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There has been growing recent interest in the development of approaches to effectively sequester, capture or convert carbon dioxide to carbon-based simple organic fuels or utility chemicals. In principle, the low-temperature electrocatalytic and visible-light-induced photoelectrochemical approaches to reduction of CO2show promise owing to their environmental compatibility and feasibility to combine with renewable energy sources. Electrochemical reductions of CO2are multi-electron and multi-proton processes with considerable kinetic barriers requiring development of carefully designed electrode materials. Furthermore, when the CO2-reduction is performed in aqueous solutions, the competitive hydrogen evolution reaction is a complicating side-reaction. An additional problem is the appearance of the poisoning or passivating CO-type intermediates. Among important issues are the development of robust specific electrocatalytic systems and stable functionalized semiconducting photocatalytic materials, as well as the understanding of structure - activity relationships. In practical electrolysis cells, the CO2-reduction (at cathode) is accompanied by water oxidation (at anode or photoanode).

Unique hybrid systems for electroreduction of CO2 under both conventional and visible-light-induced conditions are proposed and designed here by over-coating copper(I) oxide with tungsten(VI) oxide nanowires. When Cu2O and WO3 nanostructures are sequentially deposited on glassy carbon substrate, the resulting system has exhibited high electrocatalytic activity toward reduction of CO2 in phosphate buffer of pH = 6.1. By introducing WO3, the Cu-based system becomes more selective against the competitive hydrogen evolution and exhibits higher CO2-reduction currents relative to the performance of single components. During electroreduction, highly catalytic Cu sites are generated or intercalated within WO3 nanowires partially reduced to mixed-valence hydrogen-absorbing tungsten(VI,V) oxide bronzes, HxWO3, co-existing with sub-stoichiometric tungsten(VI,IV) oxides, WO3-y. Strong adsorption and activation of CO2 molecule has been demonstrated at the WO3-decorated Cu2O interface. Under photoelectrochemical conditions involving illumination with sun-light, the proposed hierarchical system of Cu2O semiconductor deposited onto the transparent fluorine-doped conducting glass electrode and decorated with WO3 nanowires is well-behaved and active toward CO2-reduction in the Na2SO4 neutral medium. In addition to the Cu2O stabilization effect, the heterojunction formed by p-type Cu2O and n-type WO3 semiconductors seems to facilitate charge distribution and separation at the photoelectrochemical interface.

This work reports the synthesis of a family of electrocatalysts (ECs) for the oxygen reduction reaction (ORR) that: (i) do not comprise platinum; and (ii) exhibit a "core-shell" morphology. The ECs are based on a "core" of graphene nanoplatelets, that are covered by a carbon nitride (CN) "shell". The active sites include Fe as the "active metal" and are stabilized in C- and N- "coordination nests" in the CN "shell". The chemical composition of the proposed ECs is determined by inductively-coupled plasma atomic emission spectroscopy (ICP-AES) and microanalysis; the performance and reaction mechanism in the ORR are elucidated by cyclic voltammetry with the rotating ring-disk electrode (CV-TF-RRDE) technique. This work is a systematic effort aimed at elucidating how (i) the pre-treatment of the graphene "core"; and (ii) the introduction of Sn as the "co-catalyst" in the active sites influence the chemical composition, the ORR performance and reaction mechanism of the proposed ECs.

This review article addresses areas where solid-state chemistry concepts can contribute to the on-going search for a "magic bullet" inorganic semiconductor that can efficiently split water or reduce CO2. First, a methodology to visualize complex ternary oxide combinations is outlined using 31 examples based on copper in both +1 and +2 oxidation states. Then the synthetic aspects are reviewed followed by a discussion of the structural characteristics. The optoelectronic aspects are considered next, culminating the review with the state-of-the-art in the practical applicability of these materials in solar fuels photogeneration and environmental (e.g., azo dye) remediation.

The chemically-reduced graphene-oxide has been used as support to anchor catalytic Pt nanoparticles and, while subsequently modified with tungsten oxide nanowires, has produced a hybrid electrocatalytic system for electroreduction of oxygen in acid medium. Such characteristics of reduced graphene oxide as defective surface and low degree of organization of graphitic structures facilitate dispersion of platinum nanocenters. Further combination with WO3 nanonowires is expected to increase the system's interfacial hydrophilicity and porosity. Most likely WO3 nanostructures are attached mainly to the edges of graphene thus preventing its stacking and creating space for the flux of oxygen and the reaction products. The results of electrochemical diagnostic experiments are consistent with the view that the electrocatalytic activity of the system utilizing tungsten oxide nanowires toward the reduction of oxygen in acid medium has been enhanced even at the Pt loading as low as 30 ug cm[?]2. Furthermore, the rotating ring-disk electrode voltammetry data is consistent with decreased formation of the undesirable hydrogen peroxide intermediate in the presence of WO3. The conclusions are supported with mechanistic and kinetic studies performed with use of double-potential-step chronocoulometry as an alternative diagnostic tool to rotating ring-disk voltammetry.

