Showing papers in "Journal of Applied Electrochemistry in 2006"

Progress in the synthesis of carbon nanotube- and nanofiber-supported Pt electrocatalysts for PEM fuel cell catalysis

Abstract: This paper reviews the literature on the synthesis of carbon nanotube- and nanofiber-supported Pt electrocatalysts for proton exchange membrane (PEM) fuel cell catalyst loading reduction through the improvement of catalyst utilization and activity, especially focusing on cathode nano-electrocatalyst preparation methods. The features of each synthetic method were also discussed based on the morphology of the synthesized catalysts. It is clear that synthesis methods play an important role in catalyst morphology, Pt utilization and catalytic activity. Though some remarkable progress has been made in nanotube- and nanofiber-supported Pt catalyst preparation techniques, the real breakthroughs have not yet been made in terms of cost-effectiveness, catalytic activity, durability and chemical/electrochemical stability. In order to make such electrocatalysts commercially feasible, cost-effective and innovative, catalyst synthesis methods are needed for Pt loading reduction and performance optimization.

Calculation for the cathode surface concentrations in the electrochemical reduction of CO2 in KHCO3 solutions

Abstract: This article presents a mathematical model that predicts the chemical conditions at the electrode surface during the electrochemical reduction of CO2. Such electrochemical reduction of CO2 to valuable products is an area of interest for the purpose of reducing green house gas emissions. In the reactions involved, CO2 acts as both a reactant and a buffer, consequently the estimation of local concentrations at the electrode surface is not trivial and a numerical approach is required. The necessary partial differential equations (PDEs) have been set-up and solved using MATLAB. The results show the local concentrations at the electrode surface to be significantly different from the bulk concentrations under typical reported experimental conditions. The importance of buffer strength and a careful quantification of the degree of mixing produced in the experimental apparatus is demonstrated. The model has also been used to re-examine previously published data, showing that the Tafel slopes in CO2 reduction are consistent with those reported for the simpler CO reduction system. Further, the effect of pulsed electroreduction was also modeled, showing that pulsing causes corresponding swings in local pH and CO2 concentrations.

Electrochemical behaviour of a magnesium alloy containing rare earth elements

Abstract: The corrosion of a magnesium alloy containing rare earth elements (WE43 type alloy) was studied in 0.05 and 0.5 M Na2SO4 or 0.1 and 1 M NaCl solutions using electrochemical techniques: linear polarization resistance, potentiodynamic polarization, impedance measurements. The electrolytes favoured anodic magnesium oxidation but the presence of rare earth elements improved the tendency of magnesium to passivation. The dissolution rates in chlorides were higher than in sulphates because chlorides, in contrast to sulphates, interfered with the formation and maintenance of a protective layer of corrosion products which decreased the severity of the attack. The effects of galvanic corrosion due to cathodic intermetallic precipitates at grain boundaries were particularly evident in chloride media at long testing times.

Hardening effect induced by incorporation of SiC particles in nickel electrodeposits

Abstract: Pure Ni and nickel matrix composite electrocoatings containing micron- and nano-SiC particles (1 μm and 20 nm respectively) were produced under direct and pulse current conditions from an additive-free Watts type bath. The effect of the particle size, codeposition percentage of SiC and type of imposed current on the microhardness as well as on the microstructure of the electrodeposits were investigated. Ni/SiC composite deposits prepared under either direct or pulse current conditions exhibited a considerable strengthening effect with respect to pure Ni coatings. The improved hardness of composite coatings was associated to specific structural modifications of Ni crystallites provoked by the adsorption of H+ on the surface of SiC particles, thus leading to a (211) texture mode of Ni crystal growth. Pulse electrodeposition significantly improved the hardness of the Ni/SiC composite coatings, especially at low duty cycles, in which grain refinement and higher SiC incorporation (vol. %) was achieved. The enhanced hardness of Ni/nano-SiC deposits, as compared to Ni/micron-SiC composites, was attributed to the increasing values of the number density of embedded SiC particles in the nickel matrix with decreasing particle size. In addition, the observed hardening effects of the SiC particles might be associated to the different embedding mechanisms of the particles, which could be characterized as inter-crystalline for micron-SiC and partially intra-crystalline for nano-SiC particles.

