gives (during electrolysis at -0.4 V vs. RHE) the Faradaic efficiency, namely, the selectivity (molar) efficiency, toward production of NH 3 on the level of 60%. Under such conditions, the NH 3 -yield rate has been found to be equal to 7.5 µmol cm−2 h−1 (21 µmol m−2 s−1). By referring to classic concepts of electrochemical kinetic analysis, the rate constant in heterogeneous units has been found to be on the moderate level of 1-2*10−4 cm s−1 (at -0.4 V). The above mentioned iron-phosphorous active sites, which are generated on surfaces of Fe 2 P particles, have also been demonstrated to exhibit strong catalytic properties during reductions of other electrochemically inert reactants, such as oxygen, nitrites and nitrates. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synergistic effects in FeN 4 @CoN 4 promote oxygen electrocatalysis. • The ORR activity of Fe/CoNx-C was characterized via SECM. • Hierarchical porous Fe/CoN x -C displays bifunctional activity. • Fe/CoN x -C cathode excels in liquid and quasi-solid Zn-air battery. Rechargeable zinc-air batteries (ZABs) hold enormous promise as energy conversion and storage system of the next generation. Here, through utilizing the Co/ZIF-8@F127 precursor and a coordinated strategy that includes 'post-absorption' and 'dual-pyrolysis', a Fe/CoN x -C possesses a hierarchical porous N-doped carbon with an ultrahigh specific area and rich defects to stabilize accessible dual metallic active sites. With a narrow potential gap of 0.71 V, the Fe/CoN x -C catalyst demonstrates excellent bifunctional electrocatalytic activity toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Noteworthily, scanning electrochemical microscopy (SECM) was used to visualize the local electrocatalytic ORR activity of CoN x -C and Fe/CoN x -C. For the applications of zinc-air batteries, the Fe/CoN x -C-based cathode provides a high peak power density of 134.97 mW cm−2 for aqueous ZABs. Moreover, quasi-solid-state ZABs (including flexible ZAB and cell ZAB)-based on Fe/CoN x -C as cathode catalyst demonstrate satisfying flexibility and durability. The theoretical calculation results further elucidate the synergistic effect that the engagement of Fe atoms in the electron transfer process of the FeN 4 @CoN 4 system reduces the energy barrier of the rate-determining-step in ORR and OER, hence facilitating the reversible oxygen electrocatalytic kinetics. [ABSTRACT FROM AUTHOR]