P.L. Antonucci

Investigation of a direct methanol fuel cell based on a composite Nafion®-silica electrolyte for high temperature operation

Abstract Operation of a liquid-fed Direct Methanol Fuel Cell (DMFC) working at 145°C was demonstrated by using a composite membrane made of Nafion ® ionomer and silica. The enhanced humidification conditions of the membrane–electrode (ME the measured methanol cross-over rate was 4×10 −6 moles min −1 cm −2 . A physico-chemical characterization of the cell components is also reported.

Influence of the acid-base characteristics of inorganic fillers on the high temperature performance of composite membranes in direct methanol fuel cells

Various recast Nafion® composite membranes containing ceramic oxide fillers with different surface characteristics (SiO2, SiO2–PWA, Al2O3, ZrO2) have been investigated for application in high temperature direct methanol fuel cells (DMFCs). Cell resistance at 145 °C increases as a function of the pH of slurry of the inorganic filler indicating a strong influence of the acid–base characteristics on the electrolyte conductivity. This effect has been attributed to the different water retention capabilities of the various membranes. Fuel cell performance at 145 °C, expressed as both maximum power density and current density at 0.5 V cell potential, increases almost linearly as the pH of slurry of the oxide materials decreases. Appropriate selection of the surface properties for the inorganic fillers allows to enhance the proton conductivity and extends the operating temperature range of composite membranes. The influence of fuel cell operating pressure on the humidification properties of these electrolytes at high temperature has been also investigated.

Composite Mesoporous Titania Nafion-Based Membranes for Direct Methanol Fuel Cell Operation at High Temperature

Composite Nafion-based membranes, containing 5 wt % of high-purity mesoporous titania with an average pore size of about 3.5 nm heated to 350, 450, and 600 degrees C as a filler were successfully recasted. Field emission scanning electron microscopy observations showed a high degree of dispersion of mesoporous titania particles in Nafion. Direct methanol fuel cell investigation of such membranes at temperatures higher than 100 degrees C revealed a considerable influence of the presence of the ceramic oxide and of its specific surface area on the electrochemical behavior. The composite membranes allowed operation up to 145 degrees C, showing a significant performance improvement with respect to pure Nafion. At 145 degrees C with oxygen feed, a power density of about 335 mW/cm(2) was recorded for the composite Nafion-based membranes, containing 5 wt % of mesoporous titania calcined at 450 degrees C. (c) 2005 The Electrochemical Society. All rights reserved.

A voltammetric study of the electrodeposition chemistry of the Cu + Se system

Abstract The electrochemical mechanism of iron sulphide deposition on a Pt substrate in organic solution (diethyleneglycol) containing FeCl2 and S8, has been studied by means of cyclic voltammetry, chronopotentiometry and coulometry. The redox processes occuring at different potentials have been investigated to ascertain the potential range at which the iron sulphide deposition occurs. The region between −0.45 and −0.65 V (sce), was identified as the one which assures a suitable composition and good adhesion of the films to the substrate at 120°C. Films have been chracterized by Energy-Dispersive X-ray analysis (EDX). A spreading in the film composition was observed which accounts for the formation of an amorphous phase. The deposition mechanism appears to involve first the reduction of the S8 species to S2−8, which absorbs onto the Pt surface while the Fe2+ ions diffuse through the double layer until they precipitate on the adsorbed sulphide species which thus constitute the first nucleation sites of iron sulphide films.

Oxygen reduction kinetics in phosphotungstic acid at low temperature

The kinetics of O2 reduction reaction on Pt in concentrated phosphotungstic acid, H3PW12O40, has been investigated at low temperatures by using the microelectrode technique. Accordingly, the exchange current density, the oxygen solubility, the diffusion coefficient and the corresponding activation parameters have been determined. H3PW12O40 manifests promising characteristics for the oxygen electroreduction process especially in terms of oxygen solubility (5.03 × 10−6 mol cm−3 at 25°C) and H+ concentration (pK1 = 4.77 in HOAc) which account for high exchange current density values (8.63 × 10−8 A cm−2 and 6.06 × 10−7 A cm−2 at 25 and 60°C, respectively). A one electron process has been singled out as the rate limiting step for the oxygen reduction, suggesting that this reaction occurs on Pt under Langmuir conditions in phosphotungstic acid. The results are compared with those reported in the literature for concentrated H3PO4 and TFMSA solutions.

Partial oxidation of methane in solid oxide fuel cells: an experimental evaluation

Operation results of a 150 W tubular solid oxide fuel cell stack prototype, directly fuelled by methane, are presented. Fuel is partially oxidized to synthesis gas as an alternative route to steam reforming. An extensive electrochemical investigation, consisting in the analysis of the performance attained during a 3000 h endurance test, shows the feasibility of the process.

Fractal surface characterization of chalcogenide electrodeposits

Abstract Electrodeposited iron sulphide and zinc telluride thin films on tin conductive oxide substrates were investigated by cyclic voltammetry (CV) and atomic force microscopy (AFM). CV analysis has allowed the determination of the potential region where selective deposition of Fe 1− x S (x = 0.17) and ZnTe semiconductors occurs. The split island method has been applied to AFM images for the characterization of the fractal properties of Fe 1− x S and ZnTe electrodeposits. Values of the fractal dimension of surfaces (2.3–2.5) account for a diffusion controlled growth model for all the samples investigated. The influence of preparative variables in determining the observed results has been discussed.

Ageing effects of electrodes in ceramic fuel cells

Abstract A physico-chemical characterization of aged electrodes of a 150 W solid oxide fuel cell (SOFC) tubular stack is presented. X-ray diffraction and electron microscopy analyses showed that significant chemical and morphological changes occurred in both anodic and cathodic components after 3000 h operation. Depletion of ceria at the anode side with operation time caused a change in selectivity of the methane oxidation reaction, leading to a significant increase of the deep oxidation products in the catalytic step preceding the electrochemical reaction. This determined both OCV drop and performance decay. Moreover, prolonged operation resulted in a narrowing of the three-phase reaction zones at the electrode-electrolyte interface.

Natural pyrite-based electrodes for photoelectrochemical applications

Abstract The screen printing technique has been used for the manufacturing of photoelectrodes based on natural pyrite. Materials have been investigated by X-ray diffraction, energy dispersive X-ray analysis and scanning electron microscopy. Information on the electrochemical reactivity of the surface has been obtained by cyclic voltammetry in alkaline solution. Photoactive anodes in polyiodide electrolyte based photoelectrochemical cells have been obtained upon thermal activation of electrodes in air. These results have been interpreted on the basis of the formation of a heterostructure composed of FeS 2 and Fe 2 O 3 phases.