Recent developments in the electrodeposition of nickel and some nickel-based alloys

Abstract: The numerous theoretical and practical studies of the electrodeposition of nickel and its binary and selected ternary alloys with copper and cobalt over the last 10–15 years are reviewed. The reported mechanisms of the electrodeposition processes and accompanying evolution of hydrogen are considered. The complex influence of different bath compositions, pHs, current densities or potential ranges and temperature on the formation of single or multiple deposition layers are compared. The determination of the structure and morphology of the deposits on different substrates, including solid surfaces and particulate materials, using a range of analytical techniques are reported.

Binder effect on cycling performance of silicon/carbon composite anodes for lithium ion batteries

Abstract: The cycling performance of a silicon/carbon composite anode has been significantly enhanced by using acrylic adhesive and modified acrylic adhesive as binder to fabricate the electrodes for lithium ion batteries. The capacity retentions of Si/C composite electrodes bound by acrylic adhesive and modified acrylic adhesive are 79% and 90% after 50 cycles, respectively. These two binders are electrochemically stable in the organic electrolyte in the working window. They also show larger adhesion strength between the coating and the Cu current collector as well as smaller solvent absorption in the electrolyte solvent than polyvinylidene fluoride (PVDF). Furthermore, sodium carboxyl methyl cellulose (CMC) plays an important role on improving the properties of acrylic adhesive, which increases the adhesive strength of acrylic adhesive and improves the activation of the electrodes.

On-line mass spectrometry system for measurements at single-crystal electrodes in hanging meniscus configuration

Abstract: We present the construction and some first applications of an On-line electrochemical mass spectrometry system for detecting volatile products formed during electrochemical reactions at a single-crystal electrode in hanging meniscus configuration. The system is based on a small inlet tip made of porous Teflon and a Peek holder, which is brought in close proximity (ca. 10–20 μm) to the electrode surface. The tip is connected to the mass spectrometer by glass and metal tubing. Because of the small amount of gas entering the mass spectrometer, no differential pumping is needed during the measurement. The tip construction and preparation introduced here leads to reproducible voltammetry with very good cleanliness characteristics. The presence of the tip has no significant influence on the blank voltammetry of a Pt(111) in sulfuric acid, and on voltammetric responses for CO adlayer oxidation, methanol oxidation, and hydroxylamine electrochemistry on Pt(111). The formation of gaseous products in these reactions can be followed accurately and is in good agreement with earlier results obtained by other mass spectrometric or spectroscopic techniques. The time response and tailing of the setup is on the order of seconds and mainly determined by the distance between the tip and the electrode.

Weight loss, polarization, electrochemical impedance spectroscopy, SEM and EDX studies of the corrosion inhibition of copper in aerated NaCl solutions

Abstract: This work reports results of weight loss, potentiodynamic polarization and impedance measurements on the corrosion inhibition of copper in aerated non-stirred 3% NaCl solutions in the temperature range 15–65 °C using sodium oleate (SO) as an anionic surfactant inhibitor. These studies have shown that SO is a very good ”green”, mixed-type inhibitor. The inhibition process was attributed to the formation of an adsorbed film on the metal surface that protects the metal against corrosive agents. Scanning electron microscopy (SEM) and energy dispersion X-ray (EDX) observations of the electrode surface confirmed the existence of such an adsorbed film. The inhibition efficiency increases with increasing surfactant concentration and time of immersion, while it decreases with solution temperature. Maximum inhibition efficiency of the surfactant is observed at concentrations around its critical micellar concentration (CMC). The potential of zero charge (pzc) of copper was studied by ac impedance, and the mechanism of adsorption is discussed. The sigmoidal shape of the adsorption isotherm confirms the applicability of Frumkin’s equation to describe the adsorption process. Thermodynamic functions for the adsorption process were determined.