Chemically-reduced graphene-oxide-supported gold or iridium nanoparticles are considered here as active carriers for dispersed platinum with an ultimate goal of producing improved catalysts for electroreduction of oxygen in acid medium. Comparison is made to the analogous systems not utilizing reduced graphene oxide. High electrocatalytic activity of platinum (loading up to 30 ug cm-2) dispersed over the reduced-graphene oxide-supported Au (up to 30 ug cm-2) or Ir (up to 1.5 ug cm-2) nanoparticles toward reduction of oxygen has been demonstrated using cyclic and rotating ring-disk electrode (RRDE) voltammetric experiments. Among important issues are possible activating interactions between gold and the support, as well as presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide. The RRDE data are consistent with decreased formation of hydrogen peroxide.

The functionalized carbon nanostructure, nitrogen and sulfur co-doped iron-containing highly porous carbon gel (obtained via carbonization of corresponding organic gel) is considered here as a non-precious metal catalyst for the electroreduction of carbon dioxide in neutral solution (potassium bicarbonate at pH = 6.8). Various electrochemical measurements (performed in distinct modes and under different conditions) have been utilized to comment about the catalyst performance and the reaction mechanism, in particular about the reaction products and the relative contribution from hydrogen evolution. At low overpotentials, the carbon dioxide reduction is favored over the hydrogen evolution reaction. Combination of conventional (stationary) stripping-type and hydrodynamic (rotating ring-disk electrode) voltammetric approaches has been demonstrated to function as an unique electroanalytical tool here. The CO2-reduction products can be identified as adsorbates (oxidative stripping voltammetry) or monitored continuously (electrooxidation) at the Pt ring electrode. Finally, the results of both electrochemical diagnostic and parallel gas chromatographic analytical measurements are consistent with the view that, in the examined range of the potentials, CO is the main CO2-reduction product.

The electrochemical reduction reaction of the nitrate ion (NO3−), a widespread water pollutant, to valuable ammonia (NH3) is a promising approach for environmental remediation and green energy conservation. The development of high-performance electrocatalysts to selectively reduce NO3−wastes into value-added NH3will open up a different route of NO3−treatment, and impose both environmental and economic impacts on sustainable NH3synthesis. Transition metal phosphides represent one of the most promising earth-abundant catalysts with impressive electrocatalytic activities. Herein, we report for the first time the electrocatalytic reduction of NO3−using different phases of iron phosphide. Particularly, FeP and Fe2P phases were successfully demonstrated as efficient catalysts for NH3generation. Detection of the in-situ formed product was achieved using electrooxidation of NH3to nitrogen (N2) on a Pt electrode. The Fe2P catalyst exhibits the highest Faradaic efficiency (96 %) for NH3generation with a yield (0.25 mmol h−1cm-−2or 2.10 mg h−1cm−2) at − 0.55 V vs. reversible hydrogen electrode (RHE). The recycling tests confirmed that Fe2P and FeP catalysts exhibit excellent stability during the NO3−reduction at − 0.37 V vs. RHE. To get relevant information about the reaction mechanisms and the fundamental origins behind the better performance of Fe2P, density functional theory (DFT) calculations were performed. These results indicate that the Fe2P phase exhibits excellent performance to be deployed as an efficient noble metal-free catalyst for NH3generation.

One of the main drawbacks of conventional energy storage systems is the possibility of electrolyte leakage due to faulty encapsulation or accidental overcharge. In this work, novel environmentally benign all-biopolymer-based hydrogels have been designed to be used as electrolytes in aqueous electrochemical capacitors. A primary component of gels, i.e. microcrystalline cellulose dissolved in NaOH/urea mixture and cross-linked with epichlorohydrin, was used in combination with agarose, or subsequently introduced agarose and poly(norepinephrine) to form the three-dimensional interpenetrated polymer network of enhanced mechanical stability. The effect of introduced components has been studied independently and investigated in terms of morphology, conductivity, swelling degree, and mechanical/structural properties. The electrochemical diagnostic tests of electrochemical capacitors utilizing acidic (H2SO4, H4SiW12O40) and neutral (Na2SO4) electrolyte-saturated hydrogels of the best overall characteristics have revealed the performance approaching the one characteristic of the liquid electrolyte-based counterparts but with lower self-discharge. The systems were characterized by the capacitance of 97–127 F g−1at 0.1 A g−1with retention of 33–89% at 20 A g−1, and cycling life of 10 000 cycles with a maximum of 10% of capacitance loss. The effect of intentionally improved hydrophilic properties of activated carbon electrodes, on the interfacial compatibility between electrode/hydrogel electrolyte is discussed as well. The results are in line with the global trend of green and sustainable energy storage designed for specific applications, i.e. in-vivo systems and wearable electronics.

