L. Giorgi

Development and characterization of novel cathode materials for molten carbonate fuel cell

Abstract In the development of molten carbonate fuel cell (MCFC) technology, the corrosion of materials is a serious problem for long-term operation. Indeed, slow dissolution of lithiated-NiO cathode in molten carbonates is the main obstacle for the commercialization of MCFCs. In the search of new, more stable, cathode materials, alternative compounds such as LiFeO2, Li2MnO3, and La1−xSrxCoO3 are presently under investigation to replace the currently used lithiated-NiO. The aim of the present work was to investigate the possibility to produce electrode based on LiCoO2, a promising cathode material. At first, LixCoO2 power samples (0.8

Development of molten carbonate fuel cell using novel cathode material

The slow dissolution of lithiated-NiO cathodes in molten carbonates is the main obstacle for the commercialization of molten carbonate fuel cells. The aim of the present work was to investigate the possibility of producing an electrode based on LiCoO2. The LixCoO2 powder samples (0.8 < x < 1.1) were obtained by thermal decomposition of carbonate, acetate and oxide precursors, in air. The syntheses were monitored by thermal analysis (TGA, DTA). The calcined and sintered powder samples were characterized by X-ray diffraction and atomic absorption spectroscopy The porous electrodes were prepared with different pore-formers by cold pressing and sintering. A bi-modal pore size distribution was observed in all the materials. Conductivity measurements were carried out in the temperature range 500–700 °C. The solubility in molten carbonates was measured. To test the cathodic performance of the materials under study, electrochemical impedance spectroscopy measurements were carried out to investigate the porous electrode/molten carbonate interface.

Nanomaterials-Based PEM Electrodes by Combining Chemical and Physical Depositions

The real market penetration of polymer electrolyte fuel cells is hindered by the high cost of this technology mainly due to the expensive platinum catalyst. Two approaches are followed to reduce the cost: one way is to increase the Pt utilization efficiency reducing at the same time the total load and the other way is to increase the catalytic activity of the catalyst/support assembly. In this work, the increase of utilization efficiency is addressed by optimizing the catalyst distribution on the uppermost layer of the electrode via electrodeposition and sputter deposition, while the improvement of the catalyst activity is pursued by nanostructuring the catalysts and the carbon-based supports. A very low Pt loading 0.006 mg cm 2 was obtained by sputter deposition on electrodes that exhibited a mass specific activity for methanol oxidation reaction better than a commercial product. Carbon nanofibers used as catalyst support of electrodeposited platinum nanoparticles resulted in improved mass specific activity and long term stability compared to conventional carbon-based supports. Finally, PtAu alloys developed by sputter deposition were found more efficient than commercial PtRu catalyst for the methanol oxidation reaction. In conclusion, polymer electrolyte membrane fuel cell electrode based on nanomaterials, developed by combining physical and chemical deposition processes, showed outstanding electrochemical performance. DOI: 10.1115/1.4003629

Fuel Cells: Technologies and Applications

A deep analysis of the Fuel Cells technologies state of the art has been done in this article. After a general de- scription of the fuel cell base structure the six most important fuel cell technologies Polymeric Electrolyte Membrane Fuel Cells (PEMFC), Direct Methanol Fuel Cells (DMFC), Alkaline Fuel Cells (AFC), Phosphoric Acid Fuel Cell (PAFC), Molten Carbonate Fuel Cell (MCFC), Solid Oxide Fuel Cell (SOFC) are explained, describing advantages and disadvan- tages of each one and pointing out their principal use. The future development are also shown.

Nanocrystalline Diamond Films by Bias Enhanced Nucleation and Argon Assisted Growth in a HFCVD System

The achievement of nanosmooth, ultrathin diamond coatings with nanosized grains is mandatory for the successful utilization of diamond in areas such as microelectromechanical systems, field emission and surface acoustic waves devices. The bias enhanced nucleation technique (BEN) allows to achieve high nucleation density diamond films, where the average distance between diamond nuclei can be as low as 10-20nm. Moreover by diluting the gas precursors (H2 and CH4) into noble gas (Ar, He) during growth, the formation of larger crystals can be inhibited, giving rise to nanocrystalline films without a degradation of the film quality, such as the presence of more graphitic bonds. In this paper we report the growth of ultrathin, smooth, high quality nanodiamond films obtained by combining the two techniques in a HFCVD reactor. A variety of nanocrystalline diamond films with a grain size as low as 10nm and thickness up to 1μm were obtained. The nucleation process and ensuing growth of the film were monitored by SEM observation. Spectroscopic measurements were also performed to study the microstructure and to assess the quality of the deposited material.

Thermal Conversion of Gels Prepared by the Complex Sol-Gel Process (CSGP) from Li+-Me2+-CH3COO−-Ascorbic Acid (ASC)-NH4+-OH−-H2O Systems to LiMn2O4 and LiNixCo1 − xO2

The spinel LiMn2O4 and layered oxides LiNixCo1 − xO2 (x = 1; 0.75; 0) have been prepared by Complex Sol-gel Process (CSGP). The appropriate sol compositions were obtained from acetate aqueous solution of metals containing ascorbic acid by alkalizing it with aqueous ammonia. Gels were produced from the systems by evaporation of water and other volatilies at elevated temperatures. A very intense foaming was observed during the heating at the temperatures higher than 140°C. To avoid foaming in the course of the final thermal treatment, a very long (lasting several days) soaking step was found necessary. However pretreated materials exhibit self-ignition at temperature range 320–500°C dependent on socking conditions. The dependence of self-ignition temperature on carbon content in bed as well as on specific surface has not been proved. Final thermal transformation of gel to solid was studied by TG, DTA, XRD, and IR methods. It was observed that final compounds are formed faster from precursors which did not contain Ni (e.g. LiMn2O4 and LiCoO2), while Li carbonate is not formed in these systems. In contrast, in Li-Ni(Co)-O the formation of Li(or Ni)CO3 was always proved. In addition, during the thermal treatment Ni species are partially reduced even to metallic phase. This effect evidently restrains the formation of pure layered oxides phase. Electrochemical properties of carbonate free compounds are definitely better than of those containing CO3.