Towards paired and coupled electrode reactions for clean organic microreactor electrosyntheses

Abstract: Electrosynthesis offers a powerful tool for the formation of anion and cation radical intermediates and for driving clean synthetic reactions without the need for additional chemical reagents. Recent advances in microfluidic reactor technologies triggered an opportunity for new microflow electrolysis reactions to be developed for novel and clean electrosynthetic processes. Naturally, two electrodes, anode and cathode, are required in all electrochemical processes and combining the two electrode processes into one “paired” reaction allows waste to be minimised. By decreasing the inter-electrode gap “paired” reactions may be further “coupled” by overlapping diffusion layers. The concept of “coupling” electrode processes is new and in some cases coupled processes in micro-flow cells are possible even in the absence of intentionally added electrolyte. The charged intermediates in the inter-electrode gap act as electrolyte and processes become “self-supported”. Hardly any examples of “coupled” paired electrochemical processes are known to date and both “paired” and “coupled” processes are reviewed here. Coupled electrode processes remain a challenge. In future “pairing” and “coupling” electrode processes into more complex reaction sequences will be the key to novel and clean flow-through microreactor processes and to novel chemistry.

Development of a continuous reactor for the electro-reduction of carbon dioxideto formate – Part 1: Process variables

Abstract: This paper reports an experimental investigation into the effects of five process variables on the performance of a bench-scale continuous electrochemical reactor used in the reduction of CO2 to potassium formate, and interprets the data in terms of reactor engineering for a (speculative) industrial process for electro-reduction of CO2. The process variables: temperature, catholyte species, catholyte conductivity, cathode specific surface area and cathode thickness were studied, along with CO2 pressure and current density, in a set of factorial and parametric experiments aimed to unravel their main effects and interactions. These variables showed complex interdependent effects on the reactor performance, as measured by the current efficiency and specific energy for generation of formate (HCO 2 − ). The “best” result has a formate current efficiency of 86% at a superficial current density of 1.3 kA m−2, with a product solution of 0.08 m KHCO2 and specific electrochemical energy of 260 kWh per kmole formate. The combined results indicate good prospects for process optimization that could lead to development of an industrial scale reactor.

Electro-Catalytic Oxidation of Methanol on a Ni–Cu Alloy in Alkaline Medium

Abstract: The electro-catalytic oxidation of methanol on a Ni–Cu alloy (NCA) with atomic ratio of 60/40 having previously undergone 50 potential sweep cycles in the range 0–600 mV vs. (Ag/AgCl) in 1 m NaOH was studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS). The electro-oxidation was observed as large anodic peaks both in the anodic and early stages of the cathodic direction of potential sweep around 420 mV vs. (Ag/AgCl). The electro-catalytic surface was at least an order of magnitude superior to a pure nickel electrode for methanol oxidation. The diffusion coefficient and apparent rate constant of methanol oxidation were found to be 2.16 × 10−4 cm2 s−1 and 1979.01 cm3 mol−1 s−1, respectively. EIS studies were employed to unveil the charge transfer rate as well as the electrical characteristics of the catalytic surface. For the electrochemical oxidation of methanol at 5.0 m concentration, charge transfer resistance of nearly 111 Ω was obtained while the resistance of the electro-catalyst layer was ca. 329 Ω.

Cathodic electrosynthesis of iron oxide films for electrochemical supercapacitors

Abstract: Cathodic electrosynthesis has been utilized for the fabrication of γ-Fe2O3 films, containing chitosan additive as a binder. The films were studied by X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, differential thermal analysis, and thermogravimetric analysis. Cyclic voltammetry and chronopotentiometry data showed that the iron oxide films exhibit electrochemical capacitance in the voltage window of −0.9 to −0.1 V vs SCE in 0.25 m Na2SO4 and 0.25 m Na2S2O3 aqueous solutions. The highest specific capacitance (SC) of 210 F g−1 was achieved using 0.25 m Na2S2O3 as electrolyte, at a scan rate of 2 mV s−1. The SC decreased with increasing film thickness, scan rate and cycle number. Heat treatment of the films at 140 °C resulted in increasing SC.