Nanostructured metallic Pd centers have been generated by electroreduction of PdII within the coordination architecture of tridentate Schiff-base-ligands. The resulting Pd nanoparticles (diameters, 5-10 nm) are stabilized and activated by ligand nitrogens, and the electrocatalytic system exhibits appreciable activity toward reduction of CO2 in 0.1 M KHCO3 (pH=8.8). Comparison has also been made to the behavior of conventional Pd nanoparticles. In addition to low degree of agglomeration and high active surface area of the Schiff-base-ligand-supported Pd nanocenters, specific interactions between electron-donor N-coordination sites and metallic Pd are expected. Furthermore, such Pd catalysts are highly active during reduction of O2 in alkaline medium (0.1 M KOH). Finally, the potent catalytic properties of Pd have been explored to study reduction of highly inert arsenate(V), OAs(OH)3, analytes in acid medium (0.5 M H2SO4).

This study concentrates on the development of catalytic materials capable of enhancing oxidation of ethanol particularly at low potentials, i.e. at conditions resembling operation of anodes in low temperature fuel cells. Indeed, the ethanol oxidation currents measured under voltammetric and chronoamperometric conditions have been significantly increased following dispersing bimetallic PtRu nanoparticle ([?]4 nm) catalysts over TiO2 (80% anatase, 20% rutile) nanostructures ([?]20-30 nm) supported onto multi-walled carbon nanotubes. The improvement in activity is attributed not only to better dispersion of PtRu centers (some increase of active surface area) or improved (carbon-nanotube-assisted) propagation of electrons at the catalytic interface but also to the presence of hydroxyl groups and high mobility of protons at neighboring (to PtRu) TiO2. Further, specific interactions between TiO2 and Pt or Ru metallic components are feasible. Importance of addition of TiO2 is also evident from kinetic analysis based on measurements of steady-state currents at different concentrations.

The proposed redox electrolyte system, concentrated solutions of Keggin type silicotungstic acid (H4SiW12O40), have been tested using the microelectrode methodology to determine mass-transport (effectively diffusional) coefficients for charge propagation and homogeneous (electron self-exchange) rates of electron transfers. Silicotungstic acid (H4SiW12O40) acts as proton conductors, and undergoes fast, reversible, multi-electron electron transfers leading to the formation of highly conducting, mixed-valence (tungsten(VI,V) heteropoly blue) compounds. To develop useful electroanalytical diagnostic criteria, electroanalytical approaches utilizing ultramicrodisk electrodes have been adapted to characterization of redox electrolytes. Combination of two parallel ultramicroelectrode-based experiments performed under radial (long-term experiment; e.g., slow scan rate) and linear (short-term experiment; e.g., fast scan rate) diffusion conditions permits determination of both effective concentration of redox centers and transport (diffusion) coefficient parameters, which are crucial to evaluation of the utility of a redox electrolyte for charge storage.

There has been growing interest in the development of durable, specific and reasonably efficient low-cost catalysts for nitrogen (N2) electroreduction reaction, or nitrogen fixation, particularly in aqueous solutions capable of producing ammonia under ambient, or near ambient, conditions. The successful electrocatalytic reduction of nitrogen (N2) and formation of NH3in alkaline an medium has been reported here using the Fe3P phase of iron phosphide. Detection of in-situ formed product has been achieved by probingthe electrooxidation of NH3to nitrogen (N2) using the additional working electrode modified with Pt nanoparticles.On mechanistic grounds, the iron (Fe0) sites seem to be electrocatalytic active during the reduction of nitrogen. The iron sites can also be generated within the phtalocyanine ring binding metal ions through four inwardly projecting nitrogen centers. Furthermore, horseradish peroxidase metalloenzyme, in which a large alpha-helical protein binds heme as a redox cofactor, is capable of inducing electroduction of N2.

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-3H2SO4) by decorating PtSn/C with bimetallic PtRu nanoparticles modified with phosphododecatungstic acid (PtRu/PW12). 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. In that respect, the Ru-oxo species originating from PtRu additives seem to support activity of Sn co-catalytic sites interacting with Pt within the PtSn heterogenous alloy. The polytungstate adsorbates on nanoparticles facilitate their distribution at the electrocatalytic interface, as well as they interact competitively with the CO adsorbates at noble metal catalytic sites. The hybrid materials composed of PtSn/C decorated with PtRu nanoparticles modified with PW12seem to act as multifunctional nanoreactors during electrooxidation of DME.

The presence of a large population of hydroxyl groups (originating from zirconia) in the vicinity of PtRu, in addition to possible specific interactions between zirconia and the ruthenium component, most likely induced oxidative removal (from Pt) of otherwise passivating CO adsorbates. Although Rh itself did not show directly any activity toward the ethanol oxidation, the metal is expected to facilitate C-C bond splitting in C2H5OH molecule. Codeposition and introduction of metallic rhodium particles to ZrO2 also improved the overall conductivity of the matrix and charge distribution at the electrocatalytic interface. Application of the nanoporous platinum electrode substrate together with Rh and ZrO2 components as well as PtRu electrocatalytic sites led to enhancement of the electrocatalytic currents larger than one would expect from simple addition of activities of single components.