CVD SYNTHESIS OF CARBON NANOTUBES ON DIFFERENT SUBSTRATES

Carbon nanotubes (CNTs) were grown using three different chemical vapor deposition (CVD) processes. Optimized conditions were studied. CNTs were grown on differently supported Ni catalytic nanoparticles on flat and bulk substrates using H2 and CH4 as precursors. The different behavior of the same metal catalyst in the presence of the same precursor varying the gas activation by different energy sources, using Hot Filament, Plasma Enhanced (PE), and pure Thermal CVD processes, was studied. By properly choosing the process parameters, dense CNTs were grown by HFCVD on 3 nm Ni thin film deposited by Evaporation and Radio-frequency (RF) Sputtering onto flat Si substrates coated with an intermediate SiO2 layer 3 (Fig. 1a). Prior to the growth, the samples were heated in H2 atmosphere and the Ni clusters distribution shown in Fig. 2a was obtained. No CNT growth was obtained on the same sample in the thermal CVD reactor, but only cluster coalescence was observed (Fig. 2b). CNT grew sparsely in the PE CVD reactor. The different results were ascribed to: i) the catalytic decomposition of the precursors was more efficient where an additional activation source was present; ii) weak interaction between the Ni cluster and the SiO2 substrate could favour cluster coalescence, which was the dominant effect in the thermal CVD process. Flat Al2O3 substrate coated by a 3nm Ni film, deposited by RF Sputtering, were subjected to the same clustering and CNT growth process in Thermal and PE CVD. The thermal process failed as in the previous case giving rise to

Effect on lacquer adhesion of solid state properties of tin oxides

Abstract To promote lacquer adhesion, different thin films of tin oxides have been grown by means of electrochemical treatments on low tin-plated ferritic steels. The chemical composition and semiconducting properties of the oxide films have been studied by means of the combimed use of X-ray photoelectron spectroscopy (XPS) and electrochemical analytical techniques. These materials were coated with an epoxy-phenolic lacquer and subject t to wet lacquer adhesion tests. Along with these adhesion measurements, XPS and electrochemical results show that the lacquer a adhesion is enhanced when there is an increase in the extent of p-type semiconduction and when the oxide film thickness is a few nanometres thick.

Electrochemical synthesis of self-organized TiO2 crystalline nanotubes without annealing

This work demonstrates that upon anodic polarization in an aqueous fluoride-containing electrolyte, TiO2 nanotube array films can be formed with a well-defined crystalline phase, rather than an amorphous one. The crystalline phase was obtained avoiding any high temperature annealing. We studied the formation of nanotubes in an HF/H2O medium and the development of crystalline grains on the nanotube wall, and we found a facile way to achieve crystalline TiO2 nanotube arrays through a one-step anodization. The crystallinity of the film was influenced by the synthesis parameters, and the optimization of the electrolyte composition and anodization conditions (applied voltage and time) were carried out. For comparison purposes, crystalline anatase TiO2 nanotubes were also prepared by thermal treatment of amorphous nanotubes grown in an organic bath (ethylene glycol/NH4F/H2O). The morphology and the crystallinity of the nanotubes were studied by field emission gun-scanning electron microscopy (FEG-SEM) and Raman spectroscopy, whereas the electrochemical and semiconducting properties were analyzed by means of linear sweep voltammetry, impedance spectroscopy, and Mott-Schottky plots. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) allowed us to determine the surface composition and the electronic structure of the samples and to correlate them with the electrochemical data. The optimal conditions to achieve a crystalline phase with high donor concentration are defined.

Pt Alloys on Carbon Nanostructures as Electrocatalysts for Direct Methanol Fuel Cell

Extensive efforts are focused on the development of Direct Methanol Fuel Cells, due to the intrinsic advantages of this type of devices for mobile power supply system. One of the major drawback of the DMFC resides in the easy poisoning of the anode electrocatalyst (platinum) by COlike reaction intermediates, which implies the need of high platinum load in order to obtain reasonable performances. The development of platinum alloys is considered one of the promising routes for overcoming this problem: the second metal in fact acts as inhibitor of the Pt poisoning. In this work we have combined the use of unconventional methods to deposit the electrocatalyst nanoparticles with unconventional carbon supports. PtAu alloys have been deposited by sputter deposition process on carbon nanofibers with platelet morphology grown by plasma enhanced chemical vapour deposition on carbon paper. Cyclic voltammetry in H2SO4 was used to determine the electrochemical active surface and the electrocatalytic performance for methanol oxidation reaction. Even at lower Pt load, respect to the ones prepared with commercial catalysts supported on carbon black, the innovative electrodes showed higher performance and stability.