Electrochemical waste water treatment: Electrooxidation of acetaminophen

Abstract: Oxidation of acetaminophen at boron-doped diamond (BDD) and at Ti/SnO2 anodes in a plug-flow divided electrochemical reactor led to electrochemical combustion, whereas at Ti/IrO2 benzoquinone was the exclusive product except at very long electrolysis times. The difference is explicable in terms of the different mechanisms of oxidation: direct oxidation at the anode for Ti/IrO2 vs. indirect oxidation involving electrogenerated hydroxyl radicals at BDD and Ti/SnO2. At BDD, at which the efficiency of degradation of acetaminophen was greatest, the rate of electrolysis at constant concentration was linearly dependent on the current, and at constant current linearly dependent on the concentration. Current efficiencies for mineralization up to 26% were achieved without optimization of the cell design.

Dissolution kinetics of WO3 in acidic solutions

Abstract: Potentiostatic polarization and rotating disk electrode techniques were used to obtain the rate constant for the dissolution of electrochemically-formed (at 1 V) WO3 on tungsten (W) in acidic solutions. The corresponding rate constant for the chemical dissolution of WO3(s) powder was found by measuring the dissolved tungsten concentration as a function of time and pH. The chemical dissolution experiments supported the view that the rate-determining step in the anodic reaction of W in acidic solution is the chemical dissolution of WO3(s) formed on the metal surface. Zeta potential measurements gave the isoelectric point (iep) of the WO3(s) powder as pH 1.5, a value that was somewhat smaller than the point of zero charge (pzc) of WO3(s) formed on W metal (pH 2.5). This difference was attributed to the highly hydrated nature of the oxide film formed on W metal in aqueous systems.

Carbon supported Pt–Cr alloys as oxygen-reduction catalysts for direct methanol fuel cells

Abstract: Electrocatalytic activities of various carbon-supported platinum–chromium alloy electrocatalysts towards oxygen reduction in 1 mol l−1 H2SO4 and in 1 mol l−1 H2SO4/1–3 mol l−1 CH3OH, were investigated by means of rotating disc electrode experiments and in solid polymer electrolyte direct methanol fuel cells. The activity of these electrocatalysts for methanol oxidation was evaluated using cyclic voltammetry. It was found that Pt9Cr/C prepared by reduction with NaBH4 exhibits the lowest activity for methanol oxidation and the highest activity for oxygen reduction in the presence of methanol, in comparison to commercial Pt/C, Pt3Cr/C and PtCr/C electrocatalysts.

Eco friendly corrosion inhibitors: Inhibitive action of quinine for corrosion of low carbon steel in 1 m HCl

Abstract: Quinine, a natural product, was investigated as a corrosion inhibitor for low carbon steel in 1.0 m HCl solution. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization were used to study the inhibition action in the temperature range 20–50 °C. The corrosion of steel was controlled by a charge transfer process at the prevailing conditions. The electrochemical results showed that quinine is an efficient inhibitor for low carbon steel and an efficiency up to 96% was obtained at 20 °C. The inhibition efficiency increases with inhibitor concentration and reaches a near constant value in the concentration range 0.48 mM and above. Application of the Langmuir adsorption isotherm enabled a study of the extent and the mode of adsorption.

Effects of structure of the ionic head of cationic surfactant on its inhibition of acid corrosion of mild steel

Abstract: Two n-alkyl-quaternary ammonium compounds were studied as corrosion inhibitors for acid corrosion of mild steel using electrochemical and weight loss methods. The two compounds are hexadecylpyridinium bromide (HDPB) and hexadecyltrimethyl ammonium bromide (HDTB). The influence of the structure of the ionic head on the inhibition action of the two cationic surfactants was studied by analyzing the data at different concentrations and temperatures. The inhibition efficiency increases with the concentration. It increases with temperature in the case of HDPB but decreases in the case of HDTB. The apparent activation energy, E a of corrosion in the presence of HDPB was found to be lower than in blank (0.5 m H2SO4). In the case of HDTB, E a was larger than that of the blank. A larger extent of adsorption for HDPB on the metal surface was evident from the larger negative values of the free energy of adsorption. The results yielded the extent and mode of adsorption of the inhibitors on mild steel. The stronger adsorption of HDPB was attributed to the differences in the molecular structures of the inhibitors.