Herein, ruthenium nanoparticles modified with mixed selenium and nitrogen overlayers (RuSexNy) were prepared via chelatation method onto the N-doped and undoped carbons (Norit and MWCNTs) under analogous experimental conditions. . The crystalographic data reveals the same type of crystallographic phases in RuSexNy crystallites, regardless of the doping of carbon support, nevertheless, as transmission electron microscopy measurements have shown the nanoparticles fabricated onto the N-doped carbons were found to be of smaller diameters. The studies of oxygen reduction reaction in acid (0.5 M H2SO4) medium using rotating ring disk voltammetry and impedance spectroscopy show that RuSexNy nanoparticles supported on the N-doped carbons exhibit higher ORR catalytic activity with generation of lower amounts of hydrogen peroxide. The spillover effect due to N- doping of carbon support was suggested to be responsible for improved decomposition of adsorbed ORR intermediates in carbon supported RuSexNy materials.

In the present study, we utilize phosphomolybdate (PMo12O403-) modified gold nanoparticle (diameters, 30-40 nm) deposits on mesoporous tungsten oxide photoanodes to study plasmon-assisted photoelectrochemical water splitting. Such n-type semiconducting oxide as WO3 (band gap, 2.5 eV) suffers from inadequate solar light absorption and, therefore, there is a need to use of a thin plasmon active layer of nanostructured Au of proper architecture to enhance the interfacial light trapping and conversion. A remarkable increase in the solar energy conversion efficiency as well as in the photooxidation current (oxygen evolution) are believed to be induced by the plasmonic excitation of Au nanoparticles occurring within WO3 absorption range. The polyoxometallate (PMo12O403-) monolayer-type nanostructures may play electrocatalytic role, improve charge distribution, in addition to the stabilization effect. In the other study, the PMo12O403- modified Au nanoparticles, when deposited on step-bunched silicon Si(111) surface have also acted as electrocatalytic centers during photoelectrochemically induced reduction of carbon oxide (IV). The applicability of phosphomolybdate-protected gold nanoparticles to create porous matrix for photoelectrochemically assisted reduction of carbon dioxide is even more pronounced when the system is further decorated with copper. We also present the result of decorating multi-walled carbon nanotubes with gold and copper nanoparticles (by chemical reduction method and through electrodeposition) acting as catalytic systems active towards CO2 electroreduction under voltammetric conditions. Carbon nanotubes have been chemically modified here with surface oxygen complexes using HNO3 and H3PMo12O40 solutions.

The successful preparation of a nanohybrid electrode made from Ta3N5 nanoparticle powders interlinked by Nafion is described. The basic photoelectrochemical properties as anode for water photolysis are investigated and gas evolution as well as corrosion reactions are determined by differential electrochemical mass spectroscopy (DEMS) and X-ray photoelectron spectroscopy (XPS). The sample shows oxygen evolution but also photocorrosion, oxidation of the Ta3N5 nanoparticles via the O 1s line in XPS experiment. The photocorrosion reaction results in a core-shell structure consisting of a tantalum oxide shell and a tantalum nitride core as seen in XPS and x-ray diffraction.

Two different commercial carbon materials, namely activated carbon Norit and multi-walled carbon nanotubes have been selected as materials for symmetric supercapacitors operating in aqueous solution of phosphododecatungstic acid (H3PW12O40) of different concentration (0.1, 0.5 and 0.8 mol dm-3). The results have been compared to those obtained for the standard aqueous electrolyte - 1 mol dm-3 sulphuric acid. and discussed in terms of ionic conductivity of the electrolyte solutions. Nitrogen adsorption/desorption method has been chosen to investigate the effect of pore size distribution of carbon materials on their electrochemical behavior during charging/discharging in two-electrode cells. The detailed characteristics of carbon/carbon supercapacitors was conducted using cyclic voltammetry, constant current methods and impedance spectroscopy. In order to determine the potential range of each electrode, the experiments with additional reference electrode were also performed. The stability of the cells was investigated by applying of over 10 000 cycles of constant charging/discharging.

In the present work we explore the phosphododecamolybdate heteropolyblue-mediated synthesis of gold nanoparticles, acting as a new generation electrocatalytic system exhibiting appreciable activity toward reduction of carbon oxide (IV) and reduction of oxygen (after combining with Co-porphyrin). We explore the ability of highly-concentrated Keggin-type phosphomolybdates to attach within the plain gold surfaces to achieve the highly shape-selective synthesis of approximately spherical or anisotropic Au nanostructures of controlled sizes. The tunable concentrations of reducing (and stabilizing) agent H3[H4P(MoV)4(MoVI)8O40] allowed us to produce a wide range of nanostructured gold with specific sizes and shapes. The aim of this work was to study the applicability of phosphomolybdate-protected gold nanoparticles to create microporous matrix for reduction of carbon dioxide and the active support for the Co-porphyrin catalytic centers towards reduction of oxygen. Keggin-type structures-stabilizing gold nanoparticles were expected to provide electrons and mobile protons to the vicinity of Co-porphyrin, while gold nanoparticles were responsible for high electronic conductivity combined with electrocatalytic activity towards CO2 and H2O2 reduction. The hybrid catalyst based on of Co-porphyrin and phosphomolybdate-protected gold nanoparticles led to synergistic effect that was evident from some positive shift of the oxygen reduction voltammetric potentials and significant increase of the voltammetric currents in all case.

