A. Pozio

Comparison of high surface Pt/C catalysts by cyclic voltammetry

A detailed procedure for comparing high surface Pt/C catalysts was pointed out. Platinum dispersed carbon was prepared from carbonaceous material and chloroplatinic acid solution using sodium formiate. The real platinum metal surface area was evaluated by cyclic voltammetry on a thin porous coated disk electrode. The performance of catalysts prepared in our laboratory were similar to those of a well-known commercial one. The results show that electrochemical active surface (EAS) measurement is strongly influenced by the gas diffusion electrode (GDE) preparative method. It is only by means of a well-defined preparative procedure and data analysis that it is possible to use this technique to compare different carbon supported platinum catalysts.

Influence of Nafion loading in the catalyst layer of gas-diffusion electrodes for PEFC

Abstract The effect of Nafion loading in the catalyst layer of cathodes for polymer electrolyte fuel cells (PEFCs) was investigated. Steady-state galvanostatic polarisation (GP), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements were carried out at 25°C in 1.0 M H2SO4 on electrodes with different Nafion loadings. EIS supplied information on the polarization resistance and CV on the electrochemical active area for the oxygen reduction reaction (ORR). These parameters, together with those derived from GP, allowed a better identification of the features governing the ORR. An optimum Nafion loading was identified. This loading was found to correspond to a minimum in the polarization resistance and in the oxygen reduction overpotential and a maximum in the electrochemical active area.

Nafion degradation in PEFCs from end plate iron contamination

Nafion degradation in polymer electrolyte fuel cells from SS316L end plate iron contamination was tested in a single cell configuration. Water collected at the cathode and anode exhausts was analysed by means of pH measurements, conductivity, fluoride and metal concentration. The investigations revealed that stainless steel is unsuitable as material for end plates in PEM fuel cells. In fact, iron contamination of membrane electrode assemblies led to polymer degradation, revealed by a massive fluoride loss. In contrast, iron-free plates (aluminium alloy) showed higher stability in the cell environment.

Modelling static and dynamic behaviour of proton exchange membrane fuel cells on the basis of electro-chemical description

Abstract A simplified dynamical model of a fuel cell of the proton exchange membrane (PEM) type, based on physical–chemical knowledge of the phenomena occurring inside the cell has been developed by the authors. The model has been implemented in the MATLAB/SIMULINK environment. Lab tests have been carried out at ENEA’s laboratories; and a good agreement has been found between tests and simulations, both in static and dynamic conditions. In a previous study [M. Ceraolo, R. Giglioli, C. Miulli, A. Pozio, in: Proceedings of the 18th International Electric Fuel Cell and Hybrid Vehicle Symposium (EVS18), Berlin, 20–24 October 2001, p. 306] the basic ideas of the model, as well as its experimental validation have been published. In the present paper, the full implementation of the model is reported in detail. Moreover, a procedure for evaluating all the needed numerical parameters is presented.

H2 and H2/CO oxidation mechanism on Pt/C, Ru/C and Pt–Ru/C electrocatalysts

The oxidation kinetics of H2 and H2 + 100 ppm CO were investigated on Pt, Ru and Pt–Ru electrocatalysts supported on a high-surface area carbon powder. The atomic ratios of Pt to Ru were 3, 1 and 0.33. XRD, TEM, EDS and XPS were used to characterize the electrocatalysts. When alloyed with ruthenium, a decrease in mean particle size and a modification of the platinum electronic structure were identified. Impedance measurements in H2SO4, at open circuit potential, indicated different mechanisms for hydrogen oxidation on Pt/C (Tafel–Volmer path) and Pt–Ru/C (Heyrowsky–Volmer path). These mechanisms also occur in the presence of CO. Best performances, both in H2 and H2 + CO, were achieved by the catalyst with the ratio Pt/Ru = 1. This is due to a compromise between the number of free sites and the presence of adsorbed water on the catalyst. For CO tolerance, an intrinsic mechanism not involving CO electroxidation was proposed. This mechanism derives from changes in the electronic structure of platinum when alloyed with ruthenium.

Electroxidation of H2 on Pt/C Pt–Ru/C and Pt–Mo/C anodes for polymer electrolyte fuel cell

Abstract Pt/C, Pt–Ru/C and Pt–Mo/C electrocatalysts are used for hydrogen oxidation in polymer electrolyte fuel cells (PEFCs). In this paper, we report a semi-empirical equation that fits experimental electrode potential versus current density data for gas diffusion anodes using these electrocatalysts. The physico-chemical interpretation of all parameters used in the equation is also given. The presence of a strong kinetic limitation on Pt–M/C (M=Ru or Mo) electrodes is demonstrated. A Heyrowsky–Volmer mechanism for the hydrogen oxidation reaction is proposed on Pt–Mo/C and Pt–Ru/C. Accurate analysis of the cell voltage versus current density plots of polymer electrolyte fuel cells with Pt–Mo/C anodes show that it is difficult to evaluate the best Pt/Mo atomic ratio from full-cell measurements, while half-cell data are more useful for kinetic studies.

A novel route to prepare stable Pt-Ru/C electrocatalysts for polymer electrolyte fuel cell

A new method for preparing high surface Pt–Ru/C catalysts at low temperature is described. Pt–Ru on carbon was prepared from carbonaceous material, Pt(NH3)4Cl2 and RuNO(NO3)x(OH)y with borohydride as a reducing agent. Simultaneous reduction of both metals was provided by means of heat treatment. Small and homogeneously dispersed catalyst particles were obtained. XRD and electrochemical measurements show that the performance of the catalyst prepared was similar to that of commercial E-Tek samples, but with increased stability.

Membrane electrode gasket assembly (MEGA) technology for polymer electrolyte fuel cells

A new technology for the production of a membrane electrode gasket assembly (MEGA) for polymer electrolyte fuel cells (PEFCs) is defined. The MEGA system was prepared by sealing a previously prepared membrane electrode assembly (MEA) in a moulded gasket. For this aim, a proprietary silicone based liquid mixture was injected directly into the MEA borders. Gaskets obtained in different shapes and hardness grades are stable in a wide temperature range. The MEGA technology shows several advantages with respect to traditional PEFCs stack assembling systems: effective membrane saving, reduced fabrication time, possibility of quality control and failed elements substitution. This technology was successfully tested at the ENEA laboratories and the results were acquired in laboratory scale, but industrial production appears to be simple and cheap.

Lithium-ion batteries based on titanium oxide nanotubes and LiFePO 4

In this paper, the morphology, the conformation, and the electrochemical performance of TiO2 nanotubes and LiFePO4 have been studied by using scanning electron microscope, XRD, and charge/discharge cycles. The electrochemical tests comprised low rate cycling, cycling at C rate, and cycling at different rates. This work was finalized to the fabrication of lithium-ion batteries based on the TiO2/LiFePO4 redox couple. Battery cells were assembled and electrochemical tests were performed to evaluate cell capacity, power, and energy. Further tests were carried out to evaluate the capacity retention as a function of cycle number and discharge current.

Effect of Low Cobalt Loading on TiO2 Nanotube Arrays for Water-Splitting

This work is intended to define a new possible methodology for the TiO2 doping through the use of an electrochemical deposition of cobalt directly on the titanium nanotubes obtained by a previous galvanostatic anodization treatment in an ethylene glycol solution. This method does not seem to cause any influence on the nanotube structure, showing final products with news and interesting features with respect to the unmodified sample. Together with an unmodified photoconversion efficiency under UV light, the cobalt doped specimen reports an increase of the electrocatalytic efficiency for the oxygen evolution reaction (OER).