Rutile TiO2-modified multi-wall carbon nanotubes in TiO2 film electrodes for dye-sensitized solar cells

Abstract: The beneficial influence of incorporation of acid-treated and rutile TiO2 (r-TiO2)-modified multi-wall carbon nanotubes (MWNTs) in TiO2 films on photocurrent–voltage characteristics of dye-sensitized solar cells (DSSCs) was studied. Two different routes were adopted for the modification of acid-treated MWNTs (a-MWNTs) with r-TiO2. The films and MWNTs were characterized by electron microscopy, energy dispersive X-ray spectroscopy, XRD and Raman spectroscopy. In the case of incorporation of a-MWNTs with r-TiO2 modification, short-circuit photocurrent (J sc) of the pertinent DSSC increased by 35% compared with that of a cell with bare TiO2 film. The open-circuit voltage remained almost the same for all cases. The enhanced J sc is explained by the increased surface area of the film, enhanced cluster formation of TiO2 particles around a-MWNTs, and improved interconnectivity of TiO2 particles in the presence of a-MWNTs.

Structures, physicochemical properties and oxygen reduction activities of carbons derived from ferrocene-poly(furfuryl alcohol) mixtures

Abstract: The structure, physicochemical properties and oxygen reduction abilities of carbons prepared by the carbonization of mixtures of ferrocene and poly(furfuryl alcohol) were studied. X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM) studies revealed that the carbons thus prepared consisted of two components; amorphous and turbostratic shell-like components. The fraction, f sharp, obtained by the analysis of the (002) peak in XRD was found to be a parameter that represented the degree of formation of the shell-like components. The formation of the shell-like components induced an increase in the mesopore volumes. Electrical conductivity increased exponentially with f sharp, which indicated that the conduction process was governed by a percolation process of the conductive shell-like components. The amount of CO-desorption by O2-TPD technique showed a maximum desorption at f sharp=0.3, and the further development in the sharp component led to a decrease in the CO-desorption. Mossbauer spectroscopy technique revealed the presence of α-Fe, γ-Fe, Fe1-x O and Fe3C in the prepared carbons, which were soluble species to acids. The oxygen reduction activity was studied in a oxygen saturated sulfuric acid solution by rotating disk electrode voltammetry. The oxygen reduction potential varied with f sharp; initially it increased by f sharp=0.3 and then it decreased at higher f sharp values. This behavior was similar to that of CO-desorption, which meant the presence of an adequate degree of the development of the shell-like structure for maximizing oxygen adsorption. Removal of the surface metal component from the carbons by acid-washing resulted in no decrease in the oxygen reduction activities of the carbons. The nature of the active sites on the carbon materials is discussed.

A novel method of hydrogen generation by water electrolysis using an ultra-short-pulse power supply

Abstract: A novel method of hydrogen generation by water electrolysis using ultra-short-pulse power supply is demonstrated. The ultra-short power supply consists of a static induction thyristor (SIThy) and a specific circuit which is called the inductive energy storage (IES) circuit. It was found that by using an ultra-short pulse with the width of 300 ns, electrolysis takes place with a mechanism dominated by electron transfer, which is different from the conventional diffusion limiting process in DC electrolysis.

Effect of Cr(III) solution chemistry on electrodeposition of chromium

Abstract: This work provides a new insight into the interaction of urea with formate during the chromium electrodeposition from a sulphate-based Cr(III) solution. The influence of solution chemistry on chromium electrodeposition in a Cr(III) bath containing sodium formate and urea as complexing agents was studied by FT-IR, XPS and AFM. The results show that good quality Cr coatings may be obtained only in those cases when the secondary ligand with the carbamidic group predominates over urea in the electrolyte. This suggests that electrodeposition of good quality chromium deposit is possible due to the formation of active chromium–carbamid complexes [Cr(carbamid)n(H2O)6-n ]3+. These complexes delay the formation of the stable oligomeric species, and thus provide a prolonged working lifetime in the Cr(III) formate-urea electrolyte.