Herein, we report on our investigation on the use of the aqueous solution of the phosphotungstate heteropolyblue as a reducing agent and stabilizer for the synthesis of gold nanoparticles deposited on multiwalled carbon nanotubes and functionalized with CO-type surface groups. Chemical reduction method allowed producing multi-walled carbon nanotube-supported gold (Au/MWCNTs) catalysts with high dispersion and loading of Au up to 5 wt%. The average diameter of Au nanoparticles on MWCNTs was 2.0-4.5 nm. The resulting gold nanoparticles were subsequently cleaned from their inorganic capping agents (PW12O403-) by converting to alkaline medium (NaOHaq). The high dispersion of gold nanoparticles at MWCNTs (pretreated with HCl, HNO3 and H3PMo12O40) was attributed to the presence of a high density of active sites for nucleation created during the functionalization procedure. The nanocomposite system based on multi-walled carbon nanotubes decorated with gold nanoparticles was probed towards electrocatalytic oxidation of methanol in alkaline medium under voltammetric conditions. The existence of mesopores created at the surfaces of multi-walled carbon nanotubes originated from an easy accessibility of the OH- groups and methanol molecules at the electrocatalytic interface. The chemical functionalization of the open ends and the side walls of MWCNTs played a vital role in tailoring their electrochemical properties. Electrochemical studies demonstrated the promotional effect of quick pseudofaradaic reactions of surface polar groups created on carbon nanotubes during the methanol electrooxidation process.

A new group of carbon-supported ruthenium- and iridium-based electrocatalysts for oxygen reduction reaction (ORR) was synthesized, using RuCl3 or IrCl3 and selenourea (as precursor of both Se and N). The heat treated catalysts (later abbreviated as RuSeN/C and IrSeN/C) were subjected to physical characterization, like X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Studies revealed changes in surface properties of Ru- and Ir- based catalysts. Catalytic performances of obtained catalysts were evaluated using Rotating Ring Disk Electrode (RRDE) in acid solution. The ORR activity and hydrogen peroxide generation on designed selenides were dependent on the ratio of metal and selenourea used in precursor blend and were separately characteristic for ruthenium and iridium. While RuSeN/C exhibited high ethanol tolerance, the ORR activity of IrSeN/C in the presence of ethanol depended on the amount of selenourea. CoSeN/C and FeSeN/C were also prepared and characterized as low-cost alternative catalysts.

Ethanol is a biofuel of potential importance to the technology of low-temperature polymer-membrane fuel cells. The alcohol can be ideally oxidized to carbon dioxide thus delivering 12 electrons. But realistically the reaction is rather slow and complex at ambient conditions. Obviously, there is a need to develop novel electrocatalytic materials. In the present work we have utilized as carriers (matrices) carbon nanotubes (CNTs) modified with nanostructured titanium dioxide. TiO2 can be considered as model robust transition metal oxide that, by analogy to tungsten oxide or zirconium oxide (also considered here), is capable of generating of interfacial reactive hydroxy groups on the surfaces. By dispersing bimetallic platinum-ruthenium catalytic nanocenters over the CNT-supported TiO2, the electrocatalytic activity of Pt-Ru nanoparticles towards oxidation of ethanol has been enhanced. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. Electrochemical diagnostic experiments have been supported with microscopic monitoring of morphology using transmission electron microscopy (TEM). In addition to the presence of active interfacial hydroxyl groups, an important issue is the improvement of overall conductivity titanium dioxide - due to the presence of dispersed carbon nanotubes. Comparative measurements aimed at investigation of the presence of dispersed nanostructured metal oxides on dynamics of the oxidation of different fuels (here formic acid).

An important issue in solar cell technology is the storage of generated electrical energy for later use. In this respect supercapacitors, as compared to batteries and electrolysis cells, offer the advantage of long-term stability and relatively low energy loss in the charge-discharge cycle. In this study, ruthenium oxide has been selected as charge storage material for coupled (integrated) dye-sensitized solar cell and supercapacitor system hereinafter called as three electrode configuration. Organic D35 dye was used to sensitize TiO2 photoanode and a conducting polymer, (poly-(3-hexylthiophene-2,5-diyl) served as hole conductor. The photovoltaic part was separated from charge storage material by utilizing a thin layer of vapour evaporated silver. The specific capacitance, power density, coulombic and energy conversion efficiency of the hybrid cell was analyzed. The system was compared to that of our previous reports, i.e. two electrode configuration built of N719 dye modified TiO2 and poly (3,4-ethylenodioxythiophene)/carbon nanotubes composite as charge storage material.