Electroactive biofilms: new means for electrochemistry

Abstract: This work demonstrates that electrochemical reactions can be catalysed by the natural biofilms that form on electrode surfaces dipping into drinking water or compost. In drinking water, oxygen reduction was monitored with stainless steel ultra-microelectrodes under constant potential electrolysis at −0.30 V/SCE for 13 days. 16 independent experiments were conducted in drinking water, either pure or with the addition of acetate or dextrose. In most cases, the current increased and reached 1.5–9.5 times the initial current. The current increase was attributed to biofilm forming on the electrode in a similar way to that has been observed in seawater. Epifluorescence microscopy showed that the bacteria size and the biofilm morphology depended on the nutrients added, but no quantitative correlation between biofilm morphology and current was established. In compost, the oxidation process was investigated using a titanium based electrode under constant polarisation in the range 0.10–0.70 V/SCE. It was demonstrated that the indigenous micro-organisms were responsible for the current increase observed after a few days, up to 60 mA m−2. Adding 10 mm acetate to the compost amplified the current density to 145 mA m−2 at 0.50 V/SCE. The study suggests that many natural environments, other than marine sediments, waste waters and seawaters that have been predominantly investigated until now, may be able to produce electrochemically active biofilms.

Kinetics of the electrochemical oxidation of organic compounds at BDD anodes: modelling of surface reactions

Abstract: This paper presents the results of a numerical study of the kinetics of electrochemical oxidation of different organic substances at boron doped diamond (BDD).

Platinum supported on resorcinol–formaldehyde based carbon aerogels for PEMFC electrodes: Influence of the carbon support on electrocatalytic properties

Abstract: Two carbon aerogels with different nanopore size distributions but both with high surface area, high nanoporous volume and low bulk density have been compared as platinum support. The influence of the nanostructure of the carbon aerogel on the platinum nanoparticle deposit was investigated. The platinum was deposited on the carbon by means of two different techniques, one employing an anionic platinum precursor, the other using a cationic one. The porosity of the carbon aerogels was characterized by combining N2-sorption and mercury porosimetry. The platinum deposit was characterized by transmission electron microscopy and rotating disk electrode experimentation to measure the platinum active surface area and its activity towards oxygen reduction reaction (ORR). The structural differences between the carbon aerogels did not yield any difference in platinum deposits in terms of Pt-surface area and ORR activity. Interestingly, the ORR mass activity of the high Pt-surface area samples, obtained by the cationic insertion technique, was several times lower than that of the samples obtained by the anionic technique. This observation was attributed to the particle size effect, detrimental in the case of platinum particle size around 1 nm.

Deposition of clusters and nanoparticles onto boron-doped diamond electrodes for electrocatalysis

Abstract: Metal and metal oxide particles and nanoparticles, differing from each other by their nature and synthesis technique, were deposited onto boron-doped diamond (BDD) thin film electrodes. The applicability in electrocatalysis of thermally decomposed IrO2 and Au nanoparticles, electrodeposited Pt particles, dendrimer-encapsulated Pt nanoparticles (Pt DENs) and microemulsion-synthesized Pt/Ru nanoparticles was studied, once deposited on BDD substrate. In all cases, the electrochemical response of the composite electrodes could be solely attributed to the supported particles. All the particles, with the exception of Pt DENs, exhibited electrocatalytic activity. Pt DENs inactivity has been attributed to insufficient removal of the dendrimer polymer matrix. It was concluded that the BDD electrode is a suitable substrate for the electrochemical investigation of supported catalytic nanoparticles.

Pulsed electrodeposition of (Bi1-xSbx)2Te3 thermoelectric thin films

Abstract: (Bi1-xSbx)2Te3 thermoelectric thin films were deposited on stainless steel discs in 1 M perchloric acid and 0.1 M tartaric acid by pulse electrodeposition in order to optimize the grain growth. The influence of the electrolyte composition, the cathodic current density and the cathodic pulse time on film stoichiometry were studied. The results show that it is necessary to increase the Sb content in the electrolyte to obtain the (Bi0.25Sb0.75)2Te3 film stoichiometry. Pulse plating reduced the grain size and the roughness, compared with continuous plating. Thermoelectric and electrical properties were also studied and it was found that the Seebeck coefficient and electrical resistivity were related to two parameters: the cathodic pulse current density and the films thickness.

Electrocatalytic behaviour for oxygen reduction reaction of small nanostructured crystalline bimetallic Pt–M supported catalysts

Abstract: A 60 wt% Pt–Fe/C and a 60 wt% Pt–Cu/C catalysts with Fe and Cu content of 5 wt% were prepared by using a combination of colloidal and incipient wetness methods; this has allowed synthesis of small nanostructured crystalline bimetallic catalysts with particle size less than 3 nm and with a suitable degree of alloying. These materials were studied in terms of structure, morphology and composition using XRD, XRF and TEM techniques. The electrocatalytic behaviour for ORR of the catalysts was investigated using the rotating disk technique and compared to that of a pure Pt catalyst with similar particle size. No improvement in performance was recorded with the Pt–Cu compared to Pt catalyst, whereas, a promoting effect in enhancing the ORR was observed for the Pt–Fe catalyst both with and without methanol in the oxygen-saturated electrolyte solution.

Polypyrrole artificial muscles: a new rhombic element. Construction and␣electrochemomechanical characterization

Abstract: A novel rhombus-shaped electrochemomechanical unit constituted by 4 polypyrrole bilayer (conducting polymer/ tape) muscles and two plastic hinges, able to transform reversible angular movements from the basic bilayers into longitudinal movements, has been successfully constructed and electrochemically characterized. During operation two of the bilayers act as anode and the other two as cathode. Thus, all the electrical energy is used, avoiding an additional metallic counterelectrode and the subsequent generation of products able to degrade the muscle. The reference electrode is short-circuited to the counterelectrode in order to monitor the muscle potential along the galvanostatic experiments and the sensing abilities of the device. The devices were checked by repetitive galvanostatic contraction/extension of up to 20% of the original length. About 50% of the devices produced irregular movements, due to different ohmic resistances in the electrical contacts between the wires and polymeric films. Once the contacts were improved, the new devices showed good reproducibility. The influence of electrolyte concentration, experimental current and weight trailed by the device indicates that the complex device maintains most of the sensing properties of the basic bilayer muscles. Then checking the life-time of the device, contact failures and fissures around the metal/polymer joint were immediately detected from the chronopotentiometric noises which appeared after several cycles. Such failures must be solved before the device can be miniaturized and in order to construct different shapes, and three-dimensional sensing muscles for robotics from combinations of basic units.

Black nickel electrodeposition from a modified Watts bath

Abstract: Black nickel coatings were electrodeposited on to steel substrates from a Watts bath containing potassium nitrate. The best operating conditions necessary to produce smooth and highly adherent black nickel were found to be NiSO4 · 6H2O 0.63 M, NiCl2 · 6H2O 0.09 M, H3BO3 0.3 M and KNO3 0.2 M at pH of 4.6, i=0.5 A dm−2, T=25 °C and t=10 min. The modified Watts bath has a throwing power (TP) of 61%, which is higher than that reported, not only for nickel, but also for many other metals electrodeposited from different baths. The potentiostatic current–time transients indicate instantaneous nucleation. X-ray diffraction (XRD) analysis shows that the black nickel deposit is pure metallic nickel with Ni(111) preferred orientation.

Electrocatalytic oxidation of ethanol on Pt-Mo bimetallic electrodes in acid medium

Abstract: Pt–Mo alloy electrocatalysts were prepared by an arc-melting furnace process to investigate the origin of their enhanced activity toward ethanol oxidation. Two Mo contents were chosen in zones of the binary phase diagram where they are supposed to form either a pure alloy mixture or a solid solution. Pt–Mo alloy catalysts were more active than Pt-alone. Gradual Mo dissolution at the electrode surface was observed after voltammetric and chronoamperometric measurements. The dissolved Mo contributed to the catalytic effect of the electrode as underpotentially deposited (upd) adatoms. This dissolution probably also leads to an increase in the electrode surface roughness. Low molybdenum content in the electrode material enhances the activity toward ethanol oxidation when compared to Pt-alone. Ethanol oxidation was also investigated by in situ infrared reflectance spectroscopy in order to determine the presence of adsorbed intermediates like CO species. Acetaldehyde, acetic acid and CO2 were also found by spectroscopic experiments.