Ruthenium admixed or nanoparticles modified with mixed selenium and nitrogen overlayers (RuSexNy) were fabricated onto different carbon nanostructured supports (that include multiwalled carbon nanotubes, Vulcan and Norit) under analogous experimental conditions. It is apparent from X-ray measurements that both Vulcan and Norit supported RuSexNy crystallites are characterized by the same type of crystallographic phases. Important parameters that influence electrocatalytic activity include the nature of functionalization of carbon support, in addition to its active surface area and morphology that affect distribution and size of active RuSexNy centers. Despite the same loading of ruthenium (40 ug cm[?]2), diameters of RuSexNy nanoparticles have somewhat differed and ranged from 2 to 6 nm, as it has been evident from transmission electron microscopy measurements. The systems have been evaluated with respect to oxygen reduction reaction in acid (0.5 M H2SO4) medium using rotating ring disk voltammetry and impedance spectroscopy. Having in mind such parameters as the half-wave reduction potential, the electroreduction current density, the heterogenous rate constant, the percent formation of the hydrogen peroxide undesirable intermediate as well as the overall charge transfer resistance appearing during oxygen reduction, the RuSexNy-based system utilizing functionalized Vulcan is characterized by the highest electrocatalytic activity.

A robust biocatalytic electrode film utilizing multiwalled carbon nanotubes intentionally derivatized with poly(diallyldimethylammonium chloride), PDDA, as well as integrated with alcohol dehydrogenase is considered here for potential application as a stable efficient anode in a biofuel cell and a specific working electrode in amperometric sensors. PDDA‐modified CNTs were characterized using transmission electron microscopy (TEM) and infrared spectroscopy (FTIR). Once immobilized on a glassy carbon electrode substrate, they facilitate not only distribution of charge but also immobilization of alcohol dehydrogenase molecules. The resulting integrated bioelectrocatalytic system was able to induce oxidation of ethanol and NADH as well as to produce relatively high currents at a fairly low potential.

Scanning electrochemical microscopy in the redox competition mode (RC-SECM) is proposed as an useful technique for local investigation of the electrocatalytic activity of different catalysts towards the oxygen reduction reaction (ORR) with simultaneous detection of the produced undesirable intermediate hydrogen peroxide. We have used cobalt porphyrin dispersed in a multiwalled carbon nanotubes (MWCNTs) matrix as a model electrocatalyst for the predominant two-electron reduction of oxygen to hydrogen peroxide. Furthermore, Prussian Blue or horseradish peroxidase were used as catalysts for the further reduction of hydrogen peroxide to water. The properties of each component of the film were examined along with their potential interactions with the other components. As a result an efficient electrocatalyst for oxygen reduction at physiological pH could be obtained.

This article reports on comprehensive studies of electrooxidation of methyl formate at different catalysts. The influence of the nanostructured palladium on the catalytic properties of platinum and platinum-ruthenium commercial nanoparticles towards electrooxidation of methyl formate is studied. All results are related to the electrooxidation process of formic acid and methanol at the same catalysts.

In the present work, Keggin-type polyoxometallates are utilized as both reducing and protecting agents during fabrication of gold nanoparticles ranging from 5 to 100 nm covered (protected) with monolayer-type films of polyoxometallates (phosphododecamolybdates). Immobilization of phosphomolybdate-modified gold nanoparticles into ultrathin layers of conducting polymer films of poly(3,4- ethylenedioxythiophene), PEDOT and polyaniline, PANI is also described. We pursue here the concept based on multiple formation of two-dimensional arrays and three-dimensional networks composed alternately of conducting polymers linking negatively charged monolayer-type films of phosphomolybdate-protected gold nanostructures performed using a layer-by-layer technique. The morphology of the resulting multilayer network films was determined using transmission electron microscopy (TEM) and their formation and electrochemical properties were examined using cycling voltammetry. Resulting monolayer and multilayer assembles composed of phosphomolybdate-stabilized gold nanoparticles have occurred to be attractive towards electrocatalytic reduction of hydrogen peroxide.

A composite system of poly (3,4-ethylenedioxythiophene)/multi-walled carbon nanotubes has been investigated and characterized as a potential charge storage material for coupled dye-sensitized solar cell/electrochemical capacitor systems. The selected material can easily operate in organic media (lithium triflate/propylene carbonate) giving a specific capacitance of 95 F g-1 and energy density of 3.1 Wh kg-1. The combination of the composite material with dye-sensitized solar cell allows to obtain a photo-rechargeable supercapacitor (photocapacitor), destined to work with dies required organic media (here with N 719 dye). The photocapacitor system was built from mesoporous TiO2 electrode, typical charge relay consisting of iodine/iodide redox couple and two charge storage electrodes separated by a liquid electrolyte. The system was tested under light illumination of 100 mW cm-2 with xenon lamp equipped with cut-off filters eliminating the ultraviolet and infrared part of the spectra.

We describe a new preparation method for preparation of a stable water-insoluble composite film containing platinum nanoparticles dispersed in conductive high-surface-area zeolite-type matrices of Vulcan XC-72 carbon supported acidic salts of cesium phosphododecatungstate (Cs2.5 H0.5PW12O40). To obtain the composite, Pt is obtained through corrosion of a Pt flag counter electrode and deposited on the working electrode (glassy carbon) substrate modified with Cs2.5H0.5PW12O40 mixed with Vulcan XC-72 carbon nanoparticles. HRTEM has been utilized to investigate dispersion platinum nanoparticles deposited on the polyoxometallate matrix. CO-stripping voltammetry has been used to determine the Pt surface area in the catalytic layer. The results have shown high electrocatalytic activity of the electrode containing low loading of Pt nanoparticles (about 2.6 ug cm-2) towards oxygen reduction. It is expected that Pt is located inside pores of Cs2.5H0.5PW12O40. Reactivity of Pt-free Cs2.5H0.5PW12O40 system towards reduction of hydrogen peroxide has also been addressed.

This study describes the activity of Pt40%/Vulcan XC-72 carbon catalyst modified with Rb2.5H0.5PW12O40 zeolite-type matrix prepared by a mixing method. The catalyst is used to induce the anodic oxidation of ethanol in an acidic medium as well as to investigate its suitability for use in direct ethanol fuel cells (DEFCs). Under the same Pt-loading, mass, and experimental conditions for ethanol oxidation, the catalysts containing the above mentioned zeolite-type supports display significantly enhanced electrocatalytic activity in comparison to unmodified Pt40%/Vulcan XC-72 carbon. Our new system containing the Nafion-treated rubidium salt of Keggin-type heteropolyacid as a matrix and the Pt40%/Vulcan XC-72 carbon catalyst was characterized with respect to its electrochemical properties and its electrocatalytic activity towards the ethanol oxidation. Results clearly indicate that proposed catalyst containing Rb2.5H0.5PW12O40 (RbPW) matrix is of potential utility to direct ethanol fuel cell.

Combination of multiwalled carbon nanotubes, cobalt porphyrin and tungsten oxide produces a multifunctional electrocatalytic system capable of the effective reduction of oxygen in acid medium. The resulting inks have been utilized during sequential deposition of components. Co-existence of Co-porphyrin, tungsten oxide together with dispersed carbon nanotubes leads to synergistic effect that is evident from positive shift of the oxygen reduction potentials, significant increase of voltammetric currents (relative to those observed at a system not containing carbon nanotube-supported tungsten oxide) and decrease of hydrogen peroxide produced during oxygen reduction. It is reasonable to expect that the reduction of oxygen is initiated at metalloporphyrin redox centers, and the undesirable hydrogen peroxide intermediate is further reduced at partially reduced tungsten oxide. In addition to the methanol tolerance other important issue is the tolerance of the proposed system to ethanol that may appear due to crossover in the cathode compartments of ethanol fuel cells.

Multiwalled carbon nanotubes (CNTs), that are modified with ultrathin layers of tetrathiafulvalene (TTF), were demonstrated to form a stable colloidal suspension. Such dispersion was exploited to fabricate an integrated mediating system (utilizing both highly conductive carbon nanostructures, CNTs, and a redox mediator, TTF) capable of facilitating electron transfers between the active sites of the enzyme (glucose oxidase) and the electrode surface. The resulting bioelectrocatalytic system produced sizeable glucose oxidation currents in phosphate buffer solution (pH 7.0). For comparison, the system utilizing TTF‐free (bare) CNTs and the glucose oxidase enzyme showed relatively much lower activity towards the glucose oxidation. Formation, electrocatalytic reactivity, durability, and morphology of proposed bioelectrocatalytic systems were examined using cyclic voltammetry, potential step techniques, rotating disk voltammetry and transmission electron microscopy. The whole concept of the preparation of CNT‐supported redox mediating systems is of potential utility to bioelectroanalytical chemistry.

Protective properties against pitting corrosion of thin coatings (on stainless steel) of poly(3,4-ethylenedioxytiophene), PEDOT, doped with phosphodedecamolybdate or silicodedecamolybdate are described here. PEDOT serves as a stable host matrix for large negatively charged polymolybdate inorganic species. Consequently, due to the formation of denser structures and to the existence of electrostatic repulsion effects, the composite coatings are capable of largely blocking access of pitting-causing anions (chlorides) to the surface of stainless steel. Reference is given to selected literature reports dealing with application of the conducting polymer type films to the pitting corrosion protection.

Combination of tetrathiafulvalene (TTF)-modified multi-walled carbon nanotubes and glucose oxidase within the film produces a bio-electrocatalytic system capable of effective oxidation of glucose in 0.1 mol dm-3 phosphate buffer (pH=7.0). An important function of carbon nanotubes is to improve transport of electrons within the film. Here carbon nanotubes have been modified with ultra-thin layers of TTF to form stable colloidal suspensions of carbon nanostructures. They have been utilized to produce Nafion-containing inks for sequential deposition of components. The presence of TTF is expected to facilitate an effective flow of electrons from the redox centers of glucose oxidase to the glassy carbon electrode. TTF constitutes a group of redox molecules that were successfully used as redox mediators in enzyme electrochemistry. Our highly porous film of carbon nanotubes on the electrode surface have presumably acted as three-dimensional network of nanowires around the enzyme molecules and have promoted the efficient electron transfers.

Polynuclear redox conducting mixed-valent inorganic materials, such as sol-gel processed nanostructured nickel(II) hexacyanoferrate(II,III), have been utilized as redox mediators (charge relays) in dye-sensitized solar cell (DSSC). The systems' granules are likely to penetrate pores of the dye-modified TiO2. An important issue is that the formal potential of nickel(II) hexacyanoferrate(II,III) is more positive (>300 mV) relative to the commonly used iodide/triiodide couple. With the same dye-modified TiO2 used, the above property led to the larger potential output of DSSC. The proposed redox-conducting inorganic materials is in a mixed-valent state in which iron(II) and iron(III) sites are at the 1:1 ratio, and the concentration gradients are maximized. Consequently, the system is characterized by fast dynamics of electron transfers. Since the structures are hydrated, they are also good ionic (K+) conductors. An important feature is high physicochemical stability of such inorganic polynuclear electroactive materials.

Modification of multi-walled carbon nanotubes with ultra-thin films of oxocyanoruthenium structures resulted in their improved capacitive characteristics, as evident from increased specific capacitances and energy densities determined using diagnostic charging-discharging electrochemical experiments (involving cyclic voltammetry, galvanostatic and AC impedance methods). The largest specific capacitance (123 F g-1) was found when the oxocyanoruthenium modified carbon nanotubes were further covered or linked with conducting polymer, namely poly (3,4-ethylenedioxythiophene) or PEDOT, structures. Among important issues are high stability of both inorganic and organic components, attractive electrostatic interactions between negatively charged oxocyanoruthenate and positively charged PEDOT, fast redox transitions of oxocyanoruthenium and high dynamics of charge propagation in PEDOT species, as well as ability to improve distribution of charge by mul ti-walled carbon nanotubes.

Combination of polyoxometallate-modified multi-walled carbon nanotubes, cobalt porphyrin, and peroxidase (horseradish, cabbage) enzyme within the film (deposited on glassy carbon) produces a bio-electrocatalytic system capable of effective reduction of oxygen in neutral media such as 0.1 mol dm-3 KCl and 0.1 mol dm-3 KCl + 0.01 citrate buffer (pH=6). An important function of carbon nanotubes is to improve transport of electrons within the film. Co-deposition of the peroxidase enzyme together with the cobalt porphyrin catalytic centers leads to bifunctional synergistic effect that is evident from sizeable positive shift of the oxygen reduction potentials and significant increase of voltammetric currents. The bio- electrocatalytic system also exhibits relatively much higher reductive activity towards hydrogen peroxide. It is reasonable to expect that the reduction of oxygen is initiated at cobalt porphyrin redox centers, and the undesirable hydro gen peroxide intermediate is further reduced at the horseradish or cabbage peroxidase enzymatic sites.

Gold nanoparticles (AuNPs) protected by an alkanethiol in nonaqueous solvent are converted to AuNPs with a surrounding layer of a polyoxometalate, AuNP‐POM, by ligand exchange and liquid–liquid extraction into aqueous solution without changing the size of the metal core. With glassy carbon electrodes modified with PMo12‐AuNP (PMo12=H3PMo12O40), the reduction of bromate was mediated by the first redox process of the MoVIcenters; the reduction occurred at a lower overpotential and yielded a higher cathodic current than that observed with PMo12alone as the mediator. This synergistic electrocatalysis, which approached a linear diffusion‐controlled process, was used to demonstrate the feasibility of the determination of bromate. A detection limit of 3 μM (k=3 criterion) was achieved by pulse voltammetry.

The modification of Pt nanoparticles of ca. 8 nm diameter by adsorbing monolayers of phosphododecatungstic acid (H3PW12O40) on their surfaces tends to activate them towards efficient electrocatalytic reduction of oxygen in acid medium. The modification steps were be performed either before or after introduction of catalytic nanoparticles onto the glassy carbon substrates. Formation of a stable colloidal suspension of phosphotungstate protected Pt-nanoparticles as a source of activated catalytic centers was required in the first case; whereas, in the second case, bare Pt nanoparticles had been deposited on glassy carbon before they were subsequently modified with ultra-thin films of H3PW12O40. Rotating disk voltammetry was used to probe the electroreduction of dioxygen in 0.5 mol dm-3 H2SO4. In addition to the 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 interface.